ASM Metals HandBook Vol. 14 - Forming and Forging
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Fig. 16 Shapes produced in the three-operation saddle forgin
g of a ring from a forged and pierced blank.
Dimensions given in inches.
Operation 1. The blank was heated to 1230 °C (2250 °F) and forged to the dimensions shown in Fig. 16, Operation 1,
by alternate saddle forging and flattening.
Operation 2. The 711 mm (28 in.) OD ring was reheated to 1230 °C (2250 °F) and forged by the same technique used
in Operation 1 to produce a 914 mm (36 in.) diam ring.
Operation 3. The 914 mm (36 in.) OD ring was reheated to 1230 °C (2250 °F) and saddle forged and flattened as
needed to obtain a 50 mm (2 in.) thickness, a 1.02 m (40 in.) outside diameter, and a 762 mm (30 in.) inside diameter.
Example 7: Mandrel Forging a Long Hollow Piece on a 40.9 MN (4600 tonf)
Hydraulic Press.
Mandrel-forging technique is utilized to produce a long, hollow, cylindrically symmetrical piece. The outside diameter of
the production piece was 1.32 m (52.0 in.). The average inside diameter was 914 mm (36.0 in.). The total overall length
was 7.0 m (23.0 ft) with a 1.59 m (62.75 in.) diam by 482 mm (19.0 in.) long flange included on one end of the piece. The
flange drops to a 1.45 m (57.0 in.) diameter, which tapers to the 1.32 m (52.0 in.) body diameter over a 229 mm (9.0 in.)
length.
Operation 1. The 2.11 m (83 in.) diam, 78,900 kg (174,000 lb) ingot of AISI 4130 grade steel was used as the starting
stock. It as heated to the forging temperature and straight forged (saddened) to 1.57 m (62.0 in.) diam size.
Operation 2. Top and bottom ingot discards were taken by flame cutting to yield a slug of 1.57 m (62.0 in.) in diameter
and 3.20 m (126.0 in.) in length.
Operation 3. The slug was upset forged by positioning it vertically under the press. The 3.20 m (126.0 in.) dimension
was reduced to 3.15 m (80.0 in.).
Operation 4. The upset slug was hot trepanned using 559 mm (22.0 in.) cutters to remove the core.
Operation 5. The slug was saddle forged to increase the inside diameter to 991 mm (39.0 in.).
Operation 6. The piece was mandrel forged on a tapered mandrel (0.8 to 1 m, or 33 to 39 in., in diameter) using the top
flat die and bottom V-die. Mandrel forging caused the metal to move in the longitudinal (axial) direction, thus producing
the desired part.
Open-Die Forging
Revised by the ASM Committee on Open-Die Forging
*
; Chairman: Ashok K. Khare, National Forge Company
Contour Forging
Open-die contour or form forging requiring the use of dedicated dies has been successfully accomplished for carbon,
alloy, and stainless steels as well as for superalloys. Contour forging can be advantageous under such circumstances as
the following:
• Enhancement of grain flow at specific locations, when demanded by product application
•
Reduction of the quantity of starting material; this is especially critical when using expensive materials
such as stainless steels and superalloys
•
Reduction of machining costs; this is critical when machinability or excessive material removal are
factors
Open-die contour forging may be a requirement, as in the case of grain flow, or it may be an option, as in the case of
material and machining cost savings. The material and machining cost savings typically outweighs the forging tooling
costs.
Die material is largely dependent on the forging hours required for the product run. Generally, when dealing with a
small production run having total forging hours of 30 or fewer, in which tooling cost has a significant impact on product
cost, H-13 would be an acceptable die material. However, larger forging runs would require the use of superalloy
material.
Set Down. It may not be possible to calculate precisely the amount of material required for the contour forging of
complex shapes. It is then recommended to run trials on low-cost material. The factors affecting the consideration would
be the condition of the forge press, operator skill, forge preheat, and the extent of the net shape design affecting metal
flow.
Turbine Wheel Forging. Turbine wheels, which are commonly 2.54 m (100 in.) in diameter, are forged by first
upsetting a block of steel and then contour forging to provide the thick hub and thin rim sections (Fig. 17). This is done
using a shaped (contoured) bottom die, which supports the entire workpiece, and a shaped partial top (contoured swing)
die. Successive strokes are taken with the top die as it is indexed around the vertical centerline of the press. The partial
top die minimizes the force required to deform the metal, yet produces the desired forge envelope.
