GRINDING A METAL REMOVAL PROCESS

PREPARED BY-SHIVANI

ROLL-1202281SECTION-M-4

Grinding is a process of removing material by abrasive action of a revolving wheel on the surface of a work-piece in order to bring it to required shape and sizeThe wheel used for performing the grinding operation is known as grinding wheelIt consists of sharp crystal called abrasive held together by a binding material or bondThe wheel may be a single piece or solid type or may be composed of several segments of abrasive blocks joined together.

INTRODUCTION…

DIFFERENT METHODS OF GRINDING…SURFACE GRINDING

•Surface grinding uses a rotating abrasive wheel to remove material, creating a flat surface.• The surface grinder is composed of an abrasive wheel, a work holding device known as a chuck, either electromagnetic or vacuum, and a reciprocating table.• Grinding is commonly used on cast iron and various types of steel. •These materials lend themselves to grinding because they can be held by the magnetic chuck commonly used on grinding machines, and they do not melt into the wheel, clogging it and preventing it from cutting.

•Cylindrical grinding (also called centre-type grinding) is used to grind the cylindrical surfaces and shoulders of the work piece. •The work piece is mounted on centres and rotated by a device known as a drive dog or centre driver.• The abrasive wheel and the work piece are rotated by separate motors and at different speeds.• The table can be adjusted to produce tapers. The wheel head can be swivelled. •The five types of cylindrical grinding are: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and centre-less grinding.

CYLINDRICAL GRINDING

ELECTROCHEMICAL GRINDING…•Electrochemical grinding is a type of grinding in which a positively charged work piece in a conductive fluid is eroded by a negatively charged grinding wheel. •Electrolytic in-process dressing (ELID) grinding is one of the most accurate grinding methods. •The grinding wheel is dressed electrochemically and in-process to maintain the accuracy of the grinding.•  During the grinding operation one side of the wheel takes part in the grinding operation whereas the other side of the wheel is being dressed by electrochemical reaction.

GRINDING WHEEL…• A grinding wheel is an expendable wheel used for various grinding and abrasive machining operations.• It is generally made from a matrix of coarse abrasive particles pressed and bonded together to form a solid, circular shape, various profiles and cross sections are available depending on the intended usage for the wheel. •To maintain uniformity throughout the country in the system of making grinding wheel, the Bureau of Indian Standard has devised a standard system to be followed by all manufacturer.•To maintain uniformity throughout the country in the system of making grinding wheel, the Bureau of Indian Standard has devised a standard system to be followed by all manufacturer-1. Abrasive 2. Grain size 3. Grade 4. Structure 5. Bond

DIFFERENT SHAPES OF GRINDING WHEELS

ABRASIVES…•It is that material of grinding wheel which does the cutting action.•Abrasives are of two types-(1) Natural (2) ArtificialNatural Abrasive : The common natural abrasives

are sand stone, emery (50-60%crystalline AL2O3+ iron oxide) corundum (75-90% crystalline aluminium oxide + iron oxide), and diamond . The sand stone is used only for sharpening some wood-working tool . Diamond is used for dressing the grinding wheel and acts as an abrasive material for hard material.

Artificial abrasive: These are manufactured under controlled conditions in closed electric furnaces in order to avoid the introduction of impurities and to achieve the necessary temperature for chemical reactions to take place.

•Example: Silicon carbide(Sic), Aluminum oxide(Al2O3)

ADVANTAGE OF ARTIFICIAL ABRASIVES…The artificial abrasives have lately superseded the natural abrasive for following reasons-1. The controlled conditions in the electric

furnace enable uniformly in the product2. The quality of production and supply can

easily be varied according to the demands3. They have largely abolished the

dependence on natural means to meet the growing demand of more abrasive material in the modern manufacturing process

EFFECT OF GRINDING ON WORK PIECE MATERIALS…•Mechanical properties will change due to stresses put on the part during finishing. •High grinding temperatures may cause a thin martensite layer to form on the part, which will lead to reduced material strength from micro-cracks.•Physical property changes include the possible loss of magnetic properties on ferromagnetic materials.•Chemical property changes include an increased susceptibility to corrosion because of high surface stress

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