IMM 4/97

We are molding a 50 percent ceramic-filled nylon 6/6 and are having problems producing a bore of .450-inch diameter by .800-inch depth that has no taper. Our core pin is straight-no draft-and has a straight baffle for cooling. We have considered thermal pins on the next generation of tooling, but we were wondering if anyone had a less-expensive alternative.

It has been my experience in the past that Ampcoloy 940 bronze material is an excellent alternative material from which to make your core pins. I would certainly keep the baffle in the core for cooling purposes. Ampcoloy bronze is a great material for thermal transfer. You also mention that the core pin has no draft. I do not know if this has been a problem, but if it has, I would suggest a poly coating that is an electroless nickel plating that is Teflon impregnated. This is easy enough to test before you have a new tool manufactured; just have a new pin made of the specifications mentioned and put it in your existing tool.
-D. Upchurch, Design Technology, Gaffney, Sc, (864) 487-1424.

Perhaps it's too late to object to the specification of zero draft, but that is the real problem. Even an 1/8º per side sill probably work wonders. That would cause a dimensional variation of about .003 inch, end-to-end. Incidentally, I assume that the core pin has been draw polished. If the production volume is not too high, perhaps a PTFE/Electroless Nickle coating on the core would help, or titanium nitride. Coatings will not last long with the material you are using.
-W. Foster, Tessy Plastics Corp., Elbridge, NY, (315) 689-3924.

Make an entire core pin of copper alloy such as Ampcoloy 945 and cool as you do now. This material can be coated to prevent material abrasion.
-L. McFarland, Mould Concepts, Mishawaka, IN, (219) 258-0705.

IMM 8/97

With the abrasive filler called out in this application, a hard pin will work best. Brush Wellman's Moldmax core pins are 40 Rockwell C, compared to 94 Rockwell B for most bronze pins, but still have a very high thermal conductivity (similar to aluminum). Of course, the pin can't make the heat disappear, so the internal baffle is still required. But the high strength of the Moldmax pin allows generous cooling circuit diameters to be employed while retaining good strength levels in the pin.

The lack of draft will make it difficult to eject the part, and a hard coating with Teflon impregnation will reduce friction. Also, try not to overcool the part; the more it shrinks down, the harder it will be to remove. Some draft would ease this situation tremendously; even a small amount of draft will help. The Mold max pins can be substituted directly for the steel pins now being used, even on your existing tools. They are available from PCS (800) 521-0546.
-S. Smyers, Brush Wellman, Cleveland, OH, (216) 383-3687.