Chapter 18 Flashcards
Primary processes
Reduce a cast material into intermediate shapes, such as slabs, plates, or billets
Secondary processes
Converts these shapes into finished or semifinished products.
Bull deformation processes
Those in which the thicknesses or cross sections are reduced or shapes are significantly changed.
Common bulk forming operations
Rolling, forging, extrusion, cold forming, and wire, rod, and tube drawing.
Sheet forming operations
Involve the deformation of a material where the thickness and surface area remain relatively constant.
Common sheet forming processes
Shearing or blanking, bending, and deep drawing. Most sheet forming operations are performed cold.
Bull deformation processes
Rolling, forging, extrusion, wire, rode, and tube drawing, cold forming, cold forging, and impact extrusion, piercing, and other squeezing processes.
Rolling operations
Reduce the thickness or change the cross section of a material through compressive forces exerted by rolls.
Rolling starting stock
Can be rolled into blooms, billets, or slabs, or these shapes can be obtained directly from continuous casting.
Bloom
Has a square or rectangular cross section.
Billet
Usually smaller than a bloom and has a square or circular cross section.
Slab
Rectangular solid where the width is greater than twice the thickness.
Plate, sheet, strip
Slabs can be further rolled to produce these.
Sheet and strip can be fabricated into products or further cold roller into
Foil
Blooms and billets can be further rolled into finished products, such as
Structural shapes, rail road rail, or semifinished shapes such as bar, rod, tube, or pipe.
Rolling process
Metal is passed between two rolls that rotate in opposite directions. Friction along the contact interface propels the metal. The metal is then squeezed and elongates.
Hot rolling
Starting material should be heated to a uniform elevated temperature. The material must first be brought to the desired rolling temperature, usually in gas soaking pits or furnaces.
Hot rolling operations are terminated
When the temperature falls to about 50 to 100 degrees Celsius above the recristallisation temperature. Such a finishing temperature ensure the production of a uniform fine grain size.
Cold rolling
Can be used to produce sheet, strip, bar, and rod products with extremely smooth surfaces and accurate dimensions.
Cold rolled sheet and strip can be obtained in various conditions
Skin rolled, quarter hard, half hard, full hard
Two high non reversing mill
The material can only pass through the mill in one direction.
Two high reversing mill
Permits back and forth rolling, but the folks must be stopped, reversed, and brought back to rolling speed between each pass.
Three high mill
Eliminates the need for roll reversal, but requires some form of elevator on each side of the mill to raise or lower the material and possibly some form of mechanical manipulators.
Cluster mills
Multiple rollers. Foil is almost always rolled on these. These rollers have a small diameter
Pack rolling
Two or more layers of metal are rolled simultaneously as a means of providing a thicker input material.
Continuous or tandem rolling mill.
Used when the volume of a product justifies the investment. Billets, blooms, or slabs are heated and fed through an integrated series of no reversing rolling mill stands. As the material is reduced in size, the rolls must turn faster than the preceding one.
Ring rolling
One roll is placed through the hole of a thick walled ring, and a second roll presses in from the outside. The wall thickness is reduced and the diameter of the ring increases. Can be used in products such as rockets, turbines, airplanes, pipelines, and pressure vessels.
Thread rolling
Alternative to the cutting of threads.
Hot rolled products
Uniform and if dependable quality. The surfaces are usually a bit rough, however, and are originally covered with a tenacious high temperature oxide known as mill scale. This can removed be an acid pickling operation
Cold rolled products exhibit
Superior surface finish and dimensional precious, and can offer the enhanced strength obtained through strain hardening.
If a crowned or barrel shaped roll
Is subjected to the designed load, it will deflect into flatness.
Thermomechanical processing time
Controlled rolling is an example. This integrates deformation and thermal processing into a single process that produces the desired shape and desire properties.
Forging
Induces plastic deformation through localized compressive forces applied through dies. Equipment could be hammers, presses, or special forging machines, deformation can be performed in all temperature regimes.
The variety of forging processes offers a wide range of capabilities.
The metal may be drawn out to increase its length and decrease its cross section. Upset to decrease the length and increase the cross section, or squeezed in closed impression dies to produce multidirectional flow.
