Research On Refrigerator Compressor Lower Cover Forming Process And Improvement In Sheet Metal Forming Technology

Sheet metal parts are widely applied to the automotive and the household appliances industries.The complex molding surface of lower cover's of refrigerator compression often occur convex cracking,light wrinkling of large area and unequal earing during the stamping process,which badly influences the quality and precision of the product,thus the difficulty of processing the products is increased and the cycle of upgrading the products is extended.In this paper,the defections occur in stamping process are analyzed,the lower cover of refrigerator compressor the optimum forming parameters and improvement process measures are obtained to avoid cracking and eliminate unequal earing.In this paper,one compressor' lower cover is taken as the research object,and the material is the hot rolled and pickled steel strip,The finite element numerical simulation and experiments have been used to study the stamping process and the technology improvement of refrigerator compressors lower cover.Microstructure and surface micrographs are analyzed by metallographic microscope,the stamping performance of blank are examined by the universal tensile experiment.Using the software eta/DYNAFORM to study material parameters and the process parameters,through the numerical simulation,influences lower cover stamping process.The stiffness and strength and the safeness of the die and has been simulated by NX NASTRAN software.The main content and conclusion of this research is as below:1)Microstructure and performance of the hot rolled and pickled steel strip were investigated and analyzed.There are coarse grains and mixed size grains at the edge of pickled steel sheet.due to it,The anisotropy and yield stress hardening modulus of it is lower than the normal fine grain.The mixed size grains microstructure easily lead to the cracking unequal earing of pickled steel sheet.2)Based on the analysis of the structure and forming characteristics of the lower cover and establishes a numerical model stamping,then did much research of the cracking on the local raised features and unequal earing at the edge of blank in the process of stamping.The simulation model was built and the simulation results show that anisotropy play an important role in stamping defections.Lower anisotropy of three direction of the blank would result in cracking and unequal earing.Large variation in thickness of in the edge of rolled plate,stamping performance below the middle strip.The highest stamping parameter of lower cover is 0.1t die gap,13T blank holder force,the 0.09-0.12 friction coefficient combination,8 mm die fillet radius.3)The better layout plan of lower cover according to sheet anisotropy and sheet thickness is proposed.The thinness of the blank and the height of unequal earing the part will be controlled through this method,meanwhile the product quality was ensured.Meanwhile,conical blank holder mold one-step forming method is investigated and to work well in this paper.Conical blank holder stamping formability will be simplified into a one-step process by which the production efficiency is improved and the cost is saved compare with the original one.4)According to the die structure analysis procedure,NX NASTRAN is used to studies the stiffness and strength.The results indicated that the maximum stress of binder appears in the part of fillet radius and the mold's on the edge of the blank.Meanwhile,A dynamic stamping die stress/strain curves of die and binder are obtained,and the security of molding is adjusted and verified.