Forging Tools Research Articles

Effects of laser on the non-smooth surface in improving the durability of hot forging tools

One of the key factors determining the lifetime or durability of hot forging tools is their resistance to wearing. The application of laser technology to prepare a non-smooth unit on the surface of hot forging tools has been found to be an effective method in improving the lifetime or durability of the hot forging tools. In this study, laser non-smooth surfaces were prepared by laser texturing technology on the surface of hot forging tools used in factories. The microstructure and the phase composition of the non-smooth unit were characterized by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Moreover, the wear resistance of the unit at different angles was also examined. Three representative unit angles were identified on the surface of the hot forging tools for the actual application in the factory. Similar results of wearing were observed in the laboratory and the actual application test in the factory. The results show that the smaller the angle of the non-smooth unit, the higher the wear resistance of the non-smooth surface. It was evidently confirmed that the 0° unit ensures the best wear resistance and provides the longest durability to the hot forging tools.

Surface structuring by laser remelting of 1.2379 (D2) for cold forging tools in automotive applications

Surface structuring by remelting with laser radiation is a new approach to shape metallic surfaces (“WaveShape”). In this structuring process, material is reallocated in its molten state instead of being removed, because the process is based on the new active principle of remelting. The surface structure and the microroughness result from a laser-controlled melt pool due to surface tension. Basic research has been conducted with promising results, especially for the hot work steel DIN 1.2343 (AISI H11) and the titanium alloy Ti6Al4V. This work is an attempt to expand the spectrum of processable materials, and the objective of this investigation is to determine the influence of crucial process parameters on characteristic surface features such as structure height for surface structuring by laser remelting of cold work steel 1.2379 (AISI D2). For the first time, an industrial laser polishing machine (“ALPINE”) was used for experimental investigations on surface structuring by laser remelting. The results achieved with this machine show that surface structuring by laser remelting is well suited to process the cold work steel 1.2379 (AISI D2) and that this industrial laser polishing machine is well suited to produce structured surfaces. In fact, for the first time, periodic surface structures with a structure height larger than 1 mm were created successfully using the WaveShape process.

Shape optimization of preform tools in forging of aerofoil using a metamodel-assisted multi-island genetic algorithm

ABSTRACTPreform design plays an important role in improving the material flow, mechanical properties and reducing defects for forgings with complex shapes. In this paper, a study on shape optimization of preform tools in forging of an airfoil is carried out based on a multi-island genetic algorithm combined with a metamodel technique. An optimal Latin hypercube sampling technique is employed for sampling with the expected coverage of parameter space. Finite element (FE) simulations of multistep forging processes are implemented to obtain the objective function values for evaluating the forging qualities. For facilitating the optimization process, a radial basis function surrogate model is established to predict the responses of the hot forging process to the variation of the preform tool shape. In consideration of the compromise between different optimal objectives, a set of Pareto-optimal solutions are identified by the suggested genetic algorithm to provide more selections. Finally, according to the proposed fitness function, the best solution of multi-objective optimization on the Pareto front is confirmed and the corresponding preform tool shape proves optimal performances with substantially improved forging qualities via FE validation.

Analysis of wear mechanisms of hot forging tools protected with hybrid layers performed by nitriding and PVD coatings deposition

This article presents the results of research on hybrid layers used to increase the durability of hot forging tools. The aim of the work is to uniformly compare mechanisms of wear of different hybrid layers deposited simultaneously on one forging tool for this purpose. The test tool was made of hot working tool steel X37CrMoV5-1, and the raw parts in the test forging process were made of 16MnCr5 steel. The tool was divided into four zones: gas nitrided substrate (GN), GN and Cr / CrN coating, GN and Cr / CrN / AlCrTiN coating, GN and CrN / AlCrN / AlCrTiSiN coating. Because the tool is axially symmetrical, each zone was subjected to destructive mechanisms during the forging process in the same way. After exploitation, the tool was analyzed for the destructive mechanisms occurring in the surface layer. It is believed that the main destructive mechanism is abrasive wear, which is intensified by thermal and mechanical fatigue, adhesive wear, the tempering of the surface layer and oxidation. In the analyzed case, the dominant influence of thermo-mechanical fatigue was observed in the form of a grid of cracks present on the surface of the forging die. The surface of tools was analyzed in light and SEM microscopy, surface roughness was tested at various stages of exploitation, the geometry of tools used was measured using a laser scanner and GOM software, and the microhardness and microstructure of hybrid layers after exploitation were analyzed. In addition, to determine how the properties of hybrid layers change during work, the scratch test was performed, in which the adhesion of the coating to the substrate was determined on the surface of specimens taken from a tool after exploitation. The results showed differences in the wear mechanisms observed on all analyzed layers and changes in properties in the surface layer that already occurred at an early stage of exploitation.

