Quality Issue Anallysis Of Column Load Cell Cracking

Column load cell is typically used for vehicle scale. Quality issue of column load cell cracking is involved many subjects.The hex button of column load cell sometimes cracked after assembled on vehicle scale for 1 year. Other parts of column load cell used for vehicle scale never cracked. The paper reviewed the cracking phenomenon of load cell hex button according to investigation of three customers. In the paper, the reason of cracking was found, mechanism analysis was implemented. improvement actions were suggested.According to force analysis, torque is thought as the main force which the hex button of column load cell beared. The crack effected by torque was thought that isⅠcrack. According to wallop analysis for column load cell, wallop value was calculated which load cell is working on rating load condition. It was pointed out that wallop is exterior factor to make column load cell cracking. It is necessary to control the wallop by customers. According to metallography analysis for load cell with crack from three customers, It showed that column load cell cracking should be stress corrosion fracture because its work condition is very bad. Heat treatment process,surface treatment process and material process were checked. It was thought that some of parameter or process is unsuitable for column load cell. These factors are interior factor to make column load cell.According to Taguchi Robust Design analysis for load cell with crack, the relation of chemical content and hardness was described. Author thought that that the Carbon content to 2Cr13 material should be control. It is better if Carbon content is lower than 0.2 percent. So the issue which column load cell hardness too high to spec could be solved.Mechanism analysis of the hex button of column load cell was implemented. It was thought that column load cell cracking is cleavage fracture. The main reason of the hex button of column load cell cracking is stress corrosion fatigue.The paper mentioned some improvement action and suggestion. It was thought acceptable that vacuum hardening temperature change 1020℃into 1000℃. Vacuum hardening in oil process could be instead by vacuum hardening in gas. Temper temperature should be changed and avoided 350℃which this temperature is in the temper brittleness area. It is thought necessary that grain size of column load cell material should higher than 5 grade. It was suggested that 2Cr13 material could be instead by 40CrNiMoA material for improve fracture toughness of column load cell. It was also suggested that customers should set speed-down block to avoid large wallop to column load cell.