Induction Heating as an alternative Localised Post Weld Heat Treatment for Friction Taper Hydro-Pillar Welds on thick-walled steam pipes
- Authors: De Klerk, Julien Vincent
- Date: 2022-04
- Subjects: Welding , Friction welding
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/58329 , vital:58984
- Description: Welding procedures regularly require a Post Weld Heat Treatment (PWHT) after the completion of a weld. This PWHT process is principally to mitigate unwanted effects of the welding process which may negatively influence the functional performance of the welded structure. Amongst the unwanted effects that may arise due to welding is the development of unintended metallurgical and mechanical properties. This includes the creation of an un-tempered martensitic structure due to the rapid cooling of the weld region from temperatures above the material’s critical temperature. This typically results in weld regions with high tensile strength and high hardness, but also characterised by low ductility and reduced toughness. In order to improve ductility and toughness a PWHT cycle is often completed on the welded structure. , Thesis (MA) -- Faculty of Engineering, the Built Environment, and Technology, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: De Klerk, Julien Vincent
- Date: 2022-04
- Subjects: Welding , Friction welding
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/58329 , vital:58984
- Description: Welding procedures regularly require a Post Weld Heat Treatment (PWHT) after the completion of a weld. This PWHT process is principally to mitigate unwanted effects of the welding process which may negatively influence the functional performance of the welded structure. Amongst the unwanted effects that may arise due to welding is the development of unintended metallurgical and mechanical properties. This includes the creation of an un-tempered martensitic structure due to the rapid cooling of the weld region from temperatures above the material’s critical temperature. This typically results in weld regions with high tensile strength and high hardness, but also characterised by low ductility and reduced toughness. In order to improve ductility and toughness a PWHT cycle is often completed on the welded structure. , Thesis (MA) -- Faculty of Engineering, the Built Environment, and Technology, 2022
- Full Text:
- Date Issued: 2022-04
Development and process verification of a linear friction welding platform for small Ti6AI4V coupons
- Mohlala, Narishe Taetso Arnold
- Authors: Mohlala, Narishe Taetso Arnold
- Date: 2020
- Subjects: Friction welding , Pressure welding
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/46196 , vital:39513
- Description: This thesis reports on a study conducted to establish the feasibility of implementing linear friction welding as a joining technique for small Ti6AI4V coupons. The main of this project is to facilitate the manufacturing of high-integrity near-net-shape components for aerospace, automotive and medical appliances. LFW is a solid-state welding technique that uses frictional heat generated by the rubbing of surfaces under an axially applied load, thereby forming a weld at temperature below beta tranus. This technique is advantageous as it has the potential to reduce defeats normally associated with conventional welding of this material. The first part of the study will describe the development of an experimental platform to facilitate the evaluation of the influence of selected process parameters on joint integrity.
- Full Text:
- Date Issued: 2020
Development and process verification of a linear friction welding platform for small Ti6AI4V coupons
- Authors: Mohlala, Narishe Taetso Arnold
- Date: 2020
- Subjects: Friction welding , Pressure welding
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/46196 , vital:39513
- Description: This thesis reports on a study conducted to establish the feasibility of implementing linear friction welding as a joining technique for small Ti6AI4V coupons. The main of this project is to facilitate the manufacturing of high-integrity near-net-shape components for aerospace, automotive and medical appliances. LFW is a solid-state welding technique that uses frictional heat generated by the rubbing of surfaces under an axially applied load, thereby forming a weld at temperature below beta tranus. This technique is advantageous as it has the potential to reduce defeats normally associated with conventional welding of this material. The first part of the study will describe the development of an experimental platform to facilitate the evaluation of the influence of selected process parameters on joint integrity.
- Full Text:
- Date Issued: 2020
Friction stir welding of thin section aluminium extrusions for marine applications
- Authors: Chikamhi, Prince Philhelene
- Date: 2020
- Subjects: Friction welding , Welding
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/46030 , vital:39410
- Description: This dissertation focuses on the development of a welding extrusion feeder, tool and schedule for implementation of defect-free butt welds on long, thin and complex-shape aluminium extrusions, as used by the marine industry. Viability of employing Friction Stir Welding (FSW) as a welding technology for joining long extrusions with a short-bed and bolt-on feeder to facilitate onsite fabrication of flat structures in shipbuilding is evaluated. An FSW feeder, tool and process control unit were designed, developed and integrated with an existing FSW platform, to facilitate implementation of continuous welds. Weld data acquired from literature review, experimentation, mechanical testing and metallographic analysis was used in design considerations for the development of a feeder. Subsequently, butt welds were implemented successfully on long 3 mm AA6082-T6 extrusions, during continuous FSW on the feeder. A specially adapted tool, the Floating Bobbin Tool, used with the feeder to implement butt welds was designed and developed from literature tool heuristics and weld trials. The tool eliminated the need for a backing bar and enabled tool-workpiece auto-alignment, beneficial with thin-section extrusions. Effect of rotational and weld speed and tool geometry of two tools (Tool 1 and 2), on weld forces and quality was tested, to establish optimum parameters for attaining high quality welds. Tool geometry had a profound effect on weld forces and integrity; Tool 2 welds exhibited superior and consistent weld quality, meeting maritime rules and standards and proving the adequacy of using FSW for joining long thin extrusions. Feeder process control, automation and optimisation, was implemented by process control unit devices, in addition to force and position control provided by the existing FSW platform. Owing to process control, automation and optimisation during continuous FSW of thin long and complex-shape aluminium extrusions, welding setup times and process variations are minimised and chances for defect-free welds increased, boosting production and cost savings in large panel fabrication in shipbuilding.
