The Method of Improving the Machining Precision of the Hole in the Thin Wall

1 Problem Analysis Due to the complex shape of thin-walled parts beam saw machine, the relative stiffness is low, so the processing technology is poor. In this paper, according to the actual situation of processing enterprises (processed parts shown in Figure 1), a solution to the deformation of thin-walled parts of the hole cutting method, thereby improving the thin-walled parts of the hole precision. Thin wall deformation caused by many reasons, the main analysis can be the following aspects: (1) the workpiece clamping conditions Thin-walled parts in the three-jaw chuck clamping, clamping force in the three claws at the concentration of the role of the workpiece deformation occurs, there is no roundness after processing error, but the workpiece removed from the chuck, Due to the elasticity of the workpiece material recovery, leaving the hole appeared roundness error. (2) cutting parameters Cutting parameters unreasonable, prone to surface stress, and will produce a lot of cutting heat, resulting in deformation of the workpiece. ① the amount of back to eat knife: the depth of the different cutting depth of the workpiece surface residual stress and its distribution is not obvious, mainly due to the increase of cutting depth on the cutting temperature and the workpiece surface residual thermoplastic deformation is not obvious. So the cutting depth of the impact of macro-cutting force, but the residual stress on the surface of the workpiece is relatively small. ② feed: feed to increase the residual stress on turning significant impact. As the feed rate increases, the cutting temperature increases, so the residual stress of turning process showed a significant increase trend, and the residual stress distribution layer also deepened. ③ cutting speed: cutting speed increases at the same time, in the cutting tool under the action of the plastic deformation of the metal layer, plus the flank surface and the workpiece surface, cutting tools and cutting the cutting heat, cutting temperature is unevenly increased . Although the increase of the cutting speed causes the cutting heat to be generated in a very short period of time and the temperature is raised, the cutting heat of the cutting base layer is delayed for a certain period of time, and the cutting heat is accumulated in the cutting bottom layer horizontal band saw, resulting in an increase in the cutting temperature Resulting in a large thermoplastic deformation. (3) choice of coolant Cutting fluid can reduce the friction on the front and rear of the tool, the chip easily discharged, take away the cutting area of ​​heat, slow down the tool and the workpiece temperature. Cutting fluid has a good lubrication, cooling effect, but also has a good cleaning and anti-rust effect. Commonly used cutting fluid is divided into three categories: aqueous solution, emulsion and cutting oil: ① aqueous solution: aqueous solution is water as the main component of the cutting fluid. Good thermal conductivity of water, cooling effect, but rust, poor lubrication performance. ② Emulsion: Emulsified oil is diluted with 95 010 – 980/0 water, milky white or translucent liquid, the emulsion has a good cooling effect, with a certain lubrication, anti-rust effect. ③ cutting oil: cutting oil is the main component of mineral oil, often used in the addition of oil additives, extreme pressure additives and anti-rust additives to improve its lubrication rust effect, poor cooling performance. (4) work materials Workpiece material is different in the heat treatment process punch equipment, its hardenability is different, it is caused by heat treatment deformation is also different.

2 Improve the program (1) for the workpiece clamping deformation Three-jaw chuck claw structure, the use of ring clamping, fixture structure shown in Figure 2. For the outer surface of the workpiece, the pressure per unit area is reduced to reduce the clamping deformation caused by the roundness error. (2) for cutting parameters The cutting force is also increased, the deformation is also large, very bad for turning thin-walled parts; reduce the amount of knife to eat, increase the feed rate, although the decline in cutting force, But the residual surface area of ​​the workpiece increases, the surface roughness value is large, so that the strength of thin-walled parts of the internal stress increases, the same parts will be deformed; Based on the above reasons, the hole to take two- Specific processing parameters are shown in Table 1 below. (3) for the choice of coolant As the hole in the workpiece for finishing, processing volume is small, the main part should ensure the accuracy and roughness. Finishing due to cutting force is small, the temperature is not high, it is appropriate to use high concentrations of emulsions and oily additives, cutting fluid. (4) for the workpiece material 8620H steel is our country from the United States AISI (SAE) standard ‘H’ structural steel in the introduction of steel, the technical requirements are particularly stringent, the hardenability of the bandwidth is very narrow, 6-8HRC, and domestic gear steel quenching Sexual bandwidth is generally 12 – 15HRC. Because of the influence of the bandwidth on the heat treatment deformation of steel, in order to reduce the influence of heat treatment deformation on its hole processing, the workpiece material from 20CrMnTi to 8620H, which effectively reduces the heat treatment deformation busbar cutting machine.

3 Conclusion Through the above analysis and improvement, the dimensional accuracy of the hole after processing to meet the design requirements, hole roundness error stability control within 0. 05mm. Practice has proved that, from the process system and processing methods to take effective measures to make the processing effect has been significantly improved to solve the hole in the thin-wall processing error of the problem, improve the economic efficiency of enterprises.

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