Production Engineering

1st Year Marine Fall 2007

Forging

Outline

Forging Characteristics. Forging Operations. Forging Defects. Force calculations.

Analytical - Open Die forging. Empirical - Impression Die forging.

Problems.

Bulk-Deformation Processes

TABLE 6.1 General characteristics of bulk deformation processes.

PROCESS GENERAL CHARACTERISTICSForging Production of discrete parts with a set of dies; some finishing operations usually

necessary; similar parts can be made by casting and powder-metallurgy techniques;usually performed at elevated temperatures; dies and equipment costs are high;moderate to high labor costs; moderate to high operator skill.

RollingFlat Production of flat plate, sheet, and foil at high speeds, and with good surface finish,

especially in cold rolling; requires very high capital investment; low to moderate laborcost.

Shape Production of various structural shapes, such as I-beams and rails, at high speeds;includes thread and ring rolling; requires shaped rolls and expensive equipment; lowto moderate labor cost; moderate operator skill.

Extrusion Production of long lengths of solid or hollow products with constant cross-sections,usually performed at elevated temperatures; product is then cut to desired lengths;can be competitive with roll forming; cold extrusion has similarities to forging and isused to make discrete products; moderate to high die and equipment cost; low tomoderate labor cost; low to moderate operator skill.

Drawing

Swaging

Production of long rod, wire, and tubing, with round or various cross-sections; smallercross-sections than extrusions; good surface finish; low to moderate die, equipmentand labor costs; low to moderate operator skill.Radial forging of discrete or long parts with various internal and external shapes;generally carried out at room temperature; low to moderate operator skill.

Forged Components

Figure 14.1 (a) Schematic illustration of the steps involved in forging a knife. (b) Landing-gear components for the C5A and C5B transport aircraft, made by forging. (c) General view of a 445 MN (50,000 ton) hydraulic press. Source: (a) Courtesy of the Mundial LLC. (b and c) Courtesy of Wyman-Gordon Company.

Characteristics of Forging

Micro structure as a Function of Manufacturing Method

Figure 14.2 Schematic illustration of a part made by three different processes showing grain flow. (a) Casting by the processes described in Chapter 11. (b) Machining form a blank, described in Part IV of this book, and (c) forging. Each process has its own advantages and limitations regarding external and internal characteristics, material properties, dimensional accuracy, surface finish, and the economics of production. Source: Courtesy of Forging Industry Association.

Ideal Deformation

FIGURE 6.1 (a) Ideal deformation of a solid cylindrical specimen compressed between flat frictionless dies. This process is known as upsetting. (b) Deformation in upsetting with friction at the die-workpiece interfaces.

Contact Area of Rectangular Specimen

FIGURE 6.7 Increase in contact area of a rectangular specimen (viewed from the top) compressed between flat dies with friction. Note that the length of the specimen has increased has increased proportionately less than its width. Likewise, a specimen in the shape of cube acquires the shape of a pancake after deformation with friction.

Grain Flow Lines

FIGURE 6.2 Grain flow lines in upsetting a solid steel cylinder at elevated temperatures. Note the highly inhomogenous deformation and barreling. The differnet shape of the botte, section of the specemen (as compared with the top) results from the hot specimenresting on the lower, cool die before deformation proceeded. The bottom surface was chilled; thus it exhibits greater strength and hence deforms less than the top surface. Source: J. A. Schey et al., IIT Research Institute.

Forging Operations

I- Open-Die Forging Operations

Cogging Operation on a Rectangular Bar

Figure 14.4 (a) Schematic illustration of a cogging operation on a rectangular bar. Blacksmiths use this process to reduce the thickness of bars by hammering the part on an anvil. Reduction in thickness is accompanied by barreling, as in Fig. 14.3c. (b) Reducing the diameter of a bar by open-die forging; note the movements of the dies and the workpiece. (c) The thickness of a ring being reduced by open-die forging.

Orbital Forging Process

FIGURE 6.16 Schematic illustration of the orbital-forging process. Note that the die is in contact with only a portion of the workpiece surface. This process is also called rotary forging, swing forging, and rocking-die forging and can be used for forming bevel gears, wheels, and bearing rings.

Piercing Operations

FIGURE 6.18 Examples of piercing operations.

Grain Flow in Forging

Figure 14.12 A pierced round billet showing grain-flow pattern (see also Fig 14.12c). Source: Courtesy of Ladish Co., Inc.

Heading

Figure 14.11 (a) Heading operation to form heads on fasteners, such as nails and rivets. (b) Sequence of operations to produce a typical bolt head by heading.

Stepped Pin

Figure 14.13 (a) The stepped pin used in Case Study 14.1. (b) Illustration of the manufacturing steps used to produce the stepped pin. Source: Courtesy of National Machinery, LLC.

Swaging

Figure 14.14 (a) Schematic illustration of the rotary-swaging process. (b) Forming internal profiles on a tubular workpiece by swaging. (c) A die-closing swaging machine showing forming of a stepped shaft. (d) Typical parts made by swaging. Source: Courtesy of J. Richard Industries.

Swaging with and without a Mandrel

Figure 14.15 (a) Swaging of tubes without a mandrel; note the increase in wall thickness in the die gap. (b) Swaging with a mandrel; note that the final wall thickness of the tube depends on the mandrel diameter. (c) Examples of cross-sections of tubes produced by swaging on shaped mandrels. Rifling (internal spiral grooves) in small gun barrels can be made by this process.

Roll Forging Operation

FIGURE 6.20 Schematic illustration of a roll forging (cross-rolling) operation. Tapered leaf springs and knives can be made by this process with specially designed rolls. Source: After J. Holub.

