Presicion Manufacturing

Precision Castings are used for various industrial and oem applications. This includes auto parts,
train components and tractor weights. These castings are made from an original wax model known
as the direct method or from wax replicas of an original pattern that need not be made from wax
composites or the indirect method.
The common wax processes establish the direct method:
1. Produce a master pattern: An artist or molds-maker creates an original pattern
from wax, clay, wood, plastic, or another material.
2. Create a molds: A molds, known as the master die, is made to fit the master pattern. If the
master pattern was made from steel, the master die can be cast directly from the pattern
using metal with a lower melting point. Rubber molds can also be cast directly from the
master pattern.
3. Produce wax patterns: Although called wax patterns, pattern materials may also include
plastic and frozen mercury. Wax patterns can be produced in one of two ways. In one
process, the wax is poured into the mold and swished around until an even coating, usually
about 3 mm (0.12 in) thick, covers the inner surface of the molds. This is repeated until the
desired pattern thickness is reached. Another method involves filling the entire molds with
molten wax and letting it cool as a solid object.
4. Assemble wax patterns: Multiple wax patterns can be created and assembled into one
large pattern to be cast in one batch pour. In this situation, patterns are attached to a
wax sprue to create a pattern cluster, or tree. To attach patterns, a heating tool is used to
slightly melt designated wax surfaces, which are then pressed against each other and left to
cool and harden. As many as several hundred patterns can be assembled into a tree. Wax
patterns can also be chased, which means parting lines or flashings are rubbed out using
the heated metal tool.
5. Apply precision materials: The ceramic molds, known as the precision, is produced by
repeating a series of steps—coating, stuccoing, and hardening—until a desired thickness is
achieved. Coating involves dipping a pattern cluster into a slurry of fine refractory material
and then draining to create a uniform surface coating. Fine materials are used in this first
step, also called a prime coat, to preserve fine details from the molds.
Hardening allows coatings to cure. These steps are repeated until the
precision reaches its required thickness. Drying can be accelerated by
applying a vacuum or minimizing environmental humidity.
6. Dewax: Once ceramic molds have fully cured, they are turned upside-down and placed in
a furnace or autoclave to melt out and/or vaporize the wax. Most shell failures occur at this
point because the waxes used have a thermal expansion coefficient that is much greater
than the precision material surrounding it—as the wax is heated it expands and introduces
stress. To minimize these stresses the wax is heated as rapidly as possible so that outer
wax surfaces can melt and drain quickly, making space for the rest of the wax to expand. In
certain situations, holes may be drilled into the mold before heating to help reduce these
stresses. Any wax that runs out of the mold is usually recovered and reused.
7. Burnout preheating: The mold is then subjected to a burnout, which heats the mold to
between 870 °C and 1095 °C to remove any moisture and residual wax, and to sinter the
mold.
8. Pouring: The precision mold is then placed open-side up into a tub filled with sand. The
metal may be gravity poured or forced by applying positive air pressure or other
forces. Vacuum casting, tilt casting, pressure-assisted pouring and centrifugal casting are
methods that use additional forces and are especially useful when molds contain thin
sections that would otherwise be difficult to fill.

9. Divesting: The shell is hammered, media blasted, vibrated, waterjeted, or chemically
dissolved (sometimes with liquid nitrogen) to release the casting. The sprue is cut off and
recycled. The casting may then be cleaned up to remove signs of the casting process,
usually by grinding.
10. Finishing: After grinding, the completed casting is then subject to finishing. This usually
goes further than grinding, with impurities and negatives being removed via hand-tooling
and welding. In the case that the part needs additional straightening, this process is usually
carried out by hydraulic straightening presses, which bring the product in line with its
Tolerances
Precision castings are made based on custom specifications. CAD drawings are conceptualized
based on-site and user conditions.