Effect of the matte powder coating on the accuracy of the measurement of a conical characteristic by optical techniques

Abstract

Three-dimensional non-contact optical measuring systems, 
which project structured light patterns, are not only widely 
used to recover the real geometry of an object, but also in 
the area of quality control. In order to carry out a precise 
measurement with optical techniques, it is necessary to avoid 
reflections produced by the light falling on the metal part. 
For this, it is necessary to cover it with matte powder. The 
coating operation is, normally carried out manually by spraying 
the powder onto the work-piece. In particular, a spray with 
magnesium oxide powder has been used, achieving a thin and 
uniform fairly layer.
In general, the aim of this article is to evaluate the possibility 
of controlling the manufacturing tolerances achieved in 
machining processes by means of optical techniques. In 
particular, the purpose of this research article is to obtain 
information on the effect the powder coating in the precision 
of an angular measurement of a conical feature by means of 3D 
optical techniques using the ATOS II scanner. The part chosen 
to perform the study is a SK40 DIN2080 tool holder cone.
A procedure is established to capture and measure the 
geometry of the part. Then, the measurements obtained are 
compared with the nominal dimensions and the accuracy 
and precision of the measurements are characterized. An 
estimation of the repeatability of the process is carried out. 
The results prove that the uncertainty in the controlled conical 
measurements remains limited. Finally, the influence of the 
applied matte coating in the systematic error is quantified, 
and some interpretations of the origin of the random error are 
proposed