Maintenance of Plastic Injection Molds

Depending on the workload, environment, and operating conditions of each injection mold and its parts, periodic maintenance schedules are set up in daily, weekly, monthly, 3-monthly, 6-monthly, and yearly intervals.

Mold Cleaning

1- The mold is opened. Once opened, the petroleum jelly inside is cleaned off with diesel fuel and cotton waste. The interior surface of the mold is checked for dents, nicks, or scratches. The tips of the ejector pins and core pins are checked for chips or dents. After the mold’s surfaces are cleaned with diesel fuel, they’re dried.

2- Polishing paste is applied and the mold is cleaned with a hand grinder and a polishing cloth. Care is taken during this process not to chip the sharp corners. It’s washed again with diesel fuel, cleaned with air, and dried.

3- A thin film layer of petroleum jelly is brushed onto the mold’s surface. The sprue is filled with petroleum jelly. The mold is closed and its outer surfaces (front and back) are cleaned with sandpaper.

4- The mold’s water system is checked for blockage by applying compressed air. Any missing water connection fittings are completed. If any section is found blocked, it’s cleaned by applying acid.

5- Any other missing bolts, slides, or safety retaining bars on the mold are completed and the mold is set aside ready for use.

Mold Polishing

Injection molds that run continuously develop, as a result, conditions that need repair, especially in the mold cavities that give shape to the product — such as wear, and loss of shine and smoothness. In this case, these areas need to undergo a repolishing process

Mold Polishing (Rubberized Abrasive) Stones

Rubberized abrasive stones generally come in three colors: white (soft), red (medium-hard), and blue (hard). Depending on the area of use, they’re available with 2.34 mm, 3 mm, and 6 mm shafts (mandrels).

Hardness, friability, abrasiveness, and dimensions are determined according to need. Each stone has its own particular properties. Stones are available in grit sizes of 60, 120, 150, 180, 220, 320, 400, 600, and 800.

They’re manufactured in various shapes. As well as cylindrical or cone-shaped ones, there are also profiles like flat, triangular, square, and knife-edge shapes.

Mold Polishing Compounds (Diamond Paste)

These were developed for polishing press and injection molds, where quality and efficiency matter. Diamond pastes are obtained from a mixture of natural and industrial diamond. The unmatched cutting power of natural diamond is combined with the hardness and durability of industrial diamond.

They’re available in both water-based and oil-based formulas, and can be used with thinner and a special softening agent.

areas of use of diamond paste — Diamond paste colors and their areas of use

Flex-Shaft Polishing Motor

The flex-shaft motors used for mold polishing generally run at 15,000, 22,500, and 25,000 rpm.

Mold maintenance polishing is carried out in two stages. In the first stage, pre-polishing is done with rubberized abrasive stones and liquid diamond pastes. For this purpose, diamond pastes of various micron sizes, as shown above, are used.

In the second stage, the actual polishing is done using felt bobs and a flex-shaft motor. High-speed motors should be preferred here.

Preventing Surface Rust

Mold surfaces are protected with special oils after use to prevent moisture-related rust.

Cooling Channel Cleaning

Regularly cleaning the cooling channels inside the mold directly affects product quality and cycle time.

Periodic Maintenance Schedule

Injection molds should be scheduled for periodic maintenance based on the shot count specified by the manufacturer.

Performing Injection Mold Maintenance

For details about maintenance
SEE: Performing Injection Mold Maintenance
You can download the monthly maintenance card here.
You can download the 6-monthly maintenance card here.

Maintenance and Repair Methods

1- Breakdown Maintenance

Repairs are made once a failure occurs. Failures occurring at unexpected times leave no room for planning. There’s a high risk of repeated failures in the same or nearby areas. This is the highest-cost approach. The reason is the production loss experienced during the failure downtime.

2- Preventive Maintenance

This is periodic maintenance. It’s based on the probable frequency of failure. Failure-preventing maintenance work orders are periodically opened based on these intervals. The risk, and the reason for its high cost to the business, is keeping repair intervals short in order to stay ahead of failures.

3- Predictive Maintenance

This is a method of addressing developing conditions before a failure occurs, through planned repair activity, along with related issues, before the failure grows. With this approach, the unnecessary maintenance work carried out under preventive maintenance is no longer needed, and at the same time, unexpected failures can be identified in advance. The reduction in downtime results in significant savings in parts and labor costs.

4- Proactive Maintenance

Repair results are tracked using data recorded before and after maintenance and the analyses performed on it. Every repair performed is verified to confirm whether it actually achieved the correct result. In addition to predictive maintenance, in proactive maintenance, this criterion is checked before the equipment goes back into service after maintenance. If the maintenance isn’t of the desired quality, it’s corrected. As a result, the intervals between required maintenance grow longer, leading to less maintenance need over the course of the year.

5- Reliability-Centered Maintenance

This is a combination of preventive, predictive, and proactive maintenance methods. All developments are tracked from a single center, under one roof. Emergency work orders are opened within the same system.