MAY 2004 / VOLUME 56 / NUMBER 5 ‹¤¤¤¤BY SUSAN WOODS, ASSOCIATE EDITOR

A mold and die shop shares the lessons it has learned Hard about hard milling. Lessons ard milling is being performed more and more by moldmakers H across the country. Moldmakers Inc., a plastic-injection and die-cast moldmaker, is no exception. For sev- eral years, the company has invested the time and money needed to hard mill on a regular basis. “Hard milling really started taking off for us about 3 years ago when the software, tooling and toolholders began to mesh together with the technology of the machine,” said Paul Klett, manu- facturing engineer for Moldmakers, Ger- mantown, Wis. The company is part of the MGS Man- ufacturing Group—a group of compa- nies that offers design and engineering

services, toolmaking, prototyping, mold All images: Moldmakers polishing, production , includ- The core of a mold for a is machined out of P-20 on a Roeders 800. ing multishot and blow-mold capabili- ties, and automated assemblies. “Going from one machine to another the decision-making process regarding Hard milling provides many bene- creates a lot more variables for which where and when hard milling can be fits. Eliminating the need to use a you have to try and control tolerances,” utilized. Together, they try to deter- sinker electrical discharge machine is said Klett. “Hard milling is definitely mine if a whole part or only certain the obvious one. With that, the costs of more accurate. We can take the part areas will be milled. “Our shop is programming the electrode-producing right off the machine and basically do unique in that the toolmaker gets in- machine, the electrode material and the little or no fitting.” Accuracy down to volved with the job early in the build,” time EDMing the steel are eliminated. ±0.0002" can be achieved, and even said Klett. Depending on the steel, workpiece closer if needed. The decision to hard mill depends, shape and amount of stock being re- in part, on what kind of concessions moved, it is also possible to eliminate Decision Time Moldmakers can get on the part itself, roughing before heat treating. At Moldmakers, the toolmaker, pro- such as whether a sharp corner can Tolerance buildup is also eliminated. grammer and designer are involved in have a radius. The company tries to the machine, if needed. Moldmakers uses shrink-fit - holders because tool life is increased. The toolholders maintain the accuracy, balance and rigidity needed for hard milling, even for smaller diameter . Moldmakers uses mostly solid-car- bide tools and inserts when hard mill- ing. “We typically use higher-quality cutting tools,” said Dennis Barkow, CNC specialist. The inserts have to be held in a solid- carbide tool body because an HSS tool can expand at the same rate as the holder, depending on the induction unit. If this occurs, the chances are slim that the HSS tool is going to come back out, rendering the holder useless for fu- ture projects that require a different tool. The company has tested several dif- ferent cutting tools. However, the tools are constantly evolving and Moldmak- ers has to keep tweaking its processes. Cutting tool companies alter the coat- A rigid setup is needed when hard milling H-13 on a high-speed machine. ing, substrate or grind to allow for more rapid stock removal. become involved up front with the de- tool life and allows a better surface fin- “We try to push the tool to its rec- sign so it can get the customer to agree to ish to be imparted. ommended chip load,” said Klett. any concessions that facilitate machin- It is also important for the CNC to “Sometimes, the machine does not ing. Most of the time, the concessions do process a lot of information quickly be- necessarily get up to the feed rate it is not affect the fit a