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44 MoldMaking Technology —— OCTOBER 2017 SKILLS CENTER Apprentice Training: The Plastics Side of Moldmaking The apprentice should understand why and when to use a hot runner, the function of its heaters, thermocouples, hot drops and tip styles. By Ryan Pohl An effective moldmaking training class not only addresses the practical considerations for build- ing plastic injection molds, but also covers the theoretical reasons for doing what moldmakers do. It is important to convey more than just what moldmakers do to build a robust mold. Moldmakers need to ensure students understand why they do it as well. With that concept in mind, this piece out- lines some of the specific topics that should be covered in a training program. (With permis- sion, this piece primarily derives content from a webinar-based class that moldmaking industry expert, Randy Kerkstra, teaches.) Mold components. Apprentices should learn about mold components and relevant terminology early on in their train- ing. They should be able to visually identify parts and explain their general purpose. Examples include ejection components such as pins, plates, slides and lifters, core pins, bushings, lead- er pins, springs, slide retainers, latch locks, parting line pullers and safety straps. Also, the apprentice must be able to correctly identify the mold half on which he or she is working. This means understanding the cavity versus the core, the A-plate versus the B-plate and the cover versus the ejector. Mold material selec- tion. Apprentices need to understand the pros and cons of various mold materials, as the mold material that the moldmaker uses depends on the application and the component. For example, an apprentice must understand why a mold is designed with a P-20 cavity block and HH P-20 slides and lifters, or vice versa. In another example, an apprentice must understand what circumstances result in the use of soft material, such as aluminum, brass or cold rolled steel, over a hardened H-13 material. The class should cover the materials used for gibs, wear plates and gate inserts too. Temperature control. Apprentices must realize that a mold requires a means to control the process temperature, as well as why and how this is conducted. Controlling the process tem- perature involves in-depth instruction on proper water circuit design and the necessary parts and components, including fittings, plugs, bubblers, ISO pipes and baffles. A focus on tem- perature control system maintenance is recommended also. Venting. Since one of the most important aspects of an efficient plastic injection mold is venting, it is vital for apprentices to understand its impact on the molding process. Understanding venting includes understanding everything from the overall vent design to specific characteristics like the land, relief and depths. Apprentices must understand how to achieve proper venting using stationary inserts, ejector pins, sleeves and cores, which includes the role of Porcerax and sin- tered vent inserts. Parting lines and support. Apprentices should come away from class with a strong understanding of the parting line in a mold, which includes recognizing shut-off areas to help them grasp the importance of locking and location concepts. They also need to learn how to properly support all of the parting line areas of the mold to prevent flex and injection pressure issues, as these problems contribute to flash. Surface finishes. Achieving the appropriate mold surface finish is another key training area. It should include a focus on a finish's impact beyond the impression that it leaves on a plastic part. Additionally, training should look at the variety of texture, media, blasting, coating and polishing types, sticking issues and part holding methods. Spotting. In addition to covering design concepts, train- ing should cover some practical tips and techniques related to spotting. Training should include the use of the various spotting tools, as well as their proper handling and care.