ASK THE EXPERT: Cutting sheet and tube on the same fibre laser machine

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Most shops have flat sheet lasers but don't have a tube laser. There's lots of flat sheet work but the margins on tube processing can be greater. Why not invest in machinery that allows you to play in both markets? PHOTO courtesy BLM Group.

Have you been putting off supplementing your sheet metal processing business with some tube work because you’re not crazy about investing in a separate tube cutting machine? There’s a hybrid solution that could provide you with the flexibility you desire as we discussed with Robert Adelman, North America laser product manager, BLM Group, in an exclusive interview.

SHOP: When does it make sense to invest in a machine that can cut both sheet and tube like BLM’s LC5?

ADELMAN: If the customer has a shift of tube but they still have need for a flat. Or if they have almost a full shift of flat and just a little bit of tube work. Most shops have flat sheet lasers but don’t have a tube laser. You will fill a flat sheet quickly but the margin on a flat sheet is not great in comparison to tube. The number of tube lasers in your area are probably nothing compared to the number for flat so customers who have the need for a flat but do some tube work should do their due diligence and look at the investment cost of a combo. You are getting a lot of savings by only purchasing one laser, one chiller, one dust collector and you get the advantage of  being able to automate our LC5.

SHOP: There have been significant increases in power when it comes to sheet laser cutting systems, which increase the working speed and therefore reduce the cost per part. We haven’t seen the same type of increases for tube processing. Is the fact that tubes obviously have a closed shape with an opposite wall that can be affected by what happens to the initial wall cut by the laser, the main reason holding back an increase in power? Or are there other important considerations?

ADELMAN: Processing sheet and tube have similarities, but they are also very different in their natures. The sheet metal is consistent. You load it on a pallet and the pallet does all the work. The material is stationary while the head does all the travelling. On a tube laser machine, the fact that we must maneuver the tube means maximum speeds are reached much faster when moving a 24-foot, and sometimes a 40-foot, piece of raw tube. The second thing is what you alluded to, that there is a second side. If we were to process all of our tube using maximum power, there would be times when you would burn the opposite side or maybe even cut through both sides. So, on our tube lasers what we do is define a set of parameters for standard cutting thicknesses but then we also define what we consider to be “small tube”. For materials of less than one inch the machine is going to throttle the speed down and allow us to dial the power down so that you’re not burning the opposite face. Heating can have a negative effect to the cutting process just as much as cutting, so we have to be aware that the tube has a second side and that the heat is absorbed in the tube much faster than on a flat sheet because of the opposite face.

SHOP: You mentioned the movement of the tube at high speed. That also places a fair bit of pressure on the machine itself I would imagine, and the machine would have to be built in such a way as to be able to withstand all the pressure placed on it?

ADELMAN: Yes, and that’s why our machines are dynamically controlled. So if you load a six-inch tube that is mild steel and quarter-inch thick, it will act and move differently than if you were to load a two-inch tube that is quarter-inch thick. Same material, same thickness, same cutting gas, but different weight per foot, therefore the machine is going to manipulate the material in a different way.

SHOP: What’s the greatest power you offer with your Lasertube systems?

ADELMAN: Our maximum power right now on a tube laser is 5000 kW. You only need that kind of power when you’re processing thick stainless, thick aluminum and thick mild steel with nitrogen or compressed air. What sets our machines apart is that we are using 5000 kW at a 50-micron level versus a lot of the competitors in the market using 100 micron. Our beam concentration and power concentration are greater, so we are able to cut faster with a lower power.

SHOP: You also offer C02 options. When would you recommend CO2 over fiber laser? Is it mainly a matter of being able to cut large diameter tubes?

ADELMAN: Yes, we still offer CO2 on what we consider our Jumbo series, which is our 14-inch and 24-inch machines. The CO2 beam is really good for very thick material and it doesn’t have as much issue with rust. Fiber is more delicate. It is able to go really fast and it’s able to cut highly reflective material but when you get to structural beams so large you can’t move them, then you have no advantage. So we continue to offer the CO2 option.  

SHOP: Is it fair to conclude then that even though the market for CO2 has been shrinking as more fabricators opt for the advantages offered by fiber, that there will be a particular segment of the market that will continue using CO2?

ADELMAN: With the technology of today, I would say yes. It makes sense for us to stay with the CO2 offering. The 24-inch machine, you actually stand on a platform over top of the machine. It’s a massive piece of equipment and enclosing equipment of that size just doesn’t make sense. In the future, however, I could see that we may be able to go forward with fiber.

SHOP: You offer both 2D and 3D options for fiber. What should be considered in deciding whether to opt for the 2D or the 3D version?

