1. Positioning and clamping
（1) The correct selection of the rough datum and the rational design of the initial positioning fixture are crucial issues in the processing technology. When pulling the positioning surfaces of the large and small heads of the connecting rod, the reference end face of the connecting rod and the three-point outer circle of the small end blank and the two points of the outer circle of the large end blank are used for rough reference positioning. In this way, the machining allowance of the large and small head holes and the processing surfaces of the cover is uniform, and the weighing and deduplication of the large end of the connecting rod is ensured, and the final shape and position of the part assembly are ensured.
（2) In the processing of the connecting rod and the assembly, the processing and positioning methods of the rod end face, the top surface and side of the small head, and the side of the large head are adopted. In the machining of the connecting rod cover in the machining process from the bolt hole to the spigot, the machining and positioning method of its end face, the two bolt seating faces, and the side face of one bolt seating face is adopted. This kind of positioning and clamping method with high repeated positioning accuracy, stable and reliable positioning, small deformation of parts, convenient operation, and can be used in various processes from roughing to finishing. Since the positioning reference is unified, the size and position of the positioning points in each process are also kept the same. All these provide good conditions for stabilizing the process and ensuring the machining accuracy.
2. Arrangement of processing sequence and division of processing stages The dimensional accuracy, shape accuracy and position accuracy of the connecting rod are very high, but the rigidity is poor and it is easy to deform. The main machining surfaces of the connecting rod are the big and small head holes, the two end faces, the joint surface between the connecting rod cover and the connecting rod body, and the bolts. The secondary surfaces are oil holes, locking grooves, etc. There are also processes such as weighing and de-weighting, inspection, cleaning and deburring. The connecting rod is a die forging, and the machining allowance of the hole is large, and it is easy to generate residual stress during cutting. Therefore, when arranging the process, the rough and finishing processes of each main surface should be separated. In this way, the deformation caused by roughing can be corrected in semi-finishing. The deformation generated in the semi-finishing process can be corrected in the finishing process, and finally the technical requirements of the part are met and the positioning datum is processed first in the process arrangement.