- Full Text:
- Date Issued: 2020
- Authors: Chikamhi, Prince Philhelene
- Date: 2020
- Subjects: Friction welding , Welding
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/46030 , vital:39410
- Description: This dissertation focuses on the development of a welding extrusion feeder, tool and schedule for implementation of defect-free butt welds on long, thin and complex-shape aluminium extrusions, as used by the marine industry. Viability of employing Friction Stir Welding (FSW) as a welding technology for joining long extrusions with a short-bed and bolt-on feeder to facilitate onsite fabrication of flat structures in shipbuilding is evaluated. An FSW feeder, tool and process control unit were designed, developed and integrated with an existing FSW platform, to facilitate implementation of continuous welds. Weld data acquired from literature review, experimentation, mechanical testing and metallographic analysis was used in design considerations for the development of a feeder. Subsequently, butt welds were implemented successfully on long 3 mm AA6082-T6 extrusions, during continuous FSW on the feeder. A specially adapted tool, the Floating Bobbin Tool, used with the feeder to implement butt welds was designed and developed from literature tool heuristics and weld trials. The tool eliminated the need for a backing bar and enabled tool-workpiece auto-alignment, beneficial with thin-section extrusions. Effect of rotational and weld speed and tool geometry of two tools (Tool 1 and 2), on weld forces and quality was tested, to establish optimum parameters for attaining high quality welds. Tool geometry had a profound effect on weld forces and integrity; Tool 2 welds exhibited superior and consistent weld quality, meeting maritime rules and standards and proving the adequacy of using FSW for joining long thin extrusions. Feeder process control, automation and optimisation, was implemented by process control unit devices, in addition to force and position control provided by the existing FSW platform. Owing to process control, automation and optimisation during continuous FSW of thin long and complex-shape aluminium extrusions, welding setup times and process variations are minimised and chances for defect-free welds increased, boosting production and cost savings in large panel fabrication in shipbuilding.
- Full Text:
- Date Issued: 2020
Influence of process energy on stress corrosion susceptibility of a friction hydro pillar repaired steam turbine rotor disc blade locating hole
- Authors: Pentz, Willem Gerhard
- Date: 2020
- Subjects: Friction welding , Mechanical engineering
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/47106 , vital:39810
- Description: Currently the power generation industry is struggling to keep older coal power plants running efficiently. One of the major hurdles is to keep repair and service cost low. Over time stress corrosion cracking (SCC) occurs in the locating pinholes of tier type rotors which locate the turbine blades. This is where this research aims to assist with an alternative repair technique, Friction Hydro Pillar Processing (FHPP) welding, to have longer service intervals thus saving cost and time. The same material can be used for welding and a new aligned hole can be drilled. FHPP welding is a solid state friction welding process. Four different FHPP axial forces were selected to compare their respective performance in subsequent tensile testing, impact testing and SCC testing. All the tensile samples extracted from preheated welds and post weld heat treated welds fracture in the parent material, which indicates good weld efficiency. The impact crack route from the weld nugget towards the parent material was identified in the energy and force graph. Axial force which promote impact toughness can be selected with this curve. SCC occurs when a tensile stress is applied to a susceptible material when in a conducive environment for cracking. A new SCC W-shape was designed and performed well during initial testing. With the SCC W-shape two specimens can be extracted opposite each other and tested. Both the preheated weld samples and the post weld heat treatment (PWHT) weld samples had improved SCC performance over their respective parent material samples. A high axial force, low process energy, and high process energy rate (low process energy and low weld time) produced a weld with improved SCC resistance. FHPP (with PWHT) is a promising repair technique as it improved on the SCC resistance and impact toughness as well as having 100% bond efficiency. More research is still required to identify the SCC mechanism of the FHPP weld.
- Full Text:
- Date Issued: 2020
- Authors: Pentz, Willem Gerhard
- Date: 2020
- Subjects: Friction welding , Mechanical engineering
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/47106 , vital:39810
- Description: Currently the power generation industry is struggling to keep older coal power plants running efficiently. One of the major hurdles is to keep repair and service cost low. Over time stress corrosion cracking (SCC) occurs in the locating pinholes of tier type rotors which locate the turbine blades. This is where this research aims to assist with an alternative repair technique, Friction Hydro Pillar Processing (FHPP) welding, to have longer service intervals thus saving cost and time. The same material can be used for welding and a new aligned hole can be drilled. FHPP welding is a solid state friction welding process. Four different FHPP axial forces were selected to compare their respective performance in subsequent tensile testing, impact testing and SCC testing. All the tensile samples extracted from preheated welds and post weld heat treated welds fracture in the parent material, which indicates good weld efficiency. The impact crack route from the weld nugget towards the parent material was identified in the energy and force graph. Axial force which promote impact toughness can be selected with this curve. SCC occurs when a tensile stress is applied to a susceptible material when in a conducive environment for cracking. A new SCC W-shape was designed and performed well during initial testing. With the SCC W-shape two specimens can be extracted opposite each other and tested. Both the preheated weld samples and the post weld heat treatment (PWHT) weld samples had improved SCC performance over their respective parent material samples. A high axial force, low process energy, and high process energy rate (low process energy and low weld time) produced a weld with improved SCC resistance. FHPP (with PWHT) is a promising repair technique as it improved on the SCC resistance and impact toughness as well as having 100% bond efficiency. More research is still required to identify the SCC mechanism of the FHPP weld.
- Full Text:
- Date Issued: 2020
Closed-loop temperature control of friction stir welding
- Authors: Pothier, Raymond Peter
- Date: 2015
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MEngineering
- Identifier: http://hdl.handle.net/10948/10362 , vital:26656
- Description: This study develops and presents a friction stir weld (FSW) quality assurance tool based on control of weld zone temperature. Apart from correct tool geometry, tool tilt angle, traverse speed and forge force during welding, one important requirement is that the weld material be sufficiently plasticised (softened). The level of plasticisation is related to weld zone temperature which is primarily dependent on spindle speed, traverse speed and forge force. When all other conditions are correct, sufficiently plasticised material flows around and consolidates behind the tool without the production of voids in the weld. Typically, weld temperature varies along the weld length which may result in variations in weld quality. Weld zone temperature control makes constant weld zone temperature possible. In this study, thermocouple sensors were embedded in the FSW tool and a weld zone temperature control algorithm was developed. Spindle speed was the actuating mechanism for controlling weld temperature. The system was modelled and controllers were designed using Matlab tools. The system was simulated and the performance was compared to the system performance during welding. The control system ensures that the weld zone temperature can be maintained irrespective of the presence of thermal disturbances. Tensile testing was conducted which confirmed a range of temperature in which the welds resulted in consistent strength.
