This article on non-contact optical scanning and inspection first appeared in the Confederation of British Metalforming magazine.
- When forming metal components how do you know that the parts produced are to drawing?
- How can you be confident that your tooling, such as a forging die, has not worn out of tolerance and requires re-working or replacing?
- And how do you capture the modifications made to a press tool during tooling tuning so they can be modelled in your CAD system and recorded for future use?
Parts and tools with simple geometries can readily be inspected with Vernier calipers and micrometers, gauges and coordinate measurement machines (CMM). When the geometries and features become larger, more complex and/or numerous these techniques may not be economically viable and may not be capable of delivering the required information. This is particularly relevant when inspecting surface form, which often needs to be compared to the master CAD model rather than measured against a detail drawing.
Non-contact optical scanning can offer an accurate and cost effective solution to these challenges. There are a variety of scanning technologies available from arm-mounted laser systems to Computed Tomography (CT) imaging; however Performance Engineered Solutions (PES) Ltd.’s system of choice is GOM’s ATOS structured light technology due to its accuracy, flexibility, traceability and position as the industry standard against which all other technologies are measured.
The GOM system works on the principles of optical triangulation and stereo viewing. The scanner head projects a structured blue light pattern over the surface of the object being measured and the images this creates are simultaneously captured from different angles by the two cameras integrated into the system.
The software then converts this information into a high density point cloud, with up to 12 million (depending on the camera sensors’ number of pixels) highly accurate three dimensional coordinates being collected with every scan (each individual scan lasts around 10 seconds). Calibrated markers applied to the object allow each individual scan to be correctly aligned to each other so a point cloud of the entire surface can be constructed by moving the scanner and/or the part.
The flexibility of the ATOS system is its ability to capture high resolution data from small objects the size of an aspirin to objects larger than a yacht. This is achieved by altering the measurement volume over which the data points are collected by selecting different camera lenses. Up to 8 million data points can be collected in a 38mm3 volume giving a resolution of around 5 microns (point spacing of 0.01 mm) for small super high accuracy applications such as the inspection of turbine blades. For larger objects up to a 2m3 measurement volume can be used to capture data at a much faster rate with a small reduction in resolution, however even with a 1m3 measurement volume the ATOS is still collecting data at a better than 50 micron resolution (point spacing of 0.31 mm).
The calibrated markers applied to the object also work with the GOM TRITOP system to enable the scanning of large objects whilst maintaining a high local resolution. The TRITOP system takes high resolution 2D images (using a digital SLR) of an object and creates an accurate 3D coordinate framework based on digital photogrammetry techniques, which can then be used to align the ATOS scan data. The TRITOP system can also be used in isolation to take fast and accurate point measurements on the surface of a component wherever a marker is positioned.
Both systems works on line of sight, so basically if you can see it you can scan it, however optically tracked touch probe measurements can be used to collect single point data from difficult to reach, or undercut features and for the measurement of primitives, using a tactile approach similar a traditional CMM. This capability is all within the ATOS system providing the ability to combine full field scanning and touch probe 3D tactile measurement.The applications of this non-contact optical scanning technology can offer significant advantages to businesses and PES has used it to offer a range of engineering solution to multiple industries including Aerospace, Automotive, Marine, Rail, Motor and Elite Sports, Medical, Oil and Gas, product and heavy industry to name but a few.
The more conventional services are focused on quality control and inspection to ensure you are producing component within the required tolerances and preventing clients from rejecting non-conforming parts. The GOM software can produce traditional inspection reports, with the ability to automate much of the process for multiples of components, as well as full deviation colour maps showing the fidelity of complex surface geometry to design intent.
However there are many more opportunities to apply such non-contact optical scanning technology to improve quality and efficiency. Rather than just inspecting the components the tooling can be measured as part of a scheduled or planned preventative maintenance programme. Where parts are batch inspected there is the potential for a worn tool to produce a run of out of tolerance components before the issue is detected and even then it may take some time to identify the root cause of the problem. By inspecting the tooling at specified intervals and monitoring its condition it is possible to determine when it may need remedial work or replacement before non-conforming parts are delivered.
PES delivered this service to a company producing high value aerospace forgings. First article inspections were conducted to evaluate the forging dies and process and then the dies themselves were scanned to evaluate wear. Replacing an out of tolerance forging blank was not a great expense, however the greater risk was that during the final machining of the components an out of tolerance forging caused the finished part to be scrapped, wasting hours of machining, impacting the critical delivery schedule and incurring penalties from the client.
The scan data can also be used for reverse engineering parts and tooling. The GOM software outputs the data collected as a high density point cloud or as a polygon mesh .stl file, which can then be imported into CAD or rapid surfacing software to recreate the object for reference or modification.
This process was used to support a large automotive manufacturer in their development of a new bonnet. The prototype press tooling for the inner skin of the bonnet had been physically modified on the shop floor to achieve the desired component geometry. The client wanted to integrate this altered geometry back into their CAD models so the press tool could be remanufactured for volume production.
By scanning the press tooling surfaces and recreating the modified areas, including the removal of any imperfections, in the CAD environment the tool could be re-engineered with the updated geometry and released for manufacture with confidence that the panels it would produce would be within tolerance.
Non-contact optical scanning can also be of benefit for pre-digital designs and manufacturing equipment where no CAD is available or detail drawings are incomplete, inaccurate or lost. Measured data can be digitally archived or used to develop a product’s design for modern manufacturing techniques and materials to improve performance and reduce production costs. It also enables companies to benchmark a competitor’s product and evaluate its performance using tools such as Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD).
In conclusion non-contact optical scanning can offer solutions to a range of challenges faced by businesses and can significantly improve productivity and efficiency. Some of the benefits of GOM non-contact optical scanning services offered by PES are listed below.
- Fully mobile national and international onsite service or UK bureau service
- Accuracy and repeatability of data
- Fast and efficient data capture
- Adaptability of the system – Scan large and small objects
- Traceability – the photogrammetry images provide a reference between the object and the scan data for total quality management systems.
Read the article online here.