(1) Precision piston rod machining suffers from the benefits of alternating loads in normal applications. There is a sealing device at φ50mm×770mm to conflict with the surface, so the place requires high hardness and wear resistance.
The precision piston rod is processed with 38CrMoALA material. After quenching and tempering and surface nitriding, the core hardness is 28~32HRC, the surface nitriding layer depth is 0.2~0.3mm, and the surface hardness is 62~65HRC. In this way, the piston rod not only has certain toughness, but also has better wear resistance.
(2) The layout of the piston rod is relatively simple, but the ratio of length to diameter is very large. It is a slender shaft part and has poor rigidity. In order to ensure the machining accuracy, rough turning and fine turning must be separated during turning, and the rough and fine turning are equally applied. Follow the tool holder to reduce the deformation of the workpiece during processing, and use the middle holder when processing the ribs on both ends.
(3) When selecting the positioning datum, in order to ensure the coaxiality of the parts and the mutual position accuracy of each side, all the processing procedures adopt the positioning of two middle holes, which conforms to the principle of the same datum.
(4) When grinding the outer surface, the workpiece is prone to knife and elastic deformation, which affects the accuracy of the piston rod. Therefore, the middle hole should be repaired during processing, and the middle hole should be clean, the tightness of the middle hole and the middle should be appropriate, and good lubrication should be guaranteed. Grinding wheels are generally selected: abrasive white corundum (WA), grain size 60#, medium-soft or medium-hardness, and ceramic bonding agent. In addition, the width of the grinding wheel should be narrower to reduce the radial grinding force. Pay attention to the selection of the grinding amount during processing. In particular, the grinding depth should be small.
(5) When grinding φ50mm×770mm outer circle and 1:20 taper, the two processes must be carried out separately. When grinding the 1:20 taper, the test piece must be ground first, and the work piece can be formally ground only after the test piece passes the inspection.
The 1:20 cone surface inspection is to use the standard 1:20 ring gauge coloring inspection, and the contact surface should be more than 80%.
(6) In order to guarantee the stability of the machining accuracy of the piston rod, manual straightening is not allowed during the whole machining process.
(7) When nitriding, the ribs should be protected by protective devices.
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