Speeding up inspection with CNC laser scanning
29 December 2015
An automotive and aerospace pressings specialist invests in bridge-type and portable arm CMMs for freeform surface data acquisition, speeding not just parts inspection, but the all-important reporting process for a demanding client.
A significant increase in orders for the supply of prototype pressings and bracketry - notably to Jaguar Land Rover (JLR) - prompted Birmingham Prototypes to install two multi-sensor co-ordinate measuring machines (CMMs) from Nikon Metrology. The goal was not only to measure the sheet metal parts more quickly but, more importantly, to speed subsequent report generation. The investment has also resulted in the establishment of a new subcontract service offering laser scanning and inspection work.
Based in Redditch, Birmingham Prototypes started working directly for JLR two years ago. To receive its supplier’s code, the subcontractor needed to be able to fulfil the OEM’s strict quality control requirements in respect of first article inspection reporting and PPAP (production part approval process) documentation. These required an increase in the number of reports that had to be produced as well as more detail on component accuracy and repeatability.
Using the former manual CMM at Redditch, report generation was a laborious process requiring entry of data and drawings by hand into Microsoft Office applications. A single report took anything from an hour to half a day, depending on its complexity, according to Birmingham Prototypes’ managing director, Mick Adams. So in 2013 he decided to install a Nikon Metrology LK V 15.10.8 ceramic bridge co-ordinate measuring machine to automate and speed the reporting process. It also allows inspection cycles to be completed faster and without operator attendance after components have been fixtured, saving further time especially when measuring a batch of identical components.
A Nikon Metrology LC15Dx laser scanner is the default method of inspecting pressings at Birmingham prototypes. It allows high accuracy resolution of freeform surfaces and geometry. For measuring tight dimensional tolerances and sometimes for initial job set-up, a touch probe is picked up automatically from the stylus changer on the LK V 15.10.8 by a Renishaw PH10M motorised indexing head.
Most drawing tolerances on pressed parts at Redditch are fairly open, ± 0.25mm being typical on surfaces and ± 1mm for trim edges. Only hole positions are measured to within tens of microns. The LK CMM is capable of measuring to an accuracy that is at least an order of magnitude better than is required for these applications.
Nikon Metrology's multi-sensor CAMIO V8 software in use at Redditch produces industry-standard DMIS programs that support both laser scanning and touch probing. The software applies the optimum measurement strategy based on the feature and sensor selected. For measuring complex surfaces, it automatically generates scan paths that result in fast and smooth laser scanning that closely follows the part surface, with full machine simulation and collision detection. CAMIO also has instant, highly productive reporting functionality based on standard templates. Tabulated tables, graphics and form plots derived from scanned point clouds and touch probing are combined in a single, concise report.
Nikon Metrology Focus 10 software manages the point clouds acquired during laser scanning and allows inspection data to be compared against the customer's original CAD model. A typical pressing at the Redditch factory, such as a prototype aluminium engine bay mounting plate for a Jaguar car, comprises seven to eight million points. Focus software produces annotated, colour deviation maps showing how the 3D scanned model correlates with, and deviates from, the original CAD file. For such global comparisons, a 0.1mm grid is generally selected by Birmingham Prototypes’ quality manager, Bob Rose.
Early in 2015, Birmingham Prototypes installed a Trumpf 5-axis laser profiling machine so that it could bring in-house the laser cutting work it was then subcontracting at a cost to the business of £350,000 per year. Birmingham Prototypes’ managing director, Mick Adams takes up the story:
“Practically every job that comes off the machine is a unique prototype that needs to be inspected, a job that was previously done by the laser cutting subcontractors before parts were delivered to us. As our CNC CMM needs to be programmed for each new part, making it more suited to our low volume, pre-production runs, it made sense for us to invest in a manual measuring system to check the output from the Trumpf laser. Rather than choose another static CMM, we decided to install a portable co-ordinate measuring arm - an MCAx from Nikon. It is twice as fast at producing inspection results for a one-off part.”
The facility is used in-house on a dedicated steel table in the quality control room. It often inspects or reverse engineers components and fixtures for other manufacturers that have requested subcontract measuring to be carried out, a service that was introduced two years ago when the CNC CMM arrived. The measuring arm has extended the scope of the service by allowing off-site inspection at customers’ premises of fabrications that are too bulky to be transported easily.
The MCAx 7-axis, counterbalanced arm with continuous rotation is used mainly with a digital laser scanner at Redditch, together with Focus 10 handheld scanning and inspection software. Occasionally a touch-trigger probe is employed if additional accuracy is needed. The arm is equipped with absolute angle encoders for high precision and the model at Redditch has a four-metre diameter measuring envelope. Features of the equipment are the ability to reliably scan steep sided and reflective components, temperature stability and zero warm-up time.
The Nikon CMMs have greatly enhanced quality control of sheet metal parts at Birmingham Prototypes and allowed the firm to increase turnover by launching subcontract inspection and reverse engineering. They are backed by ISO 9001:2008 quality management accreditation, which has been held for over ten years.
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