What are the common defects in aluminium sheet processing and transformation: longitudinal cracks, transverse cracks, easy shrinkage, dead zone shear and folding, bending of aluminium sheet parts, cross-section size discrepancy caused by tension and contraction, large residual stress and coarse grained rings, etc.
The effective way to prevent dead zone fracture and folding is to improve lubrication and temperature and then control the die. The concave die with conical angle can also be used. The function of conical angle is to make the force have a component parallel to the conical surface, which is opposite to the direction of friction, so as to facilitate the deformation and flow of metal. According to different conditions, a suitable cone angle can be determined by calculation to offset the effect of friction.
Shrinkage hole is one of the reasons for defects in aluminum veneer processing. The main reason is that when zone A flows to the die hole, the metal in zone B flows together, leaving the upper end face of the punch to be concave. This kind of shrinkage hole is formed by the action of radial compressive stress. The countermeasure to prevent is to control the height of pressure surplus correctly and increase the reverse thrust when necessary. Qingdao Zhongwang Nonferrous Metals Co., Ltd. is an early domestic aluminium plate manufacturer. Its main products are high-precision ultra-flat aluminium plate, alumina plate, 6061 aluminium plate, 5083 aluminium plate and 6082 aluminium plate.
Aluminum veneer processing, often in the bottom of the die to form a difficult deformation zone, we generally referred to as "dead zone". Because the metal in this area does not deform and the upper metal adjacent to it is deformed and flowing, strong shear deformation occurs at the junction. In severe cases, it will cause metal shear, i.e. dead zone crack. Sometimes, folding may occur because of the large flow of the upper metal with the flow of dead zone metal.
Therefore, in the processing of aluminum veneer, when the deformed metal passes through the orifice part, due to the influence of friction, the surface metal flows slowly and the axis part flows fast, which further aggravates the non-uniform deformation formed in the cylinder, and the inner and outer metal flows differently, but the two are a whole, so the phase must be formed. The value of additional tension stress is increased by the internal force of mutual balance.
When we process hollow parts, if the gap between the orifice and its surroundings is not uniform and the gap is small, because of the relatively large friction resistance, the metal temperature decreases greatly, the metal flow is slow, and the effect of additional tensile stress may cause transverse cracks. The part with fast flow is limited by the part with slow flow and is subjected to additional compressive stress. However, its end is subject to tangential tensile stress, so longitudinal cracks often occur.
It is suggested that when the hole shape of the die is complex, the friction resistance in the thinner area is larger, so the cooling will be faster. Therefore, the flow is slower and the cracks are easy to occur, especially when the aluminum veneer is processed with low plastic materials.