Process analysis of chrome plated steel bar parts

- Jul 22, 2019-

Process analysis of chrome plated steel bar parts


(1) The piston rod is subjected to alternating load during normal use. The sealing device reciprocally rubs the surface at φ50mm×770mm, so the hardness and wear resistance are required. The piston rod is made of 38CrMoALA material, and the φ50mm×770mm part is subjected to quenching and tempering treatment 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 has both certain toughness and good wear resistance.


(2) The structure of the piston rod is relatively simple, but the aspect ratio is very large. It belongs to the slender shaft type parts and has poor rigidity. In order to ensure the machining precision, the roughing and finishing vehicles are separated during turning, and the rough and fine cars are used. Use the tool holder to reduce the deformation of the workpiece during machining. Use a center frame when machining the threads at both ends.


(3) When selecting the positioning reference, in order to ensure the coaxiality tolerance of the parts and the mutual positional accuracy of each part, all the machining processes are positioned with two center holes, which conforms to the principle of standardization.


(4) when the cylindrical grinding surface of the workpiece so that the knife is easy to produce, the elastic deformation of the piston rod affect accuracy. Therefore, in the cleaning process should repair research center hole, and to ensure that the center hole between center hole and the top tightness to be appropriate, and to ensure good lubrication. Wheel generally choose: white alumina abrasive (WA), # 60 size, hardness or soft, the ceramic binding agent, further narrower wheel width should be selected to reduce the radial grinding force, the grinding amount of attention to the selection of the processing, In particular, grinding depth is smaller.


(5) at the grinding φ50mm × 770mm cylindrical and taper 1:20, two steps must be performed separately. At 1:20 taper grinding, grinding first specimen, the specimen after passing the examination before the actual grinding work.

Check 1:20 conical surface, with a standard 1:20 coloring check ring gauge, the contact surface should be less than 80%.


(6) In order to ensure the stability of the machining accuracy of the piston rod, artificial alignment allowed the whole course of processing.


(7) When the nitriding treatment, etc. should be taken to protect the threaded portion of the protection device.


The working mode of the piston rod is a reciprocating motion. In order to increase the life of the piston rod and reduce the wear of the piston rod, the blank is made of alloy structural steel of 38CrMoAlA. Since the production type belongs to batch production, in order to improve production efficiency, a free forging method is preferably used to manufacture the blank. According to the technical requirements and assembly requirements of the piston rod, the center holes of the left and right end faces and the end faces of the piston rod should be selected as the fine reference. Many surfaces on a part can be machined with the end faces as a reference. Benchmark conversion errors can be avoided and the benchmarking principle is followed. The center axis at both ends is the design basis. The center axis is selected as the reference to ensure the final machining position accuracy of the surface and achieve the coincidence of the design basis and the process reference. Since the finishing process of the two-axis surface requires a small and uniform margin, it can be used as a reference.