Liam Blunt - Profile on Academia.edu (original) (raw)

Papers by Liam Blunt

Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, Apr 1, 2001

This paper proposes a lifting wavelet model for enhancement of accuracy of surface roughness char... more This paper proposes a lifting wavelet model for enhancement of accuracy of surface roughness characterisation. In this work, the theory and fast algorithm of the lifting wavelet are briefly introduced and a lifting wavelet model for extraction of roughness of surfaces has been developed. The rough surface recovered has good refinement accuracy in contrast to the least squares polynomial fitting. Applications are conducted by using a series of typical surfaces, planes and curves, measured by contact (stylus) and non-contact (phase-shifting interferometry) instruments, to demonstrate the feasibility and applicability of using the lifting wavelet model in the analysis of these surfaces.

Wear, Sep 1, 2007

It has long been recognised that wear analysis of total joint replacements is an important means ... more It has long been recognised that wear analysis of total joint replacements is an important means in determining failure mechanisms, functionality and improving longevity of these devices. The standardised method for assessing wear volumes in such joints is through gravimetric means and it has been shown that this method is a useful tool for indicating simulated wear volumes. This method is, however, of little value when considering the case of a clinically explanted bearing surface for which, by definition, there is no 'pre-wear' data. The purpose of this study is to present a co-ordinate measuring machine (CMM) based technique for assessing the volumetric material loss in explanted total hip replacement joints and to establish its effectiveness. A 3D CAD model was created of an idealised surface representing the pre-wear surface of the explanted acetabular cup to be measured. Here, two methods are proposed for discovery of a good estimate of the original pre-wear surface, which may differ significantly from the idealised CAD model. The first uses an unworn identical component as a baseline measurement and the second utilises the unworn portion of the explanted acetabular cup to create a more accurate 'zero-cycle' CAD entity. From these pre-wear surfaces, it is possible to directly calculate volumetric material loss and to graphically map the wear 'scar', i.e. the penetration of the femoral head into the acetabular cup.

In-process surface metrology for thin film flexible electronic devices

WIT transactions on engineering sciences, 1970

Over the past eight years the subject of 3D surface metrology has developed from something of a n... more Over the past eight years the subject of 3D surface metrology has developed from something of a novelty to a position where it has now become a crucial tool in the characterisation of engineering surfaces across a broad range of applications. It is widely accepted that the nature of the topography of a surface has a significant influence on the efficiency and functional performance of the surface. The functions that have been identified in various studies include wear, friction, lubrication, corrosion, fatigue, coating, paintability, etc. It is also increasingly being recognised that in order to fully study and control surface manufacture to enhance the above applications, studies need to be carried out from a 3-D perspective. Until recently however, the vast majority of research, industrial applications and national and international roughness standards were based on 2-D measurement techniques. It is now recognised that the characteristics of surfaces cannot be completely interpreted in some cases without 3-D information and many models established for understanding surface performance based on 2-D profiles have been unsuccessful. A number of key research groups have been working in this area in an effort to produce definitive 3D surface roughness standards. This paper reviews the most recent work in the field of 3D surface characterisation undertaken by the authors as part of a European multi partner project and outlines the development towards a 3D surface roughness standard.

Synthetic wavelength to increase the snapshot optical sensor’s elevated vertical measurement ranges

