BEYOND JUST BEING BENT

It is a popular misconception that telescopic steel covers used for machine tool protection are nothing more than some bent sheet metal parts. Perhaps 30 years ago, when machine feed and traverse rates were slow, a good sheet metal craftsman could have made a workable product. Today, at 2 G traverse rates, considerable research and development must be done to devise machine covers that will withstand such speed and acceleration/deceleration rates. Additionally, for these high rates, the shapes of telescopic covers are becoming more complex to keep pace with the intricate shapes of machine tool ways.

One problem to overcome is the dampening of shocks that occurs when the individual boxes telescope either toward or away from each other. The mass of each cover box is, in some cases, sufficiently substantial to destroy a box within a motion cycle, unless special designs allow for a gentle contact with each box. These dampening devices could be simple elastic bumpers, which smooth the shock or springs to decelerate the boxes and reduce impact or sophisticated shock absorbers, which dampen the shocks drastically.

Additionally, a variety of mechanisms are used to guide the boxes in parallel, avoiding "skewing" or uneven extension or compression of the boxes. Scissor-type equalizers have made a good improvement for medium speed telescopic steel covers. However, for high-speed covers, they did not satisfy the requirements. Through many trials and errors, the Hennig R&D (Machesney Park, IL) department finally devised a unique product termed the "High Speed Module," which was recently patented and has revolutionized high speed telescopic steel cover design.

This product is based on a chain and sprocket mechanism, which allows the boxes to telescope smoothly and in parallel, eliminating "skewing" at even the highest speeds. In order to test these "High Speed Module" designs, the company developed, engineered and built a high-speed test stand, with computerized controls to allow combinations of strokes, speeds and acceleration/deceleration rates, to simulate modern "High Speed Machining" centers.

The speed is variable up to 1312 ft/min (400 m/min). Acceleration can be adjusted to 4 G. These extreme values can only be achieved with a state-of-the- art linear motor drive.  Accelerated masses with forces up to 1304 ft-lb (5800N) can be tested.

Though it requires a substantial investment, this unique test stand allows the evaluation of new and innovative shock absorbers and dampeners, including the above described "High Speed Module" and thus enabled construction of high speed telescopic steel covers for use up to 656 ft/min (200 m/min) and accelerating rates to 2.5 G. 

Hennig, Inc., 2500 Latham Street, Rockford, IL 61103, 815-316-5277, Fax: 815-962-6483, www.hennigworldwide.com.