Chapter 11 – Mechanical Methods of Change of FormForging - “plastic deformation by compressive forces” Hand Forging exactly what the blacksmiths did. Drop Forging – a drop forge raises a massive weight and lets it fall. The two basic types of forging machines are presses and hammers.  Presses exert enormous forces, which are applied slowly enough that the metal has time to “flow.”  The hammer machines are designed to raise a massive weight and let it drop.o Power hammers add to gravity with pneumatic or hydraulic assistance.o Counterblow hammers use two opposed hammers Open Forging - Presses the billet between two flat plates to reduce its thickness. Cogging – is a forging process that reduces the thickness of a single BILLET by small increments. Closed forging - The billet is forced into the cavities of one or more dies.  Flashing is the excess material squeezed out from a BILLET in a CLOSED FORGING or stamping process. Coining - the process used to form faces of coins on coin blanks. Heading - is the process of “upsetting” metal to form heads on nails or screws. Swaging is the forging process by which a hollow cylindrical part is forced tightly arounda rod or wire to permanently attach the two parts. It is also known as RADIAL FORGING. Lubricants for Forging 1. improve the flow of the material into the dies2. to reduce die wear3. to control the cooling rate4. to serve as a parting agent Pressures Involved in Forging The force needed to forge a part depends on: 1. the compressive strength of the metal2. the area including flashings of the metal being forged3. the temperature at which the forging is being done4. the amount of deformation each compressive stroke of the ram or hammer performs.Hydroforming – Forcing a BILLET into a mold with a bag of liquid.1Extrusion – Extrusion is the process of forcing a material through a DIE to produce a very long WORKPIECE of constant shape and cross section. Extrusion can be done “cold” (at room temperature) or “hot” so that the material is softened slightly.  Direct or forward - The product moves Indirect (reverse or backward) - product stationary, die moves Hydrostatic Extrusion – In hydrostatic extrusion a fluid is placed between the ramand the metal being extruded. This produces two advantages: o (1) The fluid presses radially inward on the billet, which helps guide it intothe opening in the die o (2) the fluid lubricates the walls of the cylinder, which reduces the friction forces in the extrusion process.  Impact extrusion - a process for making hollow containers from ductile materials.  Hollow Extrusion – Hollow pieces such as pipes and tubing can be made by extrusion if some “obstacle” is part of the die design.Rolling Rollers are pressed together with enough force so that whatever passes between them must take the shape of the space between the rollers.  Bend rods or sheets into curved surfaces  Change the grain structure of cast bars or sheets  Form billets into structural shapes such as flanges, channels, or railroad rails  Produce tapers or threads on rods  Straighten bent sheets, rods, or tubing Bending by Rolling: Crimped by rolling.  Tube forming by rolling Threaded parts by rolling - faster than machining the threads and leaves a harder grain structure.  Forming ball bearings Straightening flat stockRolling Shapes  Plate is defined as stock that is thicker than 0.25 inch (6 millimetres) Sheet runs from 0.25 inch down to about 0.0003 inch (0.008 millimetre) Foil is considered to be less than 0.0003 inch thick. Large flange beams (I-beams), channels, and even wire are made by rolling.2Hot Versus Cold Rolling  Hot rolling – Billets heated to the red hot range rapidly form an oxide coating or scale.  Cold rolling - Softer materials such as aluminum and copper are cold rolled. o rolling material at room temperature provides better surface finish and closer toleranceso characterized by fine grain size. The finer the grain, the harder and less malleable the metal becomes. Factors Affecting Rolling  The material being rolled  The material of the rollers  The shape being rolled  The size of the stock being rolled  The size of the rollers  Power requirements Bending Brake – general use device for bending sheet metal.Punch and Dies – shaping material by punching it into a die. Punch is the moving form, Die is the stationary form. Press brake - an extension of the punch-and-die set extended along one dimension to make complex bends in a long piece of sheet stock.Drawing – the pulling of a bar through a Die to reduce the cross section. -Used to make wire-Seamless TubingSpin forming is a forming process in which a sheet of metal is held to a mandrel, rotated, and forced onto the mandrel to shape the sheet.