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Bernard Rolfe

Deakin University, Engineering, Faculty Member

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Bernard Rolfe completed a combined Economics and Engineering degree with honours in 1995 from the Australian National University (ANU). During his degree he was employed as a graduate research engineer at the BHP Research Labs, investigating better control systems for hot strip steel mills. After he obtained his degree he worked for several years as a Business Systems consultant with Andersen Consulting (Accenture) before returning to the ANU to pursue a PhD in novel methods of inverse modeling metal forming processes (completed in 2002). This research included an IMechE award winning journal paper. In 2005 Bernard joined Deakin as a Lecturer in Mechanical Engineering. In 2008 Bernard led the Deakin’s successful team for “Creating the Model-T for the 21st Century – a Global University Challenge”. This vehicle concept outclassed several other top Universities around the world to be awarded joint winner along with the concept from the University of Aachen (RWTH), along with $25000 prize money. In 2015 Bernard received the Vice Chancellor’s award for Industry Engagement.
Currently Bernard is an Associate Professor (Mechanical) at Deakin University in Australia. This is equivalent to a tenured Professor in the US system. He has been a part of over fifteen successful nationally competitive large research grants, totalling over $15 million in awarded funds. He has published over 150 refereed articles. His current research focus is the forming of light weight structures, including the development of better material models for metal forming.

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Papers by Bernard Rolfe

Analysis of Acoustic Emissions for Determination of the Mechanical Effects of Scratch Tests

Applied Sciences

Acoustic Emission (AE) is a promising technique for measuring tool wear online and in real time. ... more Acoustic Emission (AE) is a promising technique for measuring tool wear online and in real time. In this work, scratch tests were conducted to better understand the “pre-wear” AE response based on loading conditions that were not sufficient to generate galling. The scratch tests used the same type of indenter against two different sheet materials: aluminum and steel. The results showed that AE parameters such as the mean frequency, Centroid frequency and Shannon entropy outperformed other frequency domain techniques by discriminating between the two sheet materials in scratch tests. From the literature, the frequency region of interest was expected to be sub 300 kHz. However, in this study, activity below this threshold was found to be noise, whereas distinct frequencies were found at much higher frequencies than expected. These results are compared against single grit “SG” tests of both mild steel- and nickel-based superalloys to allow comparison of the two test methods and materia...

The surface temperature prediction on steel-tool steel sliding pairs

2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO), 2019

This study examines the theoretical and numerical prediction of temperature at the sliding contac... more This study examines the theoretical and numerical prediction of temperature at the sliding contact surfaces of steelsteel pairs using the pin-on-disc and Archard models. The steeltool contact pair is important to the tribological and forming community. The results show a good correlation between numerical and theoretical calculation of contact temperature. There was abrupt increase in the contact temperature at the contacting surfaces as the sliding speed was increased beyond 35 mm/s. Localization of high peak temperature at the contact regions of the sliding surfaces observed in this study may be important in the wear mechanism of sliding bodies and wider manufacturing community.

A comprehensive investigation of abrasive barrel finishing on hardness and manufacturability of laser-based powder bed fusion hollow components

The International Journal of Advanced Manufacturing Technology, 2022

One of the main issues of laser-based powder bed fusion (LB-PBF) parts is surface quality and dim... more One of the main issues of laser-based powder bed fusion (LB-PBF) parts is surface quality and dimensional deviations, which require post-processing. Conventional post-processing such as turning and milling cannot machine internal surfaces and therefore is not suitable for hollow components. In this paper, Ti–6Al–4 V components with different hollow shapes were printed by LB-PBF and post-processed by centrifugal barrel finishing (CBF). Samples were printed based on Taguchi L18 design of experiments (DoE) on the (L18: 21 × 33) matrix and polished in abrasive solution by porcelain triangular media 2 × 2 mm. The effect of process parameters including rotation direction, speed, time and volumetric percentage of abrasive on hardness and manufacturability, including surface quality, material removal rate (MRR) and dimensional deviation, are discussed. The novelty of this work is the application of this process to clean both the internal and external surfaces of LB-PBF parts, where previous...

