Tight tolerances: precision operation prevents bar material from grinding to a halt.

Position:Centerless grinding

While the market for precision ground bar stock has grown, suppliers have been hampered in their ability to consistently produce the material with the required tolerances.

This factor recently led Bohler-Uddeholm of South Boston, VA, a supplier of high-speed steels and powder metallurgy produced tool steels, to upgrade its centerless grinding capabilities. The improved process included a larger grinding wheel with more abrasive area to reduce the stock removal per revolution of the part and thus increase grinding wheel life, and additional monitoring devices to help control straightness of bars.

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The company has two older Cincinnati centerless grinders capable of meeting the industry standard tolerances of +/-0.001" to 0.002" on diameter for high-speed tool steel in sizes from 1/8" to 1.5" diameter, according to Steve Lewis, Bohler-Uddeholm's manufacturing manager.

"But we could not achieve the necessary tolerances for precision-ground bars on a repeatable basis without investing in new technology," he explained.

High-volume manufacturers of cutting tools, dental instruments, solenoid valves, and other precision products must have a reliable source of bar material in various sizes, finishes, and metallurgical compositions to meet their processing requirements.

In some cases, specialty metal bars with precise tolerances on diameter are specified, due to the end use application or where machining operations are performed using Swiss-type screw machines with pull-through chucks. These bars are produced in lengths up to 14' using centerless grinders to control size and finish in what amounts to a continuous process.

To evaluate new centerless grinding equipment, Bohler-Uddeholm executives formed a team including several machine operators and maintenance personnel. The team eventually selected a Landis Cincinnati Viking Super Series II centerless grinder from Cinetic Landis Corp. of Hagerstown, ME), to add to its in-house grinding capabilities.

The company recently purchased a second Viking centerless grinder for additional capacity for precision finished bars.

The Viking grinders are arranged to automatically grind bar stock using a through-feed grinding cycle. Each machine is fitted with an automatic bar loading and unloading system.

Infeed and outfeed

The automation, which includes an infeed table and outfeed table, facilitates the automatic operation of the grinder by supporting and feeding bars as they are ground. The...

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