Milling Machines

Milling Machines Milling is the operation of removing excess material from the work piece with the rotating cutting tool called milling cutter Here the W/p is stationary and is fed against the multi point cutting tool rotating at high speeds

Principle of Milling • Down Milling • W/p is fed in direction opposite to that of rotating cutter • W/p is fed in same direction as that of rotating cutter Up Milling

Types of Milling Machine Horizontal MM Vertical MM Universal MM Fixed bed type MM Planer type MM Special Purpose MM

Horizontal Milling Machine This is most popular type of milling machine and is named so because of its horizontal spindle

Vertical Milling Machine Similar to horizontal milling machine expect the spindle is held in vertical position The spindle head is fixed to the vertical column and may be either fixed, sliding, Swivel head type of combination of all

Universal Milling Machine

Parts of Milling Machine BASE- Foundation of machine upon which other parts are mounted COLUMN- Vertical hollow casting that houses main drive and spindle KNEE- Can slide up and down on vertical guide ways provided on front face of column. Knee supports the saddle SADDLE- Supports the work table and can be moved on the guide ways. WORKTABLE- Rests on the saddle and is provided with T-slots for mounting vice or other work holding devices SPINDLE- Hollow shaft supported by column. It obtains power from motor and transmits it to arbor. The arbor carries a cutter which rotates about horizontal axis

Milling Process Plain or Slab Milling- Performed on HMM for producing plain horizontal surfaces

End Milling- Process in which a cutter called END MILL is used for machining end surfaces Slots keyways Pockets on metallic parts

Slot Milling- Operation of producing slots in W/p Such as T-slots Dove tail slots etc. The cutter used is chosen according to the shape of the slot to be produced

Angular Milling- Process used for milling all types of angular cuts , Grooves on the work piece.

Form Milling- Used to produce curved profiles Concave, Convex , Spine etc. using cutters that have specially shaped teeth

Straddle milling- Process in which a pair of side milling cutters is used for machining two parallel surfaces on the W/p simultaneously

Gang Milling- Process used to make different profiles on the W/p say one side plain and other side angular

Grinding Machines • Process of removing excessive material by the abrasive action of the rotating wheel called as grinding . Basically this is a finishing operation. • The grinding wheel consists of sharp crystals called abrasives that are held together by suitable bonding

Principle of grinding • Here the excess material is removed by the rubbing action of abrasive particles. This process removes very small material in the form of chips

Abrasives • These are mineral crystals that act as a cutting edges in a grinding wheel. The hardness of crystals is much higher than that of W/p • Types of Abrasives • Natural Abrasives • Sand stone Diamond

Artificial Abrasives • Cubic boron carbide • Aluminum Oxide • Boron carbide • Silicon Carbide

Bonding materials • These are bonds which holds the abrasives crystals • Vitrified Bond----Commonly used bonding material made of clay and feldspar. This bond is strong rigid and not affected by fluids.

Silicate bond– Made of sodium silicate and used in operations that generate less heat not strong as vitrified bond • Resinoid bond- Synthetic plastic or resin that becomes hard after heating has good strength and elasticity

Rubber Bond—Made of natural or synthetic rubber but are less heat resistant . Used where good surface finish with high dimensional accuracy is required • Shellac Bond- Organic bond like resin and rubber. Has good strength and elasticity

Abrasives • Abrasive is the material employed for sharpening, grinding and polishing operations. • Natural abrasive – emery, corundum, quartz, sandstone, diamond, etc. • Artificial abrasive – carborundum, aloxite, alundum, etc. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Applications of abrasives • Corundum : is a natural mineral which consists of aluminium oxide. Hardest natural substance after diamond. • Used for shaping, finishing and polishing other tools. • Emery : natural abrasive consisting of aluminium oxide and little amount of iron oxide. • Silicon carbide : synthetic abrasive harder than aluminium oxide. • Used to grind metals like iron, brass and soft bronze. • Used in non metals like wood and leather industries. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Zirconia aluminia : it is a mixture of zirconium oxide and aluminium oxide. • Used in casting and foundry industries. • Cubic boron nitride : is made up of boron nitride with a cubic crystalline structure. • Used for hard coating material. • Diamond : www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Bonding materials • These are adhesives which holds the abrasive grains together. • Vitrified process : • Silicate process : • Elastic process : • Rubber or vulcanite process : www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Grinding machines • Grinding machine is a power operated machine tool where, the work piece is fed against constantly rotating abrasive wheel to remove thin layer of material from work. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Principle of grinding machines • Work piece is fed against the rotating abrasive wheel. • Due to action of rubbing or friction between the abrasive particles and work piece material is removed. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Classification of grinding machine • Bench grinding machine • Surface grinding machine • Cylindrical grinding machine • Center less grinding machine • Internal grinding machine • Special purpose grinding machine www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Surface grinding machine • It is machine basically used to grind flat surface. • Job is mounted to a table which moves longitudinally as well as in transverse direction. • Manual feed or power feed. • Work piece can clamped in two ways • Manual clamps. • Magnetic chuck. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Internal pump and piping arrangement for coolant. • Protective guard for safety. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Base • Column • Table traverse and vertical feed hand wheel. • Wheel guard and protective guard. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Working • Work piece is clamped to the table by operating magnetic chuck. • Required grade of grinding tool is fixed to spindle. • Grinding operation is carried out be operating both table traverse wheel and vertical feed hand wheel. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Cylindrical grinding machine • It is a process of grinding curved surfaces. • Surface may be straight or tapered. • Work piece is mounted on two centers, one is tailstock centre and the other is headstock centre. • Head stock center may or may not revolve. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Working principle www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

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Centre less grinding machine • It is used to grind curved surface work piece which are long and slender. • Work piece rests on a work-rest blade and is backed by a second wheel called as regulating wheel. • Grinding wheel pushes the work piece down the work-rest blade against the regulating wheel. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Cutting terminology • Speed : it is the peripheral speed of the work piece per unit time. (m/min) • Feed : it is the distance travelled by the tool during each revolution of the work piece. (mm/revolution). • Depth of cut : it is the perpendicular distance measured from the original surface to the machined surface of the work piece. (mm) www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Grinding Machines

Surface Grinding Machine Horizontal Spindle • This type of machine is used in grinding flat, angular and ir-regular surfaces

Cylindrical Grinding Machine • This type of machine is used for grinding external cylindrical surfaces that may be either plain or taper

Center-less Grinding Machine • This type of machines is used to grind surfaces of w/p that cannot be held between centers ex long shafts or bars

Milling Machines