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The Troubleshooter: How to Prevent Mold-Change FailuresThe Troubleshooter: How to Prevent Mold-Change Failures

Pulling and setting a mold may seem simple, but ignoring these steps can lead to catastrophic results.

Garrett MacKenzie

November 14, 2023

5 Min Read
road sign pointing to success and failure in opposite directions
abluecup/iStock via Getty Images

Molding operations are highly dependent on productivity, efficiency, down time, and scrap levels. Failure in any of these categories can be catastrophic.

One of the most critical procedures in any molding strategy is setting up a new job. Pulling and setting a mold may seem simple, but there are factors in a mold change that can make or break a successful startup. This article will address some of the common failures that occur during mold changes and how to avoid them.

  • Pulling and setting. Several types of failure can occur when a mold is being replaced. First, if a mold is damaged in any way during removal, it’s critical to address the problem immediately. Too often, the mold is set aside with good intentions, but it can lead to down time because of damaged fittings, knockouts, and so forth. Setting the mold is another important task that requires close attention to detail. Make sure both platens are clean and plan clamp placement carefully. Make sure knockouts are correct and of equal length. Verify that you are using the right number of clamps to safely hold the mold in place. If stripped holes are found, mark them with a paint marker for repair later. Verify the mold is level, especially when end-of-arm tooling on the robot will be removing parts.

  • Water lines. Water is a very important consideration during a mold change. Water lines should be hooked up the same way every time to ensure consistent flow. It is good practice to chase water through the return line into a bucket to verify that air isn’t trapped in a circuit. When using multiple lines, start at the bottom of the manifold and work your way up. This will ensure that the water lines lay on each other evenly. It also helps when troubleshooting becomes necessary because of water-related defects. Inspect hoses and fittings for wear and missing O-rings. Use the cover/over-ejector/through rule. Hoses attached to the stationary half of the mold should be run over or under the tie bar. Hoses attached to the moveable half should be run between the tie bars. Once all hoses have been installed, use zip ties to mount them to ensure no hoses are rubbing when the mold opens and closes. At the end of the mold change, verify that water temperature is correct based on the setup sheet and that flow is adequate by feeling each line individually for flow and pressure.

  • Hot runner. Several common failures can occur when setting up the hot runner. Cables should be connected carefully to prevent breaking or bending pins. Make sure cable lines are not in danger of being smashed between the mold halves as they open and close. If the hot runner utilizes multiple sets of cables, verify that all zones correlate with setup sheet requirements. At the mold change, verify that all zones are at the proper setpoint and are heating properly.

  • Valve gates. Manually fire the valve gates individually to verify that they are hooked up properly and working. Check that timers and positions have been set correctly on the controller via the setup sheet.

  • Cleaning the mold. This is one of the most critical aspects of the mold-change procedure. Never spray mold cleaner directly on a mold half that has moving components, such as ejectors or hydraulic cores. The cleaner breaks down the grease into an oil that can cause extremely poor startup events. In addition, inspect components that require grease, such as guide pins and slides. It is also a good time to inspect the mold for damage from a previous run. In addition, be on the lookout for worn or broken moving components.

  • Final audit. The most important step in the mold-changeover process is the final audit of the mold change. This step is quite often performed by the process technician who will start the press. One of the easiest ways to perform verification is to apply the \"5 M’s\" of molding procedure — man, mold, machine, material, and method. Man refers to having the operator at the press for startup. Mold references all setup concerns as they relate to the mold itself. Machine involves the barrel temperatures, robot, and all auxiliary equipment. Material refers to verification of the material and purging it through until it is clean and ready for startup. Method is the process setup itself. All setup sheet setpoints should be verified to match the machine.

Setup is key to the success or failure of your production system. Failure to take the proper steps to perform mold changes correctly will result in long down times and poor startup events. In addition, improper setup can also be the primary cause of excessive scrap. Take the time to perform your mold change events consistently and with great care. This will result in higher revenue for your company and a sense of pride in what your organization has achieved.


Got a problem with this, that, or the other thing? You might find answers in some previous "Troubleshooter" columns:

How to Identify and Correct Shear-Related Splay Defects

The Role of Moisture in Injection Molding Splay Defects

Preventing Flash in Injection Molded Parts

How to Prevent Common Failure Modes in Injection Molding

Building a Validated Plastic Injection Molding Process

Fixing Color Defects in Injection Molded Parts

Key Steps for a Stable Injection Molding Process

Fundamentals of an Injection Molding Plant or Cell Startup

What to Consider When Buying an Injection Molding Machine

About the author

Garrett MacKenzie is the owner/editor of plastic411.com and a consultant/trainer in plastic injection molding. He has provided process-engineering expertise to many top companies, including Glock, Honda, Johnson Controls, and Rubbermaid. MacKenzie also owns Plastic411 Services, which provides maintenance and training support to Yanfeng Automotive Interior Systems, IAC, Flex-N-Gate, and other top automotive suppliers. He was inducted into the Plastic Pioneers Association (PPA) in 2019, where he serves on the Education Committee evaluating applications from college students seeking PPA scholarships. You can reach him via e-mail at [email protected].

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