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How to reduce machining deformation of thin-walled parts

Metal parts, especially thin-walled parts in the process of processing due to the state of the material itself and the process of thermal stress and other factors, deformation is inevitable, mainly because of the thin-walled parts of poor rigidity, weak strength, easy to produce deformation in processing, so that the shape of the part error increases, it is not easy to ensure the quality of parts processing.

In the process of machining and processing, the selection of a suitable fixture to clamp thin-walled parts and improve the fixture structure according to the requirements of the machining process of the parts can effectively improve this problem. In this article, we will introduce a thin-walled part fixture and share the improvement of the fixture by an enthusiastic user in the process of designing the fixture for thin-walled parts.

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Aluminum thin-walled parts
The external clamping type hydrostatic expansion jig is a kind of ultra-high precision jig, the clamping rotary accuracy can reach ≤3μm; it is especially suitable for clamping thin-walled workpieces and solving the clamping problems in high-precision machining.

Structural principle of external holding hydrostatic expansion fixture

Figure 1 is a schematic diagram of the structure of the external clamping type hydrostatic expansion jig. There is an annular closed oil cavity between the main body of the fixture and the thin inner wall of the clamping hole. When the expansion screw is tightened, the oil pressure in the oil cavity rises, so that the thin inner wall of the clamping hole is subjected to uniform external pressure, shrinking uniformly to the center and holding the outer cylindrical surface of the clamped workpiece; when the expansion screw is released, the oil pressure in the oil cavity falls back, and the thin inner wall of the clamping hole returns to its original diameter under the action of elastic return force and releases the clamped workpiece.
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Fig. 1 The structure of external clamping type hydrostatic expansion jig schematic diagram

The external clamping type static expansion jig application

In machine tools, chucks are often used to clamp the workpiece outer circle, for example, in lathes and grinders. But when the workpiece is thin-walled or requires clamping accuracy ≤ 10μm, the chuck is difficult to meet the requirements, then the hydrostatic expansion jig can show its superiority.
Figure 2 is an external clamping type hydrostatic expansion jig for lathe, the jig is directly connected with the lathe spindle, the clamped workpiece is a kind of thin-walled sleeve, and the two outer cylindrical surfaces of the sleeve are processed in one clamping.
Clamping advantages

  • Clamping the outer cylindrical surface in two external holds, solving the problem of over-positioning clamping.
  • Uniform clamping force, small deformation of the clamped workpiece, suitable for clamping of thin-walled workpieces.
  • ③ High rotary accuracy of the fixture, the radial runout of the workpiece bore to the clamped outer circle after machining is ≤6μm.

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Figure 2 External clamping type hydrostatic expansion jig for lathe

Enthusiastic users share-jig structure improvement case

When a company was producing a piston, the piston wall was very thin and the material was aluminum alloy, so it was easy to be deformed during the machining process. Therefore, the customer asked the fixture company to make a set of fixtures to improve the deformation. Since piston products have requirements for roundness, the fixture engineer initially used the Humberg external clamping expansion sleeve.
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Figure 3 The initial clamping solution
Due to the positioning of the product, it can only be clamped on the blank, and the surface of the blank is not uniform, resulting in uneven force, the product processing down or a trace of deformation, lathe processing, the chuck is not loose, the product roundness is good, but once the chuck is relaxed the roundness of the product will be deformed again.
Improvement of fixture structure.
After the discussion of the fixture designer, the structure of the fixture was modified. Because the center of this product can only locate the blank, so the designer reduces the clamping strength of the rising sleeve, the rising sleeve pulling rod from the previous rotary cylinder for spring tension, in addition to the compression structure, rising sleeve drive is driven by spring, compression by rotary cylinder pulling pressure plate.
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Figure 4 improved up the sleeve design

Conclusion

For the thin-walled parts in the process of processing, by the clamping force and cutting force caused by the deformation of the workpiece, not only to choose the correct fixture, but also according to the real situation of parts processing, reasonable design of its positioning and clamping method, the fixture structure to make changes.

Source: China Thin-walled Parts Manufacturer – Yaang Pipe Industry (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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