Measurement strategy impact on dimensional inspection by portable camera-based measuring systems

In dimensional inspection of large objects, portable measuring systems are greatly involved in a wealth of applications, such as automotive, motorsports and aerospace industries. Metris K-series Optical CMM (Coordinate Measuring Machine) system is one of the metrology solutions with relatively high accuracy and flexibility. This paper focuses on measurement strategy via repeatedly measuring a length using Metris K610 camera system. The paper proposes a link between measurement strategy and the system performance that can be achieved. The result of the statistical analysis are also given based on the uncertainty propagation of the CMM

The effect of clamping sequence on dimensional variability of a manufactured automotive sheet metal sub-assembly

The use of holding and inspection fixtures is common across many sectors of manufacturing. The concept of a fixture for holding a component, for the purposes of assembly or inspection, is straightforward. The fixture design and the associated clamping strategy can have a significant impact on the process. This paper presents a methodology for investigating the effects of clamping sequence for a production inspection fixture, on the dimensional variability of an automotive production-representative sheet metal sub-assembly, along with experimental findings and analysis of measurement data. The study utilises both a coordinate measuring machine and laser tracker to capture a range of features and surface points, and compares four different clamping sequences, including the manufacturer’s defined sequence, to evaluate their effect on the dimensional results from a predetermined measurement plan. The results from the study show that there was significant variation in measurements taken from the four different clamping sequences, and these variations can show the same points and/or features being within tolerance for one clamping sequence and out of tolerance for another. This clearly has major implications for product development and subsequent volume manufacture, so needs to be considered and optimised in the measurement planning process

Moving towards in-line metrology : evaluation of a Laser Radar system for in-line dimensional inspection for automotive assembly systems

The increasing interest towards intelligent systems has led to a demand for the development of zero-defect strategies, with a paradigm shift from off-line and dedicated to in-line metrology with integrated robotic systems. However, a major barrier preventing the systematic uptake of in-line metrology is the lack of evaluation of system capability in terms of accuracy, repeatability and measurement time, when compared to the well-established coordinate measuring machine (CMM). In this study, a robotic Laser Radar (LR) solution is assessed in the context of automotive dimensional inspection of Body-In-White (BIW) applications. The objective is both to understand the effect of robot re-positioning error on measurement accuracy and repeatability and to compare measurement results against a CMM. Eighty-one surface points, six edge points, twenty-five holes and sixteen slots were selected from an industry standard measurement plan. Whilst LR exhibits a lower measurement accuracy than twin-column CMM, its repeatability is well within the specification limits for body shell quality inspection. Therefore, as a real-time in-line metrology tool, it is a genuine prospect to exploit. This research makes a significant contribution toward in-line metrology for dimensional inspection, for automotive application, for rapid detection and for correction of assembly defects in real time, with subsequent reduction of scrap and number of repairs/re-works

Evaluating the capability of laser scanning to measure an automotive artefact : a comparison study of touch trigger probe and laser-scanning

Abstract: In the automotive industry dimensional quality control is an important part of the production process, often carried out using coordinate measuring machines (CMMs). However, CMMs used in conjunction with touch probes have a relatively low measurement speed. There is also a close link between the cost of measurement and the number of discrete points captured, leading to a trade-off between the number of points that can be measured and the measurement time. Laser scanners offer a faster alternative to touch probe measurement, but have certain limitations. A number of studies have considered the accuracy of laser scanning using small artefacts; however, little work has been done on the verification of on-CMM laser scanning systems for large volume, industry-relevant measurement applications. In this research, a nominal representation of a vehicle body was used and 104 standard features were measured. The results show that the laser scanning sensor and CMM used in this study would, for the majority of measurements, provide a level of accuracy and repeatability better than which is typically required by automotive manufacturers for body shell quality inspection applications

Evaluation of a multi-sensor horizontal dual arm Coordinate Measuring Machine for automotive dimensional inspection

Multi-sensor coordinate measuring machines (CMM) have a potential performance advantage over existing CMM systems by offering the accuracy of a touch trigger probe with the speed of a laser scanner. Before these systems can be used, it is important that both random and systematic errors are evaluated within the context of its intended application. At present, the performance of a multi-sensor CMM, particularly of the laser scanner, has not been evaluated within an automotive environment. This study used a full-scale CNC machined physical representation of a sheet metal vehicle body to evaluate the measurement agreement and repeatability of critical surface points using a multi-sensor horizontal dual arm CMM. It was found that there were errors between CMM arms and with regard to part coordinate frame construction when using the different probing systems. However, the most significant effect upon measurement error was the spatial location of the surface feature. Therefore, for each feature on an automotive assembly, measurement agreement and repeatability has to be individually determined to access its acceptability for measurement with a laser scanner to improve CMM utilisation, or whether the accuracy of a touch trigger probe is required

