It probably doesn’t take much to convince you that machining at higher speeds can save you time and money. But like driving down the highway in your car, increasing your speed means that you are also increasing the inherent risk in the situation. A tool holder rotating at 35,000 RPM poses more of a danger than the same tool holder rotating at 8,000 RPM, just based on the kinetic energy involved. If a high- speed operation goes awry, you won’t have much time to act, and typically it’s your part, workholding or machine itself that bears the brunt of the damage, not to mention potential danger to the operator. Greater cutting speeds also mean greater heat and chip generation. Nevertheless, with great risk comes great reward, and those who master machining at high speeds quickly reap the benefits of increased productivity. If necessity demands that you run at higher speeds, you need to choose the proper tooling and cutting strategies to reflect this or you may be doomed before the race even begins. Nowadays when machinists talk about high-speed machining, they are usually discussing optimizing toolpaths and feeding strategies through CAM. You will hear phrases such as tool engagement, stepover and trochoidal milling. A big revelation that many machinists have at some point in their career is that once you reach a certain cutting speed, the cutting temperature decreases. It may be counterintuitive, but in addition to decreasing cycle times, you are also increasing the life of the
tool because heat dissipation is improved. Whatever feeding strategy you utilize, they all serve the same purpose: maximizing your material removal rate with the equipment you have. Fortunately, HSM toolpaths are usually a built-in feature to CAM software, so not much programming effort needs to go into this. Decades of research and countless papers are dedicated to this topic alone (and for good reason), however it’s still only one piece of the puzzle. To maximize your speed potential, a holistic approach that considers tool, holder, machine and operator is essential. Spindle speed and balance The first step, as common sense as it may be, is knowing the maximum speed of your spindle. This will be your absolute ceiling when it comes to speed. The next natural inclination is
to look at your cutting tool. This means trading in your high-speed steel tools for carbide, or your carbide for super hard materials like PCD or CBN. Increasingly hard cutting tools largely translate to increasingly fast cutting speeds and today’s modern cutting geometry designs have made possible previously unthinkable speeds. But many ignore the interface between the two: the tool holder. Machining speed, besides depending on the physical limitations of the machine tool and cutting tool, will largely be governed on how well balanced the tool holder is. Balance is usually the focus when you’re talking about high-speed tool holders because it offers the greatest opportunity for improvement, but keep in mind that your maximum speed will only be as fast as the “weakest link” allows. If you have a 12,000 RPM spindle, inserts that allow you to cut at 9,000 RPM, but your tool holder is only balanced for 8,000 RPM, then 8,000 is your max RPM.
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