Die Service Life Research Articles

Enhancing the life of forging dies by investigating different heat treatment methods

ABSTRACT The present study investigates the impact of a Conventional Heat Treatment (CHT) and a Modified Heat Treatment (MHT) method that incorporates a deep cryogenic treatment in the process, on the mechanical properties, the microstructure of samples, and the lifespan of forging dies. The samples treated with the modified heat treatment showed less variation in elongation at similar strengths. The addition of deep cryogenic treatment in the heat treatment process increased the volume of fine, uniformly distributed carbides, enhancing secondary hardening compared to conventional methods. This treatment, followed by tempering, improved the die's service life and resulted in moderately higher impact toughness. The average lath length and width were reduced with modified heat treatment when observed after the second tempering. The wear of the forging die was reduced with modified heat treatment, and the service life was increased.

Mechanism for friction reduction of aluminum alloy at high-pressure and ultra-low temperature

Temperature and pressure have a significant impact on friction in aluminum alloy ultra-low temperature forming. In this paper, cryogenic strip drawing test (CSDT), morphologies analysis and microstructure characterization were used for friction mechanism investigation of aluminum alloy under different temperatures and pressures. The findings indicated that the coefficient of friction (COF) first increased and then decreased as pressure increased. From 2 to 10 MPa, the lowest COF was observed at −190 °C. The formation of fine deformation microstructure enhanced surface material plasticity and resistance to deformation leading to reduced adhesive friction or plowing friction, resulting in low COF at high-pressure and ultra-low temperature. Furthermore, higher temperatures and pressures increased the adhesion, which was detrimental to prolonging the service life of die.

Experimental and Numerical Study on Friction and Wear Performance of Hot Extrusion Die Materials.

For the aluminium alloys produced by the hot extrusion process, the profile is shaped according to the bearing at the exit of the extrusion die. The tribological process has significant effects on the die service life, profile dimensional tolerances, and profile surface finish. Recently, new technologies have been introduced to the hot extrusion die, such as cemented carbide insert die and surface coating. However, under hot extrusion working conditions, quantitative studies on their friction and wear performances are lacking. In this work, the friction and wear performances of three typical extrusion die materials, traditional hot tool steel (H13), cemented carbide (YG8), and chemical vapour deposition (CVD) coating, were studied. Macro and nano hardness tests, Pin-on-disk friction and wear tests, optical profiler and SEM observations, and experiments and simulations of hot extrusion were conducted. The results show that the coefficients of friction of CVD coatings and H13 hot work tool steel specimens were smaller under the hot extrusion condition than at room temperature. The wear mechanisms of H13, YG8, and CVD coatings at 500 °C are adhesion, abrasive, and fatigue, respectively. Moreover, the tribology results were validated by the extrusion experiments and the finite element analysis of hot extrusion. The conclusion of this manuscript is useful not only for the numerical simulation of the hot extrusion process but also for the surface finishing of the extrusion profile.

Optimization of trimming process in cold forging of steel bolts by Taguchi method

In this study, die-service life analysis of hexagonal trimming dies with different edge radius and cutting width was performed. The trimming dies were prepared by grinding the front face of the die due to desired cutting width and edge radius. Prepared dies were used in cold forging of steel M6x25 hexagonal bolts and service life of each die were determined in terms of number of bolts that they can produce until they experience fracture. Numerical models of trimming operation with varying cutting width were also prepared in finite element software simufact.forming to conduct stress analysis. Production trials and finite element analysis showed that service life of trimming die was significantly affected by cutting width. It was seen that die-service life increases linearly with increasing cutting width within an optimum range of 0.8 and 1.2 mm. Similarly, the die-service life improved with increasing edge radius values. Moreover, the trimming operation carried out by using hexagonal trimming die was optimized with Taguchi method by defining 5 design parameters and 3 levels for each parameter. Minimizing the peak trimming load and maximizing the peak damage value were determined as the objective functions to find the most effective design parameters. According to the Taguchi results, the cutting width and stopping distance were seen to have significant impact on peak trimming load while the edge radius was determined to be effective on the peak damage value.

