Process Analysis of Digital Control CNC Machining
(1) Structural Features of Parts
The part is made from hard aluminum LY12, which offers excellent machinability and belongs to a typical thin-walled disc structure. The outer dimensions are relatively large, while the thickness of both the internal and external ribs is only 2mm. The cavity depth reaches 27mm. If the process plan or machining parameters are not properly set during the operation, the part is prone to deformation, leading to dimensional inaccuracies and an oversized difference.
(2) Process Analysis
The blank for the part is selected from bar stock, and a roughing and finishing approach is applied. The specific processing sequence is as follows: blank → rough turning → rough milling → aging → fine turning → fine milling. During roughing, a 1.5mm finishing allowance is reserved on the outer diameter and end face, and a center hole is pre-drilled. In the rough milling stage, a 1.5mm margin is left on the side and bottom of the cavity, and process holes at the φ12mm positions are pre-drilled. Aging is performed to relieve internal stresses caused by material removal and machining. Fine turning involves finishing the end face, outer diameter, and boring the φ6mm process hole. This step requires a single clamping to ensure coaxiality and provide a stable base for subsequent operations. Finally, the fine milling ensures that all final specifications of the part are met.
(3) Rough Milling of the Cavity
Rough milling is primarily used to remove large material allowances and prepare the surface for the finishing stage. Therefore, a low-cost conventional digital control CNC milling machine is used for this process. The inner contour must be machined according to the structural diagram, with an R5mm arc at the corners. A uniform finishing allowance of 1.5mm is left. Additionally, the positioning holes required for the finishing stage must be pre-processed at the φ12mm hole locations.
(4) High-Speed Machining Technology for Finishing
High-speed machining has become a widely adopted technique in recent years. It features lower cutting forces, reducing part deformation, making it ideal for thin-walled components. The chips are removed quickly, and most of the cutting heat is carried away by them, minimizing thermal deformation of the workpiece. This helps maintain dimensional and shape accuracy. Moreover, high-speed machining can achieve superior surface quality and significantly shorten the processing cycle. Given the characteristics of thin-walled disc parts, high-speed machining is utilized during the finishing of the cavity.
(5) Machining of Positioning Holes
This part uses the φ6mm and φ12mm holes as positioning references. Therefore, the cavity must be machined first before the finishing stage. The φ6mm center hole is honed to φ6H8 when the outer diameter of the turned surface reaches φ301.5mm. The φ12mm hole is drilled using a digitally controlled CNC milling machine and then reamed to φ12H8.
(6) Positioning and Clamping 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, simplifying the tooling setup. The tooling utilizes a cylindrical pin and a flat pin as positioning elements. Since the part is a thin-walled component, it is susceptible to deformation. When clamping, the pressure plate should be applied to areas with good rigidity, and the clamping force should be evenly distributed to ensure secure and reliable clamping. Excessive force may lead to unacceptable deformation or misalignment of the workpiece. This clamping method aligns well with the capabilities of the machining center, allowing the cavity and all holes to be processed in a single setup.
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