Honing Is a Life-Saver for Aerospace Component Maker

While the OD is machined to standard dimensional tolerances and is repeatable, the ID must meet tolerances of 5 microns to 7 microns (0.0002 in to 0.0003 in).

The ID surface finish of the fuse pins is also critical, and while the precise surface finish specs are proprietary information, Franks says they fall in the range of 8 RMS to 16 RMS.

Consistent size and finish of the ID are very important, as size variations or surface irregularities could affect the performance of the pin.

The ID geometry of the fuse pins can vary from a thru hole to a blind hole with an angle and a radius, or just a bottom radius.

To achieve this delicate ‘hold-or-fold’ balance, Sonic relies on a new Sunnen SV-1000 CNC honing system to produce the 5 micron to 7 micron ID tolerance and proprietary finish that are critical to the part’s performance.

Prior to acquiring the SV-1000, Sonic honed fuse pins manually with Sunnen MBB 1805 and CV-616 machines.

“We needed to increase productivity and decided that automating the honing process was the best way to accomplish it,” said Roy Franks, the facility manager of Sonic. “Before purchasing the SV-1000, we conducted time studies with Sunnen that indicated we could achieve the production levels we were looking for. The new system has since exceeded the time study estimates and the finish is superior to the previous manual-honing method.”

In fact, the SV-1000 allowed Sonic to meet increased customer demand when it replaced the manual honing system, reducing cycle times from 40 minutes to 10 minutes and increasing productivity from nine parts to 40 parts per day.

By upgrading to the new system, Sonic is now able to use Sunnen MMT superabrasive tools that achieve the required micron-level accuracy.

These tools are specifically designed to work with SV-1000 series machines. Each tool is custom-engineered to the application based on width, length, expansion angle, and number and placement of stones.

This customization produces accuracies of 0.0006 mm (0.000027 in) for diameter, roundness, straightness and taper. MMT tools are precision-machined with a body and feed wedge made from hardened tool steel, and typically last five times longer than conventional designs, reducing per-part cost by 30 percent.

More importantly, the custom design of the tools allows placement of abrasives to cope with challenges like blind holes.

Another advantage for Sonic by going to the SV-1000 is the machine’s longer stroke length. “Our old machines were labor-intensive and had a maximum stroke length of 9 in,” recalled Franks. “They limited the parts we could produce. But now we’re able to make more sizes, and we’re doing it faster.”

The SV-1000 handles diameters up to 3 in and has a 31 in stroke length.

Automating the honing process also freed up machine operators to attend to more than one machine.

“With the manual hones our process was hone a little, then check the part, hone a little more, then check the part again.” explained Franks. “With the CNC hone we ‘dial in’ the settings on the machine and 99 percent of the time the part comes out to spec. That means the operator can have one eye on the honing machine and one on another piece of equipment.”

After honing, parts are measured using a scanning air gage.

Sonic was able to achieve a more than 300 percent increase in productivity, but Franks thinks that number can climb even higher.

“We didn’t get the rotary table that can be attached to this machine. We could bump up productivity even more by loading three parts in the rotary table and continuing to hone parts while others are being checked. We’re looking at possibly purchasing another SV-1000 and we’ll be considering the rotary table with that one.”

Sunnen Products Company, 7910 Manchester Road, St. Louis, MO 63143, 800-325-3670, Fax: 314-781-2268, www.sunnen.com, sales@sunnen.com.