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Analysis of machining process of thin wall parts

Due to the small wall thickness parameters, thin-walled parts are prone to stress deformation and temperature deformation in machining, which reduces the machining quality of parts. Based on the understanding and research of the characteristics of thin-walled parts, this paper puts forward the processing technology of this kind of parts to prevent quality problems in the processing process and improve the processing efficiency and quality of parts.

In the processing of thin-walled parts, NC machine tools need to be used to complete the processing work, and the specific processing work can be completed by completing the program design and writing according to the design drawings. However, in terms of actual effect, the current defective rate of parts processing is high, and a large number of parts have deformation problems in processing. In the future processing, it is necessary to select reasonable processing technology to avoid this phenomenon.

Analysis of deformation factors of thin-walled parts in machining

In the processing of thin-walled parts, it is necessary to use fixtures to fix the raw materials and semi-finished parts, and use relevant NC machine tools to complete the subsequent processing work. In the whole machining process, the deformation factor is the fixture factor first. For thin-walled parts, the requirement for the fixture is to provide due stress and prevent part displacement. On this basis, reduce the pressure applied by the fixture, especially for high parts. When the force applied by the fixture is too large, it will inevitably damage the edge structure of the part, Cause part deformation.
The second is the tool parameters. Different tools have different machining accuracy for parts. For thin-walled parts, it is necessary to select tools with higher accuracy. At the same time, it is also necessary to consider the machining efficiency of parts. When the adaptability between the selected tools and the machining process of parts is insufficient, it is easy to cause part deformation.
Finally, it is the tool path. In the processing of parts, when the entry and exit of tools are too frequent, it not only has a certain impact on the tool life, but also means that the contact frequency with parts is too high. For thin-walled parts, plastic deformation is easy to occur in tool contact. When there is too much contact, this plastic deformation will accumulate in the parts, The actual size of the part is inconsistent with the design size.

Machining process of thin-walled parts

Formulation of process route

In the formulation of the process route, the processing needs to be completed according to the application method of the parts and the relevant requirements of the parts. The specific processing process is rough machining, heat treatment, semi finishing and finishing. In the operation of the whole system, the relevant parameters of the parts need to be considered. For the parts with large deformation, The processing flow is rough milling, heat treatment, fine milling, shell, fine milling, inner cavity stiffener removal, part correction.
For the rough milling process, the vice can be used to fix the blank, and the milling cutter can be used to finish the rough machining of the part shape. After the shape shaping is completed, the inner cavity of the part can be machined with a suitable milling cutter, and stiffeners are set in the inner cavity of the part. Allowance needs to be set at both ends of the part, usually 1 ~ 2mm.
After rough machining, there is color six stress in the processed parts. In order to prevent stress deformation, low-temperature annealing can be used to eliminate machining stress and improve machining accuracy.
There are three steps in the finishing process. First, to complete the processing according to the design size of the part, use the pressing plate to fix the part, and further complete the part processing with reasonable milling tools to ensure that the shape of the whole part meets the design requirements.
Secondly, in order to implement the NC milling work, for the inner cavity of the part, the milling cutter shall be reasonably selected according to the depth of the inner cavity, so that the machining accuracy of the inner cavity can meet the design requirements in this process. At the same time, in the process of NC milling, it is also necessary to complete the milling of the outer surface of the parts, and select the milling cutter according to the design size of the parts. In the processing of parts, it is necessary to prevent the deformation of parts caused by the impact of milling cutter, and the arc feed method needs to be applied. The main work content is to program on the NC milling machine and complete the processing of parts according to the specific design parameters.
Finally, in order to remove the stiffener, the processing quality of the part is analyzed. When the accuracy requirements are met, the part can be delivered.

Selection of fixture

In the current part processing, the commonly used fixtures are three jaw chuck, vice and pressing plate. The application methods of these fixtures are different.
The application principle of the three jaw chuck is that three or four movable components are set in the high-strength disc, which are connected with the mechanical transmission equipment. After the machined parts are extended into the fixture, the whole fixture rotates to drive the machined parts to rotate. This fixture is only suitable for lathe, and has high requirements for the strength of components. Obviously, it can not meet the processing requirements of thin-walled parts.
The application principle of the vise is that the two symmetrical points of the part are regarded as the fixture installation point, and the fixture installation point needs to have high strength. In order to prevent displacement during milling, the vise will exert a great force on the part. For thin-walled parts, the overall structure will be damaged when the vise is applied, resulting in the deformation of the whole part.
The application principle of the pressing plate is that the pressing plate is used to fix the parts on the processing table, the pressing plate will apply pressure evenly to the parts, and adjust the pressure according to the part type. From the perspective of operation principle, this method can prevent the deformation caused by uneven stress by applying pressure to the whole part structure. Therefore, on the whole, this machining method is more suitable for finishing of thin-walled parts.

Selection of milling process

In the selection of milling process, the specific analysis content is the tool path. At present, there are two commonly used tool paths, one is line cutting method, the other is ring cutting method. The principle of line cutting method is that the tool used completes the milling of parts in behavioral units, and ring cutting method can be regarded as an integral milling process.
In the process selection, the line cutting method will produce greater stress in the process, and this stress will occur many times, which is prone to part deformation. In addition, for the parts with symmetrical cavities, the machining efficiency of this method is too low, and it is easy to cause the asymmetry of the two cavities, so the method selected in this paper is the ring cutting method.
For the parts with cavity, the rough machining has been completed before finishing. When machining the outer wall of the cavity, the forward milling method is used to complete the machining. In the application of this method, the vibration on the parts is small, so the machining accuracy can be better controlled and the part deformation caused by the machining accuracy can be effectively prevented.
In face milling, when it is necessary to feed from the outside of the part, the method of vertical feeding can not be applied to prevent the part from being deformed by the impact. The applicable feeding method is circular arc feeding, which can minimize the impact.

Conclusion

To sum up, in the processing of thin-walled parts, the deformation factors of parts include fixture factors, tool factors and tool path factors. It is necessary to reasonably select the applicable equipment according to the parameters of parts. In the processing of parts, first complete the selection of fixtures, then select a reasonable milling process, and finally complete the formulation of process route to improve the processing quality of parts.

Source: China Pipe Sleeve 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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