Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
Turning up the productivity of CMMs in aerospace
Keywords Aerospace industry, Measurement, Technological developments
The aerospace industry has come to rely on co-ordinate measurement machines (CMMs) but the quality and efficiency improvements delivered by CMMs are now reaching a plateau. As the industry grapples with the competing demands of manufacturing to ever tighter budgets, and timescales, whilst at the same time improving quality, what is now needed is a way of "turning up" the productivity of CMMs.
In an ideal world, an aerospace manufacturer wants to cut every feature of a part and inspect it only once at the end of the production cycle, but the complexity of the parts more often than not will not allow this. The increasing trend, therefore, has been for CMMs to be used where products are part manufactured and then checked before moving to the next stage of manufacture. As a result, CMM inspection has become integral to the production process, with CMMs often found next to machine tools within production cells. Parts can be inspected as much as ten times during production. Moreover, the old acronym CAD/CAM has now given way to CAD/CMM/CAM as CMMs completed the transition from being "simple" inspection tools to becoming part of a concurrent engineering strategy.
But a production CMM measuring a complex part involving 100-200 dimensions, for example, can take up to two months to set up by programming the CMM online. And even then collision avoidance cannot be guaranteed. With a motorised probe head costing as much as »10,000, there is an obvious business case for better collision detection.
"Turning up" the productivity of CMMs is where off-line programming (OLP) is beginning to prove its worth. OLP means setting up the CMM well ahead of it leaving the production line for inspection by visualising the component from CAD system input and programming the CMM accordingly. As the product reaches the CMM it can be measured immediately, saving valuable time during the inspection stage, and avoiding plant standing idle while the inspection is set up on the CMM.
OLP tools can also visualise the CMM itself, enabling engineers to discover whether or not there is a risk of collision between the component and CMM and take steps to ensure collision avoidance. Indeed, OLP can be a valuable aid to CMM procurement, allowing engineers to visualise the CMM "in action" and assess its suitability for the components to be inspected.
The aerospace industry has its own unique challenges for OLP CMMs that place it at the forefront of this technology. Unlike other industries, such as automotive, where parts are developed "visually" using CAD systems, aerospace components are often developed mathematically to meet exacting aerodynamic requirements. Until now OLP for CMMs has focused on the geometry of prismatic elements (blocks with holes in them), limiting their use in some areas of aerospace manufacture. The new generation of OLP now makes possible "iterative alignment" using 3D visualisation as the starting point and then off-line programming the CMM to "find", for example, an engine aerofoil, using the "blading" technique of refining the search and measurement with each inspection cycle.
For aerospace companies then, the benefits of OLP CMMs are faster program generation, where individual programs can be developed for particular features such as an aerofoil and then put together to form a single inspection program.
Many CMM manufacturers now offer OLP but these tend to be proprietary offerings and nearly all come with CAD links featuring IGES translation when what is needed is CATIA translation. Boeing, for example, will not accept IGES translation.
By focusing on proprietary OLP languages the CMM industry is creating a competitive scenario in which the aerospace companies are likely to be the losers. Tied to a single product, the CMM's output is either in the vendor's own language for their own CMM or DMIS. Unfortunately, DMIS output is not able to use some commands that are only available in the native programming language, so limiting its usefulness. If the productivity of CMMs is to be increased using OLP then what is needed is a single programming tool that can be applied to all CMMs such as Adept Technologies' CimStation. By providing a single programming environment that can be used by both engineers and inspection professionals for all CMMs, it overcomes the problem of learning multiple languages for each make of CMM. What is more such an approach is consistent with the thrust of concurrent engineering based on multiple CMMs in a production line.
Bombardier Aerospace, Shorts in Northern Ireland has been using CimStation for off-line programming of CMMs for sometime. It was the company's success with the Learjet 45 and Bombardier Global Express that lead to the investment in OLP as a way of reducing the load on CMMs and the time required to inspect each component.
Moreover, by increasing the productivity of the CMMs, the aerospace company also planned to introduce concurrent engineering. According to Bombardier Aerospace, Shorts, the results from using CimStation have been impressive. It has now established a concurrent engineering environment, in which CAD/CMM/CAM are integrated to the extent it is now on course to deliver an 80 per cent increase in throughput with only a 20 per cent increase in overall costs over the next three years. The inspection regime is a key element of this.
Asked if the aerospace company would go back to online programming of CMMS, their response was that it now operates solely by exploiting digital technology to reduce costs and time to market.
CimStation is available in the UK from: Applied Computing and Engineering. Tel: +44 (0)1925 830085.
For further information contact: Stewart Allinson, Applied Computing and Engineering (Tel: +44 (0)1925 830085); or David Owen, Agenda PRM Ltd (Tel: +44 (0)161 718 2829).