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The Troubleshooter: Developing Robust Maintenance Procedures in Plastic Injection Molding Operations

Unplanned downtime erodes customer confidence and profits. Follow these simple steps to implement a planned maintenance strategy.

Garrett MacKenzie

June 18, 2024

3 Min Read
factory workers huddled around a tablet
Amorn Suriyan/iStock via Getty Images

At a Glance

  • Order parts in advance and have all tools in place before shutting down the press.
  • If repairs exceed 30% of press value in a year, it’s probably time to buy a new machine.
  • Tracking historical data is critical to an efficient maintenance approach.

Plastic injection molding efficiency is dependent on the ability of a molder to control and reduce unplanned downtime. A chaotic maintenance strategy leads to scheduling failures, erosion of customer trust, and reduced profits. This article will explain the difference between planned and unplanned downtime. It will also provide insights into ways to reduce down time and explain how to turn unplanned maintenance into a planned maintenance strategy.

Planned maintenance.

Planned downtime events are developed based on prediction and frequent inspection. Plants using a truly methodical approach will achieve better control of their maintenance approach. Parts are ordered for a planned event in advance, so lead times are known, which helps develop the repair/replace plan. An evaluation of needed tools and equipment is completed prior to the event, and all tools are in place before the press is shut down

Unplanned maintenance.

Unplanned maintenance is often the result of a “fix it when it breaks” mentality. Technical support scrambles to develop a plan to make repairs. Parts quite often require expedited ordering. Some parts have lead times of four to 12 weeks, leaving the press disabled and the scheduler frantically looking for similar presses to make up for the handicap. Shorter runs and more mold changes are often the result, leading to increased scrap and larger downtime numbers.

Fleet age and condition.

Press age and condition are huge identifiers of whether press replacement is needed and required. As a general rule, presses that are more than 10 years old are reaching the age of retirement and should be monitored frequently. This does not negate the possibility of a five- to 10-year-old machine showing signs of age. If press repairs exceed 30% of press value in a year, it is likely that a replacement is needed. Older presses become unreliable and result in chaos in terms of productivity and efficiencies. You can have the best maintenance team in the world and still fail if your press fleet is weak and breaking down frequently. 

Machine historical data.

Tracking machines’ historical data is critical to an overall maintenance approach. Predictive maintenance relies upon this data to determine the frequency of needed repairs from a planned event perspective.

Inspection frequency.

It is important to note that the industry has established basic industry frequencies for the inspection and replacement of press components. Bear in mind, though, that these standards do not specifically outline the needs of the presses in your plant! Like people, presses have their own identities, and maintenance logs need to be consulted for proper identification of frequencies and approach.

A strong maintenance approach requires frequent analysis and planning for each press. Planned and predictive maintenance is based on visual inspection, process monitoring, and historical data as it relates to each individual press. Eliminating unplanned maintenance is key to high quality, full utilization of available machine time, and higher profits.

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

Setting Up Your Injection Molding Process for Success

A Primer on Plastics Processing Fundamentals

How to Interpret Plastic Injection Molding Data

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

How to Prevent Mold-Change Failures

Fundamentals of Injection Molding Press Startups

Preventing Speed- and Time-Related Defects in Injection Molded Parts

About the Author(s)

Garrett MacKenzie

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 Plastics 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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