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Core Logic of CNC Machining Processes: Centered on the principles of “reference positioning—separation of roughing and finishing—parameter optimization—path planning,” and taking into account the characteristics of the machined material, this approach establishes practical machining solutions. The key technical points and parameters are as follows; all parameters have been verified through practical application and can be directly applied.
1. Core Steps of Process Analysis (Including Technical Specifications)
Part Drawing Interpretation: Focus on verifying dimensional tolerances (IT5–IT7 precision parts), geometric tolerances (parallelism ≤ 0.01 mm/m, perpendicularity ≤ 0.015 mm/m), and surface roughness (Ra ≤ 0.8 μm as the finishing standard). Confirm the machinability of the material (45# steel, 6061 aluminum alloy, TC4 titanium alloy).
Reference Positioning: Use single-face, two-pin positioning (locating pins Φ8H7, tolerance +0.010 to +0.002 mm). Ensure the reference surface flatness is ≤0.008 mm to prevent dimensional deviations caused by reference offset. For thin-walled parts (thickness ≤2 mm), use elastic fixtures to reduce clamping stress.
Process Division (Precise segmentation to prevent cumulative errors):
Rough Machining: Remove most of the stock (2–3 mm). Use deep cuts (1–2 mm), medium feed rates (0.2–0.3 mm/r), and medium spindle speeds (800–1500 rpm). Select carbide roughing end mills (YT15 grade) to prioritize efficiency.
Semi-finishing: Remove residual stock from rough machining (0.3–0.5 mm). Use a spindle speed of 1500–3000 rpm and a feed rate of 0.15–0.2 mm/r to correct geometric and positional errors.
Finishing: With a remaining stock of 0.1–0.2 mm, a spindle speed of 3000–6000 rpm (high-speed machining can reach over 10,000 rpm), and a feed rate of 0.05–0.1 mm/rev, this ensures dimensional accuracy and surface quality.
2. Tool Selection and Parameters (Specific Models + Recommended Applications)
Tool Material Selection (Based on Workpiece Material):
Machining 45# steel: Carbide tools (YT15, YW2) with a TiN coating (hardness HV 1800–2000), resulting in a 30% increase in tool life.
Machining of 6061 Aluminum Alloy: Diamond-coated tools (PCD), spindle speed 5000–8000 rpm, to prevent built-up edge, with surface roughness as low as Ra 0.4 μm.
TC4 titanium alloy machining: Cubic boron nitride (CBN) tools, cutting speed 30–50 m/min, feed rate 0.05–0.1 mm/r, using low-temperature cooling (–50°C) to reduce tool wear.
Tool models and geometric parameters:
End mill: Φ16 mm (YT15), main rake angle 45°, front angle 15°, back angle 8°, cutting edge radius 0.2 mm, suitable for face milling.
Ball-nose cutter: Φ10 mm (PCD material), cutting length 20 mm, suitable for surface finishing, feed rate 0.1–0.2 mm (adjusted according to surface curvature).
Drill bit: Φ8mm (HSS-Co), point angle 118°, feed rate 0.1mm/r, spindle speed 1200rpm, suitable for drilling 45# steel; ensure the drill bit remains straight to prevent drilling deviation.
3. Optimization of Cutting Parameters (Practical-level parameters that can be adjusted directly)
| Processing stage | Materials to be processed | Cutting speed (m/min) | Feed rate（mm/r） | Cutting depth（mm） | Cooling method |
|---|---|---|---|---|---|
| Rough machining | 45#Steel | 80-120 | 0.2-0.3 | 1-2 | Emulsion cooling |
| Rough machining | 45#Steel | 150-200 | 0.05-0.1 | 0.1-0.2 | Emulsion cooling |
| Rough machining | aluminum alloy6061 | 300-500 | 0.3-0.5 | 1.5-2.5 | Compressed air cooling |
| Rough machining | aluminum alloy6061 | 600-800 | 0.1-0.15 | 0.08-0.15 | Compressed air cooling |
| Rough machining | aluminum alloyTC4 | 30-50 | 0.05-0.1 | 0.5-1 | Low-temperature cooling |
| Rough machining | aluminum alloyTC4 | 60-80 | 0.03-0.08 | 0.05-0.1 | Low-temperature cooling |
4. Toolpath Planning (Including Collision Avoidance Techniques)
Flat Milling: Use up-milling (to avoid vibrations caused by down-milling). Employ a circular cutting method for the toolpath, with arc transitions (radius R2–R5 mm) for entry and exit to prevent tool marks. For large flat surfaces, use zone milling with 5–10 mm overlap between zones to avoid seam marks.
Curved Surface Machining: Use contouring (suitable for steep surfaces) or helical path planning (suitable for gentle surfaces). Adjust the step size based on the tool radius and surface finish requirements (step size = tool radius × 0.6–0.8) to prevent overcutting (verify the path using Vericut simulation).
Deep Hole Machining (Diameter ≤ 10 mm, Depth ≥ 50 mm): Use a tap-drilling cycle (G83 command) with a feed rate of 5–10 mm per pass and a 2–3 mm retraction for chip removal. Use high-pressure emulsion coolant (pressure 0.8–1.2 MPa) to prevent chip clogging.
Interference Avoidance: In 5-axis machining, simulate tool-to-workpiece and tool-to-fixture interference using CAM software (UG NX 2206), and adjust the swing angles (A-axis ±10°, C-axis ±180°) to ensure machining safety.
5. Practical Programming (Including Complete Program Examples)
Manual Programming Example (Machining a 45# Steel Stepped Shaft, CNC Lathe CK6140): O0001 (Program Number) G21 G99 G97 (Metric units, feed rate mm/r, constant speed) T0101 (No. 1 external turning tool, tool offset active) M03 S1200 (Spindle forward rotation, speed 1200 rpm) G00 X42 Z2 (Rapid positioning to starting position) G01 Z-50 F0.2 (Linear feed, turning the outer diameter to Z-50 mm, feed rate 0.2 mm/rev) X38 Z-30 F0.15 (Turning the shoulder, feed rate 0.15 mm/rev) G00 X100 Z100 (Rapid retraction to safe position) M05 (Spindle stop) M30 (End of program, reset)
Automatic Programming (UG NX 2206): Import the part’s 3D model (IGES/STEP format), enter the machining module, select “Cavity Milling” (roughing), set cutting parameters (refer to Table 2.3), generate toolpaths, then use post-processing (FANUC system compatible) to generate G-code. Export and import the G-code into the CNC machine, debug, and start machining.
