Forjado de Metales

Ing. Carlos Andrés Pérez Tristancho 1


Forging technology occupies a very important place among all the manufacturing processes as it produces parts with excellent properties and with minimal wastage.

Through a series of operations, metals with very simple geometry are physically deformed into products of complex configuration.

In the forging process the metal is heated up by applying compressive force and given shape by plastic deformation.

The compressive force is applied by hammer blows using a power hammer or a press. Powered by compressed air, hydraulics electricity or steam. The weight of the hammer can be 500 pounds to thousands of pounds.

Forging has the capacity to refine the grain structure and improve the physical properties of the metal.

FORGING PROCESS


Typically a forged metal results in the following:

1.Dowing Out of the Metal: Increased length decreased cross-section.

2.Upsetting the Metal: Decrease in length Increased cross-section.

3.Change in Length; Change in Cross-section: Resulting in favourable grain flow for strong parts.

FORGING PROCESS


Automobile Industry: Wheel spindles, kingpins, axle beams and shafts, torsion bars, ball studs, idler arms and steering arm.

Agro-Industries: Engine and transmission components, levers, gears, shafts and spindles to tie-rod ends, spike harrow teeth and cultivator shafts.

Aerospace: Bulkheads, hinges, wing roots, engine mounts, brackets, beams, shafts, landing gear cylinders and struts, wheels, brake carriers and discs and arresting hooks, blades, buckets couplings etc.

Hand Tools: Sledges, pliers, hammers, wrenches and garden tools, as well as wire-rope clips, sockets, hooks, turnbuckles and eye bolts are common examples.

Industrial Equipment: Connecting rods, blanks, blocks, cylinders, discs, elbows, rings, T's, shafts and sleeves.

APPLICATIONS OF FORGING PROCESS


Impression Die Forgings

Net Shape

Open Die Forgings

Roll Forgings

Upset Forgings

Press Forgings

Swaging

METHODS OF FORGING


Impression die forging accounts for the majority of forging production. In this process, two dies are brought together.

The workpiece is then subjected to plastic deformation till its enlarged sides touch the die side walls.

Materials then begins to flow outside the die impression forming flash. As the flash cools down and increase its resistance to deformation, in effect it becomes part of the tool itself.

This creates pressure in the bulk of the workpiece and in the process helping the material to flow into the unfilled impression.



Closed die forging is another form of impression die forging. It does not depend on flash formation to achieve complete filling of the die. Material is deformed in a cavity that allows little or no escape of excess material, thus placing greater demands on die design.

Closed Die Forging


Precision die forgings that is produced on a horizontal forging machine (upsetter) is known as upsetting.

In Upsetting, stock is held between a fixed and moving die while a horizontal ram provides the pressure to forge the stock. After each ram stroke, the multiple-impression dies opens to permit transfer of stock from one cavity to another.

Precision Die Forgings


I As, it's a common occurrence that forging results in wastage of material in the form of material flash and machining operations.

This can reach 70% for gear blanks and even around 90% in case of aircraft structural parts. Net-shape and near-net-shape processes helps in minimizing this enormous waste by making precision dies and making parts with very little draft angle (less than 1º)

LimitationThis process is expensive in terms of tooling requirements and the capital expenditure involved. It can be only suited for processes that are very wasteful and the material savings made will pay for the rise in tooling costs.

Net Shape


Open die forgings are done with repeated blows in an open die, with the operator manipulating the workpiece in the die.

The process is called Open Die Forgings as the metal does not remain confined laterally by impression dies during the forging process.

Generally flat dies are used for open die forgings.

Round swaging dies and V dies can also be used together or with a flat die.

Generally heavy parts like shafts are forged. Part weights can range from 5 to 5,00,000 lbs.

Open die forgings can forge all ferrous and non-ferrous alloys, corrosion-resistant refractory alloys and materials like age-hardening super alloys

Open Die Forgings


Open Die Forgings


First the ingot or billet has to be lengthened either by reducing the cross-section or by dowing out.

