Process Analysis of Digital Control CNC Machining
(1) Structural Features of Parts
The part is made of hard aluminum LY12, which offers excellent machinability and is a typical thin-walled disc structure. The outer dimensions are relatively large, with only 2mm thickness on the surrounding and internal ribs, and a cavity depth of 27mm. Due to its structural characteristics, improper process planning or machining parameters can easily lead to deformation, causing dimensional deviations.
(2) Process Analysis
The blank is selected from bar stock, and a roughing and finishing process plan is adopted. The specific process flow is as follows: blank → rough turning → rough milling → aging → finish turning → finish milling. During roughing, 1.5mm of finishing allowance is reserved on the outer and end faces, and a center hole is pre-drilled. For rough milling, 1.5mm of margin is left on the side and bottom of the cavity, and a process hole is pre-drilled at the φ12mm hole position. Aging is used to relieve residual stress in the material. Finish turning involves finishing the end face, outer diameter, and boring the φ6mm process hole, requiring a single clamping to ensure coaxiality and provide a solid foundation for subsequent operations. Finally, the finish milling ensures that the final requirements of the part are met.
(3) Rough Milling of Cavity
Rough milling is primarily aimed at removing large amounts of material and preparing the surface for finishing. Therefore, a low-cost conventional digital control CNC milling machine is chosen for this step. The inner contour should be machined according to the part's structural drawing, with an arc radius of R5mm and a uniform finishing allowance of 1.5mm. Additionally, positioning holes required for the finishing stage must be pre-processed at the φ12mm hole positions.
(4) High-Speed Machining Technology for Finishing
High-speed machining is a modern manufacturing technology that has been widely applied in recent years. It features low cutting forces, reducing part deformation, making it particularly suitable for thin-walled components. In high-speed machining, chips are removed quickly, and most of the cutting heat is carried away by the chips, minimizing thermal deformation of the workpiece. This helps maintain dimensional and shape accuracy. Additionally, high-speed machining produces a superior surface finish and significantly shortens the processing cycle. Given the characteristics of thin-walled disc parts, high-speed machining is employed during the final cavity finishing.
(5) Machining of Positioning Holes
This part uses the φ6mm and φ12mm holes as positioning holes. Therefore, the cavity must be machined first before finishing the cavity. The φ6mm center hole is honed to φ6H8 when the outer diameter after precision turning reaches φ301.5mm. The φ12mm hole is drilled using a digitally controlled CNC milling machine and then reamed to φ12H8.
(6) Positioning and Clamping of Parts During Final Cavity Machining
To ensure quick and accurate clamping of the workpiece on the machine tool, and to avoid individual alignment for each batch of parts, a positioning method using one pin and two pins is adopted. The existing φ6mm and φ12mm holes on the part serve as positioning holes, with a cylindrical pin and a flat pin used as positioning elements. Since the part is a thin-walled component, it is prone to deformation. When clamping, the pressure plate should be placed on a rigid section of the workpiece, and the clamping force should be evenly distributed to ensure secure clamping without causing unacceptable deformation. This clamping method is fully compatible with the features of a machining center, allowing the cavity and all holes to be machined in a single setup.
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