A Near-Surface Layer Heat Treatment of Die Casting Dies by Means of Electron-Beam Technology

Increasing the service life of die casting dies is an important goal of the foundry industry. Approaches are either material- or process-related. Despite new material concepts, hot work steels such as H11 are still predominantly used in the uncoated condition for die casting dies. In order to withstand the stresses that occur, this steel is used exclusively in the quenched and tempered condition. Required properties such as high high-temperature strength and high hardness combined with high toughness are, in principle, contradictory and can only be adjusted consistently over the entire die by furnace-based heat treatment. However, the results of various investigations have shown that improvements in the thermal shock resistance and wear resistance of hot work tool steels can be achieved by thermally influencing the microstructure near the surface. Based on these studies and related findings, an approach to surface heat treatment using the electron beam was developed. Due to the particle character of the radiation and the associated possibility of high-frequency beam deflection, the electron beam offers significantly greater flexibility in energy input into the workpiece surface compared with lasers or induction. The overall technological concept envisages replacing furnace-based heat treatment in the production of casting dies by localized and demand-oriented boundary layer heat treatment with the electron beam. The experiments include, on the one hand, the experimental determination of a suitable temperature–time interval with a focus on short-term austenitization. On the other hand, a simulation-based approach of boundary layer heat treatment with validation of a suitable heat source is investigated. Regarding short-term austenitization, the corresponding temperature and time range could be narrowed down more precisely. Some of these parameter combinations seem to be very suitable for practical use. The test specimens show a hard surface layer with a depth of at least up to 6 mm and a very tough buffer layer. Numerical simulation is used to estimate the resulting metallurgical microstructure and the achievable hardness as a function of the temperature–time interval. In addition, the results provided show the possibility of determining and optimizing the material properties by means of a simulation-based approach within the framework of a purely digital process planning and subsequently transferring them into a process planning. In the technical implementation, a temperature control was first established by means of a two-color pyrometer. In the further course of research, the pyrometer will be supplemented by an internally installed infrared camera, which will allow the reproducible setting of specified temperature profiles even for complex, large-area contours in the future.

Effects of DLC/TiAlN-coated die on friction and wear in sheet-metal forming under dry and oil-lubricated conditions: Experimental and numerical studies

Experimental and numerical analyses were conducted to explore the influence of DLC/TiAlN-coated die surfaces in sheet-metal forming under dry and oil-lubricated conditions. In this study, ironing and deep-drawing experiments were performed to determine the potential of the DLC/TiAlN coating in the sheet forming of stainless steels under different tribological conditions. The performance and physical properties of the DLC/TiAlN-coated die surface were obtained through load, surface roughness, and wear measurements as well as hardness and microstructure examination. The experimental results indicated that the DLC/TiAlN coating strongly resists galling under dry friction and thin film lubrication conditions that reduces the friction and forming load. The presence of a thin oil film reduces the sliding-originated surface tensile stresses of the DLC/TiAlN coating, improving the wear resistance of the die surface even at high temperatures and high contact pressures. Thermomechanical numerical analysis supported the experimental results, which confirmed that the lubricant discharged the heat generated in the die–workpiece contact region to reduce the friction and forming load. With the DLC/TiAlN coating, the plain mineral oil with no extreme pressure additives can function as effective as chlorinated paraffin oil for protecting the die surface, thus extending the die service life.

Study on the forming accuracy of the three-cylinder crankshaft using a specific die with a preformed dressing

The complexity and specificity of the three-cylinder crankshaft lead to under-filling in the balance slider. Normally, way of the precision of the crankshaft is to increase the blank diameter or the bridge size of flash, which result in high forging load, low service life of die, and material utilization. Therefore, a preformed dressing is designed in the balance slider of the pre-forging die. During the pre-forging period, a dressing will be formed in the balance slider, which is used to ensure the precision of the three-cylinder crankshaft in the final forging period. First, CAD models of the die and billet are established, then which are simulated by the Deform-3D software. The forging load and die wear depth are analyzed, and the area of the balance slider is under-filling. Second, a new pre-forging die is designed with a preformed dressing by the CAD software. Third, response surface analysis (RSA) and finite element technology are combined to optimize the pre-forging die of the three-cylinder crankshaft. According to variance analysis, the preformed dressing is not a significant influence factor on the die wear depth and load. Optimized factors’ R, D, H of the pre-forging die are 19 mm, 84 mm, and 6 mm, respectively. Fourth, the flash height of the final forging die is optimized, and the balance slider is filled well, and the die wear depth is reduced. Finally, physical experiment and practice forging are carried out to verify the optimal scheme of the finite element method (FEM), and the results of the experimental and finite element have a good consistency.

