Papers by Keyword: Die Material

Abstract: The rebound-effect that frequently occurs during electromagnetic sheet metal forming is one of the main causes of deviations in the shape and dimensional accuracy of flat surfaces. The selection of the die material and its corresponding energy absorption capabilities has a critical impact on this effect. This article analyses materials with different physical properties in terms of their energy absorption behavior under dynamic impact load. A variety of model tests are being conducted to examine a wide range of impact velocities and energies. The experimental setups comprise two variations of a drop tower test, which can be used to determine the percentage of impact energy absorbed at high and low momentum. To achieve higher impact velocities, a third experiment involving an electromagnetically accelerated impact body was conducted for the material that demonstrated the best result in the preceding tests.

Abstract: The work purpose is to evaluate the application of nickel-based CrNi73CuBeTeAl superalloy (tungsten-free), made by electroslag remelting as a die tool material for isothermal forming. Isothermal deformation was simulated by tests for high-temperature cyclic creep. The specimens with high and × in plan dimensions (both parallel and perpendicular to the ingots central axis) were cut from the bottom, top and central zone, near the lateral surface and in the ingots central axis area. The tests were performed at 900, 940 and 980 °C constant temperature with 100, 200 and 300 MPa cyclic pressure in 0.02, 0.2 and 2.0 mm/s velocities range corresponded to 10-3-10-1 1/s strain rates. Such tools application field is compressor blades Ti-forgings die forging and sizing with ε = 1.0-3.0% residual upsetting deformation of dies during operation. It is shown that the die life can be extended to 400-700 loading cycles at 850-950 °C operating temperature and pressure up to 150 MPa.

Abstract: 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.

Abstract: The machining of titanium alloys is challenging in every aspect. In order to avoid waste material by cutting processes and to improve mechanical properties, forming processes offer many advantages but harbor also challenges. To face these challenges, especially techniques like isothermal forging are promising methods. Isothermal forging is an appropriate process for achieving a microstructure with excellent properties for high performance applications in aviation technology and turbine construction. One of the main challenges in this special process is the determination of a tool material with a high temperature resistance as well as a high resistance against the work load of forging processes. Given their high hardness, temperature resistance and wear resistance, technical ceramics feature properties classifying them as generally suitable for this application. This article deals with the complete design of an isothermal forging process with ceramic tool material for titanium forming. The material characterization of the forming material by flow curve determination is performed to receive data for FE analyses. Afterwards, a ceramic tool system for isothermal forging is designed and manufactured. The tests show that especially the brittleness of technical ceramics restricts their application as tool material for isothermal titanium forming. Additional investigations on isothermal forging using carbide metal as tool material show the benefit of isothermal titanium forging. The results of metallographic analyses are given.

Abstract: Hot-stamping technology applies hot-stamping dies to the forming and quenching of austenitized high-strength steel plates to produce super-high-strength parts. To carry out these forming and quenching functions, the hot-stamping dies must be able to withstand shock and high-temperature friction under harsh working conditions, and hence high-quality die materials are necessary. However, since the material performance requirements of hot-stamping dies have not been standardized, and special die materials have not been developed, the choice of materials is based on improving the safety coefficient, which leads to material waste and increased costs. In this article, the performance of the hot-stamping process is analyzed to obtain the main resistance indices and a material selection formula for hot-stamping dies, enabling the selection of hot-stamping die materials to be quantified, and thereby establishing a scientific basis for the selection process.

