Chasing that Roadrunner …and Thermal Growth

“Roadrunner, if he catches you you’re through. Roadrunner, the coyote’s after you.” As an engineer I’ve always had a soft spot for Wile E. Coyote. The self-described super genius always seemed to identify the best “technology” required to catch the Roadrunner. He just never seemed to apply it correctly…and then looked at us sadly as he fell off yet another cliff. Luckily he always lived to chase another day. Beep. Beep…

Thermal Growth – As Hard to Catch as the Roadrunner

There is a point here for the real world. Old “Wiley” usually had the right idea – predict where the Roadrunner would be (by putting a pile of corn in the road, and then trying to drop an ACME anvil on his head) – but he never accounted for unpredictable events that would cause the Roadrunner to move over a step or two. When you are chasing microns or tenths in the CNC machining process, predicting heat deformation of the machine is just as elusive. Having that "crystal ball" would make life much simpler.

25 Years of Test Data Hold the Secrets

But there is a solution for thermal effects on CNC machining that would make even the Coyote smile. Okuma’s “Thermo Friendly Concept” is uniquely designed to do just that. Everyone purports to have Thermal Compensation but that’s not the whole story. For the last 25 years Okuma has been studying the effects of heat (and cool) on the CNC machining process. Our temperature-controlled test chamber was installed in 1987. By analyzing reams of test data we have engineered the perfect balance of CNC machine design and compensation algorithms that ensure your results stay within tolerance, without constantly chasing size with operator-entered tool offsets. This holds true whether you’re cutting the first part at 8 a.m. when the shop is cool (with NO warm up cycle, BTW) or you’re finishing up the last part with the sun beaming through the windows directly on the spindle head.

How Do We Do That?

It starts with two critical aspects of the CNC machine design:

• First, we take advantage of mechanical symmetry everywhere it is possible. For example, our mills are designed with bridge-type construction to ensure that the machine grows in predictable directions. This is not possible with typical C-Frame mills that bend in angles that are not predictable, rendering compensating for the deformation nearly impossible. Similarly, our CNC lathe platforms are designed to keep the spindles and axes in the same plane to ensure inevitable thermal growth also occurs in the same direction.
• Second, isolating all heat sources from the casting is essential and integral to our CNC machine construction. Those ballscrews won’t turn without electric motors, and electrical cabinets generate heat. And as much as we’d like to eliminate hydraulics, hydraulic pressure is still the most effective means for clamping a chuck or tool. So we mount them both away from the casting. Oh, and those hot chips? Special thermal covers insulate the castings, and coolant flush systems get the hot chips out of the cutting area immediately. Keeping all of these heat generators off the casting is a critical factor in our CNC machine construction. It costs a bit more, but it makes a big difference!

But there’s still the question of unpredictability. That’s where the CNC control steps in.

• Okuma’s THINC^®-OSP control is unique in our industry. Having control engineers and mechanical designers in the same building is an advantage no other builder enjoys. All those reams of data have been the basis for the development of our Thermo Active Stabilizer (TAS) system for real-time compensation. TAS is the third leg of our “Thermo Friendly Concept” and involves TAS-S (Spindle) and TAS-C (Construction), which monitor strategically placed sensors on the castings and the spindles to automatically compensate for thermal effects. This allows you to maintain 5 microns (0.0002”) tolerance over an 8 degree Celsius (46 F) temperature change (e.g. LB-3000EX). You don’t chase the offsets, we do it for you!

Seeing is believing…bring us the parts you cut over the course of the day and we’ll show you the difference that saves time, money and aggravation.

Are you as frustrated as Wile E. Coyote? Comment below, or contact us and let’s talk about managing your thermal growth. That Roadrunner can be caught.

Brian Sides is Director of Technology, Okuma America Corporation