Understanding and applying indexable microtools

Many part manufacturers don’t think indexable tools and micromanufacturing are a good match. In reality, indexable tools are often used in conjunction with Swiss-style CNC machines to produce parts down to 0.005" in diameter.

On a daily basis, indexable tools are used on Swiss machines to produce dental implant screws, watch parts and circuit board components, all of which fall into the micromanufacturing realm. Proper application of indexable tools can provide machine shops with a competitive advantage in serving these markets.

A dental implant single-point-turned on a Swiss-type lathe. Photo courtesy of Sandvik Coromant.

Tool maintenance is a good place to start when evaluating the use of indexable tools in micro applications. Proper maintenance of the toolholder directly affects tool life, component quality and machine downtime. Each time an insert is changed, inspect the toolholder for stripped screws and debris in the insert pocket, and for damaged inserts, shims or mounting surfaces.

To maximize tool performance over time, follow recommended torque specs for the insert screw. An anti-seize compound is applied to the screw before you install the insert. This anti-seize treatment eliminates the transfer of heat to the screw and, without it, significant levels of heat can weld the screw to the tool holder. Also, be sure to clean insert pockets when replacing an insert and always discard damaged tools.

Choosing the proper feeds and speeds can dramatically improve microtool performance. At the start of this process, identify the material type and diameter, machine type, component fixturing, machining process, coolant type and coolant pressure. Once these questions have been answered, a proper insert grade and geometry can be selected.

At this point, initial feeds and speeds are determined. As an example, Figure 1 shows recommended feeds and speeds for a turning tool with a 0.002" nose radius and a 0.01" DOC. Notice that feed rates are relatively low. This is because excessive pressure will break microtools. Also, use an uncoated carbide grade for aluminum and titanium, and a PVD-coated grade for steel and stainless steel.

Once starting values have been determined, it is time to observe the tool in the cut. The first thing to examine is chip control. Are chips breaking cleanly or are they long and stringy, wrapping around the workpiece and tool? If it’s the latter, gradually alter the feed rate at an increment between 0.0002 ipr and 0.0005 ipr. If these adjustments fail to solve the problem, reset the feed rate to the starting parameters and raise or lower the cutting speed in 10 percent increments. Should chip issues persist, the initial cutting speed should be reinstated, with DOC increased or decreased by 0.002". Changing one parameter while others are held constant identifies the cause of the problem.

Figure 1: Recommendations for a turning tool with a 0.002" nose radius and operating at a 0.01" DOC.

Coolant is the final area to consider when applying a microtool. Due to pressure from the U.S. Environmental Protection Agency and the costs associated with waste disposal, many companies are moving away from using coolant. New inserts have been designed to provide extended tool life and excellent surface finish without using coolant.

Despite this, there are still important benefits to using coolant in some applications. Where extreme tolerances are required, coolant helps maintain workpiece temperatures. It can also play a significant role in drilling and boring operations, aiding in chip evacuation and surface finish. High-pressure coolant systems can even help break chips when working with difficult-to-machine materials, such as heat-resistant superalloys and stainless steels.

Micromanufacturing can be challenging, but an unprecedented number of technologies have been developed to help companies succeed in this growing industry. By understanding the basics in key areas such as tooling, manufacturers have a much better chance of successfully meeting the market’s unique demands. µ 

About the author: John Dotday is business development specialist at Sandvik Coromant Co., Fair Lawn, N.J. Telephone: (201)794-5075. E-mail: john.dotday@sandvik.com.