One emerging technology that is receiving notable attention is ultrasonic-assisted machining, or—more strictly speaking—rotary ultrasonic vibration-assisted machining, sometimes referred to by a simple acronym, UAM. Wikipedia has published the acronym RUM in its explanation of the process. Time will tell which one wins.
Certainly the technology is a winner as evidenced by impressive, practical results. Essentially the equipment is a hybrid of a three- to five-axis VMC combined with high-speed spindle rotation and high frequency vertical vibration of a diamond abrasive cutting tool. Unlike older ultrasonic machines (USM) that create an abrasive liquid slurry that covers the tool tip and workpiece and microchips material, UAM uses a cutting tool coated with polycrystalline diamonds that grind down the surface of the part. The rotational speeds on the UAM-assisted technology we represent from Tongtai are up to 24,000 rpm. The vibration frequency is in the 15–45 kHz range, and the amplitude span is 1–10 μm. Essentially this approach impacts the material with higher contact speed and thereby reduces the cutting forces. Forces are reduced as much as 30–300% depending on the material. As such, most of the benefits surround surface finish and integrity—finishes with an Ra of less than 0.2μm are possible and there’s a great reduction in surface and subsurface damage, such as microcracks and chipping. Naturally with less force, tools last longer, too.
Most of the questions we answer about the technology involve applications such as, “What are the most ideal parts for ultrasonic-assisted machining?”
As both our team of applications engineers and our customers are gaining experience in this burgeoning technology, here are sound guidelines: First, with regard to materials, consider those that are softer than the diamond cutting tool or hard and brittle. For instance, zirconium dioxide, aluminum oxide, aluminum alloys, ceramic, silicon and tungsten carbide, a wide variety of steels, titanium, Inconel and quartz are good candidates for this process.
Second—and you’ve likely guessed by the parameters provided so far—microdrilling is highly successful with UAM. Silicon wafer drilling quickly springs to mind as an example as do other parts with small holes that may be created currently with EDM or laser cutting technologies. Many parts with a vertical orientation machining approach that also require a superb finish could also move onto a rotary ultrasonic-assisted VMC. Molds, for example, are rough machined in the conventional VMC mode and the UAM mode finishes, polishes and deburrs in one setup, saving time and improving geometrical accuracy. In one case involving a jewelry mold, the customer slashed time by 40%. Dental molds are another ideal application for the system as are certain medical prosthetics and instruments. In the automotive industry, companies are realizing the benefits of using UAM in valve deburring. In aerospace, the process is being used to drill compression veins and to give titanium blades a precise surface finish. Manufacturers working in ceramics and glass are using it to drill, polish and chamfer parts. Tongtai has published that in the exact same cutting conditions of an intricately designed workpiece in Al6061 the following finishes were achieved:
|Without UAM||With UAM|
|Rmax 3.28 μm||Rmax 1.28 μm|
|Rz 3.13 μm||Rz 1.43 μm|
|Ra 0.44 μm||Ra 0.20 μm|
Occasionally the question surfaces about the pros and cons of wire EDMing versus UAMing. While the initial equipment investment for a UAM is higher than a basic EDM package, the ROI can be quicker with UAM as long as the applications are suitable. Also, there are essentially two machines in one with the VMC/UAM configuration, providing users with tremendous versatility. If the parameters outlined here are similar to the work you frequently do, then it is worth your time to explore UAM further.