Manufacture of Spherical Blanks

FIGURE 6.21 Production of steel balls for bearings by the skew-rolling process. Balls for bearings can also be made by the forging process shown in Fig. 6.22.

FIGURE 6.22 Production of steel balls by upsetting of a cylindrical blank. Note the formation of flash. The balls are subsequently ground and polished for use as ball bearings and in other mechanical components.

I- Closed-Die Forging Operations

Impression-Die Forging

Figure 14.5 (a) through (c) Stages in impression-die forging of a solid round billet. Note the formation of flash, which is excess metal that is subsequently trimmed off (see Fig. 14.7). (d) Standard terminology for various features of a forging die.

Load-Stroke Curve in Closed-Die Forging

FIGURE 6.15 Typical load-stroke curve for closed-die forging. Note the sharp increase in load after the flash begins to form. In hot-forging operations, the flash requires high levels of stress, because it is thin-that is, it has a small h-and cooler than the bulk of the forging. Source: After T. Altan.

Impression-Die Forging

FIGURE 6.14 Schematic illustration of stages in impression-die forging. Note the formation of flash, or excess material that is subsequently trimmed off.

AnalysisSimple shapes, without flashSimple shapes, with flashComplex shapes, with flash

3-55-88-12

F = (Kp)(Yf)(A)

TABLE 6.2 Range of Kp values in Eq. (6.21) for impression-die forging.

Finite Element Simulation

FIGURE 6.11 Plastic deformation in forging as predicted by the finite-element method of analysis. Source: Courtesy of Scientific Forming, Inc.

Features Of A Forging Die

FIGURE 6.27 Standard terminology for various features of a typical forging die.

Hot-Forging Temperature RangesMetal °C °F Metal °C °FAluminum alloysCopper alloysNickel alloys

400-450625-950

870-1230

750-8501150-17501600-2250

Alloy steelsTitanium alloysRefractory alloys

925-1260750-795

975-1650

1700-23001400-18001800-3000

TABLE 6.3 Hot-forging temperature ranges for various metals.

Forging A Connecting Rod

FIGURE 6.26 Stages in forging a connecting rod for an internal combustion engine. Note the amount of flash that is necessary to fill the die cavities properly.

Forging a Rod, Fullering, and Edging

Figure 14.7 (a) Stages in forging a connecting rod for an internal combustion engine. Note the amount of flash required to ensure proper filling of the die cavities. (b) Fullering and (c) edging operations to properly distribute the material when preshaping the blank for forging.

Trimming Flash After Forging

Figure 14.8 Trimming flash from a forged part. Note that the thin material at the center is removed by punching.

Closed-Die Forging Versus Flashless Forging

Figure 14.9 Comparison of closed-die forging with flash (left side of each illustration) and precision or flashless forging (right side) of a round billet. Source After H. Takemasu, V. Vazquez, B. Painter, and T. Altan.

The Coining Process

Figure 14.10 (a) Schematic illustration of the coining process. The earliest coins were made by open-die forging and lacked precision and sharp details. (b) An example of a modern coining operation, showing the workpiece and tooling. Note the detail and superior finish that can be achieve in this process. Source: Courtesy of C & W Steel Stamp Co., Inc.

(b)

Forging Defects

Internal Defects In Forging

FIGURE 6.24 Internal defects produced in a forging because of an oversized billet. The die cavities are filled prematurely, and the material at the center of the part flows past the filled regions as deformation continues.

FIGURE 6.23 Laps formed by buckling of the web during forging.

Defect Formation In Forging

FIGURE 6.25 Effect of fillet radius on defect formation in forging. Small fillets (right side of drawings) cause the defects. Source: Aluminum Company of America.

Metals in Decreasing Order of Forgeability

Principles of Various Forging Machines

Figure 14.17 Schematic illustration of the principles of various forging machines. (a) Mechanical press with an eccentric drive; the eccentric shaft can be replaced by a crankshaft to give the up-and-down motion to the ram. (b) Knuckle-joint press. (c) Screw press. (d) Hydraulic press.

Speed Ranges of Forging Equipment

Cost-per-piece in Forging

Figure 14.18 Typical (cost-per-piece) in forging; note how the setup and the tooling costs-per-piece decrease as the number of pieces forged increases if all pieces use the same die.

Forging Analysis: Slab Method

Grid Deformation In Upsetting

FIGURE 6.3 Schematic illustration of grid deformation in upsetting: (a) original grid pattern; (b) after deformation, without friction; (c) after deformation, with friction. Such deformation patterns can be used to calculate the strains within a deforming body.

Stresses in Plane-Strain Compression

FIGURE 6.4 Stresses on an element in plane-strain compression (forging) between flat dies. The stress øx is assumed to be uniformly distributed along the height h of the element. Identifying the stresses on an element (slab) is the first step in the slab method of analysis for metalworking processes.

Formulas

pav≈Y ' 1 a fh f

Forging a rectangular workpiece

Forging a cylindrical workpiece

F= pav2a f w f

Assuming Slipping friction condition

pav≈Y 12 r f3h f

Assuming Slipping friction condition

F= pav r f2

=lin hh0

pav≈Y ' 1a f2h

Assuming sticking friction condition

pav≈Y 1r f3 h f

Assuming sticking friction condition

Y '=2

3Y

Problems

Calculate the force required to obtain a 30% reduction in height of a 1020 steel cylindrical workpiece of an initial hight and diameter of 90 mm and 130mm respectively. [ is 0.2 and Y=295 Mpa]

What will be your answer for frictionless upsetting. What is the efficiency of the process. What will be your answer if we assume a sticking friction condition.