Tools

GENERAL INTRODUCTION of MACHINE TOOLS

ToolsIt is the part in contact with the job for doing different operation or generation of surfaces is called tool. It may be classified according to the power supplied to it as a) Hand tools and b) Machine tools.

2Hand toolsHand tools are tools which are held and used by the hand for shaping and sizing the work. There is no mechanism in them. The quality and accuracy of the job depends on the performance of the operator. For example Files, Saw, Chisel etc. are the hand toolsMachine tools Machine tool is a device provided with mechanisms which enable a cutting tool up on a piece of material to produce the desire shape and size by cutting away material in the form of chips. Generally for such operations hand power is insufficient and prime mover is used to supply power to the machine. In most of the cases both the job and the tool held rigidly with the machine. Lathe, Drilling machine, Boring machine etc. are the example of machine tools.

3MACHINEA machine is a combination of mechanisms intended for transference, transformation or utilization of energy. e. g. Printing press.MECHANISM A mechanism is used to transfer or transform motion from one element into another.

4Classification of machine tools

According to the purpose1. a) General purpose machine tools: This type of machine tools are used for general machining operations. These are also called as Basic machine tools. Lathe, Drilling machine, Shaper, Milling machine etc. are the General purpose machine tools.1. b) Production purpose machine tools: The machine tools which are used to produce similar type of job at very high rate, called as production purpose machine tools. In this type of machines generally special accessories and multiple tools are used. Capstan Lathe, Turret Lathe, Copying Lathe, Plano-miller etc. are production purpose machine tools.1. c) Special purpose machine tools: The type of machine tools which are used to produce a particular type of job in large numbers, are called as Special purpose machine tools. For example Crank Shaft Grinder, Screw Cutting Machine etc.1. d) Transfer machine tools: The machine tool in which a number of machine tools are arranged in the sequence of operation to act as a single unit, is called transfer machine tools. The job is fed at one end and it will automatically transfer from one machine to other and finally finished job is produced. The operating cost of such machine is less.1. e) N.C & C.N.C. machine tools: These are the most modernized machine tools and replacing the conventional machine tools. In N.C. machine punched tape is used to control job and tool motion of the machine. In case of C.N.C. machine computerized sequence program is used to control the job-tool motion in the machine. Both the accuracy and rate of production of these type of machines are very high but suitable only when similar type of jobs are to be produced in large numbers or in mass production.According to the type of surface generated2. a) Plane surface: The machine used to produce plane flat surfaces are fall in this category, such as Shaper, Planer etc.

2. b) Curved surface: The machine used to produce curved surfaces in the work, fall in this category, such as Lathe, Drill etc

2.c) Gear teeth : These type machines are used to produce gear teeth. Such as Milling machine, Hobbing machine etc.

According to the motion of the tool3. a) Stationary tool: The machines in which tool remains fixed during machining operations. For example Lathe, Boring machine etc in which the tool remains fixed during operation but feeding motion is given to the toll.

3. b) Rotary tool: In this type of machine tool rotates during machining operations. For example Drilling machine, Milling machine etc.

3. c) Reciprocating tool: this type of machine tool reciprocates during machining operations. For example Shaper, Planer etc.

Common elements of machine toolA machine tool must have the following elements Base and Frame: This is the skeleton of the machine tool. Strength and rigidity of the machine tool primarily depends on the construction of its base and frame and hence accuracy and quality of surface finish also depends on it.

Prime mover: Prime mover is the source of power to be supplied to the machine during its operation. Generally electric motor is used for this purpose.

Transmission mechanism: It is the process by which power from the prime mover is transmitted to the desired places in the machine tool to perform the required operations.

Job holding devices: In each machine tool provisions must be there to hold the job rigidly in the desired position so that machining operations can be performed by the machine tool easily.

Tool holding mechanism: Suitable tool holding mechanism must present in the machine tool so that the tool can be removed and fitted easily and also provide desired rigidity.

Guide ways: In each machine tool, there is relative movement between the job and the tool. Such relative movement is controlled by the guide ways. This guide ways not only allows relative motion but also ensures proper strength and rigidity of the machine.

Purpose or function of machine toolIt gives desired shape and size of the job by removing all excess material in the form of chip.It holds and supports the job to be machined.It holds and supports the tool used for machining.It regulates proper relative motion between the job and tool.It provides proper speed, feed and depth of cut during machining operation.Accuracy of machine toolAccuracy of a machine tool primarily depends on the following factors Strength : All parts of the machine tools must have sufficient strength to withstand the cutting force.Rigidity : It is property by virtue of which it resist deformation under external load. So all parts of the machine tool must have sufficient rigidity for higher accuracy.Wear Resistance : In every machine tools, job-tool relative movement is there. Naturally wearing of the guide ways reduces accuracy of the machine. So especially the guide ways of the machine tolls must have high wear resistance capacity.Damping capacity : Damping is the phenomenon of absorbing vibrations. Machine tool parts especially the base and frame must possess high damping characteristic.

Types of machine tool driveMachine tool drive is the transmission system through which power of the prime mover is transmitted to the different required places of the machine tool and thereby helps in material removing. Generally following drives are used for transmission of power in machine tools Types of machine tool drive Mechanical Drive: Almost every machine tool the source of power is an electric motor. The power of such motor is transmitted to the tool or job or to the both through different mechanical drives. Gear, Chin & Sprocket, Belt & Pulley, Rack & Pinion etc. are the example of mechanical drives. Electrical Drive: Though the main source of power is an electric motor but sometimes in machine control of electrical power controls the power received at the job or tool or both. Such drives are called electrical drive. Hydraulic Drive: Sometimes hydraulic drives are used to control of the job or tool or both. Such drives are called as hydraulic drive.

Elements of machine tool drive

machine tools drives 1. Individual Drive or Self Contained Drive :

In this system each machine has its own prime mover. Generally electric motor and starter is used for this purpose. Power of the motor is directly transmitted to the machine by belt or chain or coupling. Now a days this system becomes very popular because of the following advantages

Considerable economy in power transmission or loss of power for transmission is less.Failure of motor cause a particular machine idle, not the entire work shop.Good control of speed and power.Wide range of speeds is available.Less work hazard.Easy in maintenance.

machine tools drives 2. Group Drive :In case of group drive one high capacity motor is used to drive all the machines present in the shop floor. In this system the motor drives one line shaft or lay shaft or main shaft. Power from this shaft is transmitted to the machine counter shaft through loose pulley & fast pulley and flat belt. Thus running and stopping of a particular machine is possible. This system has low initial cost but at the same time it has got following disadvantages

Loss of power is more.In case of motor failure, all the machines become idle.Work hazard is more.Variation of speed and power is limited.Layout of the shop floor is complicated.During replacement of belt for a particular machine cause all the machines idle.