Applied Optics, Nov 14, 2019

Screening manufactured products that are conducted faster to enhance the contemporary manufacture... more Screening manufactured products that are conducted faster to enhance the contemporary manufacture processes and quality is possible by implementing enhanced quality control. Such quality control of manufactured products has increased the market for process-focused precision metrology that can execute evaluations faster while providing significant feedback for the manufacturing system. This investigation examines spatial dispersive interferometry's potential for producing accurate surface profile measurements by emphasizing vertical range measurements and identifying a system that can enable them to increase incrementally while maintaining the results' quality. Thus, this investigation selected Fourier transform profilometry (FTP) to assess surface profile measurements, as it provides the most reliable and fastest outcome data regarding this sensor. Exploring new surface scanning methods is important, as crucial weaknesses hinder several common approaches. As optical metrology sensors are bulky, difficult to establish, and expensive, the investigation will prove that FTP can resolve these restrictions. The investigation uses the synthetic wavelength approach for addressing vertical measurement limitation concerning optical systems for extending surface step height's vertical measurement range. Though it was observed that the FTP technique surmounts the vertical height limitations, certain limitations were also noted, with all outcomes considering key variables, including the scanning objective lens, system resolution, the spectrometer resolution, and diffraction grating. Future examinations must examine a wider vertical range to expand the snapshot spatial dispersive interferometry process's scope. Further, the step-height repeatability is enhanced, showing a good outcome range from 22 to 20 nm.

International Journal of Machine Tools & Manufacture, Apr 1, 2002

In many countries the most common polishing practice in die making is to hand polish the part as ... more In many countries the most common polishing practice in die making is to hand polish the part as a finishing operation after the electro discharge machining process (EDM). The usual polishing abrasives are silicon carbide paper and diamond paste of different grit sizes. However, during the last decade researchers especially in Japan and the USA have tried to combine EDM and electrochemical machining (ECM) in one machine so as to use the positive aspects of each individual process. The ECM process uses high density, typically 50 A/cm 2 , and also a pulse current with a servo-controlled electrode. These investigators have mostly used sodium nitrate solutions (of different concentrations) as the electrolyte. This paper deals with an experiment that was undertaken in order to assess the effect of four different electrolytes in an electrochemical polishing process (ECP) on the surface topography of EDM surfaces. The primary set of 3D surface parameters was used as a basis to characterise the surface produced by the combined processes in different electrolytic media.

University of Huddersfield eBooks, Dec 7, 2006

Aseptic loosening at the stem cement interface has been noted as a prominent failure mode in ceme... more Aseptic loosening at the stem cement interface has been noted as a prominent failure mode in cemented total hip replacement. It can be attributed to a tissue reaction to particulate debris generated by wear of the components. Wear can occur not only at the articulating surface but also at other load bearing interfaces due to relative micromotion. The stem cement interface has been consistently cited as a weak link. In the present study, characteristics at this interface were investigated through a series of pull out tests and a fretting wear simulation. The static shear strength was compared across a range of commercially available bone cements, with the result being higher than other studies. Fretting wear was successfully reproduced in vitro, which complied well with retrieval investigations. The research has gained a deep insight into the characteristics at the stem cement interface.

University of Huddersfield eBooks, Dec 1, 2009

Surface features have been recognised to be significant in many fields and the characterisation t... more Surface features have been recognised to be significant in many fields and the characterisation techniques are being constantly improved. The surface characterisation systems are developed by various instrument companies and institutions. However, the lack of good extensibility, reusability and maintainability is a serious obstacle to the system innovation. Component based software development offers a promising solution to the surface characterisation system with better extendibility and maintainability. This paper presents an overview of surface characterisation techniques, analyzes current surface characterisation systems, and then proposes a component based architecture for the surface characterisation system.

Charactering taper junction wear helps understand the mechanism of failure of metal on metal hip ... more Charactering taper junction wear helps understand the mechanism of failure of metal on metal hip replacements.

Journal of Bone and Joint Surgery-british Volume, Mar 1, 2013

Taper wear contributes only a third of the total volumetric material loss in large head metal on ... more Taper wear contributes only a third of the total volumetric material loss in large head metal on metal hip replacement