Remanufacture of hot forging tools and dies using laser metal deposition with powder and a hard-facing alloy Stellite 21\xae

Additive Layer Manufacturing (ALM) processes are attracting interest in the forging industry due to their potential suitability for remanufacturing and repair of tools and dies. The ALM process known as Laser Metal Deposition with powder (LMD-p) can be used to provide a hard-facing alloy repair to hot forging tools. This is particularly important on complex tool geometries due their superior wear resistance. The Advanced Forming Research Centre (AFRC) has established a low cost standard test method to evaluate abrasive and adhesive wear on hot forging H13 tool steel dies on an industrial scale 160 kJ Schuler screw press. The bespoke tool design allows researchers to benchmark new and novel coatings, lubricants and additive layers against a known standard. Furthermore, AFRC metrology standard methods ensure repeatability and reproducibility of benchmark results. To evaluate the performance of LMD-p for remanufacturing of hot forging tools and dies, a cobalt based alloy (Stellite 21®) was selected. Stellite 21® is widely used as a hard-facing alloy as it provides excellent machinability coupled with superior wear characteristics. AFRC standard dies were coated with LMD-p Stellite 21®. The LMD-p coating was then machined to final geometry and then subjected to hot forging under AFRC standard conditions to compare to benchmark wear characteristics. Adhesive and abrasive wear was evaluated. It was shown that the Stellite 21® LMD-p additive layer performed better in both adhesive and abrasive conditions than standard H13 tools steel dies.

Wear study of hot forging punches coated with WC-CoCr and Cr3C2-NiCr through high-velocity oxygen fuel (HVOF) process

Wear is the main factor that causes most of the failures and reduces the lifetime of forming tools. The demand from industrial users for lower costs, higher productivity, and better quality is among the justifications for researching methods to increase the performance of these tools. In this work, the wear that occurs for hot forging tools was investigated. Herein for the first time, a high-velocity oxygen fuel (HVOF) technique was used for punch coatings in a hot forging process. Two punches coated by HVOF were analyzed for wear, one with chromium carbide (Cr3C2-NiCr) and the other with tungsten carbide (WC-CoCr). It was observed that both punches suffered a combination of several types of wear, mainly from thermal fatigue and abrasive wear. It was found that coating properties, such as roughness and hardness, influenced the wear mechanisms. The results showed that WC-CoCr presented a lower roughness and higher hardness, thereby offering a higher resistance against wear compared to Cr3C2-NiCr. The HVOF-coated punches showed a higher resistance against wear, which indicates that HVOF is a promising technique that is capable of increasing the lifetime of forging tools.

Influence of both hardfaced and nitrided layers on the durability of hot forging tools

This paper presents the results of preliminary operational tests of forging dies made with a new hybrid technology combining the self-shielded arc surfacing (hardfacing) and gas nitriding operations. Heat-treated and nitrided tools as well as hardfaced tools were tested as a reference. Dies were used for a similar number of forging cycles and then withdrawn from production and analyzed. Analysis covered the measurement of wear geometry using a three-dimensional scanner, macroscopic tests, microstructure study, microhardness analysis and observations under scanning electron microscopy. Test results indicate a beneficial effect of the new technology’s application, since elevated resistance to fatigue cracking and abrasive wear was demonstrated. Results were compared with reference tools prepared by only hardfacing or only nitriding, which were less resistatnt, of which nitriding brought more resistance to wear than hardfacing. These preliminary studies justify further studies leading to the development of this new technology for surface layer treatment of forging tools by hardfacing combined with nitriding.

Evaluation of different levels of prestressing for cold forging tools by numerical simulation analysis

Cold extrusion is known as a metal forming process and used due to its dimensional precision. However, the process definition is obtained by empirical methods where experiments are performed previously and based on a “trial and error” method. To reduce costs, companies have been looking for the support of numerical simulation softwares with metal forming application. This study describes the investigation of the effect of different levels for prestressing of cold extrusion gear tool by using the software Simufact Forming. The dimensional deviations of the gear tooth were obtained from two numerical simulations and compared. The application of shrink rings for the prestressing of tooling was evaluated using two different methods to compare their efficiency. The first one is using conventional shrink rings with tool steel, while the second is the stripwinding concept developed by the company STRECON. To produce spur gears, the low carbon steel SAE 10B22 was used.

