Shree Presentation

8/2/2019 Shree Presentation

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Mechanism of chip formationin machining process.

Presented by:SHRADDHA SANGOLE


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Content

Machining. Chip. Mechanism of chip formation. Piispanens card analogy. Direction of elongation of crystals.

Types of chips.


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Machining is a process of gradual removal of excess of material from the preformed blanks inthe form of chips.


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The portion of the material that has been cutaway from the work material by the cutting toolis called the chip.


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A wedge shaped tool is moved relative to the work piece.

Shearing stresses is initiated in the work material. At the zone near the contact of the tool-work,

the strain becomes very intense. At either side of the intense shear, the materialcurves around to form chip. Chip moves upward along the rake face. Continued application of force causes thematerial to rupture and reaches a point of plastic flow passing across the face to tool or it

fractures and breaks away in the form of chips.


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The formation of chip and its motion along the

tool face can be visualized from an idealizedmodel in which a stack of inclined playing cardsis pushed against a tool. As the tool advances, segments which had beenpart of the w/p bec0me part of the chip. The card closest to the tool point slips to afinite distance.

When the tool reaches the next card, thepreviously slipped card moves upward alongthe tool face as a part of chip. Thus in this way the chips are formed.


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Discontinuous chips Continuous chips Continuous chip with built up edges (BUE)


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I t is a series of discontinuous elements or

segments. Fracture takes place above the cutting edge of the tool. It occurs when the compressive forces exceedthe fracture limit of the work material.


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Factors responsible :Brittle materialLow cutting speedSmall rake angle

These chips are easily handled and disposedoff. And give good surface finish.


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Formed due to plastic deformation of work material. They are smooth on back face with almostuniform thickness throughout.

Factors responsible:Ductile materialsHigh cutting speedLarge rake angleCutting fluid

There is low friction between chip and tool facemaking it more desirable.

Use of chip breakers.


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These chips appear in large segmented coils and not assmooth as continuous chips. Formation of built up edge. Tool edge is covered with BUE and so there is poorsurface finish.


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Factors responsible:Ductile materialsLow cutting speed

Small rake angleInsufficient cutting fluid

There is high power consumption and poorsurface finish. Hence undesirable.


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