Characterization and Industrial Performance Evaluation of Duplex-Treated AISI H21 Die Steel during Hot Forging Process

Abstract Die/tooling failure during the hot forging process is mainly due to repeated varying mechanical loads, rigorous thermal shocks, as well as strong friction and erosion. These cause different failure mechanisms, such as wear, thermal fatigue, and plastic deformation. The enhancement of die service life for a hot forging industry is necessary now in order to be competitive globally. Four nitride coatings—TiN, TiAlN, TiCrN, and AlCrN—were deposited onto plasma-nitrided AISI H21 hot work die steel using the cathodic arc evaporation physical vapor deposition technique. The coatings were characterized by scanning electron microscope (SEM), SEM–energy dispersive x-ray spectroscopy (EDS), x-ray power diffraction (XRD), line scan EDS, and x-ray mapping tests and microhardness tester. The wear characteristics were examined using a pin-on-disk method at high temperature and speed against EN31 bearing steel disk. It was observed that the AlCrN and CrTiN coatings have lower wear rates than other coatings at high temperature (550°C). Also, these coatings performed best during actual industrial practice. The enhancement in die life was reported to be 55 and 76 % in terms of parts being hot forged. The low value of the coefficient of friction for all coatings at 550°C can partly be attributed to lower hardness difference between the pins and disks, decreased plastic deformation in the contact, and, consequently, less ploughing (abrasive wear action). Predominately, wear was the main die failure mode there was; when used, dies were observed microscopically.

Finite Element Modeling of Shrink-Fit Design for Improvement of Die-Service Life in Hot Forging Process of a Bevel Gear

In a hot forging process, die-service life is one of the most important factors affecting the production cost. This paper illustrates about a shrink-fit design used to improve the die-service life in the hot forging process of a bevel gear. In this process, there are two-operation steps of forming, preform and finishing steps. The major problem was that the forging die in finishing step prematurely fractured at small fillet radius due to mechanical fatigue. In order to eliminate the problem, the forging die was redesigned to shrink fit into the optimum shrink ring. Furthermore, Finite Element Modeling (FEM), which was set up and verified by the existing process, was used as a tool to study the effect of a shrink-fit ratio and diameter of a shrink ring on the die stress. The FEM results showed that both parameters influent on the die stress directly and the maximum principle stress of the new design at the fracture area significantly reduces because of pre-compression stress from the shrink ring. Finally, the FEM result was proved by experiment in the actual process and then it was found that the die-service life is improved approximately 17 times when comparing to the initial design.

Structural Strength and Service Life of the Extrusion Forming Die for Agricultural Engine Piston Heads

Three-tier high-strength prestressed combination concave dies are designed to manufacture highpower corn combine harvester engine piston heads. This design integrates the advantages of traditional casting or hot die forging and warm extrusion. The following key parameters, viz radial dimensions of each mating layer, axial bonding and radial contact interaction, are obtained by theoretical calculation. Nonlinear analysis of the contact interaction was carried out, and the die contact condition was studied at no-load and full-load. Based on the Archard wear theory, thermomechanical bonding was studied in operation of the die. Through numerical simulation of the die wear in each operation cycle, the univariate linear regression equation of the die service life was derived, and the reliability of this equation was verified. The results show that the die contact is both stable and reliable if the radial contact interaction of the inner and outer layers is δ2 = 1.9716 mm and δ3 = 1.3870 mm, respectively. With the nitriding layer thickness of 0.24 mm, the extrusion die service life in the production of piston heads corresponds to 6357 pieces.

Multi-objective optimization of swash plate forging process parameters for the die wear/service life improvement

For the forging process of the swash plate, the author designed a kind of multi-index orthogonal experiment. Based on the Archard wear model, the influences of billet temperature, die temperature, forming speed, top die hardness and friction coefficient on forming load and die wear were numerically simulated by DEFORM software. Through the analysis of experimental results, the best forging process parameters were optimized and determined, which could effectively reduce the die wear and prolong the die service life. It is significant to increase the practical production of enterprise, especially to reduce the production cost and to promote enterprise profit.

