DFM Review Skill

Purpose

The DFM Review skill provides capabilities for systematic design for manufacturing review and optimization, enabling cost-effective and producible mechanical designs.

Capabilities

• Manufacturability assessment
• Process selection guidance
• Tooling feasibility analysis
• Cost driver identification
• Design modification recommendations
• Tolerance and surface finish review
• Material availability assessment
• Supplier capability consideration

Usage Guidelines

DFM Principles

Core DFM Guidelines

1. Minimize part count
2. Use standard components
3. Design for ease of fabrication
4. Design for ease of assembly
5. Design for ease of service
6. Consider process capabilities
7. Minimize secondary operations

Process-Specific Guidelines

Process	Key DFM Considerations
Machining	Access, fixturing, tool reach
Casting	Draft, wall thickness, gates/risers
Injection molding	Draft, undercuts, sink marks
Sheet metal	Bend radius, hole-to-edge, grain
Welding	Access, joint design, distortion
Assembly	Part orientation, fastener access

Machining DFM

Feature Guidelines

Holes:
- Standard drill sizes preferred
- L/D ratio < 5 for drills
- Flat bottoms require end mill
- Provide drill point clearance

Pockets:
- Corner radius = tool radius
- Max depth < 4x tool diameter
- Provide tool access

Threads:
- Standard thread sizes
- Depth 1.5-2x diameter sufficient
- Provide thread relief

Wall thickness:
- Minimum 1-2 mm for steel
- Consider deflection during machining

Tolerance Capability

Dimension Type	Typical Capability
Linear (milling)	+/- 0.025 mm
Linear (turning)	+/- 0.013 mm
Hole diameter	+/- 0.013 mm
Surface finish	Ra 1.6-3.2 um
Flatness	0.025 mm/100 mm

Casting DFM

Design Guidelines

Draft angles:
- External: 1-3 degrees minimum
- Internal: 2-5 degrees
- Deep pockets: increase draft

Wall thickness:
- Minimum: 3-5 mm (sand casting)
- Minimum: 2-3 mm (die casting)
- Uniform thickness preferred
- Gradual transitions

Radii:
- Internal corners: R > 3 mm
- External corners: R > 1 mm
- Avoid sharp transitions

Shrinkage Allowance

Material	Shrinkage %
Aluminum	1.2-1.5
Steel	1.5-2.0
Cast iron	0.8-1.2
Bronze	1.0-1.5

Injection Molding DFM

Design Guidelines

Wall thickness:
- Uniform 1.5-4 mm
- Transitions < 25% thickness change
- Avoid thick sections (sink marks)

Draft:
- 0.5-1 degree per side minimum
- Textured surfaces: add 1 degree per 0.025 mm depth

Ribs:
- Thickness: 50-75% of wall
- Height: < 3x wall thickness
- Spacing: > 2x wall thickness

Bosses:
- Wall: 50-75% of base wall
- Height: < 2x diameter
- Add gussets for strength

Sheet Metal DFM

Bend Guidelines

Minimum bend radius:
- Soft materials: 0.5x thickness
- Hard materials: 1-2x thickness
- With grain: smaller radius OK
- Against grain: larger radius

Minimum flange:
- Flange > 4x thickness
- Flange > 3 mm practical minimum

Hole-to-bend:
- Distance > 2x thickness + bend radius
- Prevents hole distortion

Punching Guidelines

Minimum hole size:
- Round: 1x material thickness
- Square/rectangle: 0.8x thickness

Minimum edge distance:
- 2x material thickness minimum
- Prevents edge deformation

Minimum hole spacing:
- 2x material thickness minimum

Cost Drivers

Cost Analysis Framework

Manufacturing cost components:
1. Material cost
   - Raw material
   - Scrap/waste
   - Special materials

2. Labor cost
   - Setup time
   - Run time
   - Inspection time

3. Equipment cost
   - Machine time
   - Tooling amortization

4. Overhead
   - Facility
   - Support functions

Cost Reduction Opportunities

Area	Opportunity
Material	Standard grades, near-net-shape
Features	Eliminate unnecessary features
Tolerances	Relax to process capability
Finish	Specify only where needed
Operations	Combine or eliminate steps
Assembly	Reduce part count, use snap fits

Tolerance Review

Tolerance Stacking

Before specifying tight tolerances:
1. Verify functional requirement
2. Check assembly chain
3. Confirm process capability
4. Consider inspection cost
5. Evaluate statistical tolerance

Cost Impact

Tolerance Class	Relative Cost
Standard (+/- 0.5 mm)	1x
Precision (+/- 0.1 mm)	2-3x
Close (+/- 0.025 mm)	5-10x
Very close (+/- 0.01 mm)	10-20x

Process Integration

• ME-005: Design for Manufacturing (DFM) Review

Input Schema

{
  "design_data": {
    "cad_model": "file reference",
    "drawings": "array of references",
    "material": "string"
  },
  "manufacturing_context": {
    "target_process": "machining|casting|molding|sheet_metal|additive",
    "production_volume": "prototype|low|medium|high",
    "target_cost": "number (optional)"
  },
  "supplier_constraints": {
    "preferred_suppliers": "array",
    "equipment_limitations": "array"
  }
}

Output Schema

{
  "dfm_assessment": {
    "overall_rating": "good|acceptable|needs_improvement",
    "manufacturability_score": "number (1-10)"
  },
  "issues": [
    {
      "feature": "string",
      "issue": "string",
      "severity": "critical|major|minor",
      "recommendation": "string",
      "cost_impact": "string"
    }
  ],
  "cost_analysis": {
    "material_cost": "number",
    "labor_cost": "number",
    "tooling_cost": "number",
    "total_unit_cost": "number"
  },
  "improvement_opportunities": [
    {
      "change": "string",
      "cost_savings": "number or percentage",
      "effort": "low|medium|high"
    }
  ],
  "process_recommendation": {
    "primary_process": "string",
    "secondary_operations": "array",
    "special_requirements": "array"
  }
}

Best Practices

1. Involve manufacturing early in design
2. Understand process capabilities
3. Challenge tight tolerances
4. Consider total cost, not just piece cost
5. Design for the target volume
6. Document DFM decisions and rationale

Integration Points

• Connects with CAD Modeling for design review
• Feeds into Process Planning for manufacturing
• Supports Trade Study for process selection
• Integrates with Cost estimation