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MI-102: Manufacturing Techniques I. I. T. ROORKEE

FORMING PROCESSES Forming is a deformation based approach used to give the

desired size and shape. Therefore, all factors affecting the deformation tendency

(ductility, yield strength, strain hardening) will eventually affect the performance of the forming processes.

In General an increase in the Temperature results in Decrease in Strength Increase in Ductility Decrease in the Rate of Strain Hardening

All these effects ease of deformation required for forming

On the basis of forming Temperature forming processes can classified as COLD Forming WARM Forming HOT Forming


COLD FORMING HOT FORMINGBelow their Recrystallization Temperature

Above their Recrystallization Temperature

Temperature of Deformation < 0. 3 Melting Temperature on the Absolute Scale

Temperature of Deformation > 0.6 Melting Temperature on the Absolute Scale

Recrystallization Temperature Varies Greatly with the Material Tin is Near Hot-Working at Room Temperature while Steel Require Temp. near 1100oC

WARM FORMING: Deformation Between 0.3 to 0.6 Times the Melting Point on the Absolute Scale


Hot Working Cold Working Processes

Forging Rolling Extrusion Hot Drawing Piercing

Squeezing: Cold Rolling, Cold Forging , Cold Extrusion, Coining, Peening, Burnishing, and Thread Rolling.Bending: Angle Bending, Roll Bending, Roll-forming, and Straightening.Shearing: Slitting, Blanking, Piercing, Notching, Nibbling, Drawing: Spinning, Embossing, Stretch Forming, and IroningSheet-metal Forming Operations


FORGING Involves application of force on metal to

cause plastic deformation so as to get the required final shape.

Forging is Generally a Hot Working but also be Cold Forging.

Forging can be done in two ways

Drawing Out: Elongates the object with a Reduction in the Cross-Sectional Area using Force Applied in a Direction Perpendicular to the longitudinal Axis.

Upsetting: increases the Cross-Sectional Area of the Stock at the Expense of its Length using Force Applied in a Direction Parallel to the Length Axis.

Drawing Out

Upsetting


FORGING TYPES

Smith Forging: Traditional Forging

performed using Open Dies with help of

Manual or Powered Hammers.

Drop Forging: uses Closed Impression

Dies by Means of Drop Hammers in a

Series of Blows.

Press Forging: is Similar to Drop Forging

with the Difference that the Force is a

Continuous Squeezing Type.

Machine Forging: the Material is only

Upset to Get the Desired Shape using a set

of dies.


SMITH FORGING

Involves Heating the Stock in the Blacksmith's Hearth and then Beating it Over the Anvil.

The stock is Manipulated in Between the Blows.

Used for low volume production of variety of designs.


The Drop Forging Die Consists of Two Halves. The Lower Half is Fixed to the Anvil of the

Machine, While the Upper Half of the Die is Fixed to

the Ram. The Heated Material Stock is Kept in the

Lower Die while the Ram Delivers Four to Five Blows on the Material, in Quick Succession so that the Material Spreads and Completely Fills the Die Cavity.

When the Two Die Halves Close, the Complete Cavity is Formed.

Since the Machined impressions in the Die Cavity help to get more Complex Shapes in Drop Forging as Compared to Smith Forging


Drop forging


Typical Products Produced by Drop Forging are Crank, Crank Shaft, Connecting Rod, Wrench, Crane Hook, etc.

Final Shape Desired in Drop Forging Cannot be Obtained Directly from the Stock in a Single Pass.

Depending on the Shape of the Component, and the Desired Grain Flow Direction, the Material should be Manipulated in a Number of Passes.


FULLERING IMPRESSION: Reducing Stock to the Desired Size.

EDGING IMPRESSION (Preforming): Ensures Defect-Free Flow of Material, Complete Die Fill and Minimum Flash Loss.

BENDING IMPRESSION: for the Parts having a Bent Shape.

BLOCKING is a Step before Finishing. The Material Flows to Deep Pockets, Sharp Corners, etc. before the Finishing Impression without Flash.

FINISHING: is the Final Impression for Actual Shape .at this stage a Little Extra Material is Added to the Stock Forms the Flash and Surrounds the Forging in the Parting Plane.

TRIMMING is removal of the Extra Flash Present Around the Forging to make the Forging in Usable .


In Press Forging, involves Single Continuous Squeezing Action results in Uniform Deformation Throughout the Depth.

