Touch trigger probes halve seal production setup

Set up times have been cut by half, tool setting optimised and quality audit data gathered following the installation of Heidenhain touch trigger probes and tool setting probes at Cross Manufacturing

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 VMCs.

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 12 mm 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.

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 advantages 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 550oC.

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.

It was against this scenario that Cross Manufacturing decided to set up a development team to investigate on-machine probing to streamline inspection.

Consisting of Aaron Bowsher, shop floor supervisor Martin Wheeler and IT manager Jonathan Howe, the team researched several suppliers and eventually selected the Heidenhain TS and TT probes.

These were considered to offer the best overall package of accuracy, consistency, performance and application support while being very cost-effective to purchase and install.

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.

Says Aaron Bowsher: "We were also impressed by Heidenhain's whole attitude.

Not only was the company quick to respond to our initial enquiry, its engineers demonstrated a genuine interest in the project and even lent our team an infrared probe for us to determine its suitability in our own time." The Heidenhain probes were installed on the Bridgeport machines in late 1999.

One TS probe is located in each tool change magazine while the TT tool probe is mounted at the corner of the work table.

The measuring sequences of the infrared probe, which are an integral part of the machining cycle, involve taking five cross-sectional readings at six different locations over the length of the curved brush seal ring segment.

This data is automatically recorded in the Heidenhain TNC control on the machine and special software converts the readings into spreadsheet format so that the results can be printed out in groups associated with a specific ring segment.

Shopfloor supervisor Martin Wheeler takes up the story: "As each operator now gets a printout of the measured results within a minute or so of completing the machining cycle, we have found this acts as a visual spur to further improve the process.

He can readily identify any slight tolerance drift and quickly adjust particular tool offsets to keep the whole machining process finely tuned for the best results." With all nine machines now working more efficiently, the introduction of infrared probing techniques has also contributed to the quality validation and fixture set-up routines while the Heidenhain table-mounted tool probes have allowed tool setting routines to be optimised.

Operators can now obtain a dynamic tool size from the TT tool probe before they take a specific cut and setting routines for both tools and fixtures can now be easily and confidently completed in less than 30 minutes which is some 50 per cent quicker than before.

Back to top