Die Material Research Articles

The Effect of Vacuum Quenching on Corrosion and Hardness of the Surface of SKD61 Steel

JIS SKD61 Steel is chromium-molybdenum hot work steel which has composition 5.58 wt% Cr – 2.51 wt% Mo. This steel is a well-known material used as a die material to get good mechanical and hardening properties. Besides this material should have good corrosion resistance. Samples made of SKD61 steel were subjected to vacuum heat treatment at 1030°C for 3 hours with step quenching in different rates of quenching. The difference in the cooling speed of each sample causes properties on the surface to vary. Micro Hardness Vickers is a tool used to determine micro-scale hardness. While to test corrosion resistance, electrochemical testing was carried out using NaCl solution with variations in concentrations of 1%, 3.5%, and 7%. X-Ray Diffraction was used to characterize the crystal structure and the crystallite size. The results show that the speed of quenching affects the hardness of the surface of the material, structure and corrosion resistance.

Modelling and Simulation of the Electrical Resistance Sintering Process of Iron Powders

In this paper, the process known as Electrical Resistance Sintering under Pressure is modelled, simulated and validated. This consolidation technique consists of applying a high-intensity electrical current to a metallic powder mass under compression. The Joule effect acts heating and softening the powders at the time that pressure deforms and makes the powder mass to densify. The proposed model is numerically solved by the finite elements method, taking into account the electrical–thermal–mechanical coupling present in the process. The theoretical predictions are validated with data recorded by sensors installed in the electrical resistance sintering equipment during experiments with iron powders. The reasonable agreement between the theoretical and experimental curves regarding the overall porosity and electrical resistance suggests that the model reproduces the main characteristics of the process. Also, metallographic studies on porosity distribution confirm the model theoretical predictions. Once confirmed the model and simulator efficiency, the evolution of the temperature and the porosity fields in the powder mass and in the rest of elements of the system can be predicted. The influences of the processing parameters (intensity, time and pressure) as well as the die material are also analyzed and discussed.

Effect of Die Materials on the Fracture Resistance of CAD/CAM MonolithicCrown Restorations

The effect of the die materials on the fracture strength of CAD/CAM monolithic ceramic crowns was studied in this research. Three different types of die materials (dentin, Ni-Cr alloy, epoxy resin) were prepared. The monolithic crowns were fabricated using a CAD/CAM System; CEREC 4. The CAD/CAM crowns were cemented to dies using a resin cement. The specimens were tested under compressive load at a crosshead speed of 1 mm/min using a universal testing machine until fracture occurred. Recorded data were statistically analyzed using one-way analysis of variance and LSD Post hoc tests (p=0.05). While CAD/CAM crowns on Ni-Cr alloy dies showed the highest fracture resistance values, CAD/CAM crowns on dentin dies showed the lowest fracture resistance values. There is no significant difference between groups statistically. Ni-Cr alloy and epoxy resin dies could be used alternatively instead of teeth for in vitro studies

Metal bellow hydroforming using additive manufactured die: a case study

Purpose Custom-designed metal bellows require alternate ways to produce the die to shorten lead time. The purpose of this study is to explore the possibility of using Additive Manufactured (AM) polymer die as direct rapid tool (RT) for metal bellow hydroforming. Design/methodology/approach Finite element analysis (FEA) was used to simulate bellow forming and to evaluate the compatibility of AM die. Fused deposition modelling (FDM) technique is used to fabricate die with Acrylonitrile Butadiene Styrene (ABS) material. To validate, the width of the metal bellow convolutions obtained from the FEA simulation is compared with convolution formed during the experiment. Findings FDM-made die can be used for a short production run of bellow hydroforming. FEA simulation shows that stress developed in some regions of die is less and these regions have potential for material reduction. Use of RT for this particular application is limited by the die material, forming pressure, width, convolution span and material of bellow. This supports the importance of FEA validation of RT before fabrication to evaluate and redesign die for the successful outcome of the tool. Research limitations/implications The given methodology may be followed to design a RT with minimum material consumption for bellow forming application. Whenever there is a change in bellow design or the die material, simulation has to be done to evaluate the capability of the die. As this study was focused on a short production run for manufacturing one or few bellows, the die life is not a significant factor. Originality/value This paper demonstrates about rapid tooling for metal bellow manufacturing using FDM technique for low volume production. Further, FEA is used to identify low stress regions and redesign the die for material reduction before die manufacturing. AM die can be used for developing customized metal bellow for applications such as defense, aerospace, automobiles, etc.

