Metal Forming Processes - Comprehensive Notes

Metal Forming Operations

Classification of Metal Forming Operations

Bulk deformation processes are characterized by significant deformations and massive shape changes.
The surface area-to-volume ratio of the starting metal is relatively small.
The term "bulk" describes work parts with a low surface area-to-volume ratio.

Sheet Metal Working

Sheet metal operations are always performed as cold working processes.
They typically use a punch and die setup.
The punch is the positive portion of the tool set, and the die is the negative portion.

Cold Working and Hot Working of Metals

Working metals below 0.75 $Tm$ is considered cold working, and above 0.75 $Tm$ is hot working, where $T_m$ is the melting point (absolute temperature) of the metal.

Comparison of Cold Working and Hot Working

(This section likely contains a detailed comparison, but specific details are not provided in the transcript.)

Forging

Forging is a deformation process where work is compressed between two dies using impact or gradual pressure.
It's used to make high-strength components for automotive, aerospace, and other applications (e.g., engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts).
Forging hammer applies impact load; forging press applies gradual pressure.

Advantages of Forging

Maintains continuity of grains/fibers in the metal structure, increasing strength.
Refines and improves grain structure.
Improves ductility and impact resistance.
Reduces thicker sections into desired shapes rapidly.
Eliminates porosity, an inherent defect in cast steel ingots.

Classification of Forging Processes

Open-die forging
Impression-die forging
Flashless forging

Open-Die Forging

Work is compressed between two flat (or almost flat) dies, allowing metal to flow laterally without constraint.
Upsetting (or upset forging) reduces height and increases diameter.

Open-Die Forging Operations

Upsetting
Fullering
Edging
Cogging (Drawing Down)
Heading

Fullering

Reduces stock between two ends at a central place to increase length.
Inclined die surfaces prevent material movement in the width direction.
Repeated strokes with workpiece rotation allow material redistribution.
Used to reduce cross-section and redistribute metal in preparation for subsequent shape forging.
Accomplished by dies with convex surfaces.
Fullering die cavities are often designed into multi-cavity impression dies for rough forming.

Edging

Similar to fullering, but dies have concave surfaces.
Distributes metal longitudinally, moving it from excess to deficient portions.
Important in closed-die forging (e.g., forging a connecting rod).

Cogging (Drawing Down)

A sequence of forging compressions along the workpiece length to reduce cross-section and increase length.
Used in the steel industry to produce blooms and slabs from cast ingots.
Accomplished using open dies with flat or slightly contoured surfaces.
Sometimes called incremental forging.
Similar to fullering, but reduces stock at one end only, increasing its length.

Heading

Upsetting done to increase the section of the stock at only one end.

Impression-Die Forging (Closed Die Forging)

Dies contain the inverse shape of the desired part.
Flash forms as metal flows beyond the die cavity into the small gap between die plates.
Flash must be trimmed in a subsequent operation.
Friction resists continued flow into the gap, constraining the bulk of the material in the die cavity.

Flashless Forging {True closed die forging (No flash)}

Requires precise process control.
Work volume must closely equal the space in the die cavity.
Excessive pressure can damage the die or press if the blank is too large.
The cavity will not fill if the blank is too small.
Best suited for simple, symmetrical part geometries and materials like aluminum and magnesium alloys.
Often classified as a precision forging process.

Lubrication in Metal Forming Operations

Rolling

Hot rolling of ferrous metals typically done without lubricant, but graphite can be used if needed.
Water-based solutions are used to cool rolls and break scale.
Hot rolling of non-ferrous metals: wide choice of compounded oils, emulsions, and fatty acids.
Cold rolling: water-soluble oils, low-viscosity lubricants such as mineral oils, emulsions, paraffins, and fatty acids.

Forging

Lubricants influence friction, wear, deforming forces, and material flow in die cavities.
They act as thermal barriers between the workpiece and dies, slowing cooling and improving metal flow.
They serve as parting agents to prevent sticking.
Hot forging: graphite, $MoS_2$ , and sometimes molten glass.
Cold forging: mineral oil and soaps. Lubricant applied to dies in hot forging, but to the workpiece in cold forging.