A comprehensive study on meltpool depth in laser-based powder bed fusion of Inconel 718

The International Journal of Advanced Manufacturing Technology, 2022

One problematic task in the laser-based powder bed fusion (LB-PBF) process is the estimation of m... more One problematic task in the laser-based powder bed fusion (LB-PBF) process is the estimation of meltpool depth, which is a function of the process parameters and thermophysical properties of the materials. In this research, the effective factors that drive the meltpool depth such as optical penetration depth, angle of incidence, the ratio of laser power to scan speed, surface properties and plasma formation are discussed. The model is useful to estimate the meltpool depth for various manufacturing conditions. A proposed methodology is based on the simulation of a set of process parameters to obtain the variation of meltpool depth and temperature, followed by validation with reference to experimental test data. Numerical simulation of the LB-PBF process was performed using the computational scientific tool “Flow3D Version 11.2” to obtain the meltpool features. The simulation data was then developed into a predictive analytical model for meltpool depth and temperature based on the the...

Prototyping of Straight Section Components Using Incremental Shape Rolling

Flexible Roll Forming (FRF) allows the forming of components with a variable cross-section along ... more Flexible Roll Forming (FRF) allows the forming of components with a variable cross-section along the length of the component. However, the process has only limited application in the automotive industry due to wrinkling in the flange which currently prevents the forming of high strength steels and limits the part shape complexity. This paper presents a new forming technology, Incremental Shape Rolling (ISR), where a pre-cut blank is clamped between two dies and then a single forming roll is used to incrementally form the material to the desired shape. The new process is similar to some Incremental Sheet Forming (ISF) approaches but with the difference that Incremental Shape Rolling (ISR) allows the manufacture of longitudinal components from high strength metal sheets. In this work, a numerical model of the ISR of a straight section is developed. Experimental prototyping trials are performed and are used to validate the numerical model which is then applied to analyse the new formin...

Numerical and analytical investigation on meltpool temperature of laser-based powder bed fusion of IN718

International Journal of Heat and Mass Transfer, 2021

Experimental investigation of tailored hot stamping parts

It is known that tailored hot stamped parts, which have locally graded properties, can improve ca... more It is known that tailored hot stamped parts, which have locally graded properties, can improve car crashworthiness. In this experimental study, a heated tool was used to decrease the temperature difference between the hot blank and the tool which led to lower cooling rates and softer properties. First, a flat heated tool was used to investigate the effects of process parameters on metallurgical and mechanical properties. Based on the range of parameters examined, press force and quenching time did not have a significant effect on the post-formed mechanical properties. In the next step, a hatshaped channel tool with heating system was used to produce tailored hot stamping parts. The results show considerable differences between hardness values of the top and side faces in the soft section, while the hardness was almost uniform in the hard section. These experimental results generally compare well with the results of previous numerical parametric studies performed by the authors, whic...

Numerical model accuracy of solid and shell elements when simulating the roll forming process

Conventional roll forming is a common manufacturing process that incrementally bends a sheet into... more Conventional roll forming is a common manufacturing process that incrementally bends a sheet into a desired cross-section by passing it though successive sets of rolls. Finite Element Analysis (FEA) is increasingly used in roll forming process design, but generally incurs large computational costs due to the specific nature of the process involving the forming of continuous sheet over multiple stands. This paper analyses the model accuracy achievable when using solid and shell elements for roll forming simulations in Abaqus. To establish the reliability of the numerical models, convergence and sensitivity studies were performed with each element type to determine the appropriate mesh densities and element properties. The simulation results were compared to the experimental results for bow, springback and longitudinal strains. The results indicate that shell elements with proper meshing strategy lead to better model accuracy compared to solid elements and this is achieved with signif...

A model for quenching and partitioning with press hardening of high strength steel

Blanks Main Stamping Operation Trimming Operation Hole Cutting Operation Finished Panels

A quality analysis trial was undertaken at Ford Geelong Stamping Plant on a press line that was f... more A quality analysis trial was undertaken at Ford Geelong Stamping Plant on a press line that was fitted with standard press sensors to measure press and binder force over the stamping cycle for each panel. The quality of randomly sampled panels was measured by obtaining the panel thicknesses at five points, for 135 panels in total. These points were chosen such that they exhibited different forming modes. This paper analyses the input force data and the output quality data from the trial to determine any potential relationships. The analysis of the production data was performed using statistical correlation techniques to determine initial potential relationships between input and output variables. An Active Shape Model was used to extract features when identifying the major sources of variation within the input data. However, the initial analysis of the data elicited no direct relationship between the input variables measured and the panel thicknesses. This result is significant as t...