International journal of automation technology, May 5, 2020

Additive manufacturing (AM) is recognized as a core technology for producing high-value component... more Additive manufacturing (AM) is recognized as a core technology for producing high-value components. The production of complex and individually modified components, as well as prototypes, gives additive manufacturing a substantial advantage over conventional subtractive machining. For most industries, some of the current barriers to implementing AM include the lack of build repeatability and a deficit of quality assurance standards. The mechanical properties of the components depend critically on the density achieved. Therefore, defect/porosity analysis must be carried out to verify the components' integrity and viability. In parts produced using AM, the detection of unfused powder using computed tomography is challenging because the detection relies on differences in density. This study presents an optimized methodology for differentiating between unfused powder and voids in additive manufactured components, using computed tomography. Detecting the unfused powder requires detecting the cavities between particles. Previous studies have found that the detection of unfused powder requires a voxel size that is as small as 4 µ µ µm 3 3 3 . For most applications, scanning using a small voxel size is not reasonable because of the part size, long scan time, and data analysis. In this study, different voxel sizes are used to compare the time required for scanning, and the data analysis showing the impact of voxel size on the detection of micro defects. The powder used was Ti6Al4V, which has a grain size of 45-100 µ µ µm, and is typically employed by Arcam electron beam melting (EBM) machines. The artifact consisted of a 6 mm round bar with designed internal features ranging from 50 µ µ µm to 1400 µ µ µm and containing a mixture of voids and unfused powder. The diameter and depth of the defects were characterized using a focus variation microscope, after which they were scanned using a Nikon XTH225 industrial CT to measure the artifacts and characterize the internal features for defects/pores. To reduce the number of the process variables, the measurement parameters, such as filament current, acceleration voltage, and X-ray filtering material and thickness were kept constant. The VGStudio MAX 3.0 (Volume Graphics, Germany) software package was used for data processing, surface determination, and defects/porosity analysis. The main focus of this study is to explore the optimal methods for enhancing the detection of pores/defects while minimizing the time taken for scanning, data analysis, and determining the effects of noise on the analysis.

Wear, Oct 1, 2001

The properties of the femoral counterface are recognised as very significant in the study of the ... more The properties of the femoral counterface are recognised as very significant in the study of the tribological design of artificial joints and the wear of ultra-high molecular polyethylene (UHMWPE). Research has shown that morphological features of femoral counterfaces heavily interfere with the wear of UHMWPE. It has been reported that if 1-2 m defects or deep scratches are presented in a diamond like carbon (DLC) coated head, the third-body damage can cause a 7-15-fold increase in a UHMWPE wear rate, and in a metallic surface. The typical third-body damage can be up to a 30-70-fold compared with smooth roughness surface. Therefore, the identification of morphology of counterface surfaces has become an important requirement in the field of wear and tribology of the hip joint system. This paper proposes a methodology for a multiscalar wavelet for addressing morphological surfaces in order to extract the significant elements of 3D bearing surfaces of orthopaedic implants. The multiscalar wavelet is used to decompose a surface signal into the scalar domain. In wavelet analysis, the Cartesian space-based information is transferred into scale-based information, which provides not only the frequency events of the original signal but also keeps their location properties; as a result, morphological features can be identified. A series of ceramic, metallic and DLC femoral heads in vivo wear have been used to demonstrate the applicability of using the multiscalar wavelet model in the assessment of the morphology of these surfaces.

Journal of physics, 2005

Total joint replacement is one of the most common elective surgical procedures performed worldwid... more Total joint replacement is one of the most common elective surgical procedures performed worldwide, with an estimate of 1.5 million operations performed annually. Currently joint replacements are expected to function for 10-15 years, however, with an increase in life expectancy, and a greater call for knee replacement due to increased activity levels, there is a requirement to improve their function to offer longer term improved quality of life for patients. The amount of wear that a joint incurs is seen as a good indicator of performance, with higher wear rates typically leading to reduced function and premature failure. New technologies and materials are pushing traditional wear assessment methods to their limits, and novel metrology solutions are required to assess wear of joints following in vivo and in vitro use. This paper presents one such measurement technique; a scanning co-ordinate metrology machine for geometrical assessment. A case study is presented to show the application of this technology to a real orthopaedic measurement problem: the wear of components in total knee replacement. This technique shows good results and provides a basis for further developing techniques for geometrical wear assessment of total joint replacements.

