Injection Molding: Focus on these Seven Areas to Set a Preventive Maintenance Schedule

It is impossible to mold parts without a working injection machine. This is something that molders can state with absolute clarity. Yet, there are still many companies that follow a “run-parts-until-the-machine-breaks-down” approach. The question we must ask ourselves is why?

Unplanned maintenance is costly. In these instances, the discussion and development of repair plans occurs with the press sitting idle. Replacement parts need to be located, assuming they are in-house at all. If no replacement parts are available, searching for and ordering components from part vendors becomes necessary. Then, if production demands it, delivery of those parts may need to be expedited, at a hefty cost.

Looming in the distance is the potential that your interruption could cause a shutdown at the customer. Will we have to perform an unscheduled mold change if we have another press available? Doing so could be incredibly costly in terms of time and money.

Preventive maintenance schedules do not have to be cumbersome. The maintenance department is certainly busy, but there are some fundamental steps of inspection. Once implemented, preventive inspections reduce downtime and the costs associated with unplanned events. This article will outline five key systems that require regular review for wear and disrepair.
 

1. Hydraulic Oil

Hydraulic-oil levels and oil integrity are key to proper machine function. Low oil can lead to poor machine performance and pump breakdowns. Oil levels should be checked weekly to ensure oil level is correct and consistent. Beyond that, send oil samples to the lab every four months to verify oil cleanliness and performance.

The screw should be pulled once a year to inspect the shank, flights and barrel I.D. against the screw manufacturer’s recommended dimensional requirements.

2. Screw & Barrel

Screw and barrel performance is critical to standardized processes. Verify that fill time, cushion, screw recovery and peak pressures remain consistent. Fluctuations in key process-control variables can be a sign of a wearing barrel, screw or check ring. The screw should be pulled once a year to inspect the shank, flights and barrel inner diameter against the screw manufacturer’s recommended dimensional requirements.

3. Heater Bands

Heater-band performance is crucial to press operation and a repeatable process. Remove the guard to inspect heater performance using a meter with a steel temperature probe. Monitor temperature fluctuations and average steel temperature across all bands. Measuring continuity of a band does not always reveal a poorly performing band. Also look for wires that can get “dipped” during purge events to prevent unneeded band changes.

4. Heat Exchanger

The heat exchanger controls oil temperature. It’s imperative that it be kept in good working condition to avoid oil overheating, which can lead to o-ring and seal failures. It is good practice to descale the heat exchanger annually with a mild acid wash to prevent scale buildup. Do a bench inspection of the coils to assure they are not wearing out. Coil failures can lead to water being mixed in the oil.

5. Electrical Cabinet

Poor cabinet conditions can lead to electrical failures or fires. Keep the cabinet free of debris and oil. Clean and inspect fan assemblies to keep the cabinet cool. Wipe down circuit boards with a dry cloth. Check the tightness of terminals, while inspecting for signs of burning or arcing.

6. Hydraulic Assemblies

Hydraulic pumps, valves and hoses are key components of press function, and should be inspected frequently for signs of leaks. Keep hydraulic assemblies and areas clean and free of leaking oil and debris to help pinpoint valves showing signs of worn o-rings. Inspect hoses for signs of wear and weeping. Inspect hose couplings for signs of damage, leaking and tightness. Take time to listen to the pumps as they run. Any strange sounds may need to be noted and investigated further.

Applying these benchmarks can reduce the frequency of unplanned downtime, increase the productivity of your operation and raise your profit margins.

7. Platen Components

Platen condition and functionality are paramount to setup and processing requirements. Platen holes should be routinely inspected for damage. Holes should be re-tapped to recondition the threads. Stripped platen holes should be clearly marked with a paint marker to be added to planned maintenance. Stone the platens between mold changes to keep them free of burrs.

Regularly inspect bushings, tiebars and linkages for proper behavior and operation. Any signs that the lubrication system is not operating properly should be addressed quickly to prevent components from wearing or breaking prematurely.

Preventive-maintenance inspections do not have to be complex to provide beneficial effects to your overall maintenance approach. Applying the benchmarks noted above can not only reduce the frequency of unplanned downtime. It can increase the productivity of your operation and raise your profit margins.

ABOUT THE AUTHOR: Garrett MacKenzie is the owner/editor of plastic411.com, as well as a consultant/trainer in plastic injection
molding. He has provided process-engineering expertise to many top companies, including Glock, Honda, Johnson Controls and Rubbermaid.
Garrett also owns Plastic411 Services, which provides maintenance & training support to Yanfeng Automotive Interior Systems, IAC, Flex-N-Gate and other top automotive suppliers. Contact:
garrett@plastic411.com.