Research on gear tooth forming control in the closed die hot forging of spiral bevel gear

To improve the tooth forming quality of forging spiral bevel gear, a systematic hot forging method for spiral bevel gear is proposed in this paper, which helps to improve some defects in the traditional forging methods, such as the insufficient gear tooth corner filling, the high forming load, and the low die service life. With Deform-3D, the simulation analyses of the closed die structures are carried out to reveal the effects from the tooth forming process parameters, which are including the forging temperature, the strike speed, the die preheating temperature, and the friction coefficient. For further meliorating the addendum of tooth toe-end filling situation, an improved forging process with tooth preformed is presented. Thereinto, the excess material is reserved at the tooth toe-end position in preformed stage, so that the material flow velocity at the tooth toe-end area synchronizes with that at tooth heel-end area. Compared with the traditional process by the numerical analysis, the improved process can not only reduce more than 6% of the forming load but also relieve the sharp rising trend of finish forging load. Finally, the effectiveness of the improved process is verified through the forming experiments, and the results are in good agreement with the simulation ones, which can provide the theories foundation for enhancing the forging quality and decreasing the scrap rate of the forged spiral bevel gear.

Multi-field coupling finite element analysis for determining the influence of temperature field on die service life during precision-forming process of steel synchronizer ring

Failure analysis shows that increased die temperature caused by severe plastic deformation of material and heat conduction between hot billet and cavity significantly affects the distortion of gear cavity in steel synchronizer ring forging process. The forging process of steel synchronizer ring and die temperature distribution under different forging conditions are analyzed through finite element method. Simulation results show that severe plastic deformation occurs in the gear cavity. The improvement of lubrication condition results in decreased die temperature. When the initial billet temperature is high, the die temperature is also high. Increasing forging speed in a certain range facilitates the die temperature decrease. The distribution of die temperature in synthetic forming technology is more reasonable than that of one step forging. The synthetic forming technology is adopted in production to reduce the effects of severe plastic deformation caused by die temperature. The ejection mechanism and control system of the double disc friction press are improved to reduce the contact time between the hot billet and cavity. Experimental results show that synthetic forming technology is reasonable, and that the die service life is prolonged.

Applied Research of Gas Tufftriding Process on Mould

Feature and theory of gas- tufftriding process was described. Reasonable gas tufftriding process selection of Cr12MoV, 3Cr2W8V and W18Cr4V mould steel was introduced, which is at 570℃ for 3 hours, carbamide 650~900g/hour, oil cooling. Nitriding time of large die mold could be extended and cool to 450℃ along with the furnace. Gas tufftriding process improved service life of die and efficiency, lowered the cost, achieved a certain economic benefits.

Improving the Corrosion Resistance of Hot-Working Mold Steel against Al Alloy Melt by Coating

In order to reduce the adhesion tendency of aluminum melt on the die casting mold and extend the service life of the die, multi-arc ion plating technique was used to deposit Ti/TiN/CrN multi-layer coating on the surface of 8418 hot-working mold steel. Corrosion resistance of the steel and the Ti/TiN/CrN coating against Al alloy melt was studied. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to study the microstructure, phase constituent and phase composition of the materials. Uniform Ti/TiN/CrN coatings with good bonding interfaces and a total thickness of about 2 μm were obtained. Results showed that Ti/TiN/CrN coating can improve the corrosion resistance of the 8418 hot-working die steel significantly against the aluminum alloy melt.

TOOLING DESIGN IMPROVEMENT OF MULTISTAGE COLD FORGING OF SPECIALTY SHAPED NUTS USING CAE AND 3D PRINTING

Given its critical role in the fastener industry, cold forging is widely performed in automotive production, manufacturing, aviation, and 3C products. Personnel experience and trying error approaches provide a subjective and unreliable background despite their extensive use in fastener forming and die design owing to the difficulty in controlling the development schedule. This study used DEFORM-3D analysis software to investigate the die service life from producing specialty shaped nuts in a multistage cold forging process. Effective stress, effective strain, velocity field, and other quantitative metrics of dies and work-pieces can be obtained from numerical simulations. Herein, 3D printing technology is also implemented to create cold forging dies and deformed work-pieces for assessing the dimension of tooling assembly. This process allows engineers to gain a better understanding of the tooling design at development phase and derives the parts, which were previously just simulation results from DEFORM-3D forming software. Results can help a multistage processing factory establish a cold forming capacity for the development of new products. Consequently, the ability of self-design and self-manufacture of specialty shaped fasteners in Taiwan could be increased widely to enhance the international competitiveness of domestic industries.

