Productivity improvements in component grinding

Keywords Geo. Kingsbury, Blohm, Grinding, Blades

Cycle time reductions of a quarter together with a halving of set-up times for each new job are the reported benefits which Lancashire subcontractor, Earby Light Engineers, has been enjoying since the installation of a Blohm profile grinding machine. We understand that the productivity improvements have helped Earby Light to achieve a significant increase in through-put in the grinding shop at its Blades Division in Kelbrook.

Supplied in mid-1998 by UK agent, Geo. Kingsbury, the German-built Blohm Profimat MT spends much of its time grinding compressor and turbine blades(Plate 1). The blades weighing from a few grams up to 40kg are for aero engines and land based gas turbines. A variety of other jobs are also undertaken on the machine for the aerospace and other high technology industries. Materials are mainly cast or forged cobalt and nickel alloys, titanium and aluminium.

 Plate 1 The Blohm Profimat MT grinding a turbine blade at the blades division of Earby Light Engineers, Kelbrook

Employing 250 people, this subcontractor uses a full range of machining techniques including turning, milling, laser drilling, spark erosion, and electrochemical machining. Aerospace and other turbine work accounts for three quarters of turnover and customers include Rolls-Royce, British Aerospace, Fiat Avio, ABB and Siemens. The remaining 25 per cent is spread across the automotive industry, particularly turbocharger component manufacture, and general engineering.

Such a diversity of work is typical of the subcontract environment. Batch sizes vary from 50- to 500-off and require the Blohm to be changed over three or four times a week. Flexibility in setting up the grinder is therefore a major consideration.

Said Brian Pulleyn, Manufacturing Engineer at the Blades Division:

Set-up time on our other 20 CNC grinders is around 10 hours but we can change over the Blohm to produce a new part in five hours, saving more than half a shift every couple of days.The majority of this saving is due to the excellent software which runs on the Siemens control fitted to the machine,enabling the automatic generation of both grinding and dressing programs; we always program our grinders on the shopfloor, so the user-friendliness of the CAP package is important to us.Furthermore, when the machine is grinding,cycle times are an average of 25 per cent shorter, according to Mr Pulleyn. He cited the fast axis movements as one reason for this, as well as the rigidity of the machine that allows heavier cuts to be taken, especially when creep feed grinding.The Blohm is by far the most productive grinder on the shopfloor;I would like to fill the shop with them ... The setters and operators like the machine and reliability is good, as is the service back-up from Geo. Kingsbury.

Components are produced mainly from inconel and some titanium. They are frequently multiple-fixtured on the table of the grinder, so that both sides of components as well as multiple features may be ground in one cycle using ganged wheels. Dimensional tolerances are generally ±25µm, although some are as tight as ±5µm.

Some of the grinding cycles are quite complex. Take, for example, the large blade for Fiat Avio. This requires profile grinding of the fir tree root and flat grinding of two wedge angles, two rhomboid faces and one rhomboid step, two hang-out faces, the end face and the lock plate groove, following which operations at the other end comprise profile grinding both interlocks and interpolating the radial tip.

The Profimat MT machine range comprises five models with up to 1,600mm x 600mm grinding area. The table moves in the X-axis at up to 25m/min while the Y-axis wheelhead travel is up to 3.75m/min. Positional feedback from both axes is via linear scales. The column effects the cross-travel (Z)at up to 4m/min. The power of the grinding spindle is 27.5kW (optionally 45kW),delivering cutting speeds to a maximum of 170m/s. Wheel size is 400mm OD by 100mm wide.

Details available from: Geo. Kingsbury Machine Tools Limited. Tel: +44(0)1705 580371; Fax: +44 (0)1705 501741; Web site: http://www.geok.com