Comprehensive Investigation of Surface Characterization Methods for Laser Sintered Parts Marc Vetterli INSPIRE AG irpd Sankt-Gallen, Switzerland DDMC14, March 13, 2014 Berlin
AGENDA: 1. Introduction 2. Methods 3. Results 4. Conclusions 5. Outlook 2
Introduction So far: The human hand is the best characterization method for the roughness of SLS parts à Surface state of SLS-produced subject to different default patterns: - Part orientation - Scan lines - Powder material à Many papers have identified the reasons for such surface state and characterized the surfaces mainly with profilometer à But how effective and representative are they? 3
Introduction Filtered out using a CUT OFF value λ c = 0.8 mm Source: ASME B46.1. Surface texture (surface roughness, waviness, and lay), 1995. 4
Introduction Arithmetic average of absolute values Average distance between the five highest peaks and five lowest valleys Source: DIN EN ISO 4287. Jul 2010, Mahr Federal 5
AGENDA: 1. Introduction 2. Methods 3. Results 4. Conclusions 5. Outlook 6
Methods Cube sintered on EOS P760 machine Dimensions: 15X15X15mm Parameter Value Unit UP Face Laser power 38 [W] Outline laser power 5.5 [W] Scan spacing 0.25 [mm] Layer thickness 0.1 [mm] Z SIDE Face Laser speed 6 [m/s] UP Face parallel to building platform X Y DOWN Face 7
Methods: Profile Investigation 1 2 1) Cube 2) Embed and polish 3) Micrograph of profile 4) B/W image processing 5) Interface recognition 6) Roughness calculation 3 1000 um 4 Side Face 5 6 Cutoff 0.8 mm Total measurement length 4 mm 8
Methods: Profilometers - Measurement length: 5.6 mm - Cut-off filter: 0.8mm - Scanning speed: 0.5 mm/s Mahr Perthometer à Tip radius of 5µm, angle of 90 Veeco Dektak 150 à Tip radius of 2.5µm, angle of 45 R a and R z(iso) are directly calculated by the integrated software. Source: Veeco Dektak 150 User s Manual à 4 measurements per direction at equidistant intervals 9
Methods: LEICA DCM 3D Interferometry + Confocal Microscopy: - Measurement area: 3.406x2.529 mm - Objective: 10X - Cut-off filter: 0.8mm - Resolution: 20 µm per data point R a and R z(iso) for both directions of the surface à Each pixel line is considered as a single surface profile in both X and Y directions Source: Leica DCM 3D User s Manual 10
Methods: GelSight GELSIGHT Elastomeric sensor covered with reflective skin 1) Sensor is pressed onto surface; its reflective skin conforms closely to it and lends it its optical properties. 2) Area is successively illuminated and photographed from six directions. 3) Pictures are computed with algorithm creating a surface normal map of the area. Optimal size of measured features: 1 100 µm 11
Methods: GelSight GELSIGHT - Measurement area: 4x4mm - Objective: 1X - Cut-off filter: 0.8mm - Resolution: 4.2 µm/pixel R a and R z(iso) for both directions of the surface. à Each pixel line is considered as a single surface profile in both X and Y directions 12
Methods: GelSight GELSIGHT Inc. - Measurement area: 4x4mm - Objective: 1X - Cut-off filter: 0.8mm - Resolution: 4.2 µm/pixel R a and R z(iso) for both directions of the surface. à Each pixel line is considered as a single surface profile in both X and Y directions 13
Methods: GelSight GELSIGHT Inc. - Measurement area: 4x4mm Objective: 1X Cut-off filter: 0.8mm Resolution: 4.2 µm/pixel Ra and Rz(ISO) for both directions of the surface. à Each pixel line is considered as a single surface profile in both X and Y directions 14
Methods: GelSight GELSIGHT Inc. - Measurement area: 4x4mm Objective: 1X Cut-off filter: 0.8mm Resolution: 4.2 µm/pixel Ra and Rz(ISO) for both directions of the surface. à Each pixel line is considered as a single surface profile in both X and Y directions 15
