Manual Coordinate Measurement Machines (CMMs) date back to 1959. These systems were very slow and had high levels of error. In 1972, the first tactile probe was invented by Dublin native Sir David McMurtry, who later on, in 1973, co-founded Renishaw. This significant development was integrated into CMMs and revolutionized automated 3D measurement systems of solid objects.
There are several styles of CMMs. They all typically use tactile measuring probes which travel around the part picking up the coordinates of points as they go along the surfaces and features. 3D scanning was developed in the last 15 years as an alternate dimensional metrology solution.
A tactile probe typically takes a low volume of data points in critical areas around the part, which are then compared against a 2D drawing or 3D CAD file to check if the part meets the set specifications. Using CMM tactile probes for quality control and inspection is a relatively slow process. However, where a limited number of points is enough to assess a parts geometry, tactile probing is the most accurate and repeatable method with a low 3D form error (e.g. 1.3 μm).
3D laser scanning heads acquire a high volume of data points across the part. There is a significant difference in the data generated from the two types of sensors. While a tactile probe CMM may acquire 300 points, a 3D laser scanning head could potentially acquire millions of points.
Another method to acquire a 3D data is through using X-ray Micro-Computed Tomography (CT). SEAM has a long track record of working with micro-CT which is uniquely suited for dimensional measurement of components with internal geometries, difficult-to-reach features, and easy-to-deform or flexible structures. However, micro-CT is not always the best tool, particularly when high speed and low cost are required. To bridge the gap between micro-CT and tactile CMM, SEAM, through an Enterprise Ireland Capital Fund, acquired an HP-L-10.10 laser scanning head for the Hexagon Global S CMM machine. It has a form error of 8 μm, which is relatively close to the 1.3μm results of the tactile probing solution. This tool gives unmatched measurement speeds, accuracy and flexibility to streamline the measurement and reconstruction of complex surfaces and work pieces.
As an example, the HP-L-10.10 laser scanning sensor was used is on the measurement of knee implants, where achieving greater throughput and accuracy of orthopaedic implant measurement is required. Accurate dimensions are critical to the success of the knee replacement and its functionality, so 100% inspection is required. Traditionally, manufacturers turned to tactile probes to ensure high precision, but this method could risk damaging the part, even when using low force tactile probes. Micro-CT could be used, but slow speeds and high costs would make it ineffective in a manufacturing environment. Hexagon’s GLOBAL S CMM paired with the 3D laser scanning head HP-L-10.10 offers a better solution. The HP-L-10.10 enables high quality and high accuracy data to be captured at full-speed on a knee joint’s various surface types and finishes while ensuing no deformation or damage to the part.
Scanning of Knee Replacement
This metrology system can also be used to reverse engineer parts by rapidly generating a point cloud of the physical part and meshed to create an accurate 3D CAD file. Analysis components can also be completed quickly, an example of a colour map produced from the actual dimensions of a test piece to the CAD model is shown below. 3D scanning in this case allows for a quick assessment of the part with a visual representation of the dimensional difference relative to the nominal CAD model.
SEAM can offer a gateway to this technology for industries in Ireland, if you are interested in seeing in action the Hexagon GLOBAL S CMM with the laser scanning head, please do not hesitate to contact us.
About the Authors:
Dr .Sara Karam holds a BEng in Mechanical Engineering from the American University of Beirut, Lebanon, and a PhD which focused on advanced sensor monitoring of manufacturing processes from the University of Naples Federico II, Italy.
Prior to SEAM, as a post-doctorate fellow at the University of Naples Federico II, she worked on two EU FP7 Projects focusing on advanced sensor monitoring of manufacturing processes for process optimisation. She joined SEAM in 2016 as an NDT Engineer. Her work focused on utilising non-destructive techniques, basically X-Ray Micro-Computed Tomography, to analyse product components. Her work also includes failure analysis, macro and microscopic measurements, and mechanical evaluation of components.
Robert Poole joined SEAM in 2023 as a Business Development Engineer. He holds a B.Eng (Hons) in Mechanical & Manufacturing Engineering from Waterford Institute of Technology.
Robert joined SEAM with 12 years’ experience from working in industry. Prior to joining SEAM Robert worked in multinational manufacturers in Ireland. Most recently as a Senior Process Engineer in West Pharmaceutical Services managing the installation, commissioning and validation of high speed inspection systems for pharmaceutical packaging. Prior to that as a Senior Technical Engineer on process development and automation of combined CNC micro-machining and metrology systems for Alcon in Cork