The
Vanadium Carbide Layer produced by the TD Process is extremely
hard. It is therefore very important that the surface finish of
the Tooling be smooth and free of all tool marks. Key points to
be considered are surface roughness and polishing
direction.
In all cases
the surface finish should never exceed
Rmax 120 micro-inch (3 micro-meter) on the working surfaces of
the Tooling.
When working
with coated/plated steels, stainless steels, high strength steels
or abrasive type materials the surface finish
of the tooling should not exceed
Rmax 40 micro-inch (1 micro-meter).
The
polishing should be performed after finish grinding of the wear
areas. Buffing starting with emery paper or stone #200 grit and
then progressively finer grit to #1000 is recommended.
The tool
can be finish buffed with 3-7 micron Diamond Compound.
All tool
and grind marks must be removed.
It is recommended
that the polishing direction whenever possible be the same as
the metal flow (see sketches).
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DRAW
RING |
FORM
BLOCK |
EXTRUDE
PUNCH |
When
machining large sections where extensive stock removal is necessary,
parts should be stress relieved prior to semi-finish machining.
Example:
AISI-A2 or AISI-D2 Tool Steels
Rough machine,
Heat to a Temperature of 1200-1250°F.
Hold for
two (2) hours, cool slowly, then Semi-Finish machine.
For all
air hardening tool steels, the recommended hardening
temperatures apply. Exceptions are high speed tool steels
or powdered particle steels where under-hardening may be desirable.
However in order to control size changes and minimize distortion
all tool steels should be double
or triple tempered after hardening.
Triple tempering tends to help stabilize a part.
If Post
Hardening of A2 or D2 is required (for compressive strength),
temper at 350°F / 400°F two (2) times for two (2) hours
per temper.
Estimated
Hardness 58-60 RC.
Examples:
TD Only
|
AISI-D2
Tool Steel, Hardening Temperature of 1850-1875°F, Double
temper at 975°F for a minimum of two (2) hours each temper,
Estimated hardness 55-58 RC. |
| TD with Post Hardening |
AISI-D2
Tool Steel, Hardening Temperature of 1850-1875°F, Double
temper at 350°F / 400°F for a minimum of two (2) hours
each temper, Estimated Hardness 58-60 RC. |
A typical
cycle for a piece of Tool Steel should be as follows:
1. Rough Machine
2. Stress Relieve
3. Semi-Finish Machine
4. Harden Heat Treat, Double or Triple Temper
5. Finish Grind and Polish
6. TD-Treatment