Common forging processes
1) open die drop gamer forging. 2) impression die drop hammer forging. 3) press forging. 4) orbital forging. 5) Upset forging. 6) automatic hot forging. 7) roll forging. 8) swaging. 9) Net shale and near net shape.
Open die hammer forging
The metal is first heated to the proper temperature, then an impact is delivered by some Thor of mechanical hammer. The simplest industrial hammer is a gravity drop hammer.
Computer controlled hammers
Can provide blows of differing impact speed for different products.
Open did hammer forging is a simple and flexible process but
It is not practical for large scale production. It is a slow operation and the shape and dimensional precision of the resulting workpiece are dependent on the skill of the operator.
Impression Die or closed die forging
Overcomes the difficulties of open die hammer forging, by using shapes dies to control the flow of metal.
Process of impression die hammer forging
Heated metal is positioned in the lower cavity and struck one or more blows by the upper die.
Flash
In impression die forging, excess metal is squeezed out along the parting line to form a flash around the periphery of the cavity. Metal fills all of the die cavity.
Flashless forging
The metal is deformed in a cavity that provides total confinement. No excess material can result.
First impression made in impression die forging
An edging, filleting, or bending impression that distributes the metal roughly in accordance with the requirements of the later cavities.
Edging vs fullering
Gathers material into a region, whereas filleting moves material away
Intermediate impressions
Are for blocking the metal to approximate its final shape, with generous corner and fillet radii. Finish shake and size knotted by a final or finisher impression.
Board hammers, steam hammers, and air hammers
Have all been used in impression die forging
Counterblow machine or impactor
These machines have two horizontal hammers that simultaneously impact a workpiece that is positioned between them.
Press forging
If larger or thick products are to be formed, this may be required. The slow squeezing action use penetrates completely through then metal, producing a more uniform deformation and flow.
Isothermal forging
Can be used to produce near net shape components with uniform microstructure and mechanical properties.
Forging presses are of two basic types.
mechanical or hydraulic
Mechanical presses
Use cams, cranks, or goggles to produce a preset and reproducible stroke. Different forces are available at various stroke positions.
Hydraulic presses
Move in response to fluid pressure in a piston and are generally slower, more massive, and more costly to operate. They are much more flexible and can have a greater capacity.
A third type of press is the screw press
In which energy is transmitted to a vertical screw, which drives a descending ram.
Impression die forging produces
Connecting rods, crankshafts, wrenches, and gears.
What is critical to successful forging
Lubricant, it acts as a thermal barrier and affects the friction and wear and associate metal flow.
Orbital forging
Uniform radius. Disk shaped. Or conical products such as gray blanks or bevel gears can be formed by a process known as orbital forging.
Orbital forging process
A conical faced upper die is tilted or inclined so a portion of the cone is in contact with the workpiece. The upper die orbits around the central axis, and sighed the upper die descenders of the lower die is raised to produce a continuous deformation.
Upset forging
Increases the diameter of a material by compressing its length. Generally employs split dies.
Uoset forging machines produce
Heads in bolts and other fasteners and to shape valves, couplings, and many other small components.
Automatic hot forging
Low cost input material and high production speeds. Minimum labor is required, and material usage is greater than with conventuel forging. Tolerances are good, surfaces clean, and tool life is nearly double that of conventional forging. To justify this operation, a large quantity of a given product must be required.
Roll forging
Round or flat bar stock are reduced in thickness and increased in length to produce such products as axles, tapered levers, and leaf springs.
Staging
Used external hammering to reduce the diameter or produce tapers or points on round bars or tubes
Swaging process
The operator inserts a rod or tube between the dies and advances it during the periods of die spew ration.
Swaging can product
Internal gears, splines, recesses, or sockets
Net shape or near net shape forging
Can form complex shapes parts with sufficient dimensional precision that little or no final machining is required.
Extrusion
Metal is compressed and forced to flow through a shaped die to form a product with reduced but constant cross section.
Advantages of extrusion
Many shapes can be produced. No draft is required. Extrusion dies can be relatively inexpensive. Small quantities can be produced economically. Good surface finish and dimensional precision
Direct extrusion
A solid ram drives the entire biller to and through a stationary die and must provide additional power to overcome frictional resistance.
