Presentation on Grinding

7/30/2019 Presentation on Grinding

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PRESENTERS ARE

Prashant Sankaran 100106251

Pragyan Kumar 100106246

Omender Sharma 100106233

Omar Ebadur Raheman 100106232


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Overview

Grinding Wheels.

Abrasives, Bonds.

Cutting action.

Specifications.

Wear: Attrition wear, Fracture Wear.

Dressing and Truing.

Max chip thickness and Guest Criteria.

Surface, Cylindrical Grinding and Centre-less Grinding.


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GRINDING WHEELS


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What is grinding? Grinding is a material removal and surface generation

process used to shape and finish components made ofmetals and other materials.

The precision and surface finish obtained through grinding

can be up to ten times better than with either turning ormilling.


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All applications of abrasive products are intended to generatesurfaces:

Industrial challenges in grindingJ.F.G. Oliveira (1)a,*, E.J. Silva b, C. Guo (2)c, F. Hashimoto (1)d

a IPT


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The requirements for efficient grindinginclude

Abrasive components which are harder than the work

Shock- and heat-resistant abrasive wheels

Abrasives that are friable. That is, they are capable ofcontrolled fracturing.


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What is a Grinding wheel?

Agrinding wheel is an expendable wheel that is composedof an abrasive compound used for various grinding(abrasive cutting) and abrasive machining operations. Theyare used in grinding machines.

The wheels are generally made from a matrix of coarseparticles pressed and bonded together to form a solid,circular shape, various profiles and cross sections areavailable depending on the intended usage for the wheel.

They may also be made from a solid steel or aluminium discwith particles bonded to the surface.


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Characteristic of a Grinding Wheel

There are five characteristics of a cutting wheel:

material,

grain size,

wheel grade,

grain spacing, &

bond type.


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Abrasives

An abrasive is a material, often a mineral, that is used toshape or finish a work piece through rubbing which leads topart of the work piece being worn away. While finishing amaterial often means polishing it to gain a smooth,reflective surface it can also involve roughening as in satin,

matte or beaded finishes. Abrasive ranges from a macroscopic grains as large as

about 2 mm to microscopic grains about 0.001 mm indiameter.

Some naturally occurring abrasives are: sand and calcite. And some artificial abrasives are ceramics and Borazon.


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Materials

The actual abrasive, is selected according to the hardness ofthe material being cut. Accordingly some materials are:

Aluminium Oxide (A)

Silicon Carbide (S)

Ceramic (C)

Diamond (D, MD, SD)

Cubic Boron Nitride (B)


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Grain size, from 8 (coarsest) 1200 (finest), determines thephysical size of the abrasive grains in the wheel. A largergrain will cut freely, allowing fast cutting but poor surface

finish. Ultra-fine grain sizes are for precision finish work.

Wheel grade, from A (soft) to Z (hard), determines howtightly the bond holds the abrasive. Grade affects almost allconsiderations of grinding, such as wheel speed, coolant

flow, maximum and minimum feed rates, and grindingdepth.

Grain spacing, or structure, from 1 (densest) to 16 (leastdense). Density is the ratio of bond and abrasive to air

space. A less-dense wheel will cut freely, and has a largeeffect on surface finish. It is also able to take a deeper orwider cut with less coolant, as the chip clearance on thewheel is greater.


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Wheel Bond

how the wheel holds the abrasives, affects finish, coolant, andminimum/maximum wheel speed.

Vitrified (V)

Resinoid (B)

Silicate (S)

Shellac (E)

Rubber (R)

Metal (M)

Oxychloride (O)


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CUTTING ACTION


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DEPTH OF CUT

It is the thickness of the material removed insurface grinding for one cut.

Depth of cut in grinding depend on the:

Cutting load Power of the machine

Finish required


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Grinding wear

The principle characteristics of Grinding wear are:

They are primarily caused by particles under high stressunder relatively low speeds.

The cutting edges dull after a series of operations beenperformed.

Change in shape due to localized high stress points.

Due to the presence of lubricant the tool tends to

smoothen along with the work piece. Both horizontal and vertical components of grinding

increases linearly with wear flat area.


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There are two types of Wearing inGrinding wheels:

1. Attritious wear

2. Fracture wear


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Attritious wear

It results in the dulling of the tips of abrasive grain byrubbing against the work piece surface.

The Attritious wear, although contributes insignificantly to

the total, is the most important form of wear.

Dulling of grains occurs due to Attritious wear


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Fracture wear

It is the removal of abrasive particle from the wheel eitherby fracturing within the grain or fracturing within the bond.

Most common type of wear.

The rate at which fracture wear occurs is directly related tothe grinding forces.


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Dressing and Truing

Truing is the process of making a grinding wheel round andconcentric with the grinding wheel spindle axis.

Truing is also the process of forming a specific shape on the

face of the wheel.

Dressing is the process of conditioning the surface of atrued wheel to expose the grain for efficient grinding

action.


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A properly trued and dressed wheel grinds with a minimumof grinding power, has no burn or chatter, and produces

good quality parts.

The technology in the rotary diamond dressing field hasimproved to such an extent that tolerances in the millionthsof an inch are being consistently met.

This method of dressing is not only the fastest but also themost accurate way to shape grinding wheels in high volumeproduction of precision parts.


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MAXIMUM CHIP THICKNESS


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Maximum chip thickness

Maximum chip thickness is the most important parameter forachieving a productive and reliable milling process.

Effective cutting will only take place when this is maintained ata value correctly matched to the milling cutter in use.

A thin chip with a hex value that is too low, is the most commoncause of poor performance resulting in low productivity. Thiscan negatively affect tool life and chip formation.

A value that is too high will overload the cutting edge, whichcan lead to breakage.


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Surface Grinding Machine

Surface grinding is the mostcommon of the grindingoperations.

It is a finishing process that

uses a rotating abrasive wheelto smooth the flat surface ofmetallic or non-metallicmaterials to give them a more

refined look or to attain adesired surface for a functionalpurpose.


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Cylindrical Grinding

The cylindrical grinder is atype of grindingmachine used to shape theoutside of an object.

The cylindrical grinder canwork on a variety of shapes,however the object musthave a central axis ofrotation.

but is not limited to suchshapes as a cylinder,an ellipse, a cam, ora crankshaft.


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Cylindrical grinding is defined as having four essentialactions:

The work (object) must be constantly rotating

The grinding wheel must be constantly rotating

The grinding wheel is fed towards and away from thework

Either the work or the grinding wheel is traversed withthe respect to the other.


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Centerless grinding is a form of grinding where there is nocollet or pair of centers holding the object in place. Instead,there is a regulating wheel positioned on the opposite sideof the object to the grinding wheel. A work rest keeps the

object at the appropriate height but has no bearing on itsrotary speed.

Centerless grinding is much easier to combine withautomatic loading procedures than centered grinding;throughfeed grinding, where the regulating wheel is held at

a slight angle to the part so that there is a force feeding thepart through the grinder, is particularly efficient

Centre-less Grinding


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Fig: A Schematic Diagram of Centre-less Grinding


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Documents

Presentation on Grinding