surface finish and surface integrity [compatibility mode]

8/3/2019 Surface Finish and Surface Integrity [Compatibility Mode]

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SURFCE FINISH

AND SURFACE

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Page 1Free Powerpoint Templates

BY

Kali dass


2/23

INDEXINTRODUCTION

SURFACE FINISHEFFECT OF MACHINING PARAMETER ON


Page 2

MEASURES OF SURFACE ROUGHNESS

SURFACE INTEGRITY

IMPORTANSE OF SURFACE INTEGRITY

METHOD OF IMPROVING SURFACE

FINISH


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INTRODUCTIONMachining operation are used to produce a desired

shape and size by removing excess stock from ablank in the form of chips. New surfaces are

generated through a process of plastic deformation

and crack ro a ation.


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A surface can be characterized by its topographyand microstructure. The formers describes its

micro-geometrical properties or texture in terms of

roughness, waviness and lay and the latter by thedepth and nature of the alternative material zone

just below the surface.


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CONTD Surface integrityt of a

component can bedefined as the degree of

the soundness,

wholeness or

Fig: surface characterization

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unimpairedness of thesurface topography and

microstructure as a result

of the given

manufacturing operation.


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SURFACE FINISH

Surface finish refers to the following properties of a

machined surface.

Roughness: It consists of relatively closely-spaced orfine surface irregularities, mainly in the form of feed

marks left by the cutting tool on the machined


.

Waviness: It consist of all surface irregularities whose

spacing is greater than the roughness sampling

length. Vibration, chatter, and tool and work piece

deflections due to cutting loads and cuttingtemperature may cause waviness.


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CONTD

Fig: Element of surface texture.



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CONTD

Lay: It denotes the predominant direction of the

surface irregularities. The lay usually specified with

respect to an edge called the reference edge of the

work piece.


irregularities, that is those which occur at someparticular location on the surface or at widely

varying intervals. Flaws could be due to inherent

defects, such as inclusions, cracks, blow-holes, etc


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EFFECT OF MACHINING PARAMETERS

ON SURFACE FINISH

Surface finish is influenced by several machining

parameters including cutting tool geometry, machine

tool rigidity, work piece material, cutting conditionsand tool material.

Tool Geometry: It is known that large the rake angles,


smaller are the cutting forces. And when the cuttingforces are small, deflections and waviness height are

also small.

Relief angles should be sufficient to prevent rubbing

against the machined surfaces.

Additional cutting force due to the rubbing action causes

harmful deflections.


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CONTD The major and the minor (i,e. the side and the

end) cutting edge should be joined by a nose

of sufficiently large radius to reduce the

sharpness or pointless of tool.


,

because it can cause vibration and chatter.

An increase in the side-cutting edge angle

reduces true feed and improve chip flow and

surface finish and large side cutting angles may

prove harmful to surface finish by causing

chatter.


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CONTD However position of a zero

degree primary end-cutting

edge angle over a length of1.5 times the feed per

revolution (as shown in fig.)

Fig: Tool provided with

wiper flat


e ps n par a y or o a y

removing the grove

generated by the noise

radius of the tool.

The flat on the end cuttingedge is figuratively called as

wiper flat.


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CONTDWork piece Geometry: Long slender workpieces have low stiffness against both static

and dynamic forces as a result wavinesseffects are more pronounced.

Machine Tool Rigidity and Accuracy: The


machine tool affects surface finish mainlythrough the extent of its rigidity, freedom

from alignment errors and accuracy of

motions Cutting Condition: cutting condition, in

general, tends to improve surface finish .


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CONTD Tool Material: Different tool material have

different hot hardness, toughness and frictional

behavior. High hot hardness of tool materialenables the tool to be used at high cutting

speeds well within the insensitive region where


built-up edge practically disappears. Cutting Fluid: Cutting fluid has only an indirect

effect on surface finish, by acting as coolant it

reduces tool wear and keeps the cutting edgeimpact , by acting as a lubricant it tends to

reduce friction between the sliding surface of

the tool, work and chip.


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MEASURES OF SURFACE ROUGHNESS

Following are the chief measures of surface roughness

a) Overall height (h max): It is the height separation

between two reference lines namely L p and L v (upper

and lower surface line) touching the highest peak and

lowest valley occurring with in sampling length L of a

given surface.


h max = L p L v

b) Leveling Depth hp: It is the mean height of the profile

above a mean line Lm where it is defined as a line so

positioned in the profile that the sum of the squares

of the deviations of the profile from the mean line is

minimum.

hp =


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CONTD

c) Centre Line Average(h CLA): It is defined

as the arithmetic average of the

deviation of the profile above and belowthe mean line.


CLA =

d) Root mean square value(h RMS): It is

defined as the geometrical average value

of the deviation of the profile above andbelow the mean line.

hp =


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SURFACE INTTYGRIYSurface integrity refers to the soundness of the

surface condition of manufactured parts.

Besides the feed marks, it depends upon plasticdeformation, micro structural changes, porosity,

micro cracks, residual stress, etc.


Plastic Deformation: The surface layer isplastically deformed. Extent of deformation

depends upon the process parameters, namely

cutting speed, dimensions of cut, tool geometry,work piece material and characteristics of the

machine tool.


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CONTD

Micro structural Changes: The structural

changes in the micro constituents include phase

transformation, intergranular attacks andrecrystallization. Phase transformation occur on

the account of intensive heating of the surface


ayer uring mac ining.Recrystallization: Recrystallization in the

surface layer may be attribute to the plastic

deformation. When the service environmentheats a machined part, Recrystallization and

grain growth of material of the surface layers

may take place.


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CONTD

Residual Stress: Residual

Stress in the surface layer of amachined piece is a result of

the removal of machining load

that caused plastic

deformation in it. The

Fig : Distribution of Residual

stress


distribution of residual stressdepends upon the cutting load,

the distribution of mechanical

stress and temperature during

chip formation. The residualstress may be tensile or

compressive high or low, deep

or shallow.


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IMPORTANT OF SURFACE INTEGRITY

Surface condition affects

fatigue strength of the

finished part and produces

distortion in the partespecially if it is thin.

Fatigue Strength: On the


account o tens e res ua

stress, plastic deformation,

micro-cracks, and face

transformation, etc. low cycle

fatigue strength of the finishparts may be substantially

decrease, so under adverse

condition of machining.


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CONTD

Distortion: Machining removes residual stress

pre-existing in the work piece. It also

introduces residual stress of its own. Onaccount of both effects, the work piece suffers

distortion. Such distortion is easily noticeable


or measurable on thin specimen. The amount of distortion also depends upon

the work material. For example, titanium

distorts much more than steel on account of itslow modulus of elasticity.


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METHODS OF IMPROVING SURFACE

FINISHSurface conditions of a work piece undergoing a

machining operation can be guarded against ill

effects as follows:

1. By using light cuts: cutting speed, feed and


ep o cu s ou e suc a no u -up

edge is formed, chip formation is continuous,

cutting forces are small and cutting

temperatures are low. This is possible by

optimizing the cutting speed and using small

feed and depth of cut.


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CONTD2. By using an effective cutting fluid: Tool

temperature, and to some extent the cutting

forces, can be decreased by using a proper

cutting fluid that can act as an effective


.

3. By using a sharp cutting tool or one that does

not have appreciable wear land.

4. By using a rigid machine-tool-work system

that ration and minimizes vibration and

chatter.


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CONTD5. By using a post-processing treatment that

includes compressive residual stress in thesurface layer and improves fatigue life. Among

such treatments are shot penning, burnishing


and tumbling.


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THANK


YOU !

surface finish and surface integrity [compatibility mode]

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