Fig. 17 Illustrations showing turbine wheel formed by using contour forging method.
Nozzle extrusion is a more complex contour-forging method (Fig. 18). Nozzle extrusions are commonly used for
thick-wall vessels in cases in which the cost of extruding the nozzle shape offsets the cost and quality risk factors
involved in producing the shell and the nozzle as a weldment. The tooling consists of a shaped bottom die and a punch.
The punch is forced through a machined pilot hole in the workpiece. The material conforms to the shape of the bottom die
and is extended forward to form the nozzle. Two possible methods of producing a shell section with a nozzle are shown in
Fig. 19. Design engineers prefer the nozzle extrusion technique over the welded nozzle because of the superior grain flow
characteristics, toughness, and favorable costs associated with the extrusion process.
Fig. 18 Illustration of nozzle extrusion, a complex contour forging method. (a) Punch position b
efore extrusion.
(b) Punch position after extrusion.
Fig. 19 Metal shells featuring nozzles formed by two different methods.
(a) Welded nozzle. (b) Extruded
nozzle.
Pressure vessel head forgings can be produced from either forged or rolled plate by either of two methods. In the
first method, full male and female dies are used to develop a dome shape (Fig. 20a). In the second method, a partial male
die and a full female die are used to produce a dome shape (Fig. 20b). The second method, although requiring more
forging strokes than the first method (the top die is swung in incremental positions for each stroke), reduces the press load
per stroke. Therefore, larger dome shapes can be made by this technique. In addition, if required, smaller presses can be
used to make the dome shapes (press capacity will determine the appropriate swing die width that can be used).
Fig. 20 Contour forming of a pressure vessel head using a (a) full male die and a (b) partial male die.
Bottleneck-shaped forgings are made as doubles from a straight forged bar (Fig. 21). For example, 292 mm (11.5
in.) radius contour dies are set down 165 mm (6.5 in.) to achieve the small diameter of 254 mm (10.0 in.) from the large
diameter of 584 mm (23.0 in.). In order to generate axial movement during the forging process, the flat die width must be
a minimum of 50 mm (2.0 in.) less than the set down dimension. In addition, the die radius adjacent to the flat and the
contour should be a minimum of 38 mm (1.5 in.) to enhance axial metal flow and to minimize material lapping.
Fig. 21 Contour forging of a straight forged bar to form a double bottleneck-
shaped workpiece. (a) Original 320
kg (700 lb) bar. (b) Contour-forged, 205 kg (450 lb) finished workpiece.
Forging quality is best achieved using a 17.8 MN (2000 tonf) hydraulic press by positioning the die to the set-down mark
as shown in Fig. 21 and manually or mechanically rotating the workpiece in 10° to 15° increments using not greater than
25 mm (1 in.) drafts. The process is continued by working from side to side, keeping the die tight to the contour, while
exercising caution to avoid lapping on the contour.
Open-Die Forging
Revised by the ASM Committee on Open-Die Forging
*
; Chairman: Ashok K. Khare, National Forge Company
Allowances and Tolerances
To make certain that forgings can be machined to correct final measurements, it is necessary at the forging stage to
establish allowances, tolerances, and specifications for flatness and concentricity.
Allowance. In open-die forging, the allowance defines the amount by which a dimension is increased in order to
determine its size at an earlier stage of manufacture. An allowance is added to a finish-machined size. Similarly, an
additional allowance is added to a rough-machined dimension to determine the forged size. These allowances provide
enough stock to permit machining to final dimensions.
The stock provided for machining increases the weight of the forging at earlier stages of manufacture. The weight of the
additional metal and the machining operations necessary to remove it increase the cost of the finished part. Consequently,
the allowances specified for each step of manufacture should be kept as small as practical while still maintaining enough
metal so that all dimensions of the finished part can be readily achieved with normal production techniques.
Table 1 shows allowances added to rough-machined dimensions of straight round, square, rectangular, or octagonal bars
of uniform cross section. The allowance increases as diameter (or section width) and length increase. Table 1 also
explains how allowances are determined for open-die forgings with more than one cross-sectional dimension.
Table 1 Allowances and tolerances for as-forged shafts and bars
Allowance is added to rough-machined dimension to obtain forged dimension. Tolerances are the variations permitted on forged
dimensions.
