11. Mold Metal Adjustments - Centering Process - Validation procedure for injection molds

>> Sunday, 8 February 2015

The eleventh step in validating a injection mold with the overall process shown in injection mold validation flow chart is Mold Metal Adjustments - Centering Process. The steps before:

1. Mold certification 
2. Dry cycle mold
3. Process stability test
4. Gage repeatability & reproducibility (R&R) test 
5. Mold viscosity test 6. Balance of fill analysis
7. Gate Freeze Test
8. Commissioning (multi-cavity analysis)
9. Design of Experiments (DOE or DOX)
10. Qualification (Process Capability Study) 

Purpose: After achieving a capability ratio (Cr) of < 0.75 for key part dimensions, the mold metal is re-cut to center the average to match target. Changing the metal in the mold based on the optimal process, even if it means remaking mold components due to non-metal safe conditions, is preferred vs. changing the process to get the dimensional variation centered. Otherwise the process may not be capable of achieving part specified tolerances. The centering process should be done for all unit tools. Each subsequent production mold can then be cut according to the centered unit tool specifications. 

Procedure:
1. Identify key dimensions that need adjusting in the steel, i.e., need centering.
2. Calculate the delta difference between the observed process mean dimension and the part tolerance mean dimension for each key dimension.
3. Either re-cut or remake mold components by the delta difference.
4. After the mold is re-cut the mold should undergo an abbreviated version of the qualification process to ensure all the components were machined properly to deliver the part dimensions on target.

The further steps are required in validating a injection mold according to injection mold validation flow chart is dry cycle mold:

12. Verification (30-day run)


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