Diamond Tools & Green Ceramics: A Winning Combination
With one of the largest ceramics machining capacities on the West Coast, Applied Ceramics is able to respond rapidly both to R&D needs for ceramic-component prototyping and to high-volume production orders. To shorten lead times, Applied Ceramics keeps an extensive array of pre-formed materials in stock, and focuses on firm control of machining times and parts yield to meet tight delivery commitments.
Ever increasing complexity in ceramic parts for semiconductor processing equipment presented Applied Ceramics with production problems in machining green ceramic molded forms. To solve these problems, the company turned to diamond tools.
Drawbacks of Carbide and PCDFor most of its green ceramic machining operations, Applied Ceramics used uncoated tungsten carbide cutting tools, resorting to PCD tools for operations where maximum tool life was imperative. Carbide tools can be made in virtually any size and configuration required, and represent the least expensive type of quality cutting tool. However, because tools wear rapidly when cutting materials as abrasive as green ceramic, machines must be stopped frequently for tool changes, extending overall machining time. Dulling of the tool’s cutting edges can cause a build-up of tool pressure, leading to chipping, cracking and other damage, requiring the machine operator to be constantly alert to incipient damage to the workpiece.
Polycrystalline diamond (PCD) tools embody a cutting surface of manufactured diamond grit sintered with (usually) cobalt into a wafer that is bonded to a carbide substrate, which is cut to size and brazed to the carbide cutting tool. Because of the fabrication involved, PCD tools cost a lot more than carbide, and are even more expensive in very small tools, such as endmills and drills in diameters below around 1/16 in. Additionally, PCD tools normally have straight as opposed to helical flutes, which detracts from their cutting ability.
Applied Ceramics thus faced a situation where uncoated tungsten carbide tools, though inexpensive, presented production problems of frequent tool changes, tie-up of machine operators watching for tool wear, and yield loss through workpiece damage. The alternative, PCD tools, were far more expensive, and difficult or impossible to obtain in the desired configurations.
CVD DiamondChemical vapor deposition (CVD) diamond tools are made by depositing a pure polycrystalline diamond coating onto the cutting edges of carbide tools. Because the cutting surface is pure diamond, there are no binding chemicals that could contaminate the surface of the workpiece material.
A major advantage is that tools of any configuration can be diamond coated, including very small tools such as endmills and drills in diameters of 1/16 in. and smaller, tools with multiple cutting edges (straight and helical flutes), and indexable inserts with multiple cutting corners, chipbreakers and other intricate surface geometry. The ability to diamond-coat tools of any size and configuration also makes it possible to supply tools to custom configurations with short delivery turn-around.
Dan Le, production manager at Applied Ceramics and a 20-year veteran in machining green ceramics, decided to see if CVD diamond-coated tools could provide the long wear life typical of PCD tools, at much lower cost, and in the tiny configurations that were increasingly required to machine new products.
Unattended Machining with ConfidenceA particular problem was a gas diffusion furnace component with 24 slots cut at an angle through the entire depth of the part. Machining this part with uncoated carbide 3/8-in. endmills typically required 10 tools to complete one part. While the CNC program controls the entire milling operation, including stops for tool changes, it can’t “see” the onset of tool wear-out. Throughout the time it took to finish one part—about 1-1/2 hours—the machinist had to watch carefully for the onset of chipping as a tool wore out, since chipping or cracking would invalidate the entire part—an expensive throw-away, especially if the part was almost fully machined. The care required to maintain product yield was the problem that particularly concerned Dan.
Now, using diamond-coated endmills, one tool easily completes five parts—a 50 times gain in tool life. Besides reducing tool change time, diamond-coated tools can be run faster than carbide in green ceramic (speeds up by 10-20%, feeds about double). But the aspect most important to Applied Ceramics is that an endmilling operation for a part can be started and left to run to completion unattended, releasing the machinist to do other work while knowing that product yield will be 100%.
Diamond Tools in Other OperationsWith diamond endmills proving successful, Applied Ceramics started using diamond drills in diameters as small as 0.018 in. Drilling is another instance where long, reliable wear life of tool cutting edges is important. Drill wear causes breakout and edge chipping, making the product unacceptable. When drilling holes that are close together, collapse or partial collapse of the wall between holes can result from drill wear.
Indexable diamond inserts are also beneficial in machining green ceramic, providing very long wear life at modest cost. Applied Ceramics uses inserts for turning and flycutting.
While most of Applied Ceramics’ diamond tool needs are met with the diamond tool supplier’s standard commercially available products, the company plans to start grinding carbide tools to its special requirements. These tools will be custom-coated by the diamond tool supplier.