FORGING OF METALS

Prepared By:- DEVESH AGRAWAL

FORGING OF METALS Metal forging is one of the important aspects of

the metal forming process where deformation is induced by localized compressive forces.

It involves application of the compressive forces to a work piece to deform it and to create the desired geometric change to the material.

The equipment can be manual or power hammers, presses, or special forging machines. Metal undergoes triaxial compression during forging .

WHY FORGING IS IMPORTANT

This process is generally used to produce the discrete parts unlike rolling.In rolling different structural components are made on a continuous basis and then after whatever length we desired we can cut that much length using the shearing machine.Typical forged parts include rivets, bolts, crane hooks, connecting rods, gears, turbine shafts , hand tools and the variety of the structural components used to manufacture machinery.

FORGEABILITY

Fogeability is generally defined as the capability of a material to undergo deformation without cracking.

The Greater the deformation prior to cracking, greater will be the forgeability.

The metals are classified in order of their forgeability.

The limit up to which the material can be forged is cracking.

Al and mg can be forged easily than Ti.

TYPES OF FORGING PROCESSES

This can be classified in several ways one is

HOT forging VS COLD forging

Most metal forging operations are carried out hot due to need to produce large amount of deformation in

the part and the advantage of increment in ductility and

reduced strength of the work material. It also eliminates the problem of strain hardened

in the material.Forces that required will be comparatively less

than cold.

Although there are some disadvantages some scale formation may takes place control over the flow of the metal is not too

much in our hand. Dimensional control may not be that good by this.

Another one is cold forging which having some advantages like

Surface finish will be considerably better. In cases where it is desirable to create a

favourable strain hardening of the part . cold die forging may be employed.

produce greater surface finish and dimensional accuracy than hot die forging.

Some specific metal forging processes are always performed cold such as coining.

Disadvantages Requiring higher forces Process is not suitable for large scale

production. Heavier and more powerful equipment is

required

There are three major classification of metal forging process

open die forgingimpression die forgingflashless forging

OPEN DIE FORGING

In this the die is not enclosed in between the flat punch and flat die we will bring our raw material which has to be forged and then it is held manually tang has been used and we are applying the compressive forces.

This raw material can either be in cold or hot state depending upon requirement.

Few points about this Simplest forging process Quite flexible but not suitable for large scale

production Slow process Quality depends on the skills of the operator.

UPSETTINGA simple type of open die forging is called

upsetting. In an upsetting process the work is placed between two flat die and its height is decreased by compressive forces exerted between the two die. These are of two types

Upsetting a flat die forging under ideal condition

Upsetting in flat die forging under real condition

COGGING Cogging is an open die forging process in which flat or

slightly contoured die are employed to compress a work piece, reducing its thickness and increasing its length . In a cogging operation, the forging is large relative to the size of the die.

Sometimes formed products such as m et al fences may be produced directly from cogging .

FULLERING

Fullering is used as an earlier step to help in distribution of the material of the work In preparation for further forging operation. Fullers are used for this. eg.-forging of connecting rod for an internal-combustion engine.

EDGINGEdging is also an open die forging process often

used in manufacturing practice, to prepare a work for sequential metal forging processes. In edging , open di e with concave surfaces plastically deform

fullering both are used to redistribute bulk quantities of the metal forging's material .

FORGING FORCEThe forging force in case of open die

forging to be applied on a solid cylindrical component can be determined from following relation

IMPRESSION DIE FORGING

It is not like a open flat punch type arrangement in this we use shaped dies to control the flow of the metal.

The shape we want to make has been exactly replicated in the form of the die. the heated metal is positioned in the lower cavity and one or more blows are struck by the upper die this makes metal to flow and fill the die cavity completely.

The excess of the metal is squeezed around the periphery of the cavity to form flash. on completion of the forging the flash is trimmed out with the help of trimming dies.

In both open and impression forging the shape may not be change from its initial to final in one step it will done in no. of steps.

PRECISION FORGING If we want that the product which we are getting

near net shape .it should be according to the desired shape & dimensional accuracy and the finishing should be extremely good then we go to precision forging no further machining is required.

it may produce some or no flash The number of manufacturing operations is reduced as well as the material wasted.

The disadvantages of these advanced forging methods are that special machinery and die are needed, also more careful control of the manufacturing process i s required.

Its most basic type is flashless forging

FLASHLESS FORGING

Flashless forging is a type of precision forging process in which the entire volume of the work metal is contained with in the die and no material is allowed to escape during the operation. Since no material can leave the mold as the part is forged, no flash is formed.

DEFECTS IN FORGINGDefects of metal forged product

include exterior cracking, interior cracking, laps, cold shuts, warping of the part, improperly formed sections and dead zones.

Cracking both interior and exterior is caused by excessive stress, or improper stress distribution as the part is being formed. high thermal gradient can cause the cracks in the forged parts.

Warping of a forged part can happen when thinner sections cool faster than the rest of the forging .

Cold shuts occur when metal flows of different temperatures meet, they do not combine smoothly, a boundary layer, (cold shut ),forms at their intersection. It indicates that there is is problem with the metal flow in the mold as the part is being formed.

Laps in a metal forging are caused by a buckling of the part , laps can be a result of too little material in the work piece.

Improperly formed sections and dead zones can be a result of too little metal in the work piece. flawed forging die design resulting in incorrect material distribu tion during the process.

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