Abstract: In our previous study, we reduced the slide marks on material surfaces by optimizing the lubricant for push-through bending. In this study, we investigate contact conditions of material deformation in dies during push-through bending. We also attempt to reduce slide marks by investigating the die material, die surface treatment of the die, and roller die set and to clarify the following. Bending deformation and flange wrinkling occur in fixed dies during push-through bending. Sliding between the material and the die begins inside the fixed die. A cemented carbide die is excellent for obtaining ideal surface roughness of the slide marks. Hard metal dies tend to have excellent sliding characteristics. Cold die steel (SKD11) and high-speed steel (SKH51) have almost equal hardness, and their qualities exist harmoniously between the bending member and the die material without the above relationship. When we treat the die surface or use the above dies, roughness of slide marks increases. The die-surface roughnesses in Diamond-Like Carbon (DLC) processing and Toyota Diffusion Coating Process (TD) are minimal, and the surfaces of their bending members are smooth. Furthermore, their efficiency is nearly equal to that of cemented carbide dies without surface treatment. Using a roller die effectively reduces slide marks. However, a roller die contacts the bending member locally, and the contact pressure is higher than with a normal die. Thus, a roller die is inferior to a normal die in its curvature, deformation, and flange wrinkling. The structure of the roller die is most suitable for parts with small curvatures.

Abstract: Immune algorithm is a computational intelligent method which imitates the information processing properties of the natural immune system. It is one of the effective global optimization algorithms with higher global convergence. In this paper, mathematic model between the mechanical properties and the constituent of Al2O3 based ceramic tool and die material is established with the method of regression analysis. The obtained relationship function works as the optimum objective function. The immune algorithm is then used to optimize the mechanical properties of material. The best value of fracture toughness, hardness and flexural strength is 5.356 MPa·m1/2, 20.702 GPa and 731.96 MPa, respectively. The volume fractions of SiC and Ti (C,N) can be obtained when the mechanical properties of material reach the optimum. The result shows that using immunity algorithm can find the global optimal solution rapidly, and avoid the premature convergence phenomena existed in the genetic algorithm. Comparing the optimal results with experimental results, the relative error is small. It suggested that the immune algorithm can well be used for the optimum design of ceramic tool and die materials.

Abstract: A new nano-composite ceramic tool and die material was prepared by vacuum hot pressing technique. The effect of hot pressing technology on the microstructure and mechanical properties of ZrO₂ nano-composite ceramic tool and die material was investigated systemically, and the ceramic tool and die material with good mechanical properties was fabricated successfully. Results show that, the highest flexural strength, fracture toughness and hardness of ZrO₂ nano-composite ceramic tool and die material reaches 1055 MPa, 10.57 MPa∙m1/2 and 13.59 GPa, respectively by means of the vacuum hot pressing technique at 1430 °C for 60min at 35MPa. The flexural strength and fracture toughness has been improved greatly by the optimization of hot pressing technology. In the materials, the optimum sinter process could ensure the t-ZrO₂ stabilized till room temperature that can enhance the toughening effect of ZrO₂. The microstructure of ZrO₂ nano-composite ceramic tool and die materials were improved by the optimization of hot pressing technology, and the fracture mode is the typical mixed trans/inter-granular fracture mode.

Abstract: Based on the requirements for ceramic materials of cutting tool and die and the aim of improving comprehensive mechanical properties of ceramic tool and die materials, nanocomposite ceramic tool and die materials with high mechanical properties were fabricated successfully with nanometer composite method. Friction and wear properties of the developed ZrO2/Ti(C7N3) nanocomposite ceramic tool and die materials were experimentally studied in detail. Morphologies of the worn surfaces were observed and analyzed by ESEM. Wear mechanisms of nanocomposite ceramic tool and die materials were discussed with comparison with that of single-phase ZrO2 ceramics. It indicates that wear mechanisms of ZrO2/Ti(C7N3) nanocomposite ceramic tool and die materials are mechanical cold welding, abrasive wear and adhesive wear.

Abstract: A new ZrO2 nano-composite ceramic tool and die material was prepared with vacuum hot pressing technique. The effects of sintering parameters on the nano-composite ceramic tool and die materials were studied. The results indicated that the mechanical properties of ZrO2 nano-composite ceramic tool and die material with the additions of TiB2 and Al2O3 are higher than that of the pure ZrO2 ceramic material. Sintering at 1100 for 120min could improve the density and mechanical properties of ZrO2 nano-composite ceramic material. The flexural strength, fracture toughness and hardness with the optimum sintering parameters can reach 878MPa, 9.54MPa•m1/2 and 13.48GPa, respectively, obviously higher than that with non-optimum sintering parameters.