- Full Text:
- Date Issued: 2015
- Authors: Pothier, Raymond Peter
- Date: 2015
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MEngineering
- Identifier: http://hdl.handle.net/10948/10362 , vital:26656
- Description: This study develops and presents a friction stir weld (FSW) quality assurance tool based on control of weld zone temperature. Apart from correct tool geometry, tool tilt angle, traverse speed and forge force during welding, one important requirement is that the weld material be sufficiently plasticised (softened). The level of plasticisation is related to weld zone temperature which is primarily dependent on spindle speed, traverse speed and forge force. When all other conditions are correct, sufficiently plasticised material flows around and consolidates behind the tool without the production of voids in the weld. Typically, weld temperature varies along the weld length which may result in variations in weld quality. Weld zone temperature control makes constant weld zone temperature possible. In this study, thermocouple sensors were embedded in the FSW tool and a weld zone temperature control algorithm was developed. Spindle speed was the actuating mechanism for controlling weld temperature. The system was modelled and controllers were designed using Matlab tools. The system was simulated and the performance was compared to the system performance during welding. The control system ensures that the weld zone temperature can be maintained irrespective of the presence of thermal disturbances. Tensile testing was conducted which confirmed a range of temperature in which the welds resulted in consistent strength.
- Full Text:
- Date Issued: 2015
Friction hydro pillar riveting process of Ti-6AI-4V titanium sheet
- Authors: Tsikayi, Davies Shamiso
- Date: 2015
- Subjects: Friction welding , Titanium alloys -- Welding , Sheet-metal
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/6357 , vital:21078
- Description: Mechanical fasteners are used extensively in the joining of two or more metal plates or sheets. Riveted joints have been the joints of choice mainly for the Aerospace Industry. However for this research, Friction Hydro Pillar Processing has been used to develop and characterise a new riveting technique termed Friction Hydro Pillar Riveting (FHPR). Two overlapping 3.17 mm Ti-6Al-4V sheets were joined together using Ø6 mm rivet which was friction processed. This research has focussed on the initial development of Friction Hydro Pillar Riveting thereby establishing a basic understanding of the influences of main process parameters, rotational speed and axial force - and also joint configurations. The results showed that with a decrease in the bottom hole chamfer angle, there was resulting overall increase in the rivet joint pull off strength. From the best performing joint configuration in pull off tests, shear tests were conducted whilst a blind hole FHPR joint was also done and tested in pull off and shear strength. The shear test fracture surfaces exhibited ductile failure. The microstructure of the joints was thus evaluated. From parent material, heat affected zone and to weld zone there was a variation in the microstructure analysed. The hardness profiles showed increased hardness in the weld zone which partly explained the shear results. The hardness increase was mainly due to grain refinement in the weld zone by the Friction Hydro Pillar Riveting process.
- Full Text:
- Date Issued: 2015
- Authors: Tsikayi, Davies Shamiso
- Date: 2015
- Subjects: Friction welding , Titanium alloys -- Welding , Sheet-metal
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/6357 , vital:21078
- Description: Mechanical fasteners are used extensively in the joining of two or more metal plates or sheets. Riveted joints have been the joints of choice mainly for the Aerospace Industry. However for this research, Friction Hydro Pillar Processing has been used to develop and characterise a new riveting technique termed Friction Hydro Pillar Riveting (FHPR). Two overlapping 3.17 mm Ti-6Al-4V sheets were joined together using Ø6 mm rivet which was friction processed. This research has focussed on the initial development of Friction Hydro Pillar Riveting thereby establishing a basic understanding of the influences of main process parameters, rotational speed and axial force - and also joint configurations. The results showed that with a decrease in the bottom hole chamfer angle, there was resulting overall increase in the rivet joint pull off strength. From the best performing joint configuration in pull off tests, shear tests were conducted whilst a blind hole FHPR joint was also done and tested in pull off and shear strength. The shear test fracture surfaces exhibited ductile failure. The microstructure of the joints was thus evaluated. From parent material, heat affected zone and to weld zone there was a variation in the microstructure analysed. The hardness profiles showed increased hardness in the weld zone which partly explained the shear results. The hardness increase was mainly due to grain refinement in the weld zone by the Friction Hydro Pillar Riveting process.
- Full Text:
- Date Issued: 2015
Development of a creep sample retrieval technique and friction weld site repair procedure
- Authors: Wedderburn, Ian Norman
- Date: 2013
- Subjects: Friction welding
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:9635 , http://hdl.handle.net/10948/d1020116
- Description: The remnant life monitoring of creep loaded high temperature and pressure components in power stations is critical to ensuring their safe and cost effective operation as failures can have severe consequences. Effective creep life condition monitoring allows for optimising component life predictions and subsequent plant maintenance decisions. In South Africa many power generation stations have been in operation well beyond their 30 year design service life, as such knowledge of the remnant creep life of high temperature and pressure components, such as steam pipelines, becomes of utmost importance. Techniques for the remnant creep life assessments of critical high temperature and pressure components must therefore be as effective as possible. The common and well accepted in-situ inspection technique for assessing creep damage in steam pipes is by the metallographic replication technique. The technique is however limited to the outer surface of the pipe, without information on damage within the wall. This research will illustrate a means of obtaining a sample for creep life analysis with depth through the wall of a pipe, as wells as an alternative technique for the repair of the sample retrieval site. A sample retrieval technique was developed that would retrieve a small diameter cylindrical sample from a cored blind hole for creep analysis by visual creep void assessment or by the small punch creep test. The small punch creep test requires only a small diameter thin disc of material for testing for which its results are comparable with conventional uniaxial creep testing which requires a much larger sample of material. The smaller sample requirement of the small punch creep test therefore allows for a vastly reduced invasive sample retrieval operation and consequently smaller repair size area. Also the fact that the sample is retrieved from a blind hole is advantageous since the pipe wall is not penetrated which would require full plant shutdown. A friction welding technique was identified as an alternative to traditional arc fusion welding for the repair of the sample retrieval site, this technique being the Friction Hydro Pillar Processing technique. Friction Hydro Pillar Processing is a solid-state welding technique and as such has a number of inherent benefits over arc fusion welding as the weld is performed below the melting temperature of the material. From a process point of view Friction Hydro Pillar Processing is ideally suited for automation, has virtually no fumes generated, minimal distortion is experienced and no spatter has to be removed afterwards. The technique has yet to see industrial application and as such development of suitable process parameters was undertaken. Finally, to apply the sample retrieval and repair operations in-situ to a steam pipe in a power plant suitable equipment was developed. Existing friction welding equipment is generally bulky workshop based equipment and is unsuitable for on-site work due to its size and weight. Therefore development of dedicated equipment was required to enable Friction Hydro Pillar Processing to be applied to steam pipes within a power plant environment.
