Uncertainty assessment for on-machine tool measurement: An alternative approach to the ISO 15530-3 technical specification

Abstract

Touch probes are commonly employed in new machine tools (MTs), and enable machining and measuring processes to occur on the same MT. They offer the potential to measure components, either during or after the machining process, providing traceability of the quality inspection on the MT. Nevertheless, there are several factors that affect measurement accuracy on shop-floor conditions, such as MT geometric errors, temperature variation, probing system, vibrations and dirt. Thus, the traceability of a measurement process on an MT is not guaranteed and measurement results are therefore not sufficiently reliable for self-adapting manufacturing processes. The current state-of-the-art approaches employ a physically calibrated workpiece to realise traceable on-MT measurement according to the ISO 15530-3 technical specification, but it has a significant limitation in that it depends on a physical workpiece to understand the performance of the systematic error contributor (ub). To this end, the aim of this paper is to propose an alternative methodology for on-MT uncertainty assessment without using a calibrated workpiece. The proposed approach is based on a volumetric error mapping of the MT prior to the measurement process, which provides an understanding of how the systematic error contributor (ub) performs. An experimental exercise is performed for a medium-size prismatic component according to the VDI 2617-11 guideline, and the results are compared with the ISO 15530-3 technical specification.

Experimental Study of the Volumetric Error Effect on the Resulting Working Accuracy—Roundness

“…The use of tracking interferometers to assess 2D geometric errors influenced by temperature change is described in [7]. The utilisation of manufacturing accuracy data for rotational error assessment is presented in [8], linear axis compensation procedures in publications [9,10], the use of the Ballbar for machine tool error assessment and compensation in [11], a comprehensive assessment of measurement methods, overexertion and their effects on large machines in [12] and the use of on-machine tool measurement in [13]. When assessing the effects of machine geometric errors on a future workpiece, it is necessary to consider all effects that increase measurement uncertainty and those that minimise these uncertainties.…”

Geometric Error Identification and Analysis of Rotary Axes on Five-Axis Machine Tool Based on Precision Balls

“…After matrix operations, the two tilt error sums C α ε and C β ε of C-axis were obtained as stated in Equations (21) and (22), in which the position error of A-axis was taken as a known constant. Equation (19) was obtained based on the coordinate transformation relationship between actual spherical point coordinate P 1 in W rC and two sets of spherical points S 1 , S 1 , S 2 , S 2 in W iC as:…”

“…After matrix operations, the two tilt error sums ε αC and ε βC of C-axis were obtained as stated in Equations (21) and (22), in which the position error of A-axis was taken as a known constant. ε αC = −ε αA + (∆x 1 ∆z 2 − ∆z 1 ∆x 2 )/(∆x 1 ∆y 2 − ∆y 1 ∆x 2 ) (22) ε βC = −ε βA + (∆y 1 ∆z 2 − ∆z 1 ∆y 2 )/(∆x 1 ∆y 2 − ∆y 1 ∆x 2 ) (23)…”

“…In the study of the geometric error measurement and identification methods of five-axis machine tools, the positioning error of each linear axis, two straightness errors, three corner errors, and the perpendicularity between the two axes can be directly measured by a laser interferometer or other optical measuring systems [19][20][21]. Laser tracer technology is used for the volumetric error mapping and compensation of geometric errors of machine tools [22]. LINARES et al [23] used a tracking interferometer to measure and compensate the geometric error of a small CNC machine.…”

Studying the influence of the machining process on the geometrical defects of the standardized S-shape test part

“…-Kinematic methods ensure the evaluation of machine movement accuracy, to quantify, in addition, defect #5 using laser trackers, for example [4];…”