Many metal centers today report being as busy as they can be. With multiple shifts, added resources, investments in new cutting machines and a backlog of orders waiting to be filled, the industry as a whole has more than weathered the recent economic storm. But how does all of this activity translate into productivity? Why is it that for many service centers and other metal fabricators, these investments are not proportionately reflected in the bottom line?
One reason is that increasing amounts of a cutting tool operator or programmer’s time is spent with non-value-added tasks associated with nesting. The effective arrangement of parts on a sheet and related cut pattern has a direct and positive impact on reducing material waste and speeding cutting and fabrication processes.
Nesting at its best maximizes cutting machine run time, delivering a quick return in investment. Not all nesting is created equal, however.
In truth, CAD/CAM nesting problems, while a daily (or even hourly) issue for many, run the full range in terms of cause, effect and complexity. Generally, these issues can be traced back to a couple of areas: manual nesting and software inefficiencies.
• Manual Nesting—In its most simple form, nesting is a simple cookie-cutter concept: arrange shapes so that the most parts can fit on a given material surface. In order to move from incremental savings to a point where nesting yields breakthrough levels of material savings and productivity requires a much deeper understanding of the factors that result in an effective nest.
Common-line cutting, for example, is the nesting practice of arranging parts with shared edges so that multiple parts share a single cut. When done properly, the result is faster run time, maximum material usage, and often extended tool life as pierce points are greatly reduced. Common-line cutting can save substantial time when working with thick plate.
Less experienced programmers can get greedy when creating nests and, in an attempt to get the absolute most out of every sheet of metal, will create a nest that is too tight. Skeleton management is an important consideration. Due to inadequate part positioning, material surrounding parts can be inadequate and will not have the strength to fully support a neighboring part once the cutting process has begun. The instability will have a direct and adverse effect on part quality. An effective work-around in this instance would be to add tabs for stability.
Other problematic issues are often related to placement of lead-in and lead-out, and heat distortion. Heat generated during the cutting process can cause an expansion effect that shifts the part, creating an opportunity for errors. Again, being aware of these hazards when programming today’s advanced cutting machines requires knowledge that comes with experience. Unfortunately for many manual nesters, or those employing less sophisticated nesting software, these lessons are too often learned through trial and error with a hefty price tag of scrapped parts and cost overruns.
• Software—Manufacturers invest heavily in new equipment to bring advanced cutting capability to the shop floor. They spend hundreds of thousands of dollars to improve productivity, accelerate throughput and entice new business. Each feature is benchmarked and scrutinized with painstaking due diligence to ensure that the best machine is purchased.
Unfortunately, many don’t take the same care when selecting the software to run these machines. Nesting software is too often an afterthought based solely on price and basic functionality. It’s like buying a high-performance sports car only to equip it with a cheap off-brand sound system. All laser, plasma, oxyfuel, waterjet, router and punch machines come with software that can nest parts, but few come with true nesting software. And that can make a big difference. Editor’s note: This article was contributed by the experts at SigmaTEK Systems.
SigmaTEK Systems LLC, Cincinnati, Ohio, offers SigmaNEST, an automated nesting and NC programming CAD/CAM software system that supports a wide range of equipment, including punching, laser, oxyfuel, plasma and waterjet cutting machines. For more information, visit www.sigmanest.com