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Process analysis of piston rod parts

        (1) During normal use, the piston rod is subjected to alternating loads. There is a sealing device at φ50mm×770mm that reciprocally rubs its surface, so this area requires high hardness and wear resistance. The piston rod is made of 38CrMoALA material. After the φ50mm×770mm part has been tempered and surface nitrided, the core hardness is 28~32HRC, the depth of the surface nitriding layer is 0.2~0.3mm, and the surface hardness is 62~65HRC. This gives the piston rod both a certain degree of toughness and good wear resistance.
 
        (3) When selecting the positioning datum, in order to ensure the coaxiality tolerance of the parts and the mutual position accuracy of each part, all processing procedures use two center holes for positioning, which is in line with the principle of unified datum.
        (4) When grinding the outer circular surface, the workpiece is prone to tool deflection and elastic deformation, which affects the accuracy of the piston rod. Therefore, during processing, the center hole should be repaired and kept clean. The tightness between the center hole and the tip should be appropriate and good lubrication should be ensured. The general choice of grinding wheel is: abrasive white corundum (WA), particle size 60#, medium hardness or medium or ceramic bond. In addition, the width of the grinding wheel should be narrower to reduce the radial grinding force. Pay attention to the selection of grinding amount during processing, especially the grinding depth should be small.
  When grinding a 1:20 taper, the test piece must be ground first, and the workpiece can be officially ground only after checking that the test piece is qualified.
The inspection of the 1:20 conical surface is to use a standard 1:20 ring gauge for color inspection, and the contact surface should be no less than 80%.
        (6) In order to ensure the stability of the piston rod processing accuracy, manual alignment is not allowed during the entire processing process.
        (7) During nitriding treatment, the threaded parts should be protected by protective devices.
       The piston rod works in a reciprocating motion. In order to increase the life of the piston rod and reduce the wear of the piston rod, 38CrMoAlA alloy structural steel is selected as the blank. Since the production type is batch production, in order to improve production efficiency, the free forging method should be used to manufacture the blanks. According to the technical requirements and assembly requirements of the piston rod, the left and right end faces of the piston rod and the center holes on both end faces should be selected as the precise datum. Many surfaces on the part can be machined using both end faces as a reference. It can avoid benchmark conversion errors and also follow the principle of benchmark unification. The central axis at both ends is the design datum. Using the central axis as the benchmark can ensure the accuracy of the final processing position of the surface and achieve the coincidence of the design benchmark and the process benchmark. Since the finishing process of the two axial surfaces requires small and uniform margins, it can use itself as a benchmark.

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