While this method generally produces acceptable results, there are inevitably inaccuracies built into the mold. Matrix' customer wanted to improve the accuracy of their tires by machining certain critical surfaces on the cast mold. An example of this would be the area of the mold commonly referred to as "the road service" (which forms the portion of the tire that actually makes contact with the road). The customer wanted to ensure that this surface was nearly perfectly round, which would increase the life of the tire and provide better performance. During the casting process, the road surface was left with an extra .040 of material to be machined off later. It was determined that a 5-axis machine would be the most ideal way to perform this operation. In addition to improving accuracy, it was thought that the use of a 5-axis machine would also reduce the number of required setups and machine time when compared to 3-axis machining.

This being determined, Matrix had to overcome two problems: They needed a 5-axis machine and they needed a way to program it. They were also on a very tight schedule. Matrix researched the machine tool market to find a machine that was suited for their application. They decided on the Micron UPC 710 high-speed machining center. With a machine on order, they now needed 5-axis programs. They initially thought of having the 5-axis programming work contracted out, but because they were worried about lead time and quality, they decided to purchase their own system. They found that there were only a few systems on the market capable of doing simultaneous five-axis contouring, and they ultimately purchased NCL multi-axis machining software from NCCS.

Says Gary Chmielewski of Matrix, "We looked at three different CAM packages, and of those NCL seemed ideal for doing tire molds. NCL was also recommended by other tire mold manufacturers." To ensure immediate production, NCCS provided on-site technical assistance, including the provision of a postprocessor for the 5-axis machine.

The mold is actually made up of 9 separate pie shaped segments, each a slightly different size. The manufacturing plan included 5-axis roughing and finishing of the road surface and 5-axis profiling around the edge of the tread walls. In addition, 115 vent holes per segment (for a total of 1,035 holes) were to be center drilled, drilled, and reamed.

One week after the machine was delivered, programs had been generated and test cuts were being made. After determining the best cutter types to use, and feeds and speeds, the NC programs were optimized and production machining began.

The results were remarkable. The roughing was done with a 3 x .02 c/r bull nose end mill using a .125 stepover running at 14,000 RPM and 120 IPM. Finishing was accomplished using a 3/16 x .03 c/r bull nose end mill using a .025 stepover running at 17,000 RPM and 120 IPM.

Says Matrix CNC Operator, Nathan Kopenhoffer, "Producing a similar finish on a 3-axis machine would have required the use of a ball nose end mill using a stepover of about .002 or less and at much slower speeds." The utilization of a 5-axis machine and the flexibility of the NCL software, saved a conservatively estimated 15 hours of machine time per segment over conventional 3-axis machining. Multiply this by 9 segments, plus a total of 4 molds, and you have a time savings of 540 hours or 132 40 hour weeks. "In addition to saving setup and machine time, we also achieved the desired accuracy with a 63 (mill) surface finish. There was virtually no benching required on the machined surfaces", said Kopenhoffer.

These savings were just on the milling operations. As you will recall, there were also over 1,000 holes per mold that needed to be drilled and reamed, all at varying angles. The c diameter through holes varied in depth from 1.25 to 2.5 inches. The hole operations took about 3 hours per segment. "The time savings over conventional methods is astounding, as each hole would have had to be manually drilled using a special fixture", stated Kopenhoffer.

Once the process was proven and well into production, preparations for a second, larger mold were under way. Because of the parametric nature of the NCL software, the tool path from the first mold was easily applied to the geometry of the second mold. NC programs were prepared very quickly, which ensured continued production on the 5-axis machine.

While 5-axis machining in the mold industry is still rare, it is beginning to catch on. "One reason for this", says William Conway, Regional Sales Manager for NCCS, "is because customers want shorter lead times and higher quality. Mold makers are scrambling for ways to become more competitive, and 5-axis technology is one way for them to do so."

"There has never been a better time to get started with a 5-axis machine", says Conway, "More machine tool manufacturers than ever before are producing 5-axis machines, and at prices that are affordable to smaller shops. With CAM products, such as NCL multi-axis machining software, users are able to take full advantage of their machine's capabilities."

Although it is unlikely that you will never experience another flat tire, you can be assured that the application of 5-axis technology can bring us better tires faster.