Analysis of Sheet Metal Tapping Screw Fabrication Using a Finite Element Method

The malformation of sheet metal tapping screw threads in the screw threading process increases the cost of screw threading dies and their maintenance. Die factories do not reveal their screw threading die design techniques, so production and maintenance processes are established by trial-and-error or worker experience and passing down such techniques and documenting quality control is difficult. In this study, screw thread forming design and process analysis were carried out by combining computer-aided design software with computer-aided metal forming analysis software. Simulation results were verified in an actual forming process. The sheet metal tapping screw forging size error was less than 0.90%, except at a sharp angle, which was associated with an error of 3.075%, thereby demonstrating the accuracy of the simulated forming process. The numerical analysis process can be utilized to shorten forming development time; to reduce the number of die tests, and to improve product quality and die service life, reducing the cost of development and promoting the overall competitiveness of the company.

Wear prediction of die coatings in strip ironing by finite element simulation

This study has used a simple method to predict wear of die coatings used in the strip ironing of steel sheet based on Archard’s wear model by using finite element (FE) simulation. This method required the information regarding the quantity of worn material and thickness of die coatings. The die stresses obtained from the FE simulation were used to calculate the wear rate and wear depth per cycle. The die and sheet materials considered were D2 tool steel and S690QL, respectively. Two types of die coatings (CrN and TiN) and their known properties were studied. The studied sliding velocities were 0.1, 1.0 and 5.0 mm s−1. The contact pressures under investigation were 15, 150 and 1500 kPa. The results showed that TiN provided higher wear resistance due to its lower quantity of worn material (1.962 × 10−16 m3). The total wear depth per cycle increased with reducing quantity of worn material (increasing hardness value). Increase in sliding velocity led to increase in wear depth per cycle. The contact pressure (15–1500 kPa) did not significantly affect wear depth per cycle. To illustrate the acquired wear depth per cycle of all the coatings under different conditions, a predictive wear map was developed. In addition, the number of operating cycles based on the die coating thickness could be calculated. Based on the findings, the wear map could be used to help select appropriate die coatings and adjust process parameters in order to extend die service life.

DEFECT IMPROVEMENT OF EXTRUSION DIES USING COMBINATION OF FEM STRESS ANALYSIS WITH THE TAGUCHI METHOD

This study aims at analyzing the influence of the maximum principal stress on Tungsten Carbide Steel die core in an extrusion die which caused the crack of die core, and then adjusts the dies assembly method in order to improve the service life of die. In this study, we combine FEM simulation software with the Taguchi Method L9(34) to choose the cobalt content for die core materials, and the quantity of shrink fit while assembling the die core and die case as the reference parameters. When carrying out the simulation process, we compared the changes of the maximum principal stress of the die core caused by the plastic deformation of die materials to achieve the minimum expected value as the goal for the most optimal die combination. Then, the results obtained are to make dies in trial and mass-production practically; as a result, the die life is improved from the original 1000 to 150,000 pcs, which is more than 150 times better than before.

Stress Analysis and Improvement of Extrusion Dies Using Combination of FEM with Taguchi Method

This study aims at analyzing the influence of the maximum principal stress on Tungsten Carbide Steel die core in an extrusion die which caused the crack of die core, and then adjusts the dies assembly method in order to improve the service life of die. In this study, combining FEM simulation software with Taguchi Method L9(34) is to choose the cobalt content for die core materials, and the quantity of shrink fit while assembling the die core and die case as the reference parameters. When carrying out the simulation process, compared the changes of the maximum principal stress of the die core caused by the plastic deformation of die materials to achieve the minimum expected value as the goal be chosen the most optimal die combination. Then, the results obtained are to make dies in trial and mass-production practically; as a result, it can be achieved that the die life is improved from the original 1000pcs to 150000pcs, which is more 150 times better than before.