Prototyping of automotive components with variable width and depth

Journal of Physics: Conference Series, 2017

On the role of process parameters on meltpool temperature and tensile properties of stainless steel 316L produced by powder bed fusion

Journal of Materials Research and Technology, 2021

Abstract This research aims to identify how meltpool temperature is determined by process paramet... more Abstract This research aims to identify how meltpool temperature is determined by process parameters in Laser-Based Powder Bed Fusion (LB-PBF) and the effect of meltpool temperature and heat treatment temperature on microstructure and tensile properties. The study illustrates how crystallographic features in 316L stainless steel were developed in response to the meltpool temperature and induced energy density of LB-PBF manufacture, and by post manufacture heat treatment. For this research, 25 samples based on a Taguchi Design of Experiments (DoE) with five parameters over five levels were printed. To improve precision, the DoE was repeated three times and a total of 75 samples were produced. A thermophysical-based analytical model was developed to measure the meltpool temperature and subsequently surface tension of the liquid in melting zones. Then, a statistical method was used to identify the effective process parameters in tensile properties including ultimate strength, fracture strain and toughness. The microstructural evaluation and crystallographic features were presented to identify the governing mechanisms for the discussed phenomena. This result verifies that the meltpool temperature is a driving factor for the microstructural evolution and observed crystallographic features. Results showed that samples with lower meltpool temperatures have smaller grain sizes, superior strength and toughness properties. The crystallographic analysis showed the weak texture and anisotropic properties are dominant by the preferred orientation growth. The geometrically necessary boundary values were also found to be a driving factor for fracture strain. The originality of this paper is identifying the effect of process parameters on meltpool temperature using an analytical model that is developed based on the thermophysical properties of the feedstock. Characterizing the effect of meltpool temperature in crystallographic features are also another contribution of this paper.

Build position-based dimensional deviations of laser powder-bed fusion of stainless steel 316L

Precision Engineering, 2021

This study investigates the effect of position on build-plate on the dimensional deviations for s... more This study investigates the effect of position on build-plate on the dimensional deviations for stainless steel 316 L samples made by laser powder-bed fusion. To understand the effect of sample position on the build-plate (substrate) with respect to shrinkage and dimensional deviation, 36 samples in a 6 × 6 array were printed with three repetitions. The value of the diameter was measured at 10 points along the vertical axis in the perpendicular and parallel directions to the flow of the assisted gas. The results of the experiment show that there is shrinkage in both directions with respect to the gas flow. However, the extent of deviation in the perpendicular direction to the gas flow is greater compared to the parallel diameters for the samples. This can be related to the pressure of assisted gas and the difference in cooling rate corresponding to the position of the samples on the building substrate. The hypothesis is proved by conducting further experiments regulating the amount of gas flow by adjusting the individual nozzle for the gas flow to the build chamber. The reason for these deviations is speculated to be related to the rheology of the melt pool. This research could lay a solid foundation for the future development of a compensation strategy to nullify the effect of shrinkage and dimensional deviations on parts made using the laser powder-bed fusion technique. The results of shrinkage of the columns appear to suggest that there is an effect on the circularity from the assisting gas.

Time series analysis of tool wear in sheet metal stamping using acoustic emission

