The life of a mold can be cut short by poor maintenance practices. Taking the time to maintain tooling properly can save thousands of dollars in repairs and downtime. Below are some quick tips to promote tool life and avoid surprises.
Start With a Good Process
No two processing engineers are going to run the same process on a part. It’s seemingly possible to run a faster cycle on nearly any molded part. In some cases, it may be necessary to max out speeds on your equipment, but slamming molds open and closed (especially a mold with actions) is not good practice. Molding machines can detect overloads in the mold closing action, but that doesn’t mean they can stop fast enough not to do any damage.
If parts don’t eject off the mold 100% of the time, fix it. The bottom line is closing a part back into the mold, even if it does cause an overload, is never okay. If it doesn’t cause any short term damage, you likely just over-packed the other cavities and sent some potential failures down the line. The use of robotics can help with this as well. When using robotics, it’s important to have grip/vacuum detection set up to inhibit mold closing in the case of a missed part.
If your molding equipment can detect overloads for mold movement and ejection, make sure they are set correctly. Setting the overloads may pick up on the added resistance before total failure. I’ve personally seen molding machines alarm off before major failure to an ejection system. Unfortunately, I’ve also seen the other side where limits were not set, and the ejection system comes to a screeching halt (literally).
If the nozzle/sprue is drooling and leaving stringers, fix the problem. Continuously closing little strings of plastic in the mold will inevitably cause damage. Those strings of plastic may lay over parting lines and eventually cause flashing. If this is a real problem, try different nozzles (orifice size and material), lower nozzle temperatures, or use the sprue break option on the molding machine. Just don’t let it go.
Keeping mold surfaces, knockout holes, and venting channels clean is critical. Some plastics tend to create more residue in venting systems (don’t forget every one of your knockouts is a vent). Allowing this to build up excessively is like sandpaper for the moving components. Clogged vents can also cause short shots and burning. Some molds may even need vents cleaned every day or every shift. For the most part, it’s a simple procedure that can save a lot of headaches.
Greasing all bearing surfaces is an absolute must. It’s best practice to clean off existing grease and to apply new. Do not just put new grease over the old. Over time debris can build up on grease and turn into what someone once referred to me as “hillbilly lapping compound.” Clean and re-grease as often as necessary. If you have ever started hearing a slight clunk as a mold opens, that is the sound of a tapered lock releasing. A little grease should instantly stop the noise.
Sensors / Switches
Installing switches on cam actions, hydraulics, and the ejection system is recommended. When building a new mold, this will usually not add much more cost but will lower or eliminate the risk of crashing components together. Most molding machines can accept basic interlock circuitry from the factory and do not require very much intervention. Most likely, it’s a simple jumper wire that needs to be removed and interrupted. This does require an extra step each time a mold it set into the press, but it’s worth it in the long run. If you’ve ever seen or heard a cam crash, you would agree.
Cam locks, especially when they are resisting gravity, should be replaced per the recommended cycle count. The cost of replacement is much less than replacing broken components from a crash or dealing with the downtime. Keep in mind though that if you installed those switches from above, a broken cam lock will stop your machine (safely that is).
Cleaning water lines
Molding facilities are running cooling water in a continuous loop. The water may pick up debris from piping, the air, other molds, and so on. More so, if the circulation water is not treated properly. At Basilius, we contract our water treatment out to a specialist that monitors it once a month. We also run a filter system on the main tank to help remove debris.
It’s important to blow out cooling lines after each run. Again, this is a simple practice but can avoid build-up of debris and rust in the cooling channels. Build up will not only reduce the cooling capacity of the cooling channel surface but will also slow the flow to other areas cause warms spots in the tooling. It’s also best practice to keep a flow/pressure valve around to put in line with a mold. Make a note of those settings when the mold is new and check it every so often.
If your building a new mold, it’s a good idea to get some spare components. It’s shocking to me to see injection molders who shut down production because of a $25 core pin. For components like knockouts and lifters, it worth the investment to keep some spares when practical. Some custom made components like inserts can be more expensive and may need to be taken on a case by case basis. It’s best to ask your tool builder what components would be good candidates for backups. It’s often much more cost-effective to make spare components along with the originals than to make them later.
A class 101 mold should be good for over a million cycles, but bad maintenance practices can make it come up short. Some basic preventative maintenance and possibly some small investments in advance can save thousands in downtime. We hope this guide keeps your molds running for millions of cycles.