Dies 3

1
Die Design
Part 3- Forming Operation
J5811 - Tool Design
(Based on notes of Prof Dr Simin Nasseri,
Southern Polytechnic State University)
Sources:
 Handbook of Die Design, Suchy
 The Ohio State University
 Manufacturing Processes, Groover

Southern Polytechnic State University2MET3331, Prof Simin Nasseri, Dies, Part 3
Forming
 Similar to bending, but the blank is bent along a curved axis.
 There is little stretching or compressing of the material.
 All forming operations deform sheet material by exposing it to tension,
compression, or both.
 Most part defects, such as splits and wrinkles, occur in forming
operations.
 Successful sheet metal forming relies heavily on the metal's mechanical
properties (the metal being formed must have the ability to stretch and
compress within given limits).
part
Some design considerations:
 Select the class of die,
 Choose number of stampings required,
 Cheapest and simplest tools may not be
the best ones.

Forming
 Most common forming operations:
 Bending (will be reviewed in detail)
 Coining
 Embossing
 Flanging
 Hole flanging or extrusion
 Beading and curling
 Ironing
 Drawing
Forming die

Coining
 Coining dies create the part's shape by squeezing the metal under
extreme pressure (up to yield strength of material).
 A simple round metal slug is placed into the die and forced to flow into a
given shape by compressing it.
 Coining also can reduce the metal thickness.
Coins are created with the coining
process.
Advantages:
 Capable of producing sharp, accurate bends
with less sensitivity to material conditions.
Disadvantages:
 High force requirements (tonnage is 5 to 10
times that required for simple air bending)
 Accelerated die wear (high forces increase
machine deflection).

Embossing
 Embossing dies use tension to stretch metal into a shallow depression.
 The dies primarily are comprised of a punch and a cavity.
 Most common applications:
 The stiffening of the bottom of a pan or container (in the form of ribs or
crosses stamped in the metal)
 A small embossment often is used as a spotweld projection nib (metal is
electrically welded together under controlled pressure and current).
 The metal's thickness and mechanical properties, along with the forming
punch geometry, determine the depth that can be achieved.

Flanging
 Flanging is bending metal along a
curved axis.
 Two basic types of flanges are
stretch flanges (or tension flanges),
and compression flanges (or shrink
flanges).
 Tension flanges are susceptible to
splitting, and
 Shrink flanges are susceptible to
wrinkling.
 Flanges are created using a
flanging die that wipes the metal
between a punch and a lower die
section.
 Check the original edge of each part to understand the difference between
compression and tension flanges.

 Flanges are made as
countersunk, burred or
dimpled holes.
Hole Flanging or Extrusion
 In extruding, the metal is flanged around the perimeter of a prepierced
hole.
 Like during stretch flanging, the metal is susceptible to splitting during
forming (this is sort of stretching operation).
 Extrusions also are referred to as hole expansions or continuous
stretch flanges.
 Often extrusions are tapped for holding fasteners used in the part
assembly process.

Hole Flanging or Extrusion (Countersunk)
 For countersunk holes, it is necessary to coin the metal
around the upper face and beveled sides to set the
material.
 The holes are made about 0.005 in (0.13 mm) deeper
than the required height of the rivet or screw head
(allows the metal compression that occurs when
squeezing the rivet in place).

Beading & Curling
 The edges of the ductile metal are formed into a roll or curl.
 This is done to strengthen the part or to produce a better-
looking product.
 Curls are used in the manufacturing of hinges, pots, pans, and
other items (sometimes wires may be rolled inside for strength).
 Radius of the curl ≥ twice the metal thickness.
Metal to be curled
Spring pad
Curling punch
Spring pad

Ironing
 Ironing dies are similar to coining dies in that they deform the metal with
compression.
 However, unlike conventional coining, ironing squeezes metal along a
vertical wall. This highly compressive process unifies a wall's thickness and
increases the drawn vessel's length.
 Items such as beverage and soup cans are made using an ironing process.
 Ironing allows an aluminum can's wall thickness to be reduced to as little as
0.002 in.

Drawing
 Sheet metal forming to make
cup shaped, box shaped, or‑ ‑
other complex curved,‑
hollow shaped parts.‑
 Sheet metal blank is positioned
over die cavity and then punch
pushes metal into opening.
 Products: Oil pans, automobile
doors and fenders, cookware,
and door knobs, beverage
cans, ammunition shells,
automobile body panels.
 Also known as deep drawing
(to distinguish it from wire and
bar drawing).

Shapes other than Cylindrical Cups
 Square or rectangular boxes
(as in sinks),
 Stepped cups
 Cones
 Cups with spherical rather than
flat bases
 Irregular curved forms (as in
automobile body panels)
 Each of these shapes presents
its own unique technical
problems in drawing

(a) Drawing of cup shaped part: (1) before punch‑
contacts work, (2) near end of stroke; (b)
workpart: (1) starting blank, (2) drawn part.
Drawing
 Draw dies utilize a
special pressure-
loaded plate or ring
called a draw pad or
blankholder to control
the metal's flow into
the cavity.
 This plate prevents the
metal from wrinkling as
it flows into the cavity.
Increasing or
decreasing the
pressure exerted under
the pad also controls
how much metal feeds
into the die.

Drawing
 Although compression can occur when the metal is drawn,
drawing uses mostly tension to obtain the part geometry.

Clearance in Drawing
Sides of punch and die separated by a clearance c given by:
c = 1.1 t
where t = stock thickness
In other words,
clearance c is about
10% greater than
stock thickness

Tests of Drawing Feasibility
 Drawing ratio
 Reduction
 Thickness-to-diameter ratio
Successful deep draw progression

Drawing Ratio DR
 Db = blank diameter;
 Dp = punch diameter
 DR Indicates severity of a
given drawing operation
 Upper limit: DR ≤ 2.0
Most easily defined for cylindrical shape:
p
b
D
D
DR =
Db
Dp
Usually Db =< 2DpTop view

t/Db and Reduction r
Thickness to Diameter Ratio‑ ‑ = Thickness of
starting blank divided by blank diameter
 Desirable for t/Db ratio to be greater than 1%
 As t/Db decreases, tendency for wrinkling
increases
Reduction r = Defined for cylindrical shape:
b
pb
D
DD
r
−
=
 Value of r should be less than 0.50

Test yourself!
 Name different
components of this die.
 Draw the drawn part
and explain how
different components
move with respect to
each other.

Test yourself!
 Draw the drawn part (the
final shape of the part)
and explain how different
components move with
respect to each other..

Forming Die- Design example
 Design a die to form rectangular shapes along a strip which is
continuously fed through the die.

Forming (Retractable Die-holder Function )
 Upward forming tool dies are
retracted out of the way of the
worksheet movements when
forming is not in operation to
avoid interference of forming
die with the workpiece or
Workholders.
 This function allows obstacle
free fast movement and
improves the quality of the
worksheet
http://www.mt-muratec.com/eg/p/product/tp/m2048lt.html

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