Creating a Mold-Repair Plan-Part III: The Repair Sheet Is Critical

In the first two parts of this series, we discussed how to collect accurate mold performance data at the press through use of an injection mold layout (IML) sheet and then how to prepare a Last Shot Inspection Report to expose part-quality defects (see Learn More). The final step in creating our mold-repair plan is to correlate the mold performance data gathered during the production run with the last-shot inspection results. This will give us the all-important Repair Sheet--a list of product defects targeted for corrective action in the tool room. These are listed separately by cavity I.D. number, under "Defects" on the bottom left of the sample repair sheet shown here. 

The repair sheet shows how different aspects of maintenance information are separated for a clearer picture of not only what defects need repair, but also what other work needs to be done to the mold, as seen in "Maintenance Instructions" at top center of the repair sheet. 

QUICK REFERENCE 

Critical to the success of any repair plan are the worksheets used by the technicians during repairs. Repair technicians must be able to quickly reference past defects and corrective actions. They seldom have the time or the patience to sift through scribbled journal entries or coded work requests to decipher past maintenance tasks. If the repair 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, the documentation method will not be accepted by repair personnel, which will defeat all efforts to systematize mold maintenance. 

On the repair sheet, all run-time information is displayed on the left side. The color-coded mold map on the right side prominently displays the location and type of the observed product defects and includes a legend for visual confirmation. Color-coding of defect locations is a great way to highlight patterns and trends in multicavity molds. Accompanying IML data (see Part I of this series) completes the picture. 

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 note specific areas of a mold where defects don't occur. 



For example, we had a 32-cavity mold running silicone rubber that suffered from sporadic parting-line flash on random cavities. Dimensionally, everything was to print. Nothing we tried fixed the problem. Desperation caused us to install new tooling and swap cavity blocks around. 

Then, while troubleshooting this problem, I color-coded this defect green in our database. This allowed me to rapidly click back and forth through 25 past repairs, concentrating on the changing positions of the green defects. 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 from the normal things you would look for--problems with the individual cavity-block parting lines, preload, cooling, gate sizes, etc.--to ask why these specific positions never flashed. 

We soon discovered that the cavity positions that didn't flash were located closer to the internal support pillars than those that did flash. We added a few pillars, increased the diameter of a couple more, and the flashing completely disappeared. This also eliminated the sensitive processing parameters required by the mold. 

BEYOND FIXING DEFECTS 

Correcting product defects is only part of a comprehensive repair plan. Other objectives include continually improving mold performance and reliability by monitoring mold frame and 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 build-up. Tooling vent paths and dumps should be checked routinely for hobbing and for correct depth. Hydraulic cylinders should have internal seals replaced before they begin leak. 

Obviously, production requirements will not allow all these objectives to be addressed at every preventive-maintenance (PM) occasion or whenever a mold is pulled. To take full advantage of allotted downtime, you must be acutely aware of mold condition and problems so that you can systematically repair all you can, when you can. 

WATCH CYCLES OR HOURS 

Levels of disassembly and inspection should be based on cycles or time run and must be defined for each tool so that molds are not over-maintained. Complete disassembly of all plates and tooling every time a mold comes into the shop is an enormous waste of time and risks damage to expensive tooling. But some mold components must be specified for removal and cleaning to ensure that they will not be overlooked during PM. 

The level of disassembly appropriate for PM of a particular mold depends on its internal contamination, tooling wear, and grease level after a specific number of cycles or hours are run. There are three levels of disassembly for most molds: wipe-down, general, and major. Hot-runner molds sometimes require a fourth level, because manifolds and components don't normally require complete disassembly as often as the mold base and tooling. 

Which tooling and plates require disassembly for cleaning is specific to each mold. See sidebar for an example. 

Levels of Disassembly 

EXAMPLE: 2004 QUARTER CAP MOLD 

1. Wipe-down disassembly is performed when the mold runs less than 10,000 cycles. 

A. Wipe down faces of stripper plate and H.H. cavity plate, leader pins, bushings, interlocks and C.H. cores only and regrease. 

B. Do not disassemble C.H., H.H. or gear rack system at this time. 

2. General PM is performed when the mold has accumulated more than 10,000 cycles since the last general PM. This includes any cleaning designated in a wipe-down. 

A. 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. Do not use Scotchbrite on bushings. 

B. Remove rear clamp plate and install new quad rings on the cores. 

C. Remove H.H. cavity plate and wipe down. Do not remove H.H. cavity blocks for cleaning at this time. 

D. Remove all H.H. cavity insert buttons. 

E. Do not disassemble gear rack or cores at this time. Regrease only. 

F. Use mold saver on rear clamp plate and H.H. cavity retaining plate before assembly. 

3. Major PM is performed when the mold has accumulated more than 750,000 cycles since the last major PM. This includes cleaning designated in wipe-down and general PM's 

A. Disassemble all plates in both halves and completely clean all cores, cavity tooling, and gear and rack system. Document excess wear. Replace all internal o-rings and seals. 

B. Measure and document H.H. cavity-block vents for correct depth. Should be 0.0005 to 0.0007 in. 

C. Clean all plates and tooling in sonic tank. 

D. Clean bubbler plate in sonic tank for 1 hr. Do not remove bubblers. 

E. Use mold saver on C.H. bubbler plate and H.H. cavity-retaining plate before assembly.