- Full Text:
- Date Issued: 2013
- Authors: Wedderburn, Ian Norman
- Date: 2013
- Subjects: Friction welding
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:9635 , http://hdl.handle.net/10948/d1020116
- Description: The remnant life monitoring of creep loaded high temperature and pressure components in power stations is critical to ensuring their safe and cost effective operation as failures can have severe consequences. Effective creep life condition monitoring allows for optimising component life predictions and subsequent plant maintenance decisions. In South Africa many power generation stations have been in operation well beyond their 30 year design service life, as such knowledge of the remnant creep life of high temperature and pressure components, such as steam pipelines, becomes of utmost importance. Techniques for the remnant creep life assessments of critical high temperature and pressure components must therefore be as effective as possible. The common and well accepted in-situ inspection technique for assessing creep damage in steam pipes is by the metallographic replication technique. The technique is however limited to the outer surface of the pipe, without information on damage within the wall. This research will illustrate a means of obtaining a sample for creep life analysis with depth through the wall of a pipe, as wells as an alternative technique for the repair of the sample retrieval site. A sample retrieval technique was developed that would retrieve a small diameter cylindrical sample from a cored blind hole for creep analysis by visual creep void assessment or by the small punch creep test. The small punch creep test requires only a small diameter thin disc of material for testing for which its results are comparable with conventional uniaxial creep testing which requires a much larger sample of material. The smaller sample requirement of the small punch creep test therefore allows for a vastly reduced invasive sample retrieval operation and consequently smaller repair size area. Also the fact that the sample is retrieved from a blind hole is advantageous since the pipe wall is not penetrated which would require full plant shutdown. A friction welding technique was identified as an alternative to traditional arc fusion welding for the repair of the sample retrieval site, this technique being the Friction Hydro Pillar Processing technique. Friction Hydro Pillar Processing is a solid-state welding technique and as such has a number of inherent benefits over arc fusion welding as the weld is performed below the melting temperature of the material. From a process point of view Friction Hydro Pillar Processing is ideally suited for automation, has virtually no fumes generated, minimal distortion is experienced and no spatter has to be removed afterwards. The technique has yet to see industrial application and as such development of suitable process parameters was undertaken. Finally, to apply the sample retrieval and repair operations in-situ to a steam pipe in a power plant suitable equipment was developed. Existing friction welding equipment is generally bulky workshop based equipment and is unsuitable for on-site work due to its size and weight. Therefore development of dedicated equipment was required to enable Friction Hydro Pillar Processing to be applied to steam pipes within a power plant environment.
- Full Text:
- Date Issued: 2013
Development of thick section friction stir welding using a sliding tool shoulder
- Authors: Chetty, Shamalin
- Date: 2013
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9633 , http://hdl.handle.net/10948/d1015081
- Description: Sliding shoulder friction stir welding (SSFSW) is an alternative joining technique to the conventional friction stir welding process. The welding mechanism comprises of a rotating probe and a non-rotating shoulder. The shoulder therefore does not contribute to any heat generation or plastic deformation. When welding thicker section material, the contribution of heat generation from the shoulder becomes less significant and most of the heat and plastic deformation must be generated by the tool probe. For this reason it was decided to develop the process for thick section AA6082-T6. Due to the stationary (non-rotating) shoulder the weld track is smooth and there is no reduction in cross-sectional area. This research is based on the development of a sliding shoulder friction stir welding tool with the ability to create joints of up to 25mm thick on aluminium alloy 6082-T6 plate as well as the associated process development. The sliding shoulder friction stir welding tool was designed, manufactured and tested by initially performing partial penetration welds with various size tool probes and then finally by performing a sliding shoulder friction stir butt weld on 25mm thick plate. As welds were performed and more knowledge gained about the process, design modifications were made. These included varying the clearance between the tool probe and stationary shoulder; the profile of the shoulder which contributes to material flow during the process; and supporting the tool probe to prevent deflection when welding thicker sections at high forge forces. From the sliding shoulder friction stir welds performed, an understanding of material flow during the process was gained when analysing the macro-sections and exit holes of the welds. Typical process forces and torques associated with the process were measured to assist with future head unit and tool designs with regard to sliding shoulder friction stir welding.
- Full Text:
- Date Issued: 2013
- Authors: Chetty, Shamalin
- Date: 2013
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9633 , http://hdl.handle.net/10948/d1015081
- Description: Sliding shoulder friction stir welding (SSFSW) is an alternative joining technique to the conventional friction stir welding process. The welding mechanism comprises of a rotating probe and a non-rotating shoulder. The shoulder therefore does not contribute to any heat generation or plastic deformation. When welding thicker section material, the contribution of heat generation from the shoulder becomes less significant and most of the heat and plastic deformation must be generated by the tool probe. For this reason it was decided to develop the process for thick section AA6082-T6. Due to the stationary (non-rotating) shoulder the weld track is smooth and there is no reduction in cross-sectional area. This research is based on the development of a sliding shoulder friction stir welding tool with the ability to create joints of up to 25mm thick on aluminium alloy 6082-T6 plate as well as the associated process development. The sliding shoulder friction stir welding tool was designed, manufactured and tested by initially performing partial penetration welds with various size tool probes and then finally by performing a sliding shoulder friction stir butt weld on 25mm thick plate. As welds were performed and more knowledge gained about the process, design modifications were made. These included varying the clearance between the tool probe and stationary shoulder; the profile of the shoulder which contributes to material flow during the process; and supporting the tool probe to prevent deflection when welding thicker sections at high forge forces. From the sliding shoulder friction stir welds performed, an understanding of material flow during the process was gained when analysing the macro-sections and exit holes of the welds. Typical process forces and torques associated with the process were measured to assist with future head unit and tool designs with regard to sliding shoulder friction stir welding.