Allowance for overall rough-machined length, mm (in.), of:
Rough-machined
diameter or width,
mm (in.)
Over 152-762 (6-30) Over 762-1520 (30-60)
Over 1520-2290 (60-90)
Over 2290-3050 (90-120)
Over 25-75 (1-3)
7.7 ( )
+ 3.2, -0 (+ , -0)
9.5 ( )
+ 3.2, -1.6 (+ , - )
11.1 ( )
+ 3.2, -1.6 (+ , - )
12.7 ± 3.2 ( ± )
Over 75-152 (3-6)
9.5 ( )
+ 3.2, -1.6 (+ , - )
11.1 ( )
+3.2, -1.6 (+ , - )
12.7 ± 3.2 ( ± )
14.3 ( )
+4.8, -1.6 (+ , - )
Over 152-229 (6-9)
11.1 ( )
+3.2, -1.6 (+ , - )
12.7 ± 3.2 ( ± ) 14.3 ( )
+4.8, -1.6 (+ , - )
15.9 ( )
+4.8, -3.2 (+ , - )
Over 229-305 (9-12)
12.7 ± 3.2 ( ± ) 14.3 ( ) 15.9 ( )
19.1 ± 4.8 ( ± )
+4.8, -1.6 (+ , - )
+4.8, -3.2 (+ , - )
Over 305-457 (12-18)
19.1 ± 4.8 ( ± ) 19.1 ± 4.8 ( ± ) 25.4 ± 6.4 (1 ± )
25.4 ± 6.4 (1 ± )
Over 457-610 (18-24)
31.8 ± 7.9 (1 ± 31.8 ± 7.9 (1 ± 31.8 ± 7.9 (1 ±
31.8 ± 7.9 (1 ±
Over 610-762 (24-30)
38.1 ± 9.5 (1 ± ) 38.1 ± 9.5 (1 ± ) 38.1 ± 9.5 (1 ± )
38.1 ± 9.5 (1 ± )
Over 762-914 (30-36)
44.5 ± 11.1 (1 ± )
44.5 ± 11.1 (1 ± )
44.5 ± 11.1 (1 ± )
44.5 ± 11.1 (1 ± )
Over 914-1070 (36-42)
50.8 ± 12.7 (2 ± ) 50.8 ± 12.7 (2 ± ) 50.8 ± 12.7 (2 ± )
50.8 ± 12.7 (2 ± )
Over 1070-1220 (42-48)
57.2 ± 14.3 (2 ± )
57.2 ± 14.3 (2 ± )
57.2 ± 14.3 (2 ± )
57.2 ± 14.3 (2 ± )
Over 1220-1370 (48-54)
63.5 ± 15.9 (2 ± ) 63.5 ± 15.9 (2 ± ) 63.5 ± 15.9 (2 ± )
63.5 ± 15.9 (2 ± )
Over 1370-1520 (54-60)
69.8 ± 17.5 (2 ± )
69.8 ± 17.5 (2 ± )
69.8 ± 17.5 (2 ± ) 69.8 ± 17.5 (2 ± )
Allowance for overall rough-machined length, mm (in.), of:
Over 3050-4060
(120-160)
Over 4060-5080
(160-200)
Over 5080-7620
(200-300)
Over 7620-10160
(300-400)
Over 10160-12700
(400-500)
Over 12700-15240
(500-600)
14.3 ( )
+4.8, -1.6 (+ , -
)
15.9 ( )
+4.8, -3.2 (+ , -
)
25.4 ± 6.4 (1 ± ) 31.8 ± 7.9 (1 ±
. . .
. . .
15.9 ( )
+4.8, -3.2 (+ , -
)
19.1 ± 4.8 ( ±
)
25.4 ± 6.4 (1 ± ) 31.8 ± 7.9 (1 ±
)
. . .
. . .
