Laser Cuts Costs For Metal Fabricator
Carl Duveneck can list many reasons why a laser is the best tool to use for blanking parts from sheet metal.
"Parts aren't square anymore. Today, customers are designing their parts with laser cutting in mind, with rounded corners and contours. It's too costly to make such parts the traditional way, by shearing a blank and then nibbling it on a turret press. You not only have tool wear, but it's bad material utilization.
"More accurate parts.
"Minimal setup. There's no hard tooling with a laser, so there's no tool changes, no tool sharpening, no die clearances to worry about.
"Our welders tell us that laser-cut parts weld so easily they just seem to fall together..."
Duveneck should know. He is Vice President of Helgesen Industries, a fast-growing, progressive, metal fabricating firm located in Hartford, Wisconsin.
Helgesen started out as a producer of fabricated steel fuel tanks and hydraulic tanks, primarily for Fortune 500 manufacturers of construction vehicles, material handling equipment, and other off-road equipment. As the company's reputation for quality spread, orders for large and small welded and machined fabrications started coming in from a growing number of customers in diverse industries.
Helgesen has a full range of modern sheet and plate fabricating equipment including two stand-alone laser cutting machines. Duveneck knows the machines very well -- he selected them, bought them, and has run most of them.
Because an increasing number of jobs were being blanked on Helgesen's two laser cutting machines, these machines were backed up two to three weeks. But no more. Helgesen found a way to reduce that backlog and is now accepting more work.
Cutting Edge Technology
Helgesen bought a two-laser, flexible manufacturing system (FMS) from Mazak Nissho Iwai Corporation. Helgesen was impressed with the equipment's productivity-boosting features.
Two supercharged laser cutting machines form the heart of this recently introduced FMS. It minimizes beam divergence by providing a constant-length beam instead of the variable length beam characteristic of flying optic machines. Its fixed beam permits uniform cutting at any point on the table and easier determination of cutting conditions. It also increases net power at the focal point, which lowers gas and power usage, and other operating costs.
The laser can cut materials up to 0.75 inch thick with consistently good accuracy and edge quality. Positioning accuracy and repeatability of the machine are plus or minus 0.0004 inch and 0.0002 inch, respectively.
The laser is equipped with a CNC control capable of storing the equivalent of just over 1000 feet of tape in up to 96 programs. Main program storage is in the line controller. Tailored to the requirements of the laser cutting process, the control automatically adjusts the parameters necessary for laser processing, thereby reducing set-up time. It also calculates part-cutting times and even alerts the operator to self-diagnosed malfunctions.
The two lasers accept sheets up to 60 by 120 inches. Each laser has an integrated, Class I safety cover that encloses the bed during cutting to confine cutting fumes, particulate, and related laser cutting light.
The most visible component of the FMS is the stocking tower, which provides the all-important advantage of making raw material continuously available to the lasers. It eliminates the labor and downtime associated with removing the material from the previous job and returning it to storage, and bringing in material for the next job.
The tower holds ten shelves, each with a capacity of 5000 pounds of sheet steel. A forklift delivers a bundle of steel to the tower and loads it on a shelf waiting on the tower elevator. The elevator then lifts the shelf to its appropriate 'floor' and stores it on the tower.
When material is needed, the elevator, operating under line controller command, retrieves the appropriate shelf, brings it down, and then pushes it through the bottom of the tower to the opposite side, making its load of sheet accessible to the FMS' load-unload material handling system.
The traversing load-unload system minimizes the amount of time that each laser must wait for the next sheet. It consists of a suction-cupped sheet loader that travels in tandem with a cut-sheet unloader on an overhead monorail. The monorail extends from the tower at the head of the cell to a finished part-stacking table at the opposite end.
To begin, the loader-unloader moves to the shelf of steel sheets positioned between the tower and first laser and picks up a sheet. The unit then travels to the next available laser, which has just finished cutting one sheet and awaits another.
The closely spaced teeth of the comb-like unloader slip beneath the cut sheet and lift the cut parts and skeleton from the laser table. The unit then continues an additional five feet or so in the direction of motion, to allow the loader to place the fresh sheet on the laser. Once the laser begins cutting the fresh sheet, the loader-unloader carries the finished sheet to the stacking table at the end of the line.
The unloader's teeth mesh with the teeth on the table. As the unloader retracts, the sheet is restrained by the vertical row of teeth and remains on the table. Cycle time for the loader-unloader to retrieve a raw sheet from the shelf, move to the idled laser, remove the cut sheet, load the fresh sheet and start cutting again is about 35 seconds. It takes another l.5 minutes for the loader-unloader to place the cut sheet on the stacking table and then return to the queue position.
As time permits, the FMS operator separates the parts from the skeletons and stacks parts on skids, which are fork-lifted to nearby press brakes for forming. The operator is aided by a printout of the nesting program that shows the nested parts, their part numbers, and the quantity of each. The printout helps avoid confusion, particularly when similar jobs are running.
