16
Remanufacturing and Advanced Machining
Lack of binders in the sand and removal of foundry gases from the mold by vacuum substantially improve working conditions in the foundry. Moreover, after the
introduction of the no-bond methods of vacuum molding, foundry does not affect the
environment and leaves comfortable conditions for human activity. The sand may be
reused with a small amount lost, ca. 5% per cycle. It is cleaned and cooled usually
using pneumotransportation outside buildings, saving the area and improving the
optimization of the plant area.
However, in practical solutions of vacuum seal molding, especially when thin-walled
components of high geometrical complexity are manufactured in rather small batches,
some problems may emerge. Technology itself allows for the application of cheaper
equipment and usually one vibration unit is projected. Its technical parameters are calculated considering an “average” mold for typical patterns expected for manufacturing
at that stage, but rapidly changing demand compels changes to manufacturing programs. As a result, the vibration unit, unable to adapt to changing patterns of different
mass, shape, and complexity, may become a bottleneck in the entire V-process.
During the process, preforms are assembled into a cluster, the cluster is invested
in dry sand in a molding box, and the sand is compacted by vibration. The conventional filling of the vacuum forming flask with sand may cause deformation or
abrasive wear of the pattern affecting the quality of a final product. This is especially important in the case of brittle patterns or patterns covered with non-stick
powders. In addition, sand movement is accompanied by dusting, which may cause
serious health problems and other violations of sanitary standards. To avoid these
complications, the cluster inside the molding box is protected with a movable screen
to provide a barrier to the sand stream. The frame-like screen inside the molding
box covers the cluster and is moved up as the sand fills the box. The sand is poured
along the perimeter of the screen between its stacks and the walls of the box, and the
screen is moved up after the box is filled with the sand. A schematic of this solution
is shown in Figure 1.3.
The pattern cluster (3) is placed in the molding box (1) on a layer of sand and
then covered with the screen (4). The sand from the hopper (7) is poured through the
flexible sleeve (5) with a distribution unit (6). As the sand is evenly filled around the
perimeter of the screen, the latter is lifted, causing the sand to pour down freely at
the repose angle of 33–38° to the pattern cluster. When the pattern is covered with
powder or viscous paint, the sand is pressed against it or sticks to it as appropriate.
When brittle patterns are processed, the screen shape may be closer to a cylinder
with a vertical side surface. Inside the screen frames, facing sand or liquid may be
placed and the screen may be lifted after the entire box is filled. The circulating sand
mixture after the casting may be reused. When low-temperature facing mixtures are
used, the screens may be fabricated out of a heat-insulating material. Ice patterns
that require low-temperature mixtures can serve as an example as the development
of new types of cryotechnology for foundry increases its environmental cleanliness,
replacing traditional polymer pattern materials with frozen water (Doroshenko et al.,
2012). Investment casting with ice patterns is similar to that with wax patterns, a
major difference being that an interface agent needs to be coated around an ice pattern to protect it from damage during the process (Liu and Leu, 2006). After the box
is filled with sand and the screen is removed, the vacuum is released and the molten
Remanufacturing and Advanced Machining
Lack of binders in the sand and removal of foundry gases from the mold by vacuum substantially improve working conditions in the foundry. Moreover, after the
introduction of the no-bond methods of vacuum molding, foundry does not affect the
environment and leaves comfortable conditions for human activity. The sand may be
reused with a small amount lost, ca. 5% per cycle. It is cleaned and cooled usually
using pneumotransportation outside buildings, saving the area and improving the
optimization of the plant area.
However, in practical solutions of vacuum seal molding, especially when thin-walled
components of high geometrical complexity are manufactured in rather small batches,
some problems may emerge. Technology itself allows for the application of cheaper
equipment and usually one vibration unit is projected. Its technical parameters are calculated considering an “average” mold for typical patterns expected for manufacturing
at that stage, but rapidly changing demand compels changes to manufacturing programs. As a result, the vibration unit, unable to adapt to changing patterns of different
mass, shape, and complexity, may become a bottleneck in the entire V-process.
During the process, preforms are assembled into a cluster, the cluster is invested
in dry sand in a molding box, and the sand is compacted by vibration. The conventional filling of the vacuum forming flask with sand may cause deformation or
abrasive wear of the pattern affecting the quality of a final product. This is especially important in the case of brittle patterns or patterns covered with non-stick
powders. In addition, sand movement is accompanied by dusting, which may cause
serious health problems and other violations of sanitary standards. To avoid these
complications, the cluster inside the molding box is protected with a movable screen
to provide a barrier to the sand stream. The frame-like screen inside the molding
box covers the cluster and is moved up as the sand fills the box. The sand is poured
along the perimeter of the screen between its stacks and the walls of the box, and the
screen is moved up after the box is filled with the sand. A schematic of this solution
is shown in Figure 1.3.
The pattern cluster (3) is placed in the molding box (1) on a layer of sand and
then covered with the screen (4). The sand from the hopper (7) is poured through the
flexible sleeve (5) with a distribution unit (6). As the sand is evenly filled around the
perimeter of the screen, the latter is lifted, causing the sand to pour down freely at
the repose angle of 33–38° to the pattern cluster. When the pattern is covered with
powder or viscous paint, the sand is pressed against it or sticks to it as appropriate.
When brittle patterns are processed, the screen shape may be closer to a cylinder
with a vertical side surface. Inside the screen frames, facing sand or liquid may be
placed and the screen may be lifted after the entire box is filled. The circulating sand
mixture after the casting may be reused. When low-temperature facing mixtures are
used, the screens may be fabricated out of a heat-insulating material. Ice patterns
that require low-temperature mixtures can serve as an example as the development
of new types of cryotechnology for foundry increases its environmental cleanliness,
replacing traditional polymer pattern materials with frozen water (Doroshenko et al.,
2012). Investment casting with ice patterns is similar to that with wax patterns, a
major difference being that an interface agent needs to be coated around an ice pattern to protect it from damage during the process (Liu and Leu, 2006). After the box
is filled with sand and the screen is removed, the vacuum is released and the molten