Thanks to Edgecam’s advanced software, Coventry-based contract machining company Kencom is making great strides in machining inlet and exhaust ports in cylinder heads for a variety of hyper-performance racecar engines. This type of machining, known as ‘porting’, deals with complex free form geometry that curves and tapers, and has extremely tight specifications on surface finishes.
For many years, Kencom had handled its porting jobs with three-axis milling plus two-axis positioning, known as ‘three plus two’ machining. However, engines for racecars have grown increasingly more complicated as designers wring every last bit of performance from the fuel. Every advance in machining and programming seems to be met with new demands from racecar engineers. To meet these challenges, the company upgraded its existing Edgecam software to include 5-axis simultaneous milling capability.
The system upgrade has given Kencom, which has an annual and growing turnover approaching £2 million and employs 35 people, an edge in the cylinder head business. The company is now attracting business from engine manufacturers in Germany and from some of the world’s most demanding engineers. It is also benefiting from significant productivity gains in programming and sharp reductions in machining time.
In cylinder head design, the most important role of intake ports is to ensure optimum mixing of fuel and air going into the combustion chamber. Both the intake and exhaust ports are cast into the cylinder heads, which are made from aluminium. “Intake ports are intricate and a real challenge to machine well,” Lee Sambrook, CNC programmer, notes. “That is why we needed full simultaneous 5-axis programming.”
He programs most of the company’s porting jobs on a Mazak Variaxis VRX630-5X with a Mazatrol Fusion 640m controller. This trunnion-type VMC is equipped with a Renishaw touch-probe for on-machine dimensional verification. The remainder of the cylinder head milling, such as exhaust ports and the tops of the combustion chambers, is also carried out on this machine.
Describing intake ports as ‘banana-shaped’ Lee Sambrook points out that he would never go back to three-plus-two machining. Originally an advocate for a competing software package, he says: “Because of Edgecam’s ease of use, I have been totally won over.” The curves vary from a 10-degree change in the axis to as much as 30 degrees. The ports also twist into helical shapes. In Kencom’s first 5-axis porting project, a 1.3-litre engine, which produces over 200 bhp, the intake ports averaged about 60 mm long and 20 mm to 30 mm in diameter. Dimensional tolerances are 0.01 mm. Overall, these particular heads measured 450 x 300 x 130 mm. Engines such as this typically redline at about 10,000 rpm.
Surface finishes are critical to avoid unnecessary turbulence, which slows the velocity of fuel-air mix as it is sucked into the engine, limiting maximum power. “We have improved the surface finishes in our intake ports by as much as tenfold,” says managing director, Adrian Vice. He speculates that gain adds as much as 10 per cent to the engine’s brake horsepower—a winning edge in a close race.
Compared to full 5-axis, three-plus-two machining has another drawback. As Lee Sambrook explains: “Three-plus-two methods resulted in inconsistent cutter loads on the tools. The difference meant some surfaces were missed and other surfaces were machined three to four microns too much, which means additional surface finish problems.”
At a more technical level, full simultaneous 5-axis machining uses circular interpolation. Three-plus-two machining is limited to less-accurate linear interpolation. “You always get better machined surfaces with circular interpolation,” he points out.
Adrian Vice, adds: “For two or three years, we skirted around the edges of the Mazaks’ capabilities with three-plus-two machining. Our customers were impressed with the technology investment and the way we made it work. It certainly raises the ‘can do’ profile of the business.”
A related challenge is blends, the CAD/CAM term for the meeting of two or more curved surfaces. “Before implementing Edgecam’s 5-axis solution, to get a good blend of the surfaces inside the port, we might have to do a total of 15 machining passes,” he says. Moreover, the second setup required by three-plus-two machining created another set of blending challenges, and those lines too were visible in the finished surfaces.
Kencom’s CAM solution has distinct elements: Edgecam simultaneous 5-axis machining module is the newest addition to Kencom’s existing Professional Milling software package. Edgecam Solid Machinist, which is solid modelling for CAM. It handles solid-model geometry and provides the tight integration needed for automatic part-design updates. The software can load native solid models from Unigraphics, Pro/Engineer, Catia, SolidWorks, Autodesk Inventor and many more via traditional IGES or STEP translation.
“We need the flexibility of Solid Machinist to import solid model files and everything that goes with them, no matter what system our customer uses,” Adrian Vice explains. “We rely on it to keep us abreast of all design engineering changes, no matter how small or subtle, Solid Machinist’s true associativity to imported solid models gives us the ability to update the CAM program automatically. This saves on the time it takes to work with customer modifications part way through the CAM process. We can do all this without having to rework the geometry and risk losing business.”
Custom automation routines have been developed jointly by Lee Sambrook and Edgecam application engineers. At Kencom, these routines contain best-practice machining techniques for porting, knowledge gained over many years.