Research on deformation and vibration analysis based on thin-walled sleeve machining

Thin-walled sleeves with thin walls and poor rigidity cause deformation and vibration during the machining of such parts due to cutting and clamping forces. This paper analyzes the causes of deformation and vibration during the machining of thin-walled sleeves, and proposes solutions that can effectively guarantee the machining quality of thin-walled sleeves after practical verification.

0. Introduction

The thin-walled sleeve itself has poor rigidity (the larger the L/d value, the worse the rigidity), and is susceptible to deformation and vibration during the machining of thin-walled sleeve due to cutting force, clamping force, positioning error and elastic deformation, which leads to poor roundness and roughness of the machined thin-walled sleeve and cannot meet the quality requirements.
In order to solve the above problems, this paper analyzes the causes of deformation and vibration during the processing of thin-walled sleeves, and proposes corresponding solutions to effectively ensure the processing quality of thin-walled sleeves.

1. Analysis of causes

1.1 Deformation caused by cutting force

In the turning process, the cutting force can be decomposed into axial cutting force PX, radial cutting force PY. Different cutting forces have different effects on the bending deformation of the thin-walled sleeve produced by turning.
The radial cutting force acts vertically in the horizontal plane of the workpiece axis, because the rigidity of the thin-walled sleeve is poor, due to the action of radial force, resulting in the workpiece bending in the horizontal plane (see Figure 1).

Figure.1 Clamping method and mechanical model of one clamp and one top
The axial cutting force acts parallel to the workpiece axis direction, which produces bending moment on the workpiece. For ordinary cylinder processing, the effect of axial cutting force can be ignored. But because the rigidity and stability of the thin-walled sleeve are poor, so when the axial cutting force exceeds a certain value, the workpiece will be bent due to the influence of axial cutting force and produce longitudinal bending deformation (see Figure 2).

Figure.2 The effect of axial cutting force and mechanical model

1.2 Influence of cutting heat

When turning the workpiece, due to the effect of cutting heat, the workpiece will gradually produce elongation and deformation with the increase of temperature. In the turning of ordinary cylinder block can not consider the issue of thermal deformation elongation, but when turning thin-walled sleeve, because the workpiece is long, the total elongation is large, need to take into account the thermal deformation, the workpiece elongation can be calculated according to the following formula.

In the formula:

• α1 – material expansion coefficient, 1/°C;
• L – the total length of the workpiece, mm;
• Δt – the workpiece temperature rise, ℃.

If L=1000mm, the material is carbon steel, Δt=200℃, α1=0.000012, ΔL=2.4mm.
From the above calculation, it can be seen that the heat deformation elongation of the workpiece is 2.4mm, because one end of the workpiece is clamped, the other end cannot be elongated, resulting in the bending of the workpiece. Once the workpiece is bent, it is difficult to carry out turning.

1.3 Influence of clamping method

In the process of thin-walled sleeve processing, generally use the center frame and three or four jaw chuck with the use of its installation on the machine tool. Hydraulic cylinder body in the chuck clamping after the elastic deformation, when its inner and outer diameter have been out of round.
When using radial force clamping, if the clamping force is too small, can not meet the requirements of the force required in processing; if the clamping force is too large, thin-walled sleeve will have plastic deformation, resulting in roundness error.

2. Solution

2.1 The reasonable choice of cutting parameters

Turning process, cutting force and cutting heat on the parts processing impact. Whether the selection of the cutting amount is reasonable, the size of the cutting force generated in the cutting process, the amount of cutting heat is different, the deformation caused by turning thin-walled sleeve is also different.
1) Cutting depth
When the stiffness is determined, with the increase of cutting depth, the cutting force and cutting heat generated during turning increases, causing the force and heat deformation of the workpiece also increases, so in turning thin-walled sleeve, the depth of cut should be reduced as much as possible.
2) Feeding amount
Cutting thickness increases, the cutting force increases. But the cutting force is not proportional to the increase, so the force deformation coefficient of the thin-walled sleeve is reduced. If from the point of view of improving cutting efficiency, increasing the feed is more beneficial than increasing the depth of cut.
3) Cutting speed
As the cutting speed increases, the cutting temperature increases, the friction between the tool and the workpiece decreases, and the force deformation of the workpiece decreases, so increasing the cutting speed is beneficial to reduce the cutting force. However, the cutting speed is too high to make the workpiece bend and vibrate under the action of centrifugal force, which destroys the smoothness of the cutting process, so the cutting speed should be controlled in a certain range. For thin-walled sleeve, the cutting speed should be properly reduced.

