fusant injection, the plastic fusant is quantitatively injected into the mold cavity. In this stage, it is very similar with traditional injection molding. We often call a gas-assisted injection as “ underfeeding injection”, because in this stage, the injection volume takes up only 55%--80% of the volume of mold cavity. Whereas the specific injection volume varies with different molding products to ensure that the surface of sufant will not be blown through upon the injection of high-pressure gas and thereby acquiring an ideal aeration volume.

you ask too much! Ok! Now I have to tell you more details about a technical process of gas-assisted injection molding. Actually a complete gas-assisted injection molding cycle contains four stages: 1) fusant injection, 2) Gas injection, 3) Gas dwell, 4) Discharge of gas.

a rough technical process of gas-assisted injection molding is where in high-pressure insert gas is injected into core part of the plastic fusant to form a hollow section and further help pushing fusant flow, thereby achieving injection, dwell as well as cooling.

today you ask me some questions about Gas-assisted injection molding, now I have some information about it at hand. I want to share with you. Actually, gas-assisted injection molding is a kind of molding technology, which can produce products with uneven wall-thickness, the products thereby acquired not only show no sign of surface shrink mark, warp and distortion. The most important part is that it not only consume very small amount of materials. But also are easy to be controlled.

since molds of high gloss can be directly used to manufacture high-gloss, mrkless and environmental-friendly plastic parts, avoiding follow-up painting technics and corresponding lead content control, which is very beneficial for environmental protection, this public technology shall bring revolution to the concept of designing and manufacturing injection molds in the future, promote technical upgrade in mold manufacturing industry and producing enormous social and economic benefit for the construction of a people-oriented harmonious society.

currently, highlight and weldless molds are used to make planner weldless plastic parts, in the case of flat-panel TV frames, they may not have to require making highlight shell, instead, deep-hole drilling is sufficient to create the media channels on the cavity. most plastic parts have some curvature on its surface. It is difficult to transfer the heat homogenously without using highlight shell, leading to weld lines and deformations.

on the other hand, it may lead to deformation, losing its dimensional accuracy. Highlight shell requires machining on both sides and thus requires high precision alignment of the workpiece on the machine table, when machining the other side. Additionally, dus to the division of the fixed mold component into two parts, the tightening requirement is extremely high in order to seal the media channels, especially after repeated exchange between cooling and heating cycles.

the design also maximizes the pipelines inside the mold and thus allows rapidly raising the temperature to the thermo plastic level. It ensures a smooth flow of the plastic material inside the runner and mold cavity, realize rapid injection, and achieve the production of plastic parts with high strength, stiffness, and luster on its surface. It also minimizes the problems of deformation, dents, welding lines and waves.
After the injection, it allows pumping cool water into the mold to quickly lower the mold temperature and thus shorten the molding cycle, up to 70%.

as for precision injection molding, now a new molding technology will help it, that is so called Highlight and weldless mold. That kind of mold have an innovative mold design and manufacturing process, making use of pressured vapor or fluids as a media to more efficiently and evenly control the heating and cooling process.

I want to tell you the Shortcoming of traditional injection molding in water cooling, because traditional water-cooled injection molds are made of steels via the material removal process, their water lines are made with drilling simple, intersecting, straight holes, it will lead to lower heat transfer efficiency, uneven temperature on the cavity surface, and warpage on the plastic part.

please remember, generally the rotary mold systems are more expensive, and the mold need two cavities and the injection machine need a large distance between tie bars in order to be rotatable, but rotary mold will offer greater design freedom.

for every application, when we choose a molding method for a particular molded part, it must be established individually from technical and economic aspects. For example, in combination injection molding, because the gate interferes during rotation or transfer, the rotary mold systems often employ hot runners for the pre-molding so as to yield a gateless pre-molding.

this kind of molding method has following disadvantages:

the most important thing is that kind of molding method does not need to open the machine and further transport of a molded part in one mold. It just need core-back technique. It works like this, when the first material is injected, then movable inserts or cores close the cavity spaces for the second material. After it complete, then the spaces for second material are opened.

do you know core-back mold? I mean a mold with retractable slides and cores, that kind of mold structure has some attractive advantages: 1) low mold cost. 2) it is possible to produce multicolor or multi-component injection molded parts.

but that kind of mold with transfer or insert technique has it’s own disadvantages, because it needs precise centering of the pre-molding, complicated rotary device and more cavities accommodated on the mold platen, so because of economic reason, these molds are preferred to rotary molds.

here is a mold with transfer or insert technique, it also can mold two-colored materials or two different materials in one mold, after the pre-molding is made in the first cavity, it is transferred by a handing device or by hand into the second cavity and molded to produce the final part with a second material.

as for mold with rotary cores, how does it work? Let me tell you some details, in this technique, the quite different part is that both mold plates remain in position, only part of the ejector or nozzle side cavity with injected pre-molding is rotated.

for example, for a two-colored part, mold with rotating mold platen or rotating mold half, the first colored section is created by injection at the first mold position. After sufficient time has lapsed for the melt to cool, the mold opens and the mold part section turns 180 degree into the section position. The mold closes to form the second cavity and the second color or another material is injected via a second injection position.