Tooling Corner : Training tool shop staff

Editor's note: Glenn Sheehan and Daniel Stephens, training professionals, share from their experience in developing more than 50 programs, including courses on mold design and moldmaking, for the plastics industry.

To be successful, a tool and die manufacturer must invest a considerable amount of time and resources in training new employees. Since even the latest in molding machine technology and state-of-the-art auxiliary equipment cannot compensate for poorly designed or constructed molds, new hires should at least be trained well enough to avoid costly mistakes.

A combination of training methods is likely to yield the best results. The opportunities fall into three basic categories: classroom instruction, on-the-job training, and self-directed, computer-based training. Each has its particular advantages. When an instructor is present—at a seminar given by SPE, SPI, or a private consultant, for example—a student can pose questions as they arise and get answers based on general industry practice.

In on-the-job training, answers to questions will generally be in the context of "how we do it here," which may or may not reflect the industry's best practices. This works for the employer and the employee in the short term, but it tends to perpetuate existing patterns rather than move toward state-of-the-art practices.

Interactive computer-based training provides great consistency, and programs can be written to reflect cutting-edge industry practices. Use of the programs depends a great deal, however, on the motivation and concentration of the student, as well as the student's willingness and ability to absorb material from a computer-based program.

Training Essentials
This article outlines recommended subject matter that new tooling staff should receive during their training. The training topics and subject matter discussed throughout this article should be integrated into any existing or future training curriculum.

An overview of important considerations for both mold design and tool construction should be presented first. This includes defining and explaining the relationship between part design, mold design, and molding machine performance. A mold's success depends on its ability to provide a conduit for the polymer to flow, form the part, cool the part, and eject the part.

Members of a tooling staff should be familiar with both established and emerging machining methods. Manual and computer numerical control (CNC) machining processes such as milling, turning, wire electrical discharge machining (EDM), die sinker EDM, surface grinding, jig grinding, cylindrical grinding, and high-speed machining are the most frequently used methods. Tooling personnel should be aware of the tolerances, stresses, and resultant surface finishes and polishing needed for each of the machining methods. Incorporating draft, steel-safe machining, the difference between machining tolerances and molded part tolerances, sealoffs, and getting the most out of inspection equipment are also significant machining topics.

Selecting the proper steel for a tool and determining the need for heat treatment, surface coating, or surface treatment are fairly technical decisions. Therefore, a working knowledge of materials and treatments is required. Curriculum for such issues should include qualitative and quantitative mechanical properties, when and why to treat steel, and alternative tooling materials.

The employee should be familiar with the full spectrum of standardized mold bases and how they are used in two-plate, three-plate, and hot runner mold construction, as well as the many components that can be integrated into the design. Moldmakers should be taught how to decide when it's appropriate and cost effective to implement interchangeable mold systems.

External and internal mold actions are complex topics and teaching them often requires the use of examples. Motion is commonly associated with slides, core pins, lifters, expandable cores, collapsible cores, and unscrewing cores.

Ejector pins, ejector sleeves, ejector blades, lifters, stripper plates, air poppet valves, two-stage ejection, and positive ejection return are all common forms of part ejection. Mold designers and toolmakers must be familiar with the design and function of each form so that the most effective method or combination is used. It is also imperative that ejection components do not interfere with the mold's cooling lines.

Trainees must be aware that parts should be cooled as quickly and evenly as possible, since more than half of the overall cycle is consumed by cooling. Aside from traditional cooling lines, perimeter cooling, inserts, baffles, bubblers, and thermal pins should be part of the curriculum.

Venting is used to prevent gas entrapment during injection, and is usually located at the parting line. New employees should be encouraged to consider venting on static and movable components, and entertain the option of using porous steels.

Cold and hot runner gates as well as gate location considerations are all important factors in mold design. Discussion of each gate type should include information about its design, machining, and typical use, along with its advantages and disadvantages. The curriculum should address whether the type of runner system used is unbalanced, naturally balanced, or artificially balanced. Other important topics to include are temperature profiles, runner cross sections, parting line location, and part orientation.

Accelerated Training
It's not uncommon for moldmakers and tool designers to receive only on-the-job training. This method is valuable and necessary, but consumes the time of both the mentor and the apprentice, and limits the knowledge passed on to a need-to-know basis. Furthermore, not every good moldmaker is an effective teacher.

Interactive training can be an effective supplement to on-the-job training. Since interactive training is a form of computer-based training, it can be integrated into any schedule. This approach to learning allows the user to absorb material at a practical pace. Interactive training programs can administer exams both before and after a participant takes a course to assess the effectiveness of the curriculum.

Contact Information

A. Routsis Assoc. Inc.
Dracut, MA; Andy Routsis
(978) 957-0700
www.traininteractive.com