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Factors and methods of machining thin wall parts

Thin wall parts have been widely used in various mechanical equipment because of their compact structure and light weight. They are mainly used to support the parts on the shaft and play a guiding role. Such parts have low rigidity, weak strength, produce vibration, a lot of cutting heat, and are easy to deform in machining, which affects the dimensional accuracy and shape accuracy of the workpiece. In view of the above problems, this paper proposes to optimize the machining process arrangement of thin-walled parts, the geometric parameters of cutting tools, the selection of cutting parameters and clamping technology.

Factors affecting machining of thin-walled parts

  • 1. The workpiece is thin-walled and easy to deform under the action of clamping force, which affects the dimensional accuracy and shape of the workpiece.
  • 2. The cutting heat generated in machining causes the thermal deformation of thin-walled parts and affects the dimensional accuracy.
  • 3. Under the action of cutting back force, it is easy to produce vibration and deformation, affecting the dimensional accuracy, surface roughness and shape and position accuracy of the workpiece.

Method for reducing deformation of thin wall workpiece

  • 1. Rough and fine turning and sequential machining are adopted: in rough turning, the corresponding clamping force is slightly larger in consideration of large cutting allowance and improving machining efficiency. Before finishing turning, properly release the claw to eliminate the deformation caused by excessive cutting force during rough turning. During finishing turning, the clamping force can be slightly smaller and the processing is completed.
  • 2. Geometric parameters of cutting tool: the reasonable selection of cutting tool parameters is an important symbol to reflect the comprehensive effect of multiple factors in the cutting process. The cutting angle and the shape of the cutting edge affect each other in cutting, focusing on maintaining the sharpness of the blade and the stability of the cutting process, so as to reduce the cutting force. A larger rake angle and a smaller tip angle should be selected. From the aspect of reducing vibration, we should use a smaller tool back angle to increase the contact area between the back of the tool and the workpiece, so as to achieve the purpose of vibration elimination.
  • 3. When finishing turning thin-walled workpieces, the rigidity of the tool handle shall be high, the polishing edge of the turning tool shall not be too long (generally 0.15mm-0.3mm), and the edge shall be sharp.
  • 4. Selection of cutting parameters: the cutting force is closely related to the back draft, cutting speed and feed rate. When the back draft and feed rate increase at the same time, the cutting force will be large and the workpiece deformation will be large; Reduce the back draft and increase the feed rate (0.6-0.8mm / R). Although the cutting force decreases, the surface residual area of the workpiece is large and the roughness increases, resulting in part deformation. Generally, during rough machining, the back feed and feed can be larger. During finish machining, the back feed should be about 0.3-0.5mm, and the feed should be about 0.15mm/min. During finish turning, high cutting speed should be selected. The three should be appropriate to improve the machining accuracy.
  • 5. Selection of clamping process: use slotted sleeve or special soft claw to increase the contact area during clamping and make the clamping force evenly distributed on the thin-walled workpiece, so as to reduce the deformation caused by clamping. Pouring sufficient cutting fluid during cutting is an effective method to prevent and reduce the deformation of thin-walled workpiece.

Using vibration absorbing materials, filling or wrapping thin walled workpieces with soft rubber tube, cotton yarn, foam, etc., can reduce vibration and eliminate noise, and also can fill thin melting material to turn thin wall sleeves, so as to reduce the deformation of workpieces. In addition, adjusting the gap of the lathe to an appropriate degree is also an important means to improve the rigidity of the lathe.

Figure 1

[Machining example]

Figure 1 shows a thin-wall workpiece of our enterprise cooperation unit. The equipment used is Shenyang CNC machine tool equipped with Guangzhou CNC system GSK980TA. In order to improve the qualified rate of parts, we have improved the tooling, optimized the geometric parameters and cutting parameters of the tool, and ensured the quality of the workpiece.

Figure 2

Part 1 is the workpiece to be processed after the inner hole size is processed, and the left end is the part clamped by the chuck, with a diameter of 100mm and a length of 50mm. Part 2 is the taper expansion tire with an opening, with a taper ratio of 1:30. Part 3 is a mandrel with the same taper. The taper opening of Part 2 is fully contacted with the workpiece by using the locking of threads, so that the workpiece can be well positioned and transmit cutting force in the fixture, which not only prevents vibration, It is also conducive to cutting. Applying lubricating oil on the mating surfaces of parts 2 and 3 is conducive to disassembly.

[Tool and cutting parameters]

The machine clamping turning tool with main deflection angle of 93 degrees and tool tip angle of 55 degrees is used for rough and fine turning of outer circle. It has strong rigidity, reduces vibration, good red hardness, wear resistance and no need to sharpen the tool.

The spindle speed of rough turning of outer circle is about 800-900r / min, the feed speed is f100-f120, and the fine turning allowance is about 0.3mm. During finishing turning, the spindle speed is 1000-1100r / min and the feed speed is about F40.

When cutting, fully pour coolant, which can take away a large amount of cutting heat, prevent workpiece deformation and ensure machining accuracy.

The above processing methods are often encountered in production practice, and there are inevitable mistakes in the above discussion. Please forgive and correct.

Source: China Thin Wall Parts Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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