Sachmann machine maximises capacity at Crest

Citation

(1998), "Sachmann machine maximises capacity at Crest", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 6. https://doi.org/10.1108/aeat.1998.12770fab.010

Sachmann machine maximises capacity at Crest

Sachmann machine maximises capacity at Crest

Keywords Aerospace, Machine tools, Mikron

Experience has taught many suppliers to the aerospace industry that, when specifying new machine tools, the bigger and more capable machine they can purchase is almost inevitably the best option. As a result, when managing director Duncan Hollows was specifying the Sachmann T20 profile mill from Mikron (Birmingham) that now dominates Crest Engineering Company's impressive new shopfloor, he went for the extended column version and specified a Heidenhain control with five-axis capability (Plate 8).

Then, even before the machine had settled on its new foundations, an additional two-axis head was then sourced to provide full five-axis machining for drilling and slot milling. Duncan Hollows explains: "We need maximum flexibility and accuracy in the machines we buy to meet customers constantly developing requirements".

He then describes how the Sachmann machine provides a wide-ranging solution, combining jig borer accuracy with complex surface machining capability and a big work envelope of 3.8 metres by 1.2 metres by 1.5 metres high. "It's a machine bought as much for future as for current needs", he says.>

Plate 8 Five-axis capability with Sachmann T20 from Mikron at Crest Engineering. Note: guards removed for photography

Crest is a major supplier of jigs and fixtures to the aerospace industry, a craft demanding the maintenance of tight tolerances over exceedingly large dimensions. Its tooling is subject to 100 per cent inspection before leaving the factory using either a large CNC co-ordinate measuring machine or, for the really large work, a laser tracking system. Tolerances vary but 0.02 mm over 2 metres is not uncommon.

Major customers include aero engine manufacturers and leading European and US-based aircraft manufacturers for which the company has to process a wide range of steels as well as cast zinc-based alloy used for stretch form tooling.

The company is part of the Hyde Group, a privately owned mini-conglomerate with diversified engineering and construction interests and annual turnover of around £70 million.

Apart from a subsidiary that built the 14,000sq.ft factory that Crest now occupies, Hyde also has an Aerospace Division capable of managing major contracts as a first tier subcontractor to the aerospace industry worldwide. With a wide variety of specialist capabilities within the group it is uniquely placed to co-ordinate projects, disseminating work between its constituent companies and outside suppliers.

Crest's business is roughly split between group-related work and its "own" work. The latter is heavily biased towards fixtures for aero engine manufacture and equipment for ground support while much of the group work relates to airframe and wing assembly jigs and fixtures, and tooling for stretch forming. The airframe work in particular can call for development of very large fabricated fixture assemblies capable of positioning and clamping an entire fuselage section and performing discrete machining operations using tooling integrated into the jig.

Duncan Hollows continued: "The Sachmann machine was bought to cater for major new aerospace projects and provides us with the capacity and accuracy needed to machine large turbine blade fixtures and large stretch form tools to very good levels of accuracy. Because it is CNC controlled we can adopt an all-electronic machining route that is traceable to the client's original CAD data and the machine is also capable of being programmed locally or used manually for single machining tasks, making it doubly useful", he says.

Choice of the Sachmann machine was made following an evaluation of various machine types. It is a reciprocating table-type machine with a moving integrated ram and column giving Y and Z linear axis movements. Although this format increases the overall floorspace for the X-axis movement, compared with a travelling column style machine, it was felt that this design, with the spindle supported between twin columns, provided superior accuracy and stability compared, for instance, with a side mounted ram-type Y-axis.

Says Duncan Hollows: "Coincidentally, the first machine that I purchased for Crest, in 1985 was a second-hand Sachmann. It was 15 years old then, but still provides us with good service today. When we came to purchase the new machine the current range of machines appeared to offer very good value for money compared with alternatives considered and we also had confidence in Mikron as a supplier".

As installed, the machine features a universal head capable of programmable positioning in 2º increments which provides full machining access to four faces of a cubic workpiece. Fully interpolative three axis machining is available, through Heidenhain's TNC 426 control system which has sufficient onboard memory for very large programs such as are needed to machine the complex surfaces demanded by stretch form tools.

Tool and fixture design, and CNC programming is performed by Hytek Services a sister company within the Hyde Group and the support company is also developing the post processor for the supplementary spindle head acquired by Crest. This adds two further programmable axes, enabling compound angled drilling or milling operations to be carried out relative to any surface of the component.

Duncan Hollows concluded: "We have been very pleased with the machine's performance and especially for contour machining where its power and rigidity provides a productivity advantage compared with our older machines and its accuracy is very good. It has quickly become a popular machine with the operators and, combined with other new equipment currently on order, it will take us forward again in terms of competitiveness and capability".

Further details are available from Mikron (Birmingham) Ltd. Tel: +44 (0) 121 788 8686.