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50.1.1 Hot Extrusion

50.1.2 Cold Extrusion

50.2 HYDROSTATIC EXTRUSION

50.3 DRAWING

50.4 EQUIPMENT

50.5 PRACTICE PROBLEMS

51. ELECTROFORMING

•Basic process,

1.A collapsible/removable metal mandrel is placed in an electrolyte solution (this will be the cathode).

2.A conductive bar of pure metal is put in the solution (this will be the anode).

3.Current is applied, and atoms liberated from the bar coat the mandrel.

4.The part is removed when enough metal has built up.

5.Rinse the part and strip it from the mandrel.

•The mandrel should be created to have a negative impression of the part to be made.

•agitating the electrolyte speeds deposition.

•Typical metals used are,

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-goldsilver

-lead

-nickel (very good properties)

-copper (very popular)

-iron

-aluminum

-zinc

•Advantages,

-0.0005” accuracy is possible

-very good reproduction of mandrel

-walls down to 0.001”

-complex shapes possible

-no theoretical limits to size

-laminate parts possible

-high metal purities possible

•disadvantages,

-production of 0.001-2” per hour

-exterior surfaces hard to control

-thin walled products preferred

-limited material selection

-edges, deep recesses and corners not suited to electroforming.

•Permanent mandrels,

-generally the part is a male or female mate that lifts off easily.

-a tapered shape makes parts easy to remove

•Disposable mandrels,

-these mandrels often have undercuts that stop a part from sliding off

-the mandrel can be dissolved, broken, etc.

-an example is aluminum mandrels that can be dissolved in sodium hydroxide with no effect on a nickel part.

•Flexible Mandrels,

-a collapsible reusable mandrel that a part is formed about.

-If the mandrel is made from a material such as PVC, it must have a conductive coating applied before every use.

•Applications,

-plastics

-electronics

-aerospace

-printing

-appliances

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•Examples,

-record pressing plates

-large reflectors

-complex piping (thin seamless pipe)

51.1 PRACTICE PROBLEMS