Die Insert Research Articles

Recurrent neural networks as virtual cavity pressure and temperature sensors in high-pressure die casting

High-pressure die casting (HPDC) is a permanent mold-based production technology that facilitates the casting of near net shape components from nonferrous alloys. The pressure and temperature conditions within the cavity impact the cast product quality during and after the conclusion of the die filling process. Die surface cavity sensors can deliver information describing the conditions at the die-casting interface. They are associated with high costs and limited service lifetimes below the achievable total cycle count of the die inserts and therefore ill-suited for industrial use cases. In this work, the suitability of long short-term memory (LSTM) recurrent neural networks (RNN) for substituting physical cavity temperature and pressure sensors virtually after the production ramp-up or at the end of the sensor service life is investigated. Training LSTMs with data of 233 casting cycles with different process parameters provides networks which are then applied to 99 further cycles. The prediction accuracy is investigated for different time interval lengths in the solidification and cooling phase. For longer time intervals, the cavity pressure prediction deteriorates, potentially due to a highly individual and hardly ascertainable buildup of casting distortion and internal stresses. Overall, however, the accuracy of the developed LSTMs is excellent for the cavity temperatures and good for the cavity pressures.

Experimental and Numerical Investigations into Heat Transfer Using a Jet Cooler in High-Pressure Die Casting

During high-pressure die casting, a significant amount of heat is dissipated via the liquid-cooled channels in the die. The jet cooler, also known as the die insert or bubbler, is one of the most commonly used cooling methods. Nowadays, foundries casting engineered products rely on numerical simulations using commercial software to determine cooling efficiency, which requires precise input data. However, the literature lacks sufficient investigations to describe the spatial distribution of the heat transfer coefficient in the jet cooler. In this study, we propose a solver using the open-source CFD package OpenFOAM and free library for nonlinear optimization NLopt for the inverse heat conduction problem that returns the desired distribution of the heat transfer coefficient. The experimental temperature measurements using multiple thermocouples are considered the input data. The robustness, efficiency, and accuracy of the model are rigorously tested and confirmed. Additionally, temperature measurements of the real jet cooler are presented.

Analisis Perbandingan Waktu Pakai Insert Die Berbahan Baja Perkakas SKD 11, ASSAB 88, dan SKH 51 untuk Produk Mur (NUT) Berbahan S45C

The wear time of die inserts for nut products was studied in this research. The die insert material used is SKD 11, ASSAB 88 and SKH 51 tool steel, while the nut product material to be produced is S45C series carbon steel. These three die insert materials have been tested in the industry. Making nuts includes a dimensional test by measuring the dimensional tolerance of the nut and a service time test by looking at the number of products produced. This test is continued with a microhardness test on the inner side of the die insert. Use time for SKD 11 tool steel is 40,105 products with dimensional tolerance changed to 0.055 mm, ASSAB 88 tool steel is 110,703 products with dimensional tolerance changed to 0.053 mm, SKH 51 tool steel is 100,404 products with dimensional tolerance changed to 0.054 mm, micro hardness test tool steel shows that the deepest part of the die insert side is on average lower than the middle of the die insert. Insert dies made from SKD 11 have the shortest life, Insert dies made from SKH 51 have the longest life, and Insert dies made from ASSAB 88 have the highest life and are slightly higher than SKH 51. The use time for SKD 11 is two to three times, while the use time SKH 51 and ASSAB 88 are estimated to have been used more than three times.

Understanding conformal cooling in the diecasting of aluminum alloys

Heat transfer and stress distribution are studied using computational fluid dynamic and structural simulation for a conformal cooling die insert made of Maraging M300 steel by selective laser melting. The phase transformation of cooling water is studied to understand the cooling effects and stress concentration on die life. The results of simulation are validated in production. The failure of the die insert has been revealed a result of enhanced stress concentration and corrosion directly related to the formation of vapor in the conformal cooling channel.

