Managing nitrogen consumption

Fibre laser technology for processing sheet metal has matured rapidly in the past few years. From machines in the 2- to 4-kW range that were really only suitable for the rapid processing of thin-gauge material, we are now seeing systems on the market in the 8- to 10-kW range that can cut 1-in. mild steel and up to 1.180 in. stainless steel or aluminum. Some believe that CO₂ laser systems still produce a better edge in thicker materials than fibre lasers, but even that point is debatable. The time savings achieved with a fibre, as well as the flexible range of parts you are able to cut and the reduced maintenance associated with an absence of the optics required in the CO₂, are quickly making fibre the machine choice that CO₂ was just a few years ago.

One cost that does go up with the introduction of a fibre laser is nitrogen gas use. Nitrogen allows shops to achieve a clean, non-oxidized finish on edges, meaning that secondary operations aren’t necessary, particularly with thin parts. But the bill for that nitrogen can be surprising at the end of the month. However, there are ways to manage that cost. Canadian Fabricating & Welding spoke to a few experts on the subject.

Consider Cost-per-Part Value

All of the experts I spoke to were quick to note that the rise in nitrogen costs needs to be put in perspective: You are getting a lot more parts from that machine per week.

“Think of it in terms of a CO₂ laser,” said Hank White, laser applications engineer for Mitsubishi Laser. “If you’ve reached your full capacity on a CO₂ laser, you could buy a second CO₂ laser to double the productivity of your shop. That investment would double your nitrogen consumption. However, at the same power level with fibre you are getting two to four times the production, which is like adding two more CO₂ machines. But this doesn’t mean you are doubling your gas consumption. You may have less gas consumption in some of your thin materials. When you are working on material that is a quarter inch or thicker, then your gas consumption might be 25 to 40 per cent higher, but it’s never double.”

It's also important to note that the nitrogen flow rate generally remains the same regardless of the power of the machine.

“A 10 kW has a cutting speed of roughly double that of a 6 kW,” said John Kemp, manager for product support at Bystronic. “Yet in both cases, the nitrogen consumption is basically equal, so your nitrogen consumption per part goes down when using the 10 kW.”

So, the higher-powered machines not only offer more flexibility in regards to parts you can cut, but your speed goes up as your gas use decreases.

Nitrogen Generators

According to a number of experts, nitrogen generators have become more popular in the past few years. Although pricey, the generators essentially pay for themselves within two years.

“I would say a large number of the sales we are making right now have involved pricing out the option of buying a nitrogen-generating system,” said White.

“We recently installed a 6-kW machine for a customer that does most of its work in 7 gauge and has a very specific product line,” said Stefan Colle, laser product sales manager for LVD Strippit. “Everything in their shop is cut with nitrogen, so they knew what their consumption was and designed their generator purchase around that.”

The key to investing in a generator is understanding what your needs are.

“If you size it for what your needs are now and not what you plan to build, you can end up starving the generator in a couple of years when you add another laser,” said Kemp. “We have seen that at a couple of customers; you can see how the edge quality on the parts varies in a given day because of the demand on the generator and how it can’t keep up.”

Make sure you talk this through carefully with whichever supplier you are working with. They can help you calculate what your needs are now and any growth you are planning.

If you are considering the nitrogen generator route, be sure to review your current supplier contract and ensure that it doesn’t restrict your ability to do this.

Shop Air Use

In many cases, you may not need to use nitrogen for cutting; shop air may be sufficient, but it is mostly limited to thin-gauge material cutting.

“[Using shop air] usually requires investing in an accumulator and a booster so that you can get the air pressure high enough to cut effectively,” said Colle. “We ran a simulation recently for a company that was considering this alternative. They were cutting 14-gauge material and didn’t need the purity of a nitrogen cut; they could still effectively powder coat the material afterward without further processing.”

“You can get into a really nice system that uses shop air to run a number of machines,” said White. With a standard air compressor, you would be limited to cutting around 11-gauge material. “You can achieve higher speeds when you cut with air, it’s a cleaner process, and it reduces the dross level you find on the bottom of some fibre-cut parts. The only negative is that you get a brown-coloured edge. If that is not an issue, you can get a cut quality that is acceptable up to a quarter inch on mild steel, stainless, and aluminum, depending on the output power of the machine. It’s also, from what I have seen, a paintable edge.”

Note also that the shop air must be oil-free and moisture-free to be used as an assist gas.

Nozzle Choice

Various companies in the market, including Bystronic, TRUMPF, and Amada, have developed special nozzles to improve the efficiency of the nitrogen use on their machines.

“Bystronic has a series of these nozzles that have a built-in shroud,” said Kemp. “What that means is the nozzle opening is in the centre and around that you have a rigid shroud that rides very close to the top of the material being cut. What that does is gives the nitrogen only one path, through the kerf, rather than escaping through the sides. This allows for a more efficient use of the nitrogen, thereby reducing the required flow rate. We’ve seen flow rates in the quarter-inch range cut nearly in half. It also improves the edge finish.”

Although these nozzles tend to be more expensive than standard nozzles, Kemp noted that they can save a shop between $400 and $800 in nitrogen costs over the life of that nozzle.

A rise in nitrogen gas consumption will not discourage a shop from investing in more efficient, more productive equipment, but it just makes sense to use it as efficiently as you can.

Editor Robert Colman can be reached at rcolman@canadianfabweld.com.

Bystronic Inc., 800-247-3332, www.bystronicusa.com

LVD Strippit, 716-542-4511, www.lvdgroup.com

Elliott Matsuura Canada Inc., 905-829-2211, www.elliottmachinery.com

MC Machinery Systems Canada Inc., 905-867-9423, www.mcmachinery.com