The Impressions Produced in the Press Forging are Cleaner as Compared to the Jarred Impressions Produced in the Drop Forged Components.

Press forging suits for smaller size components than drop forging as former needs higher Press Capacity for Deforming in Closed Impression Dies. No such Limitation for Press Forging in Open Dies.

Presses Capacities May Range from 5 MN to 50 MN for Normal Applications and as High as 600 MN for Special Heavy Duty Applications.

PRESS FORGING


Initially Developed for Making the Bolt Heads in a Continuous Fashion.

Due to Beneficial Grain Flow Obtained in Upsetting, it is Used for Making Gear Blanks, Shafts, Axles and Similar Parts. Some Typical Parts Produced by Upset Forgings are Shown in the Figure.

The Die Set Consists of a Die and a Corresponding Punch or a Heading Tool.

MACHINE FORGING


The Upset Forging Cycle

Movable Die comes closer to Stationary Die to Grip

the Stock.

The Two Dies in Closed Position Form the

Necessary Die Cavity.

The Punch Upsets stock to Fill the Die Cavity.

After Upsetting, Punch Moves Back to its Position.

Movable Grippes Release the Stock.

Similar to Drop Forging, the Upsetting Operation is

Carried Out in a Number of Stages or Passes.

The Material Stock is Moved from One Stage to the

Other in a Proper Sequence Till the Final Forging is

Ready.

MACHINE FORGING


Some Typical Upset or Machine Forged Components


FORGING DEFECTS

Unfilled Sections: of Die Cavity by the Flowing Material due to: Improper Design of Forging Die or Faulty Forging Techniques.

Cold Shut: A Small Crack at the Corners of the Forging due to Improper Design of the Die e.g. Corner and Fillet Radii are Small which in turn results in small cracks due to poor flow of materials at the Corner.

Scale Pits: Irregular Depressions on the Surface of the Forging primarily due to improper Cleaning of the Stock Used for Forging.

The Oxide and Scale Present on the Stock Surface Gets Embedded into the Finished Forging Surface. When the Forging is Cleaned by Pickling, these are Seen as Depressions on the Forging Surface.


Die Shift: CAUSES: Die Shift is Caused by the Misalignment of the Two Die Halves

Making the Two Halves of the Forging to be of Improper Shape.

Flakes: These are Basically Internal Ruptures due to poor ductility of surface layer during deformation caused by Rapid Cooling


ROLLING

Rolling is a Process where the Material is Compressed Between Two Rotating Rolls for Reducing its Cross-Sectional Area.

Rolling is Normally a Hot Working Process unless specified as Cold Rolling.

At Entry, the Surface Speed of Rolls is Higher than that of the Incoming Material, whereas the Material Velocity at the Exit is Higher than that of the Surface Speed of the Rolls due to difference cross sectional area.


Scheme of Rolling Process


Rougher Rolls Achieve Greater Reduction than Smoother Rolls. But, the Rough Roll Surface may Get Embedded into the Rolled Metal thus Producing Rough Surface.

The Reduction that could be Achieved with a Given Set of Rolls is Designated as the Angle of Bite. This Depends on the Type of Rolling and the Conditions of the Rolls as shown in Table.


ROLLING STAND

2-High Reversing Rolling Stand:

Direction of Roll Rotation can be Reversed these reduce Handling of the Hot Material in Between the Rolling Passes.


3-High Rolling Stand:

Arrangement is Used for Rolling of Two Continuous Passes in a Rolling Sequence without Reversing the Drives.

A Table-Tilting Arrangement is Required to Bring the Material to the Level with the Rolls.


4-High Rolling Stand: Backup Rolls for Providing the Necessary Rigidity to the

Small Rolls.


Since Required Final Shape Cannot be Obtained in a Single Pass The Rolling Mills are Generally need More

than One Pass to other stands or by Reversing the Roll Direction or

The Steel Ingot: 600 x 600 mm. These Ingots are Further Processed in Rolling Mills to Produce the Intermediate Shapes such as Blooms, Slabs and Billets.

Blooms: 150 x 150 mm to 400 x 400 mm (square).

Slabs: 500 to 1800 mm and Thickness from 50 to 300 mm (rectangle).

Billets: from 40 x 40 mm to 150 x 150 mm (rectangle).


Roll Pass Sequence can be Broadly Categorized into THREE Types:

1. Break Down Pass: Used for Reducing the Cross-Sectional Area

Nearer to what is Desired. 2. Roughing Pass:

The Cross-Section Gets Reduced, but Shape of the Rolled Material also Comes Nearer to the Final Shape.

