CIMdata PLM Industry Summary Online Archive

25 June 2008

Implementation Investments

Simultaneous 5-axis Machining Powers up Racecar Engine Porting

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 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 Mazak’s 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 Machinists 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.

Edgecam application engineers also helped Kencom over some rough spots in the transition. A big one, Lee Sambrook recalls, was the Mazak 5-axis datums. They are in a unique co-ordinate system that initially took some special effort to understand. This was later automatically built into the post-processor; Edgecam account manager Phillip Gill personally worked with Kencom and Mazak to get this data.

These included the physical locations of the X, Y and Z axis zero points, the offsets unique to each machine tool axis (supplied by the factory and printed on the machine), how the workpiece is located and oriented on the trunnion in 3D space, and the positioning of the trunnion on the machine tools worktable.

These datums determine workholding and cutting tool offsets in the post-processor. A bespoke post-processor was supplied by Edgecam as soon as the system was delivered. This ensured Kencom’s ability to hit the floor running in full 5-axis machining as soon as the software was installed.

In addition to results for Kencom’s customers such as better surface finishes from 5-axis programming and machining, Kencom benefits directly. Machining time for a typical cylinder head, ports and all, has dropped from three hours to just one. Lee Sambrook explains: With three-plus-two you are cutting fresh air as much as 80 per cent of the time. It requires a minimum of three passes to do what you can do with one 5-axis pass. Sometimes we needed seven passes and 10 in the worst case.

Three-plus-two also required peck milling - cut and back off, cut a little more and back off again. That took a lot of extra time, he notes. Peck milling also created some blend-line and surface-finish problems.

Programming time has been cut in half, courtesy of the tight integration with Edgecam Solid Machinist, 5-axis capabilities, and automation routines in use. This adds up, as Lee Sambrook writes dozens of programs a week.

Among the less easily quantified benefits of full 5-axis machining are better programs. Lee Sambrook now has time to optimise the cutter paths, balancing surface finish against machining time. He continually pushes Edgecam with different speeds and feeds, different cutters, different approaches into the material, and different machining strategies. Kencom has also experimented with its cutting tools as porting requires long-shank lollipop cutters. Lee Sambrook has tried several variations and these tools are easily accommodated in Edgecam’s SQL-based Tool Store.

With full 5-axis programming, we have at last been able to achieve the potential of our Mazak Variaxis machines with a programming system we know and trust, says Adrian Vice. This has opened up an entirely new market to us with these very powerful but very costly machines.

Kencom confidently expects more cylinder head business, with engine heads and blocks for racing currently representing about one-fifth of its business. The company also specialises in machining cast components, particularly light alloys, in prototype and low-volume production batches for the automotive and aerospace markets. It also machines rapid prototypes and aerospace components from solid billet, which the new software will make much more efficient.

We see a great amount of interest by our customers in the way we are applying 5-axis technology, Adrian Vice says. In the forthcoming year, we anticipate a number of engine projects that will require specialist porting. That’s why we are considering buying a sixth 5-axis Mazak. In fact, Kencom is well equipped for this type of work. Its other machining centres include four more 5-axis VMCs - two VRX630s, one VRX500 and one VRX200, all equipped with Renishaw probing. Three are high volume production machines with twin-pallet loading systems. Kencom also has six 3-axis vertical machining centres - a Hartford, two Leadwells and three Matsuuras and four twin-pallet 4-axis horizontal machining centres - two DMGs, a Mandelli and a Makino.

Adrian Vice expects these performance gains to morph into a business transformation for his company. We will certainly be in a position to increase our sales of ported engine heads and, by inference, non-ported work this year. This new business will have a knock-on effect in other areas of sales, he adds.

He goes on to say: We anticipate that 5-axis will help us improve the accuracy, finish and cycle times of other components that we machine from the solid model as well as parts we machine from solid billet.

This success is also encouraging Kencom to fully integrate three-dimensional inspection, using co-ordinate measuring machines (CMMs) with Virtual D-MIS software for verification of dimensions and tolerances, and conformance to specifications. The CMMs allow us to perform a full-form port verification against the solid model, Adrian Vice says. That means much more complete and more reliable data than ever before.

Previously Kencom used measured data and a best-fit approach for the inspection of ports. The problem, Adrian Vice explains, was those methods had too little data to really measure what the customer needed to know. To resolve any lingering uncertainty, Kencom’s quality team and its customers had to meet face to face to review the inspection data. The distance, travel time and the associated expense put Kencom at a potential competitive disadvantage.

Kencom is making dramatic strides in keeping pace with evolving hyper-performance engine technology. Simultaneous 5-axis programming is a key part of this, but so is the added value of the relationship developed with Edgecam. The help we got from Edgecam gave us the confidence in our own ability to make a business success of this transition in machining technology, Adrian Vice concludes.

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