The Tool's the Thing
For material removal on a micro scale, the tool's the thing
By Jim Destefani
Making precision parts for medical devices is one of the fastest-growing segments of the metalworking market. (For more on precision machining for medical applications, see the articles immediately following this one.) But medical is only one facet of the micromachining industry, which is expanding by leaps and bounds in die/mold, automotive, and other application areas as well.
"Microtools have always been part of machining for the medical and information technology markets," says Bill Pulvermacher of Mitsubishi Materials USA Corp. (Irvine, CA). "But now we're seeing them utilized in machining of parts for automotive, hydraulic/pneumatic, power generation, controls, and other markets. The possibilities are almost limitless. If the part to be manufactured requires detail and close tolerance adherence, microtools will be better suited than regular tools."
Here's a look at the current state of cutting tool technology for micromachining applications.
Emphasis on Swiss-type turning machines for making medical components and other small precision parts has led many cutting tool suppliers to focus on this area of the market more than on milling/drilling applications.
For example, Mitsubishi Materials worked with builders of Swiss-type CNC turning machines to develop a line of tools for external and internal turning, drilling, and end milling. Designed for use in gang-tooled, cam, and turret-type machines, tools include a true ISO G-class insert with height, corner radius, and IC tolerances that Mitsubishi says are the strictest in the industry. Inserts are available with a sharp edge without hone and highly accurate small radii. Materials include coated carbide as well as cermet, coated cermet, CBN, and PCD grades.
Other microtools from Mitsubishi Materials include Micro MZS drills covering a diameter range from 1.0 to 2.9 mm, and two and four-flute solid-carbide end mills in square, ball and radius types and a range of sizes.
Another supplier focused mainly on tooling for small turned parts is Sandvik Coromant (Fair Lawn, NJ). "We've concentrated our efforts on applications for CNC sliding-headstock machines and small CNC lathes, and will continue to do so," says the company's Steve Piscopo. "We view sliding-headstock machines as essentially small multitasking machines, where many different machining operations--turning, milling, and drilling--are performed using a broad variety of tools."
Sandvik's offerings in the micromachining market include two tooling systems for high-precision, small-part machining in sliding-headstock CNC machines. CoroCut XS is aimed at external turning operations on parts as small as 1 mm diam, and includes a line of narrow part-off tools. CoroTurn XS was developed for internal turning in bores down to 1 mm. The latter tooling system features four sizes, CXS-04, -05, -06 and -07, each including inserts for a range of hole diameters and available in different lengths to suit different applications. Inserts locate into boring bars using a locating pin for consistent positioning of the cutting edge. Bars are designed with internal coolant supply, and two nozzles direct coolant at the cutting edge to improve chip evacuation and cooling. Boring bars range from 10 to 25.4-mm diameter.
For milling, Sandvik produces indexable end mills as small as 8 mm diam and solid tools down to 0.4-mm diam.
U J Baid of Kennametal (Latrobe, PA) sees manufacturers of medical and electronic components as the main users of micromachining technology. "Users are producers of medical and dental screws and components, producers of components such as disk drive shafts and bearings, and producers of other computer and telecommunications components," he says.
In response to growing interest in micromachining, Kennametal has formed a Micro Machining team to develop new products and expand the company's current tooling lines for the micro and small-part markets. Much of the effort is based around the company's KM Micro quick-change tooling system, said to be the only quick-change tooling system available for Swiss-style tool platforms. The system consists of a clamp unit that attaches to the gang plate like a conventional Swiss-style toolholder. A cutting unit attaches to the clamp unit using a coincidental-cone arrangement to provide three-surface contact. Operators can index inserts on an extra cutting unit while the machine is running, then swap out one cutting unit for another in about 30 sec.
The KM Micro line also includes boring bars for bores as small as 0.062" (1.57-mm), threading tools for production of threads as fine as 48 tpi, and microgrooving bars that accept standard 0.015" (0.38-mm) width inserts. Kennametal's rotating microtool offering includes a line of high-performance solid-carbide end mills down to 1/64" (0.4-mm) diam.
For milling and drilling, advances in cutting tool manufacturing technology and tool materials are enabling production of smaller diameters and more complex geometries, according to Sherwood Bollier, president, Niagara Cutter (Amherst, NY).
"Several key technologies have developed over the last ten years to allow cutting tool manufacturers to serve the micromachining market," Bollier says. "Manufacturing technology includes the use of high-accuracy, six-axis tool grinders. Temperature control and coolant conditions are key elements of the process, where tolerances on a 0.005" [0.13-mm] diam ball end mill require 0.0001" [0.0025-mm] TIR." Improvements in diamond grinding wheel technology and inspection technology have also contributed to quality and productivity in microtool manufacturing, he adds.
Bollier believes another key to improved microtools is continuing development of new tungsten carbide materials. Application-specific carbide grades have enabled development of, for example, Niagara's micro-decimal end mills. The tools use extra-fine grain cemented carbide material that allows production of a sharp cutting edge with good ground finish.
