Page 28 - MetalForming Magazine August 2022

Fabrication: CNC Punching
CNC punching machines take advantage of rapidly evolving nesting software to produce parts quickly and accurately, while optimizing material utilization. Such software also can perform smart-sort nesting to combine parts into nests that use similar tooling, eliminating the need for excessive tool and sheet changeout.
An OEM-fabricator project provides a case in point, with Carnall and the Metamation team tackling challenges.
“By scanning more than a thousand parts produced by this fabricator on a turret punch press, we were able to determine tool usage,” Carnall recalls. “Using the data, we identified needed and unneeded tools. For example, sup- pose a fabricator must punch a 1-in.- square, a 0.75-in. square and a 0.50- in. square to nibble out the middle of a part to make an aperture. This does not require three different square punches, which eliminates the need for some tools. Doing so may require an extra hit or two, but it frees turret capacity to allow for other needed tools.
“By scanning and eliminating unneeded tools, we came up with a standard turret load,” he continues. “This allowed mixing of an optimal variety of parts when nesting, providing much higher material utilization as well as greater throughput. In this proj- ect, dynamic nesting combined with machine management reduced needed sheets from 130 sheets to 69 for the production run—a huge material sav- ings as well as improved productivity. Nesting obviously played a big role, but proper machine management played a bigger role.”
Bottom line: Nesting software brings a lot, but be sure to look at the punch- ing machine—how it runs, the tooling being used, etc.
Group Similar Parts
Along these lines, grouping similar parts and part jobs provides more gains, according to Carnall, who offers ways for this to be done using specific software capabilities as an example.
“The software accomplishes this in two core ways,” he says. “It may create what we call our nest job that includes the day’s requirements. When nesting, the nesting engine analyzes the required tools. If a scenario involves the need for more tools than the machine can provide in one go, it automatically splits the tur- ret configuration. It groups as many parts as possible in turret configuration A, and then creates turret configuration
disadvantage commonly attributed to CNC punching. On the other hand, he notes, some advantages chalked up to laser cutting over CNC punching can become disadvantages downstream. “For example, in theory, a part can be nested at any angle for laser cutting. But should that laser-cut part then require bending, a bend may crack the part due to unfavorable grain direction.”
So, grain direction then becomes a consideration in nesting for laser cut- ting and CNC punching.
The particular style of CNC punch- ing machines also affects nesting.
“Punches trace the outer profile of the part when making a square, for example,” Carnall says. “The type of punching machine determines how that’s done. Turret- and rail-style punching machines require different methods, and each serve particular niches very well.”
To this point, on a rail-style machine, a tool can rotate to any angle, Carnall explains, which provides flex- ibility in nesting and performance. A turret-style machine, with some excep- tions, can’t do that, or has reduced functionality with perhaps a few tools that can rotate.
“Punching two 1⁄4-in. rectangles in a turret-style machine, for example, might require nesting one at a 0-deg. orientation, and the other at a 90-deg. orientation,” he says. “This eliminates
some capacity and ability for material savings and speed.”
But again, each style of machine has a home.
“An OEM, for example, may not require a lot of tools,” Carnall says, due to a limited and more-uniform part portfolio. “A rail-style machine may be more beneficial here. Turret-style machines offer the possibility of more available tooling—a consideration for job shops.”
Combine Machine Management with Nesting Knowhow
For each machine style, machine management and nesting can bring significant gains in performance and overall equipment effectiveness (OEE). Machine management plays a crucial role, according to Carnall, as effective nesting means much more than just the number of parts placed on a sheet.
“Some manufacturers will fill a sheet with 30 parts,” he explains, “but maybe they only needed 10 of those parts that day. The rest will become inventory or work in progress (WIP) that sits for a week until delivery or additional pro- cessing. Excess inventory becomes a substantial added cost.”
Combining nesting capability with proper machine management—sched- uling, determining proper sheet size, etc.—adds efficiency to the overall pro- duction process.
24 MetalForming/August 2022
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