Thick-to-thin laser cutting enabled by improved controls, linear drives. (Applied Solutions).

Jimmy Gay
1,479 words
1 November 2002
Control Solutions
ISSN: 1532-1274; Volume 75; Issue 11
English
Copyright 2002 Gale Group Inc. All rights reserved. COPYRIGHT 2002 PennWell Publishing Co.

When machine builder W.A. Whitney embarked on the development of its PlateLASER, the company had a specific goal in mind--namely, to respond to an emerging market for a thick-to-thin laser cutter (Fig. 1).

We at Whitney had considerable plate experience with our laser and plasma technologies, but saw an opportunity to develop a machine that could run the broader material gamut, in the downward direction. However, rather than simply engineer a lower-powered laser, we wanted to investigate ways in which to take a 6 kW cutter into the thinner material range, without creating the proverbial hull in a china shop. We already had plate customers that were either passing up thin gauge jobs, or immediately thinking they needed a different machine.

Some of the challenges we faced included the need to vary assist gases, the wide speed ranges encountered with these jobs, residual heat and "crater eruption" when piercing thick plate, automatic lens focal adjustment to accommodate the wide variety of materials processed and, of course, cost factors. No machine then on the market had the ability to cut 1 1/4 in. down to 22 gauge aluminum with position accuracy to 0.001 inch, plus speeds to 7,000 ipm. Difficult as they were, we set these as our goals (Fig. 2).

Control challenges

Software engineers Bill Long and I worked on the control challenges for Whitney. After we selected our laser/resonator supplier, we needed a third party with independent PG-based controls capable of handling the linear motor drives, all the cutting and machine speeds from 7000 ipm down to 8 or 9 ipm with satisfactory accuracy, and a flexible laser compile cycle to allow us a lot of different scenarios. We wanted, for example, the ability to create a control cycle for walk-away thin cuts, synchronous actions on contour cutting, varied laser power for cornering and piercing on a wide thickness range, and more. These requirements left all but a handful of suppliers out of the running. When we added the 6-axis movement, a 7th-axis option, plus all the application engineering, service and next-day replacement part provisions, the field narrowed even further. In the end, only two suppliers were considered.

After an intensive review, the decision was made to implement a Siemens Sinumerik 840D control package, as well as the company's direct drive linear motors on the PlateLASER.

The Profibus-DP interface allowed us to program the I/O schemes on the fly, making adjustments as our remaining curve dictated.

Our customers are pleased, too

One of Whitney's PlateLASER customers was very pleased with the control package's advantages. Observed Gary Geller, president of Lasertron in Sunrise, FL, "The machine control takes a huge load off the operator, plus the program is simple, presented in plain language, and features a terrific job parameter library. Focal length, nozzle, and gas-assist pressures, contour and corner retrace, and frequency and duty cycles are all there in plain English, for pre-production or in-process set-up and adjustment." The PlateLASER control operates on Windows NT with a Pentium[R] processor and 20 GB hard drive.

Geller continued, "When you're piercing such a wide variety of materials and material thicknesses [Lasertron does 22 gauge carbon up to 11/4 in. stainless], you encounter myriad pierce point speeds and cutting conditions [Fig. 31. The adjustments we need to make on the fly are pretty incredible sometimes and the PlateLASER control handles them easily. We'll often go at 400 ipra on a straight cut, then ramp down to 75 ipm for a .050 in. diameter hole with no problem. Likewise, the holes in thick-and especially stainless-materials were always problematic for our older laset; which had less power and motion control."

Lasertron also specializes in prototypes and some very large stainless pieces, made for the Disney World amusement park. Though his PlateLASER was purchased for production cutting, the combination of power, size and speed were beneficial for Gary Geller's overall product throughput. The PlateLASER accommodates workpieces up to 80 x 160 in. and 4,600 lbs., plus the dual shuttle tables are a real time saver (Fig. 4).

At the heart of the machine, however, are the Whitney ILC (Intelligent Laser Control [see Figure 5 on page 40], featuring the Siemens CNC) and MPL (Material Parameter Library). "Our operators," said Geller, "love the PlateLASER, because the precision results are so predictable. You get the same thing, time after time."

With linear motor drives onboard (see Figure 6 on p 40), the machine motion keeps up with cutting speed, especially on thin materials, and that's critical to the use of this machine for such a broad spectrum of jobs.

As Geller explained, "We added the PlateLASER to our shop floor specifically to cut thick plate and large parts, which it does quite well. But, it also consistently cuts thin gauge parts we formerly processed on lower-powered lasers. Today, we use this machine for everything thicker than 1/4 in. carbon or 3/16 in. stainless."

Thick and thin cut machines historically couldn't co-exist, because of the many differences in aperture, lens axis, focal point and beam delivery characteristics. So, we needed to rely on a CNc supplier, who had expertise and the manufacturing flexibility to get us where we needed to go with the PIateLASER.

Our reputation for quality plate processing in the market has been established for years. We knew there would be challenges because the size of the PlateLASER raises attendant stability issues, especially when the machine included our PlateHANDLER (Fig. 7). The overall Siemens control and drives package was a real plus for the integration of all these components onto one master module. Customers have been most impressed.

Another practical advantage on big workpieces was made possible by the additional control afforded by the Sinumerik 840D.

A retrace block search over a short section allows us to provide more precision in the cutting path, without always returning to the pierce point, as was the case with most previous machines. This results in a lot of auto start/stop functions, but the open architecture and controller power made it easy.

The combination of Siemens control and our in-house engineering resulted in a machine that can be entirely programmed off line, then run with no operator on-screen editing.

The linear motion drives have a real advantage over a rack-and-pinion system, which wears faster and loses a lot of accuracy, resulting in downtime. And, in this arena of machines, downtime can have a severe impact on a company's profit picture. By partnering with Siemens, we've heightened reliability tremendously.

We're talking about reductions in the pulsing in terms of microseconds, instead of milliseconds. The difference these controls can make are far beyond what anybody cutting plate could have envisioned just a few years ago. Best of all, we maintain weekly contact with our control supplier, because the technology is moving just that fast. We feel that there are new doors opening for us every day, because of this machine.

Gary Geller at Lasertron said he purchased his PlateLASER with the same idea in mind and has been most satisfied.