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An RMP600 strain-gauge probe from Renishaw has enabled high-accuracy measurement of small hole diameters, contours and geometric tolerances at aerospace stretch-forming firm Triumph’s shop.

With no lobing and a repeatability of 0.25um (0.00001in), the strain-gauge probe delivers high accuracy when triggered from any direction, after a one-time calibration routine.

The RMP600, combined with Renishaw’s OMV Pro software, gives the company’s Zimmerman CNC fve-axis portal mill CMM-like capability, allowing complex parts to be ‘bought off’ the machine with measurement results that routinely come within 0.025mm (0.001in) when double checked with other devices.

As a result, offline checks of work on a true CMM have been essentially eliminated, saving the company many hours of production delays, potential damage and accuracy problems that arise when moving and re-fixturing high-value parts.

Triumph Fabrications’ core capability is stretch forming of sheet, extruded, rolled shape and light plate metals for the aerospace industry.

The company’s press capacity ranges from 10 to 750 tonnes, with the ability to stretch-form reverse forms using bulldozer attachments of 150 and 400 tons on its Cyril Bath presses.

The company also has the stretch-forming capabilities needed to support complex single-plane and multi-plane forming of a variety of metals.

Various types of CNC machine tools are used to produce features on these formed parts, as well as to shape the forming dies themselves.

Supporting this work upstream and downstream is a CAD/CAM department equipped with Catia V4 and V5, Vericut 7.0, Renishaw OMV Pro, AutoCAD, Inventor and other desktop engineering tools.

CAD/CAM department manager Gary Medlock says on-machine probing is vital to the company’s goal to reduce cycle time, eliminate rework and reduce errors that can creep in from multiple fixturings of a part.

Typically, parts processed on the Zimmerman mill are formed sheet metal, 0.635mm (0.025in) to 3.18mm (0.125in) thick, that require machined holes and cutouts.

These parts are vacuum fixtured.

Holes of 2.5mm (0.098in) to 9.5mm (0.375in) – typical of aircraft applications – are drilled and reamed to accuracies of 0.05mm (0.002in), with true position tolerances of 0.30mm (0.012in) to 0.71mm (0.028in).

Triumph has two Zimmerman portal mills.

The newer FZ-30 model built in 2008 is equipped with a Siemens 840D CNC.

This particular machine has a 6 x 2.8 x 1.5m (236 x 110 x 59in) X-Y-Z linear axis range, 110 A-axis and 360 Z-axis.

Its spindle produces a maximum of 40kW power and 48Nm torque, with a top speed of 25,000rpm.

The plant itself is climate controlled.

The probing program runs on the CNC to collect the measurement data, which is then evaluated offline in OMV software with CMM-type algorithms.

The software compares the measurement data with the map/model file and produces graphical and numerical reports.

The software reports on the deviations from the nominal and will plot a graph to show the ranges.

A GD and T wizard in the OMV software leads programmers through the process of creating standardised report elements based on internationally recognised symbols, allowing comparison of measurement results from the machine to the manufacturing drawing.

The RMP600 is fundamentally different from conventional machine-tool probes in that its patented Rengage sensing mechanism eliminates lobing, an error inherent to all conventional machine tool probes.

If the lobing is excessive and high enough to impact-measurement accuracy, users must compensate by calibrating the probe along each measurement vector.

This requires a complex calibration cycle and management of numerous probe offsets.

The RMP600 eliminates this.

Strain gauges measure the contact force applied to the stylus and generate a trigger once the strain threshold is exceeded.

This results in low trigger forces, less stylus bending, sub-micron repeatability, no lobing and a true three-dimensional triggering characteristic.

The RMP600 delivers significantly higher metrology performance, especially on 3D surfaces where many sensing directions are used, or in setup, when approach vectors to the workpiece may not be known.

Logic inside the probe eliminates unexpected triggers resulting from shock and vibration by determining whether the strains seen at the gauges are caused by contact with the part surface or a random event.

Renishaw

A world leader in engineering technologies, Renishaw’s core skills in measurement and precision machining serve sectors as diverse as dimensional metrology, spectroscopy, machine calibration, motion control, dentistry and surgical robotics.

A world leader in engineering technologies, Renishaw’s core skills in measurement and precision machining serve sectors as diverse as dimensional metrology, spectroscopy, machine calibration, motion control, dentistry and surgical robotics.

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