High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of a... more High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of aluminum alloys and of wear of sliding surfaces in thrust bearings and seals. This paper describes investigations of femtosecond laser texturing for reduction of interface friction on sliding surfaces. Direct-write femtosecond pulsed laser micromachining is used to create microgroove patterns with varying size and density on metal forming dies. Ablation of patterned textures using a Digital Light Processor (DLP) programmable mask and a homogenized femtosecond laser beam is also studied. The achievable resolution and depth profiles and material removal rate for laser micromachining of lubrication-enhancing features is characterized. In metal forming tests, the effectiveness of various laser–machined patterns for enhancing interface lubrication is determined.High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of aluminum alloys and of wear of sliding...
Journal of Reinforced Plastics and Composites, 1998
An analytical model is presented to estimate elastic properties of polymer composites with voids ... more An analytical model is presented to estimate elastic properties of polymer composites with voids of various sizes and locations. The model is based upon a multi level homogenization procedure incorporated with a micromechanics model. Different scenarios of voids in fiber reinforced composites are considered and their effects on deterioration of elastic properties of the composites are analyzed. Comparisons with finite element numerical results and available experimental results for unidirectional fiber reinforced composites are also provided as an evidence of the applicability of the model.
High-performance failure-critical parts such as aeroengine disks are manufactured in a sequence o... more High-performance failure-critical parts such as aeroengine disks are manufactured in a sequence of processing steps such as solidification, deformation, heat treatment and finishing. The fatigue and failure performance of these parts are often governed by the material and processing state. Uncertainties in the material structure, defects and anomalies play a major role in the uncertainties in performance. This paper includes a hybrid computational framework for integrated materials and process design with achieved through model decomposition based on Bayesian probabilistic formulation. Efficacy of this approach is demonstrated by applying it to the selection of forging parameters for maximizing life of titanium disk with hard alpha anomaly.
PurposeTo investigate the ProMetal 3D printing technique for its application to dies, for low vol... more PurposeTo investigate the ProMetal 3D printing technique for its application to dies, for low volume hot forging of 7075 aluminum helicopter parts.Design/methodology/approachThermo‐mechanical and tribological behavior of the ProMetal 3D printed tools were characterized by hot upset and ring tests. Finite element simulations of the test application were conducted using special purpose metal forming simulation software FORGE3. Results obtained from the tests along with finite element analysis were used to validate behavior of the printed dies during forging trials.FindingsProMetal‐printed materials exhibited relatively low thermal conductivity and high friction. Cavities were printed, machined and evaluated in hot forging trials. Dies exhibited substantial settling during the manufacturing (3D printing) process. Some collapse of dies was also observed at locations where forging pressures were high.Practical implicationsAfter initial plastic settling, the printed dies provide satisfact...
During the fabrication of very small or fine hole, usually referred to as micro-hole, technical d... more During the fabrication of very small or fine hole, usually referred to as micro-hole, technical difficulties often arise due to limitation on the precision capability of tooling systems including those associated with alignment. The present project attempts to develop a new process for piercing micro-hole, using high pressure water beam. In this paper, a numerical model for the micro-hole manufacturing is developed which provides helpful insight into the mechanics of the micro-hole forming process and the tooling design. The ALE (Arbitrary Lagrangian-Eulerian) method of dynamic FEM model is used to simulate water hammer and the water beam penetration into the workpiece material. An experiment for hydro-piercing process is also developed to validate the numerical model. The effects of micro-hole parameters, diameter and workpiece thickness, and water pressure on the micro-hole formation are investigated. It is found that the fracture occur near the die corner in workpiece material an...
ABSTRACT There are various surface defects which occur during the hot rolling of steels. It is di... more ABSTRACT There are various surface defects which occur during the hot rolling of steels. It is difficult to correctly identify and control these defects due to the different inspection techniques on different materials and sizes. Also, the statistical data analysis techniques typically used like the principal component analysis, factor analysis etc. require a lot of plant data and are computationally very intensive. Before a detailed analysis of the actual cause of the defects can be done, it is necessary to separate the defects as those coming from the continuous casting or the rolling mill. Once this is done, analysis on the individual components can then be completed to find the root cause. To accomplish both these analysis, Bayesian hierarchical modeling is done on the automated inspection of the bars to form a causal relationship of the defects to the process equipments. Variance reduction model is used at the top of the analysis and regression models are used in the next level.
