Manufacturing is the industrial activity that changes the form of raw materials to create products or in other word manufacturing has been accurately defined as the activities that are performed in the conversion of stuff to useful thing (product). It is the application of physical and chemical processes to alter the geometry, property and/or appearances of given starting material to make part or product. The derivation of the word manufacture reflects its original meaning: to make by hand. As the power of the hand tool is limited, manufacturing is done largely by machinery today. Manufacturing technology constitutes all methods used for shaping the raw metal materials into a final product.The development of new tool materials opened a new era for the machining industry in which machine tool development took place.

Machining is the removal of the unwanted material (machining allowance) from the work piece (WP), so as to obtain a finished product of the desired size, shape, and surface quality. The practice of removal of machining allowance through cutting techniques was first adopted using simple handheld tools made from bone, stick, or stone, which were replaced by bronze or iron tools. Water, steam, and later electricity were used to drive such tools in power-driven metal cutting machines (machine tools).

The importance of machining processes can be emphasized by the fact that every product use in our daily life has undergone this process either directly or indirectly. It is important to understand the metal cutting process in order to make the best use of it.

In the metal working industries work piece of different shape, dimension and materials are worked. The various working processes to make these fall into two groups :

Metal Working Chip-less Process (Metal Forming) e.g. forging, pressing , drawing etc.Chip Forming Process (Metal Cutting) e.g. turning, drilling, milling etc.

A Cutting tool may be used either for cutting apart, as with a knife, or for removing chips. Part are produced by removing metal mostly in the form of small chips.

All cutting tools can be divided into two groups they are: Single point cutting tools Multi-Point cutting tools

Single point cutting tool having a wedge like action find, a wide application on lathe, and slotting machine. Multi point cutting tools are merely two or more single point tools arrange together as a unit.TYPE OF CUTTING TOOLS

SINGLE POINT CUTTING TOOLS FOR LATHE MACHINE

MULTI POINT CUTTING TOOLS

MULTI POINT CUTTING TOOLS

MECHANICS OF CUTTING AND CHIP FORMATION In figure tool is considered stationary, and the work-piece moves to the right. The metal is severely compressed in the area in the front of cutting tool. The metal in front of the tool rake face gets immediately compressed, first elastically and plastically. This zone is traditionally called shear zone.

CHIP F0RMATIONThe metal in front of the tool rake face gets immediately compressed first elastically and then plastically.The actual separation of the metal starts as a yielding or fracture, depending upon the cutting conditions, starting from the cutting tool tip. The chip after sliding over the tool rake face would be lifted away from the tool, and the resultant curvature of the chip is termed as chip curl.

Mechanics of cutting and Chip Formation Metal cutting as a slide of card which would slide over one another as the wedge shape tool moves under these cards as shown in figure.

The chip is variable both in size and shape in actual manufacturing practice. Study of chip is one of the most important things in metal cutting.

FOUR BASIC TYPES OF CHIP IN MACHININGWhether the cutting condition can be, the chip produced may belong to one of the following type :

Discontinuous chipContinuous chipContinuous chip with Built-up Edge (BUE)Serrated chip

Brittle work materialsLow cutting speedsLarge feed and depth of cutHigh toolchip friction DISCONTINUOUS CHIPS

DISCONTINUOUS CHIPSDiscontinuous ChipWhen brittle materials like cast iron are cut, the deformed material gets fractured very easily and thus the chip produced is in the form of discontinuous segments.Cutting force becomes unstable with the variation coinciding with the fracturing cycle.Higher depths of cut (large chip thickness), low cutting speeds and small rake angles are likely to produce discontinuous chips.

Ductile work materialsHigh cutting speedsSmall feeds and depthsSharp cutting edgeLow toolchip frictionCONTINUOUS CHIPS

CONTINUOUS CHIPS Continuous chips are usually formed at high rake angles and/or high cutting speeds.A good surface finish is generally produced.Continuous chips are not always desirable, particularly in automated machine tools,Tend to get tangled around the toolOperation has to be stopped to clear away the chips.

CONTINUOUS CHIP FORMATION

Ductile materialsLowtomedium cutting speedsTool-chip friction causes portions of chip to adhere to rake faceBUE forms, then breaks off, cyclically

BUE consists of layers of material from the workpiece that are gradually deposited on the tool.

