super finishing & cleaning processes 5

DITE

PRESENTATION ON

SUPER FINISHING & CLEANING PROCESSES

BY.

JATIN YADAV

Why a smooth surface?

Reduction in FrictionHeat - Bearings

Reduction in WearBushings/Bearings

AppearanceCar Body, Furniture

ClearanceDisk Head

SharpnessCutting Tools

How do we get a smooth surface?

Remove MaterialAbrasive Machining

FlattenBurnishing

Fill in VoidsAdd material

PaintFinishWax

INTRODUCTION

The parts produced by various machining operations like turning,drilling,milling etc.although are fairly accurate in size.They do not carry a very high degree of surface finish.In many industrial applications ,very high degree of surface finish is required.

When very high dimensional accuracy is required foll operations are performed……

1)Abrasive machining.2)lapping,3)Honing,4)superfinishing.

SURFACE FINISHING & CLEANING PROCESSES ARE AS FOLLOWS:

POLISHINGBUFFINGTUMBLINGBURNISHINGHONINGLAPPINGGRINDING

The below table illustrates gradual improvement of surface roughness produced by various processes

shown below.

POLISHING

A process using very fine abrasive materials for little or no material removal where visual appearance is primary purpose.

It is a surface finishing process performed by special abrasive coated wheel,these wheels are made of canvas,felt or wood.

OBJECTIVES1)THIS PROCESS IS EMPLOYED FOR REMOVING SCRATCHES,TOOL MARKS.A VERY SMALL AMOUNT OF METAL IS REMOVED.2)IRRESPECTIVE OF SHAPE IT IS USED FOR ACCURACY AND SURFACE FINISH.3) POLISHING IS OFTEN USED TO ENHANCE THE LOOKS OF AN ITEM, PREVENT CONTAMINATION OF MEDICAL INSTRUMENTS, REMOVE OXIDATION, CREATE A REFLECTIVE SURFACE, OR PREVENT CORROSION IN PIPES.

Below is an example of hand metal polishing using a wheel with an abrasive belt.

Examples ofPolished Parts

BUFFING

THIS A PROCESS OF OBTAINING A VERY FINE SURFACE FINISH, HAVING A “GRAINLESS” APPEARANCE ON METAL OBJECTS.

BUFFING TYPICALLY USES A CLOTH WHEEL AND VERY FINE

ABRASIVE.

Using cloth wheels combined with compounds, buffing is a final mechanical finish that results in a mirror bright finish, depending upon the base metal and/or prior mechanical finishing steps. Buffing does not remove a large amount of metal and, therefore, is sometimes applied after a plating process.

TUMBLING In this process, a plastic

or rubber barrel is loaded with tumbling material such as stone. All these elements have similar or same hardness. They also add some abrasive grit to the barrel along with a lubricant. Silicon carbide is commonly used as grit and water as a universal lubricant. The barrel is then placed on a slowly rotating guide rails for rotation.

Tumbling is used to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing, and break off die cast runners.

A full cycle can take anywhere from 6 to 24 hours with the barrel turning at 20 to 38 RPM.

The disadvantages of this process are that the abrasive action can be limited to only certain areas of the part, cycle times are long, and the process is noisy.

BURNISHING

The burnishing process consists of pressing hardened steel rolls or balls into the surface of the workpiece and imparting a feed motion to the same.

Ball burnishing is also used as a deburring operation. It is especially useful for removing the burr in the middle of a through hole that was drilled from both sides.

Roller burnishing, Typical applications for roller burnishing include hydraulic system components, shaft fillets, and sealing surfaces

Advantages of Burnishing Process

Improves the size and finish of revolution like cylinders and conical surfaces.

Internal and external surfaces can be burnished

Improves surface hardness. Increases, wear-resistance, decreases

fatigue and fights corrosion. It also eliminates the Grinding and

Honing processes which can be costly.

HONING

Honing is a finishing process, in which a tool called hone carries out a combined rotary and reciprocating motion while the workpiece does not perform any working motion. Most honing is done on internal cylindrical surface, such as automobile cylindrical walls.introduction of high performance diamond and cBN grits it is now possible to perform the honing operation in just one complete stroke.

Honing tool

Honing tool used to improve the surface finish or ground holes

Hole defects correctible by honing

. The important parameters

that affect material removal rate (MRR) and surface roughness (R) are: (i) unit pressure, p (ii) peripheral honing speed, Vc

(iii) honing time, T

LAPPING

Lapping is regarded as the oldest method of obtaining a fine finish. Lapping is a machining operation, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine

Pressures range from 7-140 kPa depending on workpiece hardness

Figure schematically represents the lapping process. Material removal in lapping usually ranges from 0.003 to 0.03 mm but many reach 0.08 to 0.1mm in certain cases. Cast iron is the mostly used lap material. However, soft steel, copper, brass, hardwood as well as hardened steel and glass are also used.

In compared to grinding and honing,lapping is minimal material removal,forces are very light and parts move freely between lap plates.Lapping operation is done with hand or machine.Lapping action is either rotary or reciprocating.Abrasive materials used include emery,corundum,iron oxide,chromium oxide,etc. mixed with a fluid medium ,usually oil is used in this operation.

Lapping process. (b) Production lapping on flat surfaces. (c) Production lapping on cylindrical surfaces.

2- and 3-BodyAbrasion

3-body abrasion: grains move freely between surface

2-body abrasion: grains are embedded in a surface

Abrasives Machining

AbrasivesSmall, hard nonmetallic particles with sharp edges and irregular shapes which can remove small amounts of material, producing tiny chips.

