Hamid Ullah

State and Rate Dependent Friction Laws for Modeling High-Speed Frictional Slip at Metal-on-Metal Interfaces

In the present paper the applicability of state and rate dependent friction laws in describing the phenomena of high speed slip at metal-on-metal interfaces is investigated. For the purpose of model validation, results of plate-impact pressure-shear friction experiments were conducted by Irfan in 1998 and Irfan and Prakash in 2000 using a Ti6Al4V and Carpenter Hampden tool-steel tribo pair are employed. In these experiments high normal pressures 1–3 GPa and slip speeds of approximately 50 m /s were attained during the high-speed slip event. Moreover, these experiments were designed to investigate the evolution of friction stress in response to step changes in normal pressure and also in the applied shear stress during the high-speed slip event. A step drop in normal pressure is observed to result in an exponential decay of the friction stress to a new steady-state characteristic of the current normal pressure and the current slip velocity. A step drop in applied shear stress is observed to lead to an initial drop in friction stress, which later increases toward a new steady-state friction stress level. In response to the step drop in applied shear stress the slip velocity initially increases and then decreases to a new steady-state level consistent with the new friction stress level. A modified rate and state dependent friction model that employs both velocity and normal stress dependent state variables is used to simulate the experimental results. A good correlation is found between the experimental results and the predictions of the proposed state and rate dependent friction model. DOI: 10.1115/1.2401217

A Petri net model for the design and performance evaluation of a flexible assembly system

Purpose – The purpose of this paper is to present a Petri net (PN) model based on assembly plan is presented for modeling a flexible assembly system (FAS) configuration, determining an optimal work‐in‐process (WIP), lead time, throughput, and utilization of each station.Design/methodology/approach – PN model is developed for design, analysis, and performance evaluation of a FAS, keeping in view the assembly line balancing. PN is optimized using weighted WIP. The throughput is bounded by the utilization of the bottleneck machines.Findings – The PN optimization gives minimum WIP corresponding to the maximum production rate. Minimum WIP leads to minimum lead time. The weighted arcs make the model simple and reduce the optimized number of kanbans. Moreover, the PN model pushes more inventory to the initial assembly phase. This reduces the total cost of the WIP.Research limitations/implications – In the proposed PN model, the transportation times are included in the transitions times. In the future research, t...

A Petri net model for sequence optimization and performance analysis of flexible assembly systems

Purpose – The purpose of this paper is to present a new generic Petri net (PN) model based on assembly plan for assembly sequence optimization. The model aims to allow modeling the flexible assembly system (FAS) configuration, determining the optimal work in process, lead time, throughput, and utilization of each station. Moreover, it aims to show assembly features (AFs) as being useful in assembly sequence planning.Design/methodology/approach – Sophisticated knowledge of AFs is used to get very few feasible assembly sequences (ASs) rather than all possible ASs for a product. A PN model is developed to find out the near optimal assembly sequence out of the sequences obtained from the AF knowledge. It is also used for design and performance evaluation of FAS. Multiple optimization criteria are used for assembly sequence optimization, keeping in view the line balancing. The PN is optimized using weighted‐WIP when the throughput is bounded by the utilization of the bottleneck machines.Findings – The results ...

Petri net versus queuing theory for evaluation of FMS

Purpose – Petri net (PN) and queuing theory are used in performance analysis of a flexible manufacturing system (FMS). They are used to determine the FMS measures of performance. These measures of performance include optimal work‐in‐process (WIP), lead time, production rate, machine utilization, and number of servers at each station. The purpose of this paper is to present a comparison between PN and queuing network tools to determine the optimum values for FMS measures of performance.Design/methodology/approach – PN model with dual kanban and closed queuing network are used for analysis and performance evaluation of FMS. Integrated network analyzer and Lingo softwares are used for performance evaluation of FMS by PN tool. CANQ software is used for performance evaluation of FMS by queuing network. In both the approaches, the throughput is bounded by the utilization of the bottleneck machines.Findings – The comparison shows that for the given number of servers, PN gives better values of performance measure...

Assembly Features: definition, classification, and usefulness in sequence planning

Unique definition and classification of assembly feature are presented. Assembly features definition is provided using the concept of assembly intents. Assembly features classification is done based on useful assembly-specific information. Assembly features provide information that result in a smaller number of assembly sequences that have to be checked in assembly sequence optimisation. Due to the reduction in assembly sequences, AND/OR graph not only reduces considerably but also becomes very simple. This can result in a significant reduction in the computation time for assembly sequence planning. Real-life examples are given to demonstrate how assembly features are useful in sequence planning.

Integration of flexible purchasing, flexible manufacturing and flexible assembly systems using Petri net

The purpose of this paper is to present a new generic deterministic Petri net (PN) model for the integration of flexible purchasing system (FPS), flexible manufacturing system (FMS) and flexible assembly system (FAS) using kanban system in a pull environment. In the methodology and/or approach used in this paper, firstly the basic building blocks of the system are developed. The building blocks are then combined together to get a PN model that integrates FPS, FMS and FAS. The model integrating FPS, FMS and FAS is called flexible integrated system in this paper. Integrated Network Analyser and Lingo software are used for performance evaluation of the system. The performance evaluation of the PN model is based on solution of linear programming. The throughput is bounded by the utilisation of the bottleneck station.

Mathematical modelling of feature conversion

After providing the assembly feature definition and mathematical representation, this paper addresses the problem of how to convert design features into assembly features, with the help of a mathematical model of feature conversion. Assembly feature is defined and represented mathematically using the concept of assembly intents. Some very useful information that can be obtained from the assembly features are mentioned. The mathematical model of feature conversion is represented by a mapping function which is a synthesis function of two process mapping functions. The process of feature mapping is demonstrated with the help of a real-life example.

Inclusive design: a step toward social integration and dependency elimination

The basic problems to stimulate the need for inclusive design are described. The key issues and approaches adopted by various groups, organisations, and researchers for solution of the basic problems are investigated. Two new terminologies for inclusive design (design for independence and design for integration) are proposed, which are more meaningful compared to the already exiting terminologies. A new and broad definition of inclusive design is also provided which gives emphasis on four important priorities of inclusive design, namely, flexibility, ergonomics, independence and integration. The important segments of a community responsible for playing their roles in the area of inclusive design are highlighted. The research trends and developments in the area of inclusive design and the various advantages inclusive design can offer are presented.

COMPARISON OF LINKER AND DIETERICH FRICTION MODELS WITH PRAKASH MODELS FOR SIMULATION OF HIGH-SPEED FRICTION

This paper compares Linker and Dieterich models with Prakash models to simulate shear resistance. One of the mathematical models on sliding friction was developed by Linker and Dieterich (1992) under quasistatic conditions using low normal stresses and low sliding velocities. Prakash (1998) developed mathematical models under High Speed Machining applications, using high normal stresses and high sliding velocities. Linker and Dieterich models show that a step change in normal stress causes a sudden change in shear stress, while Prakash models show that a step change in normal pressure gives an exponential change of the shear stress to a new steady stale, characteristic of the current normal pressure and the current slip velocity. Prakash models have been found suitable for simulation of shear resistance at tool-workpiece interface during high speed machining applications.