Processing analysis of stainless steel pipes in thin-walled machinery industry

In the machining industry, thin-walled workpieces are prone to vibration and deformation during the turning process due to poor rigidity, and their form and position tolerances and dimensional tolerances cannot be guaranteed. If the solution is improper, the processing may even be impossible to proceed.

1. Raising the processing problem

The processing of thin-walled parts is a tricky problem in turning. The reason is that thin-walled parts have poor rigidity and weak strength, and are extremely easy to deform during processing, which increases the shape and position error of the parts, and it is difficult to ensure the quality of the parts.

For this reason, strict requirements are put forward for the clamping of thin-walled parts, the reasonable selection of cutting tools in turning and the selection of cutting parameters.

The thin-walled stainless steel pipe we processed is a thermal shock-proof sleeve for the nozzle of a certain product, as shown in Figure 1. This workpiece is a large-diameter thin-walled workpiece, the outer diameter of the pipe is 292mm, the material is Z2CND17-12 nitrogen-controlled stainless steel, the wall thickness is 4mm, the total length of the workpiece is more than 550mm (with clamping allowance), the roundness is required to be 0.05mm, and the overall surface roughness is required. The value Rau003d6.3μm, which determines that the accuracy factor of this workpiece is very high.

2. Formulation of processing technology

(1) Increase the process chuck to increase the length from 550mm of the finished product to 610mm.

(2) Divide the processing stages:

①Rough machining stage. Rough turning and rough boring are used to remove the margin. In rough machining, the amount of back-grabbing and feed can be larger; in finishing, the amount of back-grabbing is generally 0.2~0.5mm, and the feed is generally 0.1~0.2mm/r, or even smaller, the cutting speed 6~120m/min, use as high a cutting speed as possible when finishing turning, but not too high.

②Semi-processing stage. Prepare for the finishing of the main surface, complete the processing of some secondary surfaces, and use semi-finishing machining to achieve the necessary accuracy and machining allowance before finishing. If the tube is clamped on the chuck with too much force, the thin-walled parts will be deformed, resulting in roundness errors of the parts. If it is not clamped tightly on the chuck, the parts may become loose and scrapped during turning. We clamp it when rough turning and loose it when finishing turning to control the deformation of the parts. In the semi-finishing stage, the amount of back knife is smaller, so that the internal stress of the thin-walled stainless steel tube is released and the deformation of the finishing is reduced.