Comparison of Different Additive Manufacturing Methods Using Optimized Computed Tomography

Additive manufacturing (AM) allows for fast fabrication of three dimensional objects with the possibility of use of considerably less resources than would be the case in traditional manufacturing. AM is a fast and cost effective method which boasts the ability to produce components with a previously unachievable level of geometric complexity in end user industrial applications in areas such as the aerospace and automotive industries. However these processes currently lack reproducibility and repeatability with some ‘prints’ having a high rate requiring rework or even scrapping. It is therefore imperative that robust quality systems can be implemented such that the waste level of these processes can be eliminated or decreased. This study presents an artefact that has been optimised for characterisation using computed tomography (CT) with representative AM internal channels and structures. Furthermore the optimisation of the CT acquisition conditions for this artefact is presented in light of analysis of form, internal feature dimensions and position and material porosity

Metrology for Bio Systems

The current paper addresses the advent of next generation bio system focussed Micro Nano Manufacturing Technologies (MNMT). These products and processes have placed significant new emphasis on specification and quality control systems, especially if these product and processes are to achieve economic scale up. Bio technology products and processes are a core element of MNMT and structured surfaces can be a key element in enabling bio system function. There examples of the application of such surfaces in bio systems for functions such as diverse as anti fouling and oseointegration. However a deficit exists in terms of metrology for bio structured surfaces and identifying suitable measurands and instrumentation remains a challenge for production engineers. Functional modelling would seem to point towards a better way of specifying metrology however for bio systems these are rare and often extensive function testing and clinical trials are used to inform the metrology selection. In the present paper the development of MNMT bio systems is discussed in the metrology context and several examples of developing metrology challenges. Four such bio related systems are discussed the solutions are outlined. The case studies cover traditional prosthetic implants, micro fluidic devices, cellular attachment and manufacture of cellular scaffolds

Assessing the material loss of the modular taper interface in retrieved metal on metal hip replacements

Measuring the amount of material loss in the case of revised hip replacements is considered to be a prerequisite of understanding and assessing the true in vivo performance of the implant. This paper outlines a method developed by the authors for quantifying taper material loss as well as more general taper interface parameters. Previous studies have mostly relied on visual inspection to assess the material loss at the taper interface, whereas this method aims to characterize any surface and form changes through the use of an out-of-roundness measurement machine. Along with assessing the volumetric wear, maximum linear penetration and taper contact length can also be determined. The method was applied to retrieved large head metal-on-metal femoral heads in order to quantify the material loss at this junction. Material loss from the female femoral head taper can be characterized as a localized area that is in contact with the stem taper surface. The study showed that this method has good repeatability and a low level of interoperability variation between operators

Digital 3D reconstruction of historical textile fragment

This paper presents a new methodology for reproducing historic fragment in 3D with realistic behaviour, providing users with a feel for the fragment detailing. The fragment piece originates from the English National Trust archive held in the collection at Claydon House. The aim is to utilize a combination of both 2D pattern software and state-of-the-art 3D technology to recreate a compelling and a highly realistic representation of historic fragment. The process starts with investigation of the textile construction. Textile fragments will be incomplete and/or have a level of deterioration therefore various recording techniques are to be explored. A combination of both photography and 3D scanning technology will be utilized throughout the methodology to accurately record the digital data. The equipment setting will be analyzed in order to produce an accurate working method. This paper forming part of a larger study, will specifically focus on the methodology for recording data from one fragment piece

Investigating the capability of microfocus x-ray computed tomography for areal surface analysis of additively manufactured parts

INTRODUCTION The ability to perform non-destructive areal surface analysis, for example of the internal surfaces of additively manufactured (AM) parts has potential advantages during product development and for production process control. This paper reports on the extraction of areal surface information from microfocus x-ray computed tomography (XCT) data. Using this novel technique a range of areal parameter values were generated from a surface section extracted from XCT scan data of an as-built (no post-processing) AlSi10Mg additively manufactured part. This was then compared with the parameter values generated from a focus variation scan of the same surface section. The data comparison method involving normalisation of data format to allow analysis using industry-standard software, such as MountainsMap (Digital Surf, Besançon, France) or SurfStand (The Centre for Precision Technologies UoH) is demonstrated. Importing the extracted surfaces into these powerful software packages allows one-click data filtering per ISO 25178-3 [1] and the generation of a comprehensive suite of areal surface parameter values. These include feature and field parameters, amplitude, spatial, hybrid and functional parameters, as defined in ISO 25178-2 [2]. A method for characterising the capability of XCT for areal surface measurement is demonstrated by comparing results obtained from samples taken from a Rubert comparator test panel, with sample surface Ra values between 0.8 μm and 50 μm

Comparison of Different Additive Manufacturing Methods Using Computed Tomography

Additive manufacturing (AM) allows for fast fabrication of three dimensional objects with the use of considerably less resources, less energy consumption and shorter supply chain than would be the case in traditional manufacturing. AM has gained significance due to its cost effective method which boasts the ability to produce components with a previously unachievable level of geometric complexity in prototyping and end user industrial applications, such as aerospace, automotive and medical industries. However these processes currently lack reproducibility and repeatability with some ‘prints’ having a high probability of requiring rework or even scrapping due to out of specification or high porosity levels, leading to failure due to structural stresses. It is therefore imperative that robust quality systems be implemented such that the waste level of these processes can be significantly decreased. This study presents an artefact that is optimised for characterisation of form using computed tomography (CT) with representative geometric dimensioning and tolerancing features and internal channels and structures comparable to cooling channels in heat exchangers. Furthermore the optimisation of the CT acquisition conditions for this artefact are presented in light of feature dimensions and form analysis. This paper investigates the accuracy and capability of CT measurements compared with reference measurements from coordinate measuring machine (CMM), as well as focus on the evaluation of different AM method

