Papers by Keyword: Hot-Forming

Abstract: More applications of hot-forming for cost-efficient lightweight solution will be considered in new car body projects of China. As a partner for hot-forming, ThyssenKrupp Steel Europe sets a 3-pillar development strategy from material, process and advanced component design for this demand. The detailed technologies and innovations are introduced together with application examples, to show how to realize the lightweight result with cost-efficiency.

Abstract: According to the actual work conditions, 3D FE model of channel bending forming is established on the platform of eat/DYNAFORM. Belytschko-Tsay (element # 2) in the cell library unit of eta/DYNAFORM is selected, and the geometric model is reasonably meshed by using topological mesh technology. In order to improve the accuracy, adaptive function is adopted. We established the proper material constitutive model for Ti-6Al-4V; gave a reasonable load curve by reasonable calculating and adjusting the loading time step in solving process; chose reasonable lubricant, provided practical coefficient of friction between the mould and blank in the simulation process by using the contact theory and classic coulomb friction law. Finally, we established the finite element model of the channel bending forming of Ti-6Al-4V actually, provided supplementary support for actual production.

Abstract: Continuous Cooling Transformation (CCT) diagrams determined with a dilatometer were used to analyse the influence of the alloying elements on the phase transitions of high strength steel sheet alloys. Mo and Cr additions showed a significant influence on the extension of the bainitic region, whereas C and B additions showed noteworthy improvement on the quenchability of these steel alloys. These alloy properties are desirable requirements to be integrated in hot formed components. In addition to these experimental results, thermodynamic calculations were done with help of the JMatPro software in order to analyse the effect of Mn and C on the resulting mechanical properties as function of the quenching rate.

Abstract: Abstract. Base on establishing the model of channel part deep drawing , the eat / DYNAFORM finite element analysis software is used to simulate and analysis the hot forming process of Ti-6Ai-4V channel part, the technological parameters which influenced the basic forming characteristics of the channel are researched. The result shows that: as with the punch and die clearance increases, the growth trend of the maximum effective stress value decreases, the thinning ratio has an increasing trend, the effect of clearance value on the material thickening ratio is small; as the fraction coefficient increases, the maximum effective stress increases in the whole forming stage, and along with the forming depths increase, friction can only influence the thinning ratio of material to a certain extent, the maximum thickening ratio decreases as the friction coefficient increases and decreases more quickly with the forming depths increase; the effect of different blank holder force on the maximum effective stress is not obvious in the forming process, under the role of first decrease and then increase type blank holder force curve, the maximum thinning ratio increases rapidly, exert the type of decreasing and the first increase then decrease blank holder force curve, the thickening ratio of the slab is small after forming, it can inhibit wrinkle and obtain better forming quality.

Abstract: Prediction and control of the microstructure to improve product performance are very important for the industry practice. In this study, microstructure evolutions of 30Cr2Ni4MoV steel under different conditions were simulated by changing the process parameters using the Deform 3D software. Effects of the forming process parameters on the microstructure were revealed: (1) the higher the temperature and the lower the strain rate, the smaller the strain are needed for the dynamic recrystallization; (2) when strain is enough, the higher the strain rate, the easier the uniform and small grain size can be obtained; (3) under a certain strain rate, the grain size increases as the deformation temperature increases. The microstructure of metal can be predicted and controlled according to the effects of hot forming process parameters on the microstructure evolution.

Abstract: Special V-shaped heat bending test was designed for 22MnB5 hot forming steel of different thicknesses. Blanks after heating 5 min at around 950°C to austenize fully were bended at different temperature conditions, and simultaneously the spring-back behavior and microstructure features of heat bending specimens were investigated. The result shows that 600-650°C temperature zone is optimal for bending forming and martensite texture transforming. Real hot forming anti-collision beams were produced at 600-650°C and comparison bending test was conducted to reveal more qualified mechanics at this temperature zone.

Abstract: High-strength sheet including 2MnB5 Boron and magnesium alloy sheet is the material commonly used in modern machinery, which is easy to induce problems such as excessive rebound, cracking, forming force increase, easy mould wear and the like. The heat analysis of 2MnB5 Boron and magnesium alloy sheet hot stamping forming process and experiments indicate that the transition process from Austenite to Martensite by controlling the sheet heating and cooling temperature is the foundation of heat forming. Only when the cooling rate reaches or surpasses the critical cooling rate, Austenite can be transformed to Martensite directly. Critical cooling rate of sheet is related to the elements of critical water flow rate, mould cooling system design, cooling medium, dented mould medium and the like. Under the condition that the elements of mould structure, cooling system, cooling medium and the like are defined, critical cooling rate is a constant value. As a result, through controlling critical water flow rate, hot forming transition process and hot forming requirements can be guaranteed to overcome the excessive rebound, cracking, forming force increase, easy mould wear and the like in hot forming process.

Abstract: A constitutive model is proposed for simulations of hot forming processes. Dominant mechanisms in hot forming including inter-granular deformation, grain boundary sliding and grain boundary diffusion are considered in the constitutive model. A Taylor type polycrystalline model is used to predict inter-granular deformation. Previous works on grain boundary sliding and grain boundary diffusion are extended to drive three dimensional macro stress-strain rate relationships for each mechanism. In these relationships, the effect of grain size is also taken into account. It is shown that for grain boundary diffusion, stress-strain rate relationship obeys the Prandtl-Reuss flow rule. The proposed model is used to simulate step strain rate tests and the results are compared with experimental data. It is concluded that the model can be used to predict flow stress for various grain sizes and strain rates. The proposed model can be directly used in simulation of hot forming processes and as an example the bulge forming process is simulated and the results are compared with experimental data.

Abstract: Ti-6Al-4V (Ti64) is the most commercially used heat treatable high strength/weight ratio, high corrosion, and thermal resistance alloy in titanium alloys. However, room temperature (RT) formability of this alloy is very poor and springback after forming is very severe due to the high yield strength and low elasticity modulus. In this research, the applicability of electrical resistance heating process which is a new and rapid heating process for hot forming application is investigated in order to improve formability and eliminate springback. The electrical resistance heating method is found to be effective for T64 alloy. Results reveal that the changes in hardness and grain size of the alloy have been found inconsiderable when the method is used. Springback compensation is achieved at high temperatures and springback free part is almost produced.

Abstract: Ultra high strength steel plays an important role of light weighting in automotive industry. The hot forming simulation of car door bar is processed with 22MnB5 ultra high strength boron steel. FEM is built with the 12 nodes shell elements and MAT 106 is selected in LS-DYNA. The hot forming processes include two heat transfers. One is the process from the oven to the tools after the blank is heated. The other is the process after the blank contacts the tools. The hot forming simulation results are obtained by LS-DYNA. The results show that the thickness distribution, the forming limit and the maximum effective plastic strain and other performances attain to standards. It is proved that the hot forming simulation method is correct.