How to solve the problem of easy deformation in machining thin-walled pipe sleeve

In the cutting process, the thin wall is easy to deform under the action of cutting force, resulting in the “waist” phenomenon of ellipse or small in the middle and large at both ends. In addition, due to poor heat dissipation during processing, thin-walled pipe sleeve is very easy to produce thermal deformation, which is not easy to ensure the processing quality of parts. The parts in the figure below are not only inconvenient to clamp, but also difficult to process. A special thin-wall pipe sleeve and shaft guard need to be designed.

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Process analysis

According to the technical requirements provided in the drawings, the workpiece is processed with seamless steel pipe, and the surface roughness of inner hole and outer wall is Ra1.6 μm. It can be achieved by turning, but the cylindricity of the inner hole is 0.03mm, which requires higher requirements for thin-walled parts. In batch production, the process route is roughly as follows: blanking – heat treatment – turning end face – turning outer circle – turning inner hole – quality inspection.
“Inner hole machining” process is the key to quality control. It is difficult for us to ensure a 0.03mm cylinder without cutting the inner hole of the outer circle and thin-walled pipe sleeve.

Key technology of turning hole

The key technology of hole turning is to solve the problems of rigidity and chip removal of inner hole turning tool. To increase the rigidity of the inner hole turning tool, the following measures shall be taken:
(1) Increase the cross-sectional area of the tool handle as much as possible. Generally, the tool tip of the inner hole turning tool is located above the tool handle, so the cross-sectional area of the tool handle is less than 1 / 4 of the cross-sectional area of the hole, as shown in the left figure below. If the tool tip of the inner hole turning tool is located on the center line of the tool handle, the cross-sectional area of the tool handle in the hole can be greatly increased, as shown in the right figure below.
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(2) The extended length of the tool handle shall be 5-8mm as long as the length of the machined workpiece, so as to increase the rigidity of the turning tool handle and reduce the vibration in the cutting process.

Solve the problem of chip removal

It mainly controls the cutting outflow direction. The coarse turning tool requires the chip to flow to the surface to be machined (front chip). Therefore, the inner hole turning tool with positive edge inclination is adopted, as shown in the figure below.
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During finishing turning, it is required that the chips flow to the centripetal front chip (hole center chip removal). Therefore, during tool grinding, pay attention to the grinding direction of the cutting edge and the chip removal method along the forward inclined arc. As shown in the figure below, YA6 is used as the alloy of finishing turning tool. At present, M type has good bending strength, wear resistance, impact toughness, adhesion to steel and temperature.
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During edge grinding, the front angle shall be grinded with a circular arc angle of 10-15 °, the rear angle shall be 0.5-0.8mm away from the wall according to the processing circular arc (arc of the tool bottom line), the K direction of the cutting edge angle c is § 0.5-1, the polishing edge along the chip edge B is R1-1.5, the auxiliary rear angle shall be grinded into 7-8 °, and the A-A points of the inner edge e shall be grinded into a circle to discharge chips outward.

Processing method

(1) A shaft guard must be made before machining. Main purpose of shaft guard: cover the inner hole of the turned thin-wall sleeve with the original size and fix it with the front and rear centers, so that it can process the outer circle without deformation and maintain the machining quality and accuracy of the outer circle. Therefore, the processing of shaft guard is the key link for the process of processing thin-walled pipe sleeve.
45# carbon structural round bar for machining shaft guard rough embryo; Turn the end face, open the B-type center holes at both ends, rough the outer circle, and leave an allowance of 1mm. After heat treatment, conditioning and setting, and then finishing turning, leave 0.2mm allowance for grinding. The ground surface shall be re heat treated with hardness of HRC50, and then ground by cylindrical grinder as shown in the figure below. The accuracy meets the requirements and will be used after completion.

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(2) In order to make the workpiece processed at one time, the clamping position and cutting allowance shall be reserved for the rough embryo.

(3) First, heat treat the wool embryo, quench, temper and set the shape, and the hardness is hrc28-30 (the hardness in the machinable range).
(4) The turning tool adopts C620. First, put the front center into the cone position of the main shaft and fix it. In order to prevent the workpiece deformation when clamping the thin-wall sleeve, an open-loop thick sleeve is added, as shown in the figure below.
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In order to maintain mass production, one end of the outer circle of the thin-walled pipe sleeve is processed into a uniform size D and t. the ruler is clamped axially, and the thin-walled pipe sleeve is pressed tightly to improve the quality of the inner hole and maintain the size. Considering the generation of cutting heat, it is difficult to master the expansion size of the workpiece. Sufficient cutting fluid needs to be poured to reduce the thermal deformation of the workpiece.
(5) Clamp the workpiece firmly with automatic centering three jaw chuck, turn the end face and rough the inner circle. Leave an allowance of 0.1-0.2mm for finish turning, replace the finish turning tool, and process the cutting allowance until the guard shaft meets the requirements of over fit and roughness. Remove the inner hole turning tool, insert the guard shaft to the front center, clamp with the tailstock center according to the length requirements, replace the outer circle turning tool, rough turn the outer circle, and then finish turn to meet the drawing requirements. After passing the inspection, use the cutting knife to cut according to the required length and size. In order to make the cut flat when the workpiece is disconnected, the blade edge shall be obliquely ground to make the end face of the workpiece flat; The small grinding section of the guard shaft is to cut off the gap left. The guard shaft is to reduce the deformation of the workpiece, prevent vibration and fall and bruise during cutting.

Conclusion

The above methods for processing thin-walled pipe sleeve solve the problem that the deformation or dimensional error and shape error can 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 grasp, the secondary completion, and the mass production is also more practical.

Source: China Pipe Sleeve Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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