Small Parts Machining
Precision processes call for miniature tooling
By Jim Lorincz
Today's manufactured products continue to shrink in size and scale. Products as diverse as medical and dental devices, cell phones, laptop computers, and aerospace and electronics components require smaller, even miniaturized, cutting tools and tooling systems.
According to Peter Matysiak, president, Emuge Corp. (West Boyleston, MA), there is a greater need for miniaturization of processes and development of cutting tools to meet processing requirements for Swiss-type machining, high-speed milling, and thread milling and tapping.
The use of thread milling is increasing and figures prominently in Emuge's recently introduced products. "Advances in machine tools have made thread milling an important holemaking process for a variety of applications including those in the medical, aerospace, defense, and computer industries," Matysiak says. "You now have CNC machines that fit on a table top, or if they don't, the larger machines have precision spindles and toolholders that can manage these small tools at spindle speeds to 60,000 rpm and higher."
Emuge's new series of miniature solid-carbide thread mills for machining difficult materials, such as stainless, titanium, K-Monel, Hastelloy, and Inconel eliminates the possibility and consequences of tap breakage, and the need for hand tapping during full bottom-threading applications. Bottom threading can be performed to within 1 pitch.
The miniature thread mills can be used for both through and blind holes, and produce excellent thread finish and gaging. "It all works hand-in-hand to be able to successfully tap or thread mill. You have to have extraordinary precision on the toolholding. That is absolutely critical so we don't produce a cutting tool without producing a toolholder that can hold the tool correctly," says Matysiak.
"The tiny scale of micromachining, along with the twin demands of production efficiency and a high return on tooling investment, typically relies upon solid carbide rather than steel as the choice for tooling construction," says Rob Keenan, president, Seco Tesco. "Three components—geometry, coating, and substrate—define the correct cutting tool for a given application," he explains.
Each workpiece material requires a slightly different carbide tool composition to optimize the tool's efficiency. A recent expansion of the Seco Jabro Mini line of end mills includes coatings, carbide grades, and cutting geometries that makes them well-suited to machining harder metals like hardened steel and titanium, softer metals like aluminum or copper, as well as highly abrasive materials such as graphite. These new tools are available in diam down to 0.1 mm.
Two new Seco Jabro Mini solid carbide end mill lines are available in diam from 0.1 to 2.0 mm with ball and bull nose end configurations. The JM100 series is specifically designed to machine tool steels hardened to RC 65, and the 400 series is intended for machining aluminum and copper. The Seco Jabro Mini series is complemented by a full range of solid-carbide cutters to provide highly productive machining for the range of applications in markets such as mold and die, medical, aerospace, or general engineering.
In small-size mold and die applications, high precision is key for producing smaller items with tighter tolerances and better surface finish. "Even though everything is smaller, in a way everything is exaggerated—the ratios can be extreme—you might be using a 2-mm diam tool that is 30-mm long, a 15:1 length-to-diam ratio," explains Jay Verellen, product manager of rotating tools, Seco Tools Inc. (Warren, MI). "Imagine trying that in an automotive application where you've got a 2" [50.8-mm] diam tool—no one would think of trying to machine with a 2" tool that is 30" long," he says.
Swiss CNC turning continues to grow in importance as more and more manufacturers recognize its versatility in machining precision engineered components. In every respect, Swiss CNC machining is every bit as complex as multitasking machining, and possibly more so because of part size.
Parts are machined from bar, typically to 32-mm diam. Bar advances through the sliding head, with work being done on the main spindle as well as often on the back spindle, with several tools working simultaneously. Programming is still complex, but many CAD/CAM software companies, such as PartMaker Inc. (division of Delcam Plc), have introduced software to facilitate its use.
"These Swiss machines have between 10–15 axes for machining parts complete, whether rectangular, circular, or any shape that you can imagine," explains John Dotday, Sandvik Coromant Co. (Fair Lawn, NJ).
