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Lord Corp. Has Zero Tolerance for Oversized Bores in Inconel

Engineers at Lord Corp., a manufacturer of expensive and complex aerospace parts, were struggling to achieve tight tolerances for precision bores on a new engine mount prototype. The stakes on this project were high -- a single scrapped part due to an oversized bore was a loss equal to the company's entire monthly budget. Lord reached out to Big Kaiser to find a way to improve the boring process reliability.

Based in Cary, North Carolina, Lord Corp. was working on a prototype design to produce an engine mount at its Dayton, Ohio, facility. The engine's forging -- made from Inconel 718 -- was heat treated to Rc40. The properties of this material classify it as a nickel-based superalloy. That means high-strength, high-temperature tolerance and corrosion resistance.

Engineers inspected the impact manufacturing deep bores in Inconel had on the tools Big Kaiser recommended for Lord Corporation's aerospace project.

 

 

These characteristics also make for very low machinability. A high nickel content makes the material very abrasive, increasing tool wear. Final machining and boring after heat treat only add to the all-around difficulty. The stakes were high with some forgings costing $30,000 each.

"I thought I had solved just about all the toughest problems, but this material and the costs associated due to scrap were the most challenging tests I have ever made," says Jack Burley, Vice President of Sales and Engineering for Big Kaiser U.S.

With help from longtime partner, Blaser Swisslube, Big Kaiser's test procedure was based on real-world requirements from Lord: Only after a hole was successfully bored in tolerance, could engineers move on to the next one. Each hole was considered a nearly completed workpiece, worth thousands of dollars, and could not be left undersized, have excessive taper or have bad surface finish. Most importantly, it could not be bored oversize.

Big Kaiser's boring heads are designed for precision production boring and their rugged design allows reliable operation, even under extreme cutting conditions.

 

 

The solution was to manufacture every hole with two passes -- with almost no adjustment in the diameter of the cutting edge in between. Due to radial forces, the first pass didn't finish the hole, so a second spring pass reached the tolerance. The spring pass removed 0.0015" more diameter material than the first pass.

As inserts wear, bores get smaller with each successive cut, so when the post-spring-pass bore is in the lowest quadrant of the specifications, the head adjusts to compensate. Big Kaiser's EWD digital head line enables these frequent adjustments.

"The heads give a zero setting that can always be a new starting point for a new insert, and each adjustment is stored in the head to give a total life for each insert, so every operator knows where the tool is," Burley says.

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Big Kaiser

Lord Corp.

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