19.1 ± 4.8 ( ±
)
22.2 ( )
+6.4, -4.8 (+ , -
)
31.8 ± 7.9 (1 ±
)
38.1 ± 9.5 (1 ±
)
44.5 ± 11.1 (1 ±
)
50.8 ± 12.7 (2 ± )
22.2 ( )
+6.4, -4.8 (+ , -
)
25.4 ± 6.4 (1 ± ) 31.8 ± 7.9 (1 ±
)
38.1 ± 9.5 (1 ±
)
44.5 ± 11.1 (1 ±
)
50.8 ± 12.7 (2 ± )
31.8 ± 7.9 (1 ±
)
31.8 ± 7.9 (1 ±
)
38.1 ± 9.5 (1 ±
)
44.5 ± 11.1 (1 ±
)
50.8 ± 12.7 (2 ± )
57.2 ± 14.3 (2 ±
)
38.1 ± 9.5 (1 ±
)
38.1 ± 9.5 (1 ±
)
44.5 ± 11.1 (1 ±
)
50.8 ± 12.7 (2 ± ) 57.2 ± 14.3 (2 ±
)
63.5 ± 15.9 (2 ±
)
44.5 ± 11.1 (1 ±
)
44.5 ± 11.1 (1 ±
)
50.8 ± 12.7 (2 ±
)
57.2 ± 14.3 (2 ±
)
63.5 ± 15.9 (2 ±
)
69.8 ± 17.5 (2 ±
)
50.8 ± 12.7 (2 ±
)
50.8 ± 12.7 (2 ±
)
57.2 ± 14.3 (2 ±
)
63.5 ± 15.9 (2 ±
)
69.8 ± 17.5 (2 ±
)
76.2 ± 19.1 (3 ± )
57.2 ± 14.3 (2 ±
)
57.2 ± 14.3 (2 ±
)
63.5 ± 15.9 (2 ±
)
69.8 ± 17.5 (2 ±
)
76.2 ± 19.1 (3 ± )
82.6 ± 20.6 (3 ±
)
63.5 ± 15.9 (2 ±
)
63.5 ± 15.9 (2 ±
)
69.8 ± 17.5 (2 ±
)
76.2 ± 19.1 (3 ± ) 82.6 ± 20.6 (3 ±
)
88.9 ± 22.2 (3 ±
)
69.8 ± 17.5 (2 ±
)
69.8 ± 17.5 (2 ±
)
76.2 ± 19.1 (3 ±
)
82.6 ± 20.6 (3 ±
)
88.9 ± 22.2 (3 ±
)
95.3 ± 23.8 (3 ±
)
76.2 ± 19.1 (3 ±
)
76.2 ± 19.1 (3 ±
)
82.6 ± 20.6 (3 ±
)
88.9 ± 22.2 (3 ±
)
95.3 ± 23.8 (3 ±
)
101.6 ± 25.4 (4 ± 1)
Allowances and tolerances for as-forged shoulder shafts
A shaft forging that has more than one
cross-sectional dimension is illustrated at
right. To compute allowances and
tolerances for a forging of this type, use
the following method:
For the largest diameter, take the
allowance given in the table above, using the
overall length of the forging.
For each smaller diameter, take
allowance given in table above, using overall
length of forging, and average this with allowance
for largest diameter. Use next-larger allowance
wherever calculated average is not found.
Allowance on each end of the overall
length is the value indicated in the first column for
the largest diameter or the value indicated on the
top line for the overall length, whichever is greater.
Allowance on each end of intermediate lengths is
same as allowance on each end of overall length.
Tolerance is as indicated in the table
above for the allowance that is applied.
Applying the rules given above to the
forging illustrated at right:
Allowances and tolerances for diameters
Machined dimension, mm
(in.)
Allowance, mm (in.) Forging dimension, mm
(in.)
Tolerance on forging, mm
(in.)
(a)
318 (12 )
25.4 (1)
343 (13 )
±6.4 (± )
241 (9 ) 22.2 [(19.1 + 25.4) ÷ 2] ( [( + 1) ÷
2])
264 (10 )
+6.4, -4.8 (+ , - )
165 (6 ) 22.2 [(15.9 + 25.4) ÷ 2] ( [( + 1) ÷
2])
(b)
187 (7 )
+6.4, -4.8 (+ , - )
127 (5)
22.2 [(14.3 + 25.4) ÷ 2] ( [( + 1) ÷
2])
(b)
149 (5 ) +6.4, -4.8 (+ , - )
Allowances and tolerances for ends
Table allowance for 2490 mm (98 in.) length
12.7 mm ( in.)
Table allowance for 318 mm (12 in.) diameter
19.1 mm ( in.)
End allowance applicable (point 3 above)
19.1 mm ( in.) per end
Tolerance on 19.1 mm ( in.) end allowance 4.8 mm ( in.) per end; 9.5 mm ( in.) on total length
(a)
From the table, for allowances of 25.4 and 22.2 mm (1 and in.).