Crack Formation And Control During Frame Tube Bending Forming And Machining Process

The frame tube is usually made of hot rolled steel strip or cold rolled steel strip after bending,welding and machining.The main materials used are Q195,08Al and so on.It is an important structural component of bicycle,electric bicycle,motorcycle and so on.It is closely related to the safety of personnel and equipment,a long process of production and processing,and more processes.However,the current research on the frame tube is usually concentrated in a certain process,such as smelting or welding process on the quality of the product,etc.There is no systematic study of the whole process of the frame tube.(1)It is found that,the cracking of the frame tube is usually associated with the steel making batch,the hot-rolling batch,the welding process.Further research findings that there is a certain relationship between the cracking of the frame tube and the steel inclusion,the rolling reduction rate,the welding current and the steel carbon equivalent.(2)Crack of frame tube bending forming and machining process mainly includes four types:tongue cracking,bar cracking,cracking after cold rolling processing,and welding point cracking.(3)The main cause of the "tongue" cracking and "bar" cracking defect are the abnormal process of steel making,which leads to excessive steel inclusion,the "tongue" cracking is mainly caused by the complex inclusions composed of silicate inclusions in steel and the sulfide and oxide particles,the "strip" cracking is mainly caused by the banded silicate inclusions and point chain oxide inclusions.(4)Cracking after cold-rolling,and the cracking of the weld seam are mainly caused by abnormal cold rolling and welding process,which results in abnormal steel structure.The cold bending cracking of the frame tube after cold rolling should be caused by the unreasonable cold rolling process or the cold rolling hardening is too high.The cracking of welded point is mainly caused by overheating of the welding line.(5)In order to reduce the cracking rate of the frame tube,the control measures according to the results of the study are as follows:the first,through the strict control of steel making and casting process,reduce the occurrence of inclusions in the parent material;the second is to control the hot rolling temperature process,using high finishing rolling temperature,low coiling temperature to improve the performance of the material;the third is to reduce the degree of cold rolling deformation,if there is no annealing treatment after the cold rolling,the total cold rolling rate should be control lower than 70%;the fourth is to optimize the welding process,for different types of steel,different specifications for the development of different welding parameters,at the same time,standardized welding parameters and corresponding welding forming coefficient,minimize the line energy,reduce the heat degree.