Ercihan Kiraci

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.

The use of laser scanning technology to improve the design process

Benchmarking competitor products helps a company to identify opportunities to improve their product relative to their competitors. This allows a company to determine the basic requirements of a new product, and target potential areas for improvement, particularly within the automotive industry where there is considerable growth and competition. Automotive firms have been increasingly focusing on development processes. Reducing time to market and improving quality whilst minimising cost. Laser scanning technology enables companies to make design and engineering improvements through the ability to analyse a competitor’s design. A case study of this generic process will be presented in this paper. The results have revealed that a company can create significant value-added activity, reduce the need for physical prototype costs and time, improve quality in new product development introduction.

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

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.

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

Ever-increasing introduction of new production technologies has significantly reduced manufacturing cycle time in recent years, especially joining technologies. For many industries, Zero Defect Manufacturing (ZDM) is considered as a key strategy to improve Right-First-Time (RFT) capability with a minimum waste of resources. There is a growing desire to move from off-line sample measurement to in-line data collection, which will only be possible with fast, accurate measurement technologies. Although metrology cycle times have improved with in-line measurement systems, their accuracy is not sufficient to meet the tight tolerance demands of typical high value manufacturing applications. A major obstacle to the uptake of new, non-contact measurement technologies is the difficultly in evaluating system capability in terms of repeatability, accuracy and calibration to recognized standards. This study considers these characteristics for a Laser Radar (LR) measurement system applied to an automotive door measurement task. To evaluate these factors, the authors consider: (1) the effect of tooling ball (TB) position and movement on part alignment and measurement feature results and (2) the feature-fitting algorithms applied to different sizes and orientations of hole. The results show that the statically-mounted LR is good at developing a repeatable coordinate system for the workpiece. Offsetting an individual TB had a statistically significantly effect on the repeatability of the measurement results. A number of feature-fitting algorithms were studied, with no algorithm providing a definitively superior result. Two data capture algorithm were considered; hatched and petal algorithm. The petal pattern algorithm is much faster, and was found to provide comparably repeatable results as the hatched pattern algorithm. These results give confidence that the LR system demonstrates good repeatability.

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.