Hard Lessons For

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 several 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 companies that offers design and engineering services, toolmaking, prototyping, mold All images: Moldmakers polishing, production molding, includ- The core of a mold for a food storage container 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 toolholders because tool life is increased. The toolholders maintain the accuracy, balance and rigidity needed for hard milling, even for smaller diameter tools. Moldmakers uses mostly solid-carbide tools and inserts when hard milling. “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 different 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 and function of the part. cause the machine moves so rapidly. It programmed for and it is difficult to “It’s easier for the designer model- must look-ahead and anticipate the control that continuously. Our experi- ing the part to keep edges straight and next move. “Otherwise, it would starve ence allows us to compensate for this.” corners sharp,” said Klett. “But he may for information and consequentially not be familiar with the difficulty of slow the machine down,” said Klett. Programming machining those sharp edges and cor- Moldmakers starts with the feed rec- All of the company’s programmers ners. If we can educate part designers ommended by the cutting tool manu- are toolmakers who have hands-on ex- to optimize parts so they can be [more facturer. “We found that this is only a perience in the shop. New program- easily] machined, it benefits everyone general guideline to start out with,” mers work on the shop floor for 6 involved.” said Klett. “As you gain experience, months. “It is pretty important that they you know when to step it up or knock get to know processes, systems and fel- Machine Requirements it down a little bit. We are at the point low toolmakers,” said Klett. “We share To hard mill successfully, a number of now where we are getting pretty good information pretty openly here. If some- factors are involved, including the capa- at getting the number right away. It re- thing is really working well or has room bilities of the machine. For hard milling, ally depends on the length of the tool for improvement, we share that info.” Moldmakers has six 3-axis machines and if that tool is cutting with the tip or The operator has to have confidence with spindle speeds ranging from 30,000 outer diameter.” in the programmer so the operator rpm to 42,000 rpm. When using these CNC machines offer a variety of pa- doesn’t have to adjust anything. “But machines, a super-rigid setup is needed rameters that increase flexibility. These if that does happen, the programmer because the machine needs to be able to parameters are adjustable and can in- will be involved,” said Barkow. stay on course when it is moving fast and fluence the outcome of the part. Mold- He added that there are times when changing vectors. It is also critical that makers sets these parameters ahead of small adjustments are needed, such as the toolholder and machine be rigid. time for roughing and finishing so it changing the spindle speeds, but not for When hard milling, the company ap- can derive peak performance from the any extended period of time. “If you plies an oil mist. The oil mist extends machine. Adjustments can be made at have to do it for an extended period that means the cutting tool is rubbing too job’s specifications. chines have cameras on them so you much or the chip load is too high,” In addition, toolmakers have the can call up a job and see that part, and Barkow said. ability to check on jobs from their even fix it, all from home. I will check Many of the company’s hard milling homes with a video feed. on it every once in a while, just for jobs run overnight or on the weekend. “Everyone has a workstation at peace of mind.” Verification software is used to double- home so we can control the machines That is also one of the lessons Mold- check all programs before running to on the shop floor without having to ac- makers has learned—it pays to have ensure that everything will meet the tually be there,” said Barkow. “The ma- dedicated employees. CUTTING TOOL ENGINEERING Magazine is protected under U.S. and international copyright laws. 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