Page 21 - MetalForming February 2012

enable automatic importing of the CAD data.
However, CAD data is not always perfect. How, then, can a fabricator guarantee reliable and accurate part information? The answer: Good engi- neering standards. We recommend that standards be attained by requiring the engineering staff to follow a well- defined set of rules for layers and meth- ods of creating clean and consistent drawings.
Before moving on to CAD data, how- ever, we need to first focus on invento- ry. Inventory records found in the MRP system must match the data in the nest- ing system in order to gain full advan- tage of the integration. Then, with the system properly set up and as material arrives at the plant and is entered into the MRP system, the inventory will auto- matically appear in the nesting system. As the material is consumed and rem- nants are created, the MRP system auto- matically receives those updates without manual intervention. Otherwise, the nesting system and the business sys- tem can result in a mess.
The CAD File
Regardless of where the CAD file originates—a vendor or the internal engineering department—it is impor- tant to use good engineering practices. This may require working with the engineering department creating the CAD file to agree on and maintain good engineering practices. DXF files should follow sound drafting rules, including how title blocks, dimension and other information breaks down into layer information. Because DXF files typi- cally are 2D CAD files, they should include text strings to pull material type, thickness and other information from the file. In addition, fabricators should implement standards for creat- ing the geometry of formed features such as louvers and embosses in a 2D CAD file, to ensure the features are handled by the nesting software.
Often, solid models can be easier to use, since the design intent is cap- tured inside the solid model. The importing configuration can be
Drawing from a greater number of components, nesting software has a better chance to arrange parts for maximum material utilization. Filler parts, or those demanded fre- quently, may be able to fill the remainder of a sheet when necessary.
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designed to have material type and thickness data pulled directly from the model upon import, and at the same time have certain features removed. In any case, maintaining consistent engi- neering standards will ease the import process from any CAD system, and ulti- mately save the company from unnec- essary duplication of effort.
The Nesting Process
At this point, much of the mundane, duplicated chores have been removed from the nesting process. Now the real fun begins.
One of the biggest challenges a user faces when nesting is selecting which parts to include in the nest. Nesting parts too early in relation to their due date can create problems, should the order change or get cancelled. Storage also can be a problem when making parts well in advance of the due date. Of course, nesting too late and not having the parts finished in time also creates headaches. So how can a fabricator keep part orders prioritized and on track?
State-of-the-art nesting software can communicate directly with the scheduling software, and label past-
due parts as higher priority than those due in a week or more. Unfortunately, as many programmers know, sched- ules can change quickly. A last-minute job can disrupt a well-planned time- table, and even cause material waste when it forces a fabricator to rush to complete the job. For this reason, soft- ware can nest a day or more in advance. Drawing from a greater number of components, nesting software has a better chance to arrange parts for max- imum material utilization. Filler parts, or those demanded frequently, may be able to fill the remainder of a sheet when necessary.
A caveat: Nesting should not look too far ahead or run too many filler parts, as this could flood the shop floor with work in process. Programmers must balance maximum material uti- lization with downstream production needs. Getting the most out of a sheet means little if a welder must sit idle awaiting a component that was not nested because it didn’t fit neatly onto a sheet. While fitting the component onto the nest might produce a little more scrap, the cost is negligible com- pared with the expense of a highly skilled welder sitting idle.