Advances in laser piercing
- November 20, 2011
Productivity and quality start with that first hole
by Jim Barnes
The productivity and quality of a laser cutting operation start with the piercing process.
The technology has changed significantly over the past decade as laser machines have become more powerful, more flexible and more automated. Programming has evolved too, and older piercing routines have been updated and new ones developed.
Popular methods include:
Piercing on the fly Essentially, this means no piercing, with the machine launching straight into a cutting routine. With zero time allocated to piercing, substantial gains in production can be made on sheets with large numbers of holes. The technique works best in the 16 ga. (1.51 mm) and thinner range, on mild and stainless steels or aluminum, notes Drew Schneider, product applications manager, Cincinnati Inc.
Pulsed piercing In these routines, power is increased step by step as you deepen the hole for maximum precision. "It keeps the material from heating up, prevents excess spatter and allows you to cut much smaller holes," notes Steve Aleshin, applications manager, Salvagnini America Inc.While pulsing (accurate) pierce time might be 0.01 sec. for thinner materials, it could be five sec. or more for thicker materials of half-inch and up.
Fast piercing This is the quickest way to burn a hole. "In the past, when we did a blow-out pierce, we would turn the resonator up as high as we could, open up the shutter and give the top of the material a huge jolt of energy. It would pop through thick plate in a matter of a second or two, instead of the 25 seconds pulsed piercing might have required,” says Keith Leuthold, director of sales, Mazak Optonics Corp. A crater normally resulted.
The challenge was to combine speed with quality, and control the beam more accurately.
On some machines, the laser optics inside the machine are flexed, to move the focal point on the fly and vary the energy applied to the part. Cincinnati Inc. uses an adaptive optic. "We use pressure on the optic to change the beam size,” notes Schneider. With the auto-focus head, you can adjust focus while you’re piercing.
Mazak developed what it calls a "servo-pierce." A servomotor on the side of the torch adjusts the lens inside the torch as piercing takes place, changing both the focal point and the power. The effect is the same as flexing the optics mechanically, without the potential for wear to the optical system, says Leuthold. "We can break through the material very quickly–just about as fast as a blow-out pierce–but we have a pinhole just as though we did a pulse pierce.”
Nozzle design is also being improved. LVD Strippit addressed the challenge of merging speed with precision with its CDP (Closed During Piercing) nozzle.
Some operators use a small nozzle to pierce the entire sheet, and then go back with a larger one for cutting. LVD Strippit saw a way to simplify that process. "For piercing, you need a small (nozzle) opening in order to have a small start hole, instead of a big crater,” says Stefan Colle, product manager for laser machinery. "For cutting, you need a bigger opening, to evacuate the melted material quickly using a low gas pressure.” LVD Strippit developed a nozzle that can be used both for piercing and cutting, eliminating the need to change nozzles.
Major improvements in controls have come over the past five years.
"The controls, in general, are much better than they were just a few years ago,” says Aleshin. The Salvagnini control has a database of tables and parameters. "When I put 20 ga. (0.91 mm) stainless steel on the machine, (the control) knows what parameters to pull off,” he says. If a change is required, you can make it quickly by calling up a tool (set of parameters) and clicking on the pierce tab. "It’s Windows-based and very user-friendly,” explains Aleshin. There are multiple cycles, depending on the type of pierce used.
This kind of advance can be surprising to users who have not kept current with laser cutting technology. "They're shocked when they see what today's technology has to offer,” says Schneider. "Modern controls offer much greater ease of use than the older units did.” All the programming and nesting can be done right on the control by the operator while the machine is cutting. "The learning curve is a lot shallower, too,” says Schneider.
"It's a common misconception that you need a highly trained operator to run one of these (laser) machines,” says Leuthold. He notes that there are two types of machines commonly available; manual setup and automated setup.
With the conventional, manual setup laser, an operator with a certain skill set is required to set the machine up. However, some users don’t take the time to set the machine up properly–especially with small jobs. The savings in time are offset by loss of productivity and quality, and excessive use of gases.
With an automated laser, most of the set-up data is built into the control. The machine automatically changes out the torch, the lens and the nozzle and sets the focal point automatically. "With these machines, we can do an entire set up in one minute, versus 15 minutes for a manual machine,” says Leuthold. That can add up quickly when you have a number of setups each day.
Ease of use has been a major focus in most control design. "We have simplified the user interface across the product line. It's all touchscreen,” says Colle. With similar interfaces, "a press brake operator can now easily migrate to laser,” he says.
Optical sensors have increased laser piercing productivity. Conventionally, operators typically program extra piercing time into the system to make sure the pierce is complete before cutting begins. If you have 300 parts on a sheet and allow an extra second on each pierce, that’s five minutes wasted on each sheet.
With the optical sensors, the control is informed when the pierce is complete based on reflected light.
Then, the system moves on to the next operation without delay. Because the amount of energy introduced into the material is controlled, the quality is better, permitting a smaller pierce.
This technology is still under development for fibre lasers, though. "When you pierce a hole, you create a plasma. When you create that plasma with a CO2 laser, the laser is partially absorbed by the plasma. It’s invisible to a fibre-optic laser,” says Aleshin.
What can users expect from laser piercing in the future? Leuthold identifies four areas where advances can be expected advances.
1. Larger resonators. At present, a 6,000 W laser can process up to 1.5 in. plate. There is a need for even more power than that.
2. Operations will be combined. As many operations as possible will be done while the material is on the table.
3. Further reductions in setup time.
4. Energy savings–for example, with fibre-optic lasers.
Laser technology is fairly mature. But in recent years, incremental improvements have been made that can definitely impact your bottom line.
Jim Barnes is a Toronto-based freelance writer with more than thirty years of experience in business journalism.
Top image: Mazak Optonics