MD Seminar

Report
GENERAL DESIGN
RECOMMENDATIONS FOR FORGING
Seminar By:
1. Arun A
2. Arun Das C
3. Jeson M F
4. Kiran V
5. Laluprasad E
6. Lin John
7. Mahesh M
8. Raja Ram P K
9. Sivaprasad S
10. Sreejith S
11. Varun A
FORGING
 Shaping of heated metal parts by plastic
deformation, usually with one or more strokes of
a power hammer or press.


Power hammers - 1. gravity type
2. power assisted type
Presses
- 1. crank press
2. screw press
3. hydraulic press
TYPES OF FORGING
1. Hand forging – made by successive blows with
simple die cavities. Operator manipulates
work piece to form a fairly crude approx. of
the finished part.
2. Blocker forging – work piece is formed
between two dies with shaped impressions in
them. It closely resembles the finished part
and are more refined
3. Conventional impression die forgings – more
refined than blocker ones . It can be made
from a blocker forging or directly from a
heated metal billet.
4. Precision forgings – they are further more refined. They
are produced by a succession of forgings in dies with
shaped impressions. Difficult to differentiate from
conventional ones.
5. Cored forging – here additional die elements along with
two opposing impression dies or clamping dies apply the
metal forces. Rams or shaped dies act upon work piece
forming may be an extrusion or upsetting. Here tighter
design tolerances are possible.
6. Ring rolling – similar to hot rolling of bar or rod except
that it progresses repetitively on the same piece of a
metal which assumes a ring shape. Rectangular or
contoured cross sections are produced.
7. Roll forging – here a relatively long, thin work piece is fed
into power driven rolls which may be shaped to vary the
section along its length.
Characteristics of Forging
 Controlled grain structure sets forging apart from other
processes.
 With proper design ,it is possible to align grain flow with
directions of the principle stresses that will occur when
the part is loaded in service.
 GRAIN FLOW is the directional pattern that metals
crystals assume during plastic deformation.
 Strength ,ductility and impact resistance along the grain
are significantly higher than they would be in randomly
oriented crystals of cast metal or weld metal.
 Because hot working refines grain structure ,physical
properties are also improved across the grain.
 Forging assures structural integrity from piece to piece.
Internal pockets ,voids ,inclusions ,laps and similar flaws
are easier to avoid by good forging.
Applications of Forging
There are two classes of application of forging:
High strength to weight characteristics or high
strength needed in a part.
An economical means of producing the part
configuraion required.
Often these two classes overlap.
Main applications:
 Used in aircrafts : Because of high strength and light
weight requirements ,makers of aircraft engines and
structures ,along with other aerospace manufacturers
are the most significant users of forging on a value
basis.
 Moving parts are forged to reduce inertial forces and
parts that must be supported by other structures are
forged to reduce overall weight and complexity.
 Parts that people lift and handle are forged to reduce
weight.
 Parts whose failure would cause injury and
expensive damage are forged for safety.
 Decorative parts are produced from forgings to
reduce scrap losses and ensure a platable surface.
FORGING NOMENCLATURE
 Shapes on a forging are named for the direction in
which metal must flow to fill the die impressions
 Walls filled by flow parallel to the die motion is a rib
 A projection is called a boss when it is filled parallel
to die motion
 Wall filled by horizontal flow, perpendicular to die
motion and parallel to the parting line is a web
 A recess is a small web area surrounded by the
thicker metal
 When die halves come together, the excess metal is
extruded into gutter at the parting line, producing a
fringe of flash metal around it
DESIGN RECOMMENDATIONS
1) Forging Drawings
 Most forgings are produced in two part impression
dies. The design of such forgings is discussed.
 Shapes and dimensions of part to be forged before
any machining is done are shown in this drawing.
 Die design and processing requirements are
expressed by the way in which the part is drawn
 Flash is not indicated in the drawing
 Alinging grain flow with principal load stresses
should be kept in mind
 An experienced designer can visualise metal flow
and the resulting grain flow pattern
2) Parting Line
 As the die halves come together and confine metal
in their cavities, their mating surfaces define a
parting line around the edges of the forging
 Parting line is indicated on the drawing and
determining its location is a critical step in forging
design.
 Ideally parting line will lie in one plane
perpendicular to the axis of die motion
 Sometimes it can be located so that one die half will
be completely flat and it will surround the largest
projected area of the piece
 If the parting line cannot lie in one plane, it is
desirable to preserve symmetry so as to prevent
high thrust forces on the dies and the press.
No portion of the parting line should incline more
than 75 degree from the parting plane and much
shallower angles are desirable
Select a parting line that will not entail any
undercuts in either die impressions as the forging
must come out of the die after it is made
Because metal flow at the parting line is outward
into the flash gutter, grain flow in the forging has a
corresponding pattern
Depending on the way in which the part will be
loaded, it may be desirable to change parting line
location to control grain flow.
3) Draft
 Die impressions are tapered so that forgings can
be removed from their dies
 So the forged surfaces that that lie parallel to die
motion are tapered
 This taper is called draft
 This draft also promotes flow into relatively deep
die cavities
 Standard draft angle will be specified on for all
affected surfaces on a forging, which simplifies
tooling for die sinking
 It is also conventional to call for matching draft
on both die halves to make surfaces of unequal
depth meet at the parting line.
Sometimes, a parting line location presents
tapered surfaces automatically because of the a
part’s shape.
For example, a cylinder lying parallel to the parting
plane has such natural draft except for small
bands next to the parting line
Low draft and no draft forgings can be produce in
some metals such as aluminium and brass.
4) Ribs, Bosses, Webs and Recesses
Metal flow is relatively easy to manage when ribs
and bosses are not too high and narrow
It is the easiest when the web is relatively thick
and uniform in thickness
Forging becomes more difficult when large
amounts of metal must be moved out of a
