Pramod Kumar Jain

Advanced optimal tolerance design of mechanical assemblies with interrelated dimension chains and process precision limits

Tolerance design is an important step in product development. The topic has been under extensive research, which has resulted in several formulations and solution algorithms for systematic tolerance design considering various aspects. An optimal tolerance design problem involving alternative manufacturing processes for realization of a dimension can be referred to as the advanced tolerance design problem, where the optimal selection of a set of manufacturing processes is also considered in addition to the optimal set of tolerances. Such a nonlinear multivariate optimal tolerance design problem results in a non-convex combinatorial solution surface. Optimal solution of the advanced tolerance design problem is difficult with the traditional optimization techniques. The problem becomes more complex with the assemblies involving interrelated dimension chains, and manufacturing processes bracketed by precision bounds. The focus of this work is on the optimal solution of the aforementioned advanced tolerance design problem. Genetic algorithm, a non-traditional global optimization technique has been proposed as the solution methodology for its inherent advantages. Application of the methodology has been demonstrated with the help of suitable examples. Concept of the set up reduction constraints has also been introduced, wherein all the similar dimensions on a single part are manufactured on a single machine, resulting in a single value of design tolerance associated to all such dimensions.

Concurrent optimal adjustment of nominal dimensions and selection of tolerances considering alternative machines

Traditional practice to tolerance design has been a part of a three-step sequential approach to the overall product design process involving (i) conceptual design, (ii) parameter design, and (iii) tolerance design, in isolation. This practice works well for linear assemblies, as the sensitivities of tolerances are fixed, i.e. independent of the nominal dimensions. However, for nonlinear assemblies after the second step, an integrated approach involving minor adjustment of nominal dimensions and selection of tolerances in the third step, can be better to control the variability in the assembly output characteristic. The latter case has been addressed in this study. Simultaneous selection of design and manufacturing tolerances, and choice of a machine from amongst the alternatives, frequently encountered in different stages of realization of individual dimensions, are important issues in product development. Optimal design problem with focus on these issues has been attempted here. The resulting optimization problem involving a combinatorial and nonlinear search space cannot be effectively solved for the global solution using conventional optimization techniques. The genetic algorithm, a nontraditional optimization technique, has been proposed in this research. The solution of the aforementioned concurrent design problem has been demonstrated with the help of a simple case study.

Preliminary manufacturability analysis using feature-function-resource considerations for cylindrical machined parts

This research paper presents a methodology for implementation of the Design for Manufacturability concept using integrated feature-function and resource information. A part is modelled using a feature-based CAD modeller and the parts feature attributes are mapped from the design space to the manufacturing space using the developed spreadsheet-based part model on top of the CAD solid modeller. The concept of feature-function analysis is introduced to integrate the designers intent (function) with that of the manufacturers about the manufacturability. Feature-function analysis is carried out to check the assigned design and technological attributes against the recommended values in the database. The factors affecting the manufacturability have been investigated and a manufacturability measure composed of a weighted sum of technological, assembly and form complexity indices is proposed to evaluate the manufacturability of a part. Fuzzy sets are used to capture the complex relationship between design and manufacturing aspects, which has a direct and/or indirect effect on the manufacturability of the part. An example part has been taken to demonstrate the system capability.

Mixture D-Optimal Desing of Electrolyte Composition in ECH of Bevel Gears

In Electrochemical Honing (ECH), most of the metal is removed by electrolytic dissolution and therefore, the electrolyte composition plays a crucial role in the study. This paper presents the experimental investigation to find out the optimal electrolyte composition in improving surface quality of gear teeth profile during surfacing finishing of bevel gears by ECH process. In this study, mixture of sodium chloride and sodium nitrate in different ratios were used as input parameter and the percentage improvement in bearing ratio of gear teeth profile was used as response parameters while the experimental runs were designed and planned according to the Mixture D-Optimal design. Analysis of variance was carried out and optimal electrolyte composition was investigated to conduct the confirmation experiment.

Study of electrochemical-mechanical finishing of bevel gears

This study discusses the performance assessment of high precision finishing of bevel gears by electrochemical-mechanical finishing (ECMF) process. In the present study, experimental investigation has been carried out on an indigenously developed experimental setup for ECMF of bevel gears of AISI 1040 steel to evaluate the process capability in improving the surface quality of gear teeth profile. Surface integrity of ECMFed surface was analysed and it was found that the process has capability to enhance the surface quality of gear teeth profile by minimising the irregularities. The emphatic features of the newly developed experimental setup have also been discussed.

Performance modeling of reconfigurable manufacturing system for different dispatching strategies under exception

A Reconfigurable Manufacturing System (RMS) is having potential for quick adjustment in its production capacity and functionality. These RMSs are considered to be one of the technologies enabling shorter lead times, more product variants, fluctuating volumes of products, shorter product life cycles and lower cost. This paper presents the performance modeling of a hybrid system comprising of dedicated and reconfigurable machine tools simultaneously. The modeling focuses on handling of exceptional situations. One such handling situation arises when there is a breakdown of any resource like machine within the system. The dedicated machines are subjected to random failures and once there is the failure, the jobs are transferred to the reconfigurable machines after suitable reconfiguration to carry out the sequential operation required on the job. Two different production scenarios, first, operation of the system over some predetermined period of time and, secondly, operation of the system for a fixed quantity of products were modeled using ARENA® discrete event simulation software. Three different dispatching strategies for reactive scheduling of parts based on total average waiting time in queue, total downtime of the failed machine and capacity of the buffer in between the machines were analyzed. The performance of the system was analyzed in terms of productivity, congestion and make-span time. Finally, the results were analyzed and were discussed in the light of previous researches carried out on the topic.

Machinability Studies in Hot Machining of Ti-6Al-4V Alloy

This work presents the influence of workpiece preheat temperatures on the machinability of Ti-6Al-4V alloy and chip formation. Machinability has been studied in terms of cutting forces, surface roughness and tool wear. Influence of preheat temperatures on chip morphology and roughness of chip back surface has been studied using scanning electron microscope and atomic force microscope respectively to get better insight of tribology at tool-chip interface. Based on overall observations, preheat temperature of 300 0C was found as the most appropriate parameter.

Modelling and experimental study of chip serration frequency in dry turning of Ti-6Al-4V alloy

This paper presents the investigation on the effects of cutting speed, feed rate and depth of cut on chip serration frequency in dry turning of Ti-6Al-4V alloy. The chip serration frequency plays a vital role in determining the machinability of this alloy as the serrated chips are observed at low cutting speed. Serrated chip formation causes a cyclic variation of cutting forces and often leads to serious vibrations resulting in chatter. The chip serration frequency is calculated by the distance between two consecutive shearing planes. Using the results of experiments, a regression model has been developed for chip serration frequency. Based on analysis of variance at 95% confidence interval the model is found to be highly significant. Cutting speed is found to be the most significant factor affecting the chip serration frequency. The effect of feed rate is much less and that of the depth of cut is insignificant.

Optimal Configuration Selection in Reconfigurable Manufacturing System

Reconfigurable manufacturing system (RMS) is considered as a major resource of providing variable production capacities and capabilities by different manufacturing companies. For different products needed in small quantities and with short delivery lead time, this is achieved through reconfiguring the system elements over the time. In the present work, various characteristics of RMS have been discussed and formulated. Weighted sum theory has been used for the selection of best manufacturing system. An illustration is given to analyze the applicability of the proposed methodology on a given system.

Study on ultrasonic-assisted electrochemical honing of bevel gears

Electrochemical honing of gears is a productive, high-accuracy, micro-finishing and long tool life gear finishing process in which material is removed by combined action of electrolytic dissolution and mechanical scrubbing action. The use of ultrasonic-assisted electrochemical honing of gears is first proposed, and it may help to enhance the process performances of the classical electrochemical honing process by scrubbing the complete surface of the gear tooth. In this technique, the honing gear is attached on the ultrasonic vibrator to provide the ultrasonic vibrations on the workpiece surface. The focus is on an optimization of the process parameters of ultrasonic-assisted electrochemical honing of bevel gear made of AISI 1040 carbon steel. The result of experiments reveals that the applied high ultrasonic frequency (kHz) on the workpiece has the maximum influence on the process performance. The maximum percentage improvement in average and maximum surface roughness using ultrasonic-assisted electrochemical honing of bevel gear is 91.04 and 71.98, respectively. The results confirm that the ultrasonic-assisted electrochemical honing can produce a better tooth surface roughness than the electrochemical honing. This will improve bevel gear efficiency and reliability in operation.