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Machine Tools Objectived.

Machine tools are the main engines of the manufacturing industry. This chapter covers a few of the details that are common to all classes of machine tools discussed in this book. After completing the chapter, the reader will be able to

>understand the classification of the various machine tools used in manufacturing industries.

>identify the differences between generating and forming of surfaces. > identify various methods used to generate different types of surfaces. >distinguish between the different accuracies and surface finishes that are achievable with different machine tools.

>understand the different components of the machine tools and their functions.

>learn about the different support structures used in the machine tools. >understand the various actuation systems that are useful to generate the required surfaces.

>Learn the different types of guideways used in the machine tools.

>understand the work holding requirements.

3.1 INTRODUCTION

The earliest known machine tools are the Egyptian foot-operated lathes.

These machine tools were developed essentially to allow for the introduction of accuracy in manufacturing.

A machine tool is defined as one which while holding the cutting tools, would be able to remove metal from a workpiece in order to generate the requisite job of given size, configuration, and finish. It is different from a machine, which is essentially a means of converting the source of power from one form to the other. The machine tools are the mother machines since without them, no components can be produced in their finished form. They are very old and the industrial revolution owes its success to them.

A machine tool is required to provide support to the workpiece and cutting tools as well as provide motion to one or both of them in order to generate the required shape on the workpiece. The form generated depends upon the type of machine tool used.

In the last two centuries, the machine tools have been developed substantially. The machine tool versatility has grown to cater to the varied needs Of the new inventors coming with major developments. For example,James Watt's steam engine could be proven only after a satisfactory method was found to bore the engine cylinder with a boring bar by Wilkinson around 1775.

A machine tool is designed to perform certain primary

functions,but the extent to which it can be exploited to perform secondary functions is a measure of its flexi bility.Generally,the flexibility of the machine tool is inc reased by the use of secondary functional attachments,s uch as radius or spherical turning attachment for a cent re lathe.Alternatively,to improve productivity,special atta chments are added,which also reduce the flexibility.

3.2CLASSIFICATION OF MACHINE TOOLS

There are many ways in which the machine tools can be classified.One such classification based on the produc tion capability and application is shown below:

1.General purpose machine tools(GPM)are those designed to perform a variety of machining operations on a wide range of components.By the very nature of generalisation,the general purpose machine tools are thou gh capable of carrying out a variety of tasks,would no t be suitable for large production,since the setting time for any given operation is large.Thus,the idle time on the general purpose machine tools is more and the mac hine utilisation is poor.The machine utilisation may be termed as the percentage of actual machining or chip g enerating time to the actual time available.This is muc