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Article courtesy of ToolingDocs, LLC
Regardless of mold type, the goal of the maintenance shop is always the same: Get a mold production-ready after it has been removed from service. Given today’s lean manufacturing climate, the objective can no longer be only getting a mold ready. To stay competitive, mold maintenance needs to be more effective and performed faster while using less tooling and fewer man-hours. Accomplishing this is not magic and does not require expensive technology or complicated systems. Instead, it depends on improving communication between the molding floor and tooling repair, analyzing accurate historical data, acquiring sound workmanship habits, and continuous training.
Smart mold builders and designers alike keep one eye on maintenance issues that affect the productivity of their molds. Like any service provider, they want their molds to run reliably and efficiently with maintenance costs held to a minimum. This keeps customers coming back. If duplicate molds or components are to be built, accurate mold history will help designers and builders improve their designs and construction methods. Mold evolution should be based on performance evaluations and maintenance requirements as much as on new technological wizardry.
We will start with the example of a 16-cavity, hot-runner mold that has been set in the press and is waiting to be fired up. First, it’s prudent to have a setup checklist to ensure that all steps necessary to hang and water the mold are implemented correctly and consistently. While the mold is being heated and conditioned to operating temperature, the process technician runs through his setup sheet to verify that all mold parameters are set correctly. When they are sure that all is well, out comes the first shot and the molding process begins. After the process has stabilized, a shot or sample part is checked and again, if all is well, it is released by QA and the run/repair cycle is under way.
Now the process technician documents specific information on an injection mold layout (IML) sheet, such as press number, start date, start time, starting technician, and mold configuration. If the mold is hard to start or fill out, flashes easily, or suffers other issues, these observations are documented on the IML sheet for toolroom evaluations.
The IML sheet is a critical element of the information chain. In sequential order, it documents mold, part, and other performance issues that may arise during a typical production run. This is important. When it comes to troubleshooting problems, the sequence of events can be an important clue in diagnosing the root cause and corrective measures to take. Whenever part of the run/repair cycle is not documented accurately, valuable time gets wasted by doing things twice, or worse. Generalized statements like “It never did that before” or “It always does that” need to be quantified to ensure time isn’t wasted heading down the wrong path.
An IML sheet has all critical information for an effective repair has been documented. Defective cavities discovered by QA or processing personnel during the run have been blocked off or noted. All that remains is for the last shot to be visually inspected for flash and other abnormalities. If potential quality issues are found, they will be noted in the repair plan or “work order”. It is helpful to have a separate last-shot sheet for recording flash lengths that are close to being over spec and other visual observations. A mold map and sign-off area for technicians performing in-press servicing are included on the IML.
The frequency and depth of in-press cleaning depends on mold and process characteristics that determine residual contamination levels. It should be the goal of every shop to set standards for frequency of in-press and out-of-press cleaning, based on the amount of internal and external residue or contamination a mold exhibits after a certain number of cycles or hours run. This is the crux of preventative maintenance.
When the decision is made to pull the mold, a last shot of all remaining parts should be gathered for inspection, along with samples from any blocked-off cavities, and both should be forwarded to the toolroom supervisor. He will then decide whether to fix it now or wait until later and just monitor the mold during the next run. This is how technicians learn to better forecast tooling wear. Does it take another 10,000 cycles for the flash to grow over-spec, or does it happen after only 100 cycles? And if it grows over-spec quickly, is that because the process changed? Accurate forecasting of tooling wear requires consistency in repair and processing.
Some companies have the luxury of entering data through PCs located at each press, but the vast majority of companies only have a PC in the molding office or at a staging area on the molding floor. This means that when something happens during a run, the processing technician needs to walk some distance to enter critical data into the PC. This probably won’t happen, because the technician can be hit with a dozen other issues during the 50-foot walk to the PC, so it gets forgotten, and the information never reaches the toolroom. Collecting IML-type data manually through a sheet that hangs at the press is more convenient and readily accepted by most process and maintenance personnel.
If a plant’s typical production runs are short and there are no issues to worry about, this mold-run data still needs to be documented for historical purposes. Molds that are run, pulled, green-tagged (okay to run again), and racked without any data being collected leaves voids in the process history that complicates everything from troubleshooting defects to tracking which lots, resin batch or parts the mold ran during a given time frame.
Fortunately, there are only a few steps involved in starting a mold and collecting accurate, usable data needed for a repair plan. The most difficult part of collecting performance data at the press is acquiring the discipline to use and manage an IML sheet. The toolroom supervisor needs to work with the molding supervisor to systemize the approach and share the IML responsibility. Repair technicians must know how a mold performs before corrective actions and improvements can be implemented effectively.
In the next installment, we will discuss using the IML sheet to create an accurate, effective repair plan.