2.2 Reasonable choice of tool

The biggest impact on the cutting force is the main deviation angle, front angle and edge inclination angle (see Figure 3).
1) Main deflection angle
The main deflection angle is too small, the cutting area increases, easy to produce vibration. When turning the main deviation angle can not be too large (not more than 90 °), otherwise cutting instability, easy to produce vibration. According to the thin-walled sleeve axial load-bearing capacity than the radial load-bearing capacity of the characteristics of the appropriate increase in the main angle of deviation, can reduce the backward force, reduce the workpiece deformation.
2) Sub-deflection angle
Increase the sub-deflection angle can reduce the contact surface between the cutting edge and the workpiece, reduce the friction and make the cutting smooth. Increase the sub-deflection angle to reduce the friction between the sub-blade and the workpiece. But the sub-deflection angle is too large, the tool heat dissipation conditions are poor, the tip of the tool is easy to wear, should be based on the actual processing situation.
3) Front angle
Increase the front angle to make the cutting edge sharp, smooth chip discharge and reduce vibration.
4) Tilting angle
The positive value of the edge inclination angle increases the actual front angle of the turning tool and reduces the edge arc. Increase the sharpness of the tool, thus reducing the cutting force and cutting heat.

Figure.3 Tool angle

2.3 Reasonable choice of clamping method

1) Change the direction of clamping force
Because the thin-walled sleeve axial bearing capacity than the radial, as far as possible to make the clamping force and the direction of the cutting force, by changing the radial clamping force to axial clamping force, can effectively reduce the clamping force.
2) Increase the clamping force area
When processing thin-walled sleeve, the three-jaw clamping force for the workpiece force area is too small, resulting in the processing of parts deformation.
If the thin-walled sleeve outer diameter of 160mm, wall thickness of 8mm, clamping force of 100MPa, by finite element simulation analysis (see Figure 4), the radial deformation of -0.5824 ~ 0.4416mm;
If the sleeve and the three-jaw chuck between the increase in tensioning sleeve, tensioning sleeve wall thickness 15mm, width 45mm, clamping force of 100MPa, the finite element simulation analysis (see Figure 5), the radial deformation of -2.258 × 10-6 ~ 1.743 × 10-6mm;
From the above finite element simulation analysis, it can be seen that the radial deformation of the thin-walled multi-stage cylinder sleeve is greatly reduced by increasing or decreasing the tensioning sleeve. We can get a small area of the workpiece localized force into a large area of uniform force, and then greatly reduce the workpiece clamping force deformation.

Figure.4 Finite element analysis of three-jaw chuck clamping

Figure.5 Increase the clamping finite element analysis of the clamping sleeve

2.4 Application of reverse cutting method

Use reverse cutting method to process the outer circle of thin-walled sleeve. Reverse cutting method means that in the process of turning the workpiece, the turning tool is fed from the spindle chuck to the tailstock direction. The axial cutting force generated in the process of machining by this method makes the workpiece pulled and eliminates the bending deformation caused by the axial cutting force. At the same time, the flexible tailstock tip can effectively compensate for the compressive deformation and thermal elongation of the workpiece in the section from the tool to the tailstock to avoid the bending deformation of the workpiece.

2.5 Other methods

1) Adjust the lathe, bed saddle, tool holder and sliding parts
If the gap is too large, adjust and reduce the gap to make the rotation and sliding parts reach the best condition.
2) Select reasonable tool bar
Increase the cross-sectional area of the toolpost as much as possible, shorten the extension length of the toolpost to increase the rigidity of the toolpost, and also choose a flexible toolpost.
3) Cutting fluid concentration
Turning whether it is low-speed cutting or high-speed cutting, in order to reduce the temperature rise of the workpiece caused by thermal deformation, must be filled with cutting fluid to fully cool. The use of cutting fluid can also prevent the workpiece from being pulled by the support claw of the tool holder and improve the service life of the tool and the machining quality of the workpiece.

3. Conclusion

This paper analyzes the causes of deformation and vibration during the processing of thin-walled sleeves, summarizes the rules, and puts forward effective solutions to the causes of deformation and vibration. Through analysis, it is concluded that:

• (1) By choosing the reasonable cutting amount and tool, the deformation of thin-walled sleeve during turning can be effectively reduced by cutting force and cutting heat;
• (2) By changing the direction of the clamping force and increasing the force area of the clamping force, the deformation of the thin-walled sleeve can be effectively reduced;
• (3) The bending deformation caused by the axial cutting force can be effectively eliminated by using reverse cutting to process the thin-walled sleeve;
• (4) The deformation of thin-walled cylinder can be effectively reduced by reasonably adjusting the lathe, bed saddle, tool holder and sliding part;
• (5) The thermal deformation caused by the workpiece heating can be reduced by reasonably matching the cutting fluid.

Authors: Wang Zhiyuan, Lu Yongchao, Zhang Yanwu, Xu Zhishuai

Source:  China Thin-walled Sleeves Manufacturer: www.epowermetals.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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