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Gantry Robot Loader Makes Chuckers as Productive as Bar-Fed lathes

Gantry Robot Loader Makes Chuckers as Productive as Bar-Fed lathes

Added to MTDCNC by MTDCNC on 23 February 2011

On the shop floor at Burnley subcontractor, BCW Engineering, an Iemca gantry robot loading system from 1st MTA has been retrofitted to a twin-spindle Biglia CNC chucking lathe supplied in 2008 by Whitehouse Machine Tools. As a result, productivity has increased by up to 50 per cent compared with when billets were loaded and unloaded manually and labour costs have been reduced significantly.

Based on these factors, BCW's operations director, Trevor Cassie, calculates that the Iemca billet loader paid for itself within 10 months.

The significant financial savings prompted the subcontractor to invest in a second, identical automated production cell, which was installed in 2009. This time, the Biglia B565YS mill-turn centre and Iemca Automata 2.5 robot loader were supplied by Whitehouse as a turnkey facility. A third cell is planned for 2011, which will mimic the original in that 1st MTA will supply the billet loader and retrofit it to a Biglia chucker already in use at BCW.

A dozen variants of steel (EN32) bodies and sleeves for valve rotator assemblies are produced in the automated turning cells at BCW's Smallshaw site in Burnley. Fitted to each valve spring in large diesel and gas engines, the rotator turns the valve slightly each time it closes, reducing wear and stress, improving cooling, lowering emissions and preventing valves sticking due to uneven carbon build-up on the face and seat.

Three steps to automation

When BCW won the contract to produce the valve rotator components, it started to produce them on a single-spindle chucking lathe. The process entailed loading the billet by hand into the chuck for the first operation, then inverting the part and re-presenting it to the spindle for machining the reverse.

Maintaining accuracy after this second handling operation was difficult, as some machined features on the back of the component are tied up to ±0.05 mm with those on the front. As a result, a significant amount of production frequently had to be scrapped, reducing profits.

To resolve the problem, Trevor Cassie researched the market for a reliable and economical 8-inch-chuck mill-turn centre with twin opposed spindles. He was also keen to find a supplier with a reputation for good service back-up. The Biglia / Whitehouse combination was considered optimal and has proved to be successful in practice. The lathe's synchronous transfer of each component between the first and second spindles within the programmed cycle virtually eliminated scrappage.

The third stage to automation was the introduction of the Iemca Automata 2.5 gantry robot load / unload system.

Keith Gordon, BCW's Smallshaw site director, said, "We needed to increase the production rate of rotator components to meet growing demand from our customer, which would have meant buying another Biglia lathe, as the first was working flat out, 24/7.

"When we evaluated purchasing the first Iemca Automata 2.5, it was clear that it could boost output from the lathe we already had. In the case of rotator bodies, productivity has increased by 50 per cent, while sleeves are produced 30 per cent more efficiently.

"We also realised that reducing attendance at the machine would lower labour costs by allowing the operator to perform other work. This is in stark contrast to having to employ an extra person to run a second manually-fed lathe. That would have doubled the labour overhead and
involved more capital expenditure earlier.

"The higher costs would have made it more difficult for us to respond to requests for price reductions from our customer, which sells into a competitive global market and frequently has to its prices to win or keep contracts."

Body and sleeve diameters vary from 25 mm up to 150 mm and at the larger end of the range, billets for the bodies weigh over 1.5 kg. Repetitive manual lifting of these heavier components and clamping them in a lathe chuck, while not contravening HSE guidelines, is nevertheless arduous and worthwhile eliminating through the introduction of robotic handling.

Accuracy problems had already ceased once automatic spindle-to-spindle transfer in the Biglia lathes had eliminated manual handling between ops 1 and 2. Automated loading of raw billets into the main spindle is less of an issue with respect to accuracy, but still has to be performed consistently by the Iemca travelling robot arm, as does removal of finished parts for return to the carousel.

The Biglia / Iemca cells underpin an exacting production process. Gordon Murphy, BCW's quality director, confirms that 1.67 Cpk is achieved, compared with an industry norm of Cpk 1.33. The higher process capability equates to three faulty parts per million and dictates that ±0.017 mm be held where the drawing tolerance states ±0.05 mm.

Availability of the cells is high, with 120 hours running per week routinely achieved &ndash over 70 per cent of available time. Cycles times are between 2.5 and 6 minutes floor-to-floor, depending on component size.

The manufacturing process involves a robot gripper picking up a billet from a stack on one of the carousel pallets, transferring it via the overhead gantry into the main spindle of the lathe, picking the previous, completely-machined component from the counter-spindle using a second gripper on the end effector, and returning it to the carousel where the part is stacked onto another pallet.

Rapid motions close to the maximum 2 m/sec linear speed and 1g acceleration are programmed so that robot gripper activity within the working area takes just seven seconds, minimising non cutting time. Other robotic travel speeds are relatively leisurely, as they are performed during the machining cycle. A carousel fully stocked with raw material can provide up to 14 hours' continuous unattended running.

Retrofitting of a network-ready (MPI / PROFIBUS) Iemca Automata 2.5 to a lathe is straightforward and was carried out by 1st MTA engineers without incident to create the first machining cell, according to BCW. The company said that the supplier's service has been good and the equipment very reliable, with only occasional minor issues.

A significant advantage of the gantry robot loader is that, although integrated with the host lathe, it is mechanically isolated from it so that vibrations cannot be transmitted to the machining area. A programmable logic controller simplifies system operation and the intuitive controls are easy-to-learn. Retooling time of seven minutes makes the equipment ideal for shops with shorter production runs.

After-sales service provided by Whitehouse is also singled out for praise, with Keith Gordon going so far as to say that the supplier's performance in this area is better than that provided by all other machine tool companies with which they have dealt since BCW was established in 2002.

Trevor Cassie concluded by putting the project into perspective.

"Capital investment in bar automatics is reasonable for lathes capable of turning up to 50 mm diameter stock, but machines of larger bar capacity tend to be very expensive.

"Automating chuckers using robotic gantry loading is the most economical way of achieving similar levels of productivity for larger turned parts and we have been delighted with how well it has worked for us."

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