Error Characterization of EOS M280 Additive Manufacturing Machine

Open Access
Author:
Lu, Yang
Graduate Program:
Industrial Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 03, 2017
Committee Members:
  • Yang Lu, Thesis Advisor
Keywords:
  • Additive Manufacturing
  • GD&T
  • Metrology
  • Powder Bed Fusion
Abstract:
Four brackets were manufactured from Inconel 718 powder on an EOSINT M280 DMLS machine. Each bracket fit within 75mm L x 66 mm W x 36mm H envelope. Geometric measurements taken from these parts revealed local size errors ranging from 0.01 mm to 0.15 mm, form errors ranging from 0.02 mm to 0.09 mm, and datum related profile errors ranging from 0.14 mm to 0.48 mm. All of these measurements were taken from surfaces that were not inclined toward the build plate. For surfaces that were, form errors ranged from 0.11 mm to 0.32 mm, and datum related profile errors ranged from 0.28 mm to 0.94 mm. This geometric variation is undoubtedly due to the interaction of the many components of the error budget of this process. These components include the starting digital model, the Z-axis table movement, the laser system, powder bed recoater as well as the physics in play during the melting and solidification of the powder and post processing of the build. Just as with other manufacturing processes, it is important for the user to flush out the relative contribution of each component and potential interactions among components of the error budget to the overall quality of the output. It is for that purpose that this thesis undertakes the experimental sampling of the quality of two important hardware components of this process: The Z-Axis table movement and the laser beam positioning system. The Z-Axis characterization process used a Renishaw Laser Interferometer and a pair of Mahr Federal Electronic Levels. Geometric error components including linear scale error, angular pitch and yaw error, and straightness error along the X-Axis were measured for the Z-Axis table. The laser positioning system was investigated using laser-etched patterns measured under an optical CMM from Optical Gaging Product (OGP) Inc. Two designs of the pattern were developed to evaluate the positioning accuracy and achievable geometric tolerance values. Pattern specifications were configured to eliminate the effects of thermal expansion. One of the patterns consisted of a circle matrix, which provided sufficient data points to fit a polynomial response surface. The other pattern included circles, lines, free form curves, and symmetric rectangles. These features were used to evaluate circularity, concentricity, straightness, angularity, perpendicularity, symmetry, composite profile tolerance, and composite position tolerance. For the Z-Axis table performance, results showed that the linear scale error of the table was quite low (4.5 microns), straightness, yaw and pitch errors were significantly higher and may contribute from 20-30 microns of form and orientation tolerances over a large size build. Laser position performance of the machine was much worse and showed a positioning system that was short by a significant amount of about 160 microns at the edges of the workspace. The largest scatter of values was observed on the position of small circular features located over the working area while the largest tolerance magnitude (239 microns) was calculated as the combined effect of location, orientation, size and form errors in the trace of a large quadrifolium etched over the working area of the laser.