Metal Forming CourseBulk-Deformation Processes

PROCESS GENERAL CHARACTERISTICS Forging Production of discrete parts with a set of dies; some finishing

operations usually necessary; usually performed at elevated temperatures; dies and equipment costs are high; moderate to high labor costs; moderate to high operator skill.

Rolling Flat 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 labor cost.

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; low to 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 is used to make discrete products; moderate to high die and equipment cost; low to moderate labor cost; low to moderate operator skill.

Drawing Swaging

Production of long rod, wire, and tubing, with round or various cross-sections; smaller cross-sections than extrusions; good surface finish; low to moderate die, equipment and 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.

Metal Forming Course

• (a) Ideal deformation of a solid cylindrical specimen compressed between flat frictionless dies.

• (b) Deformation in upsetting with friction at the die-workpiece interfaces.

Open-Die Forging

Metal Forming Course

Grain Flow Lines

• Grain flow lines in upsetting a solid steel cylinder at elevated temperatures. The highly inhomogenous deformation and barreling. The differnet shape of the bottem section of the specimen (as compared with the top) results from the hot specimen resting on the lower, cool die before deformation proceeded.

Metal Forming CourseImpression (Closed) Die Forging

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

Metal Forming CourseLoad-Stroke Curve in Closed-Die Forging

• 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.

Metal Forming Course• Schematic

illustration of orbital-forging process. 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.

Metal Forming CourseHeading

• Forging heads on fasteners such as bolts and rivets. These processes are called heading.

Piercing Operations

• Examples of piercing operations.

Metal Forming CourseCogging Operation

• Schematic illustration of a cogging operation on a rectangular bar. With simple tools, the thickness and cross-section of a bar can be reduced by multiple cogging operations. Note the barreling after cogging. Blacksmiths use a similar procedure to reduce the thickness of parts in small increments by heating the workpiece and hammering it numerous times.

Metal Forming CourseRoll Forging Operation

• Schematic illustration of a roll forging (cross-rolling) operation. Tapered leaf springs and knives can be made by this process with specially designed rolls.

Metal Forming CourseManufacture of Spherical Blanks

• Production of steel balls for bearings by the skew-rolling process. Balls for bearings can also be made by the followingforging process.

•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.

Metal Forming CourseInternal Defects In Forging

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

• Laps formed by buckling of the web during forging.

Metal Forming CourseDefect Formation In Forging

• Effect of fillet radius on defect formation in forging. Small fillets (right side of drawings) cause the defects.

Metal Forming CourseForging A Connecting Rod

• 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.

Metal Forming CourseFeatures Of A Forging Die

Hot-Forging Temperature Ranges

Metal °C Metal °C

Aluminum alloys Copper alloys Nickel alloys

400-450 625-950

870-1230

Alloy steels Titanium alloys Refractory alloys

925-1260 750-795

975-1650

Metal Forming Course

Presses Used In Metalworking

• Schematic illustration of various types of presses used in metalworking. The choice of the press is an important factor in the overall operation.

Metal Forming Course

Flat-And-Shape-Rolling Processes

Metal Forming CourseFlat-Rolling Process

• Schematic illustration of the flat-rolling process. A greater volume of metal is formed by rolling than by any other metalworking process.

• Relative velocity distribution between roll and strip surfaces. Note the difference in the direction of frictional forces. The arrows represent the frictional forces acting on the strip.

Metal Forming CourseRoll Bending and Workpiece Spreading

• (a) Bending of straight cylindrical rolls because of the roll force. (b) Bending of rolls, ground with camber, that produce a sheet of uniform thickness during rolling.

•Increase in the width of a strip (spreading) in flat rolling.

Metal Forming CourseDefects In Flat Rolling

• Schematic illustration of typical defects in flat rolling: (a) wavy edges; (b) zipper cracks in the center of strip; (c) edge cracks; (d) alligatoring.

Metal Forming CourseShape Rolling

• Stages in shape rolling of an H-section part. Various other structural sections, such as channels and I-beams, are also rolled by this process.