Numerical Parameters for Characterisation of Topography

2 Numerical Parameters for Characterisation of Topography Liam Blunt and Xiangqian Jiang School o... more 2 Numerical Parameters for Characterisation of Topography Liam Blunt and Xiangqian Jiang School of Engineering, University of Huddersfield, UK 2.1 Introduction Numerical parameters for surface texture ... Sds should be assessed after Wolf pruning at 5% of Sz (default)[16, 17]. ...

Development of a Basis for 3D Surface Texture Standards "Surfstand" Liam Blunt, Xiang Jiang This ... more Development of a Basis for 3D Surface Texture Standards "Surfstand" Liam Blunt, Xiang Jiang This publication deals with the latest developments in the field of 3D surface metrology and will become a seminal text in this important area.

Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, Oct 1, 2005

It is a well known fact that the EDM process results in the formation of a hard, brittle recast l... more It is a well known fact that the EDM process results in the formation of a hard, brittle recast layer on the component's surface. Several investigations have been carried out in order to assess the nature of the recast layer in terms of its phase structure, the microhardness, presence and the density of cracks, and other surface features. Some researchers [Barash, Delpretti] have reported mathematical relationships between the thickness of the white layer and 2D amplitude surface roughness parameters (such as R a and R t ). But so far no investigation has been reported which correlates the thickness of the white layer with 3D surface roughness parameters, especially those related to spatial parameters. This paper presents an experimental investigation of the effect of the EDM process factors (current and pulse on-time) on the thickness of the white layer. Empirical equations relating the thickness of the white layer with 3D surface texture amplitude, spatial and volume parameters are presented and their physical basis is discussed. The results of this study show that a better correlation can be obtained between the average thickness of the white layer (AWLT) and the spatial parameter, S ds as compared to other 3D surface texture parameters. This is believed to be mainly due to the similar effect of the current and pulse on-time on both AWLT and S ds . The possible effect of surface tension between the solid and liquid phases on the thickness of the white layer during erosion is also discussed.

A New Approach to Surface Metrology - Structured Surfaces

euspen eBooks, 2007

Optimization of surface determination strategies to enhance detection of unfused powder in metal additive manufactured components

A series of cutting trails have been carried out utilising milling operations and the development... more A series of cutting trails have been carried out utilising milling operations and the development of chatter on the machmed surface has been analysed. 3D surface metrology techmques have been used to characterise the surface and particular attention has been paid to the use of Areal Auto Correlation Function (AACF) and Areal Power Spectral Densities (APSD). Both the AACF and APSD have been shown to effectively characterise the development and appearance of chatter and the implications of the use of these techniques for potentially controlling the machining process have been outlined.

Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, Apr 1, 2001

This paper proposes a lifting wavelet model for enhancement of accuracy of surface roughness char... more This paper proposes a lifting wavelet model for enhancement of accuracy of surface roughness characterisation. In this work, the theory and fast algorithm of the lifting wavelet are briefly introduced and a lifting wavelet model for extraction of roughness of surfaces has been developed. The rough surface recovered has good refinement accuracy in contrast to the least squares polynomial fitting. Applications are conducted by using a series of typical surfaces, planes and curves, measured by contact (stylus) and non-contact (phase-shifting interferometry) instruments, to demonstrate the feasibility and applicability of using the lifting wavelet model in the analysis of these surfaces.

Wear, Sep 1, 2007

It has long been recognised that wear analysis of total joint replacements is an important means ... more It has long been recognised that wear analysis of total joint replacements is an important means in determining failure mechanisms, functionality and improving longevity of these devices. The standardised method for assessing wear volumes in such joints is through gravimetric means and it has been shown that this method is a useful tool for indicating simulated wear volumes. This method is, however, of little value when considering the case of a clinically explanted bearing surface for which, by definition, there is no 'pre-wear' data. The purpose of this study is to present a co-ordinate measuring machine (CMM) based technique for assessing the volumetric material loss in explanted total hip replacement joints and to establish its effectiveness. A 3D CAD model was created of an idealised surface representing the pre-wear surface of the explanted acetabular cup to be measured. Here, two methods are proposed for discovery of a good estimate of the original pre-wear surface, which may differ significantly from the idealised CAD model. The first uses an unworn identical component as a baseline measurement and the second utilises the unworn portion of the explanted acetabular cup to create a more accurate 'zero-cycle' CAD entity. From these pre-wear surfaces, it is possible to directly calculate volumetric material loss and to graphically map the wear 'scar', i.e. the penetration of the femoral head into the acetabular cup.

