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Better, faster engines - WIP - race car engine products - Brief Article

Automotive Design & Production, Sept, 2001

Think of this as a NASCAR Winston Cup vehicle replete with sponsor stickers:

* Renishaw

* SORC

* Daewoo

And, of course, those would just be a Few of the images on a given quarter panel.

The issue here is some of the gear that is being used by Joe Gibbs Racing (Huntersville, NC) to field its two cars, the Home Depot Pontiac driven by Tony Stewart, 1999 Rookie of the Year, and the Interstate Battery Pontiac piloted by Bobby Labonte, 2000 Winston Cup Champion.

The items in question are used by the team in order to perform design, reverse engineering, duplication, and machining of the cylinder head ports of the engines that power the cars.

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Central to the activities are the Renscan 200 on-machine scanning system from Renishaw [Hoffman Estates, IL]. As Mark Bringle, Joe Gibbs Racing CNC manager, explains, "We wanted a cost-effective, yet accurate scanning system that would take minimal ramp-up to start producing finished heads. At one-tenth the cost of a coordinate measuring machine, the Renscan 200 gave us scanning simplicity and precision, but not sticker shock."

The system uses Tracecut software that permits the duplication of ideal port and combustion chamber designs and the generation of NC code necessary to machine the profiles in aluminum heads.

One of the keys to winning in Winston Cup is the best engine (which, of course, is arguably the same for any racing series, but, for example, in the CART open-wheeled series, the engines are provided by the engine builders sealed; the race teams cannot modify the engines in CART, as they can in NASCAR--as long as the NASCAR teams' modifications meet series spec, of course]. Because the NASCAR series is run on several types of tracks, the engine setups required are typically different from week to week [e.g., short tracks require high torque; high horsepower is key on super speedways). So the heads the Joe Gibbs team receives from General Motors undergo some significant modification in the 145,000-[Ft.sup.2] facility that the team operates.

Gibbs' engineers develop port models both through hand grinding and the SDRC computer-aided design [CAD] tools. Prototypes produced, then flow bench tested. There are two reasons why a scanning capability is important, according to Bringle: "The slightest modification to CAD-designed profiles renders the CAD file useless and requires scanning to capture the new profile. And even though hand porting may yield a good single profile, it's impossible to replicate that design for all eight cylinders without scanning."

The scanning is performed on a Daewoo Ace H-SOD horizontal machining center with pallet changer. A dedicated head-scanning pallet is fitted with live-axis rotary table and special head fixture. The Renscan 5P2-1 scanning probe mounts in the spindle using a standard EAT taper shank.

Given the configuration of a cylinder head port--which resembles that of a bent tube--it isn't possible to scan all aspects from a single angular table position; six scanning routines, or patches, are required for each intake port. Scanning patches are performed in a waterline method at predetermined A-and B-angles from the manifold side and through the valve opening in the combustion chamber. The patches are overlapped slightly to assure the entire port is scanned. There are some 125,000 data points captured within a couple of hours for each intake port. Exhaust ports are scanned in a similar manner; combustion chambers are scanned from a single fixture position.

After scanning, the Tracecut software generates wireframe models that are copied and mirrored to replicate the profiles For all eight cylinders. The software then translates the data into three-axis NE code for machining. Bringle doesn't shoot For a particular surface finish, but attains the type of surface required by using a 0.025-in, incremental tool step-over. After cleaning, heads are ready for assembly, with no hand blending of tool marks required.

Automotive Industry

Better, faster engines - WIP - race car engine products - Brief Article

Automotive Design & Production, Sept, 2001

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