Metal Forming CourseRing-Rolling

• (a) Schematic illustration of a ring-rolling operation. Reducing the thickness results in an increase in the part’s diameter. (b) Examples of cross-sections that can be formed by ring rolling.

Metal Forming CourseThread-Rolling Processes

• Thread-rolling processes: (a) flat dies and (b) two-roller dies. These processes are used extensively in making threaded fasteners at high rates of production.

Metal Forming Course

Machined And Rolled Threads

• (a) Schematic illustration of machined or rolled threads. (b) Grain-flow lines in machined and rolled threads. Unlike machined threads, which are cut through the grains of the metal, rolled threads follow the grains and are stronger, because of the cold working involved.

Metal Forming CourseMannesmann Process

• Cavity formation by secondary tensile stresses in a solid round bar and its use in the rotary-tube-piercing process. This procedure uses the principle of the Mannesmann mill for seamless tube making. The mandrel is held in place by the long rod, although techniques have been developed in which the mandrel remains in place without the rod.

Metal Forming CourseTypes Of Extrusion

• Types of extrusion. (a) direct; (b) indirect; (c) hydrostatic; (d) impact.

Metal Forming CourseExtrusion

• Extrusion and examples of products made by sectioning off extrusions.

• Schematic illustration of three different types of metal flow in direct extrusion.

Metal Forming CourseCold and Impact Extrusion

• Examples of cold extrusion. Arrows indicate the direction of material flow. These parts may also be considered as forgings.

•(a) Impact extrusion of a tube (Hooker process).(b) Two examples of products made by impact extrusion, these parts may also be made by casting, forging, and machining, depending on the dimensions and materials involved and the properties desired. Economic considerations are also important in process selection.

Metal Forming CourseChevron Cracking

• (a) Deformation zone in extrusion, showing rigid and plastic zones. Note that the plastic zones do not meet, leading to chevron cracking. The same observations are also made in drawing round bars through conical dies and drawing flat sheet plate through wedge-shaped dies. (b) Chevron cracking in round steel bars during extrusion. Unless the part is inspected properly, such internal detects may remain undetected and possibly cause failure of the part in service.

Metal Forming CourseExtrusion of Seamless Tube

• Extrusion of a seamless tube. The hole in the billet may be prepunched or pierced, or it may be generated during extrusion.

Metal Forming CourseExtrusion of Complicated Shapes

• (a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders. This part is 8 mm thick and is sawed from the extrusion. (b) Components of various dies for extruding intricate hollow shapes.

Metal Forming CourseDrawing

• Variables in drawing round rod or wire.

• Variation in strain and flow stress in the deformation zone in drawing. Note that the strain increases rapidly toward the exit. The reason is that when the exit diameter is zero, the true strain reaches infinity. The point Ywire represents the yield stress of the wire.

Metal Forming CourseTube Drawing

• Various methods of tube drawing.

Metal Forming CourseDrawing Dies

• Terminology for a typical die for drawing round rod or wire.

• Schematic illustration of a typical wear pattern in a wire-drawing die.

Metal Forming CourseSwaging

• Schematic illustration of the swaging process: (a) side view and (b) front view. (c) Schematic illustration of roller arrangement, curvature on the four radial hammers (that give motion to the dies), and the radial movement of a hammer as it rotates over the rolls.

• Reduction of outer and inner diameters of tubes by swaging. (a) Free sinking without a mandrel. The ends of solid bars and wire are tapered (pointing) by this process in order to feed the material into the conical die. (b) Sinking on a mandrel. Coaxial tubes of different materials can also be swaged in one operation.

Metal Forming Course

Cross-Sections Produced By Swaging

• (a) Typical cross-sections produced by swaging tube blanks with a constant wall thickness on shaped mandrels. Rifling of small gun barrels can also be made by swaging, using a specially shaped mandrel. The formed tube is then removed by slipping it out of the mandrel. (b) These parts can also be made by swaging.

Metal Forming Course

Forming Processes For Rocket Casings

• The forming processes involves in the manufacture of solid rocket casings for the U.S. Space Shuttle.

Metal Forming Course

The End