metal working processes

metal working methods commonly used

hot working

cold working

extruding

hot working

is the process of forming metal at an elevated temperature when it is in its annealed, or soft condition

types of hot working

rolling

forging

rolling

is a process of reduction of the cross sectional area or shaping a metal piece through the deformation caused by a pair of rotating in opposite directions metal rolls.

bloom

6x6 in or larger

billet

less than 6x6in

slabs

rectangular sections in which the width is greater than twice the thickness

forging

is a process wherein a piece of metal is worked at temperatures above its critical range

Types of forging

pressing

hammering

upset forging

roll forging

pressing

is used to form large and heavy parts.

pressed powdered metal part

combination of different metals or metal and non-metals, that do not ordinarily alloy can be joined together

hammering

A type of forging that is usually used on small parts because it requires a metalworker to physically hammer a piece of metal into its finished shape.

hammering

This type of forging is usually referred to as smith forging and is used extensively where only a small number of parts are needed

hammer forging

It is a hammering process whereby a hot ingot is placed between a pair of formed dies in a machine called a drop hammer and a weight of several tons is dropped on the upper die.

hammer forging

(drop forging) is forming a preheated workpiece by using impact energy of the falling hammer forcing the metal to fill the space between the punch (a part attached to the hammer) and the forging die (a part attached to the anvil).

upset forging

Forging operation which is employed for manufacturing head of bolts, valves, artillery shells and other parts where increase of cross section dimensions of the workpiece is desired.

roll forging(swaging)

Forging operation involving reduction of the workpiece diameter (with increase of its length) by rolling it between two grooved rolls rotating at the same rotating direction.

cold working

is performed well below a metal's critical temperature and ranges from the manual bending of sheet metal for skin repairs to drawing seamless tubing and wire.

types of cold working

cold rolling

cold drawing

shot peening

burnishing

cold rolling

Usually refers to the rolling of metal at room temperature to its approximate size.

cold drawing

is used in making seamless tubing, wire, streamlined tie rods, and other forms of stock.

shot peening

a cold work process, in which the metal part is struck by a stream of small hard spheres (shot) creating numerous overlapped dimples on the part surface.

burnishing

a cold working process in which the surface layer of a work piece is plastically deformed by a hard tool: either roller or sliding ball.

extrusion

is the process of forcing metal through a die which imparts a required cross-section to the metal.

heat treatment

is a series of operations involving the heating and cooling of metals in the solid state.

most common forms of heat treatment for ferous metals

hardening, tempering, normalizing, annealing, and case hardening

Critical Temperature of a Metal (Critical Range)

the temperature at which the internal structure of a metal takes on a crystalline form.

hardening

consists of heating the steel just above the critical range, holding the metal at that temp. until thoroughly heated and then rapidly cooling by immersing the hot steel.

brine

fastest quench that produces the hardest steel.

water

produces slightly less hardness.

oil

slowest quench that produces the least.

tempering

Consists of reheating the hardened steel to a temp. well below the critical range, followed by soaking and quenching.

annealing

is the opposite of hardening. A form of heat treatment in which a metal is made soft.

hardening

The metal is heated at the furnace with a temperature above its critical temperature, quench it at this temperature, and allow cooling at room temperature.

tempering

is done by holding it at a specific temperature for a period of time and then allowing it to cool in still air.

annealing

is accomplished by heating the metal to just above the upper critical point, soaking at that temperature, and cooling very slowly in the furnace

types of annealing

process annealing

spheroidizing

shop annealing

process annealing

commonly used in sheets and wire industries to restore ductility.

spheroidizing

applied particularly to high-carbon steels to improve their machinability.

shop annealing

heating steel in a welding torch 900°F to 1000°F and dropping it into a pail of ashes or lime to restrict the cooling rate.

normalizing

removes the internal stresses set up by heat treating, welding, casting, forming, or machining. Stress, if not controlled, can cause distortion or cracking

normalizing

is accomplished by heating the steel above the upper critical point and cooling in still air.

case hardening

The steels best suited to casehardening are the low-carbon and low-alloy steels

produces a hard wear-resistant surface or case over a strong, tough core.

case hardening

The surface of the metal is changed chemically by introducing a high carbide or nitride content.

methods of case hardening

carburizing

nitriding

carburizing

A case hardening process in which thin layer of high carbon steel is infused into the surface of low-carbon steel.

When the carburized steel is heat treated, the case is hardened while the core remains soft and tough.

types of carburizing

pack carburizing

gas carburizing

liquid carburing

pack carburizing

is done by enclosing the metal in a fire-clay container and packing it with a carbon-rich material such as charcoal. The container is then sealed, placed in furnace, and heated.

gas carburizing

is similar to pack carburizing except the carbon monoxide gas combines with gamma iron and forms a high-carbon surface.

liquid carborizing

produces a high-carbon surface when a part is heated in a molten salt bath of sodium cyanide or barium cyanide.

nitriding

A method of case hardening steel by heating it in an atmosphere of ammonia. The nitrogen in the ammonia reacts with the surface of the steel to form extremely hard nitrides.

harder case is obtainable to this method

aging

heat treatment of nonferrous metal

aging

The characteristics of certain aluminum alloy that causes them to gain hardness over a period of time after they have been heated in a furnace and quenched.

types of aging

solution heat treatment

precipitation heat treatment

solution heat treatment

Also called Natural Aging

It is the process of heating certain aluminum alloys to allow the alloying elements to mix with the base metal.

precipitation heat treatment

Also called Artificial Aging

This process develops hardness, strength, and corrosion resistance by locking a metal's grain structure together.

Works by accelerating the aging process by cooling at an elevated or moderate temperatures.

non heat treatable alloys

3003

5052

nit alloys

. These special alloys contain aluminum as one of the alloying elements and are called