Residual Stress In Materials Machined By WEDM And Its Influence On Deformation

Compared with other traditional mechanical processing means,WEDM technology has the advantage of processing complex shapes,as well as some hardness of the material,has become a metal material widely used to fine a processing process.However,modern advanced equipment manufacturing has put forward higher requirements on the processing quality,in the experimental process found that the uneven temperature field formed by WEDM will cause the material surface residual stress,for the small or thin thickness of the product,this surface residual stress will cause the component deformation,seriously affect the material processing and measurement accuracy,so it is essential to understand the distribution of residual stress field,and it is therefore necessary to understand the distribution of the residual stress field and to study its deformation law.In this paper,several common metallic materials such as low alloy steel,stainless steel,aluminium alloy,titanium alloy and cast iron are selected for study.Firstly,a layer-by-layer thinning cutting experiment is designed,and the strain gauge monitoring technology is used to obtain the magnitude of the stress generated after the deformation caused by the WEDM,and the law of the deformation behavior of the measured material is discussed.The results show that:no matter which material is used,a certain bi-directional tensile stress is generated in the remaining material;when the remaining thickness of the material is large,wire cutting does not lead to significant deformation of the material and the deformation stress is negligible;when the thickness of the sample is reduced to a critical value,the deformation stress caused by wire cutting increases gradually or even suddenly;when the remaining thickness of the sample is less than 2mm,the relative surface of the cut layer produces elongation deformation,forming a deformation stress of 40～110MPa.The experimental results were used to analyse the mechanism of this deformation stress caused by wire cutting and to observe the microstructure of the material.It was concluded that the different thermomechanical properties of the material determine the shape of the molten layer formed on the machined surface of the wire cutting.X-ray diffraction method was used to measure the residual stress on the cutting surface and thickness direction of Q345 material.The results showed that:the tensile residual stress on the cutting surface reached 310 MPa,which was close to the yield strength of the material;it was more than 0.3 mm away from the cutting surface,and within the range of 3 mm,the residual stress is compressive stress.Through the finite element simulation technology,the finite element analysis model was established by using MSC.Marc finite element analysis software,and the temperature field and stress field results of Q345 material WEDM were simulated.The results showed that:during the discharge process,the discharge center The highest temperature on the surface of the material reaches 1359℃,and the radius of the heating area is within 0.8 mm;the thermal stress generated by the WEDM surface under the action of the heat source,after the discharge,the surface presents residual tensile stress,σ1 can reach 326MPa,σ2 can reach 227MPa;within the range of 0～2mm from the cutting surface,compressive stress will be generated inside the material to maintain balance.The peak value of compressive stress appears at a position about 0.4mm away from the cutting surface,and the peak value of residual compressive stress is σ1=-91MPa,σ2=-82MPa.