Electronic Product Mold Overview
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The injection molding process generally includes four stages of filling, holding, cooling, and demoulding.
Filling is the first step in the whole injection cycle, starting from the closure of the mold to the filling of the mold cavity to about 95%. In theory, the shorter the filling time, the higher the forming efficiency. But in practice, the forming time or injection speed are restricted by many conditions.
Electronic Product Mold
On the Forming of Thermoplastics
It is generally advisable to design dies by the following methods:
(1) For plastic parts, the shrinkage of outer diameter is smaller and that of inner diameter is larger, so that there is room for modification after test.
(2) The form, size and forming conditions of the gating system are determined by the trial mould.
(3) After the post-processing, the size change of the plastic parts must be determined (the measurement must be 24 hours after the demoulding).
(4) Modify the die according to the actual shrinkage.
_Re-test the die and modify the shrinkage slightly to meet the requirements of the plastic parts.
According to the requirements of die design, the fluidity of common plastics can be roughly divided into three categories:
Good fluidity: nylon PA, polyethylene PE, polystyrene PS, polypropylene PP;
(2) Medium fluidity: polystyrene series resins (such as ABS, AS), PMMA, POM, PPO;
(3) Poor fluidity: polycarbonate PC, polyphenylene sulfide PPS, polysulfone PSF, polyaromatic sulfone PSU, fluoroplastic PTFE.
Thermoplastics can be divided into crystalline plastics and amorphous plastics according to whether crystallization occurs during their condensation.
The so-called crystallization phenomenon refers to the phenomenon that the molecule moves independently from melting state to condensation state, completely in disorder, and then stops the free movement of the molecule in a slightly fixed position, with a tendency to make the molecule arrangement a normal model.
Generally, the amorphous materials are transparent (e.g. plexiglass). But there are exceptions, such as ABS is amorphous but not transparent.
When designing and selecting injection moulding machine, the following requirements and precautions should be paid attention to for crystalline plastics:
It needs more heat to rise the material temperature to the forming temperature, so the equipment with high plasticizing ability should be used.
(2) When cooling and solidifying, it emits a lot of heat, so it should be fully cooled.
(3) The proportion difference between melt state and solid state is large, forming shrinkage is large, shrinkage and pore are easy to occur.
The anisotropy is significant and the internal stress is large. After demoulding, the uncrystallized molecule tends to continue to crystallize and is in the state of energy imbalance, which is prone to deformation and warping.
Electronic Product Mold