Extrusion

Hot extrusion: glass is an excellent lubricant with steels, stainless steels, and high-temperature alloys.
Cold extrusion: lubrication is critical, especially with steels, to prevent sticking.
Most effective lubricant: phosphate conversion coating on the workpiece, followed by a coating.

Other Deformation Processes Related to Forging

Coining

A special application of closed-die forging where fine details are impressed into surfaces.
Little metal flow, but high pressures are required.

Upsetting

Cylindrical work part increased in diameter and reduced in length.
Can be performed as closed-die forging.
Widely used in the fastener industry to form heads on nails, bolts, etc. (often termed "heading" in these applications).

Swaging and Radial Forging

Reduce the diameter of a tube or solid rod.
Swaging often creates a tapered section on the end of a workpiece.
Swaging uses rotating dies that hammer the workpiece radially inward.
Radial forging is similar, but the work rotates instead of the dies.

Roll Forging

Reduces the cross-section of a cylindrical (or rectangular) workpiece by passing it through opposing rolls with matching grooves.
Rolls rotate through only a portion of one revolution.

Orbital Forging

Deformation occurs with a cone-shaped upper die rolled and pressed into the work part.
Only a small area of the work surface is compressed at any moment.
Reduces press load required for deformation.

Hubbing

A hardened steel form is pressed into a soft steel (or other soft metal) block.
Often used to make mold cavities for plastic molding and die casting.
The hardened steel form (hub) is machined to the part's geometry.

Trimming

Removes flash from the work part in impression-die forging.
Usually accomplished by shearing in a punch and die setup.
Usually done hot, requiring a separate trimming press.

Plastic Deformation and Yield Criterion

(This section likely contains detailed discussion, but specifics are not in the transcript.)

Analysis of Pressure Distribution in Rectangular Block Forging under Sliding Condition. (Derivation & Numericals)

(This section is derivation and numerical analysis based, the specifics are not in the transcript.)

Extrusion

Confining metal in a closed cavity and allowing it to flow through one opening (die) to take the shape of the opening.
Analogous to squeezing toothpaste.

Extrusion Principle

Heated metal billet is loaded into a cylinder or container.
Die plate with opening is fixed on one end.
Plunger or ram compresses the billet against the container walls and die plate, forcing it to flow through the die opening.
Extruded metal is carried away by the metal handling system.
A dummy block (steel disc) protects the ram from heat and pressure.
Can produce components with constant cross-sections over any length (like rolling).
Can create more complex parts than rolling, with easier die creation.
It's a single-pass process.
Allows for large reductions.
Can extrude brittle materials.
Can produce sharp corners and re-entrant angles.
Can create shapes with internal cavities using spider dies.
Can produce large-diameter, thin-walled tubular products.
Pressures range from 35 to 1000 MPa.

Types (Classification) of Extrusion Processes

Forward Hot Extrusion

Metal flows in the same direction as the ram.
Friction is prevalent between the heated billet and cylinder walls.
Lubricants are used, such as oil and graphite at lower temperatures, and molten glass for steels at higher temperatures.
Finished quickly and the cylinder is cooled before further extrusion.

Advantages of Hot Extrusion

Rapid process.
Low tool costs.
Dense metal structure due to high pressures.
Cheaper than pressure die casting in some cases.
Ideal for producing parts of uniform cross-section in large quantities.

Backward Hot Extrusion

Metal is fully confined by the cylinder.
Die is housed in a hollow plunger or ram.
Metal flows in the opposite direction to ram movement.
Billet remains stationary, eliminating friction.
Extrusion pressure is not affected by billet length.
Good surface quality.
Not extensively used due to handling issues of extruding metal coming out through the moving ram.

Comparison between Forward and Backward Extrusion

(May contain detail comparison details between the two extrusion processes.)

