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DIY CAD CAM

CAD/CAM plays large in small shop - computer-aided design/computer-aided manufacturing

Tom Beard

This small mold maker has made CAD/CAM an integral part of its array of technical tools - and secured its position as a high-tech manufacturer of complex tooling.

Not so long ago a successful formula for a die and mold shop was a relatively small dose of technology and a huge measure of know-how. If a journeyman toolmaker couldn't make it with a print and a Bridgeport, well, then it just couldn't be done.

The formula is vastly different today. Enter the age of CNC, CAD/CAM, EDM, digitizing, TQC and more. Shops need both excellent knowledge and excellent tools in order to keep up with rapidly advancing standards for quality and efficiency, all the while having to deal with ever more complex workpiece designs. And shops have to be fast, with lead times shrinking by the day.

What's a small shop to do in this environment? The answer is as straightforward as it is harsh: Keep up, or perish.

Fehrman Tool & Die, a small shop in Byesville, Ohio, has chosen the latter course of action. With just ten toolmakers, they make some of the more complex molds you'll find anywhere. Is this shop remarkable? In some ways, yes. But the truth is they are mostly just flexible - willing, that is, to apply new technology as it becomes available and affordable, and particularly CAD/CAM. This has elevated the shop's capability to compete with virtually anyone in the mold making business. And armed with good tools, their small size becomes a major strategic advantage; it makes the company all the more nimble in responding to new challenges. Here's how the formula works in Fehrman's shop.

Rapid Change

Fehrman Tool & Die was founded in 1977 by two brothers, one expert in mold and die design, the other in machining. Today, Ron Fehrman continues as president, while his son Eric leads the engineering department.

Well, actually, the engineering department consists of just two people, but that doesn't mean the company is short on either its technical skills or tools. What they have is an efficient team, both in the office and in the shop, that is well tuned to serving the demands of some rather demanding customers that include (directly or indirectly) Honda, London Industries, Hoover, Ford, General Motors, Evenflow and Grief Brothers. Suppliers don't do business with these kinds of companies without having the house in order. Fehrman does, and in fact stakes its reputation on the ability to do the most complex work. But much has changed at the company in order to be able to keep up with their ever more challenging customer requirements.

Initially Fehrman was a typical tool and die shop, making a little bit of everything, but over time they grew increasingly focused on making molds. Today they make more plastic injection molds than anything, but also make tooling for thermoset injection molding, die casting, and some stamping dies. They can handle just about anything within a 30-inch square, and some things up to 40 inches, a limitation determined only by the size of the shop's two Hurco vertical machining centers.

Also typical, they began making their tooling mostly on manual mills - indeed doing things on those machines that many less experienced people today would think impossible - and doing the more complex cavity work with patterns and tracer mills. Then in 1988, Ron Fehrman decided to take a major leap into a new era. Within the span of a month or so, he acquired the shop's first CNC machining center, an Elox ram-type EDM, and CAD and CAM systems. The need for all this technology stemmed from the dramatic changes happening all around the mold and die industry: higher quality standards combined with significantly more complex part designs; the upsurge in parts being designed entirely in CAD by the original equipment manufacturers; the reduction in lead-time allotted to build new tooling; and more frequent design changes.

As such, Fehrman's production concept rapidly shifted from a hand-skills orientation, where process plans were conceived on the fly in the shop, to an engineering orientation, where it all had to be planned beforehand, and ultimately captured in part programs for intricately milling mold cavities or electrodes. Growing comfortable with CAD/CAM was central to making this transition possible.

Creating Tool Path

Eric Fehrman, who one day may inherit the shop, first inherited the job of getting the CAD/CAM system functional. With expensive new CNC and EDM equipment on the floor, clearly the first priority was to get out the programs to keep those machines running. It was, as he says, "CAM by fire," working both on his own to figure out how to use the system and with the experienced machinists to determine how best to cut the mold cores and cavities. After six months or so, the function was beginning to live up to their expectations in terms of productivity.

Initially, the shop purchased a Cadkey (Windsor, Connecticut) 3D CAD system and a separate CAM system, both running on personal computers. The CAM system's methodology for doing cavity work was primarily to generate 2D cutter paths across sections of a 3D wireframe representation of the form. Though not a true surfacing system, the CAM system proved quite functional for most of Fehrman's CNC work at the time. In more time, however, the limitations of the system became increasingly evident. Part geometry was growing more complex, and then Fehrman finally took a job that simply could not be programmed with the existing CAM system.

After five weeks of frustration with that part, Fehrman decided to upgrade the CAM capabilities to a true surfacing system from Surfware, Inc. (San Fernando, California). This term, "true surfacing" is an important distinction for die and mold making. Lower level systems typically approximate a free-flowing 3D form with a cloud of data points, a set of cross sections, or a grid of intersecting curves. With true surfaces, however, the entire skin of the form is mathematically defined.

Moreover, a higher functioning system provides wide latitude in manipulating surfaces. Individual surfaces can be created from scant input, such as a few cross sections or defining edge curves. Multiple surfaces can be smoothly blended together. Then these simple or complex forms can be modified later. And finally, the tool path code can be generated from this composite definition of even a very complicated cavity form.

