The need for delivering high-quality, tight-tolerance holes is growing significantly in many manufacturing segments, including aerospace, energy, transportation and medical. "Traditionally, this has meant dedicated jig boring or other fine-boring capital equipment requiring expensive setups, sister tooling, extensive operator training and time-consuming test cuts," said a Kennametal spokesperson.
Newly upgraded Romicron precision fine boring tools from Kennametal can be used on existing machine tools and produce finished bores in automated production with tolerances of a few microns in diameter (1 micron = 0.001 mm or 0.000039"). Using cartridges or boring bars, every Romicron tool can be adjusted in diameter with a dial ring in 2-micron increments to achieve close tolerances. To provide instant adjustment feedback, Romicron has a clicking mechanism so machine operators not only see the adjustment at the scale, but also hear and feel it.
The Romicron AVS tooling covers the diameter range of 25 to 79 mm (0.984" to 3.11") and can run in high-speed spindles up to 20,000 RPM. It accommodates standard ISO inserts, including the latest Kennametal Beyond tooling, and can run with high-pressure coolant systems up to 120 bar for better chip evacuation and reduced temperatures at the cutting edge.
The Romicron system consists of proprietary slide-gate mechanics that work similar to a transmission and translates an adjustment in a relationship of about 10:1. This means a small adjustment by the operator at the tool is converted into a still smaller change of diameter at the cut. The slide-gate valve mechanism is self-locking, so no clamping screw is required. The spindle is decoupled from the cutting force and the entire mechanism has nearly no backlash. "Almost no training or experience is necessary to use Romicron," said the spokesperson. "The nearly backlash-free adjustment mechanism allows adjusting to larger or smaller diameters without rotating more than required compared to numerous back and forward movements with conventional compensating for backlash. Since adjustments with the Romicron system are easy and require no tools or additional measurement devices, adjustments can be made on the machine for higher uptime and process stability. Some 'clicks' are done in a few seconds, other systems require at least minutes for adjustment."
Furthermore, because the Romicron does not require a lock screw or additional tools, the adjustment process can be automated by a machine tool's CNC, resulting in a closed-loop boring (CLB) system. With respective in-process measurement equipment, current hole dimension measurement data can be sent to a machine tool's CNC after machining. The CNC calculates the number of adjustment increments to bring the hole within tolerance. To achieve this adjustment the machine moves the Romicron tooling inside of the machine to a position. A retractable, spring-loaded locking pin is located and engages at respective CLB holes on the Romicron tool's adjustment ring. Based on the calculation, the spindle rotates the required increment to adjust the Romicron tool and continues machining until the next planned measurement and adjustment cycle. "Existing machines become capable of extremely close-tolerance hole finishing, increasing a shop's capabilities and productivity," said the spokesperson.
Tips for Ultra-Fine Hole Finishing
According to the spokesperson, "Romicron boring systems can produce finish bores with tolerances of a few microns in diameter and bore-to-bore variations of just a few tenths of a micron under ideal machining conditions, including the following:
- Stock removal of the finishing cut should be regularly and evenly distributed concentrically, and stock removal should be kept within 0.010 in. (0.25 mm) or smaller.
- Feed should be at 0.006 in. (0.15 mm) or less per revolution depending on the material to machine and surface requirements.
- Tool tip radius should be properly checked prior to boring.
- A tolerance equivalent to ISO precision class IT6 can be achieved under normal conditions. At larger sizes IT5 might be able to be reached as well.
- Solid, secure workholding is key. Thin-walled workpieces, for example, are prone to distortion and must be clamped properly.
- Special shanks may be required if bore lengths exceed 2.5 x D.
- Exotic materials must be carefully examined to determine best machining methods.
"Rules and recommendations are by nature general. For specific advice regarding ultra-high-accuracy boring, contact Kennametal or visit www.kennametal.com."
For more information contact:
Kennametal Inc.
P.O. Box 231
1600 Technology Way
Latrobe, PA 15650
724-539-5000
www.kennametal.com