AM Metrology at NPL. Stephen Brown. Tuesday 8 th December 2015

Transcription

1 AM Metrology at NPL Stephen Brown Tuesday 8 th December

2 NPL in brief We are UK s national standards laboratory Founded in 1900 World leading National Measurement Institute ~700 staff, from over 150 different nationalities; 500+ specialists State-of-the-art laboratory facilities The heart of the UK s National Measurement System to support business and society Experts in Knowledge Transfer Government owned and operated in conjunction with two UK universities, since early m Laboratories purpose built 2

3 Rationale Additive manufacture ~ Complex parts / internal features Roughness issues~ measurements required Need for Standards 3

4 Standards Engagement NPL has a strong engagement with dimensional standards ISO 213 WG10 ~ ISO10360~ Coordinate measurement (Dimensional and geometrical product specifications) BSI TDW/4 (Technical Product Realization) Member of ASTM F42, ISO TC261 Additive Manufacturing Ensuring measurement best practice is included in AM standards and standards are developed Member of UK Government AM Group 4

5 Contents: Some dimensional measurements techniques considered at NPL: CMM Dimensional Probe force Probe size Optical Dimensional CAD comparison XCT Dimensional Magnification Filter 5

6 Design of an example NPL standard Corkscrew distortion during build Prismatic simple geometric structures Equivalent internal structure Allow traceability Effects of beam hardening AM capability Parallel flat side faces Include cube and cylinder Internal cube and cylinder Tooling balls External cylinders of a variety of material Conventional manufactured Manufactured from XCT compliant materials: AlSi10Mg and Al for conventional 6

7 Dimensional measurement techniques and data Visualisation: Tactile, Optical and XCT Tactile Optical XCT 7

8 Tactile measurements CMMs Relies on physically touching the specimen directly. Two main types: Hard probes Touch trigger probes Example errors: Ball tip~ size /form error Pretravel Probe force Probe diameter Probe speed 8

9 Overview of dimensional tests carried out using contact CMM A Measurements of large flat areas on the AM surface. Evaluation of best fit plane Corkscrew distortion Measurement of cylinder at different heights, above the plane A : (18.5, 21, 23.5, 26, 28.5) mm Best fit circle and standard deviation of data External (and internal proposed work) comparison measurements. AM allows easy to build but, unfortunately, sometimes difficult to measure. 9

10 Contact CMM: Probe effects Force on both AM and reference Aluminium flat surfaces Measurement of both materials, each on opposite faces at a various probing forces using a common probe of 5 mm in diameter. A grid of 3 x 5 points is measured over two opposite faces. These points are measured at forces of: (0.05, 0.1, 0.25, 0.5, 1) N At the same probing force: Deviation from average x value At the different probing forces: Plotted average of the distance between paired points vs force (N) Tests repeated on AM and Machined part 10

11 Y-axis/mm Distance from Centre Line Y-axis/mm Distancefrom Centre Line Probing force Analysis of data(shape) Deviation from average width at probing force 1000 mn AM Cube Z-axis/mm Height Deviation from average width at probing force 1000 mn Machined block Z-axis/mm Height The average of the distances between the probed points is calculated and this is then taken away from the distance between the point pairs indicates non-parallelism. Solid; indicates the width is greater than the average. Maximum deviation from average width (Circle size): AM = 230 µm Machined = 7 µm The average of the standard deviation for the different probe forces, i.e. the change in the form of the surface as a function of force: AM = 6 µm Machined = 1 µm 11

12 Change in length/mm Probing force Analysis of data(deformation) Change in distance with probing force AM Machined AvgDia Force/mN Change in distance with probing force, indicates the difference between the maximum width and the width measured at that probing force. Displacement is a linear function of force agrees with Brinell hardness. 12

13 Contact CMM: Probe effects - Size Measurement of cylinder using the probes of the following diameter: 3 mm, 4 mm, 5 mm. Measurement of cylinder at the following heights: (18.5, 21, 23.5, 26, 28.5)mm Best fit circle and standard deviation of data Data collected as a scan (Number of points: 3 mm=4724, 4 mm=5074, 5 mm=5187) Same settings of probe speed and contact force used Comparison of best fit LS (least squares) cylinder diameter, min/max, standard deviation 13

14 Circle diameter(bestfit)/mm Probe size Analysis Probe Height/m Dia/mm m Dia/mm Std/mm Variation in cylinder diameter with probe diameter Probe diameter/mm There is a maximum size the circle can be defined regardless of the probe diameter Reducing the diameter of the probe allows it to drop further into the crevices of the surface reducing the size of the defined sphere The standard deviation of the best fit will, potentially, increase as the size of the probe decreases 14

