PRODUCTION TECHNIQUES FORGING OF METALS - …badrossamay.iut.ac.ir/sites/badrossamay.iut.ac.ir/files//files... · PRODUCTION TECHNIQUES FORGING OF METALS ... Solid cylindrical billet

Production techniques_forging

Mohsen Badrossamay 1

Dep. of Mech. Eng.

DEPARTMENT OF MECHANICAL ENGINEERINGISFAHAN UNIVERSITY OF TECHNOLOGY

PRODUCTION TECHNIQUES

FORGING OF METALS

Dep. of Mech. Eng.

An introduction to forging process

Dating back at least to 4000 B.C., to make jewelry, coins,..

Shaping the workpiece by compressive forces applied through various dies and tooling

Include large rotors for turbines; gears; bolts and rivets; hand tools; machinery components; aircraft, railroads,…

Production of discrete parts with good strength and toughness

Very reliable for highly stressed and critical applications2



Dep. of Mech. Eng.

Forging temperature: at room temperature (cold forging) at elevated temperatures (warm or hot forging)

Cold forging characteristics: Requires higher forces The material must have sufficient ductility at room temperature to

undergo the necessary deformation without cracking Parts with good surface finish and dimensional accuracy

Hot forging requires lower forces; dimensional accuracy and surface finish of the parts are not as high as in cold forging

Forgings generally are subjected to additional finishing operations, such as heat treatment to modify properties and machining to obtain accurate final dimensions and surface finish


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Dep. of Mech. Eng.

The finishing operations can be minimized by precision forging

The quality, dimensional tolerances, and surface finish of the forging depend on how well these operations are performed and controlled

Dimensional tolerances range between ±0.5 and ±1.0% of the dimensions of the forging

Tolerances for hot forging of steels usually are less than ±6mm in good practice

In precision forging as low as ±0.25mm


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Dep. of Mech. Eng.

Forged Components

(a) Schematic illustration of the steps involved in forging a knife. (b) Landing-gear components for the C5A and C5B transport aircraft, made by forging. (c) General view of a 445 MN (50,000 ton) hydraulic press (Courtesy of Wyman-Gordon Company).

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Dep. of Mech. Eng.

Microstructure as a Function of Manufacturing Method

Schematic illustration of a part made by three different processes showing grain flow:

(a) Casting by the processes described in casting processes chapter

(b) Machining form a blank, to be introduced later

(c) Forging.

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Dep. of Mech. Eng.

Characteristics of Forging

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Dep. of Mech. Eng.

Open-die forging The simplest forging operation Parts weights 15 to 500 kg, but as heavy as 270 tones have

been made Part sizes range from nails and pins to very large (up to 23m

long shaft for ship propellers) Flat or shallow cavities dies to produce simple forgings Flat-die forging or upsetting includes placing a solid

workpiece between two flat dies and reducing its height by compressing it Ideal condition is frictionless upsetting Actual operation develops the part to a barrel shape (pancaking)

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Dep. of Mech. Eng.

Upsetting with Barreling

(a) Solid cylindrical billet upset between two flat dies. (b) Uniform deformation of the billet without friction. (c) Deformation with friction.

Barreling is caused by frictional forces at die-workpiece interface that oppose the outward flow of the materials

Also can develop in upsetting hot workpiece between cold dies

Barreling can be minimized using an effective lubricant Thermal affected barreling can be reduced, or eliminated by

using heated dies, and thermal barriers such as glass cloth

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Dep. of Mech. Eng.

Forging force in upsetting

2 2 13f

rF Y rh

WhereYf is the flow stress of the material, µ is the coefficient of

friction between the workpiece and the die, and r and h are the radius and height of the workpiece, respectively

Example: Calculate the forging force at the end of an upsetting process where a solid cylindrical slug made of 304 stainless steel with 150 mm diameter and 100 mm height is reduced in height by 50% at room temperature. Assume that the coefficient of friction is 0.2.

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Dep. of Mech. Eng.

