To streamline the manufacture of a family of 12 hydraulic-pump components for the yellow-goods industry, a Traub automated turn-milling centre has been installed alongside a Gleason hobber and a Pfauter shaper to form a production cell on the shopfloor of the sub-contract manufacturer Muffett Gears.

The Tunbridge Wells-based company specialises in hobbing, shaping, skiving and grinding gears with pitch circle diameters (PCDs) ranging from 4 to 400mm 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 — supplied by Gosport-based Geo Kingsbury Ltd (www.geokingsbury.com) — has twin-opposed spindles and a 65mm bar capacity; it is also equipped with an LNS magazine capable of feeding sawn billets, or bars up to 1,600mm long. At the output side of thr machine, an integral arm removes each finished component from the counter-spindle and places it on a conveyor. This arm can handle the heaviest component in the family of shafts made by Muffett — some 3.5kg — while its generous travel allows finish-machined components up to 400mm long to be pulled clear of the counter-spindle. No other machine shortlisted by the sub-contractor could match this performance.

Tony Smith, managing director of Muffett Gears and grandson of the company’s founder, said: “We were turning the pump gear-shafts from 45 and 50mm-diameter steel bar on a single-spindle single-turret lathe, but we 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 that would require a minimum of operator attendance. 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 the optimum ratio of price to performance for our applications would be obtained using a turn-mill centre with three turrets. The TNX lathe was installed as a turn-key package last September.”

Increased productivity

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

To complete operations on the front end of the shaft, as well as on the reverse end after synchronous pick-up by the counter-spindle, the cycle time is just 4min. Previously, on the single-spindle lathe, turn-milling took 12-15min, which included the time needed to manually invert the component in the spindle for the second operation.

“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; it also achieves very tight tolerances — measured in microns.”

A particular feature of the 10-tonne TNX 65/42 is its heavily ribbed cast-iron slant-bed construction, which dampens vibrations and promotes close-tolerance machining. In addition to travels in X and Z of 650 and 175mm respect-
ively, there is ±40 mm of Y-axis movement on each turret. The synchronous main spindle and counter-spindle each have a C axis and an identical rating of 24kW 5,000rev/min.

Control is provided by the TX 8i-s; this runs Traub’s in-house-developed software, which has been optimised for the manufacturer’s lathes. Furthermore, realistic 3-D simulation shortens set-up times and avoids collisions when producing first-off components.