MAURBHANJ SCHOOL OF ENGINEERING

BARIPADA : 757107 , ODISHA

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TOPIC- Finishing Operations

BRANCH- MECH.

SEMISTER- 4^rd

SUBJECT- MANUFACTURING TECHNOLOGY

FACULTY- ER KHAGESWAR PATRA

Estd:.1994

CONTENTS

• INTRODUCTION
• TYPE OF FINISHING PROCESS
• LAPPING
• BUFFING
• HONING
• SUPER FINISHING

Manufacturing Technology

Finishing Operation

• To ensure reliable performance and prolonged service life of modern machinery, its components require to be manufactured not only with high dimensional and geometrical accuracy but also with high surface finish.
• The surface finish has a vital role in influencing functional characteristics like wear resistance, fatigue strength, corrosion resistance and power loss due to friction.
• The finishing operations are assigned as the last operations in the single part production cycle usually after the conventional or abrasive machining operations, but also after net shape processes such as powder metallurgy, cold flash less forging, etc.

Manufacturing Technology

• Finishing Operations
• Lapping
• Buffing
• Honing
• Super finishing
• Wire brushing
• Polishing
• Electro polishing
• Magnetic-field-assisted polishing

Manufacturing Technology

Lapping

• In lapping, instead of a bonded abrasive tool, oil-based fluid suspension of very small free abrasive grains (aluminum oxide and silicon carbide, with typical grit sizes between 300 and 600) called a lapping compound is applied between the work piece and the lapping tool.
• The lapping tool is called a lap, which is made of soft materials like copper, lead or wood. The lap has the reverse of the desired shape of the work part. To accomplish the process, the lap is pressed against the work and moved back and forth over the surface.
• Lapping is sometimes performed by hand, but lapping machines accomplish the process with greater consistency and efficiency.

Manufacturing Technology

Lapping

• Lapping is regarded as the oldest method of obtaining a fine finish. 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 0.08 to 0.1mm in certain cases.
• The cutting mechanism in lapping is that the abrasives become embedded in the lap surface, and the cutting action is very similar to grinding, but a concurrent cutting action of the free abrasive particles in the fluid cannot be excluded.
• Lapping is used to produce optical lenses, metallic bearing surfaces, gages, and other parts requiring very good finishes and extreme accuracy.

Manufacturing Technology

Characteristics of lapping process:

• Use of loose abrasive between lap and the work piece
• Usually lap and work piece are not positively driven but are guided in contact with each other
• Relative 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 work piece.

Manufacturing Technology

Lapping

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Schematics of lapping process showing the lap and the cutting action of suspended abrasive particles.

Manufacturing Technology

• Lapping

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Figure (a) Schematic illustration of the lapping process. (b) Production lapping on

flat surfaces.(c) Production lapping on cylindrical surfaces.

Manufacturing Technology

• Abrasives of lapping
• Al2O3 and SiC, grain size 5~100μm
• Cr2O3, grain size 1~2 μm
• B4C3, grain size 5-60 μm
• Diamond, grain size 0.5~5 V
• Lubricating materials of lapping
• Machine oil
• Rape oil
• grease
• Technical parameters affecting lapping processes are
• unit pressure
• the grain size of abrasive
• concentration of abrasive in the vehicle
• lapping speed

Manufacturing Technology

Polishing

• 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 speed. The abrasive grains are glued to the outside periphery of the polishing wheel. Polishing operations are often accomplished manually.

Buffing

• Buffing is a finishing operation similar to polishing, in which abrasive grains are not glued to the wheel but are contained in a buffing compound that is pressed into the outside surface of the buffing wheel while it rotates. As in polishing, the abrasive particles must be periodically replenished.
• As in polishing, buffing is usually done manually, although machines have been designed to perform the process automatically.
• Buffing wheels are made of discs of linen, cotton, broad cloth and canvas

Manufacturing Technology

Buffing

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Manufacturing Technology

Honing

• Honing is a finishing process, in which a tool called hone carries out a combined rotary and reciprocating motion while the work piece does not perform any working motion. Most honing is done on internal cylindrical surface, such as automobile cylindrical walls.
• The honing stones are held against the work piece with controlled light pressure. The honing head is not guided externally but, instead, floats in the hole, being guided by the work surface
• It is desired that
• honing stones should not leave the work surface
• stroke length must cover the entire work length.

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Manufacturing Technology

Honing

• Honing is a finishing process performed by a honing tool, which contains a set of three to a dozen and more bonded abrasive sticks. The sticks are equally spaced about the periphery of the honing tool. They are held against the work surface with controlled light pressure, usually exercised by small springs.
• The honing tool is given a complex rotational and oscillatory axial motion, which combine to produce a crosshatched lay pattern of very low surface roughness

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Honing tool

Manufacturing Technology

Honing

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Manufacturing Technology

• Stone
• Al2O3 or SiC bonded abrasives
• The critical process parameters are:
• Rotation speed
• Oscillation speed
• Length and position of the stroke
• Honing stick pressure
• Parameters that affect material removal rate (MRR) and surface roughness (R) are:
• Unit pressure, p
• Peripheral honing speed, Vc
• Honing time, T

Manufacturing Technology

Super finishing

• Super finishing is a micro finishing process that produces a controlled surface condition on parts which is not obtainable by any other method. The operation which is also called ‘micro stoning’ consist of scrubbing a stone against a surface to produce a fine quality metal finish.
• The process consists of removing chatter marks and fragmented or smear metal from the surface of dimensionally finished parts. As much as 0.03 to 0.05 mm of stock can be efficiently removed with some production applications, the process becomes most economical if the metal removal is limited to 0.005 mm

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Manufacturing Technology

Super finishing

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Figure Schematic illustrations of the super finishing process for a cylindrical part. (a) Cylindrical mircohoning, (b) Centerless microhoning.

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