Welcome to the 12th Tooling Conference & Exhibition, Tooling 2022, held on 25-27 April 2022 in Örebro, Sweden.
The Tooling conferences have been held since 1987 and attract speakers and participants from all continents. The conference topics are Cold and hot working tool steels, High speed steels, Plastic mold steels, Hard metals and cermets, Steel/material design, Tool steel development, Microstructure, properties and performance, Production of tool steels, Simulations and modelling, Additive manufacturing, Processing, machining, polishing, Heat treatment, Surface engineering and coating, Wear resistance, Fatigue under mechanical and thermal cyclic loads, Corrosion resistance, Tooling applications, Tooling contributions to e-mobility, Digitalization in the tool steel and toolmaking industry, Sustainable toolmaking including health aspects, Circular economy and tooling supply chain.
Extended Abstract Submission: October 17, 2021
Notification of Acceptance: October 29, 2021
Full paper Submission: January 28, 2022
The speech will also focus on the production of Metal Powders and Powder Metallurgical Steels and especially its associated production technologies like HIP, MIM and AM. As they are and will become key future core technologies for a number of demanding products and thus for the usage in different associated industries. The presentation will also highlight the actual supply and demand situation of metal powders and the manufactured metal powder steels, will introduce leading manufacturers of both powders and steels, and summarizes installed capacity and new capacity that are on the way as well as new players that enter this high value industry. The presentation will also highlight the recent developments in the world of Forged Special Steels and remelted steels (nickel alloys, stainless steel, alloy tool steel and alloy steel) as well as will give an overview about end-user demand and structures of these special steels and also summarize the actual status of installations on a global scale.
Today's tool and die making industry is characterized by increased individualization and complex manufacturing processes. Therefore, toolmaking companies are forced to always push the limits of what is technically feasible. The usual heterogeneous use of different manufacturing technologies generates high manual planning efforts and requires a cross-technology process understanding. A large number of influencing and disturbing variables affect the individual process steps, which can be caused by individual production machines, peripherals or the entire production environment. Currently, this process knowledge is only available in individual and small batch production as implicit technical and experiential knowledge of long-term employees in the companies.
An OWL-based ontology is presented in order to make the described implicit technical and experiential knowledge of the employees usable on a long-term basis. Due to a very high semantic expressiveness, ontologies allow to represent even the most complex data models with logical relations beyond a pure hierarchical subdivision (taxonomy) of contents. In practice, they are increasingly used in knowledge management, natural language processing, e-commerce and information retrieval.
The proposed domain specific ontology allows a shared and common understanding of machines, work pieces, operating resources and manufacturing processes. The use of Semantic Web technologies makes it possible to pose concrete search queries to the system and, for example, to compare the actual performance of multiple milling machines with the theoretical performance. In addition, the developed domain-specific ontology enables the unambiguous referencing of specific tools (e.g. milling tools) used to manufacture a work-piece.
The developed ontology solves the problem of the non-existent possibility of merging manufacturing data and formalized classification of different manufacturing technologies and enables the use of implicit technical and experiential knowledge in tooling.
Due to the increase of the complexity of the products and the shorter time-to-market, it is also necessary to develop the required tooling to attend to the planned deadlines. This scenario requires advancing the state-of-the-art frontier to improve the tooling competitiveness and productivity.
To achieve such improvement and increase in competitiveness, it is necessary to insert the tooling chain in the context of Industry 4.0. Therefore, the focus could be on the use of digitization technologies for data gathering and analysis, seeking out continuous improvement in the process of development, production, and service provision of tools and devices. In the context of Industry 4.0, real-time condition monitoring and control of manufacturing processes can be achieved using IoT concepts, advanced sensors, Big Data, and machine learning algorithms.
These technologies enable smart monitoring of the manufacturing process, resulting in new tool adjustments and new process parameters in a semi-autonomous way, reducing human-machine interactions and more accurately attributing process improvement.
This paper aims to present the results of a pilot project to develop and validate a machining conditioning monitoring system combining measures conducted directly in the spindle unit and fixture devices. The system is based on different sensors and machine learning. The pilot project has been developed in an automotive company and partnership with two universities and targets the development of applications for a real operational environment.
This research project also aims to develop a system integrator algorithm for real-time data acquisition from the sensors, installed both on the spindle and at strategic points of the fixture devices, enabling the continuous operation monitoring of tools and deviations on the fixture devices, as well as the optimization of the application usage parameters.
The present work focuses on the knowledge-based expert system to develop an automated die and punch tools design for the sheet metal forming process (deep drawing operation). The major limitation of the conventional forming process is the manufacturing of dies. As the attributes of the final component varies, the configuration of the tooling (punch and die) require to be modified. Hence, the tooling cost and inventory increases and results into higher production cost. Therefore, to address this issue, a hybrid intelligent system is proposed considering the concept of image processing and knowledge based architecture. A novel algorithm is proposed which consists of bunch of rules to construct the conventional forming tools design. Python and AUTOCAD-VBA tools are used to develop the intelligent model. Such, hybrid model is able to handle large variety of configurations with semi skilled operator. The benefits like reduced trial and error method with minimum production cost can be achieved.
The development of martensitic steels suitable for exposure to corrosion with simultaneous wear attack is a challenging task, as corrosion and wear resistance are opposite properties in terms of alloying. With the development of NbC-containing corrosion-resistant steels, it has been possible to combine these properties. Due to its higher hardness, NbC increases the wear resistance of the steel more effectively than chromium carbide. In addition, the solubility of chromium in NbC is very low, so that no chromium depletion occurs due to the carbide formation and the chromium in the alloy is almost completely available for the formation of the passive layer.
Until now, steels containing NbC have not been produced according to the industrial powder metallurgy route, because even in low contents Nb tends to form primary carbides catching the carbon in the melt, which leads to clogging of the nozzle during the atomization process.
Diffusion alloying can circumvent this problem by first atomizing a C-free melt and adding the carbon to the steel powder in the form of graphite. However, this complex process is difficult to implement in the industrial production of powder metallurgical steels.
In the work presented, a corrosion-resistant martensitic steel with a volume content of 2 % NbC was developed with the aid of computer-controlled alloy development, which can be produced by the usual powder metallurgical route. The NbC are present as an evenly distributed dispersion with a carbide size < 1 μm. The steel achieves a hardness of >750 HV30 and exhibits very good pitting corrosion resistance in 0.9% NaCl solution. This combination of properties also leads to excellent tribocorrosion resistance.
Production on the industrial PM route has already been successfully carried out.
The powder metallurgical incorporation of hard phases in steel matrices is an established concept to form a metal matrix composite with excellent mechanical properties. Especially TiC has been extensively used in a wide variety of steel matrices in the past. This is primarily due to its high hardness and decent bonding behavior towards steel matrices. While the stability of TiC particles is known to be low when powder consolidation involves a liquid phase, the thermodynamic stability during solid-state consolidation is less investigated. Moreover, the influence of particle size on the thermodynamic stability has not been examined in detail until now. Since the reaction of TiC with steel influences the chemical composition, and hence properties of the steel matrix, and reaction phases might affect its bonding behavior, which is assigned to be one crucial property for the abrasive performance of MMCs, it is of great importance to understand the parameters governing this behavior. To this end, this work investigates the thermodynamic stability and thus reaction phase formation as a function of the normalized surface area of TiC particles within a heat treatable steel consolidated by hot isostatic pressing. The evolved microstructures are investigated by scanning electron- and scanning transmission electron microcopy coupled with energy dispersive x-ray spectroscopy as well as x-ray diffraction.
To predict the solidification and product properties of tool steels with complex chem-ical compositions, an understanding of the transformation behaviour during and after solidification, depending on the chemical composition, is crucial. Therefore, the qua-ternary Fe-C system with 10 w.t.-% Cr and 3% W (subsystem of cold work steels, with M7C3 and M23C6 carbides) and the Fe-C system with 6% W and 5% Mo (simplified high speed steel without vanadium, with M6C and MC carbides) were selected.
As common DSC (differential scanning calorimetry) measurements of as-cast materi-als may not allow the equilibrium transformation temperatures of carbides to be de-tected, a unique time-temperature DSC setup was developed. Regular diffusion an-nealing of as-cast carbidic steels is time-consuming, but with in-situ heat treatment during the DSC measurement in the semi-solid zone (30-50% liquid phase fraction), a status close to equilibrium can be achieved within minutes due to the high diffusion. To prove the potential of the in-situ high-temperature equilibration by partial pre-melting in the DSC, additional “equilibration and quenching” experiments were per-formed at selected temperatures in a Tammann-type furnace and investigated using SEM-EDS and XRD analysis. By combining these methods, carbide types and the transformation temperatures can be verified to evaluate and construct complete phase diagrams.