In-process surface metrology for thin film flexible electronic devices

WIT transactions on engineering sciences, 1970

Over the past eight years the subject of 3D surface metrology has developed from something of a n... more Over the past eight years the subject of 3D surface metrology has developed from something of a novelty to a position where it has now become a crucial tool in the characterisation of engineering surfaces across a broad range of applications. It is widely accepted that the nature of the topography of a surface has a significant influence on the efficiency and functional performance of the surface. The functions that have been identified in various studies include wear, friction, lubrication, corrosion, fatigue, coating, paintability, etc. It is also increasingly being recognised that in order to fully study and control surface manufacture to enhance the above applications, studies need to be carried out from a 3-D perspective. Until recently however, the vast majority of research, industrial applications and national and international roughness standards were based on 2-D measurement techniques. It is now recognised that the characteristics of surfaces cannot be completely interpreted in some cases without 3-D information and many models established for understanding surface performance based on 2-D profiles have been unsuccessful. A number of key research groups have been working in this area in an effort to produce definitive 3D surface roughness standards. This paper reviews the most recent work in the field of 3D surface characterisation undertaken by the authors as part of a European multi partner project and outlines the development towards a 3D surface roughness standard.

Synthetic wavelength to increase the snapshot optical sensor’s elevated vertical measurement ranges

Applied Optics, Nov 14, 2019

Screening manufactured products that are conducted faster to enhance the contemporary manufacture... more Screening manufactured products that are conducted faster to enhance the contemporary manufacture processes and quality is possible by implementing enhanced quality control. Such quality control of manufactured products has increased the market for process-focused precision metrology that can execute evaluations faster while providing significant feedback for the manufacturing system. This investigation examines spatial dispersive interferometry's potential for producing accurate surface profile measurements by emphasizing vertical range measurements and identifying a system that can enable them to increase incrementally while maintaining the results' quality. Thus, this investigation selected Fourier transform profilometry (FTP) to assess surface profile measurements, as it provides the most reliable and fastest outcome data regarding this sensor. Exploring new surface scanning methods is important, as crucial weaknesses hinder several common approaches. As optical metrology sensors are bulky, difficult to establish, and expensive, the investigation will prove that FTP can resolve these restrictions. The investigation uses the synthetic wavelength approach for addressing vertical measurement limitation concerning optical systems for extending surface step height's vertical measurement range. Though it was observed that the FTP technique surmounts the vertical height limitations, certain limitations were also noted, with all outcomes considering key variables, including the scanning objective lens, system resolution, the spectrometer resolution, and diffraction grating. Future examinations must examine a wider vertical range to expand the snapshot spatial dispersive interferometry process's scope. Further, the step-height repeatability is enhanced, showing a good outcome range from 22 to 20 nm.

International Journal of Machine Tools & Manufacture, Apr 1, 2002

In many countries the most common polishing practice in die making is to hand polish the part as ... more In many countries the most common polishing practice in die making is to hand polish the part as a finishing operation after the electro discharge machining process (EDM). The usual polishing abrasives are silicon carbide paper and diamond paste of different grit sizes. However, during the last decade researchers especially in Japan and the USA have tried to combine EDM and electrochemical machining (ECM) in one machine so as to use the positive aspects of each individual process. The ECM process uses high density, typically 50 A/cm 2 , and also a pulse current with a servo-controlled electrode. These investigators have mostly used sodium nitrate solutions (of different concentrations) as the electrolyte. This paper deals with an experiment that was undertaken in order to assess the effect of four different electrolytes in an electrochemical polishing process (ECP) on the surface topography of EDM surfaces. The primary set of 3D surface parameters was used as a basis to characterise the surface produced by the combined processes in different electrolytic media.