Forward Cold Extrusion – Hydrostatic Extrusion

Metal billet compressed from all sides by a liquid.
Eliminates the need for lubricant and uniformly compresses material.
Can extrude brittle materials like grey cast iron.
Pressure-transmitting fluids used: castor oil with 10% alcohol, SAE 30 mineral lubricating oil, glycerine, ethyl glycol, and iso pentane.
Hydrostatic pressure range: 1110 to 3150 MPa.
Limited commercial applications: reactor-fuel rods, cladding of metals, wires of less ductile materials.
Normally used for simple shapes, better surface finish, and improved mechanical properties (e.g., cans, aluminum brackets, shock absorber cylinders, rocket motors).

Backward Cold Extrusion

More common, particularly with softer materials like aluminum and its alloys.
Impact extrusion: punch descends at high speed and strikes the blank (slug), extruding it upward.
Extruded tubular section thickness depends on the clearance between the punch and die cavity.
Applied primarily to lead, aluminium, manganese, tin, zinc, and their alloys.
About 95% of the products are collapsible paste tubes.

Extrusion of Tubing

Solid billet is pierced and extruded in one step.
Piercing mandrel is actuated by a separate hydraulic system and moves coaxially with the ram but is independent of its motion.

Extrusion Defects

Centerburst

Internal crack that develops due to tensile stresses along the centerline.
Occurs under conditions causing large deformation away from the central axis.
Promoted by high die angles, low extrusion ratios, and impurities in the work metal.
Difficult to detect (internal defect).
Also called arrowhead fracture, center cracking, and chevron cracking.

Piping

Sink hole formation in the end of the billet in direct extrusion.
Using a dummy block with a slightly smaller diameter than the billet helps avoid piping.
Also called tailpipe and fishtailing.

Surface Cracking

Caused by high work part temperatures that lead to cracks at the surface.
Occurs when extrusion speed is too high, leading to high strain rates and heat generation.
Other factors: high friction and surface chilling of high-temperature billets in hot extrusion.

Wire and Bar Drawing

Wire refers to small diameter products under 5 mm drawn rapidly on multiple-die machines.
Bar drawing is for large diameter bar and rod stock.
Wire sizes down to 0.03 mm are possible.
Usually performed as a cold working operation.
Most frequently used to produce round cross sections, but other shapes are also drawn.
Important industrial process producing electrical wire and cable, wire stock, and rod stock.

Wire Drawing

Stretching a metal rod into a small diameter wire by passing it through a die.
Die has a tapering hole to gradually reduce rod size.
Wires are drawn through one die or a series of dies (decreasing hole diameter).
Area reduction per pass is rarely greater than 30–35%, requiring multiple reductions.
Raw material is available in coiled form.
Metals used incluse carbon steels, copper, aluminium, stainless steel, titanium and high temperature alloys.
Draw dies are made of tool steels or cemented carbides.
Dies for high-speed operations use diamond inserts.
Dies are cooled by water circulation.
Change in size is given by the area reduction:
Draft is the difference between original and final stock diameters:

Rod Drawing

Generally a single-draft operation.
Stock is straight rather than coiled due to large diameter.
Limits the length of the work.

Tube Drawing

Used to reduce the diameter or wall thickness of seamless tubes and pipes after initial production by other processes (e.g., extrusion).
Can be carried out with or without a mandrel.

Tube Sinking

Simplest method, uses no mandrel and is for diameter reduction only.

Fixed Mandrel Tube Drawing

Uses a fixed mandrel attached to a long support bar to establish inside diameter and wall thickness.
Support bar length limits the tube length that can be drawn.

Floating Mandrel Tube Drawing

Uses a floating plug that finds a "natural" position in the reduction zone of the die.
Removes limitations on work length.
Controls both the inner and outer surfaces of the tube for better dimensional accuracy compared to tube sinking.
Friction is higher with a fixed (mandrel) plug, so area reduction seldom exceeds 30%.
With a floating plug, area reduction can be approximately 45%, or drawing loads will be less for the same reduction.