Enlarging the diameter of the ingot or billet by upsetting or reducing the length.

Sometimes to forge a rough contoured ring a combination of upsetting, dowing out and piercing method is combined with forging

The forging workpiece is continuously hammered or pressed, and manipulated repeatedly between the dies until it reaches final forged dimensions

The process is not exactly precise and considerable workpiece stock allowances are kept to accommodate forging irregularities.

Operating Open Die Forgings


The forged part is then machined (both rough and finish) to final dimensions.

The metal to be forged is always hot worked above their recrystallization temperatures. It is done as the repeated change in the workpiece positioning makes its temperature fall below the recrystallization temperatures.

It has to be re-heated before further forging takes place. For e.g a 24 ft long and 2 ft diameter shaft requires four to six heats before the forged dimension is achieved.

A sub process of open die forgings is the Compression between flat dies, or Upsetting process. Whereby an oblong workpiece is placed at the end of a lower die whose height is reduced by the downward movement of the top die. The friction between the end faces of the workpiece and dies prevents the free lateral spread of the metal. Thus a barrel shape of the metal is produced. The barrel is resistant to deformation as contact with the cool die surface chills the end faces of the metal.

Operating Open Die Forgings


In the process of roll forging, a bar stock, round or flat is placed between die rollers which reduces the cross-section and increases the length to form parts such as axles, leaf springs etc.

Roll forgings has a wide spread use. As it can easily be made continuous by the use of multiple roller and dies.

Roll forging can also be said to be a type of dowing forging process as the workpiece is gradually drawn out into the requisite shape.

Application of Roll Forgings:

Propeller blades, tapered axle shaft shapes, continuous uniform shapes.

Roll Forgings


Roll Forgings


It's the production process under which high pressure deforms plastically metal into high strength components. It is also called hot heading process.

Using this process cross-sectional size of a bar can be increased, either at ends or at some point along the length. Specially designed upsetting machines using closed dies are used to control size and shape. They can be made in various sizes.

The mechanical press producing these components operates horizontally. The dies are split up allowing material to reach beyond the mechanical press. The forming force is supplied by a third die attached to the header. The process when done cold is called Cold Heading.

Upset Forgings


Upset Forgings


Advantages of Upset Forgings

Greater Strength:As the material grain flow is oriented to the component's shape, compared to parts machined from bar stock, upset forgings offer greater strength.

Piercing and Trimming Operations:This contribute towards component weight reduction and eliminate machining operations.

Economical Production:As Upset forgings require fewer operations, have lower scrap costs, that can result in more cost efficient production

Application of Upset Forgings:Artillery shells, cluster gear blanks, heads of bolts, valves, single and cylinders for radial engines are examples of parts made by upset forging.

Upset Forgings


In this process a slow continuous pressure is applied to the area to be forged.

The pressure extends deep into the material. Press forging can be either cold or hot. Cold press forging is generally used on thin, annealed materials, while a hot press forging is done on works such as locomotive armor plating and heavy machinery.

Cost wise, Press Forging is more economical than hammer forging (except when low production is required) and closer tolerances can be achieved.

A greater quantity of the work done is passed on to the workpiece. This way it differs from the hammer forging operation, where most of the work is absorbed by the machine and foundation.

This production process is ideally suited for larger forgings, as there is no limitation in the size of the machine.

Press Forgings


This method is related to the open die forging process where a tube or rod is forced inside a die and the diameter gets reduced as the cylindrical object is fed.

The die hammer is rotated to apply multiple blows at the diameter which can go up to 2000 per minute. This causes the metal to flow inward making the outer diameter of the tube or rod to take the shape of the die.

Application of Swaging:

Used for making pointing tube, bar ends, stepped columns and shafts with declining diameter.

Swawing


Swawing

Forjado de Metales

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