Tool and die welding refers to the repair and
manufacture of metal parts that change the shape of other metals or
materials. The nature of its job dictates that tool steel must be
capable of cutting, stamping, drawing, punching or in some way changing
the shape of other metals without itself becoming worn or distorted.
According to the type of tool steel we are referring to, it will have
certain characteristics that make it special and different from other
tool steels. The Society of Automotive Engineers (SAE) and the American
Iron and Steel Institute (AISI), Tool Steel designations are self
explanatory as to the function of that particular steel.
Tool Steel Designations AISI SAE
W1 Thru W5 Water Hardening
01 Thru 06 Oil Hardening
A2 Thru A10 Air Hardening
M1 Thru M47 High Speed
S1 Thru S7 Shock Resisting
L1 Thru L7 Special Purpose Steels for Die Blocks
P1 Thru P21 Mold Steels
D1 Thru D7 High Carbon; High Chromium
H10 Thru H43 Hot Work
T1 Thru T15 Tungsten High Speed
Most tool steels have the capability of being annealed (becoming soft).
When the die or tool is made, it must be soft enough to be machined.
After the part is made, it must be capable of being heat treated to
bring it into the desired hardness range (hardness is explained in the
wearfacing section). Shops that deal with Tool and Die work have a close
association with heat treating. Terms such as anneal, temper, and harden
should be understood in order to see how the manufacture or repair of a
die is achieved.
Tool and die welding takes place when:
1. Dies have to be repaired
2. Correcting design changes
3. Manufacture composite dies
4. Fix mistakes
1. Repairing dies is a major part of tool and die welding. Parts that
wear in certain areas, or chips that develop must be repaired as quickly
as possible without having to completely rework the die by annealing and
reheating. Filler alloys such as MG 700 and MG 710 can be deposited and
in most cases subsequent heat treating is not necessary.
2. Correcting design changes as a die is being worked
in or changed over could mean adding a small amount of metal or great
amounts of metal such as on cutting edges. Tool steel welding will
permit the addition of comparable metal at the desired points to salvage
expensive tools or dies.
3. Manufacturing composite dies is becoming more popular because of
companies trying to reduce costs of manufacture. Rather than make tools
or dies completely from a particular type of expensive tool steel like
4130 or 4140. Then the parts that will be exposed to the cutting or
stamping is built up using a suitable tool steel filler alloy.
4. Fixing Mistakes usually occurs at the machine shop level. If a part
being repaired or fabricated is over-machined, compatible tool steel
filler alloys must be applied to bring the part back up to tolerance.
MG Tool Steel alloys are most often used to repair or correct a design
change or fix mistakes. The MG Tool Steels are hard as deposited or can
be annealed to facilitate machining. MG 700 is basically a modified high
speed tool steel compatible to most other tool steels. It is used where
higher hardness is needed. MG 710 is a modified air hardening type tool
steel also compatible to most other tool steels. It is used where very
high hardness is not needed or when the part must be forged or annealed
then re-heat treated.
A mistake often made by tool welders in repairing broken dies is using
tool steel electrodes as a joining rod. When the broken tool is being
put together using the tool steel electrode, the joint will become hard
and brittle and not capable of taking impact. This is because the
alloying elements in this type of electrode make the deposit hard
throughout the joint area. The proper procedure would be to prepare the
joint for welding, then use MG 600 to join the broken parts together.
The joint should be built up to within three passes of the finished
dimension. The appropriate tool steel electrode is then used to cap off
the surface of the working area. MG 700 is used where high hardness is
needed and MG 710 is used when medium high hardness is needed.