When U.S. Technical Ceramics (USTC) in Morgan Hill, Calif., wanted to improve productivity and product quality in its green machining operations several years ago, it decided to test carbide tools with CVD diamond coatings from sp3, Inc. As a custom manufacturer of high-tech ceramic components, USTC is continually challenged to improve process reliability and quality while keeping costs to a minimum. According to Brian McElligott, manufacturing engineer, the CVD diamond coating appealed to him from the very beginning. “When sp3 first approached me with this new coating, I was eager to test it. The simple fact that the coating lasts so long, preventing downtime and enabling our operators to make parts instead of grind tools, convinced me that it would be worth the investment.
“I’ve never been one to look at just the first cost,” he adds. “If something’s going to last longer, I’ll take the chance. Obviously diamond is going to last longer than straight carbide. But I was also curious to see just how much it would improve the performance of our tools.”
One tool tested was a 3⁄8-in. diameter, 0.030-in. radius carbide end-mill. USTC was extensively using an uncoated version of this tool to machine 99.5 and 99.9% aluminum oxide parts that it produces for a variety of customers. Using a material application code (MAC) matrix developed specifically for the coatings (see sidebar: Matching the Tool to the Application), sp3 engineers recommended that a MAC 5 standard diamond coating be applied to the tools. A summary of the test results is shown in Table 1.
The dramatic improvement in productivity demonstrates that a decision about tooling should not be made based merely on the upfront cost of the tool. In this case, a 10X improvement in productivity reduced the actual per-part cost by 300%.
Every test run continued to confirm that measured productivity was increased with a corresponding reduction in actual tool costs. Based on this information, USTC decided to switch all of its production end-mills to CVD diamond-coated mills.
With the encouraging results using the CVD diamond-coated end-mills, the company turned its attention to the many carbide inserts that it used to machine components up to 18-in. diameter. In this application, standard turning inserts were selected with a recommended MAC 17 diamond coating. The results were similar to those achieved with the coated end-mills. With 200-300% improvements in tool life and corresponding reductions in both set-up time and cycle time, the decision to change to CVD diamond-coated inserts was also easy to reach.
Since the coated tools don’t need to be reground as often as uncoated tools, they’ve also enabled the company to experience gains from minimized downtime.
“Most of our machining operations are now running with CVD diamond tools, and we’re convinced that there are more gains to be achieved as we continue to pursue our evaluations of other diamond applications,” says McElligot.
The first challenge was to create sufficient adhesion or bond strength between the diamond and the carbide surface. It is not inherent that a chemically sound bond can exist between diamonds and a dissimilar material such as tungsten carbide. After considerable study and research, sp3 researchers developed patented surface preparation methods that ensure adhesion.
The second challenge was to develop a reactor that could both produce production quantities of coated material and maintain uniform consistency throughout the coating chamber. To overcome this challenge, sp3 researchers developed a state-of-the-art reactor chamber with computer-controlled cycles that provides the capacity and coating quality necessary to produce high-performance diamond coated tools.
As a result of these and other research and development efforts, CVD diamond coated tools are now becoming widely available on the commercial market.