Lecture 15 Extrusion die design Course Hour: 2 Basic requirements: Grasping the principles of die design, acquainting with die materials Emphasis: Die design principles Difficulties: Die design principles

Hot Extrusion — Die Design Difficult and requires a lot of experience Square dies (die angle = 90o) give rise to dead metal zones around the die Dead metal zones give bright finishes to aluminum alloys (no surface exposed to air) Spider dies produce hollow shapes How is the cross section completed?

Extrusion-Die Configurations Typical extrusion-die configurations: (a) die for nonferrous metals; (b) die for ferrous metals; (c) die for T-shaped extrusion, made of hot-work die steel and used with molten glass as a lubricant

Components for Extruding Hollow Shapes (a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders. This part is 8 mm (5/16 in.) thick and is sawed from the extrusion (see Fig. 15.2). (b)-(d) Components of various dies for extruding intricate hollow shapes.

Cross-Sections to be Extruded Poor and good examples of cross-sections to be extruded. Note the importance of eliminating sharp corners and of keeping section thicknesses uniform

Lecture 16 Cold extrusion Course Hour: 2 Basic requirements: Acquainting with cold extrusion practice; Grasping different types of extrusion defects and their causes and prevention Emphasis: Extrusion defects Difficulties: Formation extrusion defects

Cold Extrusion More recent development (1940's) Includes some operations similar to forging Advantages – Improved mechanical properties – Work hardening – Good control of tolerances – Improved surface finish – Elimination of heating costs – High production rates Disadvantages – Higher stresses require more expensivetooling and die material – Difficult die design essential to success – Lubrication critical

Cold Extrusion Two examples of cold extrusion. Thin arrows indicate the direction of metal flow during extrusion.

Further Examples of Cold Extrusion Production steps for a cold extruded spark plug. A cross-section of the metal part showing the grain flow pattern.

Product Quality Issues Surface cracking (tearing, fir-tree cracking, speed cracking, bamboo defects) – Caused by • high temperature • high speed • high friction • Surface appearance – Oxides, scratches, discolorations Pipes (tailpipe, fishtailing) – Caused by surface oxides and defects being piped to the middle by the flow pattern – Results in significant lengths being scrapped – Can be minimized by machining billet surface first, making the flow pattern more uniform

Product Quality Issues Internal Cracking – Caused by a state of hydrostatic stress at the center of the extrusion which results from poor die design

Chevron Cracking (a) Chevron cracking (central burst) in extruded round steel bars. Unless the products are inspected, such internal defects may remain undetected, and later cause failure of the part in service. This defect can also develop in the drawing of rod, of wire, and of tubes. (b) Schematic illustration of rigid and plastic zones in extrusion. The tendency toward chevron cracking increases if the two plastic zones do not meet. Note that hte plastic zone can be made larger either by decreasing the die angel or by increasing the reduction in cross-section (or both).

Typical uses of extrusions Windows and doors (aluminum) Aircraft components – stringers, ribs Tubing – copper and plastic for plumbing, – aluminum, steel for lawn furniture Discrete parts (sawn off)