The final major component of the FMS is the line controller, which sequences all the material-handling equipment, downloads all cutting programs, and stores nested programs by date, quantity, material and thickness. It also provides production data to management. The line controller is Helgesen's first experience with a hierarchical control, but company personnel have found it easy to learn and have taken it in stride.
The FMS gives Helgesen a greater increase in laser-cutting capacity than would have been possible by purchasing two more stand-alone lasers. Helgesen's existing stand-alone machines operate three shifts per day, five days per week, providing a total of 30 eight-hour laser shifts per week using both lasers.
The laser FMS operates three shifts per day, seven days per week, operating in an unattended mode over weekends, to provide 42 eight-hour laser shifts per week -- which represents a 140 percent increase in capacity. The actual increase is greater, however, because the FMS lasers have a higher average output than the stand-alone machines.
"We can load the tower with 50,000 pounds of sheet," explained Duveneck. "The FMS can be programmed to run several different jobs. When one job ends, the shelf containing the material for that job is returned to storage and the shelf containing the sheet for the next job is moved into position while the lasers continue to cut. By that time, the new cutting program has been loaded into the machine. No cutting time is lost. The operator can add new jobs to the schedule or quickly adjust the schedule to meet downstream requirements, and as long as the material tower has the right steel, the FMS will keep right on working.
"The FMS will continue to operate until 10,000 pounds of steel have been processed and delivered to the stacking table," he added. "It will then shut down until the operator removes the cut parts. He then pushes a button and the system starts working on the next 10,000 pounds.
"Processing that 10,000 pounds of steel can take from 6 to 24 hours depending on the complexity of the part," Duveneck explained. "With the ability of the FMS to run unattended, on Friday night when we're getting ready to shut down for the weekend, we program the system to run a long job. When we come back Monday morning, the finished parts are waiting for us on the stacking table."
Long-running jobs are nice, but Helgesen has more small runs than long, and expects the percentage to increase as just-in-time orders, involving smaller and more frequent part orders, become more prevalent. Duveneck feels that the FMS can handle short run work more efficiently than the stand-alone machines.
First, it can make the corresponding material and program changes for new jobs without losing cutting time, while more frequent job changes can only increase the down time on the stand-alone lasers.
Second, he is impressed by the nesting software's ability to nest several different jobs calling for the same material and thickness on the same sheet.
Immediate Labor Savings
Because the shop's stand-alone lasers require operators to be present for loading/unloading, they stand idle over the weekend. The additional 12 shifts per week on the FMS consist of unattended, weekend operation, when the plant is 'closed'. Thus, they are obtained at zero operator labor cost.
The FMS produced immediate benefits for Helgesen, and Duveneck feels it will make an even greater contribution to productivity as job sizes continue to shrink. "As much as possible, we try to attract business that involves long-term, ongoing work," he emphasized. "Nevertheless, it is not unusual for each of our welders to do two to five different jobs in a day, or for our press brake operators to run five to 15 different jobs in a day. As a result, we typically spend more time setting up for jobs than running them.
"With the cost of materials and finished parts continuing to rise, our customers are no longer tying up capital in large orders," Duveneck continued. "For the same reason, we cannot afford the cost of producing a year's worth of parts in a single run to achieve the economy of scale and storing them against the customer's repeat orders. Like everyone else, we have been forced to find ways to produce smaller quantities more efficiently. Our laser FMS, with its ability to rapidly switch from one job to another with no loss in laser cutting time, is a major step in that direction."
Duveneck and Helgesen President Ron Marshall realize the effect of the laser FMS on customers and take advantage of every opportunity to invite them in to see the FMS in operation. It provides an opportunity to discuss new jobs with existing customers.
As a result of the laser FMS, Helgesen has gone from a two to three week backlog to open time and is able to accommodate new business. "Some customers selected us over competitors because we have laser cutting," Duveneck believes. "Many of them feel, as we do, that laser cutting is the leading edge of sheet metal fabricating technology."
Duveneck envisions a time when most of its sheet steel will go directly to laser cutting machines for blanking instead of being sheared to smaller sizes for processing on machines such as turret presses. However, he is not concerned about the possibility of future business swamping the capacity of the laser FMS. For a company operating only stand-alone laser cutting machines, such an occurrence must necessarily force the decision that Duveneck faced before, whether to buy another stand-alone laser or two.
But Helgesen now has its laser FMS, and the system is modular in nature. Therefore, it can expand incrementally as required, for example, by adding another laser. Helgesen's laser cutting capacity can grow as needed -- without increasing labor and with the least disruption to the existing system. Best of all, the FMS provides Helgesen with the level of metal-cutting accuracy and efficiency it feels it will need to compete for business in the 21st century.
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