Research On Multi-point Digital Forming Process Experiment And Numerical Simulation

Multi-point forming is a novel technology which can form various kinds of workpieces only by one mold.It is efficient,reconfigurable and easy to realize automatic production.With the improvement of the living standards,traditional single and mass production has been unable to meet people's needs,diversification and personalization have become the mainstream of the times.Therefore,it is very important to study the multi-point forming technology.The technology of flexible blank-holder in multi-point formingis a novel forming process,which is proposed based on the flexible method and can realize the fast,efficient and digital forming of the sheet.It can inhibit the wrinkle defecteffectively compared with the results without blank-holder device.In the past,corresponding curved surface can be obtained according to the different shape of the forming surface,the blank-holder pressure is also controlled.However,the size of sheet is fixed,when the forming part is small,the material utilization is very low.In this paper,a new type of flexible pressure forming technology is studied.The size of the blank-holder block and the layers of the blank-holder strips can be adjusted optionally according to the actual situation of forming parts.So material utilization rate is improved greatly,the manufacturing cost is reduced and at the same time,the contour cutting process can be omitted after forming.On the other hand,it broadens the application of multi-point molds and confirms its versatility in the forming of metal and nonmetal sheet through the application of multi-point forming technology to the thermoforming of artificial marble.The main contents and conclusions of this paper are as follows:(1)The study of flexible blank-holder process and experimentsA new flexible blank holder device is designed,and its working principle is briefly introduced.The equipments,materials,forming devices and technological process in this technology are described in detail.The influence of the blank-holder area and the number of the striplayers on the forming results was discussed.The results show that the forming device is more flexible and the forming quality is better when 3 layers of 1mm strip are arranged on the upper and lower of the plate with the blank-holder area of 24 × 10 mm.Comparing to the results of no pressure,it shows that no matter what kind of material,flexible blank-holder process can inhibit wrinkle defects effectively.(2)Numerical simulation offlexible blank-holder processThe finite element model of flexible blank-holder process is established.The material parameters,contact,friction type,load,boundary conditions,the unit type and grid partition are given in detail.The effects of theblank holder area,the strip layers and the pressure on the forming results are discussed.The results show that the stress and strain distribution can be more uniform and reasonable when the area of blank-holder block is 24× 10 mm and the strip layer is 3;it is the key to ensure the quality when the blank-holder force is reasonable and the excellent blank-holder force accepted in the final is 8-5-0.5MPa.(3)Comparative analysis of forming results with and without blank-holder device.The finite element model without blank-holder device is established,the simulation results are compared with the forming results with blank-holder device.It is show that the wrinkle defects can be avoided effectively,the stress and strain distribution is more uniform and the value is smaller when the blank-holder device is used.On the other hand,the sheet metalflow is limited to a certain extent,so that the thickness distribution is more uniform and reasonable and the forming quality is better.(4)The study of artificial marble thermoforming process and experimentsThe characteristics and advantages of the artificial marble sheet as while as the principle of the thermoforming are introduced in detail.The experiments are carried out according to the principle of single variable.It is show that the surface of the workpiece is smooth and without any defects when 10 mm silicone elastic pad is used;the surface of the workpiece appears regular indentation when there is no elastic pad;the shape error is small when the forming force is 80000 N,temperature is 165 ? and holding pressure to 82 ?.(5)Numerical simulation of multi-point thermoforming process of artificial marbleThe main defects of multi-point forming are introduced,and the finite element model is established.The influence factors are analyzed by numerical simulation method.The results show that the thicker the elastic pad the smaller the wrinkles,the harder the elastic pad the better the forming quality,the smaller the base size the higher the quality,the thicker the sheet the smaller the wrinkles.When the thickness of the elastic pad is 15 mm,the hardness of the polyurethane elastic pad is 89 A,the size of the basic punch is 10×10mm,the quality of the workpiece is best.