micro finishing machines

8/6/2019 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.

micro finishing machines

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