University of Huddersfield eBooks, Dec 7, 2006

Aseptic loosening at the stem cement interface has been noted as a prominent failure mode in ceme... more Aseptic loosening at the stem cement interface has been noted as a prominent failure mode in cemented total hip replacement. It can be attributed to a tissue reaction to particulate debris generated by wear of the components. Wear can occur not only at the articulating surface but also at other load bearing interfaces due to relative micromotion. The stem cement interface has been consistently cited as a weak link. In the present study, characteristics at this interface were investigated through a series of pull out tests and a fretting wear simulation. The static shear strength was compared across a range of commercially available bone cements, with the result being higher than other studies. Fretting wear was successfully reproduced in vitro, which complied well with retrieval investigations. The research has gained a deep insight into the characteristics at the stem cement interface.

University of Huddersfield eBooks, Dec 1, 2009

Surface features have been recognised to be significant in many fields and the characterisation t... more Surface features have been recognised to be significant in many fields and the characterisation techniques are being constantly improved. The surface characterisation systems are developed by various instrument companies and institutions. However, the lack of good extensibility, reusability and maintainability is a serious obstacle to the system innovation. Component based software development offers a promising solution to the surface characterisation system with better extendibility and maintainability. This paper presents an overview of surface characterisation techniques, analyzes current surface characterisation systems, and then proposes a component based architecture for the surface characterisation system.

Charactering taper junction wear helps understand the mechanism of failure of metal on metal hip ... more Charactering taper junction wear helps understand the mechanism of failure of metal on metal hip replacements.

Journal of Bone and Joint Surgery-british Volume, Mar 1, 2013

Taper wear contributes only a third of the total volumetric material loss in large head metal on ... more Taper wear contributes only a third of the total volumetric material loss in large head metal on metal hip replacement

International journal of automation technology, May 5, 2020

Additive manufacturing (AM) is recognized as a core technology for producing high-value component... more Additive manufacturing (AM) is recognized as a core technology for producing high-value components. The production of complex and individually modified components, as well as prototypes, gives additive manufacturing a substantial advantage over conventional subtractive machining. For most industries, some of the current barriers to implementing AM include the lack of build repeatability and a deficit of quality assurance standards. The mechanical properties of the components depend critically on the density achieved. Therefore, defect/porosity analysis must be carried out to verify the components' integrity and viability. In parts produced using AM, the detection of unfused powder using computed tomography is challenging because the detection relies on differences in density. This study presents an optimized methodology for differentiating between unfused powder and voids in additive manufactured components, using computed tomography. Detecting the unfused powder requires detecting the cavities between particles. Previous studies have found that the detection of unfused powder requires a voxel size that is as small as 4 µ µ µm 3 3 3 . For most applications, scanning using a small voxel size is not reasonable because of the part size, long scan time, and data analysis. In this study, different voxel sizes are used to compare the time required for scanning, and the data analysis showing the impact of voxel size on the detection of micro defects. The powder used was Ti6Al4V, which has a grain size of 45-100 µ µ µm, and is typically employed by Arcam electron beam melting (EBM) machines. The artifact consisted of a 6 mm round bar with designed internal features ranging from 50 µ µ µm to 1400 µ µ µm and containing a mixture of voids and unfused powder. The diameter and depth of the defects were characterized using a focus variation microscope, after which they were scanned using a Nikon XTH225 industrial CT to measure the artifacts and characterize the internal features for defects/pores. To reduce the number of the process variables, the measurement parameters, such as filament current, acceleration voltage, and X-ray filtering material and thickness were kept constant. The VGStudio MAX 3.0 (Volume Graphics, Germany) software package was used for data processing, surface determination, and defects/porosity analysis. The main focus of this study is to explore the optimal methods for enhancing the detection of pores/defects while minimizing the time taken for scanning, data analysis, and determining the effects of noise on the analysis.