The ability to work with multiple surfaces is critical. It's not at all unusual for a single cavity to be constructed from 300 or more individual surfaces that must be pieced together to create a smooth, continuous form. Also, Mr. Fehrman must be able to slice through that model in the appropriate place in order to create a proper parting line for a mold.

And just as important by Mr. Fehrman's reckoning is the control he must have in generating the tool path. First of all, the system must not gouge. With the prior system, he says, the cutter "would follow an individual section, but be totally oblivious to others around it," which was particularly problematic in sharp internal corners or with sheer vertical walls. In such cases, tool paths or specific geometry had to be individually edited in order to prevent the violation of adjacent surfaces. Subtle gouges were difficult to detect, and sometimes could only be discovered by trial cuts in wax.

Also, he now has the flexibility to flow cuts with surfaces of his own choice, rather than machine in successive straight sections. He can machine in continuous cuts over multiple surfaces, yet also establish boundaries for such cuts. This allows him to confine a specific machining method to a portion of a mold where it makes sense, but not be locked into that method for the entire job. He also can rough in constant Z depths, allowing the use of much more efficient flat-bottom end mills, and then move to ballnose cutters for the semi- and final-finishing passes.

The Front Door

As indispensable as CAD/CAM is for creating machining programs, it holds similar value in providing Fehrman with a tool to compile and manage critical workpiece information, and do this work in a way that inspires a high level of confidence from the shop's important customers. It is the tool by which customers' sometimes specific and sometimes sketchy requirements are interpreted and defined for Fehrman's own manufacturing process.

The shop must be prepared to accept job information in a variety of ways. As Mr. Fehrman puts it, "We get everything from old, washed-out cavities to IGES files." Between those extremes are prints, old patterns, previously molded parts, and sometimes a combination of two or more of the above.

As for the jobs that come in the form of some sort of physical model, Fehrman has also secured the capability to digitize those forms. The surface measurement is done on a Starrett (Athol, Massachusetts) coordinate measuring machine, which feeds data points to a PC running RevEng data collection software from Design Automation (Raleigh, North Carolina). The RevEng software allows a great degree of flexibility in gathering data. In addition to being able to simply collect an ordered cloud of points, the software can go the next step and create surface geometry using ordered or random clouds of point data.

Once the geometry is captured, it is exported either into the Cadkey or Surfware systems where it can be further manipulated - to clean up or detail the form, and finally to place it into a block of material along with all the other form features that together comprise a working mold. From this point forward, the process is essentially the same, whether the geometry was entered from digitizing, an IGES file, or created entirely from scratch on the shop's CAD or CAM systems.

Besides allowing Fehrman to get a handle on part geometry for their own purposes, CAD/CAM makes Fehrman easier for their customers to do business with. If customers want electronic data exchange - and some demand it - Fehrman can easily comply. With one customer, for example, the only paper they use are the prints for shop floor documentation. Or, if the customer is at a loss to fully describe what they need, the shop can help realize the customer's dimly defined objectives.

Ironically, Fehrman's tool makers are skilled enough that not all this electronic assistance is always necessary, at least in terms of creating a quality product. "We have the kind of people that you could just hand a print to, and they'd be able to get the job done right," says Mr. Fehrman.

But such a system no longer lives up to customer expectations, particularly the kinds of blue chip companies the shop does business with. "Customers can't see your skills," says Mr. Fehrman, "but they can see the equipment and the kinds of controls a shop has on its manufacturing processes."

In addition, the shop can do these things in much less time than they once required, which may be the most important benefit of all. Anyone who makes dies and molds these days knows what's happened to turnaround time, and tools that help compress the engineering cycle are very welcomed indeed. Moreover, the shop must be prepared to accommodate the much more frequent prototype and design changes common today. That's much easier and expeditious to deal with electronically in CAD and CAM files.

Balance

All these things said, Mr. Fehrman is quick to point out that "CAD/CAM won't solve all your problems." If anything, it's now a necessary tool just to stay even with rising customer expectations for quality, service and particularly for quicker delivery cycles. Increasingly, says Mr. Fehrman, their "biggest hurdle is fighting the clock." That means the shop can ill afford mistakes, creating all the more pressure on engineering to get it right the first time.

Which returns the discussion to the shop's resident body of know-how. To achieve the highest levels of performance, the shop can't afford to lean too heavily on any single tool. They must marshal all their resources, human and technical, to the greatest effect. Some work still does belong on the manual machines. Not every CNC job should be programmed off-line. And tool makers must be free to apply their expertise on the shop floor, even if the job was planned another way in the office.

One of the major advantages a small company enjoys is the ability to accommodate this level of flexibility without having to create some elaborate management structure to make it happen. The company barely has any supervision; training is imparted in the traditional mentoring process; and everyone is permitted - indeed, expected - to pursue improvements in tool design or manufacturing wherever they see an opportunity. When it comes time to execute changes in the shop's procedures, there's no red tape to wade through. "We just call in all the guys," says Mr. Fehrman, "talk about it, and that's it. It's done."

Maybe it's a eliche, but the company really does have a family environment, and this extended family seldom loses any of its members. But just being nice guys is not nearly enough to remain competitive in today' s environment. "You can' t have limitations," says Mr. Fehrman, and that means both in terms of your people and your tools.

For more information on surfacing CAM from Surfware, Inc., circle 35 on the Postpaid Card.