Growing demand for microparts challenges suppliers, users

Ever machined parts so small that they not only fit on a penny but can sit on old Abe’s nose? Cutting parts and part features in this Tom Thumb world often comes with Titanic-sized challenges, such as unexpected cutting tool breakage, deburring parts the size of typical burrs and machine tool spindles speeds that come up short.

Sometimes just handling ultrasmall parts is a gargantuan task.

Elfin Endmills

Micromachining is made easier by partnering with a toolmaker that specializes in small. One such company is Midwest Industrial Tool Grinding Inc.

“As the manufacturing industry moves into increasingly smaller products, tooling must be aligned to match those requirements,” said Jennie Nelson, director of sales and marketing at MITGI, Hutchinson, Minn. For example, “diametric and form tolerances of ±0.0001” are becoming very common, and we are frequently asked to go even smaller. At this scale, everything is proportionally more difficult: Tolerances are reduced, tool cores are smaller and web thicknesses become very small.

At the microscale, everything about cutting tools is proportionally more difficult: Tolerances are reduced, tool cores are smaller and web thicknesses become very small. Image courtesy Midwest Industrial Tool Grinding.

“Add to this the growing use of harder workpiece materials,” Nelson said, “and the future of tool manufacturing looks to be both challenging and very exciting indeed.”

This excitement also extends to MITGI’s customers, who often have machine tools with inadequate spindle speeds for the jobs at hand. “In these cases, companies often consider whether upgrading to newer equipment with higher spindle speeds is necessary for a specific job or for their business in general,” Nelson said.

Hans Liechti, tool manager at Mikron Corp. Monroe (Conn.), agreed that a sufficient rpm is required for effective micromachining, but it must be achieved using the right hardware. “Some shops try to compensate for inadequate rpm with air speeders, but we find these are not rigid or powerful enough, especially in tough materials,” he said. “We suggest 40,000- to 60,000-rpm, direct-drive spindles. Anything faster than this doesn’t seem to offer an advantage in tool life, although some productivity might be gained by running faster.”

Lietchti added that micromachinists also need a motion-control system to calculate accurate toolpaths at high speeds, “and should not slowdown in corners or make jerky motions. This very often results in tool breakage.”

Breaking Up Isn’t Hard to Do

Would-be micromachinists might gripe about the relatively high price of submillimeter endmills and drills, but these complaints are likely misplaced.

Liechti said the scrap rate for microtool grinding is often high. “They’re very fragile. On a tool measuring 0.008″ in diameter, you may end up scrapping 20 to 30 out of every 100. Even the smallest amount of roughness on an insufficiently dressed grinding wheel is enough to break the tool.”

Mikron offers through-the-shank coolant in tools down to 0.012″ (0.3mm) in diameter. Image courtesy Mikron Corp. Monroe.

Despite the difficulties, Liechti said the market for microtools is growing, especially in the aerospace and medical industries, where titanium and nickel-base alloys add fuel to the small-part-machining fire. Anyone who’s machined an Inconel turbine blade or a cobalt-chrome prosthetic implant knows the importance of through-coolant. But how is this achieved when tools are thinner than pencil lead? Liechti said the best way to overcome stringy chips and high heat generation when cutting difficult metals is by placing coolant holes through the shank and forcing cutting fluid down the flutes and into the cutting zone. Mikron offers this feature in tools down to 0.012″ (0.3mm) in diameter.

Of course, buying the most accurate toolholders available is important too. “Even with a very precise tool, you need to check the runout at the tool tip,” Liechti said. “Some customers just assume it is good, put it in the machine, and then the cutter breaks. Depending on the size of the tool, runout probably shouldn’t exceed a few microns.”

Joel Kuhn, senior applications engineer at Chicago-based machine tool builder Microlution Inc., agreed on the need for highly responsive and accurate motion control, but said CAM capabilities are equally essential. “You absolutely need chip thinning and consistent chip loads; adaptive clearing, dynamic milling, whatever terminology the CAM provider uses, it works really well on the microscale.”

Kuhn said there’s no single cause of failure when micromachining, and success depends on perfectly matching machining parameters to mechanical systems. Even then, it’s the little things that often cause the biggest problems.