metal extrusion and drawing process and equipment

introduction

in extrusion, large deformation can take place without fracture as the material is under high triaxial compression

products made by extrusion are railings for sliding doors and window frames

extrusion and drawing is used for continuous manufacturing of discrete products from metals and alloys

the extrusion process

4 basic types of extrusion

indirect or reverse

hydrostatic

direct

lateral

exist friction

long length

high force

limited force

limited length

no friction

for less ductile material

no friction

less floor area

limited force

geometric variables in extrusion are the die angle and extrusion ratio


metal flow in extrusion

metal flow pattern in extrusion is important as it influence the quality and mechanical properties of the extruded product


process parameters

lower speeds are preferred

dimensional tolerances in extrusion are in the range from 0.25 to 2.5 mm

extrusion ratios, R, usually range from about 10 to 100

in coaxial extrusion, or cladding, coaxial billets are extruded together

hot extrusion

to reduce forces required, extrusion is carried out at elevated temperature

As the billet is hot, it develops an oxide film, unless it is heated in an inert-atmosphere furnace

metals and alloys do not have ductility at room temperature

Die design

tubing is extruded from a solid or hollow billet

hollow cross section can be extruded by welding-chamber and using varies dies known as a porthole die, spider die and bridge die

square dies (shear dies) are used in extruding nonferrous metals

guidelines for proper die design in extrusion

die design requires considerable experience

avoidance of sharp corners

avoidance of changes in die dimensions

symmetry of cross section

lubricant

lubricant is important as it has effects on

glass is an excellent lubricant for steels, stainless steels and high temperature metals and slloys

surface finish and products quality

extrusion forces

material flow during extrusion

manufacture of aluminum heat sinks

hot extrusion of aluminum is preferred for heat sink applications

tooling for hot extrusion can be produced through electrical-discharge machining

cold extrusion

is a general term for a combination of operations such as direct and indirect extrusion and forging

used widely for components automobiles

cold-extruded part

investigating material flow during the deformation of the slug helps avoid defects.

part is sectioned in the mid-plane, polished and etched to display the grain flow

advantages

good control of dimensional tolerance

improved surface finish

improved mechanical properties

production rates and costs that are competitive

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impact extrusion

similar to indirect extrusion

hydrostatic extrusion

pressure required in the chamber is supplied through an incompressible fluid medium

brittle materials can be extruded successfully as the hydrostatic pressure increase the ductility of the material

extrusion defects

extruded products can develop defects that effect their strength and product quality

some defects are visible to the naked eye while others can be detected only by some techniques

surface cracking

cracks are intergranular caused by hot shortness

can be avoided by lowering the billet temperature and the extrusion speed

high surface temperature can cause surface cracking and tearing

pipe

pipe defect, tailpipe, fishtailing

reduced by having more uniform flow pattern ( decrease extrusion ratio, increase angle die )

type of metal-flow pattern in extrusion will draw surface oxides and impurities toward the center of the billet

internal cracking

center of the extruded product can develop cracks called (-------)

extrusion equipment

basic equipment for extrusion is a horizontal hydraulic press

vertical hydraulic presses are used for cold extrusion

capable of applying a constant force over a long stroke

have less capacity than hot extrusion but take up less floor space

the stroke and speed of the operation can be controlled

crank-joint and knuckle-joint mechanical presses are used for impact extrusion to mass-produce small components