Journal of Physics: Conference Series, Sep 1, 2017

Galling is an adhesive wear mode that often affects the lifespan of stamping tools. Since stampin... more Galling is an adhesive wear mode that often affects the lifespan of stamping tools. Since stamping tools represent significant economic cost, even a slight improvement in maintenance cost is of high importance for the stamping industry. In other manufacturing industries, online tool condition monitoring has been used to prevent tool wear-related failure. However, monitoring the acoustic emission signal from a stamping process is a non-trivial task since the acoustic emission signal is non-stationary and non-transient. There have been numerous studies examining acoustic emissions in sheet metal stamping. However, very few have focused in detail on how the signals change as wear on the tool surface progresses prior to failure. In this study, time domain analysis was applied to the acoustic emission signals to extract features related to tool wear. To understand the wear progression, accelerated stamping tests were performed using a semi-industrial stamping setup which can perform clamping, piercing, stamping in a single cycle. The time domain features related to stamping were computed for the acoustic emissions signal of each part. The sidewalls of the stamped parts were scanned using an optical profilometer to obtain profiles of the worn part, and they were qualitatively correlated to that of the acoustic emissions signal. Based on the wear behaviour, the wear data can be divided into three stages:-In the first stage, no wear is observed, in the second stage, adhesive wear is likely to occur, and in the third stage severe abrasive plus adhesive wear is likely to occur. Scanning electron microscopy showed the formation of lumps on the stamping tool, which represents galling behavior. Correlation between the time domain features of the acoustic emissions signal and the wear progression identified in this study lays the basis for tool diagnostics in stamping industry.

Investigation of Galling Wear Using Acoustic Emission Frequency Characteristics

Lubricants, 2020

In the sheet metal stamping process, during sliding contact between the tool and sheet, it is exp... more In the sheet metal stamping process, during sliding contact between the tool and sheet, it is expected that severe events such as tool wear or fracture on the sheet generate acoustic emission (AE) burst waveforms. Attempts have been made in the literature to correlate the AE burst waveform with the wear mechanisms. However, there is a need for additional studies to understand the frequency characteristics of the AE burst waveform due to the severity and progression of the galling wear. This paper will determine the AE frequency characteristics that can be used to monitor galling wear, independent of the experimental process examined. The AE burst waveforms generated during the stamping and scratch tests are analysed in this paper to understand the change in the AE frequency characteristics with the galling severity. These AE burst waveforms were investigated using the Hilbert Huang Transform (HHT) time-frequency technique, band power, and mean-frequency. Subsequently, these AE frequ...

Effect of the forming method on part shape quality in cold roll forming high strength Ti-6Al-4V sheet

Journal of Manufacturing Processes, 2018

High strength titanium alloy sheet, in particular Ti-6Al-4V, is used for structural applications;... more High strength titanium alloy sheet, in particular Ti-6Al-4V, is used for structural applications; roll forming has been found to be an appropriate cold forming process for the manufacture of long components in Ti-6Al-4V. Roll forming Ti-6Al-4V at room temperature requires extensive FEA-assisted process development and optimisation to keep springback and part shape defects to a minimum. Currently the material behaviour of Ti-6Al-4V in the roll forming process is not well understood. Two major roll forming approaches, the constant bend radius and the constant arc length method, are used in roll forming but the effect of each approach on springback or final part shape in high strength sheet materials such as Ti-6Al-4V is not well documented. A fundamental understanding of this will enable rapid and reliable process design for the cold roll forming of high strength titanium alloys. The primary aim of this study is to explore the potential use of different roll forming methods to reduce springback and part shape defects in the cold roll forming of Ti-6Al-4V sheet and to develop a deeper understanding of the material behaviour of Ti-6Al-4V in the process. For this, experimental roll forming trials and their simulation are performed and a novel constitutive material model based on the homogeneous anisotropic hardening (HAH) approach is used to represent the forming behaviour of Ti-6Al-4V under cold forming conditions. The experimental and numerical results indicate that the constant radius forming method leads to fewer shape defects in the process and reduced springback. A detailed discussion is provided explaining in part the observed trends.

The FEM simulation and experiment of quenching distortion of a U-shape sample and the sensitivity analysis of material properties

Materials Research Express, 2019

Application of a Model for Quenching and Partitioning in Hot Stamping of High-Strength Steel

Metallurgical and Materials Transactions A, 2018

Forming parts over small radii

Journal of Physics: Conference Series, 2016

Stamping simulations usually make the plane stress simplifying assumption. However, this becomes ... more Stamping simulations usually make the plane stress simplifying assumption. However, this becomes less valid when material draws around features with radius to sheet thickness ratios less than 20. Pereira, Yan & Rolfe (Wear, Vol.265, p.1687 (2008)) predicted that out-of-plane stress equivalent to material yield can occur because a line contact forms briefly at the start of the draw process. The high transient stress can cause high rates of tool wear and may cause the 'die impact line' cosmetic defect. In this work, we present residual strain results of a channel section that was drawn over a small radius. Using the neutron source at the Institut Laue-Langevin, in-plane and out-of-plane strains were measured in the channel part to show some support for the conclusions of Pereira et. al.