Influence of the application of a PN+Cr/CrN hybrid layer on the improvement of the lifetime of hot forging tools

This article presents the results of field tests performed on forging tools in a selected lid hot forging process. The aim of the studies was to increase the durability of hot forging tools. Different coating types dedicated to hot forging tools were proposed and first tested in laboratory conditions. Based on the laboratory test results, the PN + Cr/CrN hybrid layer was selected to improve tool durability. Tools (upper punches used in second forging operation) with a PN + Cr/CrN layer applied on them were tested in comparison with gas-nitrided tools. The hybrid layer was produced on a plasma-nitrided substrate, onto which a PVD Cr/CrN coating was deposited. All the analyzed tools were tested in industrial conditions through the manufacturing of specific quantities of forgings. Next, the wear of each tool was analyzed by surface scanning and then compared to the CAD model. All the tools were checked for changes in the surface layer under an optical and a scanning electron microscope, as well as by way of a microhardness measurement. The results obtained in industrial conditions confirmed the effect of improvement of the forging tool lifetime owed to the application of the PN + Cr/CrN hybrid layer.

Durability analysis of forging tools after different variants of surface treatment using a decision-support system based on artificial neural networks

This article concerns a decision-support system based on artificial neural networks (ANN) enabling analysis and forecasting of the durability of forging tools used in the hot forging process of a cover forging – a sealing element of the driveshaft in road freight vehicles. The process of knowledge acquisition, adopted neural network architecture and parameters of the developed network are presented. In addition, 3 variants of a hybrid layer (gas nitrided layer GN+PVD coating) were applied to the selected tools (punches applied in the 2nd top forging operation): GN/AlCrTiN, GN/AlCrTiSiN, and GN/CrN, in order to improve durability, and the resultant tools were also compared to standard tools (with only gas nitriding) and regenerated tools (after repair welding regeneration). The indispensable knowledge about the durability of selected forging tools (after various surface engineering variants), required for the process of learning, testing and validation for various neural network architectures was obtained from comprehensive, multi-year studies. These studies covered, among other things: operational observation of the forging process, macroscopic analysis combined with scanning of tools’ working surfaces, microhardness measurements, microstructural analysis and numerical modeling of the forging process. The developed machine-learning dataset was a collection of approx. 900 knowledge records. The input (independent) variables were: number of forgings manufactures, pressing forces, temperature on selected tool surfaces, friction path and type of protective layer applied to tool. Meanwhile, output (dependent) variables were: geometrical loss of tool material and percentage share of the four main destructive mechanisms. Obtained results indicate the validity of employing ANN-based IT tools to build decision-support systems for the purpose of analyzing and forecasting the durability of forging tools.

New environmentally friendly coatings for hot forging tools

Two alumina coatings are developed to protect tool surface in hot forging: pure γ-alumina matrix loaded with α-alumina particles and pure γ-alumina matrix loaded with h-BN particles. The coatings are deposited on stainless tools by using a sol-gel procedure. Adherent coatings are obtained with an average thickness ranging from 200 to 300 nm. The coatings are tested according to the conditions of contact encountered in hot forging processes: coated tools slide against the surface of hot specimens where they generate a plastic strain. The design of experiment involves specimens heated to 1100 °C, lubricated and unlubricated contact, small and large specimen plastic strain, uncoated and sol-gel coated tools. Tests results are the Coulomb's coefficient of friction, SEM-EDS and roughness measurement of the tool surfaces after a sliding length of 40 mm.Results show that the tested sol-gel coatings remain firmly bonded to the tool surface. Compared to uncoated tools, alumina sol-gel coatings limit the amount of material transfer from specimen surface to tool surface. Loading the alumina sol-gel coating with h-BN particles significantly improves its friction behaviour: the friction coefficient is lower and sticking phenomena are reduced.

Design of overlay coated region with hardfacing, transition and damage diminution layers for the reduction of damages of hot forging tools

Hot forging dies are damaged by the mixed failure modes including wear, thermal cracks, impact cracks, corrosion cracks, etc.. In order to extend the service life of the hot forging die, the diminution technology of the mixed failure modes should be developed. The aim of this paper is to design an overlay coated region consisting of a Hardfacing layer (HL), a Transition layer (TL) and a Damage diminution layer (DDL) to reduce damage of hot forging tools. The HL and the DDL are contrived to improve the wear resistance and the ductility of the overlay coated region, respectively. The TL is adopted to prevent thermal fatigue induced by the difference in the thermal expansion coefficients between successive layers. In order to estimate design alternatives of the overlay coated region, the effects of the thickness and the assignment of the DDL on stress-strain distributions in the overlay coated region are investigated via Finite element analyses (FEAs). The influence of the assignment of the DDL on thermal behaviors of the overlay coated region is investigated through thermal fatigue experiments. From the results of the FEAs and the thermal fatigue experiments, an appropriate design of the overlay coated region is determined.

