How to overcome deformation of thin-walled parts by CNC turning?

In the cutting process, thin wall by the role of cutting force, easy to produce deformation, which leads to the appearance of elliptical or small, two big "waist" phenomenon. In addition thin-walled casing due to processing, poor heat dissipation, very easy to produce thermal deformation, it is not easy to ensure the quality of parts processing. The following parts not only clamping is not convenient, and processing parts are also difficult to process, need to design a special thin-walled sleeve, shaft protection.

process analysis

According to the technical requirements provided by the drawing, the workpiece is processed with seamless steel tube, the surface roughness of the inner hole and outer wall is Ra1.6μm, which can be achieved by turning, but the cylindricity of the inner hole is 0.03mm, which is a higher requirement for thin-walled parts. In mass production, the process route is roughly as follows: cutting - heat treatment - turning end face - turning cylindrical - turning internal bore - quality inspection.

"Bore machining" process is the key to quality control. We put aside the cylindrical, thin-walled casing, it is difficult to guarantee 0.03mm cylindrical inner hole cutting.

Key Technology of Bore Turning

The key technology for turning holes is to address the rigidity and chip removal of the bore turning tool. To increase the rigidity of the bore turning tool, the following measures are taken.

(1) Increase the cross-sectional area of the shank as much as possible. Usually, the tip of the bore turning tool is located on the top of the shank, so that the cross-sectional area of the shank is less than 1/4 of the cross-sectional area of the hole, as shown in the left figure below. The cross-sectional area of the shank in the hole can be greatly increased if the tip of the bore turning tool is placed on the center line of the shank.

(2) The extended length of the tool shank can be 5-8mm longer than the length of the machined workpiece to increase the rigidity of the tool shank and reduce the vibration during the cutting process.

Solve chip removal problems

Rough turning requires chips to flow to the surface to be machined (front chip evacuation), for this purpose, a bore turning tool with positive flute angle is used.

When precision turning, it is required that the chip flow to the center leaning forward chip discharge (hole-centered chip discharge), so the grinding tool should pay attention to the direction of grinding the cutting edge, to the front leaning arc of the chip discharge method, as shown in the figure below precision turning tool alloy with YA6, the current type M, which has better flexural strength, abrasion resistance, impact toughness, as well as anti-stick and temperature with steel.

When sharpening, the front angle is 10°-15°, the back angle is 0.5-0.8mm away from the wall according to the processing arc (the bottom line of the tool along the arc degree), the cutting edge angle k is §0.5-1 for R1-1.5 along the cutting edge at point B, the secondary back angle is 7°-8°, and the A-A point of the inner edge of the E is ground into a circle to discharge the chips outward.

Processing Method

(1) Processing must be done before a guard shaft. The main purpose of the guard shaft: the thin-walled bore of the car to the original size of the set of holes, with before and after the center fixed so that it in the case of processing the outer circle without deformation, to maintain the quality of the outer circle processing, precision. Therefore, the processing of the guard shaft is the key to the process of processing thin-walled sleeve.

The bushings are made of 45# carbon steel; the end face is turned, the two B-shaped holes are opened, and the outer diameter is roughly turned, leaving 1mm allowance, and the bushings are tempered and shaped by heat treatment, and then fine-turned, leaving 0.2mm allowance for grinding. Re-heat the broken fire surface, hardness HRC50, and then grinded by the external grinding machine as shown in the picture below, accuracy up to the requirements, completed to be used.

(2) To finish the workpiece at one time, the blank is left in clamping and cutting.

(3)First, heat treatment and quenching of the embryo, hardness of HRC28-30 (the hardness of the processing range).

(4)Adopt C620 as turning tool, first put the front center into the tapered position of main shaft and fix it, in order to prevent the workpiece deformation when clamping the thin-walled sleeve, add a thick sleeve with open ring.

In order to maintain mass production, one end of the thin-walled sleeve is machined to a uniform size d, and the ruler of t is axially clamped, and the thin-walled sleeve is pressed to improve the quality and maintain the size of the inner hole. The workpiece expansion dimension is difficult to grasp because of the cutting heat generated. It is necessary to pour sufficient cutting fluid to reduce the thermal deformation of the workpiece.

(5)Clamp the workpiece firmly with self-centering three-jaw chuck, turn the end face and roughly turn the inner circle. Leave a margin of 0.1-0.2mm for fine turning, put on the fine turning tool to cut the margin to the full over fit and roughness requirement of the guard shaft. Remove the inner hole turning tool, insert the guard shaft to the front top, clamp the top of the tailstock according to the length requirement, change the outer circle turning tool for rough turning, and then finish turning up to the drawing requirement. After passing inspection, cut off the workpiece by cutting knife according to the length required size. In order to make the cut of the workpiece flat when it is disconnected, the edge of the knife should be grinded obliquely to make the workpiece end face flat; the guard shaft is grinded small in order to cut off a gap and grinded small, the guard shaft to reduce the deformation of the workpiece, to prevent vibration, and cut off when it falls off and bruise the original reason.

The above methods of processing thin-walled casing, solving the problem of deformation or resulting size and shape errors and not meet the requirements, practice has proven that processing efficiency is high, easy to operate, and suitable for processing longer thin-walled parts, size easy to grasp, one-time completion, mass production is also more practical.