Audio signal analysis for tool wear monitoring in sheet metal stamping

Mechanical Systems and Signal Processing, 2017

Analysis of Acoustic Emissions for Determination of the Mechanical Effects of Scratch Tests

Applied Sciences

Acoustic Emission (AE) is a promising technique for measuring tool wear online and in real time. ... more Acoustic Emission (AE) is a promising technique for measuring tool wear online and in real time. In this work, scratch tests were conducted to better understand the “pre-wear” AE response based on loading conditions that were not sufficient to generate galling. The scratch tests used the same type of indenter against two different sheet materials: aluminum and steel. The results showed that AE parameters such as the mean frequency, Centroid frequency and Shannon entropy outperformed other frequency domain techniques by discriminating between the two sheet materials in scratch tests. From the literature, the frequency region of interest was expected to be sub 300 kHz. However, in this study, activity below this threshold was found to be noise, whereas distinct frequencies were found at much higher frequencies than expected. These results are compared against single grit “SG” tests of both mild steel- and nickel-based superalloys to allow comparison of the two test methods and materia...

The surface temperature prediction on steel-tool steel sliding pairs

2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO), 2019

This study examines the theoretical and numerical prediction of temperature at the sliding contac... more This study examines the theoretical and numerical prediction of temperature at the sliding contact surfaces of steelsteel pairs using the pin-on-disc and Archard models. The steeltool contact pair is important to the tribological and forming community. The results show a good correlation between numerical and theoretical calculation of contact temperature. There was abrupt increase in the contact temperature at the contacting surfaces as the sliding speed was increased beyond 35 mm/s. Localization of high peak temperature at the contact regions of the sliding surfaces observed in this study may be important in the wear mechanism of sliding bodies and wider manufacturing community.

A comprehensive investigation of abrasive barrel finishing on hardness and manufacturability of laser-based powder bed fusion hollow components

The International Journal of Advanced Manufacturing Technology, 2022

One of the main issues of laser-based powder bed fusion (LB-PBF) parts is surface quality and dim... more One of the main issues of laser-based powder bed fusion (LB-PBF) parts is surface quality and dimensional deviations, which require post-processing. Conventional post-processing such as turning and milling cannot machine internal surfaces and therefore is not suitable for hollow components. In this paper, Ti–6Al–4 V components with different hollow shapes were printed by LB-PBF and post-processed by centrifugal barrel finishing (CBF). Samples were printed based on Taguchi L18 design of experiments (DoE) on the (L18: 21 × 33) matrix and polished in abrasive solution by porcelain triangular media 2 × 2 mm. The effect of process parameters including rotation direction, speed, time and volumetric percentage of abrasive on hardness and manufacturability, including surface quality, material removal rate (MRR) and dimensional deviation, are discussed. The novelty of this work is the application of this process to clean both the internal and external surfaces of LB-PBF parts, where previous...

A comprehensive study on meltpool depth in laser-based powder bed fusion of Inconel 718

The International Journal of Advanced Manufacturing Technology, 2022

One problematic task in the laser-based powder bed fusion (LB-PBF) process is the estimation of m... more One problematic task in the laser-based powder bed fusion (LB-PBF) process is the estimation of meltpool depth, which is a function of the process parameters and thermophysical properties of the materials. In this research, the effective factors that drive the meltpool depth such as optical penetration depth, angle of incidence, the ratio of laser power to scan speed, surface properties and plasma formation are discussed. The model is useful to estimate the meltpool depth for various manufacturing conditions. A proposed methodology is based on the simulation of a set of process parameters to obtain the variation of meltpool depth and temperature, followed by validation with reference to experimental test data. Numerical simulation of the LB-PBF process was performed using the computational scientific tool “Flow3D Version 11.2” to obtain the meltpool features. The simulation data was then developed into a predictive analytical model for meltpool depth and temperature based on the the...