- Full Text:
- Date Issued: 2013
Finite element analysis of the heat transfer in friction stir welding with experimental validation
- Authors: Vosloo, Natalie
- Date: 2012
- Subjects: Finite element method , Heat -- Transmission , Friction welding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10511 , http://hdl.handle.net/10948/d1019981
- Description: Friction stir welding is a relatively new joining process. The heat transfer involved is crucial in determining the quality of the weld. Experimenrtal data, though important, does not provide enough information about the heat transfer process and experiments can be costly and time consuming. A numerical model, using the finite element method, was developed to stimulate the heat transfer in the workpiece in which the heat generation due to friction and plastic deformation was modelled as a surface heat flux boundary condition. This model was applied to Aluminium AL6082-T6 and Titanium Ti6A1-4V for different welding condiitions. Results were validated with experimental results. The model was shown to give better predictions of the maximum temperatures at locations in the workpiece than the overall temperature trend. A parametric study was also performed on the Aluminium model in order o predict temperature fields of the workpiece for welding conditions that were additional to those undertaken experimentally. It was found that rotational speed had a larger effect on the change in temperature than the feed rate. From the parametric study it was also clear that lower rotational speeds (300 to 660 rpm) had a greater effect on the change in temperature than the higher rotational speeds (840 to 1200 rpm). It was concluded that the model was well suited for the estimation of temperatures involved in the FSw of Aluminium Al6082-T6 but was not as accurate when applied to the FSW of Titanium.
- Full Text:
- Date Issued: 2012
- Authors: Vosloo, Natalie
- Date: 2012
- Subjects: Finite element method , Heat -- Transmission , Friction welding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10511 , http://hdl.handle.net/10948/d1019981
- Description: Friction stir welding is a relatively new joining process. The heat transfer involved is crucial in determining the quality of the weld. Experimenrtal data, though important, does not provide enough information about the heat transfer process and experiments can be costly and time consuming. A numerical model, using the finite element method, was developed to stimulate the heat transfer in the workpiece in which the heat generation due to friction and plastic deformation was modelled as a surface heat flux boundary condition. This model was applied to Aluminium AL6082-T6 and Titanium Ti6A1-4V for different welding condiitions. Results were validated with experimental results. The model was shown to give better predictions of the maximum temperatures at locations in the workpiece than the overall temperature trend. A parametric study was also performed on the Aluminium model in order o predict temperature fields of the workpiece for welding conditions that were additional to those undertaken experimentally. It was found that rotational speed had a larger effect on the change in temperature than the feed rate. From the parametric study it was also clear that lower rotational speeds (300 to 660 rpm) had a greater effect on the change in temperature than the higher rotational speeds (840 to 1200 rpm). It was concluded that the model was well suited for the estimation of temperatures involved in the FSw of Aluminium Al6082-T6 but was not as accurate when applied to the FSW of Titanium.
- Full Text:
- Date Issued: 2012
Analysis and modelling of the temperature distribution during the friction taper stud welding of 10CrMo910
- Van Zyl, Carlo Angelo Antonio
- Authors: Van Zyl, Carlo Angelo Antonio
- Date: 2008
- Subjects: Friction welding , Pressure welding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9630 , http://hdl.handle.net/10948/720 , http://hdl.handle.net/10948/d1012898 , Friction welding , Pressure welding
- Description: Heat generation during the FTSW process plays and important role in determining the characteristics of the weld. In order to obtain temperature fields, a transient temperature heat analysis is required. An area is the maximum temperatures reached within the base material during the FTSW process. These temperatures will be measured during experimentation, and compared to the welding simulation done using FEA. From the literature search it appeared that no heat transfer analysis had been done using finite element methods.
- Full Text:
- Date Issued: 2008
- Authors: Van Zyl, Carlo Angelo Antonio
- Date: 2008
- Subjects: Friction welding , Pressure welding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9630 , http://hdl.handle.net/10948/720 , http://hdl.handle.net/10948/d1012898 , Friction welding , Pressure welding
- Description: Heat generation during the FTSW process plays and important role in determining the characteristics of the weld. In order to obtain temperature fields, a transient temperature heat analysis is required. An area is the maximum temperatures reached within the base material during the FTSW process. These temperatures will be measured during experimentation, and compared to the welding simulation done using FEA. From the literature search it appeared that no heat transfer analysis had been done using finite element methods.
- Full Text:
- Date Issued: 2008
A fuzzy logic control system for a friction stir welding process
- Authors: Majara, Khotso Ernest
- Date: 2006
- Subjects: Friction welding , Fuzzy logic , Automatic control , Fuzzy systems
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9594 , http://hdl.handle.net/10948/405 , Friction welding , Fuzzy logic , Automatic control , Fuzzy systems
- Description: FSW is a welding technique invented and patented by The Welding Institute in 1991. This welding technique utilises the benefits of solid-state welding to materials regarded as difficult to weld by fusion processes. The productivity of the process was not optimised as the real-time dynamics of the material and tool changes were not considered. Furthermore, the process has a plastic weld region where no traditional modelling describing the interaction between the tool and work piece is available. Fuzzy logic technology is one of the artificial intelligent strategies used to improve the control of the dynamics of industrial processes. Fuzzy control was proposed as a viable solution to improve the productivity of the FSW process. The simulations indicated that FLC can use feed rate and welding speed to adaptively regulate the feed force and tool temperature respectively, irrespective of varying tool and material change. The simulations presented fuzzy logic technology to be robust enough to regulate FSW process in the absence of accurate mathematical models.
- Full Text:
- Date Issued: 2006
- Authors: Majara, Khotso Ernest
- Date: 2006
- Subjects: Friction welding , Fuzzy logic , Automatic control , Fuzzy systems
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9594 , http://hdl.handle.net/10948/405 , Friction welding , Fuzzy logic , Automatic control , Fuzzy systems
- Description: FSW is a welding technique invented and patented by The Welding Institute in 1991. This welding technique utilises the benefits of solid-state welding to materials regarded as difficult to weld by fusion processes. The productivity of the process was not optimised as the real-time dynamics of the material and tool changes were not considered. Furthermore, the process has a plastic weld region where no traditional modelling describing the interaction between the tool and work piece is available. Fuzzy logic technology is one of the artificial intelligent strategies used to improve the control of the dynamics of industrial processes. Fuzzy control was proposed as a viable solution to improve the productivity of the FSW process. The simulations indicated that FLC can use feed rate and welding speed to adaptively regulate the feed force and tool temperature respectively, irrespective of varying tool and material change. The simulations presented fuzzy logic technology to be robust enough to regulate FSW process in the absence of accurate mathematical models.