Effect of Heating Temperature and Die Insert Draft Angle on the Flowability of Hot Forged SCM435 Steel

The problem of flowability in a closed forging process for heavy equipment industry is still widely found and this may affect the quality of the resulting product. To obtain the solution for this problem, in this work, the effect of heating temperature and die insert draft angle on the characteristic of hot forged SCM435 steel used for undercarriage track roller has been examined. The workpieces were heated at temperature variations of 1150 °C, 1200 °C, 1250 °C and were hot forged at die insert draft angles of 3°, 5°, and 7° to form undercarriage track roller products. The mechanical properties of the products were characterized through hardness and dimension examination, whereas the microstructure was characterized using an optical microscope. The results showed that increasing the heating temperature and die insert draft angle resulted in good flowability. The best result was obtained from the heating temperature of 1250 °C at the die insert draft angle of 7°, with diameter and height of 191.2 mm and 53.6 mm, respectively. This characteristic of the obtained hot-forged product agreed with that of the specified forging design for the undercarriage track roller

Sliding and impact induced damage on industrial-scale D2 die inserts during trimming of advanced high strength steel using optical interferometry

Die wear during trimming of advanced high strength steel (AHSS) sheets adversely effects the edge quality of trimmed sheets. Due to the large size of the industrial scale dies, it is difficult to measure the wear at the trim edge of the die inserts as a function of the number of trimming cycles. In this work, an optical surface profilometry method was used to determine sliding wear and impact damage on AISI D2 die inserts used to trim 1.4mm thick DP980 sheets through a semi-industrial scale trimming press. Reduced peak height (Spk) and reduced valley depth (Svk) were determined by establishing the bearing ratio curves in the damaged areas of the trim dies as a function of the number of trimming cycles up to 80,000 cycles. The sliding-induced percentage of total volumetric loss (SPOTV) decreased with the number of trimming cycles on the upper sliding plane revealing that the main damage mechanism changed from sliding-induced wear to impact fracture. The dominant damage mechanism on lower sliding plane was fracture induced as SPOTV on this plane maintained a low and constant value and evidence for chipping was observed on the trim die edge. The performance of trim dies could be improved by increasing the fracture toughness of the lower die and increasing the wear resistance of the upper die by applying proper coatings.

Designing die inserts by additive approach: a test case

The die manufacturing industry is widely based on the use of conventional machining tools. However, several studies have proposed Additive Manufacturing (AM) for molds and die inserts in the last ten years. The AM flexibility allows designing and manufacturing complex surfaces. This flexibility can be used to optimize the cooling channels of die inserts (conformal cooling). The research aims to evaluate whether Design for Additive Manufacturing commercial tools can be employed in redesigning die inserts. Besides, the paper describes a method to redesign a die insert for High-Pressure Die Casting using Selective Laser Melting. A test case is proposed to analyze an AM die insert’s redesign process for improving the thermal exchange and the material distribution. The simulation of the AM process supports the drafting conclusions from the results.

Effect of Gas and Ion Plasma Nitriding on the Structure and Properties of Forging Die Inserts

The possibility of raising the wear resistance and prolonging the service of forging die inserts is analyzed with the aim to elevate the efficiency of the production process and to reduce the cost of forgings. Three sets of inserts fabricated from the same grade of die steel and subjected to the same heat treatment are studied. Additional nitriding (gas or ion plasma one) is applied to two sets for comparison. It is shown that the inserts subjected to ion nitriding have the highest wear resistance and endurance.