Prototyping of Straight Section Components Using Incremental Shape Rolling

Flexible Roll Forming (FRF) allows the forming of components with a variable cross-section along ... more Flexible Roll Forming (FRF) allows the forming of components with a variable cross-section along the length of the component. However, the process has only limited application in the automotive industry due to wrinkling in the flange which currently prevents the forming of high strength steels and limits the part shape complexity. This paper presents a new forming technology, Incremental Shape Rolling (ISR), where a pre-cut blank is clamped between two dies and then a single forming roll is used to incrementally form the material to the desired shape. The new process is similar to some Incremental Sheet Forming (ISF) approaches but with the difference that Incremental Shape Rolling (ISR) allows the manufacture of longitudinal components from high strength metal sheets. In this work, a numerical model of the ISR of a straight section is developed. Experimental prototyping trials are performed and are used to validate the numerical model which is then applied to analyse the new formin...

Numerical and analytical investigation on meltpool temperature of laser-based powder bed fusion of IN718

International Journal of Heat and Mass Transfer, 2021

Experimental investigation of tailored hot stamping parts

It is known that tailored hot stamped parts, which have locally graded properties, can improve ca... more It is known that tailored hot stamped parts, which have locally graded properties, can improve car crashworthiness. In this experimental study, a heated tool was used to decrease the temperature difference between the hot blank and the tool which led to lower cooling rates and softer properties. First, a flat heated tool was used to investigate the effects of process parameters on metallurgical and mechanical properties. Based on the range of parameters examined, press force and quenching time did not have a significant effect on the post-formed mechanical properties. In the next step, a hatshaped channel tool with heating system was used to produce tailored hot stamping parts. The results show considerable differences between hardness values of the top and side faces in the soft section, while the hardness was almost uniform in the hard section. These experimental results generally compare well with the results of previous numerical parametric studies performed by the authors, whic...

Numerical model accuracy of solid and shell elements when simulating the roll forming process

Conventional roll forming is a common manufacturing process that incrementally bends a sheet into... more Conventional roll forming is a common manufacturing process that incrementally bends a sheet into a desired cross-section by passing it though successive sets of rolls. Finite Element Analysis (FEA) is increasingly used in roll forming process design, but generally incurs large computational costs due to the specific nature of the process involving the forming of continuous sheet over multiple stands. This paper analyses the model accuracy achievable when using solid and shell elements for roll forming simulations in Abaqus. To establish the reliability of the numerical models, convergence and sensitivity studies were performed with each element type to determine the appropriate mesh densities and element properties. The simulation results were compared to the experimental results for bow, springback and longitudinal strains. The results indicate that shell elements with proper meshing strategy lead to better model accuracy compared to solid elements and this is achieved with signif...

A model for quenching and partitioning with press hardening of high strength steel

Blanks Main Stamping Operation Trimming Operation Hole Cutting Operation Finished Panels

A quality analysis trial was undertaken at Ford Geelong Stamping Plant on a press line that was f... more A quality analysis trial was undertaken at Ford Geelong Stamping Plant on a press line that was fitted with standard press sensors to measure press and binder force over the stamping cycle for each panel. The quality of randomly sampled panels was measured by obtaining the panel thicknesses at five points, for 135 panels in total. These points were chosen such that they exhibited different forming modes. This paper analyses the input force data and the output quality data from the trial to determine any potential relationships. The analysis of the production data was performed using statistical correlation techniques to determine initial potential relationships between input and output variables. An Active Shape Model was used to extract features when identifying the major sources of variation within the input data. However, the initial analysis of the data elicited no direct relationship between the input variables measured and the panel thicknesses. This result is significant as t...

Prototyping of automotive components with variable width and depth

Journal of Physics: Conference Series, 2017

On the role of process parameters on meltpool temperature and tensile properties of stainless steel 316L produced by powder bed fusion