- Full Text:
- Date Issued: 2006
Monitoring and intelligent control for complex curvature friction stir welding
- Hua, Tao
- Authors: Hua, Tao
- Date: 2006
- Subjects: Friction welding , Fuzzy systems
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9612 , http://hdl.handle.net/10948/420 , Friction welding , Fuzzy systems
- Description: A multi-input multi-output system to implement on-line process monitoring and intelligent control of complex curvature friction stir welding was proposed. An extra rotation axis was added to the existing three translation axes to perform friction stir welding of complex curvature other than straight welding line. A clamping system was designed for locating and holding the workpieces to bear the large force involved in the process between the welding tool and workpieces. Process parameters (feed rate, spindle speed, tilt angle and plunge depth), and process conditions (parent material and curvature), were used as factors for the orthogonal array experiments to collect sensor data of force, torque and tool temperature using multiple sensors and telemetry system. Using statistic analysis of the experimental data, sensitive signal features were selected to train the feed-forward neural networks, which were used for mapping the relationships between process parameters, process conditions and sensor data. A fuzzy controller with initial input/output membership functions and fuzzy rules generated on-line from the trained neural network was applied to perceive process condition changes and make adjustment of process parameters to maintain tool/workpiece contact and energy input. Input/output scaling factors of the fuzzy controller were tuned on-line to improve output response to the amount and trend of control variable deviation from the reference value. Simulation results showed that the presented neuro-fuzzy control scheme has adaptability to process conditions such as parent material and curvature changes, and that the control variables were well regulated. The presented neuro-fuzzy control scheme can be also expected to be applied in other multi-input multi-output machining processes.
- Full Text:
- Date Issued: 2006
- Authors: Hua, Tao
- Date: 2006
- Subjects: Friction welding , Fuzzy systems
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9612 , http://hdl.handle.net/10948/420 , Friction welding , Fuzzy systems
- Description: A multi-input multi-output system to implement on-line process monitoring and intelligent control of complex curvature friction stir welding was proposed. An extra rotation axis was added to the existing three translation axes to perform friction stir welding of complex curvature other than straight welding line. A clamping system was designed for locating and holding the workpieces to bear the large force involved in the process between the welding tool and workpieces. Process parameters (feed rate, spindle speed, tilt angle and plunge depth), and process conditions (parent material and curvature), were used as factors for the orthogonal array experiments to collect sensor data of force, torque and tool temperature using multiple sensors and telemetry system. Using statistic analysis of the experimental data, sensitive signal features were selected to train the feed-forward neural networks, which were used for mapping the relationships between process parameters, process conditions and sensor data. A fuzzy controller with initial input/output membership functions and fuzzy rules generated on-line from the trained neural network was applied to perceive process condition changes and make adjustment of process parameters to maintain tool/workpiece contact and energy input. Input/output scaling factors of the fuzzy controller were tuned on-line to improve output response to the amount and trend of control variable deviation from the reference value. Simulation results showed that the presented neuro-fuzzy control scheme has adaptability to process conditions such as parent material and curvature changes, and that the control variables were well regulated. The presented neuro-fuzzy control scheme can be also expected to be applied in other multi-input multi-output machining processes.
- Full Text:
- Date Issued: 2006
Development and analysis of a friction stir spot welding process for aluminium
- Authors: Stephen, Michael George
- Date: 2005
- Subjects: Friction welding , Electric welding , Aluminum alloys -- Welding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9631 , http://hdl.handle.net/10948/1351 , Friction welding , Electric welding , Aluminum alloys -- Welding
- Description: Friction Stir Spot Welding (FSSW) has been developed from the conventional Friction Stir Welding (FSW) process, developed at The Welding Institute (TWI). FSSWs have been done without the keyhole being eliminated. Elimination of the keyhole would result in the process being more commercially viable. This dissertation focuses on an attempt of eliminating the keyhole using a retractable pin tool as well as a comparison of the weld integrity of a FSSW to that of a conventional Resistance Spot Weld (RSW). Welds were conducted on aluminium alloy 6063 T4. Comparisons between different weld procedures were done. Further analysis of the weld integrity between FSSW and RSW were conducted, comparing tensile strengths, microstructure and hardness. For the above welding procedure to take place, the current retractable pin tool, patented by PE Technikon, was redesigned. Problems associated during the welding process and the results obtained are documented. Reasons for the keyhole not being eliminated as well as recommendations for future work in the attempt to remove the keyhole are discussed.
- Full Text:
- Date Issued: 2005
- Authors: Stephen, Michael George
- Date: 2005
- Subjects: Friction welding , Electric welding , Aluminum alloys -- Welding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9631 , http://hdl.handle.net/10948/1351 , Friction welding , Electric welding , Aluminum alloys -- Welding
- Description: Friction Stir Spot Welding (FSSW) has been developed from the conventional Friction Stir Welding (FSW) process, developed at The Welding Institute (TWI). FSSWs have been done without the keyhole being eliminated. Elimination of the keyhole would result in the process being more commercially viable. This dissertation focuses on an attempt of eliminating the keyhole using a retractable pin tool as well as a comparison of the weld integrity of a FSSW to that of a conventional Resistance Spot Weld (RSW). Welds were conducted on aluminium alloy 6063 T4. Comparisons between different weld procedures were done. Further analysis of the weld integrity between FSSW and RSW were conducted, comparing tensile strengths, microstructure and hardness. For the above welding procedure to take place, the current retractable pin tool, patented by PE Technikon, was redesigned. Problems associated during the welding process and the results obtained are documented. Reasons for the keyhole not being eliminated as well as recommendations for future work in the attempt to remove the keyhole are discussed.
- Full Text:
- Date Issued: 2005
Analysis of material flow around a retractable pin in a friction stir weld
- Authors: Georgeou, Zacharias
- Date: 2003
- Subjects: Friction welding , Aluminum alloys -- Welding
- Language: English
- Type: Thesis , Masters , MTech (Mechanical Engineering)
- Identifier: vital:10812 , http://hdl.handle.net/10948/196 , Friction welding , Aluminum alloys -- Welding
- Description: Friction StirWelding (FSW) has been researched for a number of years since its inception in 1991. The work thus far has been based on understanding the material and thermal flow using the standard fixed pin tool. The keyhole resulting during tool extraction in a FSW weld, is a disadvantage and a current limiting factor. Eliminating this effect from a weld using a movable pin tools would make FSW more commercially viable. This dissertation focuses on the design of a novel retractable pin tool, and highlights the problems encountered during the welding of Aluminum plates, Al2024 and Al5083. Previously studied techniques of material and thermal flow were used, to investigate the effect of the tool during extraction in a FSW weld. A prototype retractable tool was designed using parametric and axiomatic design theory, and implementing a pneumatic muscle actuation system. The resulting problems in the calibration of the retractable pin tool and the resulting welds are presented, these results confirming previous studies. The movable pin produced discrepancies the heat generation around the shoulder during a FSW weld. The failure of this tool to produce a reasonable weld showed that previous ideas into the workings of a retractable pin tool requires further investigation, furthermore a fresh approach to the interpretation and understanding of the FSW weld process needs consideration.
