Mold maintenance is the easiest job to postpone in the production plan. If the machine is running and parts are coming out, maintenance is left for "later". But mold failures rarely arrive slowly: they usually appear in the middle of a shift, just when there is delivery pressure.
The cost of unplanned mold downtime is not only the repair bill — the stopped machine, the delayed order and the secondary damage caused by a rushed repair must also be taken into account. Planned maintenance turns all of this cost into a much smaller and predictable item.
What happens when maintenance is postponed?
| Symptom | Root cause | Consequence |
|---|---|---|
| Increasing flash | Dents or deposits on the parting surface | Scrap, labor for manual deflashing |
| Ejector marks and strain | Unlubricated or worn ejector system | Part deformation, broken ejectors |
| Lengthening cycle | Scaled-up cooling channels | Loss of capacity, unbalanced cooling |
| Dimensional drift | Wear on slides and cores | Out-of-tolerance parts |
| Local burn marks | Blocked vents | Scrap, permanent damage to the mold surface |
| Leaks | Aged seals and fittings | Water leakage, corrosion, electrical risk |
When most of the defects in this table appear, the first attempt is to solve them with process settings. Yet if the source is in the mold, changing parameters hides the problem and lets it progress. To tell which defect comes from which root: Defect troubleshooting guide
A maintenance plan based on shot count
The maintenance schedule should be set up by shot count, not by days. A mold making 200 thousand shots a month cannot be tied to the same schedule as one making 20 thousand.
| Period | Tasks |
|---|---|
| Every shift | Visual check: leaks, unusual noise, deposits on the parting surface, new marks on the part |
| At every mold removal | Cleaning the parting surface, protective oil, checking fasteners |
| ~10,000 shots | Lubricating the ejector system and slides, checking the vents |
| ~50,000 shots | Checking seals and fittings, measuring cooling circuit flow, checking hot runner thermocouples |
| ~100,000 shots | Detailed inspection with the mold opened: wear on cores, cavities and guide pins; cleaning the cooling channels |
| ~500,000 shots | Planned replacement of worn elements, surface measurement, overhaul if necessary |
The figures are starting values. If abrasive raw material (glass-fiber, mineral-filled) is used, the periods must be shortened; with corrosive materials such as PVC, cleaning and protection frequency increases.
Inspection items
Cooling channels — the most neglected
Because cooling channels are enclosed they cannot be seen, and so they are forgotten. Over the years scale and corrosion narrow the cross-section; the water flow falls, the mold cannot be held at the target temperature and the cycle time quietly lengthens.
The symptom is usually this: the same mold, with the same settings, is running slower than before. The check method is flow measurement — looking at the difference between inlet and outlet temperatures also gives an idea.
Equipment that keeps the mold temperature stable: mold temperature control units · More on the subject: How to shorten cycle time
Ejector system
When ejector pins run without lubrication they both strain and leave marks on the part. A broken ejector damages the opposite surface as the mold closes — skipping a small piece of maintenance turns into a major repair.
Vents
The air in the mold must be expelled as the melt fills it. Over time vents become blocked with material residue and plate-out. The trapped air heats up under pressure and creates a local burn mark at the end of filling.
Hot runner
Heater and thermocouple failures usually come gradually: first a zone reaches its target late, then it cannot reach it at all. The zone-based alarm records in the control unit should be reviewed regularly. The connection cables should also be checked; a cable that moves constantly can break internally.
For these, see the Hot Runner Control Systems and Mold Connection Cables pages.
Parting surface
The smallest dent or deposit on the parting surface produces flash. When flash appears, the first reaction is to increase the clamping force — which damages the dented surface further. The right approach is to check and clean the surface.
Opening and tilting the mold safely
On the shop floor this operation goes by the names mold turning, mold tilting and mold rotating; what is meant is the same thing — laying the mold over by 90° in a controlled way. It is also the riskiest part of maintenance. The common method — lifting with a crane and working on wooden blocks — is both unsafe and a waste of time:
- The mold swings while suspended and moves in an uncontrolled way
- The operator has to work between the mold halves: risk of crushing
- Because the crane is busy, maintenance work becomes dependent on crane traffic
Equipment designed for this job removes the risk:
- Mold inspection table — the mold is held fixed at a suitable height, and maintenance is done standing and in comfort
- Mold inspection unit — hydraulic opening and tilting; a light curtain stops the movement when the operator enters the danger zone
- Electric mold tilting unit — needs no hydraulic power unit, no risk of oil leaks
- Die splitter — separates the mold halves in a controlled way
Products: Mold tilting, turning and maintenance equipment
Storage and corrosion
A mold spends most of the time it is not in production in the store. Three things are decisive in storage:
1. Protective oil — corrosion starts quickly, especially on surfaces taking moisture from the water circuits 2. A dry environment — a mold standing on the floor or against a damp wall rusts 3. Accessibility — finding and removing the mold that is wanted should be easy
Stacking molds on top of each other or crammed together means that others have to be moved to get out the mold that is needed — both a loss of time and a risk of damage. Drawer-type storage racks allow the mold to be taken by sliding it out instead of pulling it off the rack with a crane.
A frequently overlooked safety detail is this: a mold that was earthed while connected to the machine loses this connection when it is taken to the store or repair area. With a mold standing on a wooden base with its heaters still fitted, this creates a hazard; a separate earthing connection must be made.
Products: Mold transport and storage solutions
No maintenance without records
If the question "When was this mold last maintained?" cannot be answered clearly, there is no maintenance plan. What should be kept for each mold:
- The total shot count and the shots made since the last maintenance
- The maintenance operations carried out and their dates
- The parts replaced
- The failures experienced and their causes
- Operating parameters: zone temperatures, mold temperature, cycle time
These records can be kept by hand, but when kept digitally they also help at mold changes: if a mold's parameter set has been saved, trial and error disappears at the next setup.
There are two practical solutions for this:
- RFID mold reader — the reader is held against the mold and that mold's data set is loaded automatically into the control unit; one label per mold is enough
- Mold documentation software — gathers mold data, diagnostic records and temperature curves from all control units on the company network in one central place
Products: Hot runner accessories
A factor that makes maintenance easier: quick clamping
If removing a mold is hard, maintenance is postponed. With bolted clamping, taking a mold down, maintaining it and putting it back can take half a shift; in that case the decision "let it hold out a bit longer" is made.
When removal and refitting come down to minutes with quick mold clamping systems, planned maintenance becomes genuinely practicable. Details: Mold change time — magnetic platens and hydraulic clamps
Suggested implementation
Follow this order when setting up the maintenance plan:
1. Take a mold inventory — give each mold a number and a card 2. Install a shot counter; if it can be read from the machine control, recording becomes automatic 3. Classify the molds by criticality and load — the mold that runs most and is most critical is inspected most often 4. Adapt the period table above to your own shot counts 5. Prepare a maintenance kit: cleaning materials, protective oil, and frequently replaced seals and pins in stock 6. Record every maintenance job; recurring failures reveal the root cause 7. If equipment is missing, complete the safety side first — opening and turning the mold is the riskiest step
For choosing maintenance equipment suited to your plant, you can consult our technical support team.