Journal of Materials Research and Technology, 2021

Abstract This research aims to identify how meltpool temperature is determined by process paramet... more Abstract This research aims to identify how meltpool temperature is determined by process parameters in Laser-Based Powder Bed Fusion (LB-PBF) and the effect of meltpool temperature and heat treatment temperature on microstructure and tensile properties. The study illustrates how crystallographic features in 316L stainless steel were developed in response to the meltpool temperature and induced energy density of LB-PBF manufacture, and by post manufacture heat treatment. For this research, 25 samples based on a Taguchi Design of Experiments (DoE) with five parameters over five levels were printed. To improve precision, the DoE was repeated three times and a total of 75 samples were produced. A thermophysical-based analytical model was developed to measure the meltpool temperature and subsequently surface tension of the liquid in melting zones. Then, a statistical method was used to identify the effective process parameters in tensile properties including ultimate strength, fracture strain and toughness. The microstructural evaluation and crystallographic features were presented to identify the governing mechanisms for the discussed phenomena. This result verifies that the meltpool temperature is a driving factor for the microstructural evolution and observed crystallographic features. Results showed that samples with lower meltpool temperatures have smaller grain sizes, superior strength and toughness properties. The crystallographic analysis showed the weak texture and anisotropic properties are dominant by the preferred orientation growth. The geometrically necessary boundary values were also found to be a driving factor for fracture strain. The originality of this paper is identifying the effect of process parameters on meltpool temperature using an analytical model that is developed based on the thermophysical properties of the feedstock. Characterizing the effect of meltpool temperature in crystallographic features are also another contribution of this paper.

Build position-based dimensional deviations of laser powder-bed fusion of stainless steel 316L

Precision Engineering, 2021

This study investigates the effect of position on build-plate on the dimensional deviations for s... more This study investigates the effect of position on build-plate on the dimensional deviations for stainless steel 316 L samples made by laser powder-bed fusion. To understand the effect of sample position on the build-plate (substrate) with respect to shrinkage and dimensional deviation, 36 samples in a 6 × 6 array were printed with three repetitions. The value of the diameter was measured at 10 points along the vertical axis in the perpendicular and parallel directions to the flow of the assisted gas. The results of the experiment show that there is shrinkage in both directions with respect to the gas flow. However, the extent of deviation in the perpendicular direction to the gas flow is greater compared to the parallel diameters for the samples. This can be related to the pressure of assisted gas and the difference in cooling rate corresponding to the position of the samples on the building substrate. The hypothesis is proved by conducting further experiments regulating the amount of gas flow by adjusting the individual nozzle for the gas flow to the build chamber. The reason for these deviations is speculated to be related to the rheology of the melt pool. This research could lay a solid foundation for the future development of a compensation strategy to nullify the effect of shrinkage and dimensional deviations on parts made using the laser powder-bed fusion technique. The results of shrinkage of the columns appear to suggest that there is an effect on the circularity from the assisting gas.

Time series analysis of tool wear in sheet metal stamping using acoustic emission

Journal of Physics: Conference Series, Sep 1, 2017

Galling is an adhesive wear mode that often affects the lifespan of stamping tools. Since stampin... more Galling is an adhesive wear mode that often affects the lifespan of stamping tools. Since stamping tools represent significant economic cost, even a slight improvement in maintenance cost is of high importance for the stamping industry. In other manufacturing industries, online tool condition monitoring has been used to prevent tool wear-related failure. However, monitoring the acoustic emission signal from a stamping process is a non-trivial task since the acoustic emission signal is non-stationary and non-transient. There have been numerous studies examining acoustic emissions in sheet metal stamping. However, very few have focused in detail on how the signals change as wear on the tool surface progresses prior to failure. In this study, time domain analysis was applied to the acoustic emission signals to extract features related to tool wear. To understand the wear progression, accelerated stamping tests were performed using a semi-industrial stamping setup which can perform clamping, piercing, stamping in a single cycle. The time domain features related to stamping were computed for the acoustic emissions signal of each part. The sidewalls of the stamped parts were scanned using an optical profilometer to obtain profiles of the worn part, and they were qualitatively correlated to that of the acoustic emissions signal. Based on the wear behaviour, the wear data can be divided into three stages:-In the first stage, no wear is observed, in the second stage, adhesive wear is likely to occur, and in the third stage severe abrasive plus adhesive wear is likely to occur. Scanning electron microscopy showed the formation of lumps on the stamping tool, which represents galling behavior. Correlation between the time domain features of the acoustic emissions signal and the wear progression identified in this study lays the basis for tool diagnostics in stamping industry.