As most steelmakers, Erasteel is fully involved in decreasing its CO2 and environmental footprint. Erasteel already produces its high-speed steel using 90% recycled material and has the ambition to reach 100% in near future. The today’s remaining 10% are mainly metallic oxides (V2O5, MoO3) or ferro-alloys (FeW, FeCr, FeSi) and cobalt (Co). The total life assessment shows that producing from 100% recycled material will lead to reduce the CO2 emission by 96% compared to producing from metallic ores.
To be able to reach 90% recycled material ratio and in near future 100%, the high value metallic alloys can be sourced from spent catalysts, used batteries, metallic scrap, metallic oxides or carbides. Recycling catalysts containing Mo and Co elements leads to the production of Mo-Co ferro alloys that can be directly used as raw material in HSS as example M35 or M42.
The metals contained in the spent catalyst are recycled with specific equipment: sulfur is removed with a patented roaster, metals and minerals are separated by melting to obtain ferro-alloys, the last step is carried out with an AOD reactor in order to remove elements such as phosphorus while non-oxidizing Mo.
Other metals contained in the industrial waste can be recycled to produce raw materials for the metal industry. As example, the elements contained in the batteries: Ni, Mn and Zn can be separated with a specific process to produce ZnO rich powder, MnO rich slag and a ferro-nickel alloy with more than 20% of Nickel. This ferro-nickel alloy is a valuable raw material for stainless steel makers.
The influence of short-time heat treatment on the widely used and commercially available ledeburitic cold work tool steel 1.2379 (X153CrMoV12; AISI D2) was examined in this work. Starting from a soft annealed initial condition, the influence of different austenitizing temperatures and holding times on the metastable microstructural states after heat treatment/hardening was investigated. The experimental implementation of the heat treatment was used in a quenching dilatometer, and a microstructural simulation model was built using these results. As validation of the model, on the one hand, the martensite-start
temperature (MS) was used, measured experimentally by dilatometry. Additionally, the carbide content and distribution, as determined by quantitative image analysis, were compared with the simulated data and used as an indicator of the model accuracy. Through the developed simulation model, arbitrary heat treatment-induced metastable microstructural states can be calculated. As a possible application of this model, we discuss the live-adaption of industrial heat treatment process in dependence on the batch chemical composition.
In hot metal forming processes, the temperature of the forming tool progressively increases under serial production conditions. Water based two-phase lubricants may be applied to cool the forming tool and moderate temperature, in which the liquid agent would evaporate or decompose rapidly with dry matter deposited on the tooling surface during the dwelling time before the forming process commences. In this study, an interactive friction model for a two-phase lubricant was developed to predict the transient lubricant behaviours, i.e., predicting the effects of tool temperature and dwelling time on the friction coefficient evolution and lubricant breakdown. Friction tests between a warm pin and hot aluminium workpiece were conducted using the advanced friction testing system, Tribo-Mate, to validate the modelling results.
Multiple cycles of tool dimensional correction during tryout process are one of the most critical aspects in manufacturing of stamping tools, causing significant impact to its production cost. An alternative to reduce tryout time and cost is to perform the dimensional corrections in a virtual model, so that ideally, all the corrections can be done to the simulation before the test of the physical tool is performed. This process is termed virtual tryout. In order to enable the testing of the tool be performed solely through simulation, the digital model must be capable of accurately representing the physics involved in the sheet metal forming process. An accurate model can ensure that the dimensional divergences between the results from the simulation and those measured in the formed specimen are as minimal as the tolerance established by the end client. Deep understanding of the physical phenomena and their variables are crucial to guarantee that the parameters that most significantly affect the results are considered during the construction of the model. In this paper the dimensional correlation between the geometry of u-drawn steel specimens and those from the simulation is studied. The sheet metal forming simulations are performed using software Pam-Stamp. Different material and plasticity models are analyzed and their impact to the final dimensional results are compared to those measured from the steel specimen, in order to find the main sources of error that cause discrepancies between the results of stamping simulations and tryout.
Wear and in particular abrasive wear in injection molding is a core research topic for the institute of injection molding of polymers at Montanuniversität Leoben. The standard application-oriented test for abrasive wear of polymers on plastic mold steels is the platelet-wear-tester method in which two steel specimens form a thin wear slit. The glass fiber reinforced polymer melt is injected through the wear slit and the surface of both specimens is abraded. In the injection molding process similar conditions often occur in thin-walled parts or in film gates. A drastic loss of hardness of a powder metallurgical steel (PM-steel) was discovered after approx. 200 injection cycles while performing platelet-wear-tests.
For experimentally analyzing the reason for the loss of the steel hardness during injection molding a new platelet-wear-testing apparatus was developed which can be used to measure the increase of the temperature inside the steel specimen while testing. In systematic experiments the comparability of results generated with the new wear testing apparatus to those of the former platelet-tester were confirmed and the phenomenon of hardness loss was investigated in detail.
First results show and support the hypothesis that a temperature increase above the annealing temperature occurred inside the steel due to viscous dissipation at the steel surface. In cooperation with the company voestalpine BÖHLER Edelstahl & Co KG, tests on the PM-steel in a dilatometer were performed to simulate the cycle-by-cycle heat pulses occurring in the injection molding process. With the results of those tests it was possible to state a hypothesis for the reason of this hardness loss.
Keywords: Plastic mold steel, hardness loss, platelet-wear-test, viscous dissipation
Corrosion-resistant mould steels are used to process chemically aggressive plastics such as PVC or PET in many plastic moulding processes such as extrusion, injection, blow and compression moulding. Free machining (sulfurized) grades are common choice for holders where the requirements are machinability and dimensional stability, whereas low sulfur grades are preferred for high surface finish requirements. But selecting the mould steel composition is not sufficient, the optimal production route is also very important. Research work was carried out on 2083 and 2085 martensitic stainless steels as well as other proprietary grades to increase the reliability and service life of the steel components used in the plastic injection mould industries. The influence of inclusions on the machinability and corrosion resistance in sulfurized or calcium-treated free-machining steels will be discussed.
Additive Manufacturing (AM) is becoming more common as manufacturing technique and the obvious benefits of freedom of design and production speed can clearly be utilized in the manufacturing of tools and molds. One of the most important criteria in producing molds for plastic injection is service life. This paper evaluates a mold produced using the conventional machining method versus mold optimized using AM. The mold manufactured using AM was optimized for uniform cooling, hence the cooling channels was placed in an optimal position. The surface temperature was evaluated using thermal imaging and the service life was simulated as well as evaluated by measuring surface damages, mainly caused by thermal stresses. Additional, this paper also includes the evaluation of the properties of a new low alloyed tool steel optimized for AM. The tool steel was firstly atomized into AM powder size distribution and the physical properties such as size and shape distributions was evaluated. The printability of the AM powder was further evaluated be evaluating the printed properties.
In this paper, a concept for hybrid forming tools with complex shape and conformal cooling channels is outlined. By using indirect additive manufacturing (AM) of sand molds via Binder Jetting technology and state of the art casting process as well as Laser Metal Deposition (LMD) and the latest of AM tool steel powder development to manufacture a complex press hardening tool, the authors show the suitability of AM for the tooling industry. Considering the materials used, this case study addresses the high demands on strength, wear resistance and thermal conductivity for such tools.
Wire is all around us and it forms joints in our structures, stabilizes our tires and transports electricity. In almost every complex product there are components made from wire. In wire drawing hot rolled material is drawn through a single or a series of tools called drawing dies, reducing the cross-section and enhancing the mechanical properties of the material. The tribological conditions in wire drawing are quite extreme and the high friction between the wire and the die which leads to plenty of heat going into the die, resulting in high tool temperatures. Previous studies have shown that by reducing the tool temperature it is possible to increase the productivity without risking an increased tool wear, this makes the
cooling of the tool of high importance for the wire drawing process. Triply periodic minimal surfaces (TPMS) which have lately been enabled to be manufactured by the use of additive manufacturing (AM) have shown great potential to be used for cooling applications with demand on high efficiency. In this study a tool holder for wire drawing was designed utilizing TPMS and was manufactured using laser powder bed fusion (LPBF). The cooling efficiency of the manufactured tool holder was evaluated and compared to a conventional tool holder in an industrial wire drawing process. The study shows promising results on improving the cooling efficiency in the process by using the TPMS AM tool
Powder metallurgy (PM) high speed steels have traditionally been used for tools but are gaining increased usage for demanding components such as rings in bearings and fuel injection. These components, but also many of the tools, are under cyclic load, sometimes several millions of cycles. For that reason, the fatigue resistance of PM-HSS (HSS) is one of the most important mechanical properties. Data and basic knowledge of fatigue resistance of PM-HSS is scarce in the open literature and this is today an obstacle for gaining more usage of PM-HSS in critical applications outside its traditional usage.