Indirect extrusion
A hollow ram pushes the die back through a stationary confined billet.
Mandrel
Use to produce hollow shapes for tubular products.
Spider mandrel die
Metal flows around the arms of the die, and a further reduction the forces the material back together.
Hydrostatic extrusion
High pressure fluid surrounds the workpiece and applies the force necessary to extrude it through the die.
Blowout
In hydrostatic extrusion, seals must be designed to contain the pressure fluid without leaking, and measures must be taken to prevent the complete ejection of the product.
Pressure to pressuré extrusion
The product emerges from an extremely high pressure chamber into a second pressurized chamber. I’m
Pressure induced ductility
Voids are suppressed in a compressed environment
Conform process
Continuous feedstock is inserted into a grooved wheel and is driven by surface friction into a chamber created by a mating die.
Wire rod and tube drawling
Reduce the cross section of a material by pulling it through a die.
Draw benches
In rod or bad drawing, draw benches are employed with finite length feedstock as the product cannot be readily bent or coiled.
Tube drawing
Can be used to produce high quality tubing where the product required the smooth surfaces, thing walls, and accurate dimensions.
Tube sinking
Thick walled tubes are often drawn without a mandrel in a process know as this.
Floating plug
May be utilized if a controlled internal diameter must be produced in a long length product.
Wire drawling
Same process as bad drawing except that it involves smaller diameter material.
Cold forming
Slugs of material are squeezed into or extruded from shaped die cavities to produce finished parts of precise shape and size
Cold heading
Used for making enlarged sections on the ends of rod or wire, such as the heads of nails, bolts, rivets, or other fasteners.
Two variations of cold heading
1) rod or wire is sheathed to a preset length and then transferred to a holder ejector assembly. Heading lunches then strike one or more blows on the exposed end to perform the upsetting. 2) a continuous rod is fed forward to produce a preset extension, clamped, and the head is formed.
Impact extrusion and
A metal slug is positioned in a die cavity, where it is struck a single blow by a rapidly moving punch.
Forward extrusion
The diameter is decreased while the length increases
Backwards extrusion
Shapes hollow parts with a solid bottom. The lunch controls the inside shape, while the die shapes the exterior.
Rotary piercing
Seamless tubing can be made. A heavy bull it is fed into the gap between two large convex tapered rolls that rotate in the same direction. A crack forms down the center axis, and a pointed mandrel enlarges and shapes the opening.
Manned Ann mills
Used in hot piercing to produce tubing up to 300 mm.
Larger diameter tubes can be produced in
Stiefel mills.
Roll extrusion or flow forming
Thin walled cylinders or cups can be produced. Internal rollers expand the internal diameter as they squeeze the rotating material against an external confining ring.
Sizing
Squeezing all or selected regions of forgings, ductile castings, or powder metallurgy products to achieve a prescribed thickness or enhanced dimensional precision.
Riveting
An expanded head is formed on the shank end of a fastener to permanently join sheets of plates of material.
Orbital forming
When a press is used for riveting, the river is usually headed in a single squeezing action, although the heading punch may rotate to shape the head in a progressive manner.
Explosive rivet
The shank in the blink of inaccessible side of an explosive rivet expands in detonation to form a retaining head when a heated tool is touched against the accessible segment.
Pop rivet
A pull up pin is used to expand a tubular shank.
Staking
A method of permanently joining parts together when a segment of one part produces through a hole in the other.
Coining
Cold squeezing of metal while all the surfaces are confined within a set of closed dies. Used to produce coins, medals, and other reproduces where exact size and fine detail are required and where thickness varies about an average.
Hubbing
Cold working process used to plastically form recessed cavities in a workpiece. The bun is pressed into an annealed block until the desired impression is produced.
Peening
Mechanical working of surfaces by repeated blows of impelled shot or a round nose tool. The impacts attempt to flatten and broaden the metal surface. Shot impellers are frequently used to peen shafting, crankshafts, connecting rods, heat teeth, and other cyclic loaded components.
Burnishing
Rubbing a smooth hard surface over the minute surface irregularities that are produced during machining or shearing.
Rolled burnishing
Can be used to improve the size and finish if internal and external cylindrical and conical surfaces.