Wear, Oct 1, 2001

The properties of the femoral counterface are recognised as very significant in the study of the ... more The properties of the femoral counterface are recognised as very significant in the study of the tribological design of artificial joints and the wear of ultra-high molecular polyethylene (UHMWPE). Research has shown that morphological features of femoral counterfaces heavily interfere with the wear of UHMWPE. It has been reported that if 1-2 m defects or deep scratches are presented in a diamond like carbon (DLC) coated head, the third-body damage can cause a 7-15-fold increase in a UHMWPE wear rate, and in a metallic surface. The typical third-body damage can be up to a 30-70-fold compared with smooth roughness surface. Therefore, the identification of morphology of counterface surfaces has become an important requirement in the field of wear and tribology of the hip joint system. This paper proposes a methodology for a multiscalar wavelet for addressing morphological surfaces in order to extract the significant elements of 3D bearing surfaces of orthopaedic implants. The multiscalar wavelet is used to decompose a surface signal into the scalar domain. In wavelet analysis, the Cartesian space-based information is transferred into scale-based information, which provides not only the frequency events of the original signal but also keeps their location properties; as a result, morphological features can be identified. A series of ceramic, metallic and DLC femoral heads in vivo wear have been used to demonstrate the applicability of using the multiscalar wavelet model in the assessment of the morphology of these surfaces.

Journal of physics, 2005

Total joint replacement is one of the most common elective surgical procedures performed worldwid... more Total joint replacement is one of the most common elective surgical procedures performed worldwide, with an estimate of 1.5 million operations performed annually. Currently joint replacements are expected to function for 10-15 years, however, with an increase in life expectancy, and a greater call for knee replacement due to increased activity levels, there is a requirement to improve their function to offer longer term improved quality of life for patients. The amount of wear that a joint incurs is seen as a good indicator of performance, with higher wear rates typically leading to reduced function and premature failure. New technologies and materials are pushing traditional wear assessment methods to their limits, and novel metrology solutions are required to assess wear of joints following in vivo and in vitro use. This paper presents one such measurement technique; a scanning co-ordinate metrology machine for geometrical assessment. A case study is presented to show the application of this technology to a real orthopaedic measurement problem: the wear of components in total knee replacement. This technique shows good results and provides a basis for further developing techniques for geometrical wear assessment of total joint replacements.

Numerical Parameters for Characterisation of Topography

2 Numerical Parameters for Characterisation of Topography Liam Blunt and Xiangqian Jiang School o... more 2 Numerical Parameters for Characterisation of Topography Liam Blunt and Xiangqian Jiang School of Engineering, University of Huddersfield, UK 2.1 Introduction Numerical parameters for surface texture ... Sds should be assessed after Wolf pruning at 5% of Sz (default)[16, 17]. ...

Development of a Basis for 3D Surface Texture Standards "Surfstand" Liam Blunt, Xiang Jiang This ... more Development of a Basis for 3D Surface Texture Standards "Surfstand" Liam Blunt, Xiang Jiang This publication deals with the latest developments in the field of 3D surface metrology and will become a seminal text in this important area.

Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology, Oct 1, 2005

It is a well known fact that the EDM process results in the formation of a hard, brittle recast l... more It is a well known fact that the EDM process results in the formation of a hard, brittle recast layer on the component's surface. Several investigations have been carried out in order to assess the nature of the recast layer in terms of its phase structure, the microhardness, presence and the density of cracks, and other surface features. Some researchers [Barash, Delpretti] have reported mathematical relationships between the thickness of the white layer and 2D amplitude surface roughness parameters (such as R a and R t ). But so far no investigation has been reported which correlates the thickness of the white layer with 3D surface roughness parameters, especially those related to spatial parameters. This paper presents an experimental investigation of the effect of the EDM process factors (current and pulse on-time) on the thickness of the white layer. Empirical equations relating the thickness of the white layer with 3D surface texture amplitude, spatial and volume parameters are presented and their physical basis is discussed. The results of this study show that a better correlation can be obtained between the average thickness of the white layer (AWLT) and the spatial parameter, S ds as compared to other 3D surface texture parameters. This is believed to be mainly due to the similar effect of the current and pulse on-time on both AWLT and S ds . The possible effect of surface tension between the solid and liquid phases on the thickness of the white layer during erosion is also discussed.