In this study we have looked at the influence from cleanliness, amount and size of non-metallic inclusions, and hardness on the tensile pull-pull fatigue resistance of PM-HSS. Results shows that high cleanliness can results in up to 50% higher fatigue strength. A novel part of the study includes the influence from voids typically surrounding non-metallic inclusions.
Direct Laser Metal Deposition (DLMD) is an additive manufacturing technique getting growing attention thanks to the possibility to produce very complex parts in short time and in a cost-effective manner. Possible applications of this technology are tools with conformal cooling channels and claddings for dies and moulds reparation. AISI H13 is a hot work tool steel, typically used for hot forming applications like die-casting tools, extrusion dies due to its high toughness and hot yield strength. One of the damaging mechanisms of tools is thermal fatigue (TF) cracking, leading to surface deterioration, and consequently also of the processed parts.
In this work the TF behaviour of DLMD-H13 submitted to two different heat treatments, namely direct tempering (T) and a quenching and tempering (QT), was investigated. Due to the different starting microstructure, as-built and Q samples had to be tempered to different temperatures to achieve the same target hardness for T and QT samples. T did not significantly change the solidification microstructure after DLMD, and microsegregation was present. On the other hand, QT produced a homogenous martensitic microstructure, since austenitizing partially amended the original solidification microstructure.
A customary laboratory test was developed to induce TF damage under a cyclic temperature variation between 630°C and 60°C. The total length of the cracks, cracks density, surface and hardness profiles, depth of cracks have been measured to evaluate the TF behaviour of H13 heat treated according to the two variants. The TF tests evidenced that the T-H13 has a slightly better TF resistance respect QT-H13, due to the higher tempering resistance of T-H13 respect to QT-H13. Thus, according to TF test results, direct tempering can be preferred to the quench and tempering, since the elimination of quenching can decrease the costs of production as well as distortions related issues, increasing the competitiveness of DLMD.
Laser additive manufacturing enables the one-step fabrication of complex parts. This technology has been applied for tooling due to advantages such as fast tool development, low material costs and high geometry freedom. However, pores and carbide networks, which are not avoidable from the LPBF process, deteriorate the fatigue strength significantly. Hot isostatic pressing (HIP) with integrated heat treatment is a powerful post-treatment, which not only densifies the material but also modifies the microstructure. In this study, AISI M3:2 samples were produced by LPBF and then were either austenitized, quenched and tempered in a HIP unit under pressure or were only hardened and tempered in a vacuum oven.
The corresponding microstructure was analyzed by optical microscopy, scanning electron microscopy (SEM) employing energy-dispersive X-ray spectroscopy and X-ray diﬀraction (XRD). The fatigue strength was determined by rotation bending tests. Fracture surfaces were observed under SEM for failure analysis. While both post-treatments lead to similar microstructure, the fatigue strength is significantly improved by the HIP process.
Laser Powder Bed Fusion (LPBF) is an additive manufacturing process that enables the production of complex shaped components. Conventional high-carbon tool steels tend to cracking and warping during LPBF due to internal stresses caused by the rapid solidification. Expensive atomization and long lead times for powder generate high costs for material development in this processing route.
The Laser Powder Bed Alloying (LPBA) of powder blends from conventionally available powders enables a more flexible approach of alloy design. For industrial use, the mechanical properties of LPBF parts must be comparable to those of conventionally manufactured parts. High chromium cold work tool steels, as used in cutting applications, need to possess sufficient abrasive wear - and corrosion resistance. In this study, AISI H13 has been modified by Cr3C2 and elemental chromium to suit these requirements. A novel alloy was modelled thermodynamically and processed by LPBA. In-depth microstructural investigations by backscatter electron imaging and electron backscatter diffraction in combination with ASTM G65 abrasive wear tests and potentiodynamic polarization curves allow microstructure property correlations for different heat-treated conditions. Crack-free processing, hardenability, formation of chromium-rich carbides and residual Cr-rich inclusions were observed and their influence on the wear- and corrosion resistance is discussed.
Die casting tools with improved cooling by conformal cooling produced using additive manufacturing allow to reduce cycle times and improve the part quality. Most available tooling materials for additive manufacturing are however, either not enough heat resistant or difficult to print. The paper presents Pearl®Micro TS700, an innovative 5% chromium, precipitation hardening tool steel, with a very good heat resistance close to 700°C and a good printability by laser melting for additive manufacturing of aluminum die casting tools. With different innovative heat treatments, the steel can be tweaked for highest heat resistance or better tenacity. Microstructures, hot hardness and temper resistance depending on heat treatment will be presented as well as impact toughness and tensile properties. Fabrication of hybrid tools will be discussed, where the part of the tool with the conformal cooling in contact with the cast part is printed onto a backing material to reduce printing time and material costs.
The use of Laser Additive Manufacturing (LAM) techniques, such as Laser powder bed fusion (L-PBF) or Laser Directed Energy Deposition (L-DED) for the manufacturing of forming tools has gained increasing interest in both industry and academia due to the processes’ high geometrical flexibility. LAM allows for a layer-wise build-up of parts based on 3D-CAD-data by either the local melting of a metallic powder bed by a laser beam (L-PBF) or a local application and laser beam melting of powder material by a nozzle (L-DED). Owing to the iterative local heat input by the laser beam, a locally and temporally unsteady heat flow as well as rapid heating and cooling occur in the part, resulting in non-equilibrium solidification, phase transformations and the formation of microstructural defects, cold cracks and distortion. In the case of carbon-martensitic tool steels, which are usually employed in tooling applications due to their high hardness and wear resistance, especially their cold crack susceptibility is problematic and is usually counteracted by a build-plate/ substrate preheating. Since preheating can increase the oxygen take-up of the powder and alter the part microstructure, preheating can be disadvantageous for part quality and powder reusability. In this study, a carbon-martensitic hot work tool steel specifically designed for the production of parts with low crack density by LAM without preheating is investigated. The study focuses on the microstructure and mechanical properties of the L-PBF- and L-DED-manufactured steel in as-built as well as heat treated condition. Results show that the steel can be LAM-processed without preheating resulting in specimen with low crack densities and a martensitic microstructure with retained austenite. Both hardness and strength can be increased by quenching and tempering. However, directly tempering the as-built specimen without previous quenching leads to a shift of the secondary hardness peak towards higher hardness and higher temperature.
In this study, different carbide morphologies of Cr-Mo-V powder metallurgical tool steels with the similar composition were compared. It is known that carbide size, height and orientation are very effective on wear properties such as galling and abrasive wear. Carbides can also act as stress points for crack initiation. In our study, larger carbides produced via new innovative process development of Uddeholms AB were subjected to abrasive wear test in order to verify the effect of carbide size on the pure abrasive wear resistance. Ductility of the material was measured by unnotched impact test. The microstructural evaluations were conducted by light-optical microscopy (LOM) and scanning electron microscopy (SEM) techniques. Abrasive wear property was studied with pin-on-disc test.
In this investigation, profiled high interstitial austenitic stainless steel parts were burnished on a profile rolling machine and afterwards the wear behavior was analyzed in a
melt of glass-reinforced polypropylene. Wear and corrosion resistance are significant properties of steel parts in plastics and food industries. The high work hardening ability of the
stainless steel enables burnishing parts with significant local hardness increase. Wear tests on a developed test stand show a wear resistance of the burnished surface near to that of a nitrided surface. Hence, it is concluded that roller-burnished austenitic stainless steel parts are suitable for corrosive environments with medium wear protection requirements.
In cold work applications, tool steels with high carbide contents are mainly used as cutting and stamping tools. The efficiency of cold forming processes depends on the tool life, which is limited by wear resistance and fatigue strength. Forming tools often fail due to fatigue fracture since fatigue design is usually not performed. Microstructural and statistical understanding of the underlying, fatigue strength influencing factors, which result directly from manufacturing, is still lacking.
To investigate the influence of manufacturing on the fatigue strength, rotating bending tests of AISI D2 (X155CrVMo12-1) and AISI M2 (HS6-5-2/-3) were carried out. Powder-metallurgical (PM) and melt-metallurgical (MM) production via conventional ingot casting followed by forging were investigated. Since in case of ingot casting, the subsequent forging produces carbide bands, which cause anisotropy, longitudinal and transverse direction were tested separately. This study presents for the first time a statistically full evaluated comparison and correlation of manufacturing with generated defect sizes, corresponding failure mechanisms and resulting fatigue strengths.