relatively thin web into deep ribs and high bosses
It is helpful to taper such webs toward the ribs
and bosses
Deep recesses are easier to forge if they have
spherical bottoms
When successive forging operations are required
it is advantageous to design for a fairly large
punch out hole in the thin web section
During finish forging, after the hole has been
punched, flash flows inward at its edges and helps
to relieve excessive die forces
Surface texture, designs, and lettering on forged
surfaces are simply very small ribs and recesses
These features are located on surfaces that are
nearly perpendicular to die motion as possible
and locate them away from zones of wiping metal
flow
5) Radii
Forgings are designed with radii on all their
external corners except at the parting line
It would require a sharp internal angle in the die
to form a sharp corner on the forging
This is a stress raiser and excessive pressure is
required to fill sharp corners
Common practice is to provide full radii at the
edges of all ribs and the same radius on each
corner of a boss, web or other shape
Fillet radii on a forging correspond to corners in
die impressions that metal must round to fill ribs
and bosses.
If metal flows past a sharp corner and then
doubles back, the forging may be flawed with a
lap or cold shut and the die may not fill
completely
This is more likely if the sharp die corner or sharp
fillet radius in the forging is near the edge of the
piece
While all the radii should be ample for easy
forging, they can be made smaller in readily
forgeable metals
The deeper the impression, the larger the radius
should be, both at the fillet around which metal
must flow and at the corner which must fill with
metal
6) Machining Allowance
Design features that promote easy forging add to
the metal that must be machined away
The machining allowance should allow for the
worst case buildup of draft, radii and all tolerances
Extra metal is provided to keep critical machined
surfaces away from the grain flow pattern that
occurs in the flash region near the parting line
Machining or finishing allowances are added to
external dimensions and subtracted from internal
dimensions
7) Other Forging Processes
Several of the limitations of impression forging
made in two part dies can be bypassed and
eliminated by upset or cored forging techniques
Shapes that constitute undercuts for the two part
dies can be forged easily
Sharp external corners are feasible
Draft can be reduced, and no draft at all may be
possible on some surfaces
POINTS TO NOTED
 It not practical to forge a through hole in a web
 When a hole through a web or a boss will be needed,
a recess may be forged in one or both sides
 The thin web remaining is punched out later and the
hole may be subsequently cleaned up by machining
 A forging should be dimensioned so that enough
metal will be available on every surface to satisfy all
the functional requirements of the finished part
SUITABLE MATERIALS FOR FORGING
 Most metals and alloys can be forged at elevated
temperatures.
 However the ease with which they deform
plastically varies widely.
 Some alloys remain strong even when heated upto
its melting point
 Some have high co-efficient of friction at forging
temperature and it is difficult to slide them along
die surfaces
 Materials may be susceptible to metallurgical
degradation or to the formation of mechanical flaws
in course of hot working
 Alloys of aluminium, magnesium, copper and mild
steel are readily forgeable.
 There are differences among them, but some of
these tend to balance out.
 For example, aluminium can be forged at lower
temperatures than steel, but it flows less readily
and requires higher pressures
 Stainless steel is resistant to plastic flow but they
are produced by conventional forging
 Super alloy forgings are used to produce only
simpler shapes
 If any part requires elaborate contours or drastic
section changes, then these features must be
provided in subsequent operations.
TOLERANCES
1) Length and Width Tolerance
 Dimensions generally parallel to the parting
plane and perpendicular to die motion are
subject to length and width tolerances
 When a forged part extends more than 150mm
from the parting plane, dimensions to its
extremities, measured parallel to die motion are
also subject to these tolerances
 Length and width tolerances are commonly
specified at +0.3% of each dimension, rounded of
to the next higher ½ mm.
2) Die – Wear Tolerance
These tolerances aply only to dimensions
generally parallel to the parting plane and
perpendicular to the die motion
The corresponding variations parallel to die
motion are included in the die closure tolerances
Die – wear tolerances are plus variations of
external dimensions and minus variations of
internal dimensions
They allow for erosion of die metal and
corresponding enlargement of forged parts
Multiply each horizontal dimension by the
appropriate factor, and round off the tolerance to
the next higher ½ mm.
3) Die – Closure Tolerances
Dimensions parallel to die motion between
opposite sides of a forging are affected by failure
of the two die halves to close precisely
There is no minus tolerance in this category
Effects of die wear on these vertical dimensions
are included in the die closure tolerances
An added tolerance of 0.3% applies to any
projection that extends more than 150mm from
the parting plane.
4) Match Tolerances
A lateral shift of one die half with respect to the
other moves all the features on the opposite sides
of the forging correspondingly.
Tolerances are given in terms of piece weight and
material
5) Straightness Tolerances
For relatively long, thin parts, a straightness
tolerance of 0.3% of length is given
When this aspect of forging accuracy is critical,
forged parts are often straightened out in
secondary cold operations
6) Flash – Extension Tolerances
The most common flash removal method is by a
punching operation in contoured dies
This may produce clean trimmed edges, but a
small bead of flash allowed.
They are specified in terms of forging weight and
alloy type.
7) Draft Angle Tolerances
Common tolerance on draft angles are +2 degree
to -1 degree.
8) Radii Tolerances
Normally the tolerance on all corner and fillet radii
is plus or minus one half of the radius
On any corner where metal will be removed later,
the plus radius governs how much metal will be
left for producing a sharp corner in final product
Minus tolerance limit sharpness of the forged
corner and is not enforced
9) Total Tolerances
 The tolerances for each dimension are arithmetic
sum of all individual tolerances that apply to
surfaces involved
 Other tolerances like draft, angle, radii, mismatch
are also additive as they affect those surfaces

similar documents