AUTOMATED LATHE JOINS HOBBER AND SHAPER IN GEAR SHAFT PRODUCTION CELL

June 10, 2016

Triple-turret, twin-spindle turning centre enables one-hit machining, reducing cycle times three to four fold and eliminating handling:

To streamline the manufacture of a family of 12 hydraulic pump components for the yellow goods industry, a Traub automated turn-milling centre supplied by Geo Kingsbury (www.geokingsbury.com) has been installed alongside a Gleason hobber and Pfauter shaper to form a production cell on the shop floor of subcontract manufacturer, Muffett Gears (www.muffettgears.co.uk).

The Tunbridge Wells company specialises in hobbing, shaping, skiving and grinding gears with a PCD (pitch circle diameter) ranging from 4 mm to 400 mm and with modules from 0.25 to 5.0. The mainly bespoke products are produced to JIS, DIN, ANSI or customer specification.

The German-built Traub TNX 65/42 lathe with twin opposed spindles and 65 mm bar capacity is equipped with an LNS magazine capable of feeding sawn billets, or bars up to 1,600 mm long. At the output side, an integral arm removes each finished component from the counter spindle and places it onto a conveyor.

The robustness of this arm allows it to handle the heaviest component in the family of shafts, weighing 3.5 kg, while its generous travel means that finish-machined components up to 400 mm long can be pulled clear of the counter spindle. No other machine shortlisted by the subcontractor was able to match this performance.

Tony Smith, managing director of Muffett Gears and grandson of the founder commented, “We were turning the pump gear shafts from 45 mm and 50 mm diameter steel bar on a single-spindle, single-turret lathe, but were struggling to keep up with demand from our customer.

“We needed to increase output and initially looked at retrofitting a robot to one of our existing lathes. However, we decided to add extra capacity and invest in a new turning centre requiring minimal attendance from a machine operator.

“Geo Kingsbury’s response to our enquiry was prompt, following which we visited Traub’s Reichenbach factory a couple of times to see the machines being manufactured.

“Although the TNX lathe is available with four turrets, we established that optimum price to performance for our applications would be obtained using a turn-mill centre with three turrets. A suitably specified TNX lathe was installed in our Tunbridge Wells facility in September 2015.”

The machine was supplied by sole agent Geo Kingsbury as a turnkey package with component unloading mechanism and conveyor, bar magazine, various component programs, some of the required tooling and training for the subcontractor’s operators.

The pump gear shafts are turned from 300 mm to 400 mm long sawn billets of black bar. Operations include turning multiple diameters, producing a circlip groove and cutting a longitudinal, semi-circular key near one end using a Woodruff mill. Nearly 1,000 components per month are required across the family of parts, so batch size is around 100-off.

Productivity has increased substantially, as now to complete operations on the front end of the shaft as well as on the reverse after synchronous pickup by the counter spindle, the cycle time has been reduced to 4 minutes. Previously, on the single-spindle lathe, turn-milling took a total of 12 to 15 minutes and additional time was needed to invert the component manually in the spindle for the second operation.

Mr Smith added, “Now that the new production process has been established for the hydraulic pump gear shafts, we have started to turn other components on the Traub lathe in a variety of materials, including stainless steel, in batches of up to 600-off.

“Many of our products are ground after turning but some are not, so we need high dimensional accuracy and good surface finish on turned diameters. The Traub lathe allows us to meet those requirements and achieves very tight tolerances measured in microns.”

A highlight of the 10-tonne TNX65/42 is the heavily ribbed, cast iron, slant bed construction that dampens vibrations and promotes close tolerance machining. In addition to travels in X and Z of 650 mm and 175 mm, there is ± 40 mm of Y-axis movement on each turret. The synchronous main and counter spindles, each with C-axis, are of identical rating at 24 kW / 5,000 rpm.

Control is provided by the TX8i-s running Traub’s in-house developed software, optimised for the manufacturer’s lathes. Realistic 3D simulation shortens set-up time and avoids collisions when producing first-off components.

Main picture:
Machining area of the Traub TNX 65/42, showing two turrets below the spindle centreline and a single turret above. A stainless steel gear shaft is being turned in a single cycle.

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