| Due to the high strength and corrosion resistance,stainless steel sheet has gradually become an important material for building curtain walls and sculptures.However,traditional stamp forming can not meet the requirements of curtain wall and sculpture parts with multiple varieties and small batch.It is an urgent demand for industrial development to explore effective and flexible forming methods for stainless steel sheet.Multi-point forming is a flexible forming method,which disperses the die into regularly-arranged and height-adjustable multi-point punches.Since the CNC system can realize the rapid adjustment for the die surface,the parts with different shapes can be formed with just a set of multi-point dies,which is especially suitable for the forming of exterior panels of the building curtain walls.However,for the stainless steel sheet multi-point forming,the springback varies with the difference of geometry,thickness,and material.It is the focus of the paper to effectively control the springback and improve the forming accuracy by taking advantage of the characteristics of multi-point die.Firstly,several different geometric compensation methods were compared and studied to solve the springback of stainless steel sheet multi-point forming.Based on the results,a compensation method was given to the multi-point forming of stainless steel parts,and its effect in different forming methods was analyzed by numerical simulation.The main contents are as follows:(1)The compensation methods for single and double curvature bending were derived.Each sheet element is regarded as a differential arc with constant radius,and a continuous modified surface is calculated according to the elastic-plastic bending theory,then cubic B-spline curve and Bezier surface are used to fit the modified surfaces of single and double curvature surfaces,respectively.The numerical simulation results show that the compensation method has high accuracy and convergence speed.(2)The influence of curvature radius,sheet thickness,material and elastic cushion on the springback and compensation accuracy of stainless steel sheet multi-point forming was analyzed.The simulation results show that the springback increases with the increment of elastic cushion thickness;the springback increases and the compensation accuracy decreases with the increment of radius of the formed part increases,the decrease of the sheet thickness and the increment of material yield strength.(3)Aiming at the problems of large springback and hard to compensate to target shape in multi-point forming,multi-point stretch forming was used to control the springback of stainless steel parts.The springback was suppressed by controlling the stretching path.Considering the effect of the tensile force,the compensation method was modified to apply for multi-point stretch forming.The simulation results show that the springback can be effectively suppressed and reduced by more than 72% by multi-point stretch forming.The presented compensation method is suitable for the multi-point stretch forming.(4)In order to achieve the precise forming of stainless steel parts with large curvature and complex shapes,the springback control of multi-point stretch-press forming was studied.The deformation characteristics in multi-point stretch-press forming were studied,and the springback compensation method of multi-point stretch forming was applied for multi-point stretch-press forming.The simulation results show that multi-point stretch-press forming can overcome springback,wrinkling and form complex parts synchronously;the compensation method presented is suitable for multi-point stretch-press forming.(5)The springback and its compensation accuracy for three forming methods were compared.The simulation results show that the springback of multi-point forming parts is large,which requires three times of compensations,while it is small in multi-point stretch forming and multi-point stretch-press forming,which requires only one compensation. |