AGENDA: 1. Introduction 2. Methods 3. Results 4. Conclusions 5. Outlook 16
Results: UP Face 25.00 20.00 RaX RaY 100.00 80.00 RzX RzY 15.00 60.00 10.00 40.00 5.00 20.00 Ra (um) 0.00 0.00 Rz (um) 17
Results: DOWN Face 25.00 20.00 RaX RaY 100.00 80.00 RzX RzY 15.00 60.00 10.00 40.00 Ra (um) 5.00 0.00 20.00 0.00 Rz (um) 18
Results: SIDE Face 25.00 20.00 RaX RaZ 100.00 80.00 RzX "RzZ" 15.00 60.00 10.00 40.00 5.00 20.00 Ra (um) 0.00 0.00 Rz (um) 19
Results: Efficiency Time needed to measure a surface: t Veeco < t Perthen < t GelSight < t Leica Amount of information obtained surface: INFO Perthen < INFO Veeco < INFO Leica < INFO GelSight All in all, the information ratio from GelSight overrides its longer processing time. 20
Results: How representative? Perthen stylus tip Gelsight data points mapping Leica data points mapping à based on relfection of light: SLS surface is shiny and rough very high scattering of light leading to information loss 21
AGENDA: 1. Introduction 2. Methods 3. Results 4. Conclusions 5. Outlook 22
Conclusion à Every method subject to important variations à Measured values vary from method to method à However Gelsight enables a rapid and good reproduction of the surface state qualitatively as well as quantitatively à Qualitatively the impressions obtained by stroking SLS parts by hand are confirmed: - UP and DOWN Faces are smoother than SIDE Face 23
Conclusion DF PA12 sand-blasted DF PA12 vibratorygrinded 24
Conclusion Orgasol, Magnification 10X, spatial resolution 0.43 µm/pixel 25
AGENDA: 1. Introduction 2. Methods 3. Results 4. Conclusions 5. Outlook 26
Outlook With help of GelSight - Comparison between vibratory-grinded and conventional surfaces including the material ratio, height and wavelength parameters à Get a benchmark for optimizing the surface and making vibratorygrinding obsolete - Application of roughness surface areal parameters - Determination of factors being able to characterize and identify orange peel 27
Thank you for your attention! Questions? 28
Introduction SLS surfaces are subject to many different default patterns Source: Tumer,Thompson,Crawford 29
Introduction From Mitutoyo adapted from DIN EN ISO 4288:1998 30
Methods: Mahr Perthometer à Tip radius of 5µm, angle of 90 - Measurement length: 5.6 mm - Cut-off filter: 0.8mm - Scanning speed: 0.5 mm/s R a and R z(iso) are directly calculated by the integrated software. à 4 measurements per direction at equidistant intervals 31
Methods: Veeco Dektak 150 (New generation profilometer) à Tip radius of 2.5µm, angle of 45 - Measurement length: 5.6 mm - Cut-off filter: 0.8mm - Scanning speed: 0.5 mm/s - Resolution 1.7 µm R a and R z(iso) are directly calculated using Veeco s software. à 4 measurements per direction at equidistant intervals Source: Veeco Dektak 150 User s Manual 32
GelSight Benchtop Beta System n n n n n Canon T3i 18 Megapixel Camera 5202 x 3465 pixel Canon MP- E 65mm macro lens Spa:al Resolu:on: 1X: 4.3 µm per pixel 2X: 2.2 µm per pixel 3X: 1.5 µm per pixel 4X: 1.1 µm per pixel 5X: 0.9 µm per pixel The first two images were captured at a spa:al resolu:on of 3.8 µm per pixel. The 10X image was captured at a spa:al resolu:on of 0.43 µm per pixel. 33
Outlook - Use of the most reliable method to determine the impact of particle size distribution on surface roughness for SLS-produced parts - Comparison of DuraForm PA and Orgasol from Arkema Same basis material (nylon polyamide 12) The accuracy of Orgasol parts is much higher and surface smoother than DuraForm FUTURE: Obtaining similar surface characteristics with DuraForm PA 34
The Surface Roughness Issue If you cannot measure it, you cannot improve it. Lord Kelvin 1824-1907 Source 35