Quality control is an expanding aspect of manufacturing, representing distinct operating divisions for many OEMS and their tier suppliers, and thus it represents a particular channel for expertise and innovation. The developments that happen in testing, inspection, and quality control of one manufacturing supply chain very quickly find relevance in other sectors.
Rapidfit, an additive-manufacturing business, has deployed a horizontal-arm coordinate measuring machine (CMM) to check the accuracy of custom gauging and holding fixtures produced for use in automotive manufacturing. Using this device, Rapidfit has reduced costs and lead-times by making use of additive manufacturing to produce workpiece locators that are added to standard fixture components. For automotive manufacturers and suppliers, this innovation means vehicle production can be streamlined further, because fixtures can be made with greater functionality and better repeatability.
Frequently, this is achieved by incorporating complex clamping elements with freeform contours that are produced by conventional machining. It is expensive, time consuming, and creates a lot of waste material. Integrating intelligent, quick-release mechanisms that do not damage the component being retained is another possibility. Even moving elements like hinges can be printed, as well as features such as clips, pins, and holes.
High-wear plastics are used to manufacture the components, sometimes with steel inserts or bushings. Alternatively, parts can be produced from aluminum-filled nylon powder, allowing robust elements to be printed that may be subsequently milled and drilled to an accuracy of ± 0.05 mm.
Users of the fixtures are mainly manufacturers of plastic and composite components for vehicles, from relatively simple, light housings or small sheet metal parts to full body panels, dashboards, and bumpers. Customers include automotive OEMs like Audi, Bentley, Lamborghini, and Volvo as well as important supply chain partners, like Mecaplast and Valeo.
Shorter lead-time from receipt of order to delivery of the fixture, especially when complex geometries are involved, is a result of not having to program a milling machine to remove typically 90 percent of material from an aluminum billet, or spending time and expense having a casting made and then machining it. Users are given more time and flexibility to fine-tune their product designs and still meet deadlines.
An added advantage is that the locators and contours are typically half the weight of their conventionally machined equivalents, so the fixture is lighter and less tiring for operators to use.
A high degree of modularity is provided using standard holding elements, such as the Aluquick range supplied by Horst Witte, to support the custom 3D-printed locators. The system allows easy modification simply by replacing them, so fixtures can be reconfigured inexpensively to accommodate design changes.
The patented products supplied by Rapidfit are of two types: gauge fixtures are for inspecting automotive components after manufacturing, to verify dimensional accuracy; while holding fixtures support components as they are built into a vehicle and measured using CMMs or other metrology equipment. Both types provide comprehensive management of dimensional accuracy, which is vital to the overall quality of the vehicles being assembled.
Accuracy is critical — In turn, this means that quality control of the fixtures is critical. At Rapidfit, in Leuven, Belgium, there was a need for greater accuracy when checking fixture calibration, and to achieve this an LK Metrology HC90 40.16.16 horizontal arm CMM was selected and installed, together with the manufacturer's CAMIO8 multi-sensor programming and analysis software. The coordinate-measuring machine allows almost unrestricted access to its 4x1.6x1.6-meter measuring envelope and features ceramic guideways and air bearings for stability at high velocity and acceleration.
A Renishaw PH10-MQ, motorized indexing head with in-quill head mount and autojoint probe mount, together with a TP200 touch trigger probe and various extension bars, formed part of the installation too. The HC90 is housed in a climate-controlled metrology room and currently it is operated over a single shift.
Rapidfit's marketing manager Stefan Roeding commented, "Customers will only accept measurement results if they trust the equipment that generates them. The accuracy and repeatability of the LK CMM is very high for its large size. It can measure two of our fixtures at a time, resulting in high productivity in the inspection department.
"Installation of the machine has been a big step forward in assuring the quality of our products before delivery and avoiding costly reworking," he continued.
CEO Filip Dehing added, “With a worldwide sales and support network, our company is in an ideal position to grow by becoming a preferred partner for large automotive companies on a global scale, and by fully exploiting new opportunities. Underpinning all of this is our commitment to high quality. Our inspection department with the LK Metrology CMM 'breathes' accuracy, making it an important marketing tool when customers and prospects visit us."
Maximizing the CMM — A typical project at RapidFit starts with the customer sending a CAD drawing of the component to be fixtured and instructions on how it should be clamped for the required application. The fixture is constructed virtually in CATIA by one of RapidFit's design engineers, and the 3D locator elements are output as STL files so that they can be produced by powder laser-sintering additive manufacturing.
After 3D printing, the locators are assembled with standard holding elements and a measuring program is created in CAMIO8 (offline, or even off-site), which makes maximum use of the CMM for inspection. As each fixture is different, ease of programming based on the original CAD file is a critical advantage.
The program is transferred to the LK HC90 and the inspection cycle is run to verify that all fixture dimensions are in tolerance. If changes are needed, engineers modify the fixture and run the cycle again. Measuring program changes can be made quickly in teach-mode, if necessary.
Turn-around for a fixture of average complexity is three to four weeks, although a very complex fixture may take up to six weeks. Then, the customer is invited to the RapidFit measurement room for acceptance and sign-off.
More recently, to check contours faster, the manufacturer has added laser-scanning capability to the CMM by incorporating a Nikon Metrology LC15Dx laser scanner. It is interchangeable with the touch probes and both are supported by LK's CAMIO8 software. The technology offers twice the resolution of camera-based optical systems, so it is suitable for quality control of RapidFit's automotive fixtures. It is therefore replacing relatively slow touch-probing routines in parts of the cycle that involve collecting freeform data.