Effects of substrate, ceramic thickness, translucency, and cement shade on the color of CAD/CAM lithium-disilicate crowns.

The aim of this in vitro study was to evaluate the effects of substrate colors, different levels of ceramic thickness and translucency, and cement shades on the color difference from a reference color of lithium-disilicate crowns. A premolar tooth preparation was made on a study model for 1.0 and 1.5 mm thick full-ceramic crowns. Digital impressions were taken (3Shape TRIOS) and crowns designed in a CAD program (DentalDesigner). Shade A1 crowns were milled (Everest, Kavo) from high-translucency (HT) and low-translucency IPS e.max (Ivoclar Vivadent) blocks. Twelve substrates were made of different colors and materials (Natural Die Material, Co-Cr, zirconia, and gold-colored alloy). Three different shades of try-in pastes were used to simulate the effect of cements (Variolink Esthetic try-in paste; Ivoclar). Shade measurement was done three times for each crown by a spectrophotometer (VITA Easyshade Advance); averages were compared to a reference crown (A1, HT, 1.5 mm, ND2 abutment, neutral try-in paste) with ΔE00 (CIEDE2000, according to the CIE latest standard) calculated. All the examined parameters influenced the ΔE00 of the crowns. The weakest effect was exerted by the try-in paste. All examined parameters influenced the final color of e.max CAD lithium-disilicate ceramic crowns. Matching the shade of ceramic crowns to the natural tooth color is a great challenge in dentistry. To meet patients' increasing esthetical expectations, CAD/CAM methods are very popular for full-ceramic crowns. However, several factors such as the shade of the abutment, luting cement color, ceramic thickness, and translucency may influence the final color. Our objective was to measure the optical effect of these factors on the final shade of CAD/CAM lithium-disilicate ceramic crowns.

Masking ability of indirect restorative systems on tooth-colored resin substrates

ObjectiveTo evaluate the masking ability of different indirect restorative systems (IRS) on tooth-colored resin substrates. MethodsA1-shaded specimens from 5 IRS (LDC–IPS e.max® CAD; YZW-Zenostar Zr Translucent; PICN-Enamic; YLD-T-IPS e.max® ZirCAD + IPS e.max Ceram; CAD-on-Zenostar Zr Translucent + Crystall./Connect + IPS e.max® CAD) were fabricated. Specimens (n = 5) were cemented with a resin luting agent (Variolink® N; shade White) on three different shades (ND3, ND8 and ND9) of a tooth-colored resin substrate (IPS Natural Die Material). Spectral reflectance and color coordinates were measured using a spectroradiometer under standardized lighting conditions (CIE D65 illumination) and optical geometry 0/45°. Color differences (ΔEab* and ΔE00) from cemented specimens and CIELAB- and CIEDE2000-based translucency parameter (TP and TP00) from non-cemented specimens were calculated. Data was statistically analyzed using one-way ANOVA and Tukey’s tests (α = 0.05). ΔE values were also analyzed using perceptibility (PT = 1.22 ΔEab* units; 0.81 ΔE00 units) and acceptability (AT = 2.66 ΔEab* units; 1.77 ΔE00 units) thresholds. ResultsThe cemented specimens of CAD-on, LDC, YZW and PICN on different substrates (ND3–ND8, ND3–ND9 and ND8–ND9) showed different ΔEab* and ΔE00 values (p ≤ 0.05), which were above AT. YLD-T showed ΔEab* and ΔE00 values below AT for all comparisons. Lowest and highest TP and TP00 values were obtained for YLD-T and PICN, respectively (p ≤ 0.05). SignificanceResin-cemented YLD-T on different tooth-colored substrates showed less translucency as well as smaller color differences (below acceptability threshold), indicating the best masking ability among evaluated systems.

