Evaluating Mold Repair Skills

The keys to proper mold repair on-the-job training are an organized, systematic shop atmosphere, and an understanding of mold repair skills requirements and the mold characteristics that challenge those requirements.


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Mold maintenance is not a job at the forefront of industrial trade groups. Electricians, machinists, plumbers, welders, etc. all can take structured courses that allow the graduate to enter the workforce being comfortable with best practice methods and having an understanding of related codes that govern what they do, as well as certification that they indeed took and passed the course. Experienced mold repair technicians will quite often be required to cross over into these other fields as they perform daily tasks on molds throughout the world.

Although there is no such public schooling for mold repair techs, there should be. While many mold repair tasks are mold/product specific, the same basic troubleshooting logic and craftsmanship skills are needed with all molds, regardless of type, style or size. Some are just more difficult than others, requiring a greater degree of focus, precision and sometimes manpower.

Mold repair skills require a certain amount of OJT (on-the-job training) to become proficient. How much depends on certain factors such as mold complexity and the availability of accurate manuals. Some 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 effectively trained also is influenced by the type of environment in which they ply their trade.

Reactive maintenance cultures breed temporary, seat-of-the-pants repairs where employees regularly pick up bad habits that result in poor mold performance. These “shortcuts” are then passed on to new employees who may add their own spin until every one has a way of doing it fast, but not necessarily right.

In an organized, systematic atmosphere problems are addressed using documented historical data, probable causes and specific corrective actions as guidelines, allowing training to be structured, ongoing and therefore much more effective.

Challenging Mold Repair Skills

Typical mold repair consists of a wide spectrum of tasks that challenge skills based on 10 aspects of mold characteristics:

1. Type of mold
Double-stack, rotary, two shot, in-mold applications are examples of molds commonly known in the industry as complex and demanding specific, pre-cision methods, skills and plastics processing knowledge.

2. Number of interrelated tooling stacks
Some molds have dimensional toler-ances 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.

3. Tolerances of tooling
The closer the tolerance (.001 or less) the tooling must be to mold a part within specification increases 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 issues.

4. Number of pieces of tooling and plates
It stands to reason, the more pieces of tooling and plates in a mold, the more time consuming and complex the maintenance becomes simply through volume and bench space required.

5. Size of mold
6,000-pound molds and under are normally manageable by one man on a bench. The larger the mold, the more hands and equipment that are required to manipulate tooling and plates.

6. Type of material
Glass-filled resins and other abrasive materials can wreak havoc on gate inserts, valve pins, vents and other close-fitting tooling. Resins such as nylon and ABS require tight-fitting tooling while silicone molds need practically a press fit to keep from flashing.

7. Type of product
Molds that produce parts where flash is hand-trimmed at the press do not require the degree of attention that a medical or pharmaceutical product with exacting dimensional and visual specifications would.

8. Hot runner molds
These molds are notorious for being difficult to work on due to thermal expansion issues and required close fits of manifold tooling and stacks.

9. 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, which peeled like a snake if not cleaned often.

10. Mold design
Some companies attempt to cut mold expenses upfront by having molds designed and built without interlocks, guided bushings, proper cooling, venting and inferior steels or by simply giving the job to the lowest bidder. 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.

Mold Repair Skills Requirements

Many companies assume (incorrectly) that only journeyman toolmakers qualify as skilled repair technicians, and require extensive machining experience in accessing potential mold repair capability. Knowledge of toolmaking may benefit the employee/company in specific situations, but on a day-to-day basis, mold/part defect troubleshooting skills and craftsmanship are much more critical to the success of mold maintenance technicians, and the molds they maintain.

To help clarify what skills are required to perform mold repair at varying levels, following is a job description for three levels of mold repair: apprentice, intermediate and advanced. These guidelines are intended for a company that performs basic and intermediate mold maintenance and minor rebuilding tasks.

Mold Repair Job Descriptions
Mold Maintenance “C” (Apprentice)

  1. Possess good mechanical aptitude and basic hand tool experience.
  2. Ability to aid in the moving, disassembly and cleaning and troubleshooting of molds and components in a safe and methodical manner and possess the basic tools, physical skills and discipline to use specific prescribed methods/procedures during this work. Could be called upon to handle simple in-press cleanings, and lubrication of molds.
  3. Understands the importance of ac-curate, legible documentation and follows prescribed methods/procedures during work.
  4. Recognizes and enjoys the challenges of this trade and demonstrates a willingness to learn and a desire to advance.

Mold Maintenance “B” (Intermediate)

  1. Has the necessary maintenance know-ledge and skills to safely, effectively and efficiently disassemble, clean, troubleshoot and assemble 50 to 60 percent of a company’s active molds.
  2. Demonstrates sound mechanical reasoning, knowledge of mold function and a desire to improve plastics processing knowledge as it relates to mold function.
  3. Can measure and calculate basic (static) tooling stack-ups to determine component preloads, clearance or to verify print dimensions.
  4. Is familiar with hot runner function, basic maintenance and troubleshooting techniques, such as probe tip cleaning, removal, reworking and basic electrical troubleshooting on probes, heaters, thermocouples and manifolds.
  5. Demonstrates the ability to work methodically and meticulously during repairs on molds.
  6. Inputs clear, concise data entries into mold maintenance manuals.
  7. Has all necessary hand tools and operating skills for BASIC machine shop equipment (grinder, mill, lathe, micrometers, calipers, etc.).

Mold Maintenance “A” (Advanced)

  1. Has the necessary knowledge, skills and tools to effectively and efficiently disassemble, clean, polish, troubleshoot/repair and assemble 90 to 95 percent of a company’s active molds. Capable of utilizing all in-house machine shop equipment to rework worn or damaged tooling or plates, and to fabricate simple tooling.
  2. Demonstrated that their molds start and run productively without repeated pulls for missing or incorrectly installed tooling components, or repeating mold/part defects.
  3. Capable of complete dimensional mold tooling stack-out (static and dy-namic) to determine tooling component preloads, clearance and fits utilizing any/all available prints.
  4. Capable of determining “best” methods/procedures to institute mold/part defect probable causes, corrective and preventative actions of shop personnel and has excellent knowledge of typical mold functions.
  5. Works in a steady, professional man-ner with little or no supervision required.
  6. Enthusiastic and interacts well in training less skilled or new employees in proper mold maintenance techniques and methodology.
  7. Has acquired a sound understanding of plastics processing requirements for molds, such as venting, heating, cooling, polishing, nozzle, sprue, and runner con-figuration and plating applications or requirements.
  8. Continuously seeks to improve know-ledge base by attending conferences, seminars or exhibitions directed toward the designing, building and maintenance of molds.

Bonus Skills

  • Computer experience
  • Welding, brazing
  • Hydraulics experience
  • Hot runner experience on various styles
  • Mold design or building experience

The keys to proper on-the-job training for your shop’s mold repair personnel are an organized, systematic shop atmosphere where problems are addressed using documented historical data, probable causes and specific corrective actions as guidelines; and, an understanding of mold repair skills requirements and the mold characteristics that challenge those skills requirements.