- Full Text:
- Date Issued: 2003
- Authors: Georgeou, Zacharias
- Date: 2003
- Subjects: Friction welding , Aluminum alloys -- Welding
- Language: English
- Type: Thesis , Masters , MTech (Mechanical Engineering)
- Identifier: vital:10812 , http://hdl.handle.net/10948/196 , Friction welding , Aluminum alloys -- Welding
- Description: Friction StirWelding (FSW) has been researched for a number of years since its inception in 1991. The work thus far has been based on understanding the material and thermal flow using the standard fixed pin tool. The keyhole resulting during tool extraction in a FSW weld, is a disadvantage and a current limiting factor. Eliminating this effect from a weld using a movable pin tools would make FSW more commercially viable. This dissertation focuses on the design of a novel retractable pin tool, and highlights the problems encountered during the welding of Aluminum plates, Al2024 and Al5083. Previously studied techniques of material and thermal flow were used, to investigate the effect of the tool during extraction in a FSW weld. A prototype retractable tool was designed using parametric and axiomatic design theory, and implementing a pneumatic muscle actuation system. The resulting problems in the calibration of the retractable pin tool and the resulting welds are presented, these results confirming previous studies. The movable pin produced discrepancies the heat generation around the shoulder during a FSW weld. The failure of this tool to produce a reasonable weld showed that previous ideas into the workings of a retractable pin tool requires further investigation, furthermore a fresh approach to the interpretation and understanding of the FSW weld process needs consideration.
- Full Text:
- Date Issued: 2003
Intelligent monitoring and control system for a friction stir welding process
- Authors: Kruger, Grant
- Date: 2003
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MTech (Electrical Engineering)
- Identifier: vital:10823 , http://hdl.handle.net/10948/273 , Friction welding
- Description: A Friction Stir Welding machine is proposed and built to allow future research into the process and to provide a framework from which the application of intelligent manufacturing to industrial processes can be investigated. Initially a literature survey was conducted upon which the design of the machine could be based. The conversion of a conventional milling machine into a Friction Stir Welding machine by applying modern monitoring and control systems is then presented. Complete digital control was used to drive actuators and monitor sensors. A wireless chuck mounted monitoring system was implemented, enabling forces, torques, temperature and speed of the tool to be obtained directly from the process. Software based on a hierarchical Open Systems Architectural design, incorporating modularity, interoperability, portability and extensibility is implemented. This experimental setup is used to analyze the Friction Stir Welding process by performing data analysis using statistical methods. Three independent variables (weld speed, spindle speed and plunge depth) were varied and the independent variables (forces, torques, power, temperature, speed, etc) recorded using the implemented software. The statistical analysis includes the analysis of variants, regression analysis and the creation of surface plots. Using these results, certain linguistic rules for process control are proposed. An intelligent controller is designed and discussed, using the derived rules to improve and optimize certain aspects of the process encountered during the experimental phase of the research.
- Full Text:
- Date Issued: 2003
- Authors: Kruger, Grant
- Date: 2003
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MTech (Electrical Engineering)
- Identifier: vital:10823 , http://hdl.handle.net/10948/273 , Friction welding
- Description: A Friction Stir Welding machine is proposed and built to allow future research into the process and to provide a framework from which the application of intelligent manufacturing to industrial processes can be investigated. Initially a literature survey was conducted upon which the design of the machine could be based. The conversion of a conventional milling machine into a Friction Stir Welding machine by applying modern monitoring and control systems is then presented. Complete digital control was used to drive actuators and monitor sensors. A wireless chuck mounted monitoring system was implemented, enabling forces, torques, temperature and speed of the tool to be obtained directly from the process. Software based on a hierarchical Open Systems Architectural design, incorporating modularity, interoperability, portability and extensibility is implemented. This experimental setup is used to analyze the Friction Stir Welding process by performing data analysis using statistical methods. Three independent variables (weld speed, spindle speed and plunge depth) were varied and the independent variables (forces, torques, power, temperature, speed, etc) recorded using the implemented software. The statistical analysis includes the analysis of variants, regression analysis and the creation of surface plots. Using these results, certain linguistic rules for process control are proposed. An intelligent controller is designed and discussed, using the derived rules to improve and optimize certain aspects of the process encountered during the experimental phase of the research.
- Full Text:
- Date Issued: 2003
Design, development and analysis of the friction stir welding process
- Authors: Blignault, Calvin
- Date: 2002
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MTech (Mechanical Engineering)
- Identifier: vital:10809 , http://hdl.handle.net/10948/1350 , Friction welding
- Description: The development of a CNC-based technology FSW machine to accurately produce friction stir weld samples that can be analyzed for research purposes is implemented and discussed. A process diagnosis and control scheme to improve the process monitoring and weld evaluation capabilities of an FSW machine are proposed and implemented. Basic CNC-based hardware implementation such as optical encoders and inverters for process control are explained and verified. The control scheme and framework of interfaces to the digital I/O cards for PC user interface are explained. An advanced monitoring system which senses process performance parameters such as tool temperature, 3-axis tool forces, torque and spindle speed are explained. Mechanical designs and manufacturing techniques such as tool, clamp and backing plate designs are explained and verified. The process parameters for quality optimization are investigated and optimized by making use of Correlation and Regression Analysis. The statistical data and analytical relationships between welding parameters (independent) and each of the performance parameters (dependent) are obtained and used to simulate the machining process. The weld research samples are tested for strength and integrity making use of various scientific testing techniques. The reliability of the samples are also evaluated and compared to that of other institutions. Process variables and the optimum operating range of the Friction Stir Welding machine is determined and a framework for further research into weld quality optimization is set.
