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PE 5662 Teknologi Manufaktur Lanjut(Advanced Manufacturing Technology)

Session : Finishing Processes

At the end of this lesson the students would be able to :students would be able to :

(i) Understand the significance of super finishing process

(ii) State various applications of the super finishing process

(iii) Illustrate various techniques of super finishing process

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FINISHING OPERATIONS

As the name of this group of abrasive operations suggests, their objective is to achieve superior surfacefinish up to mirror-like finishing and very close dimensional precision.

The finishing operations are assigned as the last operations in the single part production cycle :• Conventional or abrasive machining operations, • EDM• Powder metallurgy, • Cold flashless forging, etc.

Surface roughness values for fine grit size grinding comparison

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Honing

H i i fi i hi i hi h t l ll d hHoning is a finishing process, in which a tool called honecarries out a combined rotary and reciprocating motion while the workpiece does not perform any working motion.

The honing head is not guided externally but, instead, fl t i th h l b i id d b th k ffloats in the hole, being guided by the work surface

1. honing stones should not leave the work surface2. stroke length must cover the entire work length.

Lay pattern produced by combination of

Honing tool

y p p y frotary and oscillatory motion

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Hole defects correctible by honing

The critical process parameters are:The critical process parameters are:

1. Rotation speed2. Oscillation speed3. Length and position of the stroke4. Honing stick pressure

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• Conventional abrasive honing stick, •High performance diamond and CBN•Honing stick with microcrystalline CBN, maintain sharp

cutting condition g• Single layer configuration with a brazed metal bond

Superabrasive honing stick with single layer configuration

The important parameters that affect material p premoval rate (MRR) and surface roughness (R) are :

(i) Unit pressure, p(ii) Peripheral honing speed, Vc(iii) H i ti T(iii) Honing time, T

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The unit pressure should be selected so as to get minimum surface roughness with highest possible MRR

Effect of honing pressure on MRR and surface finish

An increase of peripheral honing speed leads to enhancement of material removal rate and decreasein surface roughness

Shows that with honing time T, MRR decreases.g

Effect of peripheral honing speed Effect of honing time on material removal rate and surface roughness

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Lapping

Lapping is basically an abrasive process in which loose abrasives function as cutting points finding momentary support from the laps.Material removal in lapping usually ranges from 003 to 03 mm but many reach 0 08from .003 to .03 mm but many reach 0.08 to 0.1mm in certain cases.

Characteristics of lapping process:

Use of loose abrasive between lap and the workpiece

Usually lap and workpiece are not positively driven but are guided in contact with each other . Fig. Scheme of lapping process

R l ti ti b t th l d th k h ldRelative motion between the lap and the work should change continuously so that path of the abrasive grains of the lap is not repeated on the workpiece.

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Figure :

Scheme of lapping process

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lap material :Cast ironsoft steel,

Abrasives of lapping:• Al2O3 and SiC, grain size 5~100µm• Cr2O3, grain size 1~2 µm

B4C3 grain size 5 60 µmcopper, brass, hardwoodhardened steelglass

• B4C3, grain size 5-60 µm• Diamond, grain size 0.5~5 V

Vehicle materials for lapping• Machine oil• Rape oil• Grease

Technical parameters affecting lapping p g pp gprocesses are:

• Unit pressure• The grain size of abrasive• Concentration of abrasive in the vehicle• Lapping speed

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Hand lapping

Hand lapping of flat surface is carried out by rubbingHand lapping of flat surface is carried out by rubbingthe component over accurately finished flat surface of master lap usually made of a thick soft close-grained cast iron block.

Manual lapping requires high personal skill because the lapping pressure and speed have to be controlled manually

Manual Ring lapping of external cylindrical surface

Manual Lapping of internal cylindrical surfaces

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Lapping Machine

Machine lapping is meant for economic lapping of batch qualities. In machine lapping, where high accuracy is demanded, metal laps and abrasive powder held in suitable vehicles are used.

flat surface cylindrical surface

2- and 3-Body Abrasion

2-body abrasion: grains are embedded in a surface

3-body abrasion: grains move freely between surfaces

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Lapping – MicrochippingClat

h

a

CradPlastic zone

Lateral cracks –remove material Radial cracks –

surface damage

Lapping Finish

Grinding Lapping

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Lapping Process

Examples of Lapped Parts

The workpieces made of aluminum oxide were ringsThe workpieces made of aluminum oxide were rings having 12 mm ID, 20 mmOD and 5 mm thickness. Its high hardness promotes a series of applications in mechanical engineering, such as bearings and seals.

Initial Ra = 0.65 µmFinal Ra (after lapping) = 0.2 µm

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SuperfinishingA finishing operation similar to honing, but it involves the use of a single abrasive stick.The reciprocating motion of the stick is performed at higher frequency and smaller amplitudes.

Superfinishing is capable only of improving the f fi i h b t t di i lsurface finish but not dimensional accuracy.

The result of these operating conditions is mirror like finishes with surface roughness values around 0.01 µm.

Superfinishing can be used to finish flat and external cylindrical surfaces.

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P li hiPolishing

Polishing is a finishing operation to improve the surface finish by means of a polishing wheel made of fabrics or leather and rotating at high speedand rotating at high speed.

Example of a Polishing Machine

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Examples of Polished Parts

Polished disk drive heads compared to the size of a dimension

Buffing

Buffing is a finishing operation similar to polishing, in which abrasive grains are not glued to theg gwheel but are contained in a buffing compound that is pressed into the outside surface of the buffingwheel while it rotates.

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Deburring

BurrsThin ridges (usually triangular) that form on the workpiece edges during production; can be detrimental to the part or its function

Traditionally removed manually; can account for up to 10% of the part manufacturing cost

Deburring Processes

- Manual (files and scrapers)- Mechanical by cutting- Wire brushing- Abrasive belts- Ultrasonic machining- Electropolishing- Electrochemical Machining

Magnetic abrasive finishing- Magnetic abrasive finishing- Vibratory Finishing- Shot blasting, abrasive blasting- Abrasive flow machining- Thermal energy (laser, plasma)

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Deburring Processes

Vibratory and Barrel FinishingAbrasive pellets are placed in a container with the workpiece; the container is vibrated or tumbled

Shot BlastingAbrasive particles are propelled at the workpiece at high velocity by an air jet or a wheel

Deburring ProcessesAbrasive Flow Machining

An putty-like substance with abrasive grains is forced around and through the workpiece; especially useful for pieces with internal spaces that cannot be reached by other means

Thermal EnergyThe workpiece is exposed to an instantaneous combustion reaction; the burrs heat up much more rapidly than the solid part and melt away

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Summary

Abrasive processes offer a way to increase surface finish and dimensional accuracy

Deburring may be necessary for proper part fit and functionand function