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

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

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

Study Regarding the Optimization of Milling Parameters for a Minimal Power Consumption

Energy consumption has become one of the environmental issues regarding all industries because of the increased development that is recorded in the last years. Thus, a major topic for furniture industry also, is to reduce the cutting power consumed while processing wood and wood composite parts. The purpose of this paper is to analyze and model the effects of the cutting speed and feed speed upon power consumption while milling. The most important parameters (variables) on power consumption are cutting speed and feed speed, so, the wood samples-beech (Fagus sylvatica) were processed with five different feed rates and cutting speeds. The results of the experiment have indicated that power consumption increased with increasing cutting speed and feed rate

The Impediments to Nigeria Understanding Oil Production Volumes, Losses and Potential Solutions

The issue of the quantity of oil produced or missing has traditionally been played down in Nigeria. This is evident as no one in or outside Nigeria is able to quote a totally reliable production volume or loss figure. The aim of this study is thus to search for the root causes as to why there are difficulties in ascertaining the quantity of crude oil produced or missing per day and for potential solutions. The research assesses the present situation and problems requiring solution concerning Nigerian oil and gas measurement control. This is achieved through an intensive review of each of the notified bodies responsible for Nigeria’s oil and gas measurement control, using secondary resources. The bodies reviewed in this study are the Department of Petroleum Resources and the Weights and Measures Department. The study has identified knowledge impediments among the designated bodies. Also discovered were inadequate measurement equipment and absence of measurement guidelines, thus, no mechanisms were in place to address any mismeasurements or losses that are discovered. Provision of comprehensive training to the regulatory body to provide it with the necessary “teeth” to ensure effective delivery of it regulatory function has therefore been recommended as the key solution

The evolution of Geometrical Product Specification and Verification in the field of surface metrology and the challenges of its vocational training

Surface metrology is the science of the measurement on micro/nano surface which plays an important role in the control of the manufacture process of a workpiece and the prediction of its performance. In the last three decades, there is an evolution in the field of surface metrology, such as the emerge of many new data collection methods, the development of novel data processing techniques and the shift of characterisation technology from profile paradigm toward areal paradigm. Therefore, in the last 10 years, ISO have developed and released lot of new standard documents to standardise the specification and verification procedure of surface texture assessment in the framework of its technique langrage, i.e. Geometrical Product Specification and Verification (GPS). It empowers engineers with a richer and unambiguous language to detail their requirement with the less specification uncertainty. However, an engineer has difficulty to develop his/her skill in use this technique language due to the increase of its complexity and flexibility. To this end, an EC founded project is undertaking to develop e-learning platform and workshop to deliver the latest development of GPS to engineers. It will use the student-centred method which focused user friendly learning environment, the learning outcomes (i.e. skill and knowledge), self-directed learning etc. This three-year project will be completed at end of 2018. In the beginning of the project, it is of importance to develop a better understanding the challenge of training and user requirement. Therefore, this paper reviews the evolution of GPS in the field of surface metrology with highlighting the issues from training aspect. It explores the current ISO standard documents and training materials, together with a short review of education theory and practise in the information era. A survey has undertaken from industrial participants which outline the requirements of its main users. The outcome of this research maps the field of this training project

Characterization of defects/porosity in additive manufactured components using computer tomography

The key barrier for many industries in adopting additive manufacturing technologies is the lack of quality assurance and repeatability. Defect/porosity analysis is the most important inspection step for any additively manufactured components. This paper presents a method for the detection of defects/porosity in additive manufactured components using computer tomography. A Nikon XTH225 industrial CT was used to analyse the relative size and location of the defects and assess the capability of the inspection process based on different levels of X-ray detector magnification. To reduce the number of process variables, all the measurement process parameters, such as filament current, acceleration voltage and X-ray filtering material and thickness, are kept constant. The acquired data processing, surface determination process and defect analysis was carried out using the VgStudio Max (Volume Graphics, Germany) software package. One Ti6AL4V component built using an Arcam Q10 electron beam melting machine (EBM) was used. The results obtained from the XCT scan are compared to the physical defect analysis, by sectioning the component and confirming pore size and location using focus variation interferometry. The effect of surface determination, repeatability and results’ accuracy are discussed. The main focus of the study is on providing best practice regarding the selection of inspection parameters such as magnification to accurately perform the defect detection

Material Loss at the Head Taper Junction of the Metal-on-Metal Pinnacle Total Hip Replacement