Comparison of in-line and off-line measurement systems using a calibrated industry representative artefact for automotive dimensional inspection

Manufacturers should understand measurement system performance to identify and control measurement errors due to changes in the quality standard and actionable measurement data in the age of Industry 4.0. This study evaluates the capability of three measurement systems, determining their feature-specific suitability for automotive inspection. A touch-trigger probe CMM and a laser scanner CMM are compared as off-line measurement systems, against a laser radar as an in-line solution. Representative common automotive features were assessed using a calibrated industry artefact. The study shows the laser radar provides the comparable accuracy to off-line systems. If tolerances are smaller than ±1.5 mm, the capabilities of non-contact systems are considerably dependent on the measured feature type. This study provides improved understanding of the non-contact measurement system that would enable automotive manufacturers to implement fast measurement strategy based on feature definition and tolerance limit without reducing the quality of measurement

Evolution of residual stresses in linear deposition wire-based cladding of Ti-6Al-4V

Neutron diffraction and curvature measurements were conducted to investigate the residual stresses associated with Plasma Transferred Arc Cladding (PTA) of Ti-6Al-4V on a substrate of the same material. The wire-feed PTA coupled with 3-axis CNC machine was used as an Additive Manufacturing (AM) technique to build parts. A combination of the process parameters was chosen to investigate their effects on residual stress evolution. Neutron Diffraction (ND) measurements of residual strains were performed on the SALSA instrument at the Institut Laue-Langevin (ILL), Grenoble, France. Longitudinal stresses were also inferred by using a Coordinate Measurement Machine (CMM) and Euler-Bernoulli beam theorem. Furthermore, Optical Microscopy (OM) of the cross section of the parts was used to analyse the microstructural evolution. The results show the effect of shorter and longer ‘dwell time’ between layers on the evolution of residual stresses

Towards in-process x-ray CT for dimensional metrology

X-ray computed tomography (CT) offers significant potential as a metrological tool, given the wealth of internal and external data that can be captured, much of which is inaccessible to conventional optical and tactile coordinate measurement machines (CMM). Typical lab-based CT can take upwards of 30 min to produce a 3D model of an object, making it unsuitable for volume production inspection applications. Recently a new generation of real time tomography (RTT) x-ray CT has been developed for airport baggage inspections, utilising novel electronically switched x-ray sources instead of a rotating gantry. This enables bags to be scanned in a few seconds and 3D volume images produced in almost real time for qualitative assessment to identify potential threats. Such systems are able to scan objects as large as 600 mm in diameter at 500 mm s−1. The current voxel size of such a system is approximately 1 mm—much larger than lab-based CT, but with significantly faster scan times is an attractive prospect to explore. This paper will examine the potential of such systems for real time metrological inspection of additively manufactured parts. The measurement accuracy of the Rapiscan RTT110, an RTT airport baggage scanner, is evaluated by comparison to measurements from a metrologically confirmed CMM and those achieved by conventional lab-CT. It was found to produce an average absolute error of 0.18 mm that may already have some applications in the manufacturing line. While this is expectedly a greater error than lab-based CT, a number of adjustments are suggested that could improve resolution, making the technology viable for a broader range of in-line quality inspection applications, including cast and additively manufactured parts

Non-reproducible alignment and fitting algorithm effects on Laser Radar measurement

In recent years, manufacturing companies have adopted a Zero Defect Manufacturing (ZDM) approach to reduce product defects and to improve Right-First-Time (RFT) capability with minimum waste of resources [1]–[3]. In order to achieve ZDM, data collection alone is not sufficient; data mining methods are critical to evaluate the inherent variation of manufacturing processes. During New Product Introduction (NPI), Statistical Process Control (SPC) and similar tools are used to identify and eliminate defects from occurring/reoccurring. In the automotive industry inspection is typically performed using Coordinate Measuring Machines (CMMs) [4], [5] that provide high accuracy and repeatability, but are housed in dedicated off-line facilities that require a controlled environment [6], [8]. This off-line process is time consuming and only a limited number of samples can be measured. There is a rising trend to move away from off-line sample measurement to in-line data collection in order to predict defects before they happen or identify trends in the production process [9], [10]