3. Finishing Pass: Gives the Required Shape of the Rolled Section.

ROLL PASSES


DRAUGHT

If the Cross Section of the Product Before and After Rolling Process is A x B and a x b Respectively, DRAFT is Defined as (A + B)- (a + b)

Roll Pass Schedule can be obtained from Draught.

If Mean Draught for Each Pass is Known, then Number of Passes can be Estimated.

Draught Provided in Each Pass also Depends on the Work Material, Angle of Bite, Roll Strength, Power of the Rolling Mill,

and Condition of the Rolls.


Draughts of All the Passes in the Rolling Sequence are NOT the Same. The Main Criteria for Choosing the Draught

is the Angle of Bite. Lower draught is used in subsequent passes. Reason for Reducing Draught in the Later

Passes: in Hot Rolling the Reduction in Stock

Thickness which Causes it to Lose Heat Quickly and thus Increases the Rolling Load.

in Cold Rolling, the Strain Hardening of the Stock Material Necessitates a Reduction in Draught in the Succeeding Passes.

Selection of draught


EXTRUSION In Extrusion Process, the Material is Confined in a Closed Cavity

and then Forced to Flow From Only One Opening so that the Material Takes the Shape of the Opening.


Used to Make Components having a Constant Cross-Section over any Length. More Complex Parts can be Obtained by Extrusion than

that of Rolling, as Die become Simple and Easier to Make.

Extrusion is a Single Pass Process. The Amount of Reduction Possible in Extrusion is Large.

Generally Brittle Materials can Also be Very Easily Extruded.

Typical Extrusion Shapes


Extrusion Ratio is Defined as the Ratio of Cross-Sectional Area of the Billet to that of the Extruded Section. Typical Values of the Extrusion Ratio are 20

to 50. The Extrusion Pressure for a Given Material

Depends on the Extrusion Temperature, Reduction in Area, and Extrusion Speed


CLASSIFICATION OF EXTRUSION PROCESS


FORWARD HOT EXTRUSION

The Direction of Flow of Material is the Same as that of the Ram.

Friction is Important Because of the Relative Motion Between the Heated Material Billet and the Cylinder Walls. Lubricants are to be used To Reduce this Friction.

Forward Extrusion

For Low Temperatures:, Oil Mixture and Graphite

For High Temperature, Molten Glass for Extruding Steels.


BACKWARD or INDIRECT HOT EXTRUSION

The Ram Compresses the Material Against the Container, Forcing the Material to Flow Backwards through the Die in the Hollow Plunger or Ram.

Since Billet in the Container Remains Stationary No Friction.

Backward Extrusion

Extrusion Pressure is Not Affected by the Length of the Billet as friction in absent

Problem is imposed by Handling Extruding Material Coming Out through the Moving Ram.


FORWARD COLD EXTRUSION

Forward Cold Extrusion is Similar to the Forward Hot Extrusion Process Except with low Extrusion Ratios and high Extrusion Pressures.

Used for Simple Shapes with Better Surface Finish and Mechanical Properties.

IMPACT EXTRUSION

It is modification of Backward Cold Extrusion Carried Out by the Impact Force of the Punch.

Material is Extruded through the Gap Between the Punch and Die Opposite to the Punch Movement.

Suitable for Softer Materials such as Aluminum and its Alloys.

Used for Making the Collapsible Tubes for Housing Pastes, Liquids and similar Articles.


Impact Extrusion


COLD EXTRUSION FORGING:

The Cold Extrusion Forging is Similar to Impact Extrusion, the Main Difference being the Side Walls much Thicker

and with More Height. The Component is Ejected by Means of the Ejector Pin

Provided in the Die


HYDROSTATIC EXTRUSION:

The Material Billet is Compressed from all Sides by a Liquid Rather than the Ram.

The Material is Uniformly Compressed from All Sides throughout the Deformation Zone. Consequently Highly Brittle Materials such as

Grey Cast Iron can also be Extruded. Commercial Applications of the Hydrostatic

Extrusion are Limited to Extrusion of Reactor Fuel Rods, Cladding of Metals, and Making Wires of Less Ductile Materials.


Hydrostatic Extrusion


WIRE DRAWING Wire Drawing is a cold working process to Obtain Wires

from Rods of Bigger Diameter through a Die.

