Plastics Technology

NOV 2018

Plastics Technology - Dedicated to improving Plastics Processing.

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ABOUT THE AUTHOR: Jim Fattori is a third-gener- ation injection molder with more than 40 years of molding experience. He is the founder of Injection Mold Consulting LLC, and is also a project engineer for a large, multi-plant molder in New Jersey. Contact; Precision Welding For Critical Plastic Components The Emerson logo is a trademark and a service mark of Emerson Electric Co. © 2018 Emerson Electric Co. For product information: The Branson GSX ultrasonic welding platform meets the growing demand for the assembly of smaller and more complex plastic components. Precise welds are achieved utilizing an advanced electro-mechanical actuation system that provides unprecedented control and position accuracy, while applying an industry low trigger force. The Branson GSX can also weld across multiple parameters, monitored in real-time to ensure quality. This is possible with a wide range of input materials and best in class repeatability across multiple Branson GSX welders. HOW TO MACHINE EJECTOR-PIN HOLES There are various methods used to install holes for ejector pins. First, every plate must be ground flat and machined perfectly square before any other machining can be performed. Years ago, plates were stacked together and the larger holes for leader pins, return pins and guide pins were "line bored" to ensure proper hole alignment. With today's precision CNC machines, line boring is no longer necessary. Typical positional accuracy is easily ±0.001 in. but can be much finer if the edges of the mold plates are ground smooth. This gives a more precise indicator reading when setting up the plates in the mill. Some tool makers like to install all the ejector-pin holes from the front of the core, before the shape of the core is machined. While this will give you excellent positional accuracy, it makes milling precarious because of all the interrupted cuts. That may be accept- able for soft materials, such as aluminum, but you risk breaking cutters on tool steel. You also never want to install ejector pins to size, prior to heat treating. Heat treating can cause the steel to "grow" or warp, which will change the locations of the holes. Drilling ejector-pin holes from the front leaves a small chamfer, or bell mouth, on the surface. Therefore, never drill from the front unless there is extra stock on the core, which will be removed later. However, if the core is fairly thick or made of pre- hardened steel, and the pin diameter is small, there is the risk that the drill bit will "drift," "walk" or wander out of position as it cuts. In this case, you can drill a smaller-diameter hole from the front, then drill and ream it to the final size from the back. Drilling from the back will leave a slight burr when you break through the front, but it can easily be stoned off. Don't forget to add a countersink to the clearance holes at the back of the core and the back of the support plate to provide a lead-in for the pins. It all comes down to this: Molds are expensive, but so is downtime. You have to find a happy balance between how many expensive extra steps to take in the mold design and mold construction, versus the risks and costs associated with mold repairs during its lifespan, as well as not being able to meet your customer's production requirements. Molds are expensive, but so is downtime. 34 NOVEMBER 2018 Plastics Technology T O O L I N G K now How

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