Let me say first that stopping and pulling molds for scheduled PMs is a good maintenance practice … period … but unfortunately not always possible in every situation if you want to keep your customers happy and in parts. What? A mold maintenance evangelist saying that regularly scheduled PMs won’t make us more money by optimizing mold performance? How can this be?

Let me clarify.
Obviously, if a mold was pulled for a good cleaning every time its maximum cycle number lit up, the mold—and those responsible for mold maintenance would obviously be grateful.

With scheduled maintenance, it is much easier to more accurately gage the labor hours required to disassemble, clean and return it to production, knowing that the tooling has not been worn prematurely with gummed up close fits. No surprises in mold repair is always a good thing for schedulers, the tooling and labor budget; however, in the real world this seldom happens. Production rules.

Molders are customer-driven—as they need to be—when it comes down to running a mold to complete an order. If a couple of more hours, shifts, days and in extreme cases—weeks are required to get an order completed, the mold will run—or lock up trying.

So why bother setting max cycle counts if they are not adhered to? Although we may not always be able to clean every mold every time it needs it, it is critical with some molds simply because of the damage that can occur when max counts are ignored. When steel is gone—it’s gone.

So the challenge in the shop is to know max counts for molds along with a safe range where molds should be pulled if possible, but if in danger of missing production schedules, may be run longer without undue damage.

Molds that require short production runs also are in danger of premature tooling wear if the tool room doesn’t track total mold cycles for a series of short orders. It is easy, without a tracking system, to damage tooling simply because cycle counts get lost in the day-to-day affairs of pulling and setting lots of molds.

Overrun molds also create situations that require more abrasive cleaning methods, which in itself can be hard on tooling and drastically reduce usable life, as noted in the following case.
An Expensive Lesson

One particular 16-cavity medical mold had a sleeve/core setup with a typical radial vent ring groove (.060 wide x .001 deep) at the bottom of the part around the core that fed in to 3 flats (.250 x .060 deep) that ran down the core lengthwise into a radial vent dump that was .125 deep x .125. wide. The part vented fine up to about 150,000 cycles, (or 20 days, or 480 hours), which historically, under normal processing parameters, was how long it took to fill up the vent dumps.

Once the vent dumps are full, and having nowhere to go now, the residue was forced past the flats, between the core and sleeve where the resulting sliding action of the core and sleeve during ejection turned the typical red powery residue in to a black gummy substance that quickly wore down the parting line of the softer, and expensive, core.

This resulted in flash on the bottom of the part. The mold builder would not let our tool room increase the size of the dump (his reasoning becomes clear) maintaining it would compromise the ability of the sleeve/core alignment during part fill and ejection.
Run It Anyway

Our particularly aggressive production manager made the controversial decision to run the mold an extra week (50,400 more cycles) to get additional uptime. When finally pulled, nine of the 16 cavities had flash over or close to spec (.003 max) requiring us to send the cores back to the builder (surprise!) to be reworked (welded, ground and plated). The sleeves were so gummy that the ejector plate could not be moved by hand (prybar) and required considerable force (e.g., a large mallet) to remove the cores from the sleeves.

Through ongoing diligent inspections during repairs, we found that even a few hours over the maximum cycle count caused excess and measurable wear, and from that point on this mold had a mandatory max count of 150,000 cycles, no exceptions.

We also found that if the mold ran over its cycle limit, the cores required scotchbriting to remove the excess ground in residue. If this was performed incorrectly—a repair tech could easily round-over the sharp, leading edge of the sealing diameter of the parting line, which in turn would cause flash, setting up yet another toolroom versus process debate over the actual root cause of the flash. But cleaned during the safe range of cycle counts, the residue was quickly and easily removed via ultrasonics, creating no additional wear whatsoever.

A hard lesson indeed, but a common problem that portrays the importance of setting accurate numbers for maximum cycle counts on molds that from time to time—get overrun.