Both PM microstructures show significantly higher fatigue strengths than MM, the latter showing only 5–10% higher fatigue strength under longitudinal compared with transversal testing. Critical defects in PM are exclusively small, spheroidal, oxide inclusions at which crack initiation occurs through interfacial detachment. In contrast, crack initiation of MM in both longitudinal and transverse directions occur mainly through fracture of large, block-like eutectic carbides or larger carbide accumulations. In addition, crack initiation can be detected in transverse directions at elongated inclusions. Statistical fracture-surface-analysis reveals that the primary factor influencing fatigue strength is the defect size. Secondly, matrix hardness plays a crucial role. Circularity and defect type represent tertiary factors. To improve fatigue strengths, the defect sizes should be focused. For PM in particular, purity alone is of importance. For MM, firstly the size of primary and eutectic carbides is essential.
Meeting increasing requirements concerning part quality and process profitability despite difficult-to-machine materials is only possible with a deep process understanding. In this context, knowledge about the process temperature is of decisive im-portance, since it affects material properties such as hardness or forming behavior as well as chemical and physical interac-tions between tool, workpiece and lubricant. A proven thermoelectric method of temperature measurement in machining, forming and blanking is a tool-workpiece-thermocouple. This setup allows an instantaneous measurement of the temperature development during the manufacturing process insitu at the contact area of tool and workpiece. The accuracy of this method depends on the calibration of the thermocouple, for which the Seebeck coefficients of tool and workpiece material have to be determined. Usually, material samples from different batches are used for this purpose although the resulting measurement errors due to slight changes in material properties are hardly known. In this study, the effects of small changes in the chemical composition and hardness on the Seebeck coefficient are investigated for the first time in order to allow a precise quantifica-tion of the measurement error resulting from the calibration process.
The industry segment of tooling applications has demonstrated significant developments in the field of Additive Manufacturing (AM) in the last decade. Progressing all the way from prototyping to high Technology Readiness Levels (TRL), thus enabling production capabilities. Especially, in relationship to Laser Powder Bed Fusion (L-PBF) and Laser Metal Deposition (LMD) technologies. The latest years though there has been an effort to explore additional AM technologies and enable further the capabilities of AM towards tooling applications. Mainly, with the assistance of Electron Beam Melting (EBM) process that offers processing of high-alloyed material concepts that appear to be challenging otherwise. The latter is due to the high pre-heating temperatures during processing offered by EMB, which allows the material to suffer less due to buildup of residual stresses from the complex thermal history and high cooling rates during the manufacturing.
Uddeholms AB has previously demonstrated on a pilot scale the performance capabilities of the EBM process in respect to the high alloyed and commercially available tool steel powder grade Vanadis® 4 Extra AM. In the present communication, a focused effort on highlighting the production capabilities relevant to industrial needs is presented. Process modifications were implemented in order to address the design complexity required for the relevant tooling applications in focus. In addition, aspects of the entire process chain such as dimensional tolerances, surface quality, post treatment operations including heat-treatment or Hot Isostatic Pressing and machining operations were all addressed and evaluated. Moreover, characterization of the product quality and assessment of its performance towards sliding wear were included in the present study. The investigation highlights the competitive side of the tool steel grade processed by EBM, achieving performance levels that are qualified in the tooling applications while presenting advantageous alternatives to conventional production routes in terms of lead times.
Additive manufacturing methods are applied in various fields of industry because of advantages like rapid production of parts or freedom in design. In most cases materials with a low amount of carbon, e.g. stainless steels, are used for 3D-printing. An important and widely used representative of these grades is the material 1.4404 (316L), which is well established because of an easy processability and good corrosion properties. However, with focus on tooling and wear resistance, materials like 316L are not suitable because of low hardness, strength and wear resistance.
As an alternative, tool steel materials like the 1.2343 or 1.2344 are used, providing a far better hardness and wear resistance. Unfortunately, L-PBF is a complex process with a small process window for these materials. Therefore, the aim of this study is to identify a material composition that offers both, good processabilty and good wear resistance.
Additive manufacturing, 3D-printing, tool steel, hardness, wear resistance, high-carbon
Stainless austenitic steels like the 316L are very popular in the field of Additive Manufacturing. This clearly is due to the easy processability of austenitc steels in the AM process. Austentic steels can be printed with little distortion, which means that less support structures are required. This again reduces cost-intensive build-time as well as post-processing requirements. One disadvantage, however, is that austenitic steels have a low hardness and - as a consequence - low wear resistance. In this study, a new and especially for the AM-process developed high manganese austenitic steel and a conventional 316L are plasma-nitrided for a comparison in surface hardness. Due to the high manganese content of the new AM steel, a sufficiently deep nitride layer with a high hardness can be achieved. Thus, the new AM steel shows a deeper nitride layer as well as a higher nitride layer hardness than the comparative steel 316L. At the same time, the high-manganese AM steel has a doubled tensile strength as well as yield strength compared to 316L.
The combination of easy processing in the AM process together with subsequent post-treatment offers a cost-optimized application opportunity for this austenitic steel as a tool steel.
Hot stamping tools require cooling channels, preferably with a variety of sizes and a high positioning flexibility. Conventionally, these are machined. This represents a disadvantage because of the limited accessibility for milling tools and the low flexibility. By means of the Directed Energy Deposition (DED) process a flexible design of the cooling channels is possible. For this, conventional material is used as a base on which the tool part with the cooling channels is added by DED. Different geometries of cooling channels can be manufactured by DED in order to control the heat balance in the hot stamping tool during forming. In this context an agreement between the additive producibility and the surface fraction of the cooling channels, which contributes to the effective heat at the tool surface, is important. Experimental and numerical analyses demonstrate the possible configurations in this field. To reduce the surface roughness after the DED process, the tool surfaces are ball burnished subsequently. In this context, the influence of ball burnishing on the resulting roughness is investigated. Furthermore texturing of the surface can be applied for influencing the material flow in the hot stamping process. Bringing a defined pattern onto the tool surfaces (texturing) can be implemented by DED or ball burnishing – depending on the material properties of the metal powder. The effect of the surface integrity on the material flow is characterized by strip drawing tests in hot conditions. The combination of the described methods allows for manufacturing hot stamping tools with near-surface cooling channels and a global or local adjustment of the surface properties of the tools.
Laser Metal Deposition (LMD) is one of the promising processes for additive manufacturing thanks to its ability to produce practically large metallic parts and complex geometries in a cost-effective manner and short lead time. Moreover, it can be utilized for reparation and cladding, making it an outstanding choice for tooling and molding. In the current work, the heat treatment behavior of X35CrMoMn7-2-1 tool steel produced through LMD is studied using dilatometry. The as-built microstructure of parts mostly consists of partially tempered martensite due to high cooling rates and cyclic reheating during the deposition, along with considerable amounts (10%) of retained austenite (RA), which is a consequence of intercellular micro-segregation. The material’s responses to heat treatment in the as-built (AB) and quenched (Q) conditions are compared to evaluate the effect of microstructural homogenization and partial recrystallization of the microstructure after quenching. The hardness drops progressively in the Q samples by increasing the tempering temperatures, while the AB samples demonstrate a secondary hardening peak around 500˚C. Charpy impact toughness results follow a reverse trend compared to that of hardness as expected. The maximum Charpy toughness observed was 16J that related to the samples tempered at 575˚C.
In the surface-critical stands in hot rolling mills, so-called indefinite-chill alloys are used as shell materials for the work rolls. The microstructure of these materials consists of cementite, graphite as well as different other carbides which are embedded in a martensitic/bainitic matrix. In the past ten years, indefinite-chill materials were intensively developed to meet the higher requirements in today's rolling mills. It was necessary to increase the fraction of wear-resistant carbides in the microstructure but still to maintain the very high surface quality of the rolls. Nowadays not only indefinite-chill or carbide-enhanced indefinite-chill can be counted to the state-of-the-art materials: the so-called graphitic HSS materials are regularly used in different hot rolling applications where highest wear resistance is needed.
To measure the increase of the wear resistance, a wear test rig was designed and developed which allows to test work roll materials under conditions which are very close to those in a rolling mill but still in laboratory scale. This paper shows the investigation results of four different indefinite-chill and graphitic HSS alloys with different carbide amounts and types. The strong influence of MC and M2C/M6C-carbides can be clearly seen but beside the carbides, also the other microstructural phases have an influence on the wear of the alloys. It could be confirmed that with higher fractions of hard carbides the wear on the tested materials decreased but the results also show clearly, that there has to be a correct balance between the different carbide types as well as the balance between the carbide, graphite and matrix fractions.
