Cnc Programming

Finishing Operations

1. Surface Finish Strategies

   Strategy	Application	Surface Finish
   Parallel	Flat surfaces	Ra 0.8-1.6 um
   Contour	Walls, profiles	Ra 0.8-1.6 um
   Scallop	3D surfaces	Ra 1.6-3.2 um
   Pencil	Corners, fillets	Clean-up

2. Step-Over for Finish

   Cusp height = r - sqrt(r^2 - (s/2)^2)
   
   For cusp height = 0.01 mm, r = 5 mm:
   Step-over s = 0.89 mm
   

Cutting Parameters

Speed and Feed Calculation

Cutting Speed (SFM): V = pi * D * N / 12 (imperial)
                     V = pi * D * N / 1000 (metric)

Feed Rate: F = f * z * N

Where:
V = cutting speed (SFM or m/min)
D = tool diameter
N = spindle speed (RPM)
f = feed per tooth
z = number of teeth
F = feed rate (IPM or mm/min)

Material-Specific Parameters

Tool Selection

End Mill Selection

Tool Life Management

Tool life tracking:
- Material removed (cm3)
- Cutting time (minutes)
- Parts produced

Replace at:
- Wear land > 0.3 mm
- Surface finish degradation
- Dimension out of tolerance

Work Holding

Fixture Considerations

1. Clamping Force

   • Calculate cutting forces
   • Apply safety factor (2-3x)
   • Distribute clamp forces
   • Avoid part distortion

2. Accessibility

   • Clear all tool paths
   • Consider tool length
   • Allow chip evacuation
   • Enable coolant flow

Program Verification

1. Simulation Checks

   • Tool collision detection
   • Fixture interference
   • Rapid traverse clearance
   • Stock remaining verification

2. First Article

   • Reduced feed rate (50%)
   • Single block mode
   • Verify dimensions
   • Adjust offsets as needed

Process Integration

• ME-018: CNC Programming and Verification

Input Schema

{
  "part_model": "CAD file reference",
  "material": {
    "name": "string",
    "hardness": "string (e.g., HRC 30)"
  },
  "machine": {
    "type": "3-axis|4-axis|5-axis|lathe",
    "controller": "Fanuc|Siemens|Haas|other",
    "spindle_max": "number (RPM)",
    "rapids": "number (mm/min)"
  },
  "tolerances": {
    "dimensional": "number (mm)",
    "surface_finish": "number (Ra um)"
  },
  "production_volume": "prototype|low|medium|high"
}

Output Schema

{
  "program_info": {
    "program_number": "string",
    "operations": "number",
    "total_tools": "number"
  },
  "cycle_time": {
    "machining": "number (min)",
    "non-cutting": "number (min)",
    "total": "number (min)"
  },
  "tool_list": [
    {
      "tool_number": "number",
      "description": "string",
      "diameter": "number (mm)",
      "length": "number (mm)"
    }
  ],
  "setup_sheet": {
    "work_offset": "string",
    "fixture": "string",
    "stock_size": "array [L, W, H]"
  },
  "nc_file": "file reference"
}

Best Practices

1. Verify model accuracy before programming
2. Use consistent tool numbering conventions
3. Include adequate clearance planes
4. Optimize tool paths for minimum air cutting
5. Simulate complete program before machining
6. Document setup requirements clearly

Integration Points

• Connects with CAD Modeling for geometry
• Feeds into Process Planning for operations
• Supports FAI Inspection for first article
• Integrates with DFM Review for manufacturability