Niagara Cutter's standard decimal end mill products range from 0.005 to 0.055" (0.13 - 1.4-mm) diam in 0.001" (0.025-mm) increments. The lineup includes two and four-flute square-end and ballnose mills, and the company also produces special tools.
Accurate holding of small-diameter tools is a requirement, because runout must be held to an absolute minimum, according to Jack Burley, VP, BIG Kaiser Precision Tools (Elk Grove Village, IL).
"Toolholders are very important concerning microtools, and often overlooked in importance," Burley says. "To put it into perspective, if you have a two-flute end mill 0.020" [0.5-mm] diam, the chipload is less than 0.0004 ipt. If the tool has a runout of 0.0002" [5 µm], you are using only one flute by a factor of 100%. This will result in unstable cutting conditions, poor surface finish, and reduced tool life and breakage."
Designed for holding micro-drills and end mills, BIG Kaiser's Mega Micro chucks are offered in small-taper sizes such as ISO30 or HSK-E32. The tools are rated to 40,000 rpm and guaranteed to have runout of less than 3 µm at 4 X diameter.
The company's microtool offering also includes solid-carbide Sphinx micro-drills covering a diameter range from 0.5 to 2 mm in 0.01-mm increments. The tools are produced to tolerance of +0/-0.004 mm, and feature a reinforced shank. Applications include machining automotive fuel injector nozzles, controls and instruments in appliance manufacturing, burner nozzles for welding equipment, and medical products.
Special Tools, Special Machines. Walter Schnecker, president, Datron Dynamics Inc. (Milford, NH), points out that machine technology is yet another key to efficient micromachining. "In order to use tools 1/2" [12.7-mm] diam or smaller effectively and economically, higher spindle speeds are required," he says. Datron advocates a new approach to high-speed precision milling using small, purpose-built machines and tooling. The company's machines use high-frequency spindles with speeds to 60,000 rpm.
"Conventional CNC machines are great for muscling a 3" [76-mm] fly cutter through dense substrates," Schnecker says. "But, when they're used with microtooling, the operator has two choices: either crawl along at painfully slow speeds, or break a ton of tools with the force of the heavy-duty spindle.
"Production with microtooling is only efficient and profitable when these small tools are run at high speeds with low force, and this calls for a special kind of machine," he concludes.
To illustrate his point, Schnecker tells the story of United Cutlery (Sevierville, TN). Several years ago, the specialty knife maker subcontracted much of its knife handle production to Asia. Long lead times, duties on imports, and the threat of "knock-offs" led United to consider alternatives to off-shoring, and in 2002 the company added Datron high-speed machining centers to its lineup of conventional VMCs.
The machines mill, drill, cut, rout, tap, and engrave, eliminating multiple setups. They feature vacuum workholding, 60,000-rpm spindles, a proprietary tool management system, ethanol mist coolant, and Datron tooling. The setup enabled United Cutlery to eliminate secondary deburring and degreasing while meeting production requirements and expanding its line of specialty knives.
Datron's line of microtools includes solid-carbide end mills and routers to 0.3-mm diam, drills as small as 0.4-mm diam, and thread mills for sizes as small as M1.0 - 1.2.n
Micro: What the Heck Does It Mean?
One of the first questions we asked for this article was: How do you define micromachining? Our sources responded in a variety of ways. Here's a selection of their answers.
Some responses centered on turning as the key micromachining process.
"For us, micromachining generally refers to components down to 1 mm in diameter," says Sandvik Coromant's Steve Piscopo, adding that the preferred term at Sandvik is not micromachining but rather "small-part machining."
According to U J Baid of Kennametal, micromachining involves production of parts 1/4" (6.4-mm) diam and smaller. "Currently, the main drivers of this market are producers of information technology and telecommunications components as well as medical and dental components," he says.
BIG Kaiser's Jack Burley takes a slightly different approach, defining micro not only by part size but also by the size of tooling used for the operation.
"Micromachining can be defined as workpiece size in which the work envelope is smaller than 30 in.3 [490 cm3]," he says. "It can also be defined as tool sizes less than 3/16" [4.8-m] diam, and as toolholders with spindle sizes of ISO15, 20, 25, and 30, or HSK 25, 32, or 40."
The answer of Niagara Cutter's Sherwood Bollier reflected his company's focus on round tools.
"Micromachining involves small-diameter cutting tools, including drills, end mills, routers, and other specialty tools," he says. "In the current manufacturing environment, high-precision end mills from 0.005" [0.13 mm] and drills from 0.002" [0.05 mm] are available as standard tools."
Also coming at the problem from the perspective of round tooling was Walter Schnecker of Datron Dynamics. "As manufactured products become smaller, their parts become 'micro,' and micromachining involves mills and drills with a diameter of 0.250" [6.4 mm] or less," he says.
And the most philosophical answer came from Mitsubishi Materials USA's Bill Pulvermacher.
"Micromachining is more a mindset set or way of thinking than a particular part size," he says. "It's all about details, in everything from the obvious, such as corner radius, to center height, roundness, surface finish, and all-around consistency in application."
This article was first published in the May 2005 edition of Manufacturing Engineering magazine.