Rolling

Forming operation on cylindrical rolls that reduces the cross-sectional area of a bar or plate, increasing length.
Metal is thinned and elongated by compression and shear forces, with slight increase in width.
Hot rolling involves passing hot metal between two revolving rolls.
Can be flat rolling or shape rolling.
Hot rolling (above recrystallization temperature) converts cast structure to wrought structure with fine grains and increased ductility.
A major and widely used mechanical working process (about 75% of steel output is treated in rolling mills).

Terminology for Rolled Products

Bloom: square cross-section 150 mm x 150 mm or larger.
Slab: rolled from an ingot or bloom, rectangular cross-section, width 250mm or more, thickness 40 mm or more.
Billet: rolled from a bloom, square with dimensions 40mm on a side or larger.
Plate: finished or semi-finished product, minimum thickness of 6.35 mm.
Sheet: thin partner of plate, maximum thickness of 6.35 mm.
Strip: narrow sheet, maximum width of 600 mm, maximum thickness of 6.35 mm.
Foil: thin strip, maximum width of 300 mm, maximum thickness of 1.5 mm.
Bar: long, straight, symmetrical piece of uniform cross-section. A circular bar is called a rod.
Wire: a thin variety of bar, available in coil form, not normally identified over 9.5 mm cross-section.

Types of Rolling Mills

The arrangement of rolls varies depending on the application.
Arrangements are named by the number of rolls employed.

Classification Based on Number of Rolls in the Stand

Two high rolling mill
Three high rolling mill
Four high rolling mill
Multi-roll rolling mill (Cluster and Sendzimir mill)
Planetary Rolling Mill
Continuous rolling mills (or Tandem rolling mills)

Two High Rolling Mill

Rolls rotate in opposite directions.
Space between the rolls can be adjusted by raising or lowering the upper roll.

Two High Reversing Mill

Incorporates a drive mechanism that can reverse the direction of rotation.
Facilitates continuous rolling through back-and-forth passes but is more expensive.

Three High Rolling Mill

Used for rolling two continuous passes without reversing drives.
Requires a table-tilting arrangement.

Four High Rolling Mill

Essentially a two-high rolling mill with small-sized rolls backed up by larger rolls for rigidity.
Commonly used for subsequent rolling of slabs.
Are typically employed for producing hot or cold rolled sheets and plates.

Multi-Roll Rolling Mill (Cluster and Sendzimir Mill)

Cluster Rolling Mill

Two working rolls of smaller diameter and four or more back-up rolls of larger diameter.
The number of back-up rolls can be as high as 20 or more.
Generally used for cold rolling.

Sendzimir Mill

A modification of the cluster mill with 20 rolls, well-adapted to rolling thin sheet or foil from high Strength alloys (e.g., Stainless Steel).
Only outer rolls are driven.
High C-steel sheets of 5 to 50 μm can be made with accuracy of 1 to 5 μm.

Planetary Rolling Mill

A pair of heavy backing rolls surrounded by many small planetary rolls.
Hot reduces a slab to coiled strip in a single pass.
Each pair of planetary rolls gives an almost constant reduction.
Feed rolls push the slab through a guide into planetary rolls.
A 2- or 4-high planishing mill is installed to improve surface finish.

Continuous Rolling Mills (or Tandem Rolling Mills)

Used to achieve higher throughput rates.
A series of rolling stands, each making a reduction in thickness or a refinement in shape.
Each rolling step increases work velocity, requiring synchronization of roll speeds.

Rolling Defects

Surface Defects

Include scale, rust, scratches, cracks, pits, and gouges.
Occur due to impurities and inclusions in the original cast material or related to material preparation and the rolling operation.

Internal Structural Defects

Include wavy edges, zipper cracks, edge cracks, alligatoring, folds, and laminations.

