12
Remanufacturing and Advanced Machining
nozzle. Moreover, peak pressure in the mold can be reduced by 80% compared to the
one prevailing in traditional injection molding. Due to the accelerated heat transfer
from the polymer molt to the mold, the time of the cooling cycle can be reduced,
which leads to the formation of equal-sized pores, steadily distributed in the molded
part volume. Microcellular polymeric foams may have cell diameters ranging from
0.1 to 100 μm and cell density greater than 10 8 cells/cm 3 (Zhang et al., 2019). The
cell size of most commercial microcellular plastics is in the range of 10–30 μm, and
careful control of the process enables to produce foams with cell density above 10 9
cells/cm 3 and small and uniform cell sizes below 10 μm (Wong et al., 2016). In comparison, a typical conventional polystyrene foam will have an average cell size of
about 250 μm, and a cell density of between 10 4 and 10 5 cells/cm 3 (Xu, 2010). For a
wide range of polymers and fillers, the molded part thickness achievable in the MIM
technology is reported between 1.5 and 4.0 mm (Sykutera et al., 2020).
Many advantages of microcellular plastics result from the foam injection molding
technology. In particular:
• Polymer melt viscosity is reduced by up to 60%.
• Rib to nominal wall thickness ratio is increased.
• Reduced viscosity allows for processing at lower plasticization temperatures.
• Pressure in hydraulic units and injection pressure are reduced by 50%.
• The entire cycle time is reduced, especially due to short holding and cooling time.
• Mass of the product is reduced.
• Petroleum-based material consumption is reduced.
• Clamping force is reduced by 50–80%
• Sink marks, warpages, and areas of residual stress are prevented.
One of the most important benefits of the МuСell ® technology is the fast production
cycle. When minimal holding and cooling times are reached, the overall cycle can
be cut by up to 40% (Trexel, 2021). Another important advantage is the material
saving, since about 70% of the cost of a plastic part is the base material cost (Xu,
2010). Regarding MuCell, manufacturers state that weight reduction and corresponding material saving of up to 30% is possible, but for technically demanding parts it
remains between 8% and 15% (Celanese, 2021).
Industrial practice indicates that adjustment of the IMM for a particular batch
in the case of microcellular injection molding takes less time. Thus, batches with
a stable quality can be produced in a shorter time, even in the case of thin-walled
parts with a wall thickness of as little as 0.5 mm. It is noteworthy that conventional
injection molding required some sort of compromise between cycle time and flatness
of obtained surfaces free from sink marks, warpages, and concentrations of residual
stresses. MIM technologies have made it possible to reach both these objectives for
many product types, such as housings or fittings, without surface defects.
Among merits of the MuCell ® technology, improved ductility, toughness, and
impact resistance of the obtained microcellular material should be named, too
(Wong, 2016). Most materials are considered suitable for microcellular foaming and
Remanufacturing and Advanced Machining
nozzle. Moreover, peak pressure in the mold can be reduced by 80% compared to the
one prevailing in traditional injection molding. Due to the accelerated heat transfer
from the polymer molt to the mold, the time of the cooling cycle can be reduced,
which leads to the formation of equal-sized pores, steadily distributed in the molded
part volume. Microcellular polymeric foams may have cell diameters ranging from
0.1 to 100 μm and cell density greater than 10 8 cells/cm 3 (Zhang et al., 2019). The
cell size of most commercial microcellular plastics is in the range of 10–30 μm, and
careful control of the process enables to produce foams with cell density above 10 9
cells/cm 3 and small and uniform cell sizes below 10 μm (Wong et al., 2016). In comparison, a typical conventional polystyrene foam will have an average cell size of
about 250 μm, and a cell density of between 10 4 and 10 5 cells/cm 3 (Xu, 2010). For a
wide range of polymers and fillers, the molded part thickness achievable in the MIM
technology is reported between 1.5 and 4.0 mm (Sykutera et al., 2020).
Many advantages of microcellular plastics result from the foam injection molding
technology. In particular:
• Polymer melt viscosity is reduced by up to 60%.
• Rib to nominal wall thickness ratio is increased.
• Reduced viscosity allows for processing at lower plasticization temperatures.
• Pressure in hydraulic units and injection pressure are reduced by 50%.
• The entire cycle time is reduced, especially due to short holding and cooling time.
• Mass of the product is reduced.
• Petroleum-based material consumption is reduced.
• Clamping force is reduced by 50–80%
• Sink marks, warpages, and areas of residual stress are prevented.
One of the most important benefits of the МuСell ® technology is the fast production
cycle. When minimal holding and cooling times are reached, the overall cycle can
be cut by up to 40% (Trexel, 2021). Another important advantage is the material
saving, since about 70% of the cost of a plastic part is the base material cost (Xu,
2010). Regarding MuCell, manufacturers state that weight reduction and corresponding material saving of up to 30% is possible, but for technically demanding parts it
remains between 8% and 15% (Celanese, 2021).
Industrial practice indicates that adjustment of the IMM for a particular batch
in the case of microcellular injection molding takes less time. Thus, batches with
a stable quality can be produced in a shorter time, even in the case of thin-walled
parts with a wall thickness of as little as 0.5 mm. It is noteworthy that conventional
injection molding required some sort of compromise between cycle time and flatness
of obtained surfaces free from sink marks, warpages, and concentrations of residual
stresses. MIM technologies have made it possible to reach both these objectives for
many product types, such as housings or fittings, without surface defects.
Among merits of the MuCell ® technology, improved ductility, toughness, and
impact resistance of the obtained microcellular material should be named, too
(Wong, 2016). Most materials are considered suitable for microcellular foaming and