15 Tactile measurements Summary Co-ordinate system defined by the tooling balls. An error in the alignment between the tooling balls and the AM part, could be as high as This alignment equates to the defined circle on the cylindrical, deviating from a circle by approximately 2 µm As the standard deviation of the best fit, is orders of magnitude greater than the 2 µm, the lack of alignment can be ignored. Item CMM A(Dia) B(Dia) C(Dia) A-B A-C B-C Height CMM Std

16 Optical measurements: Line scanner A Optical, could be a Fringe or Line scan Measurement of the cylinder at the following heights above the plane A : (18.5, 21.0, 23.5, 26.0, 28.5) mm Best fit and standard deviation of data Diameter and distance between tooling balls this highlights the systematic shift of the diameter of the tooling balls due to translucency Comparison to CAD: Gives an overall picture, large datasets Texture effects More research is needed at looking at fringe projection as a valid technique. R s R ss 16

17 Optical measurements - Summary 18.5 mm 21.0 mm 23.5 mm 28.5 mm Deviation from CAD model at heights from datum plane A. Deviation from CAD s 14 mm diameter cylinder, indicates that the circles are approximately 150 µm smaller than design. The discrepancy between the tactile diameter measurements and the optical measurements, may be due to: scatter, transparency, data filtering.. Item Optical A(Dia) B(Dia) C(Dia) A-B A-C B-C Height Optical Std

18 X-Ray Computed Tomography NPL system Uses, limitations. (speed, penetration) Brief mention of artefacts (errors) scatter, beam harden, drifts, gun, filter, Best practice and calibration (ballbars) Cone-beam system Reflection target Maximum voltage 225kV Spot size: ~3 µm at 7 W ~225 µm at 225 W Scintillation detector detector pixels 200 µm pitch size MPE 9+L/50 µm (L in mm) 18

19 XCT measurements: Dimensional A Surface defined using, Define material and Advanced mode settings in VGStudio Max 2.2 Measurement of the cylinder at the following heights, above the plane A : (18.5, 21.0, 23.5, 26.0, 28.5)mm Best fit circle and standard deviation of data Diameter and distance between tooling balls Comparison to CAD: Gives an overall picture, large datasets Texture effects 19

20 XCT Measurements - Summary Changing the threshold value (Th), changes the defined circle: Th=15, Dia= mm Th=80, Dia= mm Average deviation of the fitted data ~ 12 µm Item XCT A(Dia) B(Dia) C(Dia) A-B A-C B-C Height XCT Std

21 Dimensional summary - Traceability Standards Tactile CMMs ISO Optical VDI/VDE 2634 XCT VDI/VDE 2630, (ISO Part XCT under development) Performance verification External dimensions Surface roughness may effects all measurement systems Young s modulus effects tactile but not optical or XCT Optical properties may effect optical techniques but do not effect tactile or XCT Internal dimensions Surface has to be accessible for tactile and optical XCT has the ability to measure both surfaces and material interfaces, through threshold values, however, not traceable. The surface roughness of the AM parts, limit the ability to make confidence dimensional measurements. 21

22 Dimensional measurements - Summary C B A Item CMM CMM- Optical CMM- XCT A(Dia) B(Dia) C(Dia) A-B A-C B-C Comparison of data from CMM, XCT and optical, all units in mm. Sphere diameter and distance Circle diameters and standard deviation (Std) Height CMM Std CMM - Optical Std CMM - XCT Std

23 Next steps~ Images of cross section of different porosity features Side view of the AM stack sample Small particles Manufactured by Concept laser powder fusion machine. Approximately 13 mm x 26 mm Material: AlSi10Mg The maximum magnification of the system can be achieved with consideration of the sample size.

24 Other measurement areas Measurements relating local micromechanical performance to microstructural characterisation Validating non-destructive defect detection using serial sectioning. Evaluating Functionally graded materials (XCT and local performance) High temperature thermophysical properties for alloys Especially for reactive alloys; Enthalpy, Density, Viscosity, Surface tension Investigating the measurement needs in other areas of AM, for instance Polymers. 24

25 Acknowledgements in brief Colleagues from NPL: Wenjuan Sun, Peter Woolliams, Michael McCarthy,.. Collaborators: Birmingham University; Moataz Attalah, Jan White,. Sheffield University; Russell Goodall,. University of Nottingham, Adam Clare, Richard Leach, Ian Maskery, 25

26 Questions. if time permits

27 The National Measurement System delivers world-class measurement science & technology through these organisations The National Measurement System is the UK s national infrastructure of measurement Laboratories, which deliver world-class measurement science and technology through four National Measurement Institutes (NMIs): LGC, NPL the National Physical Laboratory, TUV NEL The former National Engineering Laboratory, and the National Measurement Office (NMO). 27