This article is from the Golf FAQ, by marcelo@nntpserver.Princeton.EDU (Marcelo A. Gallardo) with numerous contributions by others.
A "positive" or master model of the clubhead is made, usually made of
aluminum, which contains all engraved markings, scoring lines, and even
the hosel hole. Wax is injected into the master, which yields a
positive "wax" clubhead. The clubhead is then dipped into ceramic
several times to produce the negative mold. The wax is then melted, and
stainless steel poured into the ceramic mold. When the ceramic casting
is removed, you have the clubhead ready to be painted.
Forging a club is very similar to what the village blacksmith used to
do. Dies are "sunk" or cut, by milling the desired impression, and
forging is accomplished with a "drop hammer". The manufacturer is then
presented with a raw forging, which is a close approximation of the
clubhead desired. The clubhead must then be finished by milling,
grinding and drilling.
A Muscleback iron, also known as a "blade", has generally been
associated as a "forged" iron. While the manufacturing process isn't
really important, the design of the clubhead is. The muscleback iron
distributes the weight evenly throughout the entire head, producing a
small "sweet spot" in the center of the head. This is to say that a
shot hit in the center of the face will produce a longer, straighter
flight trajectory. Shots which aren't hit pure (off-center) will
produce a shorter, unpredictable flight trajectory.
A cavity back iron, also known as perimeter weighted, has generally
been associated as an investment cast iron. Again while the
manufacturing process isn't really important, the design of the
clubhead is. The cavity back iron distributes the weight around the
perimeter of the head, producing a large "sweet spot". This makes the
off-center shots more forgiving, flying longer and straighter, than an
off-center shot with a muscleback iron.
** Investment cast **
o Usually a Cavity back
o Peripheral weighting, if cavity back
o More forgiving, due to cavity back
o Stainless steel
** Forged **
o Usually a Blade or Muscleback
o Central weighting, if a blade or muscleback
o Better "feel", due to muscleback design
o Carbon steel & chrome
Now what you really want to know: When investment cast heads were first
introduced, several companies claimed that the "feel" of the head was
lost. These same companies also claimed it was more difficult to "work"
the ball with the cast heads. Keep in mind that most golfers tend to
believe that a muscleback iron (usually forged) produces more "feel"
than the cavity back models (usually investment casted). They also say
that it is easier to "shape" the shot using the blades over the
perimeter weighted clubs. Before making a decision, you should try a
few muscleback and cavity back irons and see for yourself. For more
information please refer to Dave Tutelman's "Designing golf clubs"