BUE then becomes unstable and eventually breaks up

BUE material is carried away on the tool side of the chip

The rest is deposited randomly on the workpiece surface.

BUE results in poor surface finish

Reduced by increasing the rake angle and therefore decreasing the depth of cut.

Semi continuous - saw-tooth appearance

Cyclical chip forms with alternating high shear strain then low shear strain

Associated with difficult-to-machine metals at high cutting speeds

Various chips produced in turning: (a) tightly curled chip; (b) chip hits workpiece and breaks; (c) continuous chip moving away from workpiece; and (d) chip hits tool shank and breaks off. Source

There are method of metal cutting, depending upon the arrangement of the cutting edge with respect to the direction of relative work-tool motion:Orthogonal cutting or two dimensional cuttingOblique cutting or three dimensioning cuttingOrthogonal cutting take place when the cutting face of the tool is 90 to the line of action or path of the tool. If, however, the cutting face is inclined at an angle less than (other than 90) 90 to the path of tool, the cutting action is known as oblique. Orthogonal cutting or two dimensional cutting

In orthogonal cutting, the cutting edge of the cutting tool is arrange perpendicular to the cutting velocity (V), where in oblique cutting, it set at some angle other than 90 to the cutting velocity (v), which gives an inclination angle . The analysis of oblique cutting being very complex, the relatively simple arrangement of orthogonal cutting is, therefor, widely used in theoretical and experimental work

Oblique cutting is more practical while orthogonal cutting is convenient for analysis.

Orthogonal Cutting Model Simplified 2-D model of machining that describes the mechanics of machining fairly accurately Chip Thickness Ratiowhere r = chip thickness ratio; to = thickness of the chip prior to chip formation; and tc = chip thickness after separation

Chip thickness after cut always greater than before, so chip ratio always less than 1.0

= =Chip Thickness RatioBased on the geometric parameters of the orthogonal model, the shear plane angle can be determined as: where r = chip ratio, and = rake angle

The current analysis is based on Merchant's thin shear plane model considering the minimum energy principle. This model would be applicable at very high cutting speeds, which are generally practiced in production

The tool is perfectly sharp and no contact along the clearance face.The surface where shear is occurring is a plane.The cutting edge is a straight line extending perpendicular to the direction of motion and generates a plane surface as the work moves past it.The chip does not flow to either side or no side spread.Uncut chip thickness is constant.Width of the tool is greater than the width of the work.A continuous chip is produced without any BUE.Work moves with a uniform velocity.The stresses on the shear plane are uniformly distributed

Why should we know?Power requirement for the machine tool can be calculatedDesign of stiffness, etc. for the machine tolerancesWhether work piece can withstand the cutting force

Fs = force which is the resistance to shear of the metal in forming the chip. It acts along the shear plane.Ns = Normal to the shear plane. This is the backup force on the chip provided by the work piece.N = force at the tool tip interface acting normal to the cutting face of the tool and is provided by the toolF = Is the frictional resistance of the tool acting on the chip. It act downward against the motion of the chip as it glides upward along the tool face.R and R are equal in magnitude and opposite in direction.

Fig. a

The two orthogonal component (horizontal and vertical) FH and FV of the resultant force R can be measure by using dynamometer. The horizontal component is the cutting force FH and the vertical component is the thrust force Fv. All these force can be represented with the help of a circle known as Merchant force circle Fig, b

Here the two force triangle have been superimpose by placing the two equal force R and R together. In the figure, is the angle of friction. In this diagram, for the convenience the resultant force have been moved to the point of the tool. Since the force FH and Fv are at right angle to each other, their intersection lies on a circle diameter R. The force F and N may be placed in the diagram as shown to form the circle diagram. Now : firm fig. b and c

Fig. cForce Fs and Ns are right angle to each other1.

.2

..3

from Fig. dFv4

..................5.6

7

.8Putting the value of Ns (from eq. 3) in this both equations (7 and 8)...9

.10

11

Or

To increase shear plane angle Increase the rake angle Reduce the friction angle (or coefficient of friction)Effect of Higher Shear Plane AngleHigher shear plane angle means smaller shear plane which means lower shear force, cutting forces, power, and temperatureEffect of shear plane angle : (a) higher with a resulting lower shear plane area; (b) smaller with a corresponding larger shear plane area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equation

Where: D= Dia. Of jobN= Velocity of job or tool rev/min

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