Introduction The ASR XL (DePuy) total hip replacement (THR) is a notable example of a modern metal-on-metal (MOM) implant design that has demonstrated unacceptable survival rates, leading to its recall by the manufacturer; national joint registries have reported revision rates at 7 years of 40% when paired with the Corail stem [1]. The ASR XL THR has a considerably greater risk of revision than the ASR resurfacing hip, which used the same bearing design. This suggests that material loss at the head-stem junction may be responsible for the greater percentage of THR failures observed in this design. The Pinnacle MOM-THR (DePuy) however used the same Corail stem as the ASR XL THR but demonstrated better clinical results, with revision rates of less than 10% at 7 years [1]. The ASR XL and MOM Pinnacle are two designs that have been widely used in hip replacement surgery. The reasons for the differences in the failure rates of the two designs are not fully understood. Comparing the mechanisms of failure of both hips will help surgeons understand whether patients with MOM Pinnacle hips will experience the same types of problems as with those seen with the ASR XL. The aims of this retrieval study were to investigate the significance of differences between the ASR XL and MOM Pinnacle in relation to: (1) pre-revision whole blood Co/Cr ratios, (2) visual evidence of taper corrosion, (3) volumetric material loss at the bearing surfaces and (4) volumetric material loss at the taper surfaces. Methods This study involved a series of failed MOM hips consisting of the ASR XL (n=30) and Pinnacle (n=30), all that had been used with a Corail stem. The bearing material in each design was cobalt-chromium and the Corail stem is of a cementless titanium 12/14 design. The ASR XL and Pinnacle had a median head diameter of 47mm (39-55) and 36mm (36-40) respectively, and a median time to revision of 38.5 months (12-74) and 55 months (14-86) respectively. Pre-revision whole blood metal ion levels were collected for each Table 1 summarises patient and implant data for the hips in this study. The female taper surfaces of all 60 heads were examined macroscopically and microscopically to assess the severity of corrosion. Each surface was graded with a score of between 1 (no corrosion) and 4 (severe corrosion) using a well-published scoring system, which has been shown to be statistically reliable. A Zeiss Prismo (Carl Zeiss Ltd, Rugby, UK) coordinate measuring machine (CMM) was used to determine the volume of material loss at the cup and head bearing surfaces. Up to 300,000 data points were collected using a 2mm ruby stylus that was translated along 400 polar scan lines on the surface. The raw data was used to map regions of material loss by comparing with the unworn geometry of the bearing. A Talyrond 365 (Hobson, Leicester, UK) roundness measuring machine was used to measure the volumetric material loss at each of the head taper surfaces. Published protocols were used to take a series of 180 vertical traces along the taper surface using a 5μm diamond stylus; worn and unworn regions were mapped and used to calculate material loss. Neither the volumetric measurement data nor corrosion scores were normally distributed. Therefore non-parametric tests were performed to assess the statistical significance of differences between the two designs in relation to the parameters under investigation in this study. Results Both the whole blood Co ion levels and the Co/Cr ratios, Figure 1, of the ASR XL hips were significantly greater than the Pinnacles (p<0.05). There was no significant difference between the whole blood Cr ion levels between the two designs (p=0.0542). 18 of the ASR XL hips presented evidence of edge wearing of the cup, compared with 14 Pinnacle hips; this difference was not significant (p=0.438). The length of the stem trunnion contact engagement length with the taper was approximated as being 10.5mm for both designs. The median time to revision of the ASR XL hips was significantly less than the Pinnacle hips (p<0.01). There was visual evidence of corrosion in 93% (n=28) and 90% (n=27) of head tapers for the ASR XLs and Pinnacles respectively. Moderate to severe corrosion was observed in 67% (n=20) of ASR XLs compared to 60% (n=18) of Pinnacles. There was however no statistically significant difference between the scores of the two groups (p=0.927). Figure 2 presents the distribution of material loss rates for the bearing and taper surfaces of the two designs in this study. The median total bearing surface (combined cup and head) rate of material loss for the ASR XL and Pinnacle hips was 4.45mm3/year (0.32-22.85) and 4.03mm3/year (0.87-62.12) respectively. There was no significant difference between the two groups (p=0.928). The median material loss rate at the taper surfaces of the ASR XL and Pinnacle hips was 0.62mm3/year (0-4.20) and 0.30mm3/year (0-3.12); this difference was not significant (p=0.198). Discussion The work of this study presents comparisons of retrieval findings between the ASR XL and Pinnacle MOM-THRs; these hip designs were two of the most commonly implanted in patients worldwide. The significantly greater whole blood Co/Cr ratios found in the ASR XL group compared to the Pinnacle group are of interest. It is speculated that a Co/Cr ratio of greater than 1 may be an indicator of corrosion of an implant whereby more Cr ions are retained on the surface, whilst comparatively more Co ions are released into the blood. In the current study we found wear rates at the bearing surfaces of both designs to be comparable, suggesting that the significantly greater Co/Cr ratios in the ASR XL hips must be due to greater corrosion at the taper junction than the Pinnacles. Although the ASR XL hips had been implanted for a significantly shorter period of time, our visual assessment of the corrosion of the taper junctions found that corrosion scores were comparable between the two designs; indeed, a marginally greater number of ASR XL tapers had evidence of moderate to severe corrosion. This finding, coupled with the elevated Co/Cr ratios suggests that the ASR XL design is more susceptible to corrosion at the taper junction than the Pinnacle hip. We found that the median rate of material loss at the ASR XL taper was over twice that of the Pinnacle taper. Whilst not statistically significant, this difference may be due to a greater risk of corrosion at this interface in the ASR XL design. The differences in material loss and corrosion that were observed at the taper junctions may be explained by considering the larger head sizes of the ASR XL hips in comparison to the Pinnacles. It has previously been shown that increasing head size is correlated with greater visual evidence of corrosion and that increased frictional torque along the taper junction due a larger head diameter can increase the risk of fretting-corrosion. It is suggested therefore that the combination of the larger head sizes of the ASR XLs coupled with the comparatively short, rough surface of the Corail trunnion results in a cumulative effect leading to greater corrosion at the taper junction. Significance The results of the study suggest that the combination of (1) increased frictional torque in the larger ASR XLs and (2) the rough Corail trunnion surface, results in greater corrosion at the taper junction in comparison to the Pinnacle hips; this helps to explain the higher risk of revision in this hip design