Form Metrology for AM. Primary Investigator: Petros Stavroulakis

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1 Form Metrology for AM Primary Investigator: Petros Stavroulakis

2 Form metrology Measurement of the external shape of something Involves large-scale measurements of metres down to centimetres generally with an accuracy of 100 s of micrometres

3 Why is form metrology important? Allows mass-assembly of mechanical products Exact measurement of shape allows for predictable performance when bringing parts together in an assembly and is required to achieve a specific performance (car engine, turbine blade) Keeping form controlled to tight tolerances minimises material waste In some cases this is the most important part of the product cost (improves profits for manufacturing plants, makes them more competitive)

4 Types of form metrology Most used solutions are: Mechanical Coordinate measuring machines (CMMs) Optical, most common: Laser scanning Fringe projection

5 Constraints introduced by AM Constraint type Constraint Reason Diffuse reflectance (an example of a flat surface created via a selective laser melting metal process is shown in Figure 3) Surface texture Typical surfaces produced via layering and powder based metal AM manufacturing technology are not optically smooth to visible wavelengths Form geometry Freeform, multiple occlusions and shadows exist Little restriction in created geometry permits for complicated shapes with large number of discontinuities and line of sight occlusions present Material range Appreciable variation of absorption/reflection properties between different materials Inhibits the overlay of specific wavelengths, more important for laser triangulation than structured light

6 Current focus of AM metrology activities in group Three top priorities: Investigation of the UK s requirements for AM metrology Creating a technical review of existing form measurement systems and their applicability to AM Use of a priori knowledge (structured light system models and object CAD data) to improve the measurement process via IRM (information-rich metrology)

7 Current focus of AM metrology activities in group The UK s requirements for AM metrology Completing the technical review of existing form measurement systems Use of a priori knowledge (structured light system models and object CAD data) to improve the measurement process via IRM (Information Rich Metrology)

8 Current status of UK AM metrology needs review Investigation plan for UK AM metrology: Look at global AM landscape Create a realistic snapshot of the current UK AM industry and supply chain Identify the greatest metrology challenges for AM industry (currently in collection) Tie challenges in with fellowship project aims

Timeline of EPSRC effort to collect AM data The EPSRC AM CIM s aim is to produce a UK-specific document regarding the current roadblocks in AM and an actionable plan to present to government after

9 Timeline of EPSRC effort to collect AM data The EPSRC AM CIM s aim is to produce a UK-specific document regarding the current roadblocks in AM and an actionable plan to present to government after election and in time for the budget Their timeline is very relevant and close to our project/fellowship needs Metrology is placed in the top requirements for evidence collection and hence will be a big part of this report

10 Metrology is mentioned among the most critical barriers for the growth of the UK AM industry Code title # workshop Post-Its # references from on-line submissions Summary of common perceived barriers: Materials Design Skills / education Cost / investment / financing Standards / regulation Measurement / inspection / testing Understanding properties in different processes/machines/applications, QA, costs, availability (IP constraints, independent suppliers), use of mixed materials, recyclability, biocompatibility. Need for guides and education programmes on design for AM better understanding of design for AM constraints, availability of AM-skilled designers, security of design data. Lack of appropriate skills (design, production, materials, testing) preventing adoption, up-skilling current workforce vs. training of next generation, education of consumers, awareness in schools. Funding to increase awareness and reduce risk of adoption (testing, scale-up, machine purchase) especially for SMEs, understanding of full costs (inc. postprocessing, testing), cost of materials. Perceived or actual lack of standards all sectors / sector specific (esp. aero / health / motorsport), for processes / materials / software / products / applications. Need data libraries, standards for tests (general and sector specific), materials/ in-process / final part, tests for higher volumes, nondestructive testing, QA through lock-in cf. open access to data. IP / protection / secrecy Balancing need for openness to share knowledge with need for commercial protection to capture value from investments, enforcement of IP rights. Source: Update report 2 UK AM National Strategy Effort

11 First results of EPSRC effort: UK AM Landscape In total 143 organisations have provided responses out of which the UK AM landscape per sector was as follows: Sector % of Sector % of contributions contributions Manufacturing 55 Automotive 3 Materials 34 Motorsport 3 Machinery 19 Nuclear 3 Information 10 Electronics 3 Aerospace 12 Construction 1 Defence 10 Rail 1 Creative industries 7 Marine 1 Life sciences 5 Oil and Gas 1

12 Current focus of AM metrology activities in group The UK s requirements for AM metrology Completing the technical review of existing form measurement systems Use of a priori knowledge (structured light system models and object CAD data) to improve the measurement process via IRM (Information Rich Metrology)

13 Technical review The technical report created which has been sent to Review of Scientific Instruments and is at peer review stage describes the following: Presentation of overview of form measurement systems available for 3D measurement Comparison of 3D form measurement systems and selection of the ones most applicable for industrial AM applications Calculation of fundamental accuracy and uncertainty limits for metrological solutions available for AM (laser triangulation, fringe projection) Presentation of practical considerations and additional sources of uncertainty (beyond the fundamental ones) and discussion of areas which need improvement

14 Summary of Technical Review: Measurement tolerances required in industry Figure from: E. Savio, L. De Chiffre, and R. Schmitt, CIRP Ann. - Manuf. Technol. 56, 810 (2007).

