Since the beginning of 2006, earthmoving plant manufacturer, Komatsu, has increased production output from its Birtley, Co Durham factory by over 40% and nearly halved delivery time for its excavators to 22 days. A key element to the improvement was the replacement of two machines at a cost of £2.7 million.

The new machining cell, which has been operating for over two years, alleviated a bottleneck in the production of fabricated revolving (revo) frames that allow the excavator cabs to swivel through 360 degrees. One of the machine tools was a CNC straightening press to take the place of a manually operated model that fed a 20-year-old Japanese SNK (Shin Nippon Koki) gantry-type, vertical-spindle machining centre. This has also been replaced by two high-speed machining centres whose horizontally opposed spindles machine both sides of the revo frame simultaneously. SNK was the chosen supplier for these machines as well, via UK sales and service agent, Matsuura Machinery.

The SNK cell reduced overall cycle time for a benchmark frame for a mid-range PC-210 excavator from 2 hours 12 minutes down to 45 minutes. The machine is so productive that the bottleneck has disappeared and the 40% growth in overall production output has been accompanied by a big reduction in the time spent machining the frames. Not only is the cycle time shorter but set-up time is faster as well, down from 45 to around five minutes. Whereas previous economical batch sizes necessitated a lot of work-in-progress on the shop floor, this has been eliminated by today's typical batches of ones and twos.

The project started back in 2001 when Komatsu researched machines available that could replace the ageing SNK machine. Although it had a twin pallet changer, allowing off-line set-up, the vertical spindle meant that the component had to be machined flat on one side and inverted using a manually operated crane to machine the reverse. Special tooling had to be employed for machining features on the sides of the frame. This worked well enough, but increasing demand for the seven models of Komatsu excavator in the 13 to 80 tonne capacity range made at Birtley meant that the machining centre was working flat out, 24 hours a day.
 
Fifteen machines were initially identified as possible replacements. The list was gradually whittled down to five and then to two potential suppliers. Capital cost, operating costs and machining efficiency were important, but so too were footprint and environmental considerations. SNK machines are used in Komatsu’s machining facilities in Japan, so choice of the same supplier made sense in terms of commonality of global manufacturing, but it was not stipulated by head office.

In June 2004, SNK was selected and the order was placed on Coalville-based Matsuura Machinery in June 2004. The company was considered best placed to undertake turnkey responsibility for the project, which involved co-ordinating the activities of outside firms including fixture manufacturer Kingsbury Engineering, cutting tool supplier Nikken, Midland Sheet Metal for the guarding and platforms, and swarf handling company Filtration Service Equipment. Barnwell Construction prepared the deep, complex foundations while the old production process continued at full tilt nearby.
 
The project was overseen by Matsuura's commercial manager, Simon Burrow, over an 18-month period. It was handed over in November 2005, on budget and one week ahead of schedule. The machining of the revo frames to meet production demand has been rethought. Central to the new arrangement is the deployment of two spindles instead of one, allowing simultaneous machining on two sides of the component. Additionally, the spindles are horizontal to allow all-round access and hence single-hit machining in one clamping of the workpiece. At the same time, feeds and speeds have been significantly raised, allowing a more than three-fold productivity increase across the milling, drilling, tapping, and boring operations.
 
Another significant development is the adoption of minimum lubrication mist to replace flood coolant, which has had a marked impact on operations. The most obvious advantage is a reduction in the amount of coolant used, down from 1,000 to three litres per month, just 1.6cc/min are used. The working environment has been improved and the benefits even feed through to increased cutter life.
 
While one revo frame is being machined, a new frame fabricated from grade 43A mild steel plate is straightened to within a couple of millimetres accuracy on the CNC press and is lifted by crane onto one of two tilting tables serving the twin SNK machining centres. The largest component size currently produced is 1,500 by 4,000 by 1,000mm, which weighs 4.5 tonnes.
 
Prior to the frame’s arrival, the appropriate fixture is taken from one of two automated storage racks and placed on the table. The operator manoeuvres the component into position and actuates the fail-safe hydraulics to effect mechanical clamping. From a central control, the operator calls up the required program to the Fanuc18MC CNC systems of the SNK machines, instructs the table to rise through 90 degrees to the vertical position, and sends the pallet to the machining area of the twin opposed, 37 kW/6,000revs/min spindles of the machining centres. Once there, the frame undergoes machining of the boom rear bores and the mounting bores, the latter to ±10 microns trueness. This is the most critical operation as the boom pivots on these, so part probing is used to verify that there is no more than 3mm of stock to be removed from the fabrication.
 
The table then turns through 90 degrees around a vertical axis to present the frame for simultaneous face milling, drilling and tapping of the machinery area on the upper side and the swing circle and flange holes on the base. A large aperture in the table and the open design of the fixture allow access to the reverse for machining. The part moves from the machining area to the second tilting table where the finished revo frame is offloaded and sent to the assembly line.
 
www.matsuura.co.uk
www.komatsu.co.uk