Heidenhain CNCs provide system advantage for M J Technologies

Citation

(2002), "Heidenhain CNCs provide system advantage for M J Technologies", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 6. https://doi.org/10.1108/aeat.2002.12774fab.001

Heidenhain CNCs provide system advantage for M J Technologies

Keywords: Aircraft, Engines, Gas turbines, Technology

M J Technologies (MJT) is regarded within the gas turbine modern aircraft engine and power generation industries as a major company for developing solutions to produce small yet highly accurate holes in both rotary and static components.

Two of the most recent innovations of the Coalville, Leicestershire based company, are a fast hole drilling (FHD) process using electro-discharge machining (EDM) to create high aspect ratio holes in difficult to machine materials such as inconel and, on the fly, laser drilling of holes in aerofoil sections involving five-axis positioning. In each of the technology sectors MJT has adopted Heidenhain TNC contouring control systems for flexibility of process control (Plate 1).

Gas turbine technology is based on continued development to optimise all elements used in the end product. Many of the internal components within the high pressure stages of a turbine, for instance, are required to function in gas streams with temperatures approaching the melting point of the materials used to make them. In order to maintain reliable operation in these conditions, many of the rotary and static components are peppered with well defined patterns of tiny holes which vary in diameter between 0.3 mm and 3.0 mm to facilitate the passage of vital cooling air.

Plate 1 Heidenhain TNC contouring control has proven ideal for 5-axis control of ‘on the fly’ laser drilling of holes on MJ Technologies Tomado laser system

To produce these holes is a highly specialised task. It demands precise control over the process and highly accurate and repeatable positioning often involving complex three-dimensional surfaces. To meet these requirements demanded by its customers, which include international blue- chip names, MJT has standardised on Heidenhain as the exclusive computer control system supplier.

MJT is a relatively young company, having been established in 1992. Since 1999 it has been part of the US-owned Winbro Group, a technology based business which is headquartered in Boston, USA. MJT’s expertise in the development and supply of highly precise laser, EDM or electro-chemical machining (ECM) based drilling systems to aeroengine and gas-turbine builders, as well as aero engine overhaul specialists, has created a customer list that comprises a Who’s-Who of western aerospace and land-based gas turbine suppliers. More recently, the company has diversified into high precision laser cutting and welding systems which takes it into a totally different scenario involving automotive and defence applications.

Although MJT offers a more-or-less standard range of machines with a work envelope up to 1,000 mm by 700 mm by 1,000 mm, its primary business is the supply of turnkey solutions. In all cases, the components tend to be complex shapes while the stipulation for the process calls for tight tolerances on hole angle, size, position and breakthrough. In addition, some holes are required to have precisely controlled forms machined into the entry/exit surface in order to optimise gas flow.

As Helen Wright, marketing manager outlines: “Satisfying the technical requirements can demand precise control of up to nine CNC axes, and in addition, we also have to achieve competitive cycle times on the process.”

The company has developed a number of proprietary technologies that have helped to reinforce its position in the market. FHD for high aspect ratio hole machining in difficult to machine materials and although it is an EDM process, utilises 140 bar high pressure, high purity water as a combined dielectric/pseudo electrolyte. This is forced through small diameter tubular brass electrodes to assist the drilling process and helps to provide cutting speeds comparable with an electro-chemical machining process. The benefit to the end user is a highly accurate hole form with good surface finish, minimal recast layer and high control over surface micro-cracking.

As with other MJT systems, the FHD machine uses software fixturing by which the system probes the component and realigns the machining process to eliminate the effect of any fixturing errors. Key to the calculation and processing of the data is the Heidenhain TNC 400 series contouring control system.

Mike Wakeham, project engineering manager, explains: “Control requirements vary according to the families of parts being processed. However, in general the current range of Heidenhain 400-series controls provide the level of flexibility we need. On an EDM machine, for instance, we often require three linear positioning axes, a C-axis for electrode rotation and an additional A- and B-axis rotary positioning for the fixture mounting.”

He follows on to explain that the control is also used to manipulate the processing slide, which carries the electrode cassette and the electrode changer system.“He describes that in order to optimise productivity on EDM, adaptive control is applied while the hole is being drilled so the rate of axis travel is determined by feedback from the process. This means the CNC control becomes key to monitor position but is not required to control the rate of feed. When the correct depth is reached the CNC system once again picks-up control of the axis.”

MJT’s laser machines normally feature up to five positioning axes comprising three linear plus a rotary B-axis on the cutting head and either a C-axis rotary table or linear positioning of the head in conjunction with a tilt/turn table. However, the machines also utilise three optical axes in order to control laser parameters.

Ease of programming the Heidenhain system has reportedly proven to be extremely important while the controls positional capabilities are crucial as, for some applications, a five-axis form has to be produced at the hole entry point on the surface of an aerofoil. In addition, some of MJT’s customers demand that the machines have to maintain a tolerance of 10 microns or better without any form of compensation. This is achieved through a combination of high quality machine construction, Heidenhain glass scale linear encoders and output mounted Reidenhain rotary encoders.

Operationally, a key advantage of using the Heidenhain control is the availability of the M204 code which can be used to open and close the energy dump of the laser beam. This feature of the Heidenhain control is said to have enabled MJT to trigger the laser to drill holes “on the fly”, while totally under CNC control, rather than having to switch the oscillator on and off. This also reportedly provides up to 500 per cent productivity gain, depending on hole size and material thickness when drilling holes on a pitch circle diameter.

The system operates by taking advantage of the laser’s natural pulsing frequency and using it in conjunction with C-axis table rotation. If, for instance, the laser’s pulsing frequency is 10 Hz and holes are required at 360 intervals on a pitch circle diameter, then by rotating the component at 60 revs/min with the shutter open, the holes can be drilled without the need for time consuming cycles that involve a stop, drill, index, stop, drill routine. This cycle is able to continue for as many revolutions as needed to achieve break-through.

Mike Wakeham explains how the Heidenhain M204 code is something that, to their knowledge, no other CNC system can offer. “In fact, it has been instrumental in ensuring Heidenhain-equipped machines are accepted by customers who had established preferences for alternative CNC systems”, he says.

The company has also found the current controls work extremely well with alignment probing routines and have ideal interface with probing systems while the PLC stage within the control is very easy to use. With the advent of the new Heidenhain 500 series of control MJT also plans to adopt the Heidenhain digital drives package which promises to further improve performance.

Details available from: Heidenhain (GB) Ltd, Tel: +44 (0)1444 247711; Fax: +44 (0) 1444 870024.