The constantly increasing requirements for tool materials continuously set new challenges concerning loading capacity, resistance to damage and crack propagation as well as the characterisation of these properties, especially at elevated temperatures that arise e.g. at cutting edges when cutting metal workpieces. Essential progress in the field of tool technology and knowledge-based selection of tool materials is only possible with the coupling of FE simulation methods. Complex material data or material laws are necessary for this. The recording of the necessary mechanical properties such as tensile / compression test, low cycle fatigue, high cycle fatigue and fracture mechanical properties in the operating temperature ranges at well over 1000°C require special testing methods for these ultra-high-strength and brittle materials. The aim of this work is to present high-end mechanical testing methods for ultra-high strength tool materials that have been developed and successfully applied at Materials Center Leoben Forschung GmbH in recent years. This concerns static (tensile, compression, creep) as well as cyclic low cycle fatigue testing under uniaxial load from room temperasture to over 1000°C e.g. of high speed steels, hardmetals or refractory metals. Further methods concern fracture mechanics characterization such as fracture toughness or cyclic crack growth. These investigation methods are coupled with high-end microstructural investigation methods, such as high resolution scanning electron microscopy with focused ion beam including high resolution / high-temperature electron backscatter diffraction. The work gives an overview of these modern investigation methods on the basis of various investigation examples on a variation of different tool materials with concrete investigation examples in a strength range from 3000 MPa to 8000 MPa and in a temperature range up to 1400°C.
The purpose of this study is to assess the impact of different combinations of cryogenic treatments and tempering regimes on tribological properties of Cr-V tool steel against a CuSn6 counterpart. Dry sliding wear experiments were performed using a pin-on-disk tribometer according to the Taguchi method. Tribological behaviour is investigated under four process parameters at mixed levels: cryotemperature (-75, -140, or -196°C), tempering temperature (170 or 530°C), sliding velocity (0.064, 0.128, 0.1885 m/s), and load (1, 5, 10N). According to the analysis, the minimum friction coefficient is obtained by cryotreatment at -196°C combined with 170°C tempering, with a sliding velocity of 0.064 m/s and load 5N. For the minimum counterpart´s material adhesion level, cryogenic treatment at -196°C followed by tempering at 530°C, sliding velocity of 0.1885 m/s, and applied load of 1 N are the optimum settings. The ANOVA model shows that the sliding velocity (45.2%), load (40.2%), and tempering temperature (5.3%) have statistical significance on the friction coefficient, while the load (57.8%) and tempering temperature (16.4%) have statistical significance on adhesion levels. The tribological behaviour of the steel is explained by thorough microstructural examinations using the scanning electron microscopy and microanalysis, X-ray diffraction, and transmission electron microscopy.
Steels for production of frames for plastic molds frequently need to be stainless, while at the same time require large amounts of machining. Machinability as a crucial property can be enhanced by the addition of sulfur, resulting in the formation of favorable sulfides, which in turn can deteriorate mechanical properties and resistance to corrosion. The detrimental effect on mechanical properties is caused i.a. by elongation of sulfides during rolling or forging. In a novel approach, a special wire treatment of the melt was performed, which resulted in improved, spherical morphology and chemical composition of the inclusions, yet leading to even enhanced machinability (tested i.a. by means of milling). Milling tests revealed an increased productivity compared to conventionally manufactured material, which means improved lifetime of milling inserts even at highest cutting speeds. At the same time, mechanical properties, in particular toughness, were slightly improved, while corrosion resistance was not severely affected.
Usually, tool steels are used in quenched and tempered condition. Due to the phase transition from austenite to martensite and the volume change during the transformation, controlling of distortion might be a challenge. The end user’s demand for high hardness of the final tool leads to a poor machinability.
Engineering steels with bainitic structure are generally based on a low alloying content due to economic reasons, especially the carbon content is rather low compared to tool steels. Bainitic steels require often a controlled cooling to get the desired microstructure and the maximum size to achieve a fully homogeneous bainitic structure is limited to a dimension far below acceptable dimensions of tool steels.
A newly developed steel focusing on a bainitic structure even for bigger dimensions shows a lower hardness at ambient temperature than conventional hot working tool steels, but with a lower temperature dependency. Therefore, at service temperature the mechanical properties are comparable to established grades. Heat treatment is simplified by a simple austenitization and cooling process without special requirement on the cooling rate. Due to a generally lower cooling rate and lower hardness compared to a Q&T process the risk of cracking is reduced, while machinability is improved.
With the combination of good weldability and rather low hardness after rapid cooling, this grade can also be processed in additive manufacturing and is well-suited for a hybrid process of conventional and additive manufacturing.
The public funded project AddSteel aims to develop functionally adapted steel materials for additive manufacturing. Based on the AM process laser powder bed fusion (LPBF) the holistic process chain, including alloy design, powder atomization, additive manufacturing and post heat treatment is considered to achieve this objective.
Tool steels are usually characterized by higher carbon content and limited weldability, leading to limited processability for LPBF. To extend these limitations, different approaches for tool steels are investigated: For high-carbon tool steels the effects of the martensite starting temperature were investigated using 1.2842 as an example. A low martensite start temperature seems to be advantageous for crack-free processing with LPBF. In order to avoid a high hardness level after rapid cooling, the use of a hot work steel with a carbon content of 0.2 wt.-% was investigated. Due to the chemical composition of the material, a preheating temperature < 300°C is required. In addition, very high scanning speeds are possible with an improved shielding gas flow.
Finally, the experience along the process chain with the standard steels was used for a modification of the alloy 1.2344. The effects of this modification on additive manufacturing and heat treatment were investigated.
Thanks to its high hardness and cracking resistance in hot-working operations, AISI H13 is acknowledged as all-around steel for die making in high-pressure die casting, extrusion, and hot stamping. In addition, the opportunities offered by Additive Manufacturing (AM) to fabricate complex shapes and closed channels strongly meet the needs of hot-work tools designers but typically are not easily exploitable. Indeed, the processability of martensitic steels such as AISI H13 by those AM technologies working at ambient temperature is challenging due to process-related thermal cracking susceptibility. Although several studies in the literature investigate the processability of this alloy by Laser Powder Bed Fusion (LPBF), the Electron Beam Melting (EBM) process has rarely been investigated. In this work, the microstructural characterization of an EBM-processed AISI H13 is presented through the correlation between the complex thermal history related to the EBM process and the as-built microstructure.
Near full-dense and crack-free AISI H13 hot work tool steel was fabricated using laser-directed energy deposition (L-DED). Two different heat treatment schedules, i.e., direct tempering of the as-built part (DT) and austenitization and quenching prior to tempering (QT), were selected. The effect of heat treatment on the microstructure, hardness, fracture toughness (Kapp), and softening behavior of the L-DED H13 was investigated. For this purpose, the optimum austenitization schedule was identified, and tempering curves were produced. At a similar hardness level (i.e., 500 HV10), QT parts showed higher Kapp (i.e., 89 MPa√m) than that of DT (i.e., 70 MPa√m). This behavior was discussed considering the microstructural homogenization and recrystallization taking place during austenitization. The fracture toughness values obtained for both heat treatment conditions were comparable to that of wrought H13. Finally, the tempering resistance (softening behavior) of the material at elevated temperatures is discussed in the light of the initial microstructures and phases of the as-built, and quenched specimens.
Böhler W360 ISOBLOC is well known as high performance hot work tool steel. The main characteristics are high thermal and wear stability, hardness in use up to 57 HRC and particularly the resistance against crack propagation. Therefore the main applications are as thermal and mechanical highly stressed tools among others for Al high pressure die casting (HPDC) inserts.
Nowadays the Laser Powder Bed Fusion (L-PBF) technology enables the production of tools with conformal cooling for e.g. aluminum HPDC. However, only few additive manufacturing powder (AMPO) alloys for additive manufacturing of dies and inserts are commercial available. Due to its easy printability, 18% Ni maraging steel (1.2709, Maraging 300 ≈ Böhler W722 AMPO) is mostly used for inserts with conformal cooling. Nevertheless, this type of alloy is originally not designed for applications in aluminum HPDC. Here, the Böhler W360 AMPO combines the material suitability of W360 ISOBLOC for pressure die casting with the advantages of additive manufacturing.
However, the resistance against dissolution in Al-melt (soldering) as well as thermal fatigue determines the performance of aluminum high-pressure die casting tool materials. In order to rate the performance, two specifically designed test setups that simulate the occurring stress under harsh conditions are developed. These are the immersion stirring- and the thermal fatigue tests. Furthermore, the performance of the commonly hot work tool steel Böhler W300 ISOBLOC (H11, 1.2343) is used as a zero respectively baseline for assessment of the investigated materials, because it is “state of the art” for HPDC.
