Manufacturing Chapter 13-15 Lecture Notes

Basic Forging Process

1) A slug or billet is cleaned and preformed 2) If needed the billet is heated and descaled 3) Hot forged dies are heated and dies are lubricated 4) Billet is forged 5) The forged object is measured and cleaned 6) The forged object is finished, heat treated if needed 7) The object is finally inspected

Basic Rolled Shapes

Blooms- have square or rectangular cross sections greater than 36 square in. Billets- smaller than a bloom. Slabs- rectangular solid with more than twice greater with than thickness.

Forging Force

Can be calculated using a basic formula.

Alligatoring

Caused by non-uniform bulk deformation of during rolling of the billet or by defects in the material to be cast.

Barelling

Caused when frictional forces oppose the outward flow of the work piece at the die interfaces.

Hot Rolling

Done during initial rolling above the re-crystallization temp. The cast structure becomes a wrought structure. Finish surface is typically poor.

Screw Presses

Presses that receive energy from a flywheel. The forge load is transmitted through a large vertical screw. They are better for smaller production quantities and can be used for high precision parts.

Drop Hammers

Presses where the ram's down stroke is accelerated by steam air or hydraulic pressure.

Orbital Forging

Process by where the upper die moves along an orbital path and forms the object incrementally.

Hubbing

Process of pressing a hard punch with a particular geometry into the surface of a block of metal. The cavity formed is then used as a die for later forming operations.

Rolling

Process of reducing thickness or cross section area of a long work piece by compressing through rollers.

Forging

Processes to make discrete parts by plastic deformation, and compressive forces by tooling and dies. May be done hot or cold.

Bulk Deformation vs Sheet Forming

Processes where thickness or cross sections are reduced. Sheet forming deforms materials but mostly preserves thickness and cross section area.

Four High Rolling Mills

AKA Cluster Mills. Use small diameter work rolls to lower roll forces, lower power consumption and reduce spreading.

Roll Forging

AKA Cross Rolling. The cross section is passed through a pair of rolls with specifically designed grooves. Typically done to produce tapered shafts, leaf springs, table knives, and hand tools.

Cogging

AKA Drawing Out. Is an open die forging method in which the thickness of the bar is reduced by successive forging steps at specific intervals.

Direct Extrusion

AKA Forward Extrusion. A billet is placed in a container and forced though a die.

Isothermal Forging

AKA Hot Die Forging. The dies in this process are heated to the same temperature as the hot work piece so that the mechanical properties are more consistent.

Rotary Tube Piercing

AKA Mannesman Process. Hot working operation for making long, thick-walled, seamless tubing.

Rotary Swaging

AKA Radial Forging. A solid rod or tube is subjected to radial impact forces using a set of reciprocating dies and the work piece is stationary.

Indirect Extrusion

AKA Reverse, Inverted, or Backward Extrusion. The die moves toward the unextruded billet.

Temper Rolling

AKA Skin pass rolling. A final light pass shortly before stretching it in a subsequent forming operation.

Heading

AKA Upset Forging. Performed on the end of a rod or wire to increase the cross section. Done with machines called headers. For larger parts they are done with horizontal upsetters.

Spreading

As a rolled metal piece becomes thinner, it also becomes wider. Can be combated with vertical rolling and strip edging.

Coining

A closed die forge process used to produce parts with high accuracy. Lubricant is not used.

Thread Rolling

A cold-forming process by which straight or tapered threads are formed on a rod or wire. They are made using reciprocating dies. Better mechanical strength than other methods.

Cold Extrusion

A combination of operations done at room temperature.

Train

A group of stands.

Open Die Forging

A metal work piece is placed between two flat dies, and reduced in height by compressing it. AKA Flat Die Forging or Upsetting

Servo Presses

A more recent type of press where the use of two servos are used to drive the ram. or dies.

Ring Rolling

A ring shaped blank is placed between two rolls, one is driven while the other idles. The thickness is decreased while the diameter is increased. Is typically used to make body casing for rockets and jet engines.

Hot Twist Test

A round specimen is twisted continuously and in the same direction until it fails. The number of turns before failure is measured.

Die Design

Dies are selected based on the mechanical properties of the metal to be extruded.

Upsetting Test

A solid, cylindrical specimen is upset between flat dies and the reduction in height at which cracking or barreling occurs is measured.

Incremental Forging

A tool forges a blank into a particular shape in several small steps. It is similar to cogging.

Precision Forging

A very precise type of impression die forging that cuts down on the need for several finishing processes.

Coaxial Extrusion

Coaxial billets are extruded together if they have compatible strength and ductility.

Various Forging Operations

Coining, heading, piercing, hubbing, orbital forging, incremental forging, isothermal forging, rotary swaging, and tube swaging.

Cracking

Cracks result from low material ductility when rolling. Edge defects must be removed before continuing with other operations.

Extrusion Design Considerations

Cross section must have symmetry, solid shapes are easier to extrude, many extrusions have some curvature that must be corrected.

Die Closing Swaging Machines

Die movements are through the reciprocating motion of wedges. The dies can be opened wider than regular rotary swagers.

Hot Extrusion

For metals and alloys that do not have good room temp ductility. Similar to hot forging the dies are heated.

Major Bulk Deformation Processes

Forging, rolling, extrusion, rod wire and tube drawing, and swaging.

