micro finishing machines
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Micro finishing machines
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The surface finish attainable in the most widely applied micro-finishing
processes such as honing, lapping and super finishing are indicated in the
table.
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Honing
Honing is an abrasive
machining process that
produces a precision
surface on a metal work
piece by scrubbing an
abrasive stone against italong a controlled path.
Honing is primarily used to
improve the geometric
form of a surface, but may
also improve the surfacetexture.
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Honing techniques
Methods:
1-longitudinal stroke honing
2-short stroke honing
3-centerless plunge honing4-through feed honing
5-profile honing
6-surface honing
7-gear honing
Area of applicationAdvantages
Disadvantages
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Honing machine:
It is the application of
bonded abrasive sticks
called Honing
Stones held on the
outside or inside ofthe honing tool as in
figure.
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Honing tool denomination
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Abrasives used for Honing
The hone is a composed of abrasive grains thatare bound together with an adhesive. Generally,honing grains are irregularly shaped and about 10to 50 micrometers in diameter (300 to 1,500mesh grit). Smaller grain sizes produce asmoother surface on the work piece.
For honing steel, Aluminium oxides and SiliconCarbides are used as abrasives in honing stickwhile for honing cast iron and non-ferrousmaterials green Silicon Carbides are used.
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Honing Stones with Corundum or
Silicon Carbide
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Honing Stones with Boron Nitride and
Diamond
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Design principle of a hydraulic feeding
attachment
1 Feeding piston
2 Piston rod
3 Feeding bar
4 Expansion cone
5 Stone holder
6 Honing stone
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Lapping
Surface lapping
principle
a) Upper lapping
plate,b) Bottom lapping
plate,
c) Work piece
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Application of the lapping
technique
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Lapping tool
Lapping wheels
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Slurry: The other component of the lapping tool is the
slurry
Lapping medium:
The grains are dispersed in the medium
Lapping abrasives
Silicon carbide is the most common lapping
powder.I
t can be used for almost all thematerials.
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Advantages of lapping
Most work pieces can be processed without being clamped orfixed.
Allowances of 0.2 to 0.5 mm are economically machinable today.
Precision and ultra-precision machining can be executed in oneoperational step.
Changeover times are very short. Components of less than 0.1 mm thickness can be machined.
The highest surface and roughness requirements can be met.
The minimal heating effect prevents undesired thermaldistortions and structural changes in the work piece.
A consistent machining quality is guaranteed for compositematerials.
Lapped surfaces rarely exhibit tensile distortion or burr formation.
It is possible to machine multiple work pieces in one operationalstep.
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Super finishing
Super finishing is a special technique forproducing high degree of surface finish by
using abrasive sticks similar to hones but with
a different kinematics for work-toolinteraction.
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Abrasives
Common abrasives used for super finishing
include:
Aluminum oxide, Silicon carbide,
Cubic boron nitride (CBN) and diamond.
Aluminium oxide is used for "roughing"operations.
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Super finishing techniques
external cylindrical surfaces
internal cylindrical surfaces
flat surfaces
circular (planetary) motion
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Machining Parameters 1. Abrasive stones:
Two types are mainly used: Al2O3 for carbon and alloy steelsand SiC (more friable) for very soft and tough steels
2. Work speed:
Roughing. 1215 m/min.
Finishing. 3060 m/min (for very fine finish, higher speeds of120 m/min may be applied).
3. Stroke length and speed of stone reciprocation:
The fast reciprocation of stones in a short stroke is a maincharacteristic that sets super finishing apart from honing.
4. Stone pressure: For normal work, ph = 1.53.0 kg/cm2
For roughing, ph = 3.06.0 kg/cm2
For extra fine finishing, ph = 1.02.0 kg/cm2
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* Specifications of super finishing machines
Advantages of super finishing
Increasing part life
Decreasing wear
Closer tolerances
Higher load bearing surfaces
Better sealing capabilities and elimination of a break in period.
Disadvantage of super finishing
Super finishing requires grinding or a hard turning operationbeforehand, which increases cost.
Super finishing has a lower cutting efficiency because of smallerchips and lower material removal rate.
Super finishing stones are softer and wear more quickly, howeverthey do not need to be dressed.