Across the Bench - The Plan Comes Together

The repair sheet is critical to the success of any mold repair plan.

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The final step in creating our mold repair plan is to correlate the mold performance data gathered during the production run (injection mold layout sheet) and last shot inspection results that we discussed in last month's article. This will give us a list of targeted product defects that will require corrective action. These are listed separately, under Defects, by cavity I.D. number onto the bottom left of the repair sheet (Figure 1). The repair sheet shows how different aspects of maintenance information are separated for a clearer picture of not only what defects need repairing, but also what other work needs to be done to the mold as seen in Maintenance Instructions (top center).

 

Quick Reference

It is important that the repair plan worksheet is formatted so that it is simple and easy to understand. Repair technicians must be able to quickly reference past defects and corrective actions; they seldom have the time or patience to sift through scribbled journal entries or coded work requests to decipher past maintenance tasks. Therefore, critical to the success of any repair plan are the worksheets used by the technicians during repairs. If these worksheets lack definition, critical information does not get documented. If they are complex or confusing and do not follow the logical flow of the job, information will be inaccurate or missing, thus the documentation method will not be accepted by repair personnel, which in turn will defeat all efforts to systemize mold maintenance.

On the repair sheet, all run time information is displayed on the left side of the sheet. The color-coded mold map on the right side prominently displays the location and type of the noted product defects and includes a legend for visual conformation. Color coding defect locations is a great way to highlight patterns and trends in muticavity molds. Researching past defects and positions is quickly accomplished by comparing past mold maps. Going a step further and entering these maps into a database allows you to flip back through the maps very quickly, scanning for repeating defects or locations. Here's a tip: during the troubleshooting stage of mold or product defects, it is sometimes just as important to see quadrants or specific areas of a mold where defects don't occur (see Troubleshooting table at end of article).

 

More Than Targeting Defects

Correcting product defects is only part of a comprehensive repair plan. Other repair objectives include continually improving mold performance and reliability by monitoring the mold frame/base condition during repairs. Leader pins, bushings, interlocks and early return mechanisms should be checked for excess wear and galling. Mold plates should be checked for straightness, hobbing, corrosion and water line buildup. Tooling vent paths and dumps should be periodically checked for hobbing and correct depth. Hydraulic cylinders should have internal seals replaced before they leak. Keeping mold tooling clean and aligned will also maximize tooling life, simplifying, troubleshooting and routing repairs allowing you to better schedule repair time for known mold frame or tooling issues. Obviously, production requirements will not allow all these objectives to be addressed at every C/R (Clean and Repair) or whenever a mold is pulled. To take full advantage of allotted downtime, you must be acutely aware of mold condition, problems and characteristics so that you may systematically begin to establish total mold control, by repairing all you can.

Levels of disassembly are based on cycles or run time and must be defined for every repair so that molds are not overmaintained. Complete disassembly of all plates and tooling every time a mold comes into the shop is an enormous waste of time and subjects expensive tooling to damage during handling and cleaning operations. Conversely, some mold components need to be specified for removal and cleaning to ensure that they will not be overlooked during a C/R. Each mold's C/R level of disassembly is dependent upon observed internal residual contamination, tooling wear and grease condition after a specific number of cycles or hours are run. There are three levels of disassembly for most molds: wipedown, general and major. The tooling and plates requiring disassembly for cleaning during these three levels is always mold specific, for example:

1. A wipedown level of disassembly is performed when the mold runs less than 10,000 cycles

  • Only wipe down faces of stripper plate and H.H. cavity plate, leader pins, bushings, interlocks and C.H. cores.
  • Do not disassemble C.H., H.H. or gear rack system at this time.
2. A general C/R is performed when the mold has accumulated more than 10,000 cycles since the last general C/R
  • Includes any cleaning designated in a wipedown C/R.
  • Remove the stripper plate. Wipe down all cores and stripper bushings. Do not remove stripper bushings from the plate. Clean as a unit in the sonic tank.
  • Remove rear clamp plate and install new quad rings on the cores.
  • Remove H.H. cavity plate and wipe down. Do not remove H.H. Cavity blocks for cleaning at this time.
  • Remove all H.H. cavity insert buttons.
  • Do not disassemble gear rack or cores at this time. Regrease only.
  • Use mold saver on rear clamp plate and H.H. cavity retaining plate before assembly.
3. A major C/R is performed when the mold has accumulated more than 750,000 cycles since the last major C/R
  • Includes cleaning designated areas in wipedown and general C/Rs.
  • Disassemble all plates in both halves and a completely clean all cores, cavity tooling and the gear and rack system. Document excess wear conditions. Replace all internal o-rings.
  • Check all vents for hobbing/wear.
  • Clean all plates and tooling in sonic tank.
  • Clean bubbler plate in sonic tank for thirty minutes.
  • Use mold saver on C.H. bubbler plate and H.H. cavity retaining plate before assembly.
Disassembly instructions for these three levels will vary with different types of mold bases. Next month, we get to work.

 

Trouble-shooting
While checking the defect history of a thirty-two-cavity mold that suffered from sporadic parting line flash on random cavities, I was able to rapidly flip back and forth through twenty-five past repair sheets, concentrating on the changing positions of the green (color-coded) defect. After a few quick shuffles, it became apparent that there were several cavity positions that had never suffered this specific defect. This shifted my focus off the normal things one would look for such as problems with the individual cavity blocks, pocket depths, cooling and gate sizes to the internal support pillars. It was soon discovered that the cavity positions that didn't flash were located closer to the pillars than those that did. A few pillars were added, the diameter was increased and the defect completely disappeared. This also eliminated the sensitive processing parameters required by the mold, and caused a processor to smile.

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