Machine tools are static power driven machines that are used to shape the work piece material or parts made of metals.
The shaping of the work piece materials are done in four ways they are
- From the work piece materials the excess parts are removed in the form of chips with the help of the tools.
- By shearing (cutting) the material
- By holding the metallic parts to obtain preferred shape.
- By applying the ultrasounds, electricity or corrosive chemicals to the work piece material to obtain a shape.
With the help of the different machines we can remove the chip from the work piece material the machines are milling machine, lathes, planer, shaper, drilling machine and grinders.Advertisement:
Machine Tool features:
Machine consists of tools and work holding devices. The depth of cut is controlled to obtain accuracy. The relative motion between the tool and the cutting edge is known as the cutting speed. When the uncut material comes in contact with the tool at certain speed then it is known as feed motion. Overheating of the tool leads to the loss of ability in the cutting forces. The generated heat must depend on the cutting speed and shear force. The shearing force must vary with the material being cut, and for high temperatures the tolerances varies with respect to the tool materials. The cutting depth speed must depend on the cutting tool material and material being cut. The shear force varies with the cut of material. The cutting material must being cut, and the tool material must vary with the tolerances for greater temperatures.
The cutting tools are divided into two types; they are single point cutting tool and multipoint cutting tool. Single point cutting tool is used to increase the holes size or boring. The multi-point cutting tools are used in the broaches, drills, milling cutters, and they have two or more cutting edges. Boring mills and lathe are used to perform the boring and turning operation.Advertisement:
Types of operations:
They are two types of operations. They are
- By keeping the work piece stationary and moving the tool along straight line path. Ex: Shaper machine
- By keeping the tool stationary and moving the work piece. Ex: Planer machine
During the process one needs to provide a rake angle for the formation of the chip, to reduce the heat and friction. Clearance angle is provided to prevent the below tool surface. Due to the rubbing action of the cutting tools, which can lead to the damage of the tip angle where the clearance angle is provided.
Materials used for tools:
For removal of the metal from the work piece material the cutting tool must be harder than the work piece material. During the time of cutting action friction is developed, at those temperatures cutting edge is maintained.
Different types of tool materials are:
High speed steels
Carbon steel is a combination of the carbon and steel. The carbon content present in the formation ranges from 1 to 1.2% that is used in the machine tool material. Compare to the other cutting tools carbon steel are less expensive, but one can see loose cutting ability at 205 temperature.
Cast alloys are the non-ferrous alloy materials. The mixture consists of chromium, tungsten and cobalt. They are mainly operative in penetrating the thick skinned on cast iron, and also to maintain the cutting capability even when red hot.
Cobalt consists of tungsten carbide. The hardness of the tungsten carbide is nearly equal to the diamond. The tools are operated at higher cutting speeds those are used with the high speed steels.
The diamonds are used in the wire drawing dies, grinding wheels and also in cutting tools. They are mainly used in the grinding wheels they acts as an abrasive particles. The diamonds are also used for cut finishing operations in the grinding wheels.
High speed steels
The composition present in the high speed steels are 18% tungsten, 4% chromium, 1% vanadium and 0.5 to 0.8% carbons are present.
In the cutting tool material oxides, ceramic, tool tips are developed. The oxide consists of aluminum oxide grains which are limited.
Cutting fluids are also known as coolants. They are used to reduce the friction and temperature present during the machining process. Coolant must act as a lubricant. Mainly in the cutting operation the coolant is required. Water acts as a best coolant medium, but it corrodes the ferrous materials.
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