Abrasive processes can produce fine surface finishes and accurate dimensional tolerances

Abrasives and Bonded Abrasives

• Conventional Abrasives Aluminum Oxide (Al2O3) Silicon Carbide (SiC)• Superabrasives Cubic Boron nitride (CBN) DiamondThese abrasives are much harder than conventional

cutting tool materials.Characteristics of abrasives: 1) hardness, 2) friabilityFriability is defined as the ability of abrasive grains

to fracture into smaller pieces.This property gives abrasives their self-sharpening characteristics.

Abrasive Workpiece MaterialCompatibility

Aluminum Oxide: Carbon steels, ferrous alloys, alloy steels

Silicon Carbide: nonferrous metals, cast irons

Cubic Boron Nitride:Steels and cast irons above 50 HRc hardness

Diamond: Ceramics, cemented carbides

Grinding Wheels

The Grinding Process

Grinding is a chip removal process that uses an individual abrasive grain as the cutting tool.

The individual abrasive grains have irregular shapes and and are spaced randomly along the periphery of the wheel.

Not all the grains are active because of the radial positions of the grains .Surface speeds in grinding is very high.

Types of Grinding

- Surface Grinding- Cylindrical Grinding- Internal Grinding- Centerless Grinding- Others

- Tool and cutter grinders- Tool-post grinding- Swing-frame grinders- Bench grinders

Surface Grinding

Cylindrical-Grinding Operations

Internal Grinding

Centerless Grinding

Bonded Abrasives/Grinding Wheels

Bonded AbrasivesMost grinding wheels are made of abrasive grains held together by a bonding material

Types of bonding material:Vitrified (glass)Resinoid (thermosetting resin)Rubber

Grinding Wheel Components

Coated AbrasivesBelt Grinding

Uses coated abrasives in the form of a belt; cutting speeds are about 2500-6000 ft/min

Increase in Machining and Finishing Costas a Function of Surface Finish Required

Increase in the cost of machining and finishing a part as a function of the surface finish required.

Protective Coating

Galvanization

Galvanization is a process in which the iron article is protected from corrosion by coating it with a thin layer of zinc.

In this process, at first iron or steel is cleaned by pickling with dilute sulphuric acid solution (H2SO4) at a temperature range of 600-900C for 15 to20 minutes.

Then after, dipped in the bath molten zinc which is at 425-450C.

PHOSPHATE COATING

Phosphate coatings are used on steel parts for corrosion resistance, lubricity, or as a foundation for subsequent coatings or painting

In this a dilute solution of phosphoric acid and phosphate salts is applied via spraying or immersion and chemically reacts with the surface of the part being coated to form a layer of insoluble, crystalline phosphates.

Phosphate coatings can also be used on aluminium, zinc, cadmium, silver and tin

CHROMATING

Chromating is the process of coating a surface film with a mixture of trivalent and hexavalent chromium for protection from corrosion.

Chromating is generally used for the protection of Zinc, Aluminum parts.

They are produced by immersion of the article in a bath of acid potassium chromate, followed by immersion in a bath of metal chromate solution.

Anodizing

Anodizing is the electrochemical process by which the surface of a metal part is converted into a metal oxide .This formation of an oxide coating by anodizing may be used to improve the wear resistance of certain metals.

Process

A cathode is connected to the negative terminal of a voltage source and placed in the the anodizing solution typically made up of sulfuric acid. A metal part is connected to the positive terminal of the voltage source and also placed in the anodizing solution. When the circuit is turned on, the oxygen from the water molecules in the anodizing solution will be liberated and combine with the metal molecules ions on the surface of the part, forming a metal oxide coating.

ELECTOPLATING

Electrolytic process in which the part to be plated will be submerged in a water solution which contains molecules of an acid, base or salt.

The Cathode (negative electrode) is usually the part to be coated and the Anode (positive electrode) will be made of the metal being plated .

Basic? Electro-plating Process

Nickel Chloride (NiCl2) The NiCl2 salt ionizes in water into Ni++ ions

and two parts of Cl- ions. The object being plated is negatively charged and so it will attract the Ni++ ions which are positively charged. These Ni++ ions reach the object, and electrons flow from the object to the Ni++ ions . Nickel atom has now been deposited on the surface of the part being coated. This process is known as electrodeposition.  The amount of metal that deposits is directly proportional to the number of electrons that the battery provides.

Before - dull

After - shiny

LIMITATION OF ELECTROPLATING & ANODIZING Anodizing process is not a useful

treatment for iron or carbon steel because these metals exfoliate when oxidized

In electroplating a uniform thickness

with electroplating can be difficult depending on the geometry of the object being plated

TINNING

The process of coating tin over the iron or steel articles to protect it from corrosion is known as tinning. Tin is a nobler metal than iron, therefore, it is more resistance to chemical attack.

In this process, at first Iron sheet is treated in dilute sulphuric acid (pickling) to remove any oxide film if present. A cleaned Iron sheet is passed through a bath molten flux.

SHERADIZING

Sheradizing is the process of cementation, using zinc powder as coating metal.

The iron articles to be coated are first cleaned and then packed with “zinc dust” in a drum. The drum is then sealed tightly so that oxidation of zinc is minimum. The drum is slowly rotated for 2 to 3 hours and its temperature is kept between 350 to 3700C, either by gas heating or electricity. During this process, zinc gets diffused into iron forming Fe-Zn alloy at the surface.

CONCLUSION

Surface finish operation are much costlier but meet our industrial application.

Surface protective operation is very much required for preventing rust ,enviroment effect, to give good look to our component and enhance the life of our product.

THANK YOU