by Kip Hanson
A Q&A on five axis high speed machining with Andy McNamara, director of sales at Doosan Machine Tools America
Every machinery dealer benefits from having experienced, knowledgeable salespeople on its staff, experts who are able to explain complex machine tool technology in terms that all of us can understand. Andy McNamara is one of these. He has worked in the industry for more than three decades, including lengthy tenures with two iconic and well-known machine tool builders.
Today, McNamara is the director of sales for Doosan Machine Tools America, which serves a broad customer base in Canada and beyond. Shop Metalworking Technology had an opportunity to pick his brain on a topic that’s growing quite important to job shops throughout Canada: what to look for in a five axis machining centre, particularly one capable of high speed milling. Here’s what he had to say:
What is high speed machining, anyway, and how is it different than so-called “regular” machining?
“What one person calls “high speed” is often quite different from someone else’s definition, with much of it depending on the industry in which that person is working,” says McNamara. “Most mouldmakers, for example, depend on the machine controller’s ability to process high amounts of toolpath information very quickly and then interpolate those motions without appreciable lag. A shop machining aerostructures has similar needs, but because the axis motions are generally much larger and the tolerances less stringent than in a typical mould, far greater feedrates rates can be achieved. Both are considered high-speed machining, as they utilize relatively light depths of cut at higher feedrates and spindle speeds than in traditional machining, and both place higher demands on the machine tool, its servo systems, and controller.”
So what role does high speed machining play in the five axis world?
“A significant one,” he says. “The mouldmaking and aerospace shops I just mentioned are increasingly reliant on five-axis CNC machine tools for their ability to more effectively produce complex parts and geometries; the faster and more accurately a shop can accomplish this, the more successful they will be. The same can be said for much of the medical industry, turbine and blade manufacturers, gearmakers, and indeed anyone producing complex shapes to close tolerances. Regardless of the industry, however, the addition of two rotary axes significantly complicates the machine builder’s job of assuring accurate motion control
and sufficient processing speed, both of which are needed to produce high-quality five-axis parts.”
What’s most important in terms of machine construction?
“A strong, accurate structure is important on any machine tool, but especially with a fourth and fifth axis, as these present an additional two degrees of freedom and the potential for positioning errors,” McNamara points out. “For instance, you might mill a flat surface at A0 and then need to blend it with one milled at A90. It’s very important in this case to know that the table actually moves the 90 degrees it’s programmed for, otherwise you’ll end up with a mismatch. Accuracy is first and foremost, which in most cases requires linear glass scale feedback and rotary optical encoders. Beyond that, the traditional worm wheel rotary tables found in many five-axis machining centres are great for a multitude of applications, but for the most demanding applications where speed and long-term accuracy are a must, I generally recommend direct drive or roller gear cam style tables to fit the application.”
What about the machine controller? Any recommendations here?
“I have experience with all of the leading machine controls and control builders and can tell you that they’re all quite good at high-speed five-axis processing,” he says. “However, it’s critical that the control is set up properly from the factory for this type of work. In addition, it’s often a good idea to bring a knowledgeable technician onsite to work with the customer. Each control has various parameters and settings that can affect or sometimes enhance machine performance, making them cut faster and more smoothly. The trick is to know which ones to set for a given machining situation, which is why having an experienced person to lean on can really help.”
Is success here due solely to the quality of the machine tool and control?
“It’s clear that a high end machine tool will outperform a commodity brand no matter what you’re cutting, and five axis is no exception,” he says. “On the flip side, you can spend all the money in the world on a machine and have poor results because you used low-quality toolholders and cutting tools. The same can be said for the toolpaths and posted G-code. We worked with a customer recently that was struggling with a medical part, and after one of our application people showed them how to use tool centre point control (TCP) and correctly set the tool inclination angle relative to the workpiece surface, their problems went away.”
Any other important points we missed?
“Yes. Proper machine setup and operator training are critical to success,” says McNamara. “The machine should be leveled before use and checked periodically to make sure it stays level. It should be calibrated on a routine basis using a kinematic compensation system such as our “Doosan Intelligent Kinematic Compensation (DIKC) or Renishaw’s “AxiSet” software—as discussed, most shops do this before any sort of critical part machining. And although a good five-axis machine is equipped with cooled ballscrews and thermal compensation, temperature variations in the shop should be kept to a minimum if you’re striving for utmost accuracy.” SMT
Doosan Machine Tools is represented in Canada by Ferro Technique Ltd. (Eastern Canada and Ontario), Paine Machine Tool Inc. (British Columbia), and Source Atlantic (Alberta, Saskatchewan, and Manitoba).
