Research On Deformation Mechanism And Equipment Development Of Rotary Blanking Process

The rotary blanking process is a method of blanking and punching with synchronously and oppositely rotating tools whereby the punches and dies are correspondingly mounted onto the lateral surface of a pair of rollers to perform a continuous blanking operation on sheet metal. It converts the intermittent reciprocating motion of the traditional blanking process into continuous rotation motion and therefore greatly improves production efficiency for periodic hole patterns. It can be used to perform various operations for less than 3.0 mm thick sheet metal, such as punching, blanking, trimming and lancing. It is widely used in industries like construction, warehousing, packaging and automobile due to its significant advantages of higher production efficiency, lower blanking force, lower noise, less occupied area and lower investment. In this paper, rotary blanking process is systematically analyzed in terms of theoretical analysis, equipment development, experimental study and finite element simulation. The main research contents and conclusions are listed as follows:The moving trajectory of any point fixed on the punch is called a cycloid. It is characterized by the significantly different entry and exit routes of punch, which causes the additional relative motion between punch and strip and affects the sheared edge quality in a negative way. The sheared edge quality can be improved along with larger diameter roller and lower punch height. The instantaneous punch-die clearance for the leading cutting edge increases with rotational motion during punch penetration, while for the trailing cutting edge it decreases.The stress-strain curves at high strain value directly extrapolated by various types of flow stress laws are significantly different. Aiming at the problem, the true constitutive relationship is determined through fitting load-displacement curve after necking according to the combined experimental and finite element approach. As a result, the whole deformation process before fracture occurs can be accurately simulated by the true constitutive relationship. The mechanisms of ductile fracture are classified into tension, shear and mixed modes based on the fracture morphologies observed by SEM under various stress conditions. The decoupled constitutive equation with ductile fracture criterion is written in Fortran language. The modified GTN model applied in low stress triaxiality condition and Lemaitre damage model are established, which are successfully implemented in finite element model of rotary blanking through backward and forward Euler integration algorithm respectively.The values of ductile facture criteria and damage models are determined by the combination of experiments and simulations. The finite element model of rotary blanking process is established in Abaqus. The simulation results of ductile fracture criteria and damage models are compared with experimental results from the aspects of damage distribution, crack initiation. crack propagation and sheared edge quality. Moreover, the effects of punch-die clearance on sheared edge quality, blanking force, torque and instantaneous clearance are discussed, as well as roller diameter, die height, die wear and sheet metal thickness.The split type idea is adopted in tool design. The cold die steel W6Mo5Cr4V2 is chosen as tool material due to high bending resistance. The punch-to-die clearance and tool dimensions are decided according to the entry and exit routes of punch. The whole equipment including guiding frame, rotary blanking frame and finishing frame is designed and manufactured, which can achieve synchronous rotation and precise positioning between punch and die. The sheared edge including roll-over, burnish zone, fracture zone, burr and indentation is observed along shearing contour line through rotary blanking experiments. The distinguishing characteristic of sheared edge is that the burnish zone titles at certain angle for leading cutting edge. The influence of blanking clearance on sheared edge is analyzed in experiments, as well as material property and sheet thickness. Besides, the microhardness distribution of sheared edge is measured.A modified rotary blanking process which employs rigid punch and polyurethane pad is developed. The collapse zone surrounding a hole is flattened by finishing frame to improve product quality after blanking and the final hole quality can meet the most demanding requirements of blanking in industry. The effects of process parameters including the overlap between punch and die. polyurethane hardness, sheet metal and thickness on sheared edge quality are investigated in experiments and FE simulations.