ABSTRACT Steel bar manufacturing process is a multistage process in which melted steel passes thr... more ABSTRACT Steel bar manufacturing process is a multistage process in which melted steel passes through multiple steps to form into a bar or rod of varying diameters. The most common cause of rejection of such products is the surface defects such as seams, scales, cracks etc. Often automated inspection in the form of image analysis is done to predict the formation of such defects. These inspections suffer from the fact that they do not include the process information and hence are not very reliable. This paper presents a novel methodology of prediction of surface defects in bar manufacturing. In this method, the surface images obtained by inspection methodology are decomposed into individual defects based on process knowledge. These are then decomposed into the physical quantities affecting them which are decomposed into design parameters on rolling mill. To achieve this decomposition, Bayesian hierarchical modeling is used. Data collected from sensors installed on rolling mill are used for model building and design. After the model is built, it is converted into an automated system called Diagnostics on Rolling Mill (DORM). DORM is installed on rolling mill and its performance is evaluated for several days. It is found that the model performs very closely with manual inspection and predicts surface defects with good accuracy. The Bayesian model also gives an insight into process parameters and physical quantities which affect the individual defects.
Journal of Engineering Materials and Technology, 2005
In machining titanium alloys with cemented carbide cutting tools, crater wear is the predominant ... more In machining titanium alloys with cemented carbide cutting tools, crater wear is the predominant wear mechanism influencing tool life and productivity. An analytical wear model that relates crater wear rate to thermally driven cobalt diffusion from cutting tool into the titanium chip is proposed in this paper. This cobalt diffusion is a function of cobalt mole fraction, diffusion coeficient, interface temperature and chip velocity. The wear analysis includes theoretical modeling of the transport-diffusion process, and obtaining tool–chip interface conditions by a nonisothermal visco-plastic finite element method (FEM) model of the cutting process. Comparison of predicted crater wear rate with experimental results from published literature and from high speed turning with WC/Co inserts shows good agreement for different cutting speeds and feed rate. It is seen that wear rates are independent of cutting time.
High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of a... more High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of aluminum alloys and of wear of sliding surfaces in thrust bearings and seals. This paper describes investigations of femtosecond laser texturing for reduction of interface friction on sliding surfaces. Direct-write femtosecond pulsed laser micromachining is used to create microgroove patterns with varying size and density on metal forming dies. Ablation of patterned textures using a Digital Light Processor (DLP) programmable mask and a homogenized femtosecond laser beam is also studied. The achievable resolution and depth profiles and material removal rate for laser micromachining of lubrication-enhancing features is characterized. In metal forming tests, the effectiveness of various laser–machined patterns for enhancing interface lubrication is determined.High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of aluminum alloys and of wear of sliding...
Journal of Reinforced Plastics and Composites, 1998
An analytical model is presented to estimate elastic properties of polymer composites with voids ... more An analytical model is presented to estimate elastic properties of polymer composites with voids of various sizes and locations. The model is based upon a multi level homogenization procedure incorporated with a micromechanics model. Different scenarios of voids in fiber reinforced composites are considered and their effects on deterioration of elastic properties of the composites are analyzed. Comparisons with finite element numerical results and available experimental results for unidirectional fiber reinforced composites are also provided as an evidence of the applicability of the model.
High-performance failure-critical parts such as aeroengine disks are manufactured in a sequence o... more High-performance failure-critical parts such as aeroengine disks are manufactured in a sequence of processing steps such as solidification, deformation, heat treatment and finishing. The fatigue and failure performance of these parts are often governed by the material and processing state. Uncertainties in the material structure, defects and anomalies play a major role in the uncertainties in performance. This paper includes a hybrid computational framework for integrated materials and process design with achieved through model decomposition based on Bayesian probabilistic formulation. Efficacy of this approach is demonstrated by applying it to the selection of forging parameters for maximizing life of titanium disk with hard alpha anomaly.