Grain Flow

Grain flow occurs when as an object is barreled. Surfaces and grain layers cool at different levels.

Counterblow Hammers

Hammers that have two simultaneous rams that approach each other horizontally or vertically to form the object.

Shape Rolling

Heated stock passes through pairs of specifically designed rolls. Can also be done cold.

Advantages of Cold Extrusion

Improved mechanical properties, good control of dimensional tolerances, improved surface finish, good production value range.

Mechanical Presses

Presses of either the crank or eccentric type. Speed varies from the top to bottom of the stroke. These presses have high production rates and are typically easier to use.

Hammers

Presses that drive their energy from the potential energy of the ram. Unlike hydraulic presses, they are fast, minimizing object cooling.

Upsetting

Increases diameter of a material by compressing its length. Can be done cold or hot.

Cold Rolling

Is carried out at room temperature and creates a fine surface finish and enhanced mechanical properties.

Pancaking

Is the increasing of the piece's diameter as height decreases and the die forging is complete.

Flash

Material flowing outward from the die during impression forging.

Fullering

Material is distributed away from the region in the dies.

Edging

Material is gathered into a localized region.

Types of Forging Machines

Mechanical presses, screw presses, hydraulic presses, hammers, drop hammers, counterblow hammers, high energy rate forging machines, and servo presses

Flat Rolling Process

Metal enters a roll gap and is thinned. There is a velocity gradient from low on the entry of the rollers to faster on the exit side. Material is pulled through using friction.

Forged Anisotropic Properties

Metal flows in varying directions. Temperatures vary within the forged material. Properties change throughout the material.

Extrusion

Metal is compressed and forced to flow through a shaped die to form a product with constant cross section. May be done hot or cold.

Basic Rolling Process

Metal is passed between two rollers that rotate in opposing directions. Friction propels material. Metal elongates as cross section area decreases.

Bulk Deformation Processes

Metalworking process in which the work piece under forces applied by various tools and dies.

Closed Die Forging

Nearly similar process as impression die forging except flash is not formed. Die volume is closely controlled.

Blocking

Occurs after edging, is used to form the rough object shape using blocker dies.

Primary Bulk Process

Operations that break a single piece to wrought metals of various shapes.

Secondary Bulk Process

Operations that reduce shapes into final or semi-final projects such as gears and bolts.

Hydraulic Presses

Presses that operate at a constant speed and are load limited. They are typically slower than mechanical presses and can be more costly.

Roll Pass Design

Rolling process sequence.

Crowning

Rolling thickness is greater at the center of the metal strip than at the sides due to deflection.

Leveling Rolling

Rolling to improve flatness and final parameters.

Stand

Set of rolls with its own housing and controls.

Impact Extrusion

Similar to indirect extrusion. A punch rapidly descends on to the blank, which is extruded backwards.

Skew Rolling

Similar to roll forging. Round wire is fed into a roll gap and spherical blanks are formed continuously.

Residual Stresses

Stresses caused by deformations during the rolling process. Occurs frequently in cold rolling. Small rollers cause surface stress and bulk tensile stress while large rolls tend to cause more bulk than surface deformation.

Extrusion Defects

Surface cracking, pipe, internal cracking

Pipe Defect

Surface defects and impurities are drawn to the center of the billet during extrusion.

Hydrostatic Extrusion

The billet is smaller in diameter than the container that is filled with fluid, and the pressure is transmitted to the fluid by a ram.

Forgeability

The capability of a material to undergo deformation in forging without cracking. Based on the upsetting and hot twist tests.

Drawing

The cross section of a solid rod, wire, or tube is reduced or changed in shape by pulling it through a die.

Extrusion Ratio

The die angle and the ratio of the cross-sectional area of the billet to that of the extruded part.

Three High Rolling Mills

The direction of material movement through the rolls is reversed after each pass using an elevator mechanism.

Wavy Edges

The edges of rolled sheet metal become waved due to roll bending and thinning of the metal at edges.

Tube Swaging

The internal diameter and the thickness of the tube is reduced with or without the use of internal mandrels.

Metal Flow in Extrusion

The metal flow pattern affects mechanical properties. Stagnation can happen in corners and at sharp angles.

Tandem Rolling

The metal strip is rolled continuously through a number of stands to thinner gages with each pass.

Piercing

The process of indenting the surface of a work piece with a punch in order to create a cavity or impression.

High Energy Rate Forging Machines

The ram is accelerated rapidly by inert gas at a high pressure and the part is formed in one blow at a very high speed. They have difficult maintenance routines.

Impression Die Forging

The work piece takes the shape of the die cavity while being forged between two shaped dies. This process usually happens at elevated temperatures.

Chatter

Vibration caused during the rolling process that affects the viability of the metal.

Preforming Operations

Typically used to enhance the distribution of the material into various regions of the blank using simple dies of various contours.

Tube Rolling

Used to reduce the diameter and thickness of pipes and tubing.

Rolling Defects

Wavy edges, zipper cracks, edge cracks, alligatoring, and residual stress.

Forging Defects

Web buckle and laps, internal cracking, grain flow pattern, an-isotropic properties.

Camber

When rollers are increased in thickness to make up for roller deflection and stop crowning.

Two High Rolling Mills

used for hot rolling an initial breakdown passes on ingots or continuous casting.