15 Other industrial requirements Characteristic: Value used: Source: Up to: ( ) mm Maximum volume of measurement area (distance): Dimensional tolerance: Resolution and accuracy: Measurement time: Varies with industry, typically 100 μm (±50 μm) As high as possible, typically ten times better than the tolerance range in order to provide adequate measurement confidence interval and appropriate process control. As fast as possible, typical requirement is to be faster than the manufacturing process itself. Recommended by VDI/VDE standard on industrial non-contact 3D scanning As per previous figure N/A N/A

16 Active vs. Passive systems There are two general families of 3D optical measurement active and passive: By active systems we mean systems that use their own light source to perform the measurement By passive systems we refer to systems that depend on already available light to perform the measurement Generally, for higher measurement speed and accuracy people select active systems whereby for cost effectiveness people prefer passive

17 List of optical systems available Classification of active and passive 3D form measurement techniques (Source: G. Sansoni, M. Trebeschi, and F. Docchio, Sensors 9, 568 (2009) ) 3D form measurement technique Passive Active Laser triangulation X Structured light X Stereo vision X Photogrammetry X Time of flight X Interferometry X Moiré fringe range contours X Shape from focusing X X Shape from shadows Texture gradients Shape from shading Shape from photometry X X X X

18 Active form measurement systems Source: S. Se and N. Pears, 3D Imaging, Analysis and Applications (2012) For our internal spec, a measurement volume of (700x700x700) mm and an accuracy smaller or equal to 100 μm is required to accommodate most AM. Laser triangulation and pattern projection are the most appropriate techniques to measure AM parts.

involved Laser point illumination Moving parts Fringe Projection Areal Intensity based Requires

19 Comparison of current popular non-contact optical form technologies in industry Laser Triangulation Point-to-point or Line-to-line Angle based Direct measurement within field of view Less software involved Laser point illumination Moving parts Fringe Projection Areal Intensity based Requires ambiguity removal: -Wrapped phase -Scaling factor More software steps involved Lamp illumination No moving parts

20 Principle of operation of laser triangulation h = d 1 - d 2

21 Uncertainty Ishikawa diagram for laser triangulation

22 Principle of operation of fringe projection

23 Uncertainty Ishikawa diagram for fringe projection

24 Where do we go from here? A) Improve fringe projection and laser scanning B) Develop other measurement technologies which could be used for form measurement

25 Shear interferometry

26 Active shape from focus Projected patterns used to texturize scene in order to assist with reconstruction of featureless objects.

27 Projection Moiré

28 Holographic profilometry

29 Frequency modulated continuous wave ranging

30 Close-range photogrammetry Source: L.M. Galantucci, F. Lavecchia, and G. Percoco, J. Comput. Inf. Sci. Eng. 13, (2013)

31 Comparison chart of promising techniques: Technique: Active focus detection through shear interferometry Best dimensional resolution reported in height axis: 10 μm (on optically smooth surfaces) resolution reduced for rough surfaces Measurement Range: Type of view: Works on optically rough surface: 300 mm Point-to-point YES Time of flight 15 μm 500 mm Full field YES Close-range photogrammetry ~15 μm 30 mm m a Full field YES Volume Holographic Profilometry 15 μm millimetres 20 cm 2 m Full field YES Holographic Profilometry Moiré profilometry 10 μm 50 mm mm depending on object reflectance typically ~25 μm depends on grating frequency used Full field YES N/A Full field YES

32 Current focus of AM metrology activities in group The UK s requirements for AM metrology Completing the technical review of existing form measurement systems Use of a priori knowledge (structured light system models and object CAD data) to improve the measurement process via IRM

33 Flow chart of IRM-enhanced structured light system operation for AM 3D model of object to be measured (AM CAD) Simulation of projections for specific object model in combination with the instrument model. Selection of minimum amount of views required to fully describe object Send optimized views to measurement rig to take measurements Comparison of initial model with points acquired Fill-in gaps found either with new projections or more accurate secondary system (triangulation)

34 Initial simulation results Confirmed the ability to crate a setup which collects scattered light from the object to correctly replicate the fringe pattern as seen by the image CCD.

35 Form Metrology lab at UoN NUB3D SIDIO XR Structured light 3D scanning system:

36 Human Testing (with consent)

37 AM reconstruction of 3D scanned point cloud

38 Future plan Aim: One-shot 3D reconstruction system with maximum available accuracy and resolution via multi-view paradigm and inspection planning that will be customized to specific objects.

39 Thank you for your attention!

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