Efficiency of Conformal Cooling Channels Inserts for Extrusion Dies

During aluminum extrusion process, critical temperatures can be reached both in the profile and in the tooling set due to the high pre-heating temperatures and to the work spent in overcoming friction at the workpiece/tool interfaces and in deforming the billet that is converted into heat. By considering that especially the rising of temperature in the profile can represents a critical aspect of the process strongly limiting the maximum achievable extrusion speed, liquid nitrogen die cooling is becoming a consolidated industrial practice in order to increase the process productivity. If cooling channels are traditionally manufactured by subtractive technologies on a third plate (the backer), a more flexible and efficient solution is offered by the selective laser melting (SLM) technology. SLM allows the design of free-form channels with the opportunity to efficiently remove the heat as near as possible to the bearing zones where the highest temperatures are reached. In the present work, the design approach and the manufacturing parameters of an SLM printed H13 die insert for the extrusion of a 10 mm round bar are presented. In addition, the extrusion process is simulated by means of the COMSOL code accounting for the nitrogen cooling effect. Experimental extrusion trials have been furthermore performed with ZM21 magnesium and 6063 aluminum alloys to assess the potentiality of the conformal cooling channel design and to validate the developed numerical model. As main result, a good experimental numerical matching has been achieved with peak errors of 7.5% and 14% in terms of temperature and extrusion load respectively.

The Impact of Prestressed die Construction with Cemented Carbide Insert on Stress Distribution During Extrusion

An important parameter for optimizing tool life is the introduction of a pre-compression stress in the die insert through the use of the compression ring. The tests were carried out for a die with a cemented carbide insert. Three die construction solutions were used in the tests. They differ by the ratio of the wall thickness of the die insert to the wall thickness of the compression ring gm/gp = (0.57; 1; 1.75) while maintaining a constant tool diameter. All construction solutions using cemented carbide insert were analysed for three values of mounting interference amounting to d = (0.004; 0.008; 0.016) mm. On the basis of the results obtained, the degree of impact of the parameters examined (the interference value d and the ratio gm/gp) on the distribution and level of circumferential stress in a die compressed by a single ring using a cemented carbide insert were determined. It was shown that the size of the interference and the quotient (gm/gp) had the great impact on the reduction of working stresses in the die insert.

Optimized Design for a Combined Die with Two Stress Rings in Cold Forging Considering Thermal-Mechanical Effects

Stress analysis and optimization of combined die structure with two stress rings were performed. Using thermoelastic deformation, the contact pressure at the interfaces between layers was calculated. Then, theoretical expressions of stress distribution for the combined die were derived. The thermal-mechanical effect under working conditions was considered. To verify the theoretical expressions, simulation work was performed. Optimization of die design was carried out by defining radius ratio and shrink fit coefficient as optimization variables. The objective was to minimize the effective circumferential stress at the inner surface of the die insert, under the constraint that the maximum equivalent stress values of die insert and stress rings did not exceed their respective yield stresses. The Kriging model was used to describe the influence of shrink fit and die dimensions on the objective function and the maximum equivalent stress. Using a genetic algorithm, optimum parameters were found with a minimum circumferential stress of 442.9MPa under a working stress of 1 800MPa. Further analysis of five selected optimal results was carried out, and the specific design parameters of these combined dies are different under the same level of circumferential stress, and the combined die is overdesigned if the thermal effect is ignored.

COMPARATIVE ANALYSIS OF THE IMPACT OF DIE DESIGN ON ITS LOAD AND DISTRIBUTION OF STRESS DURING EXTRUSION

In the paper a numerical comparative analysis of stresses in a steel die compressed by a ring during the extrusion process was presented. In the research, three design solutions of the die were used. The solutions vary depending on the quotient of the wall thickness of the die insert and the wall thickness of the compression ring while maintaining a constant tool diameter. The stresses occurring in the areas of the ring and the die were calculated depending on the design version of the tool and the pressure value. The analysis was carried out for the quotients of the die wall thickness to the ring wall thickness of 0.57, 1 and 1.75 and three press-in values of 0.004, 0.008 and 0.016 mm. The conducted research allowed determining the impact of the die design and assembly interference on the load bearing capacity. It was discovered that the use of a die insert with a smaller thickness compared to the thickness of the compression ring was the most advantageous from the point of view of the circumferential stresses.

