Probing puts the seal on machining accuracy

Citation

(2002), "Probing puts the seal on machining accuracy", Sensor Review, Vol. 22 No. 1. https://doi.org/10.1108/sr.2002.08722aaf.003

Probing puts the seal on machining accuracy

Probing puts the seal on machining accuracy

Keywords: Infrared, Machining

Set up times have been cut by half, tool setting optimised and quality audit data gathered during the machining cycle allowing operators to finely tune the operation following the installation of Heidenhain touch trigger probes and tool setting probes at Cross Manufacturing (1938). With the retrofitting of Heidenhain equipment to nine Bridgeport VMC 1000 vertical machining centres both component measuring routines and tool setting procedures have been streamlined.

The Heidenhain TS 630 infrared probes are principally used for on-machine measuring of key sectional profiles which form part of large brush-type sealing ring components while the TT 130 tool probes are utilised to set any of the 22 tools held in the magazine of the Bridgeport VNCs. Both probe types were supplied by Heidenhain (GB) of Burgess Hill in West Sussex.

Developed for the power generation sector, the large brush-type turbine seals, made from up to either six or eight ring segments, involve intricately curved profile sections. Once machined, the plates are then TIG welded in order to form a sandwich containing thousands of wires which act as the sealing mechanism. Diameters vary from 406 mm to some 2,000 mm and sections range from 12mm to 25 mm.

The 100 per cent measurement of the sectional profile features on each ring segment used to take around one hour when carried out in the inspection department. However, with the introduction of Heidenhain infrared touch trigger probes to the machining centres, inspection routines are now carried out automatically in under a minute (Plate 4).

Plate 4 Cross manufacturing has cut tool setting times by half since retrofitting Heidenhain probing technology to nine Bridgeport VMCs

As test and development engineer, Aaron Bowsher explained: "With each of our nine Bridgeport machines producing a number of brush seal segments a week, the inspection time savings through the Heidenhain probes become significant.

However, he also maintains there are other benefits of probing. "As the recorded data is automatically imported onto a spreadsheet it can provide a print out of the tolerances of all key features which aids both machining efficiency and our quality management routines. We also use probing to position the curved fixtures which locate the brush seal segments during machining and this routine has reduced workholding set-up times to half those with our previous conventional dial indicator based methods, he says.

Cross Manufacturing has its roots firmly in the production of coil-based products such as piston rings, metal seals, lock washers and wire thread inserts which are supplied to the automotive and aerospace sectors. Today, the company's brush seals, which do not feature such coiling techniques, are a growing part of the business because of the advantates they can provide to improve the efficiency of turbine machinery. The seals ensure a marked improvement over conventional labyrinth seals as they reduce leakage and extend service life, particularly in high temperature applications up to 550^oC.

Previous inspection procedures, which involved the use of a co-ordinate measuring machine and some hand instruments, were quite lengthy and could also cause hold-ups in the machine shop as the operator waited for a set of results before the next ring segment could be produced.

A major advantage of the Heidenhain TS 630 infrared 3-D touch probe, is the use of an internal contact-free optical switch to trigger the signal. Because it is non-contact, the sensor will not wear and long term stability of consistent measurement can be maintained. Already built into the Heidenhain TNC contouring control used on the Bridgeport machines are a number of cycles which provide automatic measurement of common geometrical forms such as holes, pockets, slots, bolt-hole circles and planes.

A wear-free optical switch is also incorporated in the machine tool table mounted TT 130 touch probe which uses a 40 mm diameter hardened steel disk-type contact for probing the cutting tool. The unit can measure length and diameter of the tool even with the spindle running and check the radius and length of individual teeth in order to monitor breakage or account for wear.

Contact: - Heidenhain (GB) Limited, 200 London Road, Burgess Hill, West Sussex RH15 9RD; Tel: +44 (0) 1444 247711