- Full Text:
- Date Issued: 2002
- Authors: Blignault, Calvin
- Date: 2002
- Subjects: Friction welding
- Language: English
- Type: Thesis , Masters , MTech (Mechanical Engineering)
- Identifier: vital:10809 , http://hdl.handle.net/10948/1350 , Friction welding
- Description: The development of a CNC-based technology FSW machine to accurately produce friction stir weld samples that can be analyzed for research purposes is implemented and discussed. A process diagnosis and control scheme to improve the process monitoring and weld evaluation capabilities of an FSW machine are proposed and implemented. Basic CNC-based hardware implementation such as optical encoders and inverters for process control are explained and verified. The control scheme and framework of interfaces to the digital I/O cards for PC user interface are explained. An advanced monitoring system which senses process performance parameters such as tool temperature, 3-axis tool forces, torque and spindle speed are explained. Mechanical designs and manufacturing techniques such as tool, clamp and backing plate designs are explained and verified. The process parameters for quality optimization are investigated and optimized by making use of Correlation and Regression Analysis. The statistical data and analytical relationships between welding parameters (independent) and each of the performance parameters (dependent) are obtained and used to simulate the machining process. The weld research samples are tested for strength and integrity making use of various scientific testing techniques. The reliability of the samples are also evaluated and compared to that of other institutions. Process variables and the optimum operating range of the Friction Stir Welding machine is determined and a framework for further research into weld quality optimization is set.
- Full Text:
- Date Issued: 2002
Characterization of friction hydro pillar process weld properties as applied to 10CrMo910 creep resistant steel for application in the power generation Industry
- Authors: Bulbring, Daniel Louis Hans
- Subjects: Materials -- Creep , Friction welding
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9636 , http://hdl.handle.net/10948/d1020586
- Description: Creep degradation of steam carrying vessels in the power generation industry is a concern that needs to be constantly monitored. The Weldcore® process has been earmarked as a potential method of creep sampling which will allow for thick-walled sections to be analysed. A component of the process involves plugging the resultant hole after removing a creep sample using a novel welding technique called friction hydro pillar processing. At the commencement of this study, insufficient data was available to warrant safe industrial application of the process. This research was conducted to evaluate the performance of 10CrMo910 friction hydro pillar process welds. The effects of downward force, stud taper angle, hole taper angle and hole base diameter on process response, defect population, static properties and dynamic performance were evaluated. The variation of downward force showed that higher forces produce significantly smaller defects and higher fatigue life. The occurrence of defects was linked to process parameters and geometry thereby identifying the correct parameters for safe use in the power generation industry. Flash formation was identified as an early indicator of weld defects and can assist with quality control in industrial applications. Methods of standardising the plunge depth and forge force were developed to identify the correct magnitudes for different geometries, without the need for testing. Defects were shown to populate specific regions of the weld and produce variations in fatigue life. Crack initiation sites were detected which will aid in identifying areas of focus in further research and development. Temperature measurements were linked to the occurrence of defects and crack initiation sites and have been identified as a method of identifying defective welds. The effects of process parameters and stud and hole taper angles on energy inputs and near interface temperatures were statistically evaluated. Downward force was shown to have the largest effect on energy input rates, total energy input and temperatures at the 11.5mm and 20.5mm positions. Smaller hole and stud taper angles produced lower energy inputs and were identified as more energy efficient than the larger taper angles. A regression model was also developed to predict the fatigue life of welds and can assist with critical process related decision making. A range of hole base diameters were identified which produced welds with low defect populations and fatigue performance similar to that of the parent plate. Larger hole base diameters were shown to produce significant defects along the hole bottom fillet, in the weld nugget and along the bond line. Temperature measurements of the larger diameter welds showed a delay in response and are attributed to a delayed contact of plasticised stud material with the sidewall. Welds with hole base diameters larger than 11mm produced unrepeatable and defective welds, and also required higher energy inputs making smaller diameters more desirable. Analysis of all welds in this study revealed that clearance and interfacial pressures characterise the quality of friction hydro pillar process welds, therefore models were developed to aid in critical decision making with respect to downward force and geometry. This study has successfully evaluated the effects of process parameters and geometry on the properties of friction hydro pillar process welds and thereby has increased understanding of the process.
- Full Text:
- Authors: Bulbring, Daniel Louis Hans
- Subjects: Materials -- Creep , Friction welding
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9636 , http://hdl.handle.net/10948/d1020586
- Description: Creep degradation of steam carrying vessels in the power generation industry is a concern that needs to be constantly monitored. The Weldcore® process has been earmarked as a potential method of creep sampling which will allow for thick-walled sections to be analysed. A component of the process involves plugging the resultant hole after removing a creep sample using a novel welding technique called friction hydro pillar processing. At the commencement of this study, insufficient data was available to warrant safe industrial application of the process. This research was conducted to evaluate the performance of 10CrMo910 friction hydro pillar process welds. The effects of downward force, stud taper angle, hole taper angle and hole base diameter on process response, defect population, static properties and dynamic performance were evaluated. The variation of downward force showed that higher forces produce significantly smaller defects and higher fatigue life. The occurrence of defects was linked to process parameters and geometry thereby identifying the correct parameters for safe use in the power generation industry. Flash formation was identified as an early indicator of weld defects and can assist with quality control in industrial applications. Methods of standardising the plunge depth and forge force were developed to identify the correct magnitudes for different geometries, without the need for testing. Defects were shown to populate specific regions of the weld and produce variations in fatigue life. Crack initiation sites were detected which will aid in identifying areas of focus in further research and development. Temperature measurements were linked to the occurrence of defects and crack initiation sites and have been identified as a method of identifying defective welds. The effects of process parameters and stud and hole taper angles on energy inputs and near interface temperatures were statistically evaluated. Downward force was shown to have the largest effect on energy input rates, total energy input and temperatures at the 11.5mm and 20.5mm positions. Smaller hole and stud taper angles produced lower energy inputs and were identified as more energy efficient than the larger taper angles. A regression model was also developed to predict the fatigue life of welds and can assist with critical process related decision making. A range of hole base diameters were identified which produced welds with low defect populations and fatigue performance similar to that of the parent plate. Larger hole base diameters were shown to produce significant defects along the hole bottom fillet, in the weld nugget and along the bond line. Temperature measurements of the larger diameter welds showed a delay in response and are attributed to a delayed contact of plasticised stud material with the sidewall. Welds with hole base diameters larger than 11mm produced unrepeatable and defective welds, and also required higher energy inputs making smaller diameters more desirable. Analysis of all welds in this study revealed that clearance and interfacial pressures characterise the quality of friction hydro pillar process welds, therefore models were developed to aid in critical decision making with respect to downward force and geometry. This study has successfully evaluated the effects of process parameters and geometry on the properties of friction hydro pillar process welds and thereby has increased understanding of the process.
- Full Text:
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