Calculation of Punch and Die Cutting Edge Dimensions

The dimensional accuracy of stamped parts is directly influenced by the cutting edge dimensions and tolerances of punches and dies. Proper clearance values are maintained through precise control of these dimensions and tolerances. Their determination requires consideration of multiple factors including shearing deformation characteristics, part precision requirements, tool wear patterns, and manufacturing constraints.

Fundamental Principles for Cutting Edge Dimension Calculation

Extensive practice demonstrates that:

Blanked part dimensions closely correspond to die edge dimensions
Punched hole dimensions align with punch edge dimensions
In measurement and application:
Blanked parts are referenced by their maximum material condition (larger end dimensions)
Punched holes are referenced by their minimum material condition (smaller end dimensions)
Both are based on the shear band dimensions.

Tool wear characteristics:

Punches gradually wear smaller during operation
Dies progressively wear larger

Based on these observations, the following design principles apply:

Reference Selection:
- For blanking: Part dimensions are die-dependent → Die serves as reference, clearance applied to punch
- For punching: Hole dimensions are punch-dependent → Punch serves as reference, clearance applied to die
  Note: As tool wear occurs during production, punch-die clearance increases. Therefore, designs should incorporate the minimum allowable clearance.
Wear Compensation:
- Blanking dies: Nominal die size should equal the lower limit of part tolerance
- Punching dies: Nominal punch size should equal the upper limit of hole tolerance
  This ensures continued production of in-spec parts throughout the tool’s service life.
Manufacturing Tolerances (δp for punch, δd for die):
- Typically 2-3 precision grades tighter than part requirements
- For non-toleranced parts:
  - Non-circular features: IT14 per GB/T “Non-Fit Dimensional Tolerances”
  - Circular features: IT10
Tolerance Notation Standards:
- Die edges: Positive deviation (+Δ)
- Punch edges: Negative deviation (-Δ)
- Center distances and non-wearing dimensions: Bilateral deviation (±Δ)
  (Refer to following Figure for tolerance zone relationships)

Calculation Methods for Cutting Edge Dimensions

Two distinct approaches exist based on manufacturing and measurement techniques:

1. Separate Punch and Die Machining

For simple geometries (round/square shapes)

Clearance control requirement:
|δp| + |δd| ≤ Zmax – Zmin

Tolerance determination options:
a) Standard values from Table 4-15
b) For regular shapes:

Punch: IT6 grade
Die: IT7 grade (per GB/T 1800.4-2009)
c) Calculated values:
δp = 0.4(Zmax – Zmin)
δd = 0.6(Zmax – Zmin)

2. Matched Tooling Approach

For complex geometries or thin materials

Methodology:

Designate one component (punch or die) as master
Machine counterpart to match with specified clearance
Only master component carries full dimensional tolerances
Matched component specifies nominal size + clearance

Advantages:

Eliminates tolerance stack-up constraints
Typical tolerance: δ = Δ/4 (Δ = part tolerance)
Reduces manufacturing complexity
Lowers production costs
Maintains tight clearance control

Implementation Guidelines:

Blanking Dies:

Master: Die
Matched: Punch
Drawing note: “Punch to match actual die dimensions with bilateral clearance Zmin”

Punching Dies:

Master: Punch
Matched: Die
Punch wear categories: Size may increase, decrease, or remain stable
Drawing note: “Die to match actual punch dimensions with bilateral clearance Zmin”

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For partnership opportunities or technical inquiries, please contact our engineering team.

Calculation of Punch and Die Cutting Edge Dimensions