ADELMAN: Many customers don’t understand what we mean by 2D versus 3D. What we are concerned with is do you want the head to remain perpendicular to the tube or do you want it to tilt so that when you get a mitre it’s a true cut. For example, our customers who are serving the furniture industry are typically dealing with smaller thickness tubes. At such smaller thicknesses, when you get to welding there is typically no difference on the penetration and the application probably doesn’t require a full weld. So, they don’t have to have a beveled edge. They don’t have to have a chamfered edge for weld prep. When you are dealing with manufacturers processing material less than a quarter inch, most likely a 2D machine is going to be perfectly acceptable because the application does not require the weld prep.

SHOP: With laser cutting there are sparks and debris and slugs that fall inside the tubing. Fabricators have developed a number of ways to deal with this from precoating to using a sacrificial tube on the inside. What can be done for spatter protection from the machine end?

ADELMAN: We offer what we call “clean tube” technology or more commonly referred to as a “spoon”. It is a device that is installed in the machine, located on the unloader, and it is equipped with a suction device as well as anti-splatter protection so that the splatter doesn’t make it to the other side of the tube. It’s captured, sucked up, and evacuated. It’s an option we offer on all the fiber lasers. Our smaller machines are used to process tubes with smaller thicknesses so there are differences in the spoon device used but they all work based on the same concept.

SHOP: How about storage for tube material? Do you recommend a tube storage system that can be paired with the tube laser machine?

ADELMAN: We offer that on our larger machines, and we absolutely recommend it. The reason why we recommend it is because, just like with flat sheet lasers the higher the power the faster the machine, so now what you’re waiting on, if you don’t have a tube storage system, is loading and reloading. Most of our tube lasers come with bundle loader so you can load a bundle and work four to six hours off that bundle. But when that bundle is done, if the operator is on a break or the person picking the new material didn’t do it, you have the machine on standby waiting on material. A better way of doing this is connecting your storage system directly to the machine so that the correct material is picked, arrives at the machine in time and you’re not having material stored that is getting bowed, twisted, or damaged in any way. You can integrate this system with your ERP so that you can track how much material you have, providing you with better inventory management. It also makes for a safer operation. You’re getting material from storage to the machine without anybody placing their hands on it.

Connecting a storage system directly to the machine ensures the correct material is picked, arrives at the machine in time and you’re not having material stored that is getting bowed, twisted, or damaged in any way. PHOTO courtesy BLM Group.

SHOP: The loading and unloading of tube material into the machine and how it’s supported is also important. What should be considered in terms of the support system, particularly when dealing with longer tubes over 4 feet? 

ADELMAN: On typical tube lasers there is a minimal length you need in order to load that automatically. With our system we use cassette drawers – either 21-foot or 27-foot. Material is loaded in the empty cassette and the storage system then places the cassette. The machine is ready to run a new job, you call up the job, the job requires X material. That’s communicated to the storage system which pulls the appropriate cassette. Once all the material is used the storage system automatically looks for the next cassette.

SHOP: If a tube that is bowed or twisted ends up in the machine, what capabilities does the machine have to assess straightness and compensate for it? What specific features for accuracy assurance are important to consider during the purchasing process?

ADELMAN: Ninety five percent of our customers go with our available technology, which is called Active Scan. It’s a device that consists of laser blades and two cameras. It’s placed right at the point of cutting. Once the tube is loaded and we go to make a cut, the first thing we do is we scan it with the laser, and we pick up pictures of the scan. We then analyze the scanned material and determine the degree of bow and twist in 0.6 seconds and then automatically compensate the holes for that tube. A lot of competitors will use probing or height sensing. All of our machines are equipped with the ability to use the nozzle for height sensing. But our customers buy Active Scan, not because probing doesn’t work but because probing kills production. It’s slower. Instead of 0.6 seconds, you’re looking at six to nine seconds. That may not seem like a big deal but what happens if your part time is 10 seconds? Your part time then has almost doubled because you got poor material in. And it might not even be poor material. It might just be that the tolerances are that high on the parts. The industry is increasingly going to laser welding. Laser welding requires high accuracy, therefore the prints that are coming out these days are calling for higher and higher accuracy, but the material conditions have stayed the same. A lot of people say you can use stronger chucks and conical rollers to push the material to the centre, but we know mild steel and stainless steel when welded together have three similar radiuses and one radius which is not. If you try to push something centre that is not symmetrical you are already introducing error. It’s not about making the tube centre, it’s about capturing the bow and the twist and compensating your hole to be centred off the actual.

SHOP: How do you address waste reduction through nesting?

ADELMAN: Our machines have the ability to load a job that can consist of 50 unique part numbers of various quantities. The machine will automatically nest those parts. The machine is able to manage the algorithm to nest bar after bar to utilize the best scrap rate. What it’s doing is looking at the length of the part compared to the length of the bar loaded. It’s taking the parts, rotating and compacting them, to create the best scrap rate possible. It can rotate a square in four different directions, a round tube 360 degrees, and a rectangle twice, to find the best nesting. We also offer offline nesting to do the same thing.

Robert Adelman is the North America laser product manager with BLM Group.


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