September 25, 2003
Bourgault Industries specializes in seeding and tillage equipment, and other agricultural products including sprayers, grain carts, and heavy harrows. The company performs all fabrication involved in manufacturing the equipment from sheet or plate to finished product. It examined its operating costs and found that setup times in several parts factored significantly in the overall cost of the part.
The seeders are large, heavy equipment and weigh as much as 50,000 pounds when fully loaded. They are constructed primarily of mild steel sheet, plate, hollow structural steel (HSS), round pipe, and shaft. The sheet steel used is from 16 gauge to 2 inches thick, with most in the 1/8- to 5/8-in.-thick range.
Like many companies in the agriculture industry, Bourgault experienced fluctuations in the demand for its products. The company tried to adjust its staff size accordingly; however, it found that decreasing its staff during slow times and increasing it for peak demand was not a workable solution.
|Bourgault Industries performs all fabrication involved in manufacturing its seeding, tillage, and other short-line agricultural products, including sprayers, grain carts, and heavy harrows.|
"We came to realize, as I am sure many other manufacturers have, that skilled labor is hard to find, and even if they are skilled, there is a long, expensive learning curve until they are trained for our specific processes," Manufacturing Leader Darren Borstmayer said. His team examined the company's operational costs in an effort to increase throughput while maintaining efficiencies.
Upon examination of operational costs, the team found that setup times for several parts factored significantly in the overall cost of the part. "In some cases, the setup cost per part was significantly higher than the run cost."
To reduce the per-part cost, the company often made parts in larger batches than needed, but that resulted in increased material handling, storage, and obsolescence costs.
Parts had to go through many different fabrication processes to become a finished part. These operations required the use of band saws, drills, shears, punching equipment, CNC oxyfuel, high-definition plasma, forming, and grinding equipment.
The company's current plasma and oxyfuel machines did not cut holes that met the hole size tolerances required, so a part often had to be routed through a drilling or milling operation to add holes and slots.
Also, parts that did not meet the nominal specifications typically caused complications in downstream welding and assembly applications.
The location of the holes relative to the edge of the plate and to each other required a tighter tolerance than could be achieved using multiple operations, in which each hole was drilled separately using a fixture that referenced the edges of the plate.
Another problem with the multiple processes was that the holes themselves depended on the accuracy of the original cut.
In addition, burrs or slag created by the plasma cutting or metal filings sometimes prevented the plate from being accurately referenced in the drilling fixture, causing part variability. With multiple processes, the parts sometimes varied more than ±1/16 in. from hole center to center because of the stackup tolerances, including how the plate was cut and then how the cut sides were referenced for drilling.
On parts that required tighter tolerances, more elaborate tooling was used. In some cases, the parts were routed through a manual milling operation at considerably more expense. As a result, the engineering staff avoided designing parts that required tight tolerances and designed holes to be oversized by as much as 1/16 in. so mating parts could be bolted together.
To combat setup and throughput problems, the team began to look at alternate fabrication techniques and methods and performed a detailed analysis of several different pieces of plasma and laser equipment.
Because Bourgault already operated plasma machines, it was familiar with the equipment's advantages and disadvantages. While plasma equipment had lower capital costs and fast cutting speeds on thick plate, the company searched for other equipment that could offer a high level of accuracy consistently.
The company considered that laser equipment could cut holes and slots as well as blank the outside profiles in one operation. Conversely, on the current equipment, those operations required that the part be routed through several machines. Borstmayer said the team suspected that a one-operation system would save them the cost associated with the extra processes and shorten the cycle time.
The team also evaluated plasma systems but did not find the automation it was looking for. "In our evaluation of plasma systems, we did not come across a company that offered the automation for plasma like the lasers have. That is not saying that it does not exist," Borstmayer said. "Also with plasma, it was still very often necessary to add holes and other features with a drill, so the setup time existed for that part of the operation."
A cost comparison of the company's current process and an automated laser process indicated that eliminating the setup costs offsets the additional operating and material costs associated with the laser system.
The team also looked at the laser cutting process' reputation for accuracy and part repeatability. It evaluated the holes cut by the laser equipment and concluded that in many cases, the laser cutter produced holes with diameters comparable to those made on a drill press.
The team compared the costs of fabricating a simple test part using a band saw, pedestal drill, and a grinder to cut, drill holes, and clean up the sharp corners with the costs of fabricating with a laser that performs all three functions (see Figure 1).
The results showed that the part that was made using the manual approach in a batch of 10 cost $4.97, 29 percent of which ($1.46) was setup. If the part was made one at a time, the cost per part could be as high as $18.09. The part would have to be run in quantities of 100 for its cost to drop to $3.51.
On a laser, also in a batch of 10, the same part cost $4.19, a savings of $.78 per part. If a laser-cut part was made one at a time, the cost still would be $4.19, because no setup time was required.
"Lasers are capital-intensive to get into and would require additional training for our operators, who are used to operating and maintaining plasma and oxyfuel systems," Borstmayer said. "We've had a high-definition plasma and we still run an oxyfuel system. On those two pieces of equipment, we've never had to send anybody to any sort of formalized training. With the lasers we have.
"Also, lasers require consistent surface finishing on the sheets to get uniform, repeatable cuts. If the surface finish of the sheet has rust spots, results can be poor edge finish or an incomplete cut so the part has to be scrapped. We used to store all our steel outside. We couldn't do that anymore," Borstmayer said. "As a result, we considered that changing to lasers would force us to change the way we handle and store our raw material."
The team considered another possible disadvantage that the company considered. "When cutting mild steel with a laser and using oxygen as an assist gas, a thin layer of scale is left behind on the cut edge that must be removed prior to painting to ensure good paint-to-metal adhesion.