Defects due to bending of Rolls:

The defects of wavy edges and zipper cracks occur due to bending of rolls.
Rolls act as beams loaded transversely, undergoing deflection.
Edges of the job get compressed more than the central portion, resulting the edge being thinner than the center, that is, the edges are thinner than the central portion, giving the sheet a ‘‘Crown’’.
Remedy is to provide a ‘‘Camber’’ to the rolls.

Defects Due to In-homogenous Deformation

In-homogeneous deformation of elements across the width:

Rounding of the ends of the sheet in the direction of rolling, Fig. (a).
This will result in elements near the edges to be under tension and the elements near the centre will be under compression.
If the conditions are very severe, the sheet might split along the centre (Centre Split), Fig. (c).

Inhomogeneous deformation in the thickness direction:

Leads to Barreled edges of the sheet, Fig. (a).
Cracks will appear on the edges at the equitorial plane, If barreling increases
Sheet may rupture at the equatiorial plane and follow the path the their respective rolls, resulting in a defect known as ‘‘Alligatoring’’, Fig. (b)

Other defects

Folds: these defects are encountered during plate rolling if the reduction per pass is very small.
Laminations : Internal defects such as fissures are encountered resulting drastically reduced strength along the thickness direction.

How to Reduce Rolling Forces

(This section likely contains strategies for minimizing rolling forces, but specifics are not in the transcript.)

Flat Rolling Terminology

The metal contacts each of the two rolls along the arc AB, which is known as the arc of contact.
This arc corresponds to the central angle , called the ‘‘angle of contact or bite’’.
The process of metal rolling is made possible by the friction that occurs between the contact surfaces of the rolls and the part being rolled.

Angle of Nip

The bite angle at rolling limits.

Ragging

The process of making certain fine grooves on the surface of the roll to increase the friction.
During plastic deformation of metals, it is assumed that the volume remains constant:
$V0 h0 b0 = Vf hf bf$
Since $b0 = bf$ (width is assumed constant) : $Vf = V0 \times (h0/hf)$
Hence, the speed at which the metal is delivered by the rolls, $Vf$ is higher and the metal entrance speed $V0$ is lower than the peripheral speed of the rolls $V_r$ .
At a section N - N in the deformation zone (shown hatched), the velocity of metal will equal the velocity of rolls. This section is called ‘‘neutral or no slip section’’ (Neutral Plane).
To the left of neutral section, the deformation zone is called ‘‘Lagging zone’’ (V0 < Vr ).
To the right of the section, it is called ‘‘Leading Zone’’, ( Vf > Vr ).

Draft (Reduction)

Defined as the difference between initial and final thickness per pass:
$Δh = h0 – hf = 2 (R – R \cos 𝛼)$
$Δh = 2R (1 - \cos 𝛼) = 2R 2\sin^2{α/2}$
$Δh = R 𝛼^2$
Projected Length $L_P$

Sheet Metal Forming

Press tool operations; Punch and Die Clearances, Sheet Metal Drawing – Drawing, Cupping and Deep drawing. Draw Die Design – Factors considered for designing a Draw Die (Numericals). Defects in drawing. Sheet Metal Dies – Progressive, Compound and Combination Dies. Bending and Bending Allowance, Rubber Forming

Press Tool Operations

Cutting operations: Workpiece is stressed beyond its ultimate strength, causing shearing stresses (blanking, punching, notching, perforating, trimming, shaving, slitting, lancing).
Forming operations: Stresses are below the ultimate strength, with no cutting, but contour change to produce product(bending, drawing, redrawing, squeezing).

Cutting Operations

Blanking

Blanking the operation of cutting a flat shape from sheet metal
The article punched out is called the ‘blank’ and is the required product of the operation. The hole and metal left behind is discarded as waste.
It is usually the first step of series of operations.

Punching (Piercing)

Punching is a cutting operation by which various shaped holes are made in sheet metal.
Punching is similar to blanking except that in punching, the hole is the desired product, the material punched out to form the hole being waste.

Notching

Metal pieces are cut from the edge of a sheet, strip, or blank.