Investigation of Galling Wear Using Acoustic Emission Frequency Characteristics

Lubricants, 2020

In the sheet metal stamping process, during sliding contact between the tool and sheet, it is exp... more In the sheet metal stamping process, during sliding contact between the tool and sheet, it is expected that severe events such as tool wear or fracture on the sheet generate acoustic emission (AE) burst waveforms. Attempts have been made in the literature to correlate the AE burst waveform with the wear mechanisms. However, there is a need for additional studies to understand the frequency characteristics of the AE burst waveform due to the severity and progression of the galling wear. This paper will determine the AE frequency characteristics that can be used to monitor galling wear, independent of the experimental process examined. The AE burst waveforms generated during the stamping and scratch tests are analysed in this paper to understand the change in the AE frequency characteristics with the galling severity. These AE burst waveforms were investigated using the Hilbert Huang Transform (HHT) time-frequency technique, band power, and mean-frequency. Subsequently, these AE frequ...

Effect of the forming method on part shape quality in cold roll forming high strength Ti-6Al-4V sheet

Journal of Manufacturing Processes, 2018

High strength titanium alloy sheet, in particular Ti-6Al-4V, is used for structural applications;... more High strength titanium alloy sheet, in particular Ti-6Al-4V, is used for structural applications; roll forming has been found to be an appropriate cold forming process for the manufacture of long components in Ti-6Al-4V. Roll forming Ti-6Al-4V at room temperature requires extensive FEA-assisted process development and optimisation to keep springback and part shape defects to a minimum. Currently the material behaviour of Ti-6Al-4V in the roll forming process is not well understood. Two major roll forming approaches, the constant bend radius and the constant arc length method, are used in roll forming but the effect of each approach on springback or final part shape in high strength sheet materials such as Ti-6Al-4V is not well documented. A fundamental understanding of this will enable rapid and reliable process design for the cold roll forming of high strength titanium alloys. The primary aim of this study is to explore the potential use of different roll forming methods to reduce springback and part shape defects in the cold roll forming of Ti-6Al-4V sheet and to develop a deeper understanding of the material behaviour of Ti-6Al-4V in the process. For this, experimental roll forming trials and their simulation are performed and a novel constitutive material model based on the homogeneous anisotropic hardening (HAH) approach is used to represent the forming behaviour of Ti-6Al-4V under cold forming conditions. The experimental and numerical results indicate that the constant radius forming method leads to fewer shape defects in the process and reduced springback. A detailed discussion is provided explaining in part the observed trends.

The FEM simulation and experiment of quenching distortion of a U-shape sample and the sensitivity analysis of material properties

Materials Research Express, 2019

Application of a Model for Quenching and Partitioning in Hot Stamping of High-Strength Steel

Metallurgical and Materials Transactions A, 2018

Forming parts over small radii

Journal of Physics: Conference Series, 2016

Stamping simulations usually make the plane stress simplifying assumption. However, this becomes ... more Stamping simulations usually make the plane stress simplifying assumption. However, this becomes less valid when material draws around features with radius to sheet thickness ratios less than 20. Pereira, Yan & Rolfe (Wear, Vol.265, p.1687 (2008)) predicted that out-of-plane stress equivalent to material yield can occur because a line contact forms briefly at the start of the draw process. The high transient stress can cause high rates of tool wear and may cause the 'die impact line' cosmetic defect. In this work, we present residual strain results of a channel section that was drawn over a small radius. Using the neutron source at the Institut Laue-Langevin, in-plane and out-of-plane strains were measured in the channel part to show some support for the conclusions of Pereira et. al.

Audio signal analysis for tool wear monitoring in sheet metal stamping

Mechanical Systems and Signal Processing, 2017

The effect of process parameters on web-warping in the flexible roll forming of UHSS

by Bernard Rolfe and M. Weiss

To reduce weight and improve passenger safety there is an increased need in the automotive indust... more To reduce weight and improve passenger safety there is an increased need in the automotive industry to use Ultra High Strength Steels (UHSS) for structural and crash components. However, due to their high strength and limited formability UHSS are difficult to form with conventional methods and this is currently limiting their application in automotive construction. One alternative solution to manufacture structural auto body parts from UHSS is the flexible roll forming process, which allows the manufacture of materials with high strength and limited ductility to complex and weight optimised components. However, the flexible roll forming of UHSS is challenging and one major concern is web-warping, which is the height deviation of the profile web in the transition zones. This paper investigates, using both Implicit and Explicit numerical models, the effect of some key process parameters on web-warping in the flexible roll forming of UHSS.