Trimming in Press Working

Definition

Trimming is a secondary press working operation used to remove the excess or unwanted material from the edges of a formed part (such as a drawn cup or a shell). It is typically performed to achieve a finished, uniform edge and the desired final dimensions of the workpiece.

Main Content

1. Purpose of Trimming

• It removes the "flange" or irregular edges that result from deep drawing or other forming processes.
• It ensures that the final component meets the precise size requirements specified by the design.

2. Trimming Methods

• Straight-line Trimming: Used for simple rectangular or square parts where edges are cut along straight paths.
• Contour Trimming: Used for complex, non-linear shapes where the punch and die must follow the specific profile of the part.

3. Tooling Considerations

• Clearance: The gap between the punch and the die must be accurately calculated based on material thickness to ensure a clean shear.
• Stripper Plates: Essential to remove the trimmed scrap material from the punch and prevent it from interfering with the next cycle.

       Punch
      |     |
      v     v
    -----------
   |   (Part)  |  <-- Excess material removed here
    -----------
      |     |
    Die Block

Visual representation of the trimming operation showing the punch removing edge scrap.

Working / Process

1. Loading the Part

• The formed workpiece is placed into a locating nest or fixture on the die set to ensure exact alignment.
• Proper positioning is critical to maintain the tolerances of the finished part.

2. Cutting Action

• The press descends, and the hardened steel punch exerts pressure on the excess material.
• The material is sheared between the punch and the die edges, effectively cutting away the waste metal.

3. Scrap Removal

• The trimmed excess (scrap) falls through the die opening or is pushed aside by a scrap chopper.
• The finished part is ejected or manually removed, and the punch returns to the top position for the next cycle.

Advantages / Applications

• Precision: Achieves high dimensional accuracy that forming processes alone cannot provide.
• Surface Finish: Improves the edge quality by removing burrs or uneven edges caused by metal flow during the forming stage.
• Applications: Used extensively in the automotive industry for body panels, in the appliance industry for sink basins, and in the production of beverage cans.

Summary

Trimming is a vital secondary press operation that removes excess material from the edges of formed metal parts to achieve precise dimensions and a clean finish. It utilizes punch and die mechanisms to shear away unwanted scrap material, ensuring components meet industrial quality standards. Important terms to remember: Shearing, Clearance, Scrap, Die, and Tolerance.