Comparison of Different Additive Manufacturing Methods Using Optimized Computed Tomography

Additive manufacturing (AM) allows for fast fabrication of three dimensional objects with the use of considerably less resources, less energy consumption and shorter supply chain than would be the case in traditional manufacturing. AM has gained significance due to its cost effective method which boasts the ability to produce components with a previously unachievable level of geometric complexity in prototyping and end user industrial applications, such as aerospace, automotive and medical industries. However these processes currently lack reproducibility and repeatability with some ‘prints’ having a high probability of requiring rework or even scrapping due to out of specification or high porosity levels, leading to failure due to structural stresses. This study presents an artefact that is optimised for characterisation of form using computed tomography (CT) with representative geometric dimensioning and tolerancing features and internal channels and structures comparable to cooling channels in heat exchangers. Furthermore the optimisation of the CT acquisition conditions for this artefact are presented in light of feature dimensions and form analysis. This poster investigates the accuracy and capability of CT measurements compared with reference measurements from coordinate measuring machine (CMM), as well as focus on the evaluation of different AM methods

MUVOT - Establishing an International Vocational Training Program on the Topic of Measurement Uncertainty

Measurement results represent important information, which are necessary for evaluating and improving the quality of manufactured products and to control manufacturing processes. Furthermore, they build the basis for numerous decisions in the field of quality management, process and production automation or product development and design. Knowledge about the acquisition, evaluation and interpretation of measurement data as well as an understanding of the relevant influences on those measurement results are essential for employees working in the field of manufacturing metrology. Measurement results are always afflicted with deviations, due to a variety of causes. It follows that in order to assign a value to the reliability and quality of a measurement result its uncertainty must be determined and considered. However, employees in the field of quality management or metrology are often not familiar with methods for determination and interpretation of measurement uncertainty, because appropriate opportunities for training are missing in current vocational education. This need has led to the creation of the European project MUVoT, which will create a course for advanced vocational training in determining measurement uncertainty. The training course is based on a blended learning concept, combining self-dependent learning via a web-based platform and face-to-face workshops. This allows the adaption of individual knowledge and skills by self-controlled learning of abstract contents whilst the exercises enable the practical application of typical methods, which are generally considered as quite complex by many employees, and thus assure correct understanding. The featured Blended Learning concept facilitates the integration of the training into a workplace setting, thus the idea of Lifelong Learning is promoted in new fields of application. The curriculum and training concept for this newly developed training program have been designed such that the course can be applied internationally. To facilitate this, a harmonized scheme for course structure and contents has been defined albeit with inherent flexibility, allowing the adaptation to specific constraints

What is required to measure the wear of explanted metal on metal hips?

Abstract INTRODUCTION There is increasing worldwide interest in the assessment of wear in explanted hip components. This is due is part to high profile failures of orthopaedic components in the US, whilst in the UK hip resurfacings have been experiencing a higher than expected failure rate. The reasons for these failures are not well understood, with data from the NJR suggesting the 43% of MoM resurfacing failures are unexplained. Wear analysis is a vital tool in determining failure mechanisms and ultimately improving the longevity of joint replacements through improved design and manufacturing control. There are currently no relevant measurement standards for the evaluation of retrieved orthopaedic components. This paper will assess two of the most commonly used techniques namely roundness measurement and co-ordinate measurement. The advantages and disadvantages of both techniques are considered in this paper. ROUNDNESS MACHINE The Talyrond 365 is a stylus based roundness machine. The component is located on a rotating table and the stylus measures the deviation from a perfect circle as the component is slowly rotated. The Talyrond measures a single profile to an accuracy of 30 nm and up to 72,000 data points per revolution. The air spindle has a radial accuracy of <0.02 μm and the Talymin gauge a minimum resolution of 12 nm. Individual roundness profiles can be stitched together to build up 3D cylinder maps, allowing 3D pictures of sections of explanted hip components to be generated. COORDINATE MEASURING MACHINE Co-ordinate measuring machines (CMMs) have been widely used in manufacturing quality and research departments for a number of years and the CMM is recognised as a powerful and important tool capable of ascertaining geometric data from a component. The CMM used in this study was a Zeiss Prismo CMM (Carl Zeiss Ltd., Rugby, UK) with a probing error of 0.7 μm. Components are securely held in a chuck fixture arrangement and the dimensions of the component in the portion of the bearing that is unworn is ascertained through measurement. The initial measurements are used to produce a reverse engineered 3D CAD surface which represents the component ‘pre-wear’ surface. The surface of the component is then scanned and the deviation from this pre-wear surface is mapped. The maximum linear wear and wear volume are then calculated directly. DISCUSSION The main advantage of CMM and Talyrond is that they are available in most metrology and measurement rooms. The CMM is a particularly versatile machine and can be used to measure any orthopaedic components. There is a need to develop a suitable Standard for both machines detailing a protocol to measure explanted hip and quantify the wear. A study is underway to measure a set of explanted hip components to allow a detailed comparison between of measurements between the Talyrond and CMM. The result of this study will be included in the paper. CONCLUSIONS The CMM and Talyrond are both instruments suited to measuring wear of explanted hips. A full evaluation of the systems and the development of robust measurement protocol and standard would be advantageous to the orthopaedic industry