Perforating

Multiple small, closely spaced holes are cut in flat material.

Slitting

Making incomplete holes in a workpiece.

Lancing

A hole is partially cut, and one side is bent to form a tab or louver. No metal is removed, so there's no scrap.

Shaving

Edges of a blanked part are refined by removing a thin strip of metal for accuracy.

Trimming

Cutting unwanted excess material from the periphery of a formed component.

Nibbling

Cutting out flat parts from sheet metal, ranging from simple to complex contours. Usually moved and guided by and as the continuously operating punch cuts away at the edge of the desired contour.

Forming Operations

Bending

Material is uniformly strained around a linear axis lying in the neutral plane and perpendicular to the lengthwise direction of the sheet or metal.
Two common methods and associated tooling: V-bending (with a V-die) and edge bending (with a wiping die).

Drawing

A flat workpiece is formed into a hollow shape by a punch forcing it into a die cavity.

Punch and Die Clearances

The die opening must be larger than the punch for a clean fracture.
Difference in dimensions between mating members of a die set is called ‘clearance’.
For punching: the punch is made to the size of the hole and the die opening size is obtained by adding clearance to the punch size
For Blanking: die opening size equals the blank size and the punch size is obtained by subtracting the clearance from the die-opening size

Drawing

Making cups, shells, and similar articles from metal blanks.The setup is similar to that used in blanking except that the punch and die are provided with the necessary rounding at the corners to allow for the smooth flow of metal during drawing.
The blank is first kept on the die plate. The punch slowly descends on the blank and forces it to take the cup shape formed by the end of the punch, by the time it reaches the bottom of the die.
Shallow drawing is defined as where the cup height is less than half the diameter. The main operations included under the sheet-metal drawing operations are
- Cupping
- Deep Drawing
- Redrawing
- Reverse Drawing
- Ironing
- Embossing

Cupping

Cupping is a press working operation that produces a cup-shaped part from a blank. For cupping operation, the gap between the punch and die is generally kept equal to about 2.5 times the thickness of blank.
A cup having deth more than1.5 times its diameter has to be drawn in more than one cupping operation.

Deep Drawing

Drawing when cup height is more than half the diameter is termed as deep drawing.
A punch forces a flat sheet-metal blank into a die cavity.
Important variables: sheet metal properties, ratio of blank diameter, punch diameter, clearance, punch radius, die-corner radius, blank-holder force, friction, and lubrication.
Wrinkling can be reduced or eliminated if a blank-holder is loaded by a certain force. In order to improve performance, the magnitude of this force can be controlled as a function of punch travel.

Redrawing

The metal bends twice inducing high strain hardening in it, reducing strain hardening punch load is reduced.
Redrawing is extensively used for food containers, fountain-pen caps, oil filter housings and shock absorber pistons etc

Reverse Drawing

A cold-worked material exhibits greater ductility when the deformation direction is reversed in successive operations (strain softening).

Ironing

Makes the cylindrical cup more uniform in wall thickness. The drawn part is therefore longer and more efficient in terms of material usage.
Beverage cans and artillery shells, two very high-production items, include ironing among their processing steps to achieve economy in material usage.

Embossing

A forming operation used to create indentations in the sheet, such as raised (or indented) lettering or strengthening ribs.
Embossing dies possess matching cavity contours, the punch containing the positive contour and the die containing the negative.

Draw Die Design

A number of variables control the performance of the drawing die.

Factors considered:

Corner Radius on Punch
Draw Radius on Die
Draw clearances
Blank Size
Drawing Force
Blank Holding Force
Ironing Force
Percent Reduction
Air Vent
Drawing Speed

Corner Radius on Punch:

A radius of four to ten times the blank thickness is customary.
Too small a corner radius causes the excessive thinning and tearing of the bottom of the cup.
Ideally, the punch radius should be the same as the corner radius of the required cup because it takes its form.

