Several manufacturing operations are available for the fabrication of micro parts, components with feature sizes less than 1 mm. Such operations include micromolding, microforming, laser machining, and mechanical micromachining, to name a few. Our focus is on mechanical micromachining.

Like its macro counterpart, mechanical micromachining uses a rotating cutting tool to remove material in the form of chips. However, extensive research shows that micromachining works differently than conventional machining. Cutting mechanics (the way a tool interacts with the material) and process parameters (feeds and speeds) do not translate directly from the macro world to the micro.

Micromachining handles a wide variety of materials from plastics, aluminum, and brass, to stainless steel and titanium. Ceramics, glass, and many exotic materials can also be shaped by micromachining. Other fabrication methods, such as microEDM, require that materials have appropriate electrical or chemical properties.

Of course, designing for manufacturability is critical. Feature dimensions are limited by the sizes and types of cutting tools. So, in a design phase, it's important to keep an eye on manufacturing by asking questions such as, “What cutting tools are available that will let me machine these features?”

The right tool lets micromachining produce a wide variety of geometric features. Micromachining is usually performed on three, four, or five-axis CNC machines, so it's not difficult to generate full 3D free-form geometry, such as smooth contoured surfaces.

Microlution's three-axis micro-milling machines, for example, address problems associated with cutting small parts on large machines. What's more, the machine's 4 ft² footprint lets it easily fit in an office, laboratory, or on a production floor.

Available with the machines is a 36 pocket automatic tool changer (ATC). It supports cutting tools ranging from 0.002 to 0.125-in. diameter. The tools are held in a rotating carousel with a robotic arm that moves them between the carousel and spindle. Users can easily remove and replace the carousel. In situations where a machine is running more than one job, each can have its own tool carousel, for smooth and quick transitions between setups. Tools are directly chucked into the spindle, eliminating the need for a tool holder. The ATC includes a built-in tool tip sensor that uses a laser to determine tool stick-out length and diameter.

A ball-and-vee kinematic mounting system for the spindle and the workpiece pallet lets users remove and replace both with sub-micron repeatability. This allows interrupting a machining operation, removing the workpiece pallet for inspection, and replacing it without reregistering the part.

When a machine is used for many jobs, each can have its own kinematic workpiece pallet. This lets several users easily transition from one setup to another without losing part registration. Such mounting also allows removing and replacing the spindle with, for example, a laser distance-sensor to perform metrology operations (for instance, surface roughness or profile measurements). The machines are built on precision-ground granite bases. And they incorporate ac linear motors and Heidenhain linear optical encoders on the X, Y, and Z stages.

If frequently encountered, it might be wise to establish a micromachining capability in-house. This lets engineers make quick design changes and fabricate prototypes from functional materials. Product design then goes faster and less expensively than with outsourcing.

HOW TO PROTOTYPE BIOMEDICAL PARTS

A medical-part manufacturer found that by machining small parts rather than micro-injection molding them, it could cut tooling costs and chop five weeks off its product development. “Microlution eliminated $30,000 in up-front tooling costs and machined the parts for us in only three weeks,” says Dan Repplinger, Director of Engineering, Knowles Electronics, Itasca, Ill (www.knowles.com). Microlution builds the 363-S micro-milling machines and also contract manufactures parts in-house. “Outsourcing the job helped us quickly get prototypes of our design concepts in functional materials so we could generate meaningful data and results.”

SOURCES OF MICRO CUTTING TOOLS

Micro-cutting tools can be hard to find at companies that deal mostly with conventional cutting tools. However, a Google search on “micro cutting tools” uncoveredseveral sources. For instance:

• Microcut Inc., Kingston, Mass., (microcutusa.com) provides end mills down to 0.002 in. diameter.

• American Carbide, Boston, Mass., (american-carbide.com) provides micro end mills, ball nose mills, and long reach mills.

• Harvey Tool, Rowley, Mass., (harveytool.com) provides a selection of miniature ball end mills, square end mills, and tapered end mills.

• Kyocera, Irvine, Calif.,(www.americas.kyocera.com) provides tools made of submicron grade carbon with optional coatings available. An example is a 0.015-in. diameter two-flute end mill.

• Performance Micro Tool, Janesville, Wisc., (pmtnow.com) provides tools such as two-flute standard end mills with cutter diameters as small as 0.001 in. The company claims to provide the smallest end mills in the world, which range from 0.0002 to 0.0009-in. diameter.