Page 34 - MetalForming February 2017

Precise
Optimize Nesting Efficiency
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filled with parts, often creating rem- nants...and waste. With JIT nesting we can avoid the tail-off issue.”
Order Cohesion
Another important consideration in managing chaos is order cohesion— the ability to schedule parts in a timely manner to ensure optimum down- stream processing, such as welding of a subassembly, where all of the parts required for the subassembly must arrive simultaneously (or nearly so) at the weld station.
“Nesting should keep parts within one order together, whether they’re processed on the same machine or on different machines in the shop,” says Lundy. The previously referenced blog post refers to this practice as “intelli- gent order management” in that the nesting software knows which parts belong together in an order, and which orders have priority.
“Further,” it states, “JIT kit nesting addresses the needs of keeping all of the parts of a single assembly together, so that they can flow through the shop as a unit. Through intelligent nesting, material efficiency can be managed to eliminate the end-of-kit tail-off and additionally reduce material waste.”
Lundy adds that JIT nesting typically boosts material efficiency by 10 percent or more compared to batch nesting. “And, the speed pickup in material flow through the shop is significant as well,” he says. “Fabricators often can progress from design to order to machine in 5 to 10 min. And, we’ve seen machine green-light times increase as a result— lasers running at 60 to 70 percent green-light time can improve to 90 per- cent, and turret presses running at a green-light time of 30 to 40 percent can improve to 70 or 80 percent.”
Manufacturable Nests
Lundy then points to another real- world demand that nesting software and those that use it must account for: Can the equipment on the shop floor produce the nests as programmed? Nesting must account for machine requirements such as reach, reposi-
tions, the number of tooling stations and kerf allowances to ensure not only production efficiency but also part quality, while avoiding machine dam- age and protecting workers.
“Nesting software can ensure that tool paths retain sufficient material integrity to hold the sheet together throughout the machine cycle,” says Lundy, “by carefully designing the micro- joints between the parts on the nest. This so-called ‘intelligent tabbing’ helps to safeguard the machine and the oper- ator, by ensuring that the skeleton won’t fall apart before parts are off-loaded.
“We also can make the clamps essen- tially disappear,” Lundy adds, “by nest- ing and programming machine action to punch where the clamps will be mov- ing to, and then moving the clamps to that previously punched or cut location and punching where the clamps already have been. And, there’s built-in collision avoidance (particularly useful during plasma, laser and waterjet cutting),” he continues, “so that nests and cutting procedures are developed to avoid part tip-up and sheet buckling.”
The trick to collision avoidance: sequencing the tool path to minimize the number of times the cutting head must raise up to safely pass over previ- ously cut paths and parts. This delivers the added benefit of eliminating slow z- axis motion that adds to processing time. In most applications, the nest should cre- ate tool paths that progress from the innermost cuts out toward the skeleton.
More on Safety
Describing an additional safety fea- ture, Lundy notes that modern nesting software helps to protect operators from the molten spatter that can be ejected from a thermal-cutting machine when piercing thick work. Here, an ideal nest will control the direction of the spatter away from the machine operator.
“First, we want to pierce on the fly,” says Lundy. “Then, we create the nests, automatically, so that the lead-ins point away from the operator. We make this a constraint with the software, rather than a nesting parameter; it’s an absolute within the knowledge base.” M F
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MetalForming/February 2017
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