Constrained Groove Pressing (CGP): Die Design, Material Processing and Mechanical Characterization

Constrained Groove Pressing (CGP): Die Design, Material Processing and Mechanical Characterization

Fatigue Failure Prediction Model and Verification of Hot Extrusion Die

Fatigue fracture is one of the most common failure modes of hot extrusion dies. The fatigue properties of materials are closely related to service conditions and heat treatment processes. In this paper, the service conditions of typical hot extrusion punches were selected as the start point, loading history of the dangerous part of the die was obtained by finite element numerical simulation. The load spectrum modified and normalized through Neuber algorithm was used as the loading curve of fatigue analysis. The tensile properties of the die materials at service temperature were obtained by experiments. Based on the Manson-Coffin model, the strain-life curve of the material was obtained through the theoretical deduction. The fatigue failure prediction model was established based on strain damage. Aiming at specific working conditions of aluminum alloy extrusion parts, the fatigue life prediction and model validation of the die were carried out. The heat treatment of die was: spheroidizing annealing + 1020 ℃ oil quenching + 580 ℃× 2 h two tempering treatment. The results show that the die life predicted by the model is 1318 times, and the actual die life is 1120 times, the failure position and service life of the die are in good agreement with the predicted results. A new way was provided for optimizing the matching of heat treatment process and service condition of the die, and has guiding significance for actual production.

Critical considerations on load-to-failure test for monolithic zirconia molar crowns

Application of monolithic zirconia crowns (MZCs) with reduced thickness to the molar region has been proposed, but potential complications have yet to be fully evaluated in laboratory tests. The present study aimed to develop a clinically relevant load-to-failure test in combination with fatigue treatments involving thermal and mechanical cycling (TC and MC) to evaluate the fracture resistance of molar MZCs. MZCs with a minimal thickness of 0.5 mm were bonded to dies made of resin-based composite (RBC), epoxy resin (EP), or polyoxymethylene-copolymer (POM-C). The samples were either untreated (UT) or subjected to TC (5–55 °C for 1 × 105 cycles) and MC (300 N for 2.4 × 106 cycles). The stress generated by TC and MC was simulated by finite element modeling. The load-to-failure test was performed using an inverse V-shaped two-plane indenter and was followed by fractographic analysis. The median values of fracture load for MZC/RBC and MZC/EP in the TC group were significantly lower than those in the UT group. MC also decreased the median value of fracture load for MZC/RBC significantly, but not that for MZC/EP and MZC/POM-C. Fractography revealed that the fracture started in the cervical area in all groups, which is similar to clinically failed crowns. The simulation confirmed stress concentration at the cervical area in both TC and MC groups. The present study suggests that the load-to-failure test using a two-plane indenter could induce clinically relevant fracture of MZCs, the vulnerability of the MZCs depends largely on the die material employed, and MZCs are more likely to be damaged by thermal fatigue than mechanical fatigue.

Improvement of Tribology in Sheet Metal Forming of High-Strength Steel Sheets by PVD-Coated Dies

During sheet metal formation, the high strength of sheet material leads to high contact stress between the die and blank material, which results in increased die wear. Moreover, the reduction in the use of lubricants because of environmental concerns has led to greater wear of sheet metal–forming dies. It is important to understand the tribological behavior of the blank die contact so that steps can be taken to reduce the die wear to an acceptable level. Die wear reduction is possible by using alternative die materials, modifying die geometry, or by creating a wear-resistant surface on sheet metal–forming dies using Physical Vapor Deposition (PVD) coatings. PVD coatings have a thickness in the micro range and greatly improve the tribological properties of the die material. In this work, three pins made of AISI D2 steel were coated with Titanium Nitride, Titanium Aluminum Nitride (TiAlN), and Aluminum Chromium Nitride using the PVD process. Friction and wear tests were conducted on the pin-on-disk testing machine as per ASTM G99, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus. The pins had diameters measuring 10 mm and lengths measuring 35 mm. They were heat treated until they reached 55 HRC and ground to a Ra value of 0.1 µm. A 5-mm-radius tip was provided on one end of the pin. D3 steel was used as counter material (disk). The normal load was 30 N, and the sliding speed was 0.3 m/s. The experiments were conducted in dry contact conditions. Based on the results, it was concluded that TiAlN coatings are an excellent choice to modify friction behavior and improve wear resistance of die material.