Analysis of Dimensional Variations of Precision Gear Forging Die Geometry Due to Shrink Fit

The usual way to shrink fit design for precision forging dies are made by thick wall cylinder approach; i.e., taking the pitch diameter of the gear as bore diameter of the die insert without considering gear tooth shape. However, the compressive pre-stress due to the shrink fitting causes dimensional variations on the gear profile of the die insert. The dimensional accuracy of the final product is dependent on the accuracy of the gear die. Therefore, the dimensional variations due to shrink fit must be pre-determined and the gear tooth profile on the die insert modified accordingly. In this study, the dimensional variations of the precision spur gear forging die because of shrink fitting are analyzed by finite element method and the results are compared with the experimental ones. The results show that the FE model is successful to simulate the cylindrical die and agree well with thick wall cylinder approach and the experimental measurements. However, both the experimental measurements and the finite element results of gear die predict much higher radial displacements than the results of cylindrical die. Therefore, the determination of shape change of the gear die profile is beyond the capability of the thick wall cylindrical approach.

Introducing Inserts for Die Casting Manufactured by Selective Laser Sintering

The advances in additive manufacturing (AM) for high grade steels has in some cases made it possible to manufacture die inserts for demanding processes like high pressure die casting (HPDC). However, several challenges remain before this becomes commonplace. There is still a need of secondary manufacturing steps on the insert after printing. Also, extensive design changes must be made on the die inserts to fully utilize the advantages of AM. Further, the die insert is only one of many parts needed in the die assembly. Much of the die manufacturing will still be done by conventional methods. In this paper, several companies involved in the manufacturing and use of dies for HPDC have been interviewed on that they think is the future role of AM in their business. The result is that the effect of just printing the inserts would will be quite limited at present. Bringing down the time spent on die manufacture is important since that time then could be spent on improving the manufacturability of the parts.

Determination of shrink fitting ratio to improve fatigue life of 2-layer compound forging die by considering elasto-plastic deformation of outer ring

The shrink fitting ratio is an important design parameter in assembling compound forging dies. However, the determination for the optimal parameter to prolong die life is often neglected in the industry. Thus, the authors propose a method to identify optimal shrink fitting ratio by the use of master fatigue diagram to achieve maximum fatigue life where the working conditions under multi-stress tension-compression mode and various oscillation amplitudes are considered. In this paper, a master fatigue diagram was made from experimental results obtained for the die insert material SKD11. The 0.2% yield stress and ultimate tensile stress boundaries of the shrink ring material SKD61 obtained from FEM are then superimposed onto the master fatigue diagram. The modified master fatigue diagram is applied to determine optimal shrink fitting ratio for the 2-layer compound forging die in axi-symmetric forging. The method shows the capability of improving fatigue life by increasing the shrink fitting ratio into the elasto-plastic region of the shrink ring material.

Wear Analysis of Die Inserts in the Hot Forging Process of a Forked Type Forging Using Reverse Scanning Techniques

Wear Analysis of Die Inserts in the Hot Forging Process of a Forked Type Forging Using Reverse Scanning Techniques

The Use of 3D Scanning Methods to Evaluate the Hybrid Layer Used in Forging Tools in Order to Improve their Durability

AbstractThis study is focused on tools used in the industrial process of hot forging of a front wheel forging (gear wheel) manufactured for the automotive industry. Five different variants were applied for the tools: 3 die inserts were coated with three different hybrid layers (PN + PVD type), i.e. AlCrTiN, AlCrTiSiN and CrN, one insert was only nitrided, and one was pad welded, to improve tool durability. The tool wear was analysed and represented by the material degradation on the working surface, based on the 3D scanning and the material growth of the periodically collected forgings. Additionally, the scanned tools were divided into two areas, in which it was found, based on the analysis, that various degradation mechanisms are predominant. Microstructural tests and hardness measurements of the analyzed tools were also performed. Based on the results, it was found that, in the central part of the die insert, thermo-mechanical fatigue, abrasive wear and plastic deformation occurred, while in the area of the bridge insert, only abrasive wear could be observed. For these areas, the loss of material was determined separately. It was established that the use of the GN+CrN and GN+AlCrTiN hybrid layers on forging tools improves their durability, while the best results in the central area were observed on the tool with the GN+CrN layer, which is the most resistant to thermo-mechanical fatigue. In the second analyzed area, good wear resistance occurred on GN+CrN, GN+AlCrTiN and pad welded inserts, for which, together with the increase of the forging number, a proportional, slight growth of the loss of material occurred.