Draw Radius on Die

Greater the radius, the greater would be the freedom for the metal to flow.
Draw radius = 4t normal = 6 to 8t when the blank holder is used
$Draw radius = 0.8 \sqrt{(D – d)t}$

Draw clearances:

The clearance between punch and die should be the same as the blank thickness.
An allowance in the range of 7 to 20% of the blank thickness is provided depending on the cup material and cup dimensions.

Blank Size:

$D = \sqrt{d^2 + 4dr}$
$D = \sqrt{d^2 + 4dh}$
Trim allowance addition: 3 mm for the first 25 mm cup diameter and additional 3 mm for each of the additional 25 mm of cup diameters.

Drawing Force:

The Drawing Force can empirically be calculated for the cylindrical shells. $P = \pi dt S C$

Blank Holding Force

The maximum limit is generally to be one third of the drawing force.

Ironing Force:

In ironing, the objective is only to reduce the wall thickness of the cup, and hence, the ironing force can be estimated using the following equation:
[The equation to estimate ironing force is missing from the text]

Percent Reduction

$P = ((D-d)/D) * 100$
$P$ should be below 40

Air Vent:

The diameter of air vent varies 10 to 20% of punch diameter.
For cylindrical shells, one vent located centrally would be enough, where as for other shapes it may be advantageous to provide two.

Drawing Speed:

$0.28m/s$ for hard material and $1.0m/s$ for soft material.

Defects in Drawing

Wrinkling in the flange

Wrinkling in a drawn part consists of a series of ridges that form radially in the undrawn flange of the work part due to compressive buckling.

Wrinkling in the wall

If and when the wrinkled flange is drawn into the cup, these ridges appear in the vertical wall.

Tearing

Tearing is an open crack in the vertical wall, usually near the base of the drawn cup, due to high tensile stresses that cause thinning and failure of the metal at this location.

Earing

This is the formation of irregularities (called ears) in the upper edge of a deep drawn cup, caused by anisotropy in the sheet metal.
If the material is perfectly isotropic, ears do not form.

Surface scratches

Can occur on the drawn part if the punch and die are not smooth or if lubrication is insufficient.

Types of Sheet Metal Dies

Classification by (i) Type of press Operation or (ii) Method of Operation

i) Type of press operation
* cutting dies and forming dies.
* The common cutting dies are : blanking dies, piercing dies, perforating dies, notching, trimming, shaving and nibbling dies etc.
* Forming Dies are Bending dies drawing dies squeezing dies etc.
ii) Method of operation
* Single-operation dies or simple dies
* Compound dies,
* Combination dies,
* Progressive dies,
* Transfer dies,
* Multiple dies

Single-operation dies or simple dies

The type of die which performs a single blanking operation with each stroke of the press and is called a simple die.

Compound Dies

In these dies, two or more operations may be performed at one station. Such dies are considered as cutting tools since, only cutting operations are carried out.
Compound dies are more accurate and economical in mass production as compared to single operation dies.

Combination Dies

Also, more than one operation may be performed a one station combines a cutting operation with a bending or drawing operation.

Progressive Dies

A progressive or follow on die has a series of stations. At each station, an operation is performed on a workpiece during a stroke of the press.
Between stroke, the piece in the metal strip is transferred to the next station.

Bending

Material, in the form of flat sheet or strip, is uniformly strained around a linear axis which lies in the neutral plane and perpendicular to the lengthwise direction of the sheet or metal.
Two methods: V-bending,performed with a V-die and edge bending, performed with a wiping died

Bending Allowances

Refers to the operation of deforming a flat sheet around a straight axis where the neutral plane lies.
[Formulas related to bending likely included here, but specific formulas are not provided in this transcript]

Rubber Forming (Guerin Process)

Uses a thick rubber pad (or other flexible material) to form sheet metal over a positive form block.
Limited to relatively shallow forms because pressures are not sufficient to prevent wrinkling in deep forms.
Advantage: Relatively low cost of tooling - Attractive in small-quantity production

Practice Questions

(The last section only includes a comprehensive list of potential exam questions which is omitted from the note)