PurposeTo investigate the ProMetal 3D printing technique for its application to dies, for low vol... more PurposeTo investigate the ProMetal 3D printing technique for its application to dies, for low volume hot forging of 7075 aluminum helicopter parts.Design/methodology/approachThermo‐mechanical and tribological behavior of the ProMetal 3D printed tools were characterized by hot upset and ring tests. Finite element simulations of the test application were conducted using special purpose metal forming simulation software FORGE3. Results obtained from the tests along with finite element analysis were used to validate behavior of the printed dies during forging trials.FindingsProMetal‐printed materials exhibited relatively low thermal conductivity and high friction. Cavities were printed, machined and evaluated in hot forging trials. Dies exhibited substantial settling during the manufacturing (3D printing) process. Some collapse of dies was also observed at locations where forging pressures were high.Practical implicationsAfter initial plastic settling, the printed dies provide satisfact...
During the fabrication of very small or fine hole, usually referred to as micro-hole, technical d... more During the fabrication of very small or fine hole, usually referred to as micro-hole, technical difficulties often arise due to limitation on the precision capability of tooling systems including those associated with alignment. The present project attempts to develop a new process for piercing micro-hole, using high pressure water beam. In this paper, a numerical model for the micro-hole manufacturing is developed which provides helpful insight into the mechanics of the micro-hole forming process and the tooling design. The ALE (Arbitrary Lagrangian-Eulerian) method of dynamic FEM model is used to simulate water hammer and the water beam penetration into the workpiece material. An experiment for hydro-piercing process is also developed to validate the numerical model. The effects of micro-hole parameters, diameter and workpiece thickness, and water pressure on the micro-hole formation are investigated. It is found that the fracture occur near the die corner in workpiece material an...
ABSTRACT There are various surface defects which occur during the hot rolling of steels. It is di... more ABSTRACT There are various surface defects which occur during the hot rolling of steels. It is difficult to correctly identify and control these defects due to the different inspection techniques on different materials and sizes. Also, the statistical data analysis techniques typically used like the principal component analysis, factor analysis etc. require a lot of plant data and are computationally very intensive. Before a detailed analysis of the actual cause of the defects can be done, it is necessary to separate the defects as those coming from the continuous casting or the rolling mill. Once this is done, analysis on the individual components can then be completed to find the root cause. To accomplish both these analysis, Bayesian hierarchical modeling is done on the automated inspection of the bars to form a causal relationship of the defects to the process equipments. Variance reduction model is used at the top of the analysis and regression models are used in the next level.
ABSTRACT Steel bar manufacturing process is a multistage process in which melted steel passes thr... more ABSTRACT Steel bar manufacturing process is a multistage process in which melted steel passes through multiple steps to form into a bar or rod of varying diameters. The most common cause of rejection of such products is the surface defects such as seams, scales, cracks etc. Often automated inspection in the form of image analysis is done to predict the formation of such defects. These inspections suffer from the fact that they do not include the process information and hence are not very reliable. This paper presents a novel methodology of prediction of surface defects in bar manufacturing. In this method, the surface images obtained by inspection methodology are decomposed into individual defects based on process knowledge. These are then decomposed into the physical quantities affecting them which are decomposed into design parameters on rolling mill. To achieve this decomposition, Bayesian hierarchical modeling is used. Data collected from sensors installed on rolling mill are used for model building and design. After the model is built, it is converted into an automated system called Diagnostics on Rolling Mill (DORM). DORM is installed on rolling mill and its performance is evaluated for several days. It is found that the model performs very closely with manual inspection and predicts surface defects with good accuracy. The Bayesian model also gives an insight into process parameters and physical quantities which affect the individual defects.
Journal of Engineering Materials and Technology, 2005
In machining titanium alloys with cemented carbide cutting tools, crater wear is the predominant ... more In machining titanium alloys with cemented carbide cutting tools, crater wear is the predominant wear mechanism influencing tool life and productivity. An analytical wear model that relates crater wear rate to thermally driven cobalt diffusion from cutting tool into the titanium chip is proposed in this paper. This cobalt diffusion is a function of cobalt mole fraction, diffusion coeficient, interface temperature and chip velocity. The wear analysis includes theoretical modeling of the transport-diffusion process, and obtaining tool–chip interface conditions by a nonisothermal visco-plastic finite element method (FEM) model of the cutting process. Comparison of predicted crater wear rate with experimental results from published literature and from high speed turning with WC/Co inserts shows good agreement for different cutting speeds and feed rate. It is seen that wear rates are independent of cutting time.
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Papers by Rajiv Shivpuri