Topic- Grinding Machines

Subject-Manufacturing Processes-1

Guided by- Alpesh Joshi sir

By- Diparsh Modh(141043119002)

GRINDING MACHINES

Grinding is an abrasive machining process done with the help of arevolving wheel mounted on a suitable Machine. Abrasivemachining processes are used under one or more of the followingconditions:-

1. The material to be cut is too hard for other machining processes.

2. The surface finish desired is superior to what can be obtainedwith other methods.

3. The dimensional accuracy requirements are too stringent forother processes.

Two characteristics features of the abrasive machining processes are that

a very large number of cutting edges may be simultaneously machining a

given surface, each taking a minute of cut of its own and that the

geometry and orientation of these cutting edges at any given instance are

completely random.

• It is the only economical method of cutting hard material like

hardened steel.

• It produces very smooth surface , suitable for bearing surface.

• Surface pressure is minimum in grinding. It is suitable for light

work,which will spring away from the cutting tool in the other

machining processes.

Grinding Process

ABRASIVES

Abrasives are hard substances with adequate toughness capable of

machining materials too hard to be cut by most other tool materials.

They can also produce better surface finish and closer dimensional

tolerances on most materials. They can be used in the machining processes

as loose grains, in the form of grinding wheels and sticks or as coatings

depending upon the type of operation.

TYPES OF ABRASIVES

1. Natural Abrasives

2. Artificial Abrasives

Types of abrasives

GRAIN SIZEThe number indicating the size of the grit represents the number ofopenings in the sieve used to size the grain. The larger the grit size number, the finer the grit.

GRADE• Grade indicates the strength of the bond and, therefore, the `hardness`

of the wheel.

• In a hard wheel the bond is strong and it securely anchor the grit inplace, and therefore, reduces the rate of wear.

• In a soft wheel, the bond is weak and the grit is easily detachedresulting in a high rate of wear.

STRUCTUREThis indicates the amount of bond present between the individual abrasivegrains, and the closeness of the individual grain to each other. An openstructured wheel will cut more freely. That is, it will remove more metal.

In a given time and produce less heat.

BOND

•Vitrified bond (V)

•Silicate bond (S)

•Shellac bond (E)

•Rubber bond (R)

•Resinoid bond (B)

SELECTION OF GRINDING WHEELFor grinding a job the right grinding wheel is to be selected. The selection of

a grinding wheel will depend on the following factors.

•Material to be ground•Amount of stock to be removed•Finish required•Area of contact•Wheel speed•Work speed•Personal factor•Method of cooling

Type of grit used for grinding

DEPTH OF CUT

• It is the thickness of the material removed in surface grinding for one cut.

• Depth of cut in grinding depend on the:

• Cutting load

• Power of the machine

• Finish required

WORK SPEED

CLASS OF WORK ROUGH

GRIND m/min.

FINISH GRIND

m/min.

Soft steel 10-20 20-25

Hardened steel 25-30 30-40

Cast iron 35-55 45-65

Aluminium and fine

brass

50-65 50-65

GRINDING WHEEL DRESSING &TRUING

• Dressing refers to the removing of clogs and blunt abrasive grains fromthe surface of the grinding wheel. Dressing exposes the cutting edgeswhich restore the correct cutting action of the wheel. Dressing is done ona glazed or loaded wheel to recondition it.

• Truing refers to the shaping of the wheel to make it run concentric withthe axis. When a new grinding wheel is mounted, it must be trued beforeuse to remove the run out.

• When the surface of a grinding wheel develops a smooth and shiningappearance, it is said to be glazed. This indicate the abrasive particles onthe wheel face are not sharp. These are worked down to bond level.

• When soft materials like aluminium, copper, lead, etc. are ground themetal particles get clogged between the abrasive particles. This conditionis called loading.

GLAZING & LOADING

Grinding wheel specification system

Grinding wheel specification

Common Grinding wheels

Surface Grinding

• It is precision grinding machine to produce flat surface on a workpiece. It

is a more economical and more practical method of accurately finishing

flat surface than filling and scraping.

TYPES OF SURFACE GRINDERS

• Horizonal spindle reciprocating table

• Horizontal spindle rotary table

• Vertical spindle reciprocating table

• Vertical spindle rotary table

Cylindrical Grinding

Centre less Grinding

Types of centerless Grinding

• Internal Grinding

• Centerless Grinding

• A Centerless grinding machine as the name suggests has no centers, driversand other fixtures required for holding the workpiece.

• It is used for grinding external cylindrical surfaces, tapers and forms withrotational symmetry.

• The essential units of the machine are the grinding wheel, the regulatingwheel, the work rest blade and the slide.

• The regulating wheel and work rest blade support the work piece.

• The regulating wheel also controls the speed and feed of the workpiece. It ismade up of a rubber bonded abrasive material with enough friction to providea good grip on the surface of the workpiece sot that the workpiece rotateswith the surface speed of the regulating wheel. The regulating wheel ismounted on a slide so that its axis of rotation can be moved towards or awayfrom the work rest table.

• The work rest blade and the regulating wheel slide are mounted yet onanother slide which is moved towards the grinding wheel for depth motion orin feed.

Centerless Grinding Machine

Advantages of Centerless Grinding

• Due to shorter loading times, actual grinding time is decreased comparedwith other methods of grinding. Once the centerless grinder has beenproperly set-up for a particular run, no further adjustment or additionalset-ups are needed as opposed to centertype (cylindrical) grinding.

• This alone offers substantial savings. The workpiece is under constant,rigid support while in the grinding mode, making it feasible to takeheavier cuts and grind fine pins, rods and wires.

• When grinding easily distorted workpieces, the centerless grinder is most

advantageous because of its lack of axial thrust. Automatic feeding offers

continuous production of large quantities of smaller size workpieces.

• Centerless machines are designed for simplicity which in itself cuts

down on machine maintenance

Thank you……