What is the maximum deformation of the head of the extended screw cold heading p

Release time：2020-01-16 18:44 Browse：

Maximum Deformation of Cold Heading for Extra-Long Screws (Head-to-Shank Ratio)

In cold heading processes for extra-long screws, the maximum deformation of the head relative to the shank (also called the upset ratio) is determined by material properties, die design, and process parameters. The key factor is the upset ratio (Lo/do), where:

• Lo = Original length of the upset section

• do = Original diameter of the upset section

1. Deformation Limits in Cold Heading

Based on empirical data in cold heading:

• Single-Stage Heading:
  Maximum upset ratio Lo/do ≤ 2.3 (beyond this, buckling or folding may occur).

• Two-Stage Heading:
  Upset ratio Lo/do ≤ 4.5 (suitable for longer blanks).

• Three-Stage Heading:
  Upset ratio Lo/do ≤ 8 (used for extra-long screws).

2. Special Considerations for Extra-Long Screws

Extra-long screws (high length-to-diameter ratio) are prone to:

• Buckling: Excessive Lo/do can cause instability, leading to head eccentricity or folding.

• Uneven Material Flow: Cutting angle deviation (1°–5°) affects force distribution, requiring trimming.

• Multi-Stage Heading: High upset ratios require progressive forming (e.g., pre-upsetting to a taper before final heading).

3. Material Influence

• Low-Carbon Steel (e.g., ML08, 10B21): High ductility, supports larger deformation (Lo/do ≤ 8).

• Medium/High-Carbon or Alloy Steel: Lower formability—requires reduced upset ratios or warm heading.

4. Conclusion

The maximum head deformation in cold heading is governed by the upset ratio (Lo/do):

• Single-stage: ≤ 2.3

• Two-stage: ≤ 4.5

• Three-stage: ≤ 8

If limits are exceeded, optimize the process (e.g., increase heading stages, adjust die angles, or use pre-forming).