CITIZEN SLIDING HEAD GEAR HOBBING CAPABILITY MAKES DP ENGINEERING THE BEST IN THE SOUTH WEST

"When you're quoting to two decimal places of a penny, as we sometimes are, you can appreciate just how competitive the sub-contract marketplace is. So, it's crucial we utilise the latest machining technology to not only stay ahead of competitors in terms of piece part costs, but also to ensure we meet our customers' delivery and quality demands."

Those sentiments by David Proctor, general manager of DP Engineering, explain why the Truro (Cornwall) company spent 400,000 (pounds sterling) last year on three Citizen sliding head autos from NC Engineering of Watford.

Complementing two similar Citizen machines - and an impressive portfolio of up to 51 mm diameter turning and up to 310 mm by 450 mm machining centre/milling, this investment in Citizens has, he says, cemented DP's position as the South West's number one turned parts specialist. It also reinforces the company's reputation as being one of the area's leading precision sub-contractors serving, OEMs in the mining, scientific, medical equipment, aerospace and domestic appliance sectors.

"Our reasons for continually going forward by installing state-of-the-art machine tools is not just about reducing set-up and cycle times," continues David Proctor, "even though, compared with the platen-type machines they've replaced, the Citizens have halved our cycle times.

"It's also to be flexible enough to respond to customer demands in terms of variable production providing more variety, smaller batches and kanban/Just in Time supply. And, in the case of our latest top of the range Citizen M32 sliding head mill/turning centre, it's about being able to gain the lead time benefits of one-hit turning and gear hobbing of parts that were formerly multi-operational."

He continues: "We were supplying batches of between 500 and 5,000 turned blanks to a customer who then subsequently produced the gear forms himself on manual gear hobbers which was a very labour intensive process.

It came to the stage where the customer wanted to single-source the parts rather than fund replacement of the gear hobbers. And, frankly, if we hadn't invested in the hobbing process, we would probably have lost the contract altogether."

The Citizen M32 presented the perfect solution, says David Proctor. With its all-electric operation and intelligent servo drives for each of its 13-axis capability, the twin-spindle machine is able to simultaneously machine with three tools. It has a triple tool-carrying turret and twin tool posts, high flexibility and a vast array of tooling options for the simultaneous front and back machining.

The concept behind the M32 is to incorporate a versatile and compact 'machining centre' into the platform for small turned parts, achieved by carrying a full complement of tools. Therefore, only minor adjustments and program call up are required for the machine to be ready for the next batch of parts.

The electrically powered 10-station turret, with drive to each tool position, for instance, can carry up to 80 tools via a programmable intermediate indexing function, and up to eight tools on a single station. A gang tool post can accommodate five turning and four driven tools while a third 'drilling post' has three tool positions which can also be driven.

Importantly, from DP's point of view, the M32 can combine 'special' operations such as gear and form hobbing and internal thread whirling, where the component is rotated at slow speed and is fed in the Z-axis over a high speed revolving threading tool.

In addition, special rotary tools for cross-angle rotary machining or thread milling and slitting can be mounted on the turret. Synchronous tapping is also available on each tool axis as well as milling interpolation and differential speed tapping.

"The Citizen M32 is able to complete a part in a single operation, and has reduced cycle times by at least 40 per cent," confirms David Proctor. "Of course, we've also eliminated inter-operation handling, and the associated duplication of set-ups and problems they can cause in terms of workpiece location/datuming, geometric relationships and overall quality levels."

"While we now also produce parts with gearcut features for other customers, the machine's 32 mm diameter capacity has additionally opened up new markets for us in terms of larger diameter sliding head work compared with the 20 mm maximum we were formerly restricted to.

"We are very pleased with the machine; its production possibilities seem limited only by the ability of the programmer - and we benefit because we have some very skilled people here. Also the extended capabilities it has given us are welcome, too!"

DP Engineering's first move into sliding head technology came in 1997 when: "we knew we had to get away from second operation work on platen-type turning machines," says managing director David Paull.

"Processing a variety of small parts - in many cases down to 2 mm diameter - we recognised the immediate benefits of using sliding head technology in terms of pick-up spindle, live tooling and the set-up and overall process advantages of one-hit machining," he says.

"Batch sizes can vary from just one to 250,000, though 1,000 tends to be our average. As a sub-contractor with short order book visibility, we need to be in a position to adapt to a changing market - and this must be
reflected in the types of machines we use."

In addition to being able to tackle small diameter, complex parts, David Proctor goes on to describe how machine flexibility and ease of use as well as service back-up and support were other main considerations in selecting the correct sliding head machine/supplier combination.

"Certainly other sliding head machines could provide live tooling for cross hole drilling and milling, for example, but none could compare to the ease of set-up and programming on the Citizens.

"These were major factors in placing the order for the first machine with NC Engineering, as was our confidence in choosing a company with a pedigree of service - which is important to us in this part of the country. Having tested the water with the first machine, and been very happy with the results, we didn't hesitate to choose Citizen again when we needed additional capacity."

DP Engineering's investment in the M32 is the latest addition to its Citizen portfolio of three L20 and a B12 sliding head autos. All are equipped with automatic bar feeds to run lights-out, and the complete sliding head section is manned by one programmer, a setter, one barman and an inspector.

The expanded sliding head capacity is the latest stage of an ongoing improvement programme at the BS EN ISO 9001 accredited company that is currently looking for larger premises to meet increasing demand.

"It may sound strange, but whenever there's a manufacturing downturn we are always very busy," concludes David Paull. "OEMs increasingly don't have the in-house capacity or can't tackle the really difficult work."

"DP has invested for as long as I can remember", he says. "Our staff are enthusiastic about new technology - they embrace it. In fact, if we hadn't invested in the Citizens we wouldn't be in business today!"