Carbide Cutting Tools and Sharpening Services In New England | KV Tooling Systems Augusta, Maine
Carbide Cutting Tools and Sharpening Services In New England | KV Tooling Systems Augusta, Maine
 

Regrinding of Ceramic "Button" Inserts

Regrinding of Ceramic Button Inserts | Carbide Cutting Tools and Sharpening Services In New England | KV Tooling Systems Augusta, Maine

Ceramic inserts are used in the turning and milling of high temperature “aerospace” alloys.

Some examples are Rene88, Inconel, and Waspalloy. These nickel based alloys are very difficult to machine due to their metallurgical properties. High percentages if nickel and chromium in the alloy can cause excessive heat buildup from large amounts of friction generated in removing the material in most machining environments. Heat destroys cutting tool materials as it does most everything on the planet.

Most every machinist has experienced “total tool meltdown” in their career. Usually it’s from trying to remove material too quickly via the feedrate, selecting the wrong cutting speed, misapplication of cutting fluid, or in a boneheaded move, run the spindle in reverse.

With nickel based alloys, you don’t really have to make a bonehead move to experience tool meltdown. It’s pretty easy given the properties of the metal. Fortunately, solutions have been developed to safely machine these materials.

Ceramics have been applied to aerospace alloys for several decades now with success. The most common is the “button insert”. Used mainly in turning applications, the button is a fairly economical and versatile tool for removing material. The ceramic material is specifically suited to hold its shape under high heat applications. In practice, the surface footages are generally run 10X the speed of carbide but with reduced chip load. The effect is a flaking off action that sends light hot chips spewing off the insert in a veritable “flameout”. Most of the cutting heat that is generated is forced into the chip and for a nano of a nano-second, it is melted and reformed into a strip of metal that shoots off into a kind of light flaky potato chip looking curl of material. The tool and workspace remain relatively cool.

When the insert becomes dull, which doesn’t take long, the tool is removed from a cut and the operator has to unclamp, rotate approximately 1/5 of a turn (depending on the depth of cut) and the machine returned to cycle. When the insert has been rolled all the way it is flipped over to the second side. One of the keys is to not let the insert begin to “notch”. Notching drastically reduces insert life by creating a large vertical crater at the cutting edge. Under magnification it resembles a canyon. Setting correct machining parameters reduce s this notch effect and increases the amount of remaining useable area on the insert. 

Once both sides have been used up it can be sent for regrind.

2 methods exist for regrinding a ½” button insert.

The first is to double disc grind both sides of the insert to downsize it from a RNG45 to RNG44. This method is usually the most economical and fastest since a large amount of inserts can be simultaneously be ground down. The thickness of the insert goes from .312 to .250. The benefit is the cost.

The drawback is that the edge prep is removed along with the wear. There are no provisions for grinding a k-land on the edge of the insert using this method. The inserts come back with a sharp edge that usually has some micro chipping. Sharp edges are weaker and can ship faster than prepped edges. Some regrind houses attempt to restore this edge prep by vibratory tumbling their inserts to add a small radius. This small radius can help but it doesn’t do as well as a k-land an doesn’t remove micro cracking.

The method we employ here at KV is to “shelf grind” the insert. (See the pics)

Regrinding of Ceramic Button Inserts | Carbide Cutting Tools and Sharpening Services In New England | KV Tooling Systems Augusta, MaineIn shelf grinding we rotary grind each edge one at a time for about .05’”radial depth and .020” axial depth around each side of the insert. We also add a light k-land of .002-.003 x 15 degrees at the outer edge. This adds strength, removes micro cracking and restores the original edge strength of the insert.

The shelf can act as a chip breaker which is very beneficial, especially in roughing operations. Since the inserts are ground one at a time, the regrind price is generally greater that those inserts which are flat ground to RNG44 size.

The tradeoff is performance. Our shelf grind process produces a more robust cutting edge that more closely simulates a new insert, and in some cases out-performs them.

The other benefit of the shelf grind is the overall thickness of the insert remains unchanged. It allows the operator to use the same lower shim, thus reducing the need to maintain an inventory if different types of shims and reducing the human error element of failing to change to the proper shim.

Turnaround times are in the 1-2 week range for orders.

Call us for ceramic insert grinding prices.

We here at KV Tooling are dedicated to provide the best solutions for your tool reconditioning needs and strive to give our customers the best value in the business.

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Manufacturers Association of Maine KV Tooling Systems | 285 Northern Avenue Augusta, ME 04330
 
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