樹脂系歯型材の物性に関する研究 : (第1報)硬化時間と硬化時温度変化

樹脂系歯型材の物性に関する研究 : (第1報)硬化時間と硬化時温度変化

Development of rubber-assisted stretch bending method for improving shape accuracy

A new "rubber-assisted stretch bending method" by which elastic rubber can be partially applied to the surface of a die for the uniform bending with a constant curvature radius was developed. The tensile stress is realized by the frictional force between rubber and specimen. It is characterized by non-requiring a special equipment and mechanism for applying a tensile force in the longitudinal direction. Since the rubber is partially affixed and the bending deformation is carried out by the metal surface of the die material, the improvement of shape accuracy can be expected. When the material contacts the rubber sequentially, the tensile force in the longitudinal direction is imparted by the frictional force of the rubber surface. The bending tests by combining four kinds of rubber types, five kinds of combinations of die patterns and four loading motions of the universal testing machine were carried out. The springback decreased by 21% in comparison with the crank motion simple bending by using ordinary metal dies.

Research on Optimized Design of Stamping Technology for Mobile Phone Keypad

This research aims at discussing the steps and fractures on the surface of PMMA mobile phone keypad after the PMMA is stamped. Such steps and fractures are caused by the die structure, which leads to inward bending and displacement of the products during the punching process. Another reason is that the raw material is hard and brittle and the stress distribution of the punched position is dispersed, which results in irregular fractures. Taguchi Methods were employed to select die steel as the die material, and to choose the main factors: pipe diameter, pipe flow velocity and circulating water temperature as the control factors in the temperature control system. L16(44) orthogonal array was adopted for the experimental design, and the S/N ratios of Maximum-is-best was applied to measuring and analyzing the circulating water temperature of the circulating pipe. The verification shows that this system can greatly improve the die design and prevent the steps and fractures from happening, and the fractures were reduced by 90%, which indicated a significant improvement.

Numerical modeling of the thermal deformation during stamping process of an automotive body part

In this study, a thermo-mechanical finite element model was developed to investigate the thermal deformation during a stamping process of an automotive body part. The stamping process was decomposed into the 6 sub-steps to reflect the physical boundary conditions found in an actual stamping equipment. The temperature distributions of the actual stamping process were measured by two thermography cameras. The developed numerical procedure was then validated against the measured temperature distributions. Due to the limited accessibility to the actual equipment and high reflectivity of the involved material, the reflectivity index for the thermal imaging device (i.e., emissivity) was experimentally determined. A sample specimen made of the same material with the die material was built. The thermocouples were placed underneath the specimen surface through holes and used to directly measure the surface temperature distribution. The emissivity for the sample specimen was then determined by comparing the temperature measured by the thermocouples to the temperature measured by the thermographic camera. When the lubrication oils were spread on the sample specimen, the emissivity was set to a value 0.7. The thermal images were corrected based on the emissivity experimentally obtained and used to validate the finite element model simulation for the stamping process. With the validated finite element model, the investigation on the variation in the temperature and stress during each sub-step was performed. With the zero thermal expansion rate, the pure thermal effect on the temperature distribution was simulated. The pure thermal deformation in the Blank (i.e., target surface) was similar to the spring back distance after the blank was released from the molds. During the stamping process, the heat generation was obtained due to either friction between surfaces and plastic deformation of the target surface. We found that the plastic deformation played a critical role in the final temperature rise.

A Comparative Evaluation of Six Commonly Used Types of Die Materials for the Property of Transverse Strength, at Two Time Intervals: An In Vitro Study

A Comparative Evaluation of Six Commonly Used Types of Die Materials for the Property of Transverse Strength, at Two Time Intervals: An In Vitro Study

An In-vitro Comparative Stereomicroscopic Analysis and Evaluation of Marginal Accuracy in Porcelain Fused to Metal Copings Fabricated in Two Different Finish Lines Using Variant Die Materials

