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Old 06-10-2017, 03:51 PM
crystallographic crystallographic is offline
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Join Date: Dec 2010
Location: Western Sierra Nevadas, Badger Hill, CA
Posts: 4,388
Default Hammering with "soft" dies

Conventional hand hammers have had the striking heads made from a variety of materials for many long decades:
Hardened steel
Soft steel
Malleable iron
Tin
Brass
Lead
Copper
Aluminum
Bronze
Leather
Rubber
Plastic
Nylon
Urethane
Fiber
Wood
and other materials ...
Some of these hammer materials are used for "non-marking" and others are used for "non-sparking."

For metal shaping/planishing purposes, steel, rubber, leather, and various urethanes and polymers can find good application. Steel is the most common die material for hammering metal.
Vulcanized rubber and leather have been good elastic "soft" materials for hammering steel and aluminum sheet. Rubber compounds vary, as we see in the tire industry.
When I started vulcanizing rubber hammer heads for my Air Hammer in 1994 they worked pretty well, though I soon learned that urethanes could also be molded to these shapes and they could also be selected from a range of durometers/hardnesses.
From that point on I found that urethanes could also be compounded for a variety of applications - like suspension bushings in NASCAR chassis, for instance. So getting the durometer right is a good basic starting point.

For my own "velocity/impact" shrinking method that I developed specific dies for in my Air Hammer in 1994, I chose a hard polymer that is softer than hard steel, but holds up well when shrinking soft metals like some aluminum alloys, copper, and soft brass. This black polymer has worked well enough for us that it has seen no changes since 1994. We even used it in our Pullmax thumbnail dies, starting in 1995, using them also to shrink 20ga mild steel.

Since that early start I have experimented with a variety of urethane compounds from a variety of companies that have patents on their urethanes.

One that we offer for stretching aluminum does rapid reverse shaping on .040 3003 half hard, and sometimes with zero annealing.
P1030887 c.jpg
Waco gear leg fairings. Front pair have been shaped and then planished with our hard polymer non-rotating reverse dies.... below. Rear fairing is only roughed with the "Expansive" urethane hammer.
P1030922 c.jpg

This heat shied/air deflector was stretched using our urethane "Expansive" upper hammer over a shaped steel die.
P1030895 c.jpg
.063 3003 half hard, perforated aluminum

P1030899 c.jpg
Same part being reversed with the Expansive urethane hammer over a shaped steel die.

P1030900 c.jpg
Same part being shrunk with our Shrinking Set for Soft Metals - black hard polymer (softer than steel)

P1030904 c.jpg
.040 perf. aluminum, 3003 half hard, being stretched with the Oversized Roughing Head (3" dia. leather hammer) over a domed steel die.

P1030910 c.jpg
Showing finished/untrimmed anodized costume visors with unfinished bare visor. These parts' edges also shrunk with the Soft Metal Shrinking set.

P1030912 c.jpg
Art lamp part, .080 6061 "0" temper, with part annealed only after first round of heavy stretching with leather Oversized Roughing Head w/ domed steel lower die. Shrinking on edges done with the Shrinking Set for Soft Metals. After continued working, the metal develops a lot of stress, so the choice is to either anneal and then continue, or continue and then weld.

In summation, many of us prefer soft dies for stretching and shrinking because of the minimal surface marking and because of the smooth contours left for subsequent planishing operations. In some cases, an aggressive soft die can stretch very rapidly - without damaging the material, like the Waco fairings were done. I developed this method back when I was doing the Hughes H1 (replica) wing root fairings, in 2001-2002.

For info on these dies see the TM Tech website, http://www.tinmantech.com/products/f...-hammers/dies/
-- hopefully they are up now. If not, then we have to wait a bit ...
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Kent

http://www.tinmantech.com

"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.

Last edited by crystallographic; 06-10-2017 at 03:54 PM.
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