Cogging Operation on a Rectangular Bar

(a) Schematic illustration of a cogging operation on a rectangular bar. Blacksmiths use this process to reduce the thickness of bars by hammering the part on an anvil.

(b) Reducing the diameter of a bar by open-die forging; note the movements of the dies and the workpiece.

(c) The thickness of a ring being reduced by open-die forging.11

Dep. of Mech. Eng.

Impression-die forging A type of closed-die forging in which the workpiece takes the

shape of the die cavity while being forged For enhancing metals ductility and lowering the force is

carried out at elevated temperatures Its characteristic is the formation of flash which is excess

metal that is subsequently trimmed off The high pressure and the resulting high frictional resistance

in the flash presents a severe constraint to the material in the die for outward flow

As a consequence the material begins to flow into the die cavity based on the principle that in plastic formation the material flows in the direction of least resistance because it requires less energy

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Dep. of Mech. Eng.

Impression-Die Forging

(a) through (c) Stages in impression-die forging of a solid round billet.

(d) Standard terminology for various features of a forging die.

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Dep. of Mech. Eng.

Die Inserts

Die inserts used in forging an automotive axle housing.

A forging die may be made of several segments including die inserts

The inserts are made of stronger and harder materials

The inserts can be replaced easily in the case of wear or failure in a particular section of the die

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Dep. of Mech. Eng.

Preparing forging blanks The blank is prepared:

a) Cropping from an extruded or drawn bar stockb) Using a pre-form from operations such as powder metallurgyc) Castingd) Using a pre-form blank from a prior forging operatione) A type of closed-die forging in which the workpiece takes the

shape of the die cavity while being forged

Preforming operations are used to distribute the material properly into various regions of the blank using simple shaped dies of various contours Fullering: material is distributed away from an area Edging: material is gathered into a localized area Blocking: forms the part into the rough shape

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Dep. of Mech. Eng.

Forging a Rod, Fullering, and Edging

(a) Stages in forging a connecting rod for an internal combustion engine.

(b) Fullering and (c) edging operations to properly distribute the material when preshaping the blank for forging.

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Dep. of Mech. Eng.

Trimming Flash After Forging

Trimming flash from a forged part. Note that the thin material at the center is removed by punching.

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Dep. of Mech. Eng.

Force in Impression Die ForgingF kY f AEstimation of the forging

force:WhereYf is the flow stress of the

material at the forging temperature

k is a multiplying factor obtained from the table

A is projected area of the forging including the

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Dep. of Mech. Eng.

Closed-die forging Although impression-die forging is a closed-die process, in

true closed-die process the flash does not form In flashless forging the workpiece completely fills the die

cavity The forging pressure is very high Accurate control of the blank volume and proper die design

are essential in order to produce a forging with the desired dimensional tolerances Undersized blanks prevent the complete filling of the cavity Oversized blanks generate excessive pressures and may cause dies

to fail or the machine to jam

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Dep. of Mech. Eng.

Closed-Die Forging Versus Flashless Forging

Comparison of closed-die forging with flash (left side of each illustration) and precision or flashless forging (right side) of a round billet.

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Dep. of Mech. Eng.

Precision forging Reducing the number of additional finishing operations

required - hence the cost Typical parts: gears, connecting rods, and turbine blades Precision forging requires:

a) Special and more complex diesb) Precise control of the blank’s volume and shapec) Accurate positioning of the blank in the die cavityd) Higher-capacity equipments

Aluminum and magnesium alloys are suitable for precision forging because of the relatively low forging loads and temperatures that they are required

Steels and titanium also can be precision forged

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Dep. of Mech. Eng.

Various forging operations Coining:

A closed-die forging process which is used in minting coins, medallions, and jewelry

In order to produce fine details the pressure required can be as high as five or six times the strength of material

Lubricants cannot be applied in coiningMarking parts with letters and numbers can be done

rapidly by this process Coining is also used with forgings and other products to

improve surface finish

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Dep. of Mech. Eng.

The Coining Process

(a)Schematic illustration of the coining process. The earliest coins were made by open-die forging and lacked precision and sharp details.