A New Approach to Surface Metrology - Structured Surfaces

euspen eBooks, 2007

Optimization of surface determination strategies to enhance detection of unfused powder in metal additive manufactured components

A series of cutting trails have been carried out utilising milling operations and the development... more A series of cutting trails have been carried out utilising milling operations and the development of chatter on the machmed surface has been analysed. 3D surface metrology techmques have been used to characterise the surface and particular attention has been paid to the use of Areal Auto Correlation Function (AACF) and Areal Power Spectral Densities (APSD). Both the AACF and APSD have been shown to effectively characterise the development and appearance of chatter and the implications of the use of these techniques for potentially controlling the machining process have been outlined.

Producing components using metal additive manufacturing processes, such as powder bed fusion, pre... more Producing components using metal additive manufacturing processes, such as powder bed fusion, presents manufacturing and measurement challenges, but also significant opportunities. The as-built surface may include overhanging (re-entrant) features not intentionally included in the design, but that aid in component functionality. In addition, the AM process presents opportunities to design and manufacture re-entrant features intentionally. Re-entrant features increase the specific surface area and, in addition, produce mechanical locking to the surface. These features may be intended to improve surface performance in areas such as biological cell attachment, coating adhesion, electrical capacitor and battery plate design, fluid flow and material cooling. Re-entrant features may prove difficult or impossible to measure and characterise using conventional line-of-sight instrumentation. The correct measurement of these surfaces is vital for functional optimisation. This paper reports on the measurement of re-entrant features using X-ray computed tomography and the extraction of actual surface area information (including re-entrant surfaces) from sample AM surfaces. The proposed new parameter, Sdr prime , is discussed. This parameter is intended to relate directly to surface function. Sdr prime is the percentage of additional surface (including re-entrant surfaces) contributed by the texture as compared to a plane the size of the measurement area. In addition to Sdr prime , the actual surface area is discussed, together with the percentage of re-entrant surface. The errors produced using line-of-sight instruments and height map parameter generation per ISO 25178-2 are discussed. Measurement results for EBM and SLM additively manufactured components will be presented.

Assessing functional performance is the most important stage of any component verification. Mecha... more Assessing functional performance is the most important stage of any component verification. Mechanical properties can be evaluated by means of destructive testing which can be both expensive and lengthy in addition to loss of the original component under test. It is therefore advantageous where possible to utilise non-destructive techniques that can achieve the same or similar outcomes through collection of three-dimensional data that can then be used in simulation to determine functionality. Such non-destructive methods are essentially density-and porosity-based testing methods. Additive manufacturing allows for the creation of complex geometrical features that are often defined based on function. Optimisation of AM component geometry based on functionality allows for the specification of components that have features that cannot be mapped efficiently to current GPS standards. In addition, the integrity of complex optimised AM structures that may lie on a critical stress or heat path must be assessed and any elements of unmelted powder must be detected. This study details the development of a Ti6AL4V artefact built using an Arcam Q10 electron beam-melting machine (EBM). Defects of between 50 and 500 microns in diameter were then machined into the surface of the artefact using a CNC machine equipped with nano-drills and end mills. Once this was achieved, the defects were characterised using focus variation interferometer. Virgin Ti6AL4V powder was added to fill 50% of the defects and then the artefact was measured using a Nikon XTH225 industrial CT. This was used to analyse the relative size and location of the defects and assess the capability of the inspection process to both assess the size of pores of this size and to detect the powder-filled defects based on different X-ray detector magnifications. 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, were kept constant. The acquired data processing, surface determination process and defect analysis was carried out using VgStudio Max (Volume Graphics, Germany). The focus of the study is on providing best practice regarding the selection of inspection parameters to accurately perform defect detection.