FE-Based Design of a Forging Tool System for a Hybrid Bevel Gear

Multi-material solutions offer numerous benefits producing tailored-made hybrid components with enhanced application-optimized properties contrary to conventional monolithic parts. However, designing of corresponding manufacturing processes is often challenging due to various technical aspects. This paper represents a process route for the manufacturing of a hybrid bevel gear by means of tailored forming technology with a focus on die forging and describes the main challenges within the forming stage. Due to local material-specific properties, uncommon material flow and complex geometry of the final part, an individual forming tool system with a geared die was accurately designed. Besides the forming tool system, the FE-based design of the forging process as well as the necessary material characterisation will be presented. Finally, the initial results of the experimental forging investigations are shown.

The influence of PVD coating on the low cycle fatigue behaviour of Cr-Mo-V steel at elevated temperatures

The paper reports on findings of an experimental investigation of the low cycle fatigue behaviour of high performance Cr-Mo-V hot working steel, which is used for the forging die inserts in hot forging operations. Fatigue tests of standardised uniform-gauge test specimens with duplex coating (plasma nitrided and hard PVD coating) were carried out in a low cycle regime at stress ratio R≈0.05 at elevated temperatures of 150°C and 500°C. These were determined for typical hot forging operations by means of computational simulations.The experimental results have shown that in a low cycle fatigue regime at stress ranges around yield strength the influence of PVD (Physical Vapour Deposition) surface coating on the fatigue behaviour is negligible. However, in a high cycle fatigue regime at stress ranges in elastic domain the PVD surface coating has a positive effect on the material fatigue behaviour, which results in a longer fatigue life in comparison to the uncoated specimens.The low cycle fatigue parameters for uncoated and duplex coated surface of treated Cr-Mo-V steel for operating temperatures of 150°C and 500°C have been derived from experimental results for the first time. The determined fatigue parameters can be used to predict the fatigue life of similar hot forging tools under low cycle fatigue conditions.

Experimental investigations of processing the high carbon cold-work tool steel 1.2358 by laser metal deposition for the additive manufacturing of cold forging tools

In the field of tool making, Laser Beam Melting of metals has been already used to fabricate injection moulds with complex inner cooling channels made out of the low-carbon maraging tool steel X3NiCoMoTi18-9-5 (1.2709). Furthermore, laser metal deposition (LMD) is an established technology for the repair of worn-out tools and the deposition of wear resistance coatings based on metal matrix composites. However, at the moment, the processing of high-carbon tool steels for the additive manufacturing of complete cold forging tools has only been investigated to a limited extent. Within the scope of the presented research, the processing of the high-carbon cold-work tool steel 60CrMoV18-5 (1.2358) by LMD is analyzed in detail. In this context, geometrically simple cuboidal structures are directly generated on dissimilar substrate plates made out of the hot-work tool steel X37CrMoV5-1(1.2343) via the application of various process parameter combinations. The manufactured cuboidal structures are metallographically prepared and subsequently analyzed with respect to substrate bonding, relative density, defect formation, microstructure, chemical composition, and microhardness. In this context, the influence of the particle size distribution of the used tool steel powder on the LMD process itself and the resulting relative density are extensively researched. For this purpose, high-speed camera measurements of the powder particle stream were conducted in order to determine both the powder particle stream diameter and the lateral powder particle distribution with regard to the distance z from the powder nozzle. Furthermore, the influence of an additional substrate preheating (maximum preheating temperature of 400 °C) on the resulting microstructure and hardness of the additively generated samples is the subject of the presented investigations.

An evaluation of H13 tool steel deformation in hot forging conditions

Plastic deformation is one of the causes of failure of hot forging tools, where the tool deforms to such an extent that parts formed are no longer within dimensional tolerance. Therefore, deformation of H13 tool steel that leads to transformation of the microstructure after forging Inconel 718 at high temperature and load was investigated. For this investigation nonlinear continuum mechanics 3D FE simulation Deform software, Scanning Electron Microscope (SEM), Electron Backscatter Diffraction (EBSD) and Microhardness tests were used. The result of 3D Deform simulation shows high localised stress and high strain of 0.38 on the sharp edge of the tool. This is one of the main reasons behind tool failure as accumulation of strain during deformation at high temperature causes changes in microstructure. SEM results confirm the severe deformation and highlight three different zones of deformation, recrystallization, martensitic and transition between each zone within the microstructure. EBSD results show low angle boundaries of 1–15° which represents mainly the deformation zone and it is associated with different dislocation substructures caused by slip. Furthermore, misorientation angles 28–32° corresponds to special boundaries ∑39a which are believed were created during martensitic lattice transformation when some of the boundaries are not perfectly match the rest. These special boundaries transform to low angle boundaries. The high angle boundaries 58–60° corresponds to twin boundaries and their parent matrix.