Limited published information is available about the influence of preparatory designs and die materials on marginal accuracy of porcelain fused to metal copings using recently developed die materials. To detect the influence of margin geometries and dimensional accuracy of contemporary die materials on vertical marginal gaps in Porcelain fused to metal coping using a Stereomicroscope (three dimensional analysis). Two chrome cobalt alloy models of mandibular first molars prepared to have shoulder and deep chamfer finish lines were CAD-CAM milled. Elastomeric impressions of these models were made in a custom tray, poured in Type IV Gypsum(n=10) and Resin modified Gypsum(n=10) and also packed with Epoxy resin (n=10) as a die material to form a total of 60 samples, 30 in each group (shoulder and deep chamfer). Wax patterns were fabricated, invested and castings in ceramic alloy were obtained in traditional manner. These copings were later analyzed on CAD/CAM models using stereomicroscope. Both the designs did not exhibit significant difference (p<0.05). Whereas, the three die materials exhibited significant difference (p<0.05) by Two way ANOVA test and Tukey's multiple Post Hoc test. Results from this study showed that vertical marginal gaps for copings fabricated on resin modified gypsum as a die material were within the clinically acceptable range. Margin geometries both shoulder and deep chamfer have equal influence on vertical marginal gaps in metal ceramic restorations. Copings fabricated on Epoxy resin dies exhibited highest value of vertical marginal discrepancy, where as least value was determined for copings constructed on dies fabricated from resin modified gypsum.

Thermomechanical Adhesion between Metallic Glass and Die Materials

Thermoplastic forming is a promising method for fabricating metallic glass (MG) products with complex shapes. This method can avoid the difficulties encountered in other manufacturing processes, such as very high cooling rate required by casting and catastrophic cracking in machining. However, during thermoplastic forming the adhesion between dies and MGs restricts the production. It is therefore important to explore the underlying adhesion mechanisms during forming and establish guidelines for selecting proper die materials. In this paper, we comprehensively studied the adhesion between La-based MG and some widely-used die materials (electroless Ni-P, Si, alumina and silicon nitride) in the thermoplastic forming process. It was found that, among these die materials, alumina has the best performance, which is attributed to its strong chemical bonds and low surface energy. The study concludes that the surface energy and the type of chemical bonds can be proper indicators for selecting die materials.

Development of trimming die with 1.2 GPa steel grade

In order to reduce the weight and to improve the crash performance of the vehicle, advanced high-strength steel of DP980 and CP1180 has been widely used in the automotive industry. However, the high-strength steel in the press parts causes severe tool wear or failures, such as adhesion, chipping and fracture at the tool cutting area during the shearing process. These result in the excess burr which deteriorates the tool life and causes serious problem in the product quality. The objective of this study was to evaluate the effect of the characteristic of sheared surface on the die material and surface treatment conditions at the shearing process with 1.2 GPa steel grade. The characteristics of sheared surface were evaluated after the shearing process of 60,000 strokes. A burr height was measured using the illuminometer. Also, tool wear of failures was analysed through observing microstructure. The shearing conditions such as die material, heat treatment and process parameter of clearance and pad force were determined as a result of the experiment analysis. The effectiveness was evaluated to manufacture the trimming die of sill side with 1.2 GPa steel grade.

The Influence of Thermal Conductivity of Die Material on the Efficiency of Hot-Stamping Process

To improve the production efficiency of the hot-stamping process from the perspective of the die materials, a numerical model of a B-pillar component was established to investigate the effects of the thermal conductivity of the die material on the cooling behavior, microstructure, and mechanical evolution of the formed component, as well as the temperature distribution of the die during the hot-stamping process. The results showed that the thermal conductivity of the die material has a more significant influence on the quenching stage than the forming stage. Under the specified simulation and boundary conditions, when the thermal conductivity of the die material improves by 76.23% at 25–300 °C, the maximum cooling rate of the component increases by 48.49% and consequently improves the quenching efficiency of the hot-stamping process by 31.82%. As the thermal conductivity of the die steel increases, the maximum temperature of the die decreases and its temperature uniformity improves. Moreover, to improve the efficiency of the hot-stamping process, steels that possess high thermal conductivity at low temperature ranges are favorable.

Characterization of the interfacial heat transfer coefficient for hot stamping processes

In hot stamping processes, the interfacial heat transfer coefficient (IHTC) between the forming tools and hot blank is an essential parameter which determines the quenching rate of the process and hence the resulting material microstructure. The present work focuses on the characterization of the IHTC between an aluminium alloy 7075-T6 blank and two different die materials, cast iron (G3500) and H13 die steel, at various contact pressures. It was found that the IHTC between AA7075 and cast iron had values 78.6% higher than that obtained between AA7075 and H13 die steel. Die materials and contact pressures had pronounced effects on the IHTC, suggesting that the IHTC can be used to guide the selection of stamping tool materials and the precise control of processing parameters.