Back to blog

Trim Scrap Analysis

Introduction

Down the scrap chute it goes, exactly as planned.  But the skilled Tool and Die professional can learn many things if given the opportunity to view engineered scrap trimmed off a draw shell.  Die gauging, blank size, material flow are among the contributing variables this tool will lead you to address.  See below to read our description of this powerful tool.

Description

Trim Scrap Analysis is an analysis of the forming process variation associated with blank size, draw-in, and blank location. Using discarded material (trim scrap) enables the user to visibly identify measureable signals that help ascertain root cause. Trim Scrap Analysis is often used in conjunction with other analytical tools.

Background

A 1990 Taguchi Study conducted by Phoenix, along with a major stamping manufacturer, found three primary sources of variation within the stamping process. These sources were blank size/shape, blank location and lubrication. Observation suggests these findings to be relevant today.

Purpose

Trim Scrap Analysis may be used when stabilizing or optimizing a process. In all cases, trim scrap is used as an output measurement of multiple input variables including blank size/shape, sheet metal displacement (draw in) and blank location, among others.

  • Trim Scrap Variation associated with blank size variation is determined by comparing findings to Blank Analysis results. Both tools are used to completely understand the nature of the variation – driving observed variation back to the source.
  • Trim Scrap Variation associated with draw in variation is determined by comparing findings to Sheet Metal Displacement Analysis.
    • Press set up sources include shut height, cushion and press applied lube
    • Die set up sources include shims, bead condition, cushion types, surface roughness, slug marks, etc.
  • Trim Scrap Variation associated with Blank Location variation is determined by monitoring process control sources including gauges, automation cups, automation settings, automation lube, blank drape, prebend, and pallet location.

Steps for problem solving

1. Prep blanks

  • Mark blanks with paint stick for identification. Place an angled mark on blank edges, repeated enough to allow for scrap cutters, but only ½” long. This allows for reconstruction of run order sequence.

2. Collect scrap

  • Work with plant to determine a safe technique for collecting samples. Possibilities include covering scrap chutes or pulling scrap from conveyor system.
  • Identify sequence of individual specimen(s).
  • Collect a 5 piece sample from each lift of material. Select samples correlated to location and nature of forming failure.
  • Stack specimen in sequence and photograph to highlight variation.
  • Measure variation to reference template (photo). Mark measure location on reference template with a tick mark for visual tracking.
  • Record measurement on standard worksheet.
    • (+) specimen is longer than reference
    • (-) specimen is shorter than reference
    • Measure to 1/2mm accuracy.

3. Compare with other analytical findings and chase root cause.

Additional methods for process control

1. Collect set up inputs that created reference template.

  • Shut height, Press speed, Press load tonnage, Cuhion, Incoming lube, Wash & Reapply, Bolster ID, etc.

2. Collect specimen after die set.

3. Compare specimen to reference template. If different, investigate set up inputs to identify source of variation.

Examples from the field

1. A tier one automotive supplier forming Body Side Outers thought they had a problem with the coating on their steel. We found excessive cutout location variation that changed strain state at critical spots near header and B pillar.

2. An American Automotive OEM making an A pillar, suffered from a tremendous scrap rate. Management approved a blank size increase to resolve the problem. It didn’t’ work and now they were paying extra for every blank. Bouncing from split to wrinkle and back, technicians were unable to determine the combination of variables driving results. Through trim scrap analysis, blank location was identified as a key input to be controlled. 

3. An American Tier one automotive supplier making Body Side Outer panels for a German OEM was experiencing high rework costs associated with buckles and scrap rate associated with splits. Convinced that technicians were not changing process set up and with no process control historical information to study, they were convinced the problem should be attributed to their steel supplier. Trim scrap analysis quickly indicated the amount of process tampering that actually occurred. Subsequent trim scrap analysis during designed experiment also exposed technicians to the impact specific process tampering actually had on the formed panel.

 

 

Contributing authors George Coates, Wil Fras, Bill Shinskey, Timothy Smith, and Kirk Wiley