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5/1/2007 | 8 MINUTE READ

Evaluating Mold Repair Skills

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A systematic approach to train mold repair skills is more effective.

Mold repair skills, as in any trade or craft, require a certain amount of OJT (on-the-job training) to achieve proficiency. Some people need to work on a mold a dozen times or more to remember specific nuances about it, while another can pick it up after only two or three repetitions.

The speed at which employees can be trained is affected by the type of environment in which they work. “Reactive” maintenance cultures breed temporary, seat-of-the-pants repairs. Employees pick up bad habits and introduce unprofessional methods to new employees.

In “systematic” maintenance cultures, problems are addressed using root-cause analysis, and specific corrective actions are documented and followed. In such cultures, training is structured and much more effective.


Elements of training

Typical mold repairs involve a wide spectrum of tasks that can differ in complexity based on 10 mold characteristics:

  • Type of mold: Double-stack, rotary, two-shot, and in-mold labeling/decorating applications are examples of complex mold types that demand specific skills and plastics-processing knowledge.
  • Number of interrelated tooling stacks: Some molds have dimensional tolerances that are “stacked” or added together from a “0” corner to arrive at a specific position required for exact alignment. This also relates to tooling stacked vertically (A side to B side) to arrive at a specific preload necessary for clean parting-line shutoffs.
  • Tooling tolerances: The closer the tolerance (0.001 in. or less) for the tooling to mold a part within specification, the greater the degree of difficulty in all stages of repair. Fitting, handling, measuring, and even cleaning must be more precise to avoid causing flash or galling.
  • Number of pieces of tooling and plates: The more pieces of tooling and plates in a mold, the more time-consuming and complex the maintenance becomes and the more bench space required.
  • Size of mold: Molds weighing 6000 lb or less are normally manageable by one man on a bench. The larger the mold, the more hands and equipment are required to manipulate tooling and plates.
  • Type of material: Glass-filled resins and other abrasive materials can wreck havoc on gate inserts, valve pins, vents, and other close-fitting tooling components. Resins such as nylon and ABS require tight-fitting tooling while silicone molds need practically a press fit to keep from flashing.
  • Type of product: Where flash is hand-trimmed at the press, molds do not require the same degree of attention as a medical or pharmaceutical product with exacting dimensional and visual specifications.
  • Hot-runner molds: These are notorious for being difficult to work on due to thermal-expansion issues and required close fits of manifold tooling and stacks.
  • Age of mold: Multi-cavity molds designed and built 20 years ago or longer are usually piecemeal—that is, each piece of tooling is custom fit to a specific spot or tooling arrangement, making replacement or repair extremely difficult. Molds built in this era also relied mostly on nickel or chrome plating for corrosion resistance. The plating peeled like snakeskin if not cleaned often.
  • Mold design: Some companies attempt to cut mold expense up front by having molds designed and built with inferior steels and without interlocks, guided bushings, proper cooling, and venting—or simply by giving the job to the lowest bidder outside the U.S. They then count on the mold to run 24/7 with no issues and rely on maintenance to get the mold to a production-ready state.
  • Any of the above 10 characteristics can increase repair complexity, requiring extensive mold experience and excellent mechanical intuition, plastics knowledge, and physical coordination just to get through a repair. Performing these tasks safely and efficiently requires a better-than-average connection from the head to the hands.


Machining skills required?

Many companies assume (incorrectly) that only journeyman toolmakers qualify as skilled repair technicians. Such firms ask for extensive machining experience in assessing potential mold-repair technicians. I would agree that knowledge of toolmaking may be helpful in specific situations, but on a day-to-day basis, mold and part troubleshooting skills and craftsmanship are much more important.


Two sad but true stories

With a grin on his face, the toolroom supervisor brandished an e-mail that he was sure would liberate him from future maintenance problems. Waving the e-mail like a “Get Out of Jail Free” pass, he revealed the contents to his technicians in a brief but cheerful summary: 

“From now on, all mold-repair technicians hired at this plant will be required to have a bachelor’s degree in mechanical engineering.” This mandate, he assured, would provide the shop with the necessary smarts to repair multi-cavity molds more quickly and accurately.

As 15 tenured repair technicians absorbed this proclamation, one disbeliever asked if these future grads would be required to have any mold-building or maintenance experience.

“No,” answered the supervisor, who himself had come from the Quality department. “Anyone with a degree in engineering can do mold maintenance.”

At that point the e-mail resembled more a ticket for a berth on the Titanic than a guarantee to reduce unscheduled downtime. Heads shook and eyes rolled as the 15 repair techs went back to work, grumbling something about what will they come up with next?

It wasn’t long before the first validated blue-chip recruit hit the shop floor. It was clear that wrench-turning was not his forte. Nevertheless, he toured the shop like pro. Examining molds in various stages of repair, and nodding enthusiastically with a “been there, done that” grunt of confidence, it was peculiar that his only questions concerned where his “office” would be located and what kind of PC he would be supplied with.

He was unceremoniously informed by one of the repair techs that his “office” was a mold bench and that his keyboard would be in the shape of prybar.

The look of confidence was now a nervous laugh. Regardless, he was offered, and accepted the job of lead mold technician, meaning he would now be in charge of the 15 repair techs and any related maintenance decisions on more than 500 high-cavitation molds running in 60 presses.

The following weeks would prove to be quite interesting, humorous, and sometimes dangerous as he tried his best to pull it off, but the engineering degree taped to the side of his rickety old roll-around just did not have the magical healing powers that many in upper management had hoped for.

He left a broken spirit, with body parts damaged but still attached, after about six months. The HR department discovered the hard way that there is a difference between book knowledge and physical skills, and in mold maintenance you need both.

Another Fortune 100 company had a very different approach to staffing the mold repair shop: It routinely rotated new employees through the shop to keep them from becoming bored. This mold shop had five new employees fresh from the cafeteria, giving them a combined shop experience of two years. And the bosses could not understand why 70% of their mold stops were unscheduled.

This firm had an “anybody can do it” philosophy born from a corner-office misunderstanding so great that it buried under tons of money maintenance issues that would never happen in shop with employees skilled in the craft of working on a mechanical apparatus with hundreds of close-fitting, interrelated pieces.

These two theories, though polar opposites concerning the required expertise, involved the same basic lack of understanding of necessary mold-repair skills. To help clarify what skills are really required to perform mold repair at varying levels, see the accompanying job description for three levels of mold repair: apprentice, intermediate, and advanced. These guidelines are intended for a company that performs routine preventive maintenance or intermediate or advanced mold maintenance with minor fabrication capabilities.



Steven Johnson worked as a toolmaker for 26 years, rebuilding and repairing multicavity molds for Calmar Inc. and then as mold-maintenance engineer for Hospira Inc., a medical device manufacturer. Today, he is the maintenance systems manager for Progressive Components and has his own business, MoldTrax in Ashland, Ohio, which designs and sells software for managing mold maintenance.