Influence of the application of a PN+CrN hybrid layer on improvement of the lifetime of hot forging tools

Abstract This article presents the results of field tests of forging tools in a selected hot forging process of cover plate. The tools with PN+CrN hybrid layer, applied to improve their operating life, were tested in comparison to gas-nitrided tools. The hybrid layer was produced on a plasma-nitrided substrate, onto which a PVD Cr/CrN coating was deposited. All analyzed tools were tested in industrial conditions by manufacturing specific quantities of forgings. Next, the wear of each tool was analyzed by surface scanning and comparison to the CAD model. All tools were checked for changes in the surface layer under a scanning electron microscope. The tests confirmed the effect of improved forging tool lifetime thanks to the application of the PN+Cr/CrN hybrid layer.

Development of Knowledge-Expandable Ontology-Based Expert System for Process Planning in Cold Forging of Flange Nuts

Abstract This paper proposed a new method of constructing an ontology-based expert system with an expandable knowledge base for process planning in cold forging of flange nuts. There are two essential parts of this method. In the first part, the software Protege is used for expressing the experiential knowledge as a Web Ontology Language (OWL) ontology and Semantic Web Rule Language (SWRL) rules. The inference is executed in Java by means of the API provided by Jess, the rule engine for the Java platform. In the second part, new knowledge is acquired from parameter optimisation experiments, combing process simulation and Taguchi methods. Deform-3D was adopted as the process simulation engine. Then the tool wear of front punch at the 4th stage was predicted for the tool life evaluation. A modified Archard wear model is used for tool wear prediction during the simulation. On the other hand, Taguchi methods is used for designing an optimal tool which makes the tool life longer than that of the existing design. The novelty of the proposed system is that the new knowledge is represented as an OWL ontology and SWRL rules, which makes the knowledge base of the system expandable. The knowledge base can thus be expanded if there are modifications or new knowledge. The system is capable of inferring a workable forging process for flange nuts. It could recommend dimensions of tools after the necessary information, such as the nominal size and specifications of the product, has been input. Users are able to reduce tool design time by taking the results from the system as a process planning decision support. In this way, when the manufacturer gets a new quotation from the client, engineers can search from the company tooling database for feasible forging tools and make the cost estimation based on the forging process plan generated by this system.

Analysis of the wear of forging tools surface layer after hybrid surface treatment

The performed research involved a thorough analysis of the phenomena occurring at an early stage of performance of selected forging tools – stamps (up to 4000 manufactured forgings), used in the second hot forging operation of a lid-type forging, which made it possible to point to the hybrid layer with the highest wear resistance, in order to increase tool life. Three different coatings were applied: AlCrTiSiN, Cr/CrN and AlCrTiN. The coatings were tested on 19 tools, and 3 representatives for each coating were selected, followed by their through research analysis. In particular, the analysis concerned the manner of wear of the hybrid layers and their resistance to specific degradation mechanisms. Based on the performed studies, it was possible to select the most optimal hybrid layer, which allows one to improve tool life.The preliminary results showed that the best effects for the whole tool working surface were obtained for the Cr/CrN layer, characterizing in high adhesion as well as the lowest Young's modulus E and hardness. In the case of high tool forces and the related friction, the best results were obtained for the AlCrTiN coating, which, beside its good adhesion properties, also characterizes in the highest abrasive wear resistance.

Numerical optimization on hot forging process of connecting rods based on RSA with experimental verification

A new method of optimization on the hot forging tools for connecting rods was developed in this paper by combining response surface analysis (RSA) with finite element method (FEM). The central composite design (CCD) was prepared with three experimental factors and two optimal targets. The experimental factors which are extracted from design dimensions of the hot forging tool involve cavity center distance, cavity rotation angle, and flash thickness. The targets comprise the maximum forming load and tool wear depth, both of which can be obtained from finite element simulations of hot forging processes. Response surface analysis was implemented to establish the relationships between the targets and the factors. According to the simulation results, the S-type region between die cavities that was dominated by three factors has a significant impact on the metal flowing and forming defects during the hot forging process. The steel billet and forging tools were dimensionally redesigned based on the optimal combination of experimental factors. Practice forging and physical experiments were performed to verify the simulation results, and good agreement between experimental value and simulation value was obtained.