(b)An example of a modern coining operation, showing the workpiece and tooling

(b)

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Dep. of Mech. Eng.

Various forging operations Heading:

Also called upset forging, is an upsetting operation usually performed on the end of a round rod or wire in order to increase the cross-section

Typical examples are nails, bolt heads, screws, rivets, and various other fasteners

Can be carried out cold, warm, or hot The length-to-diameter ratio of the bar has to be in a range to

prevent buckling of the bar (limited less than 3:1) Higher ratios can be carried out if the diameter of die cavity is not

more than 1.5 times the bar diameter

Piercing: The process of indenting the surface of a workpiece with a

punch in order to produce a cavity or an impression

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Dep. of Mech. Eng.

Heading

(a) Heading operation to form heads on fasteners, such as nails and rivets.

(b) Sequence of operations to produce a typical bolt head by heading.25

Dep. of Mech. Eng.

Grain Flow in Forging (piercing)

A pierced round billet showing grain-flow pattern. Source: Courtesy of Ladish Co., Inc.

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Dep. of Mech. Eng.

Stepped Pin

(a) The stepped pin from SAE 1008 steel used as a part of a roller assembly to adjust the position of a car sit

(b) Illustration of the manufacturing (cold-forging) steps used to produce the stepped pin. Source: Courtesy of National Machinery, LLC.

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Dep. of Mech. Eng.

Swaging

(a) Schematic illustration of the rotary-swaging process. (b) Forming internal profiles on a tubular workpiece by swaging. (c) A die-closing swaging machine showing forming of a stepped shaft. (d) Typical parts made by swaging. Source: Courtesy of J. Richard Industries.

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Dep. of Mech. Eng.

Swaging with and without a Mandrel

(a) Swaging of tubes without a mandrel; note the increase in wall thickness in the die gap. (b) Swaging with a mandrel; note that the final wall thickness of the tube depends on the mandrel diameter. (c) Examples of cross-sections of tubes produced by swaging on shaped mandrels. Rifling (internal spiral grooves) in small gun barrels can be made by this process.

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Dep. of Mech. Eng.

Forgeability of metals The capacity of a material to undergo deformation without cracking

Tests for quantifying the forgeability:

(a) Upsetting test: a solid, cylindrical specimen is upset between flatdies, and the reduction in height at which cracking on the barreledsurfaces begins is noted; the greater the deformation prior tocracking, the greater the forgeability

(b) Hot-twist test: a round specimen is twisted continuously in thesame direction until it fails. This test is carried out on a number ofspecimens and at different temperatures, and the number ofcomplete turns that each specimen undergoes before failure isplotted. The temperature at which the maximum number of turnsoccurs then becomes the forging temperature for the maximumforgeability

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Dep. of Mech. Eng.

Metals in Decreasing Order of Forgeability

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Dep. of Mech. Eng.

Speed Ranges of Forging Equipment

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Dep. of Mech. Eng.

Economics of Forging

Typical (cost-per-piece) in forging; note how the setup and the tooling costs-per-piece decrease as the number of pieces forged increases if all pieces use the same die.

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Dep. of Mech. Eng.

Comparison of a connection rod costs made by Forging and Casting

Relative unit costs of a small connecting rod made by various forging and casting processes

Sand casting is the most economical process for fewer then about 20,000 pieces.

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Dep. of Mech. Eng.

Case studyLotus Elise Series 2 and Vertical Suspension Uprights

(a) The Lotus Elise Series 2 Sports car; (b) illustration of the original design for the vertical suspension uprights, using an aluminum extrusion; (c) retrofit design, using a steel forging; (d) optimized steel forging design for new car models. Source: Courtesy of Lotus Engineering and the American Iron and Steel Institute. 35

Dep. of Mech. Eng.

Case study Comparison of Suspension Designs for the Lotus

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PRODUCTION TECHNIQUES FORGING OF METALS - …badrossamay.iut.ac.ir/sites/badrossamay.iut.ac.ir/files//files... · PRODUCTION TECHNIQUES FORGING OF METALS ... Solid cylindrical billet