"What makes these multitasking machines different is the sliding headstock. Instead of the turret moving in the Z axis, the bar moves in a Z direction, feeding the bar out with the turret moving in to make a cut. As a result, machining is very rigid, with the cutting done close to the guide bush. The tool is only about 0.040–0.080" [1.02–2.04 mm] away from the guide bush. The tools and the material are so rigid that you can take heavy depths of cut and produce parts with excellent finishes without any vibration marks on them," Dotday explains.
"OD turning is done with positive inserts. The CCET, DCET, and VCET inserts we introduced a year ago have a very sharp edge line, almost dead sharp," Dotday says. "They are capable of taking heavy depths of cut, which is a requirement of Swiss machining. The part has to be turned down to the diam size in one shot. Tools must have the capability of taking heavy depths of cut, but at low feed rates—between 0.0008–0.003" [0.02–0.08 mm]—with DOC 0.100–0.200" [2.54–5.08 mm] on a variety of materials."
"Probably 60–70% of the Swiss machining is going to be used in the medical device industry for bone screws, trauma plates, and the like," says Dotday. "We are seeing a lot of materials such as 300 series stainless, 17-4 PH, a lot of titanium, cobalt chrome, Inconel 718, and hard part-turning of steels."
US industry is just now discovering the advantages of micro tooling for medical, electronics, aerospace, and high-speed mold and die machining. "There is a lot of use of micro tools in Japan, as well as in Europe," explains Sherwood Bollier, president of Niagara Cutter (Amherst, NY). "The use of these tools is just starting to catch on in the US," he says.
"The potential continues to grow. The number of precision high-speed machine tools that are available to machine with carbide end mills from 0.005" [0.13 mm] and up is increasing," Bollier says. Much of the work is proprietary, but micromilling and miniaturization are fueling the interest of manufacturers as well as driving cutting tool suppliers to capitalize on the potential for growth.
Typical applications, in addition to small precision medical devices and components, include electronics, aerospace, and hard-die milling, as well as highly specialized applications in machining precision metals and gold jewelry. The increasing availability of high-speed precision machines from leading machine tool builders, including Sodick, Makino, Roku Roku (MC Machinery), Roeders, Mikron Corp. (Monroe, CT), Datron, and Kern, is a key driving factor.
Niagara Cutter has introduced a MicroTool line of small-diam precision carbide cutting tools designed for use in the electronics and medical machining industries. Available in two-flute and four-flute configurations, the MicroTool line includes square and ball-style end mills with diam ranging from 0.005 to 0.120" (0.13–3 mm). In addition to the standard uncoated carbide tools, MicroTools are also available with a proprietary TiAlN coating to enhance tool life and performance.
There are more than 30 standard product styles (square-end, ball-end, stub, regular, long, long-reach) in two, three, and four flute, ranging from 0.005 to 0.125" (0.13–3.2 mm) in increments of 0.001" (0.03 mm), with options for uncoated or PVD TiAlN or CVD diamond coated. Micro end mill customers also order a high percentage of special blueprint products, designed for their application. Smaller diameters (less than 0.005" or 0.13-mm) are available as special products.
"When I think of micromachining, I think of machining that's actually done under a microscope, with drills smaller than a needle or with end mills down to 0.006" [0.15-mm] diam and drills down to 0.003" [0.08 mm] for computer circuit boards," says Kerry Cranford, product manager for global small tools, Kennametal Inc. (Latrobe, PA).
"The biggest growth right now in small parts machining relates to Swiss machining, Swiss automatics, small lathes, and gang-type machines, especially for medical and dental applications," says Cranford. Small replaceable-type solid carbide tooling and small indexable cutting tools form the basis of the new comprehensive small-parts machining catalog that Kennametal will introduce in 2008.
Swiss turning tools will include a full range of ID and OD tooling. "On the ID side, boring tools will be available that go down to a 0.010" [0.25-mm] minimum bore, which is smaller than a needle, and tools will be able to profile in a 0.062" [1.6-mm] diam hole, groove within a 0.110" [2.8-mm] diam hole, and thread down to a #5, which is a 0.100" diam hole. Face grooving tools can be as small as 0.016" [0.41 mm] and even range to 0.010" [2.8 mm]," he says.