"Cutting with nitrogen as an assist gas is an option that eliminates the scale, but it's more expensive. It would have increased our operating cost, and because we cut plate thicknesses, we would have lost cut speed," Borstmayer added.
|As the part becomes more complex, requiring it to be routed through different operations, the setup and run cost climbs at a faster rate than the cost of the additional time required to cut the part on a laser.|
After weighing all of these factors, the team decided that the laser cutting systems were a good fit for its need to produce small batches of parts on a just-in-time (JIT) basis, to reduce setup time, and improve accuracy.
In July 2001 Bourgault purchased a Mazak Laser FMS, a flexible manufacturing system (FMS) with two 5- by 10-ft.-bed, 4,000-W Mark II lasers. The system has a material storage and retrieval system and an automatic load and unload system for the lasers. It holds 10 different sheet steel thicknesses and can switch from one thickness to another in 45 seconds.
The equipment's high wattage was required to handle the thickness of parts typically being cut.
Borstmayer said that the laser system improved accuracy and repeatability, reduced cycle time, and eliminated setup time.
Accuracy and Repeatability. Now most parts are cut with tolerances of ±0.008 in. or tighter, and part-mating problems have been eliminated. This variability reduction has allowed the engineers to design mating parts with significantly less allowance for stackup tolerances. Parts can be designed to fit tighter without putting the part through expensive secondary operations.
Cycle Time, Setup Time. Shearing, sawing, cutting to length, blanking, and drilling now are being done in one operation, which has reduced cycle time. Also, fewer stamping and cutting fixtures and secondary processes also have saved tooling time, Borstmayer reported.
The ability to switch material sizes quickly with no setup time was a key element in the decision to purchase the lasers, Borstmayer said.
Having the capability to cut parts precisely and the flexibility of revising the part at any time with no tooling implications have affected the downstream welding and assembly processes. "We believe this is an important advantage for small to medium-sized operations like ours, in which the quantity demands for specific parts are relatively low and the capital cost of dedicated equipment is high," Borstmayer said.
Previously a weldment on the running gear of a seeder was made with 29 parts from 16 different raw materials, including HSS tubing, profile cuts, various flats, and a few cold-drawn seamless mechanical rounds. The accuracy of the laser-cut parts enabled the company's engineers to redesign the weldment with only 22 parts from six materials, including 1/4-, 3/8-, 1/2-, and 1-in. sheet and two different cold-drawn seamless mechanical (CDSM) sizes.
Better Welding. Bourgault has noticed benefits related to welding laser-cut parts. "We found that having more accurately cut parts enables the welder to put the parts into the weld fixture faster," Borstmayer said. Also, concern about possibly damaging a part if it has been force-fit into the fixture has been eliminated.
The accuracy and repeatability of the laser-cut parts prepares them better for robotic welding too. Using the previous design, it was necessary to weld the assembly in several stages because several parts had to be welded in place before more could be added.
This increased the complexity of the fixture to the point that it was no longer feasible to do robotic welding, thus requiring the welding to be done manually.
Reduced Number of Parts. Incorporating highly accurate laser-cut parts into the assemblies has enabled the engineers to redesign assemblies with fewer parts and fewer different raw materials, Borstmayer said. For example, a part of a running gear called a weldment, has been redesigned with 22 parts instead of the original 29 and six different raw materials instead of 16 (see Figure 2).
This accounts for a 63 percent reduction in the number of raw materials needed. All the parts interlock with slots cut in the various subweldments, making a self-fixturing part (see Figure 3). Assembling this part for welding requires the items to be put together in a specific order like a 3-D puzzle, but once it is done, it is essentially freestanding; no welding fixture is needed.
Other Parts Can Be Made."Lasers also have benefited our operation by replacing several parts that in the past were made from barstock and required several different steps to complete," Borstmayer said. "We have roughly 5,000 different parts that can be cut on the lasers, potentially."
This exploded view of the laser-cut weldment illustrates how the parts fit together like a 3-D puzzle. The new design eliminated the need for a weld fixture.
Greater Design Flexibility. The laser systems not only have a profound impact on the accuracy of the part, affecting the fit and finish, they also have significantly lessened lead-time from conception to production, partially because parts no longer have to be tooled up, Borstmayer said.
"The shorter cycle time also shortens the development cycle. Laser-cut parts not requiring tooling or setup time offer the flexibility to change the parts. Little changes that were very expensive to do with hard-tooled fixtures now are not a problem," he said.
This empowers the design and manufacturing staff to react to customer comments and suggestions quickly, instead of having to take the time required to schedule and modify hard tooling, he added.
In the last 21 months the company has purchased three more lasers. A third Mazak has been added to the automatic feed system, as well as two large Tanaka lasers—one with 6,000 W of cutting power on an 8- by 57-ft. table and one with 4,000 W of cutting power on a 10- by 42-ft. table.
"The change has had a huge impact on our operations," Borstmayer said. "Several parts are made at a lower cost than previously manufactured, the tolerances are much tighter, and the design staff has the ability to truly exercise their creative abilities. In my opinion, we have only started to tap the possibilities these lasers have opened up to our organization."
Mazak Nissho Iwai Corp., 140 E. State Parkway, Schaumburg, IL 60173, 847-252-4500 www.mazaklaser.com.
Metal Processing Systems Inc. & Tanaka Laser, 1096 National Parkway, Schaumburg, IL 60173, 847-310-6363 www.tanakalaser.com.
Photos and illustrations courtesy of Bourgault Industries, St. Brieux, Saskatchewan.