In this study the performance of Böhler W360 ISOBLOC as well as W360 AMPO according to the thermochemical and thermal fatigue resistance is compared. Additionally, the Böhler W722 AMPO is considered in the comparison in order to determine its suitability for HPDC. The results will be discussed in this presentation.
The need to develop products with superior performance has led to the development of new materials and heat treatments. In the case of tools, well designed and controlled heat treatment is crucial to achieve appropriate combination of superior properties. In the huge number of heat treatment and surface engineering techniques, deep cryogenic treatment (DCT) shows very promising results. However, despite the potential and capability of DCT, these processes are still hardly known and implemented in practice. The main reason lies in the fact that the development of DCT has been mainly empiric, without a clear understanding of the scientific basics. Furthermore, for many years DCT had the reputation of being a quick fix for poor heat treatment practice. And although many different studies on DCT have been conducted, waste diversity of steel grades and heat treatment parameters were used and different testing methods applied, resulting in DCT effects being reported as highly positive, neutral and even negative. This makes comparison and true evaluation of DCT effectiveness practically impossible.
The aim of our research work was to systematically evaluate the effectiveness of DCT when it comes to tribological properties and wear resistance of tool steels, including influence of steel type, composition and hardening temperature. Since tools are subjected to different contact conditions and wear mechanisms, which require different tool steel grades, three representatives from each group (HSS, hot work tool steel and cold work tool steel) having different combination of alloying elements were selected and DCT treated in combination with quenching from high and low austenitizing temperature. Effect of DCT was evaluated in terms of abrasive and adhesive wear resistance under sliding, galling resistance in forming and impact wear resistance. Finally the results were correlated to changes in microstructure, hardness and toughness.
The improvement of material properties for tool applications has always been an overriding development topic. To minimize wear, tool steels, special alloys based on nickel
or cobalt and metal matrix composites (MMC) have been developed – either as molten or as powder metallurgical materials. In this study a new kind of material is described which combines the outstanding properties of CoCrW-alloys at high temperatures and the improved wear-resistance of MMCs incorporating additional hard phases in a matrix. A gas atomized powder of a carbide-rich matrix (Co = Balance, Cr = 28%, W = 4.5%, C=1%) is reinforced by titanium carbides (TiC, 10 ma.-% of total composition) and solidified by hot-isostatic pressing. The present study shows selected results on microstructure (e.g. SEM, EDX anal- yses), mechanical properties (e.g. hardness, bending fracture strength) as well as application examples.
Wire drawing is one of the oldest and most used metal forming processes. In a conventional wire drawing process, the cross-section of the wire is reduced to the final dimension by drawing the wire through a series of drawing dies made of cemented carbide or poly crystalline diamond. Despite the use of different types of lubricants wear of the dies, frequently resulting in time-consuming die changes, is a problem which limits the possibility to increase the productivity of the process. Also, the requirements for a high wire surface quality have become very high during the last years, especially for products such as spring steel wires. In the present work, the gradual surface degradation and wear of uncoated and PVD-coated (AlCrN+DLC) cemented carbide drawing dies have been investigated when drawing low alloyed carbon steel wire.
The results show that the initial wear of uncoated cemented carbide dies is due to preferential removal of the Co binder metal in combination with plastic deformation and cracking of individual carbide grains resulting in a topographic surface. The increased surface topography tends to increase the tribological interaction with the mating steel wire surface increasing the tendency for cracking and fragmentation of the carbide phase and the wear rate (steady state wear conditions). PVD coated cemented carbide dies exhibit an increased wear resistance compared to uncoated cemented carbide dies by significantly reducing the wear initiation of the cemented carbide and extending the transition from the initial wear regime (low wear rate) to the steady-state wear regime (high wear rate). The prevailing wear mechanisms are illustrated and characterized using optical surface profilometry, high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy.
Although anisotropic surface textures have been used to improve tribological performance in various mechanical systems in recent years, relatively few researchers have investigated the use of such textures in metal forming processes. In addition to achieving a better understanding of how anisotropic surfaces influence forming behaviour, it must also be considered that directional friction coefficients will also need to be developed for process modelling and analysis purposes. In the present study, experimental ring tests were used to calculate friction coefficients for H-13 platens which had an anisotropic texture (i.e. uni-directional grooves or surface lay). Friction factors were calculated parallel and perpendicular to the platen lay direction and then used to simulate hot compression of 6061-T6 Aluminium rings and bars using the DEFORM® system. The simulation results showed good agreement to experimental data and suggest that ring testing can be used as a means to establish numerical values for tool surfaces having directional grooves. The results also show that specimen orientation relative to the lay direction affected the degree of uniform flow and the resulting forming load. An example application based on strip rolling is also presented to illustrate the potential utility of anisotropic tool surfaces in hot working processes.
It has long been recognized that die surface roughness and lay have significant effects on flow behavior in sheet metal forming processes. In comparison, relatively little research has been conducted to explore similar effects in bulk forming processes. In the present paper, an experimental study was conducted using warm and hot working conditions to investigate how directional (anisotropic) tool topography on friction and planar flow. The study was conducted using lubricated AISI H-13 steel platens which had unidirectional finishes on the working surfaces. Six sets of tools with different surface roughnesses were used to compress 6061-T6 Aluminum and AISI 1018 steel specimens which had an isotropic surface finish. Ring tests were used to measure and compare friction parallel and perpendicular to the platen lay for each experimental condition. Prismatic pieces were side pressed at different angular orientations to study changes in planar flow behavior. In contrast to sheet forming, friction factors parallel to the lay were lower than those in the perpendicular direction though this effect depends on the type of lubricant. Increased flow stress and the resulting decrease in asperity penetration were also found to affect friction differences in the directions parallel and perpendicular to the lay. Based on calculated spread ratios, die surface roughness and workpiece orientation were both found to have an effect on planar metal flow though this effect is also modified by lubricant type and process conditions.
Intelligent temperature control of die casting moulds opens up enormous potential for improving cycle times, tool life, as well as the structure and warpage of the cast parts. In this context, “intelligent temperature control systems” are three-dimensional, contour-adapted temperature control systems that can be produced using generic AM processes. Moving them close to the component and "thermally fast-acting" tools make casting processes in the sense of a Foundry 4.0 approach controllable, more robust and more cost-effective. In die-casting, such temperature control systems are still exotic, while in polymer injection moulding they represent the latest state of the art.
In order to establish such new, expensive and risky technologies, the evidence of their effect on the die casting process and the cast components plays a central role. With the help of the virtual design and optimization of casting processes, which has been established for over 30 years, the effects of any temperature control measures on cycle time, tool life, as well as structure and warpage of the cast parts can be proven and quantified.
This contribution deals with the virtual layout and the optimization of complex three-dimensional, contour-adapted temperature control systems, as they can in principle only be represented by AM processes. Tool materials with different thermal conductivities and the evaluation of the temperature control for the tool life form complementary focal points.
The objective of this work is to verify the machining process behavior of the Cr3C2 25NiCr HVOF coating. which can be used for the automotive, aerospace industries and naval, improving the sufarce finish of the thermal spray. The coating is machined with a 12mm diameter carbide ball nose tool, in which the tool is parallel to the surface, with a cutting speed of 100m/min, and a feed of 0.1mm/revolution, where the machining is carried out at an angle, between 1° and 2°, from the top of the coating to the substrate, in the zig zag, concordant and discordant directions. Before and after machining microhardness, optical profilometry and SEM tests were performed on the samples. After microhardness tests, it was verified a hardness increases of the coating after machining, probably due compression process carried out with machining. Optical profilometry and SEM observed that the surface showed a similar Ra, Rp and Rv, than substrate. A significant difference was observed on the Rv value, where the roughness the average valleys in the coating is much higher than substrate. This occurred because the machining process removes some lamellas from the sprayed coating.
Electro-slag remelting is an important process to produce high quality tool steels. Thereby the slag composition has a strong effect on the remelting behavior in general and on the electric energy consumption as well as on the removal of non-metallic inclusion. Later aspect is strongly related to chemical reactions taking place between the slag and the metal and thereby determines the necessary compositions of the slag. Also the electrical conductivity of the slag is determined by the slag composition, and a high resistivity, among other factors, is desirable to reduce energy consumption.
The effect of different slag compositions with a wide range of electrical conductivity was investigated regarding their general remelting behavior such as slag movement, slag surface temperature and slag skin thickness as well as their impact on chemical reactions and the removal of non-metallic inclusions. Therefore a laboratory scale ESR-unit, equipped with several measurement devices and a typical plastic mold steels were used for the experimental trials.
