Tips for HRSA Machining with Ceramic Inserts

By Chad Miller, Product Manager – Advanced Materials

CS100 ceramic grade

Our new CS100 ceramic grade provides excellent rough machining performance in heat-resistant super alloys (HRSA), including Inconel, MAR, RENE, Nimonic and Waspaloy. We designed this grade to reduce machining time and increase productivity by allowing for higher cutting speeds. In fact, the high-speed capabilities of ceramic result in metal removal rates that are four to eight times greater than carbide.

However, to effectively utilize the CS100 at high speeds, your workpiece set up and machining conditions need to be as stable as possible to prevent chipping of the grade. Here are some important tips to keep in mind before utilizing this sialon-based solution.

Toolholders

It’s best to use a toolholder that’s intended for securely holding ceramic inserts. You can gain improved stability by choosing a toolholder with a large shank size, such as boring bars made from heavy metal or carbide. 

As with any machining process, it’s important to keep your tool overhang as short as possible. However, when long overhangs are unavoidable, such as in boring applications, it’s best to avoid negative inserts due to high radial cutting forces. Instead, go with a positive insert geometry and tool holder combination with a 90-degree angle between the leading edge of the insert and the machining surface.  

When machining high-temperature materials, you can improve tool life by using toolholders with large lead angles, as those less than 15 degrees will leave you unsuccessful. A large lead angle will thin out your chips and possibly increase your cutting parameters. 

Inserts

You should utilize the strongest insert geometry possible for your application. A round insert works best in roughing operations, and you’ll want to keep its arc of engagement low (not to exceed 45 degrees) to prevent chatter and slippage. However, if a round insert isn’t an option, then choose an insert with the largest possible radius. Also, the thicker the insert the more strength and predictable tool life you’ll have. 

Insert geometry strength from highest to lowest:

• Round

• 100-degree corner of 80-degree diamond

• 80-degree diamond

• Trigon

• Triangle

• 55-degree diamond

• 35-degree diamond

Having the correct edge prep for your workpiece material is also an important consideration. A chamfered edge with a hone is preferred for applications that involve the roughing of high-temperature materials.   

Coolant

Concentration-level controlled flood coolant is important when machining with ceramic tooling – and you’ll want plenty of it, as an intermittent coolant supply will make for a disastrous situation. The coolant should also be clean because any contamination will shorten your tool life. 

You should not use high-pressure or high-velocity coolant (1000 + psi) during the machining process. Doing so reduces the temperature of the cutting zone and keeps the material from softening, thereby increasing cutter forces and accelerating tool wear. High-pressure coolant also causes erosion that will, in turn, decrease tool life. You also don’t want to use oil as a cutting fluid as that becomes a fire and smoke hazard.  

Application of Inserts

Insert geometry and radius size influence what feed rate you can effectively run in your machining operations. For instance, the weaker your geometry and the smaller your radii, the lower your feed rate must be. When possible, you should use larger radius sizes when machining components with large diameters. If smaller radii are absolutely necessary, then you must reduce your feed rate. 

These are just a few items to consider when machining with ceramic tooling, so if you’re interested in learning more, please don’t hesitate to contact me. I’d also be glad to go into detail on how the new CS100 can decrease your cost per part and improve your overall machining performance. 

About the Author

Chad manages Seco's advanced materials product lines, including all CBN and PCD products. When he's not helping customers implement advanced metalcutting solutions, you can find him training for and running 5K, 10K and 1/2 marathon races and triathlons. Chad can be reached at cmiller@secotools.com.