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Indexer doubles bow production.

Indexer doubles bow production

An SMW Model PT200 indexer maximized uptime to essentially double production of dental instrumentation at Denar Corp, Anaheim, CA. It also increased accuracy by a factor of five, providing a highly consistent product. These benefits helped the indexer pay for itself within a year.

The indexer, retrofitted to a Kitamura CNC vertical machining center, machines four sides of a U-shaped part in a single setup. The workpiece is the bow of an Omni articulator.

Use of the indexer reduces setups from four to one, slashing setup and handling time. To further maximize uptime, four of the sand-cast articulator bows are fixtured to the indexer at one time. This means fewer cycle stops and less time wasted waiting for the operator.

Machining of the four sides of each part from load to load now takes 12 min, less than half the time it took before installation of the indexer. Actually, the bows were machined manually before use of the indexer. Without this device, the VMC could handle only one workpiece at a time, and fixturing and re-fixturing caused downtime to exceed tool-in-the-cut time.

All of the holes were drilled on drill presses, a very slow process.

"But that was the best we could do at the time," says Bill Lawrence, director of operations. "Now the indexer allows us to put a number of parts on a fixture. It rotates 90 degrees when machining of one side is finished, permitting the next side to be machined right away. This ensures that the machining center's chipmaking time is maximized.

"The indexer has eliminated about 50 percent of our previous operations. We now have one person on one machine doing the work of four other machines.

"Furthermore, we can machine more consistently, thanks to the new indexer. That's because it positions the bows more precisely than manual fixturing. Parts are square; centerlines are more accurate; and drilled holes on the four sides are virtually identical from one model to the next. As a result, assemblies fit together like a hand and glove."

Consistency is made possible by a precision hardened-and-ground face gear on the indexer that provides positioning accuracy of [plus or minus] 5 arc sec and repeatability of 2.5 arc sec.

Step by step

In VMC operation, four bows are clamped to a special fixture mounted on the indexer. First the machine drills, reams, and taps two holes on the first side. One diameter is 0.0780", and the other is 0.3125". Then the indexer rotates the bows 90 degrees. Here, seven holes are drilled and reamed. Three are 0.1875" dia; two are 0.1250" dia; and two are 5/16-24 tapped holes.

Again, the fixture indexes 90 degrees, and the VMC drills, reams, and bores two more holes: 0.078" and 0.3125" dia. Then, the unit indexes to the fourth position for bottom-side machining, where two 5-40 holes are tapped into each arm.

Indexing continues for other boring and tapping tools, until all machining is completed.

The SMW indexer also plays an important role in machining a similar part used in the Mark II articulator. The indexer permits this part to be machined in one setup, compared to six previously required. The resultant reduction in material handling leads to an additional benefit--improved cosmetic appearance. With higher machining precision and fewer scratches and gouges, there is less scrap and less need for rework. Because reduced handling dramatically increased cosmetic quality, Denar has doubled lot size production to 5000.
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Title Annotation:dental instrument machining
Publication:Tooling & Production
Date:Oct 1, 1989
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