The results show a strong impact on the remelting behavior as well as on the specific energy consumption. Standard slags thereby show a good agreement with earlier reports form industrial scale results of a similar tool steels. The findings form the chemical analysis and detection of non-metallic inclusions indicate, that a similar metallurgical behavior is feasible despite large differences in the energy consumption.
During machining, the employed cutting tool experiences thermo-mechanical loads that cause wear
at the interacting surfaces, hence, limiting the tool life. The speed of chip sliding and contact pressure on the
tool dominate the magnitude of wear; therefore, these factors were considered in the developed interactive
friction model. Considering high heat generation results in a temperature increase in the cutting zone, the effect
of temperature was included in the developed model. The experimental results of the orthogonal cutting of
AISI304L steel with TiN coated WC cutting tool has been used to calibrate the model. The model has the
capability to adjust the friction and residual coating due to the enforced complex and dynamic loading (i.e.,
change in speed or pressure). Practical complex loading conditions of the orthogonal cutting have been
employed in the developed interactive friction model (IFM) to project the instantaneous behavior of coefficient
of friction as well as the residual coating thickness and coating depletion rate.
The typical heat treatment of martensitic stainless steels consists of hardening and subsequent tempering once or several times. During tempering the common tempering
mechanisms occur, such as carbide precipitation, relaxation of the fresh martensite, destabilisation of the retained austenite and subsequent transformation of austenite into martensite. In the case of low-alloyed steels, Quenching & Partitioning (Q&P) can be carried out as a heat treatment, whereby a certain retained austenite content is set and subsequently stabilised. Such partitioning effect can also take place in martensitic stainless steels. In this study, different retained austenite contents are set for martensitic stainless steels using a Q&P-typ heat treatment and then the effect of the retained austenite on the steels properties is investigated. For this purpose, samples were heat treated by dilatometer as well as in furnaces in order to set specific retained austenite contents in the microstructure after tempering. This is mainly possible by varying the quenching temperature in combination with different tempering temperatures. Even small temperature variations can have an influence on the retained austenite content. After the heat treatment of the samples, hardness and impact toughness were determined and the values were compared with each other. Additional microstructural investigations were performed including XRD and optical metallography.
Retained austenite is widely regarded as a detrimental microstructural constituent in high-alloyed tool steels. However, an undesired amount of it often remains in the microstructure due to the incomplete transformation of austenite into martensite during the hardening process of tool and high-speed steels. Resulting effects are dimensional instabilities and internal stresses after the heat treatment, which leads to limited tool performance. This paper addresses the preconditions of retained austenite formation and its microstructural and sub-microstructural appearance. Even though the retained austenite content can be difficult to detect, there are reliable methods for determining its volume in high-alloyed tool steels such as X-ray diffraction, electron backscatter diffraction and transmission electron microscopy. Specified heat treatment such as sub-zero treatments or multi tempering steps of tools can help to avoid excessive retained austenite content and therefore extend tool life significantly. Evidence of the negative effects of un-transformed austenite and different solutions to avoid this phenomenon are given and discussed in this paper by means of real tooling cases in various fields of application. The first case shows the undesired effects on the dimensional stability of a die plate made of 1.2379 (X153CrMoV12). A further case presents a cold forming punch made the of high speed steel HS 4-3-1.5 which failed after a short period of time and showed fatal fractures originating from an suboptimal microstructure due to an insufficient after heat treatment.
Keywords: Retained austenite, tool steels, high-speed steels, metallography, heat treatment, die plates, cold forming
Chromium- and chromium-vanadium ledeburitic tool steels are extensively used in industry, for cold work tooling. The applications where abrasive wear is dominant such as fine-blanking, punching, cropping, shearing or trimming are typical examples. For these applications the steels must have high strength and hardness. On the other hand the tools have to withstand the chipping or cracking in real industrial processes. Hence, they should have at least acceptable fracture toughness. It is known that the strength and toughness are in strong conflict in most cases. The current paper deals with the possibility to balance between these properties, through application of different schedules of cryogenic treatments and tempering. The Vanadis 6 steel is used as a model material. Vacuum austenitized and gas quenched steel was subjected to cryogenic treatments at -75, -140, -196 or -269 °C, which was followed by different tempering. The fracture toughness of treated steel was determined by 10 × 10 × 55 mm prior fatigue pre-cracked specimens, by three-point bending tests. The testing of fracture toughness was complemented by careful microstructural investigations, hardness measurements and fractography. It has been established that cryogenic treatment makes it possible to simultaneously increase the hardness and toughness, albeit in relatively limited extent. The most promising way how to do it is the application of -140 °C for the cryogenic treatment followed by suitable tempering regime.
The die-casting molds employed with molten aluminum under high pressures are subjected to severe localized corrosion, which is due, mainly, to the intense thermal cycling at temperatures around 700 °C. The recovery of molds usually involve the removal of the damaged region and reconstruction through welding. By a different approach, the resistance and lifespan of the recovered piece can be improved with multiple surface treatments to assure tribo-mechanical corrosion and thermal fatigue strengths. One of them is the surface nitriding, which promotes load bearing capacity to subsequent deposited films. The tool steel H13, presenting the lath martensite structure, was plasma nitrided at temperatures from 400 °C to 560 °C, providing hardened cases ( up to 12 GPa) with 100-220 μm thick. The modified surfaces consisted in graded layers, with a composite region on the top (mostly iron nitrides) and an underneath expanded nitrogen martensite. As an initial testing phase, 400 ºC nitrided surfaces received DLC coatings with ~120 μm thick. The wear coefficient reduced ~25 % for the nitrided surface as compared with the H13 steel that was only DLC coated. Thermal cycling tests in a homemade aluminum-bath apparatus, carried out under different amount of cycles with heating and cooling steps, disclosed the surface integrity was closely related with the nitrided surface structure.
High pressure die casting (HPDC) is a well established manufactory process which allows, specially the automotive sector, to make high precision components in fast paced rates. Furthermore, the increasing need for lighter components stimulate the use of low density alloys, making the HPDC suitable for this emerging demand. Nevertheless, every manufacturing process has spaces for improvement. Regarding to HPDC many wear mechanisms cause it to fail or not be as well rounded over the time. Corrosion induced by molten metal is one of many failure modes for dies. Corrosion not only changes the geometry but also modifies the surface roughness, which may lead to die soldering. All combined wear not only changes the dimensional precision of the manufactured parts but also the surface quality, requiring rework. The maintenance is quite often expensive and its price imbedded to final product price. Many techniques are applied to decrease wear and even recovery the surface by additive methods. However, there is a lack of study on additive techniques and how farther the operation will be extended. The study of recovering HPDC machines components via thermal sprays still lacking on the literature. By thermal spraying mechanical components, it is possible not only to improve the surface properties but also recovery the geometry changes caused by aluminum attack. The main idea is to verify the possible use of thermal spray coating on surfaces exposed to wear on HPDC processes and how the aluminum interaction changes material properties and geometry.
Low Pressure Die Casting (LPDC) is a widely used process for the manufacturing of automotive components. These components have high mechanical requirements, which
are difficult to achieve reproducibly within standard boundary conditions in LPDC. To ensure part feasibility, some areas are oversized to improve filling behavior and therefore local me-
chanical properties. Targeting these issues of high mechanical requirements an “active insert” has been developed, which actively influences the casting process using magneto hydraulics principles and therefore the part quality significantly. The process reliability due to porosity
reduction was increased compared to the existing LPDC parts. For characterization, tensile tests and microstructure analyses were carried out. It could be proven that the casted parts show an average grain size reduction, a more homogenous microstructure and reduced local
dendritic porosity, resulting in improved ultimate tensile strength and elongation values in an AlSi7Mg0.3 alloy.
For industrial mechanical food processing steps, like cutting, slicing, grating, passing or similar applications, tools of martensitic stainless steels are preferably used because of their high hardness and corrosion resistance. The latter is decisive to avoid contamination of foodstuff by elements transferred from the steel alloy into the processed food.
In this work various martensitic stainless steels in different heat treatment conditions were investigated regarding their metal release behavior in food simulants. Therefore, migrations tests were carried out according to the guideline of the Council of Europe. During the examination, the migration of specific elements was determined and compared to defined release limits, which take into account the different toxicity for the human body. The results allow an assessment of the suitability of the tested grades and heat treatment conditions as contact material for different types of food.
