In-mold
assembly molding of polymer micromachines is a new technology in which
technological bottlenecks of micromachines micro-assembly manufacturing process
can be effectively solved, however, the
thermal-fluid-solid coupling effect between polymer high temperature viscoelastic melt flow and
preformed micro solid part can be caused which induces preformed micro solid
part producing frequently the thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon, how
accurate control and predict thermal-fluid-solid coupling deformation and
necking fusing fracture phenomenon is key scientific issues of in mold micro
assembly molding technology industrialized application.
Therefore,
based on the developed variable combination
mold and Auto model FB-110C polymer co-injection molding machine, the
polymer micromachines In-mold assembly molding experimental research platform
was established, by which the influencing rule and influencing mechanism of
process parameters and properties of polymeric materials on preformed micro
shaft thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon
were systematically studied, key
regulatory parameters of thermal-fluid-solid coupling deformation and necking
fusing fracture phenomenon in in-mold micro assembly molding process was
clarified; the scientific foundation of the research and development of
thermal-fluid-solid coupling deformation precision-shaped control
technology and the prevention technology of necking fusing
fracture phenomenon was laid. The main innovations and achievements as follows.
The variable combination mold of typical micro mobile motion pair in-mold
micro assembly molding was developed, and Based on the developed variable
combination mold and Auto model FB-110C
polymer co-injection molding machine, the polymer micromachines In-mold
assembly molding experimental research platform was established.
The influencing rule and influencing mechanism of secondary molding melt
injection temperature, secondary molding melt injection pressure and
screw stroke on necking fusing fracture phenomenon of preformed micro
shaft, the research results show key
regulatory parameter of preformed micro shaft necking fusing fracture
phenomenon is secondary molding melt injection volume, when the secondary molding melt injection
volume exceeds its critical melt injection volume, the critical melt injection
volume of induced preformed micro shaft necking fusing fracture phenomenon
depends on secondary molding melt injection temperature, which is positively
proportional to secondary molding melt injection temperature. Improving of
secondary molding melt injection temperature will help improve the critical
melt injection volume of induced preformed micro shaft necking fusing fracture
phenomenon, which increase the secondary molded part density and strength in
In-mold assembly molding process, at the same time, but also to avoid preformed
micro shaft necking fusing fracture phenomenon.
Experimental research results show
that the micro shaft unidirectional necking fusing fracture phenomenon possible
ways have two main factors, firstly, the
axial tensile force is too large; secondly, the preformed micro shaft
near-surface temperature in a secondary molding process is too large, which led to partial
melting and a sharp decline of elastic
modulus. The heat transforms time contact between secondary molding high
temperature and preformed micro shaft will prolong with increasing of secondary
molding melt injection volume, which make the preformed micro shaft
near-surface temperature improve with increasing of screw stroke.
When the preform micro shaft near-surface
temperature exceeds the glass transition temperature, local micro assembly
interface of preformed micro shaft will experience continuous phase transition
evolution from elastoplastic solid state to viscoelastic plasticity glassy
state ,final to viscoelastic high-elastic state, which led to a sharp decline
of elastic modulus and make polymer material in local phase transition
evolution region lost the ability to resist deformation, preformed micro shaft
in local phase transition evolution region of micro assembly interface must
produce necking phenomenon under tensile force effect.
When the tension force reaches a
certain level, preformed micro shaft will produce the necking fusing fracture
phenomenon. In order to preform micro shaft near-surface temperature does not
exceed the glass transition temperature, which requires its secondary molding
melt injection volume does not exceed the critical injection volume. Based on
above necking fusing fracture mechanism, the preparatory proposed necking fusing
fracture mechanism theory and prevention technical method of preformed micro
shaft necking fusing fracture provide technical support for the industrialized
application of In-mold micro assembly molding technology.
Experimental research results show that the
preformed micro shaft thermal-fluid-solid coupling deformation depends on
secondary molding melt injection temperature，secondary
molding melt injection pressure ，secondary
molding melt injection volume and preformed micro shaft material properties，and
the process parameters affect its thermal-fluid-solid coupling deformation by adjusting pre-formed micro shaft micro
assembly interface to withstand the impact of the thermal-fluid-solid coupling
pressure, viscoelastic supporting normal stress, viscous friction drag shear
stress and micro shaft stiffness against deformation，the
preformed micro shaft thermal-fluid-solid coupling deformation increase with
increasing of secondary molding melt injection temperature，secondary
molding melt injection pressure, secondary molding melt injection volume, and
based on key regulatory parameters of viscoelastic supporting normal stress,
viscous friction drag shear stress and micro shaft stiffness against
deformation, the formation mechanism of preformed micro shaft thermal-fluid-solid
coupling deformation was revealed.
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