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On the NASCAR circuit, high-tech = high performance.

One of the hottest drivers on the NASCAR Winston Cup circuit this year was Davey Allison. Driving his #28 Ford Thunderbird, Mr Allison won the Daytona 500, the Talladega 500, the North Wilkesboro First Union 400, the Michigan 400, and the Winston race. Until his accident at Pocono International Speedway on July 19th, he had led every NASCAR race at least one lap and had the lead in more overall laps than any other driver. Unquestionably, a record like this says a lot about the driver and his car.

Robert Yates Racing, Charlotte, NC, builds Mr Allison's cars. Lately, the company has recorded productivity gains in the design and manufacture of its engines that are as impressive as Mr Allison's track record. Yates' NC programmer Brett Conway explains:

"In September of 1991, we purchased a PC-based CAD/CAM system (Mastercam CAD/CAM software from CNC Software Inc, Tolland, CT) to design the cylinder-head shapes and surfaces and to program the cutting-tool instructions for CNC machining. We also purchased a Mori-Seiki MV 40 vertical machining center to machine the heads."

The new technology has resulted in dramatic gains. "It used to take us 100 hours to hand grind a set of cylinder heads," continues Mr Conway. "Now, we program and machine them in three hours."

PC-based CAD/CAM

"We use the CAD portion of the software to change the combustion chamber design and to revamp the design of the intake and exhaust ports," Mr Conway says. "With respect to CAM, the big benefit has been the ability to define tool paths for complex radii and contours exactly the way we want to, then have that tool path drive the machine tool to machine the parts exactly to specifications."

CMM & CAD/CAM

Yates' Ford engines are revised versions of the old Cleveland 351 cu-in V-8. The process begins with a digitizing operation.

"We pour liquid rubber into one of the heads to make a male representation," Mr Conway says. "When the rubber hardens we extract the male form and digitize the ports and chambers with a Brown & Sharpe DCC coordinate measuring machine (CMM), using Brown & Sharpe's Avail contour three-axis software. This gives us the X, Y, and Z points in space," he continues. "We load those points into Mastercam and then enter a minimal amount of basic information, like start and stop points and direction of cut.

"From that, Mastercam automatically calculates the lines, arcs, splines, and surfaces that comprise the port shape. We design the finished ports in a wireframe rendition, fit the toolpath to the shape, and use that toolpath to determine the tooling.

"We machine the part in a single setup, using the fourth axis of the machine tool," he says. "We set the head on a special fixture plate mounted to the fourth axis for rotation to present the different sides for machining."

The machining steps are performed by a series of ten specially made tools housed in the 30-tool automatic toolchanger. For example, the machining of the ports is done with a spherical carbide mill; a special angle cutter roughs the valve seat areas.

"We use 6" to 8" rigid tungsten shanks to reduce vibration," Mr Conway says. "We make all the tools ourselves--we design them in Mastercam, along with the fixtures--and send them out to a local carbide-grinding house for finish grinding."

Tolerances range from 0.0005" for hole locations and diameters to 0.005" for the profiles of the chamber and port surfaces. Surface finishes get as smooth as 16 rms, especially down in the port.

"In the port, we have to machine little hills and valleys, in order to atomize the fuel mixture properly," Mr Conway says. "Fuel is six times heavier than air, and if the fuel separates from the air it won't burn. So we have to keep the fuel suspended as a vapor. These bumps keep the mixture turbulent and bouncing around so the fuel can't separate."

The protrusions are actually tiny radial bumps machined into the port surface. Mr Conway uses a ballnose end mill to machine them, programming "jumps" between each point where the tool engages the material, leaving a series of hills and valleys.

For some cylinder heads, the NC program has to be a little different. "We have to vary the bumps with respect to spacing and surface finish, depending on the kind of race the cylinder heads are being prepared for," Mr Conway says. A family-of-parts feature in the software minimizes the need to recreate entire programs.

Programming flexibility

Mr. Conway says the key benefit of the software is the ability to effect these and other kinds of changes to the NC program quickly.

"In 15 minutes, we can alter a design, write an NC program, and be ready to cut metal," he says. "We do the CAM first--design the geometry for the toolpath--and then go to the CAD dimension. Then we send the full 3D drawing to an HP DraftPro D-Series plotter for our hard-copy output."

Mr Conway is a strong advocate of PC-based CAD/CAM. "I compare this with the best of the workstations out there," he says. "We're doing complex surfaces, with changing entities all over the surfaces, not just contouring and pocketing."

He says that even complex surfacing work is pretty straightforward. "We like the software because we don't have to know a lot about surfaces to get precise shapes and exacting tolerances. Really, the software does all the work."

CNC Software, Tolland, CT, circle 287.
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Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Machining Controls & Software; National Association for Stock Car Auto Racing
Publication:Tooling & Production
Date:Dec 1, 1992
Words:914
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