Efficient processes offer a promising approach to meet requirements from global trends like sustainability or resource shortage. The process of orbital forming is established
for the manufacturing of functional components with a gradient in sheet thickness, like for example in a clutch. Nevertheless, the present tool setup disposes a lack in economic efficiency and is restricted by a maximum tumbling angle and a complex tool design. In this context, an innovative quasi-incremental process combination of tilting and turning is investigated with regard to the manufacturability of functional components with circumferen-
tial and cyclic symmetric elements. Due to the adapted kinematics, the contact area between tool and workpiece increases from the center in radial direction, resulting in a predominantly radial material flow. The aim within this research is the establishment of a comprehensive
process understanding of the forming parameters. Therefore, components out of the case-hardening steel C10 are manufactured and evaluated, regarding the geometrical and
mechanical properties. Different process strategies, like a varying number of tilting steps or the forming along different axis, are applied in order to improve the forming results. The
potential of the alternative tool setup for the manufacturing of the components is qualified by comparing the parts with conventionally orbital formed specimens.
Improving tool life under cyclic loadings is of great economic interest, since forming tools often fail due to fatigue fracture initiated at volume or surface defects. Increasing the fatigue strength of tool steels can be achieved through improved steel making or properly chosen case hardening. Diffusion layer plasma-nitriding has never been investigated statistically or microstructure-dependently, especially for carbide-rich tool steels. This study provides a complete, statistically evaluated comparison of plasma-nitriding effects on the fatigue strength, additionally considering microstructural characteristics.
Rotating bending tests of plasma-nitrided specimens from AISI D2 (X155CrVMo12-1) and AISI M2 (HS6-5-2/-3) were performed. Thereby powder-metallurgical (PM) and melt-metallurgical (MM) production via ingot casting with forging in longitudinal/transversal direction were distinguished to furthermore consider manufacturing-related differences in purity, carbide and defect sizes. Nitriding leads to greater surface hardness and reduced case toughness due to precipitation hardening, but no negative effects can be statistically demonstrated. For MM of AISI M2 in longitudinal/transverse direction no positive effect occurs. Plasma-nitriding results in an increase of fatigue strengths for MM of AISI D2. The effects of plasma-nitriding not only depend on defect sizes but also on the initial matrix hardness and are thus depending on a combination of the primary and secondary influencing factor.
In contrast to MM, nitriding results in a remarkable increase of fatigue strength for both PM steels. Defect sizes and fatigue mechanisms do not change by nitriding, since nitrides are significantly smaller compared to carbides and thus not relevant for crack initiation. In PM steels with comparatively high purity and much smaller defects, the generated compressive residual stress leads to retardation and delay of crack initiation at small oxide inclusions. Since defect sizes in MM are much larger, nitriding has less or no positive effects on fatigue strengths, that strongly depend on the matrix hardness set during heat treatment.
ROTA 2030 (in English, Route 2030) is a Brazilian strategic program for developing the automotive sector. Among its priority lines, it focuses on bringing competitiveness to the Brazilian tooling industrial sector. Called “Ferramentarias Brasileiras Mais Competitivas” (in English “More Competitive Brazilian Tool Shops”), it is a line organized in four axes, among which the first three support projects with different levels of maturity. The fourth axis proposes the use of “demonstrators” to identify challenges and gaps in the Brazilian tooling sector. In this context, this paper briefly introduces the project, named after the acronym of Demonstrador de Estampagem de Superfícies Classe “A” - DEMESTAA (in English, Class “A” Surface Die Demonstrator). Class “A” surfaces are known in the automotive industry for their difficult-to-reach aesthetic, with often surface defects. The DEMESTAA demonstrator consists of a Die Set for producing an automotive door as a single part. It aims at representing all the main challenges faced by manufacturers to make those aesthetic automotive parts. Remarkably, this paper presents the methodology adopted in the DEMESTAA Project for defining requirements and setting up the technical specification of the demonstrator. It discusses the main challenges faced in this process as well as the solutions adopted. This specification encompasses the first four phases of the die tool lifecycle, known as Die Engineering, Die Design, Manufacturing, and Try-out. Among the discussed issues are: how to assure the representativeness of the specification; how to characterize the best practices adopted by automotive OEMs; how to deal with the lack of public standards representative of the automotive requirements; how to define information and data to be collected in the development process and the main operational bottlenecks in the construction of a tooling; between consensus among the more than 20 industrial partners that participate in the DEMESTAA Project.
The growing importance of lightweight construction to reduce resource consumption is leading to the increased use of multi-material systems consisting of components with varying geometric and mechanical properties. However, the joining processes to manufacture these assemblies are gradually reaching their limits, which is why innovative processes and methods are required. To enhance the versatility of the established but comparatively rigid joining process of self-piercing riveting, a new approach is to superimpose it with a tumbling kinematic. For this purpose, a tool is presented that consists of two synchronised axes that allow free movement and any position of the tumbling punch in a polar coordinate system in the form of a circle. Due to the chosen combination of axes, an in-situ control of the tool in the joining process allows to detect individual process sections and specifically influence the joining process by adapting the tumbling strategy. Controlling the tool with a combination of a programmable logic controller (PLC) and integrated Matlab scripts enables completely free kinematics and gives the possibility to react to parameters measured in the process. Continuously variable tumbling angles of the punch between 0° and 6° can be set and the combination of axes enables predominantly linear and rotating movements of the punch with comparatively high dynamics. This makes it possible to investigate the conventional tumbling kinematics in the form of circular and spiral trajectories, each with several tumbling angle increments. The influence of both force- and displacement-controlled punch movement is investigated and the rotational tumbling speed of the punch can be varied for the tests. The materials used are the typical multi-material aluminium alloy EN AW-6014 and the dual-phase steel HCT590X+Z with different sheet thicknesses. In order to gain a comprehensive understanding of the resulting influences force displacement curves and geometrical joint characteristics are examined.
Intelligent material combinations for the production of multi-material systems as well as lightweight construction to save weight are becoming increasingly important in industrial applications. But the joining process of dissimilar materials, such as high-strength steel and aluminium as well as steel and continuous fiber-reinforced plastics (CFRT), which are often used in multi-material systems, poses challenges to established joining processes due to different mechanical properties and chemical incompatibilities and lead to a need for new, versatile joining technologies. In this context, joining with pin structures has proven to be a promising process for both metal/CFRT and metal/metal joints. The use of cold extruded pins made from the sheet metal plane is the subject of current research due to the added potential for weight saving and the advantage of process-induced work hardening. For the production of these pins and especially for multi-pin structures however, new tool concepts are needed. In the present work, a multi-acting tooling design is presented to produce a multi-pin array consisting of a 3x4 matrix by extrusion from the sheet metal plane. The tool allows the punches, the blank holder and the ejector to be controlled independently. This enables the blank holder pressure, which prevents the sheet from bulging and reduces the radial material flow during the process, to be controlled independently of the punch movement. The individual pins can be formed both simultaneously in one stroke and sequentially to control the formation of each pin individually. The numerical model utilised for designing the active parts of the tool is used to analyse the complex, resulting material flow and to gain insights into the pin forming. Furthermore, first experimental results of cold extruded multi-pin arrays are presented, to obtain a basic scientific understanding of the influence of the tool on the process in combination with the numerical results.
Copper-Beryllium precipitation hardening alloys are widely used to manufacture molds in plastic injection moulding due to the excellent thermal properties combined with good mechanical strength and corrosion resistance. However, the lower hardness and wear resistance compared to tool steel, as well as the higher cost, limited their wider use. A tool steel cladding on copper alloy substrate represents a suitable solution to overcome these limitations. Among the candidate cladding techniques, direct laser metal deposition (DLMD) seems to be a proper solution due to its flexibility, the possibility to fabricate thick cladding (1mm) and even 3D structures. However, a direct DLMD of tool steel showed critical issues such as cracks and lack-of-fusion. Substrate preheating can inhibit above defects but it will meanwhile damage the substrate strength due to overaging. Thus, appropriate deposition strategies were considered in order to avoid the use of substrate preheating.
In this work, AISI H13 hot-work tool steel was cladded by DLMD on Moldmax-HH Cu-Be alloy substrate. Different deposition strategies involving i) an intermediate buffer layer (austenitic stainless steel and Ni-superalloy) and ii) functionally graded architecture, were considered to try to inhibit cracking and lack-of-fusion.
The microstructure of samples was analyzed by optical and scanning electron microscopy. Energy Disperse Spectroscopy was used to evaluate interface diffusion of Cu, Fe, and alloying elements. Microhardness profiles were determined to evaluate the influence of buffer layer and functionally graded structure on surface (tool steel) and substrate (CuBe) hardness. The mechanical and thermal properties including load bearing capability (LBC) and thermal conductivity (TC) were also investigated. The results showed that the Ni-superalloy buffer led to crack-free cladding. FGM suppressed cracking but did not totally eliminate it. LBC and TC can be tuned changing the ration between cladding/substrate thickness.