Advanced Materials Research Vols. 189-193

Abstract: Core shift is the phenomenon that the core will be shifted under the injection pressure during its molding process. Excessive core shift will bring variation in frozen-crust thickness which will lead to the buckling deformation of products and lower their structural performance. This paper takes the shell of U-disk as an example and analyzes the reasons of core shift in the injection mould designing with AMI, and its analyzed findings can be used for mould designing to shorten the developing period of products and decrease the cost of products and increase their economic benefit.

Abstract: Forming conical parts is one of the difficult fields in sheet metal forming processes. Because of low contact area of the sheet with the punch in the initial stages of forming, too much tension applied to the sheet that it causes bursting. Furthermore, since the major part of the sheet surface between the blank holder and punch tip is free, wrinkles appears on the wall of the drawn parts. These parts are normally formed in industry by processes such as spinning, explosive forming or multistage deep drawing. Hydroforming deep drawing is one of the special deep drawing processes which have been introduced in order to overcome some inherent problems in the conventional deep drawing with rigid tools. In the present work, an experimental program has been carried out to form and compare the forming pure copper conical-cylindrical cups by hydroforming and conventional multistage deep drawing processes. The conical parts in conventional deep drawing process formed in two stages. The results of the study demonstrate that thickness distribution are more uniform in the parts formed by hydroforming compared to conventional multi stages deep drawing processes.

Abstract: Tailor welded blanks (TWBs) get popular used in the automobile for the light-weighting, and the assessments for TWBs formability are more and more important owing to the TWBs with different thicknesses. In this paper, based on the tensile test and low carbon high strength steel (ZStE220P), the influences of seam location and the length of sample on the elongation are studied, and the results shows that the location of seam has greater effect on the formability of TWBs and elongation is getting decreased with the seam shifting to the thinner part.

Abstract: In this paper, the flow rule of metal during the deep drawing of the non-symmetry workpieces was investigated by means of the numerical simulation of deep-drawing processes of square cup under bilateral constrained conditions. The numerical simulation was carried out by advanced analysis software Dynaform5.5. SUS304 stainless steel was used as the deforming materials. The influence of different friction coefficient and blank holder force on the drawing forming quality was analyzed. The results showed that the material flow in different areas has different trends with increase of friction coefficient and blank holder force.

Abstract: Series of rod samples of Zr55Al10Ni5Cu30 alloy were prepared by magnetic suspend melting and copper mold suction casting method using 99.9wt% high purity zirconium and 99.4wt% low purity sponge zirconium respectively, the effect of purity of zirconium material on mechanical properties and microstructure of Zr-based bulk metallic glass were investigated. The result shows that high purity material alloy could enhance the thermal stability and glass forming ability of Zr-based bulk amorphous alloy, compression fracture surface analysis indicate that the vein patterns density increase with the material elements purity increase, the average compressive fracture strength is increased to 8.52% than that of low purity samples.

Abstract: A new micro-forming method, combining a metal’s super-plastic behavior with hot extrudsion technology, has been developed for manufacturing micro-gear from brass H62. The micro-gear, which modulus m = 0.125mm, pressure angle α = 20°, number of teeth z = 6, tip diameter d = 1mm, was selected and its dies were designed with a better die approach angle based on the DEFORM-3D FEA simulation results of the hot extrusion process. Finally the micro-gear was successfully hot extruded at 650°C from blank Φ3mm×3mm with extrusion ratio about 17. A good dimensional accuracy for micro-gear was obtained by using this hot extrusion technology. In the special die set, the split die structure was designed, and the special die materials were chosen, such as the pressure ram was made of tungsten carbide, and the other dies were made of mold materials 4Cr5MoSiV1.

Abstract: The software for the continuous flexible forming process was developed using Visual C++ platform. It can directly read the triangular mesh data of the CAD model. The three-dimensional model was reconstructed rapidly by using the core function of the OpenGL. Moreover, the mathematical model of adjusting the flexible rolls and the longitudinal curvature were established by this software. Using these mathematical descriptions the simulation of the continuous flexible forming process can be finished from the viewpoint of geometry.

Abstract: On the basis of in-depth simulation analysis of stress and strain, thickness and forming limit changes in the property sphere during the drawing process for the stamping part of the spiral step surface, combined with the comprehensive simulation analysis of flanging, punching and other operations for the parts, it is concluded that the most obvious non-uniform changes of sheet thickness occur in the drawing process and then in the flanging process. The possibility and the distribution of tension fracture in ironing and wrinkles in thickening has been predicted and the production feasibility of low-cost drawing process without the blank holder and multi-operation forming process for stamping parts of spiral step surface. The validity of multi-operation numerical simulation results has been verified by the actual measurement of finished product rate and product thickness in trial production.

Abstract: Co-deposition of silicon carbide particles and carbon (or carbon sources) particles is essential for preparation of reaction bonded silicon carbide (RBSC) products by slip casting. The way of co-depositing of silicon carbide particles and carbon particles during slip casting process, and the influence of composition of raw particles on particle co-depositing in green bodies were studied. The experiment results show: 1.Co-deposition of binary particles is greatly affected by particle size distribution, and large proportion of rigid SiC particles increases the difficulty in demoulding procedure because of small shrinkage; 2. Dispersants in deposited cake trend to enrich at the surface in contact with mould wall, while this enrichment of dispersant has little effect on mechanical performance of RBSC products; 3. Sharp edges on surface of raw particles could result to friction among particles, which afford strength to green bodies but prevent particles packing more closely.

Abstract: The continuous extrusion process would refine the microstructure effectively and increase the formability and properties of extrusion products, without preheating and post-mechanical treatment. During the continuous extrusion operation the microstructure of brass alloy significantly influences formability and properties. So the microstructure evolution rules of brass alloy during the whole continuous extrusion process were analyzed, and the hardness changing laws of the extruded brass alloy were also researched in this paper. By observing the microstructure evolution at different regions, the evolution rules of microstructure and properties of the continuous extrusion brass alloy were obtained. It was found that the dynamic recrystallization occurred at the right-angle bending region, which was proved by the hardness evolution of the extruded brass alloy. Therefore, it is feasible to control the properties of the extruded products by concentrating the right-angle bending region. This work gives the researching foundation of low formability materials based on continuous extrusion operation.