What is Manufacturing Not Getting From Its CAD?

Why can't CAD and manufacturing get along? Statistics show that sales of U.S. machine tools have been declining throughout the last five years. With this decline invariably come the people who declare manufacturing dead and buried - but that's not what is happening. What has happened in the last half-decade is that a lot of the bigger companies are getting out of manufacturing and starting up companies to do their manufacturing for them. Working with lower overhead, these small companies buy second-hand machine tools, refurbish them, and put them into parts production. In fact, one of the few e-businesses making money is an American company marketing second-hand machine tools on the Internet. "Fine," you might say, but what does this have to do with the CAD-manufacturing disconnect?

Two opinions must be considered, and both have their pros and cons. The first opinion is on integrated CAD/CAM systems. These systems can have their problems because, as critics have pointed out, some U.S. and European-based designers do not possess the necessary manufacturing knowledge to exploit them. This is attributable to training methods that lean toward avoiding designers having to experience life on the shop floor. One thing discussed by CAD/CAM industry people is the move from geometric modeling to product modeling. This is key because the objective here is to provide complete computer-interpretable product data for manufacturers. If manufacturers receive an engineering drawing, it may be complete, but not computer-interpretable. CAD is capable of supporting parametric representations, but parametrics should not be confused with nonnominal data in the CAD model directly, because the two are one and the same - one is a definition mechanism, whereas the other is used to define an envelope of acceptability. Of course, there are exceptions to this view, but at times, designers do not have enough manufacturing knowledge to know what the machines can do. All of the immense detail involved in passing on part design information to the manufacturer has not worked as well in the integrated systems as it could.

The second opinion is to say, "Let's not worry too much about integrating things; let's just take the key bits of information - such as surfaces and indentations - to a local manufacturing system, remodel it in a way that the machine tool sorts, let the production engineers know at this stage and then make the parts." With this approach there is a certain amount of remodeling going on, and there might be some discrepancies found in the part, but it is better to find it during this stage than later in the process.

"I don't think CAD has addressed manufacturing's needs very well," says Mike Evans, director of Cambashi Limited (Cambridge, UK) - a software/hardware consulting firm. "Designers see it fundamentally as a geometry problem. Once I headed a development team in which there was a lot of ignorance among the designers regarding what it was like to work on a shop floor. I sent the system designers to a one-week course in which they learned to operate the various machine tools. This greatly improved their ability to understand the problems encountered on the shop floor. Delcam (Windsor, ON) - a developer of CAD/CAM solutions - Evans continues, "does this sort of thing, too, but I'm not aware of many others."

Geometric Versus Product Modeling

Currently, most design systems are focused on the product's basic geometric definition or nominal geometry. Nominal geometry is dimensionless because it does not represent geometric dimensions or tolerances. In manufacturing, dimensions and tolerances are the stuff that defines reality and effects how something is manufactured. For example, when creating a block in a CAD system, the user will tell it to make a 2 in. x 4 in. x 6 in. block. Most CAD users would assert that this is all the information needed to make that part. But from manufacturing's perspective, this simplistic, nominal definition does not cut it.

Because there is no tolerance information, the manufacturing engineer does not know what the envelope of acceptability is. Without geometric tolerances, the engineer does not know the details of flatness, surface finish, parallelism, perpendicularity or anything else that would constrain the product as it might exist in the real world. Even something as simple as this block example leaves so much undefined that the cost to produce it could vary considerably. When specifying the 2 in. x 4 in. x 6 in. block, the designer thinks he has defined everything in the real world, but in essence, he has not.

"How do designs get made from CAD systems," asks John Callen, vice president of marketing for Gibbs and Associates (Moorpark, CA) - developers of CAD/ CAM applications. "Most design systems today consist of a 3-D modeling package with this drafting subsystem appendage. They have a drafting subsystem because, where else are you going to put all of this engineering data? Unfortunately, this data remains isolated in the drafting subsystem's digital paper space, not in the core design model. As a result, most CAD systems create a geometric model with a product, not a consolidated product model. A CAM user who wants to manufacture something from a CAD system will end up having to get two files. The part geometry can be transferred using an industry standard file such as IGES or STEP file; a proprietary standard such as DWG, ACIS or Parasolid; or the native CAD file. The engineering information is transferred either as a hardcopy blueprint or digital drawing formats such as DWG or IGES. The information is not provided in a single complete, unambiguous, computer-interoperable, digital representation."

Improving the CAD-Manufacturing Relationship

"CAD can give us the size, but not the tolerances," says Dave Pelligrino, tooling manager for Hi-Tech Mold, Inc. (Pittsfield, MA) - a tool mold and die manufacturer. "We still must have someone physically look at every feature and dimension and attach tolerances to it. From manufacturing's end, it does not look as if that will be changing any time soon."

STEP Steps In

"STEP is filling the void in the relationship between CAD and manufacturing," says Martin Hardwick, president of STEP Tools, Inc. (Troy, NY) - a CAD development company. "It is a high-level language for describing manufacturing operations, and like any other high-level language, it must be compiled before it can be executed on a specific machine, and this has many benefits. The same program can be compiled to run on many different machines, machine tool vendors can compete to provide fast machines, last-minute tool changes can be made and creating control data is much more efficient."

However, those reading this article should not come away with a feeling of doom and gloom. Software has made it easier for products to be manufactured, lowered production costs, and increased part quality while decreasing time-to-market. However, there remains the challenge of interoperability. To be sure, the CAD/CAM people have come a long way in trying to accommodate those in manufacturing, but for now, neither really can talk to one another.

"Software should not be used to drive manufacturing," says Evans. "It should be used as a tool in supporting manufacturing as well as supporting the goals of shorter time-to-market, higher quality and lower cost."