Investigating the Evolution of Progressive Die Wear on Uncoated Dp1180 Steel in Production Environment

A study of die wear was performed using an uncoated dual phase, 1,180 MPa ultimate tensile strength steel (DP1180) in a progressive die. The objectives of the current study are to evaluate the die durability of various tooling materials and coatings for forming operations on uncoated DP1180 steel and update OEM’s die standards based on the experimental results in the real production environment. In total, 100,800 hits were performed in manufacturing production conditions, where 33 die inserts with the combination of 10 die materials and 9 coatings were investigated. The die inserts were evaluated for surface wear using scanning electron microscopy and characterized in terms of die material and/or coating defects, failure mode, failure initiation and propagation. Surface roughness of the formed parts was characterized using a WYKO NT110 machine. The analytical analysis of the die inserts and formed parts, combined with the failure mode and service life, provide a basis for die material and coating selection for forming AHSS components. The conclusions of this study will guide the selection of die material and coatings for high-volume production of AHSS components.

An alternative design method for the double-layer combined die using autofrettage theory

Abstract. The double-layer combined die is used for its longer life in forging. Autofrettage is a well-known elastic–plastic technology that increases the durability of thick-walled cylinders. This study explores an alternative design method of the double-layer combined die using autofrettage theory. An analytical solution for the autofrettage process of the double-layer combined die is obtained based on Lamé's equation. The relationship between the autofrettage pressure and the yield radius of the die insert is obtained, and expressions of residual stresses and displacements, which are directly related to geometric parameters, material properties and internal pressure, are derived. The finite-element simulation of a specific case is performed, and good agreement between theoretical calculations and simulation results is found. Furthermore, the effects of important parameters, including the ratio of the plastic area and yield strength of the die insert and the outer diameters of the die insert and stress ring, on the autofrettage effect are investigated. Compared with the conventional combined die, the autofrettaged die can bear larger working pressure, as expected. The use of the autofrettaged die can reduce the amount of expensive material required for the die insert and the working space of the die set, which would benefit the practical forging process.

Application of the reverse 3D scanning method to evaluate the wear of forging tools divided on two selected areas

This study is focused on tools used in the industrial hot forging process of a front wheel forging (eventually–gear wheel) manufactured for the automotive industry. Four different variants were applied for the tools: 2 die inserts were coated with two different hybrid layers (GN + PVD type), i.e. AlCrTiN and AlCrTiSiN, one insert was only nitrided, and one was pad welded, to improve tool durability. The tool wear was analysed and represented by the material degradation on the working surface, based on the 3D scanning and the material growth of the periodically collected forgings. Additionally, the scanned tools were divided into two areas, in which it was found, based on the reliminary analysis, that various degradation mechanisms are predominant. Microstructural and hardness measurements of the analyzed tools were also performed. Based on the results, it was found that, in the central part of the die insert (area A), thermo-mechanical fatigue and wear occurred, while in the area of the bridge insert (area B), only abrasive wear could be observed. For these areas (A and B), the loss of material was determined separately. In area A for the inserts with hybrid layer GN+AlCrTiSiN and gas nitrided, an intensive increase of wear took place, which was not observed for the pad welded and GN+AlCrTiN layer insert, for which, together with the increase of the forging number, a proportional growth of the loss of material occurred. In area B the weakest results were obtained for the insert with GN+AlCrTiSiN layer, while wear of other die inserts grew similar and proportional.