Small replaceable-type solid carbide systems and holders feature Kennametal's KM micro system, which allows the users to replace interchangeable heads in the machine itself, so that all these OD and ID operations can be performed from one toolstation.
"When we talk about the indexable portion of this system, the smallest minimum bore that the indexable tools will go into is 0.180" [4.8-mm] minimum bore. This is an 80° diamond insert that comes with chipbreakers, and all the coated grades that are presently being used with specific grades for the titanium and stainless, for example. We also offer indexable threading and grooving inserts that you can put in the same bar and do work within a 0.272" [6.9-mm] diam hole, as well as indexable inserts for face profiling, profiling inserts."
Mikron Corp. Monroe (Monroe, CT) now offers another line of small to medium-sized cutting tools for high-end precision-engineered small parts machining, including medical, dental, high-speed communications, nanotechnology, fuel injection, micro hydraulics, and pneumatics components. Its standard drill lines include the CrazyDrill for high-speed drilling in longer production runs, and the recently introduced MiquDrill for shorter production JIT runs.
The MiquDrill features three types of drills: center drills in various diam from 0.5 to 6 mm for the smallest drilling diam starting at 0.5 mm, while simultaneously performing a 90° or 120° chamfer. The short drill MiquDrill 200, drills holes approximately 2–3 x D, up to diam 1.5 mm. The universal MiquDrill 210 is available for diam 0.1 to 3 mm. Both drills are designed for micromachining, and are available uncoated in diam down to 0.1 mm, and coated from 0.3 mm in increments of 0.01 mm, up to diam 2 mm, and subsequently in 0.05-mm increments to the maximum diam of 3 mm.
"The MiquDrill is a two-flute solid, made of a high-quality micrograin substrate just as is the Crazy Drill, however the geometry is different from the CrazyDrill. It gives the manufacturer a lower cost-per-piece option for drilling in shorterrun JIT jobs," says Robert Couture, manager technical salestooling. The MiquDrill is well-suited for medium batch quantities and minimal holes per workpiece.
Iscar Metals Inc. (Arlington, TX) continues to improve machining methods, overcoming the heat or abrasion associated with machining small parts from exotic metals, explains Andy Kelling, national screw machine manager. "The challenge always is to fight against the breakdown of carbide tools under extreme pressure and intense heat. Often times exotic materials overcome the hot hardness of conventional carbide grades," Kelling explains.
"Synthetic crystal, ultra hard cutting tool materials (PCD/PCBN), and in some cases cermets, are very effective, and so are newer carbide grades, coatings and surface treatments like Iscar's new Sumo grades," says Kelling. "We also employ sophisticated chip forming geometries as well as edge preparations, which have the effect of making brittle cutting edges stronger. Coatings such as TiAlN can be effective."
The Picco MF (multifunction) and the Picco MFT (multifunction with threading) tools are intended for use on Swiss machines and for producing miniature parts, as well as for other applications. The Picco MF can be used for drilling, face turning, internal chamfering, internal turning/boring, internal profiling, external chamfering, and external turning. The Picco MFT tools can perform all of those applications in addition to internal and external 60° threading. The MF and MFT tools are available in both right and left-hand orientations for twosided machining operations, in 4, 5, 6, 7, and 8-mm diam with a DOC ratio of two and three times diam. In addition, each tool is produced with an external ground slot to help direct the flow of coolant to the cutting edge.
For machining hardened steel with RC 48–65 hardness, NS Tool's two-flute micrograin ball end mills feature a Mugen coating and new design to improve chip removal and reduce chatter. "Hard milling molds, dies, punches, and even production parts is becoming more and more popular in North America," says Doug Kline, Single Source Technologies (SST; Auburn Hills, MI). The new tooling is available in 0.05–3-mm radiuses and in standard and long-neck versions.
This article was first published in the January 2008 edition of Manufacturing Engineering magazine.