The End of the Rod is Made into a Point Shape and Inserted through the Die Opening then Pull the Wire through the Die with help of griper

Material to be Wire Drawn should be Sufficiently Ductile.

DRAWING


Wire Drawing Set Up

Various Die Materials Used are Chilled Cast Iron, Tool Steels, Alloy Steels, Tungsten Carbide and Diamond.


In Tube Drawing, a Mandrel of the Requisite Diameter is Used to Form the Internal Hole.

The Tubes are also First Pointed and then Entered through the Die where the Point is Gripped in Similar way as the Wire Drawing and Pulled Through.

TUBE DRAWING


SHEET METAL OPERATIONS

Metal Sheet: Plates of thickness < 5 mm Sheet metal operations use different types

of stresses for processing Shear stress is primarily used in sheet

metal processing

Stress Induced Operations

Shearing Shearing, Blanking, Piercing, Trimming, Shaving, Notching, Nibbling

Tension Stretch-Forming

Compression Ironing, Coining

Tension and Compression

Drawing, Spinning, Bending, Embossing, Forming


SHEARING The Sheet IS deformed between two shearing

Blades (developing tensile and compressive stress). Then cracks nucleate and grow when material near

cutting edges is elongated beyond fracture limit which later join for separation.


BLANKING:

Process of obtaining a small piece of strip by cutting (shearing from the Stock with help of a Punch.

The removed strip is Called Blank used for further processing to get useable product.

Blanking/Punching Die

PUNCHING: Similar to blanking except that objective is to make Holes in Sheet and removed strip is considered as scrap


WITHOUT PROPER GRIPPING OF SHEET

ROUGH EDGE


WITH PROPER GRIPPING OF SHEET

CLEAN AND SMOOTH EDGE


TRIMMING:

Removing Small Amount of Extra Material Spread Out Near the Parting Plane such as Drop Forging and Die Casting.

SHAVING Removal of the Burrs Generated during the Shearing Process

in the Blanking or Punching Operation so as to achieve the Close Tolerance Work.

NIBBLING: Removing the Material in Small Increments to Cut a Specific

Contour on a Sheet using repeating Punching.

Nibbling is Used When the Contour is Long and a Separate Punch is Impractical and Uneconomical.

NOTCHING: Cutting a Specified Small Portion of Material Towards the Edge of the Material Stock.


STRETCH-FORMING

The Sheet is Clamped at ends and Stretched over the Die so as to achieve plastic State and permanent deformation.

SHEET METAL OPERATIONS INVOLVING TENSION


Stretch forming


IRONING

It involves thinning and lengthening of the wall of material by generating compressive stress between the Die and Punch having using the Clearance (spacing) finer than the Drawing Operation.

Up to 50% thinning can be obtained in a Single Ironing Operation

Ironing Operation

SHEET METAL OPERATIONS INVOLVING COMPRESSION


COINING It is just like a Cold Forging Operation except that the

Flow of the Material Occurs Only at the Top Layers

and NOT in the Entire Volume. The Punch and Die have Engraved Details Required on

Both Sides of the Final Object and uses high pressure

(1600 MPa) to get Fine Details on the Surface.

For Making Coins, Medals & Impressions on Decorative Items


DRAWING/DEEP DRAWING

Drawing is the Process of Making Cups (high < half diameter), and similar product, from Metal Blanks.

When the Cup Height is More than Half the Diameter, the Drawing Process is known as Deep Drawing.

SHEET METAL OPERATIONS INVOLVING TENSION and COMPRESSION


Blank Holding in Deep Drawing


SPINNING Used for Making Axi-Symmetrical Cup Shaped Articles. Force (moving) is Applied on the Rotating Blank is Held

Against the Form Block so as get Shape of the Form Block (of wood).


BENDING

Operation of Deforming a Flat Sheet Around a Straight Axis at the Neutral Plane.

When material is subjected to plastic deformation, the Neutral Axis Moves Downward due to differential strain on both sides of neutral axis as the Materials Oppose Compression in much Better way than Tension.

Nomenclature of Bending and Type of Bending Methods are Shown in Following Figures.


Nomenclature of Bending


Type of Bending Methods


EMBOSSING

An Operation for Making Raised Figures/letter on Sheets with its Corresponding Relief on the Other Side.

The Process Involves Drawing and Bending of the Material.

Generally Used for increasing the Rigidity by localized deformation and for Decorative Sheet Work.

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