Angel, Jais Andreas Breusch

Cantatore, Angela

De Chiffre, Leonardo

This work deals with the study of stability and material investigation for manufacturing of step gauges for CT scanning verification. Four replica step gauges were fabricated using a bisacryl material for dental applications and the stability over five months was monitored using a tactile CMM. The material was unstable, probably due to a modification of the chemical composition which lowered the hardness. New step gauges were manufactured through milling. Polyetheretherketone (PEEK) and Polyp-phenylenesulphide (PPS with 40% glass) fulfil the requirements regarding hardness and mechanical properties and two series of five step gauges (one series for each material) were manufactured by milling. Results show a significant improvement in terms of form stability and surface geometry quality of the new step gauges with respect to the replica step gauges in Luxabite, as reported below

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017Material investigation for manufacturing of reference step gauges for CT scanningverificationCantatore, Angela; Angel, Jais Andreas Breusch; De Chiffre, LeonardoPublished in:Proceedings of the 12th euspen International ConferencePublication date:2012Link back to DTU OrbitCitation (APA):Cantatore, A., Angel, J. A. B., & De Chiffre, L. (2012). Material investigation for manufacturing of reference stepgauges for CT scanning verification. In Proceedings of the 12th euspen International ConferenceProceedings of the 12th euspen International Conference – Stockholm – June 2012 Material investigation for manufacturing of reference step gauges for CT scanning verification A. Cantatore, J. Angel, L. De Chiffre Department of Mechanical Engineering, Technical University of Denmark, Building 425, Produktionstorvet, DK-2800 Kgs. Lyngby, Denmark  acan@mek.dtu.dk  Abstract This work deals with the study of stability and material investigation for manufacturing of step gauges for CT scanning verification. Four replica step gauges were fabricated using a bisacryl material for dental applications and the stability over five months was monitored using a tactile CMM. The material was unstable, probably due to a modification of the chemical composition which lowered the hardness. New step gauges were manufactured through milling. Polyetheretherketone (PEEK) and Polyp-phenylenesulphide (PPS with 40% glass) fulfil the requirements regarding hardness and mechanical properties and two series of five step gauges (one series for each material) were manufactured by milling. Results show a significant improvement in terms of form stability and surface geometry quality of the new step gauges with respect to the replica step gauges in Luxabite, as reported below.  1 Introduction A 42mm-long replica step gauge (2 mm reference step length and 4 mm pitch), originally intended for optical scanner verification, was moulded in February 2009 using a bisacryl material for dental applications (Luxabite). Good stability of the step gauge was assessed over a period of 6 months, by computing incremental step lengths with both uni-directional and bi-directional strategies using a tactile coordinate measuring machine (CMM) [1]. The item was used for performance verification of a CT scanner with good results in terms of error characterization and system optimization [2]. In order to better characterize material stability, a wider sample was chosen and new four replicas were moulded in October 2010. The stability was investigated over five months (from March 2011 to August 2011). The results show average deviations ranging from 3 µm to 9 µm for uni-directional distances  and Proceedings of the 12th euspen International Conference – Stockholm – June 2012 deviations ranging from 12 to 27 µm for bi-directional ones, with expanded uncertainty (confidence level = 95%) higher than 30 µm for same measurands. These high values point out problems associated with measurement repeatability and form errors, due to the presence of holes in correspondence to the CMM probing points (average peak to valley height = 17 µm and average maximum width = 345 µm, measured with an Infinite Focus microscope by Alicona). The conclusions are that the material is not stable enough to be employed for reference items, as the manufacturing and replication did not allow to reach sufficient surface cooperativeness. This discrepancy with previous results can be due to the fact that in one year the chemical composition of the material was changed. Figure 1: Examples of holes present on the measurement surfaces of Luxabite step gauges, measured with an Infinite Focus microscope  2 Material investigation for manufacturing of reference step gauges Starting from these results, an investigation on proper materials for manufacturing of reference step gauge for CT scanning applications was carried out. Focus was kept on plastic materials, since they are commonly used in industrial CT scanning. Two materials were selected: Polyetheretherketone (PEEK) and Polyp-phenylenesulphide (PPS with 40% glass). These polymers fulfil requirements in terms of hardness, mechanical properties, surface cooperativeness and stability. Two series of five step gauges (one series for each material) were manufactured by milling. This process improved significantly the surface quality with respect to replica step gauges in Luxabite, with form errors of the order of 5 µm for the PEEK step gauges and of 3 µm for the PPS with 40% glass step gauges. The material hardness results also improved. It was measured using a Vickers hardness test, taking average and standard deviation of five repeated measurements. (Figure 3). An increase of around 50% with PEEK and PPS with 40% glass with respect to Luxabite is detected.  Proceedings of the 12th euspen International Conference – Stockholm – June 2012  Figure 2: PEEK (left) and PPS with 40% glass (right) step gauges   Figure 3: Hardness measurements on Luxabite, PEEK and PPS with 40% glass specimens measured with Vickers hardness test. Results are expressed in Vickers units (HV) and were obtained with a load of 10 kgf  3 Experimental investigation The stability of the new step gauges was investigated with the same approach used for the Luxabite step gauges. The stability was monitored over a period of three months (from November 2011 to January 2012). Uni-directional and bi-directional distances were considered. Deviations with respect to the first measurements were computed together with related uncertainties (confidence level = 95%). Uncertainties were evaluated following GUM guidelines and considering the following contributes: MPE, workpiece form error, temperature effect and reproducibility (the parts were repositioned and measured again five times). In Figure 4 are displayed the outcomes for two measurands regarding PEEK step gauges: the uni-directional with nominal value = 20mm and the bi-directional, with nominal value = 22mm. The stability resulted significantly improved in comparison to Luxabite replicas, with maximum deviations below 4 µm for PEEK and limited expanded uncertainty (below 6 µm). Similar results were obtained for PPS with 40% glass and for all measurands. Proceedings of the 12th euspen International Conference – Stockholm – June 2012 Figure 4: Deviations and expanded uncertainty for the new manufactured step gauges in PEEK in correspondence of 20mm (uni-directional) and 22 mm (bidirectional) lengths. For the first measurements (November 2011) just expanded uncertainty is reported  4 Conclusions The work encompasses the study of stability and other mechanical properties of step gauges intended for CT scanning verification. Due to stability and surface geometry problems pointed out in previously moulded replica step gauges in Luxabite, other two plastic materials (PEEK and PPS with 40% glass) were selected on the basis of their good mechanical properties for manufacturing other step gauges through milling. Stability measurements results over 3 months and hardness measurements show a significant increase in surface geometry quality and stability in comparison to Luxabite step gauges.  Acknowledgements The authors wish to thank Jakob Rasmussen, René Sobiecki and Peter Sanderhoff for their valuable contribution to the work.  References: [1] A. Cantatore, L. De Chiffre, S. Carmignato, “Investigation on a replica step gauge for optical 3D scanning of micro parts”, Proceedings of the Euspen International Conference – Delft - June 2010, p. 200-203. [2] A. Cantatore, J. L. Andreasen, S. Carmignato, Pavel Müller, L. De Chiffre, “Verification of a CT scanner using a miniature step gauge”, Proceedings of the Euspen International Conference – Como Lake - May 2011, p. 46-49. 

Material investigation for manufacturing of reference step gauges for CT scanning verification

http://orbit.dtu.dk/ws/files/9812026/P3%2010_Cantatore.pdf

Material investigation for manufacturing of reference step gauges for CT scanning verification

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology