Design

To design is either to formulate a plan for the satisfaction of a specified need or to solve a problem. If the plan results in the creation of something having a physical reality, then the product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable.

Design is an innovative and highly iterative process. It is also a decision-making

process. Decisions sometimes have to be made with too little information, occasionally with just the right amount of information, or with an excess of partially contradictory information. Decisions are sometimes made tentatively, with the right reserved to adjust as more becomes known. The point is that the engineering designer has to be personally comfortable with a decision-making, problem-solving role.

Design is a communication-intensive activity in which both words and pictures are used, and written and oral forms are employed. Engineers have to communicate effectively and work with people of many disciplines. These are important skills, and an engineer’s success depends on them.

A designer’s personal resources of creativeness, communicative ability, and problemsolving skill are intertwined with knowledge of technology and first principles.

Engineering tools (such as mathematics, statistics, computers, graphics, and languages) are combined to produce a plan that, when carried out, produces a product that is functional, safe, reliable, competitive, usable, manufacturable, and marketable, regardless of who builds it or who uses it.

Mechanical Engineering

McGraw−Hill Primis

ISBN: 0−390−76487−6

Text:

Shigley’s Mechanical Engineering Design,

Eighth Edition

Budynas−Nisbett

Shigley’s Mechanical Engineering Design,

Eighth Edition

Budynas−Nisbett

McGraw -Hill

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Design Activities

People have always designed things. One of the most basic characteristics of human beings is that they make a wide range of tools and other artefacts to suit their own purposes. As those purposes change, and as people reflect on the currently-available artefacts, so refinements are made to the artefacts, and sometimes

completely new kinds of artefacts are conceived and made. The world is therefore full of tools, utensils, machines, buildings, furniture, clothes, and many other things that human beings apparently need or want in order to make their lives better. Everything around us that is not a simple untouched piece of Nature has been designed by someone. 

In traditional craft-based societies the conception or 'designing' of artefacts is not really separate from making them; that is to say, there is usually no prior activity of drawing or modelling before the activity of making the artefact. For example, a potter will make a pot by working directly with the clay, and without first making

any sketches or drawings of the pot. In modern industrial societies, however, the activities of designing and of making artefacts are usually quite separate. The process of making something cannot normally start before the process of designing it is complete.

In some cases- for example, in the electronics industry- the period of designing can take many months, whereas the average period of making each individual artefact might be measured only in hours or minutes.

Perhaps a way towards understanding this modern design activity is to begin at the end; to work backwards from the point where designing is finished and making can start. If making cannot start before designing is finished, then at least it is clear what the design process has to achieve. It has to provide a description of

the artefact that is to be made. In this design description, almost nothing is left to the discretion of those involved in the process of making the artefact; it is specified down to the most detailed dimensions, to the kinds of surface finishes, to the materials, their colours, and so on.

In a sense, perhaps, it does not matter how the designer works, so long as he or she produces that final description of the proposed artefact. When a client asks a designer for 'a design', that is what they want: the description. The focus of all design activities is that end-point.

Engineering Design Methods

Strategies for Product Design

THIRD EDITION

Nigel Cross

The Open University, Mi/ton Keynes, UK

JOHN WILEY & SONS, LTD

Chichester- New York. Weinheim • Brisbane. Singapore. Toronto

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Grinding Process

The tool in the grinding process is the grinding wheel, which is generally composed of two materials: grits and bonding agent. The hard abrasive grits (small hard particles) are affixed to rotating hub or axis in the

general configuration of a wheel to erode material away from a workpiece as the wheel spins. Grinding wheels are formed into shape by casting and curing a slurry of bonding material with the grits. The cured wheel forms a three-dimensional matrix of grits held in place by the bonding agent. This yields a complex operation by nature, as the uneven and truly random distribution of grit surfaces of the wheel and the contact they make with the ground part are difficult at best to systematically model.

History and Perspective

Abrasive material removal (grinding) is one of the oldest machining technologies employed today, and has been utilized by people in the manufacturing of parts since the Stone Age (Malkin, 1989). A simplified grinding process can be thought of as milling using a “cutter” with a large number of teeth of irregular

shape, size, and spacing (Fig. 3.2.). Each grit can be seen as a cutting tooth with varying orientation and

sharpness. These grits are suspended in a bonding agent that holds the three-dimensional matrix of grits

together in a form. The grinding process can vary for many reasons including: wheel sharpness, wheel microstructure, workpiece material variation, loading of workpiece material on the wheel, and other phenomena that contribute to the changing nature of the grinding process. (Loading is the phenomena of the ground material becoming attached to or embedded onto the surface of the grinding wheel. This effect begins with the material filling in the voids around the grits, and if permitted to continue, the material can eventually cover the grits. This occurs more commonly with softer materials.)

The variable nature of the grinding process has been linked to the physical descriptions of the actions between the grits with the workpiece. Grinding is a complex operation that can be seen as three separate and concurrent process actions: (1) cutting, (2) plowing, and (3) rubbing (Hahn and Lindsay, 1971; Samuels, 1978; Salmon, 1992). The cutting action produces tangential forces that are related to material specific energy in the generation of chips. Although a small part of this energy is transferred to the chip as kinetic energy, the majority of the material specific energy is dispersed in several other ways including: friction, heat conduction, radiation, surface formation, residual stresses, etc. The second grinding process action is plowing. In plowing material is plastically deformed around the sides of dull grits, leading to ruts and uneven surfaces. No material is removed with plowing. Rubbing occurs as material loads onto the wheel or if the grits are exceptionally dull (causing attritious flat wear). Rubbing is a high friction condition with essentially no material removal and is the most detrimental of the three grinding actions.

The generated frictional heat (that can yield “burning”) from rubbing is dissipated into both the ground

part and the wheel. If coolant is not used, thermal damage may occur. Damage created from excess forces

or from plowing ruts can be hidden by the migration of material during rubbing, only to result in premature failure of the part in use. In general, all three grinding process actions occur simultaneously in varying distributions depending on the grinding wheel, material, and operating conditions. As stated previously grinding is stochastic by its nature, making detailed process analysis, modeling, and control difficult. This is also brought out by the variety and complexity of grinding models presented later.

COMPUTER-AIDED DESIGN,

ENGINEERING, AND MANUFACTURING

Systems Techniques And Applications

VOLUME

V I

Editor

CORNELIUS LEONDES

Boca Raton London New York Washington, D.C.

CRC Press

MANUFACTURING

SYSTEMS PROCESSE

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LATHE

INTRODUCTION

The lathe is father of all machine tools; in early days it was equipped with a fixed tool rest and was used for woodworking. In operation, the lathe holds the job between two rigid supports called centres or by some chuck or face plate screwed to the nose or and of the spindle.

Function of lathe

The main function of lathe is to remove metal from a piece of work to give it the required shape and size. This is accomplished by holding the work securely and rigidly on the machine and then turning it against cutting tool, which will remove, metal from the work in the form of chips.

Types of lathes

Lathes of various designs and constructions have been developed to suit the various conditions of metal machining. But all of them employ the same fundamental principle of operation and perform the same function. The lathes are classified as follow.

1. Speed lathe

 Wood working

 Centering

 Polishing

 Spinning

2.Engin lathe

 Belt drive

 Individual motor drive

 Gear head lathe

3.Bench lathe

4.Tool room lathe

5.Capstan and turret lathe

6.Special purpose

Wheel lathe

 Gap bed lathe

 T-lathe

 Duplicating lathe

7.Automatic lathe

The speed lathe

 The speed lathe, in construction and operation, is the simplest of all types of lathes. It consists of a bed, a headstock, and a tailstock and tool post mounted on an adjustable slide. There is no feed box, lead screw or conventional type carriage. The tool is mounted on the adjustable slide and is fed into work purely by hand control. This characteristic of the lathe enables the designer to give high spindle speeds, which is usually, range from 1200 to 3600 r.p.m. As the tool is controlled by hand, the depth of cut and thickness of chip is very small.

 Light cut and high speed necessitate the use of this type of machine where cutting force is minimum such as in wood working, spinning, centering, polishing, etc.

The engine lathe or center lathe

This lathe is most important member of lathe family and is most widely used. Similar to the speed lathe, the engine lathe has got all the basic parts, e.g. bed, headstock, and tailstock. But the headstock of an engine

lathe is much more robust in construction

and it contains additional mechanism of driving the lathe spindle at multiple speeds.

The engine lathe that can feed the cutting tool both in cross and longitudinal direction with reference to the lathe axis with help of a carriage feed rod and lead screw.

The bench lathe

This is a small lathe usually mounted on bench. It has practically all the parts of an engine lathe or speed lathe and it performs almost all the operations, its only difference being in size this is used for small and precision work.

The tool room lathe

A tool room lathe having features similar to an engine lathe is much more accurately built and has a wider range of spindle speeds ranging from a very low to a quite high speed up to 2500 r.p.m.This lathe is mainly used for precision work on tools, dies, and gauges and in machining work where accuracy is needed

Numerically Controlled Lathes

In these lathes the path of the tools to produce the desired shape, along with other auxiliary functions like speed/feed changes, turret indexing, tail stock positioning, coolant supply, etc., are controlled by pre-programmed numerical data input in the form of punched tape to an electronic control system. One of the latest developments is the computer control of NC machines which is popularly called the computer numerical control (CNC). With the concept of numerical control, the configuration of lathes has undergone radical changes with features like slant bed design infinitely variable seed headstock, antifriction lead screws, auto-tool changing, etc. Numerically controlled lathes are available in various versions. The control system employed on NC lathes enable straight cut and continuous path control.

The cutting tools on a CN C turning center are usually mounted in a device called a turret. The turret is then mounted on a heavy cross slide and carriage similar to that of a conventional lathe. The turret can be indexed very rapidly to automatically change to the next tool.

A number of smaller CNC lathes have also come to market in recent years to compete with the turret lathes and automatic screw machines.

fr:NETTUR TECHNICAL TRAINING FOUNDATION

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