Quality Applications

Benefits Very low probing forces suitable for  delicate materials Can be fitted with styli as small as 0.3 mm Scans 140 points/sec and up to 118 in./min www.renishaw.com

Standalone Digitizer Smoothes Engine Head Production
Renishaw Cyclone Scanning System

CNC Cylinder Heads of Pinellas Park, Florida, strives to make the highest performing custom-ported heads for professional automobile engine builders who know that precisely ported heads mean better engine efficiency. Using a uniquely designed system that incorporates the Cyclone digitizer from Renishaw Inc., the company is achieving this goal.

 It's impossible to identically size each port volume by hand, or to accurately replicate an "ideal" port design on another head. It's also time-consuming, often taking a highly skilled person up to 40 hours to complete a set of heads--a very inefficient process.

 Computer numerical controlled (CNC) tools that machine heads in three axes boost efficiency by speeding throughput, but machining in only three axes leaves tool marks that cross over one another in various directions, requiring hand polishing and blending to smooth surfaces. Not only does this add time to the process, but it also removes additional metal, making the port larger and inconsistent with the original port design. Hand-polished ports result in higher performance, assisting flow by reducing restrictions, but a head with mismatched port volumes can't deliver its full horsepower potential.

 With these shortcomings in mind, Bob Hudgins, president of CNC Cylinder Heads, developed a system to solve both problems. Employing a special combination of high-tech equipment, including vertical CNC machining centers (VMCs), custom-built head fixtures with A- and B-axis CNC rotary tables and specialized CAD/CAM software, he machines aluminum and cast iron heads in five axes simultaneously. The process produces a mirror-smooth surface finish, without tool marks, straight off the machine. To solve the problems posed by duplication, Hudgins uses Renishaw's Cyclone digitizer as part of this system.

 A continuous-contact reverse-engineering tool, the Cyclone probes port and combustion chamber wall surfaces collecting dimensional data to produce a 3-D wireframe model of the internal features. A three-axis digitizer, the Cyclone is fitted with Hudgins-designed thin probe styli and a special fixture that rotates the head in the A (rotation about the X-axis) and B (rotation about the Y-axis) axes to allow access to hard-to-reach port areas.

 When first developing his system, Hudgins used a three-axis scan-and-duplicate digitizer that was fitted to one of his VMCs. With this device, whatever was scanned was machined, meaning the three-axis CAM software drove the machine tool in the same path as the probe. The probe's path was not always the quickest or most efficient for the machine tool. And while the machine tool was being used for scanning, it couldn't be used for cutting.

 Hudgins found it much more efficient to have a machine tool cutting a head at the same time a stand-alone digitizer was probing another. Because the Cyclone is a continuous-contact digitizer, probing routines can be done much more quickly than point-to-point probing on a machine tool, effectively cutting the scanning routine from days to hours.

 Cyclone duplication is vital to CNC Cylinder Heads for two reasons. Professional engine builders approach CNC Cylinder Heads to replicate their new port designs and cut them into numerous other castings. Builders for NASCAR teams may order up to 20 sets at the beginning of each racing season but often come back with new designs throughout the season because their head research and development is ongoing. When they develop a better design mid-season, they can get quick turnaround from CNC Cylinder Heads. The company's in-house engineers are also continuously developing their own port designs on a variety of manufacturers' castings for street performance and racing applications. After a newly designed head passes various flow, bench and swirl meter tests, the Cyclone digitizes the finalized design for duplication.

 To digitize deep inside a port, CNC Cylinder Heads uses a specially designed Cyclone fixture that can be rotated in the A and B axes. As the Cyclone probes within the port, rotary encoders register the angular position of the fixture and a digital display shows position to 0.001 degree. When all areas of the intake port that can be reached from the intake side of the head are probed, the head is rotated to finish probing the intake port through its valve opening, begin probing the exhaust port through its valve opening, and completely probe the combustion chamber. The head is then rotated again to finish probing the exhaust port from the exhaust side of the head. The Cyclone uses Tracecut software to establish the datum, or home position, and to collect the probe data.

 Separate probing data files, called patches, are stored for each angle position. The patches are downloaded into SURFCAM software, which has a provision for inputting patch angular position. Having various mirroring and copying features, SURFCAM is used to manipulate and translate the data into five-axis NC code for all ports and combustion chambers. As it's much less expensive than a high-end UNIX workstation, Hudgins found SURFCAM to have very good five-axis capabilities for the money.

 Accurate to within 0.002 inches, the continuous-contact Cyclone scans at a rate of 140 points per second at a maximum scanning speed of 118 inches per minute. A small block Chevrolet head, one of the most common that Hudgins machines, can be scanned in a couple of hours.