How to overcome deformation? CNC turning tips for machining thin-walled parts

In the cutting process, the thin wall is easily deformed by the cutting force, resulting in the phenomenon of ellipse or "waist-shaped" with a small middle and two large ends. In addition, due to poor heat dissipation during processing, thin-walled casing is easy to produce thermal deformation, and it is not easy to ensure the processing quality of parts. The parts below are not only inconvenient to clamp, but also difficult to process the processing parts, and it is necessary to design a special thin-walled casing and shaft.

Process analysis

According to the technical requirements provided by the drawings, the workpiece is processed with seamless steel pipe, and the surface roughness of the inner hole and outer wall is Ra1.6μm, which can be achieved by turning, but the cylindrical degree of the inner hole is 0.03mm, which is higher for thin-walled parts. In mass production, the process route is roughly as follows: blanking - heat treatment - car end face - car outer circle - car interior hole - quality inspection.

The "inner hole machining" process is the key to quality control. We throw away the outer circle and thin-walled casing and it is difficult to guarantee a 0.03mm cylinder for the cutting of the inner hole.

Key technology for bores

The key technology of the turning hole is to solve the rigidity and chip removal problems of the inner hole turning tool. To increase the rigidity of the inner hole turning tool, take the following measures:

(1) Try to increase the cross-sectional area of the shank, usually the tip of the inner hole turning tool is located above the shank, so that the cross-sectional area of the shank is less, less than 1/4 of the cross-sectional area of the hole, as shown in the figure on the left below. If the tip of the inner hole turning tool is located on the center line of the shank, the cross-sectional area of the shank in the hole can be greatly increased, as shown in the figure on the right.

(2) The extension length of the tool holder can be 5-8mm long with the length of the machined workpiece, so as to increase the rigidity of the turning tool holder and reduce the vibration during the cutting process.

Solve chip removal problems

Mainly controlling the direction of cutting outflow, rough turning tools require chips to flow to the surface to be machined (front chip removal), for which an inner hole turning tool with a positive edge inclination angle is used, as shown in the figure below.

When refining turning, the chip flow is required to centripetal tilt front chip removal (hole core chip removal), so when sharpening the knife should pay attention to the grinding direction of the cutting edge, to the front inclined arc chip removal method, as shown in the figure below fine turning tool alloy with YA6, the current M type, its bending strength, wear resistance, impact toughness and steel anti-sticking and temperature are better.

When sharpening, the front angle is milled at a circular arc angle of 10-15°, the back angle is 0.5-0.8mm from the wall according to the machining arc (the bottom line of the tool is along the arc), the k direction of the cutting edge of the c cutting edge is §0.5-1, the polishing edge is R1-1.5 along the chip edge B point, the secondary back angle is ground to 7-8 ° is appropriate, and the A-A point of the E inner edge is ground into a circle to remove chips outward.

Processing method

Before machining, a guard shaft must be made. The main purpose of the shaft guard: to cover the inner hole of the thin-walled sleeve of the car in its original size, and fix it with the front and rear tips to make it process the outer circle without deformation, and maintain the quality and accuracy of the outer circle processing. Therefore, the machining of the guarding shaft is a key link in the process of machining thin-walled casing.

45# carbon structure round steel for machining shaft blanks; The end face of the car, open two B-type top holes, rough car outer circle, leaving a margin of 1mm. After heat treatment, quality adjustment and shape, and then refined car to leave 0.2mm margin grinding. Re-heat treated the crushed surface with hardness HRC50, and then ground by cylindrical grinding machine as shown in the figure below, the accuracy meets the requirements, and it is ready to be used after completion.

In order to make the workpiece complete the processing at one time, the blank remains in clamping position and cutting margin.

First, the raw embryo is heat treated to adjust and shape, and the hardness is HRC28-30 (hardness of the machinable range).

The turning tool adopts C620, first put the front tip into the spindle cone position to fix, in order to prevent the workpiece deformation when clamping the thin wall sleeve, add an open-loop thick sleeve, as shown in the figure below.

In order to maintain mass production, one end of the outer circle of the thin-walled casing is processed into a uniform size d, the ruler of t is an axial clamp, and the thin-walled casing is pressed to improve the quality of the inner bore and maintain the size. Considering the cutting heat generated, the expansion size of the workpiece is difficult to grasp. It is necessary to pour sufficient cutting fluid to reduce the thermal deformation of the workpiece.

Use the self-centering three-jaw chuck to clamp the workpiece firmly, the end face of the car, and the inner circle of the rough car. Leave a margin of 0.1-0.2mm fine turning, replace it with a fine turning tool to process the cutting allowance to the guard shaft full of excessive fit and roughness requirements. Remove the inner hole turning tool, insert the guard shaft to the front tip, clamp it with the tailstock tip according to the length requirements, replace the outer round turning tool rough turning the outer circle, and then refine the turning to meet the drawing requirements. After passing the inspection, cut off with a cutting knife according to the length required size. In order to make the cut when the workpiece is disconnected, the cutting edge should be sharpened obliquely to make the end face of the workpiece flat; The small section of the guarding shaft is to cut off the gap and grind small, the guarding shaft is to reduce the deformation of the workpiece, prevent vibration, and fall and bruise when cutting.

conclusion

The above method of processing thin-walled casing, solves the problem of deformation or dimensional error and shape error and does not meet the requirements, practice has proved that the processing efficiency is high, easy to operate, and suitable for processing long thin-walled parts, the size is easy to master, the secondary completion, mass production is also more practical.