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Inside a small-parts lathe.

Inside a small-parts lathe

Here's a look at a current CNC automatic lathe. This type of machine tool complements conventional cam automatics, handling all but the longest runs.

Tens of thousands of cam-operated single-spindle automatics are in use today. For long-term large-volume batch production, there's still no better manufacturing means, according to statements made at 8.EMO by Traub AG, Reichenbach, West Germany.

However, batch sizes continue to decrease because of modern just-in-time (JIT) production. At the same time, mechanical parts are getting smaller and functionally more demanding. They're becoming more complex to produce, must be turned, milled, and drilled from all sides, and need to be internally and externally completed in one machining cycle.

The advent of 32-bit control technology with its capability of multiple processing and high-speed reaction offers a chance to replace the classic multislide cam automatic with the CNC multiple-turret turning center. But is it the right concept for the 1990s?

Where small components require intensive milling, drilling, and other internal machining operations (i.e., operations that have to be carried out successively and therefore dictate the cycle time), even a third, fourth, or fifth slide can do nothing to increase productivity. Therefore, according to Traub, the concept for the '90s cannot be replacement of all cam automatics by the CNC multislide automatics. Instead, the CNC machine must complement the cam automatic, so that turned-parts manufacturers can remain competitive during the decade.

Users require more than flexible production aids. New equipment must give maximum productivity over the entire component spectrum, the complicated parts as well as the easier ones. New machines must provide as many tools as possible in a minimum number of tool carriers.

Bar-turning solution

Engineers designed the Traub TNS 26 CNC bar-turning center to complement existing automatic lathes. The high-speed turning center with inclined bed can machine components up to 26 mm (1") dia. The automatic is available in single-and twin-turret versions, and employs a second, opposite, spindle with capacity similar to that of the main spindle. The second spindle moves longitudinally, powered by its own Z-axis drive. It also has its own C axis and therefore operates independently of the main-spindle C axis.

The C and Z axes of the second spindle can be interpolated with the X and Z axes of the two turrets and with the Y axis of the upper turret. Each turret accepts up to 12 tools. The drawings show the various turret movements that are available.

Simultaneous machining

A Traub engineer explains, "Tool bores in our lathes are situated at the circumference, allowing machining of two workpieces simultaneously, one in each spindle working with a corresponding toolholder in each turret. This arrangement allows fast changeover from twin-turret to twin-spindle operation.

"Each turret station can power drilling, tapping, and milling tools. In addition, the upper turret can drive thread-milling and polygon-turning tools. The Y axis in the upper slide allows direct access to center-offset drilling positions and direct programming for straight-line and contour milling.

"The turning tools can be fitted in twin-holders, one cutting tip facing the main spindle, the second facing the second spindle. The tools in the two turrets are directly accessible, and there is room for such a wide variety of tools that a single load can machine many different workpieces."

The firm states that the fast 32-bit control can reduce idle time to such a degree that cycle times match those of conventional automatics. Sometimes it's even faster. The concept also cuts setup time, making the machine efficient for short and medium runs.

Traub believes that batch sizes must be of a volume equaling classic mass production before the standard single-spindle automatic can produce more economically than the new CNC machine.

PHOTO : Overall view of the Traub TNS 26D CNC automatic.
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Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Feb 1, 1990
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