counterparts. They have geometric considerations all their own. For example, the 1mm SPHINX drill can run at 80xD. But this is only possible because the cylindrical shaping extends further down the tool, closer to the tip, to facilitate pecking and maintain strength. Tool carbide should be ultra- fine grain (nano or submicron grain size) to ensure high abrasion resistance and good toughness. Coatings are valuable too, but it’s important to understand how coatings can negatively impact micro tool performance. Micro tools have extremely fine surface finishes and sharp cutting edges. Coatings can fill in valuable space – a flute on a drill, for example – needed for proper chip evacuation, which is critical in these applications.
provide this directly.
Chips and small tooling naturally do not get along well. Compensating for low spindle speeds with tools that have more flutes support an ideal feed rate, but chip evacuation may suffer. Determining the appropriate chip load – as close to the cutting edge as possible – allows operations at the highest possible spindle speed, accelerating the cycle and improving surface finish. Optimal conditions exist when the chip load is relatively equal to the cutting edge radius. Many micro end mills are designed so the cutting edge radius has a positive rake angle to create a shearing action. A chip load less than the cutting edge radius often results in a negative rake angle where the tool rubs
The MEGA MICRO COOLANT NUT for MEGA MICRO Chuck 6S provides a more efficient coolant supply for micro cutting tools. Ideal design for high-speed micro machining up to 6mm.
Coolants
Another trend in medical manufacturing being driven by the U.S. Food and Drug Administration (FDA) is clean machining without the use of water-soluble coolant. Super- chilled CO 2 or cryogenic machining with liquid nitrogen are considered possible replacements. Where protecting small holder parts at the nose from coolant has always been a concern, using gas requires more attention for holders to be effective. We are focusing on two features: • Holders that remain
completely sealed to outside atmosphere
• Very small delivery holes in collet faces or clamping nuts that properly restrict gas flow
This hydro-clamping tool holder system for Swiss-type lathes would make the decades-long approach of using ER collets obsolete by making it possible to perform a simple drill change on a gang slide in seconds.
Tooling
Tool considerations also must be taken into account to keep up with the demanding medical field. Better results often cannot be achieved by simply increasing spindle speeds or using smaller tools; a deeper understanding of cutters is necessary. We consider tools with diameters less than 3mm to be micro tools. These aren’t simply smaller versions of their macro
Coatings must be ultra- thin (<.001mm) and smooth; our experience shows that misapplied coatings result in poor tool life due to breakage; the coating reduces cutting edge sharpness, increasing torque force on the drill. When coating is necessary, consult with the cutting tool manufacturer to
rather than cuts. This increases the force required and generates more heat which can result in built-up edges and poor tool life. A chip load significantly bigger than the cutting edge radius often leads to premature failure because the tool is not robust enough to withstand such forces.
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