Micro vertical injection machine includes a plasticizing unit, in which a feeding channel is provided and a screw or a plunger for transporting the molten material is provided in the feeding channel; an injection unit adapted to receive a metered amount of molten material from the plasticizing unit; an injection mold adapted to receive the metered amount of molten material from the injection unit; at least two thrust cylinders adapted to close the injection mold before injection and open the injection mold after injected parts solidified.

The injection unit includes an injection cylinder, the injection cylinder is connected with the feeding channel of the plasticizing unit, and a vertically reciprocating plunger is provided in the injection cylinder, which can expel air above the molten material in the injection cylinder by its upward advancement and then push the molten material into the injection mold. The micro vertical injection machine according to the invention can eliminate the need for valves, avoids air entrapment in the molten plastic, provides a very high speed injection and reduces dead zones in the injection process that trap and degrade the material quality.

It is well known that the injection molding process provides the capability to mass-produce intricate parts in a precise manner. And more and more injection machines have been used for manufacture of micro component parts.

In the prior art, a vertical injection machine consists of an injection unit mounted either with a horizontal or vertical orientation and a clamp system oriented vertically to hold the molds including an upper mold and a lower mold together underforce sufficient to resist the pressure exerted by the molten material. The upper mold and the lower mold define a molding cavity therebetween when brought together by a relative vertical movement between them. The molten material can be injected intothe mold. After the part cools and solidifies, the mold is opened and the part can be ejected.

Based on the known vertical injection machine, a conventional micro vertical injection machine includes further a plasticizing unit, an injection unit and a reciprocating screw through which the molten material is fed to an injection cylinder ofthe injection machine. The molten material is injected by moving the screw forward to force material through a nozzle into the cooled mold cavity. After a desired volume of material in front of the screw has been injected, the axial movement of thescrew is stopped. Then the mold cavity is cooled and the injected material is fixed to the desired shape of the part.

Injection molding of micro size parts requires the injection of very small volume of molten material at high precision. The known micro vertical injection machine uses valves to shut off the molten material and use the movements of screws and/orplungers to meter the exact amount of material to be injected into the mold cavity. The design and manufacture of micro valves that would not trap molten material in a dead zone face many difficulties. Therefore, many new injection machine designs onthe market are attempting to resolve these problems.

A valve member is provided to open and close the connectionbetween the plasticizing portion and the injection portion. The plasticizing portion further includes a plasticizing air cylinder which drives a plasticizing plunger within the plasticizing chamber or bore. However, since the plasticizing plunger ismoved in the downward direction to compress the molten material, the air entrapment in the molten material cannot be effectively eliminated, which would influence the qualities of the micro-parts.

U.S. Pat. No. 6,403,010B1 describes a method for injecting plastic or other injectable material into an injection molding tool, which includes: transporting the molten material from a plasticizing apparatus into a dosing apparatus, which has afirst fluidic connection to the plasticizing apparatus, and specifically in essentially precisely the quantity that is to be introduced into the injection molding tool; transporting the molten material, essentially in that quantity which is to beintroduced into the injection molding tool, from the metering apparatus into an injection apparatus, via a second fluidic connection, while at the same time preventing the molten material from backflowing from the metering apparatus into the plasticizingapparatus; injecting the entire material, which is situated in the injection apparatus, into the injection molding tool by an injection piston, while at the same time preventing the material from flowing from the injection apparatus back into themetering apparatus. In this way, since the molten material is transported from the top down firstly and then transported horizontally to compress the molten material, the air entrapment in the molten material cannot be effectively eliminated, whichwould also influence the qualities of the micro-parts.

The micro vertical injection machine according to the invention comprising: a plasticizing unit, in which a feeding and melting channel is provided and a screw or a plunger for transporting the molten material is provided in the feeding channel;an injection unit adapted to receive a metered amount of molten material from said plasticizing unit; an injection mold adapted to receive the metered amount of molten material from the injection unit; at least two thrust cylinders adapted to close theinjection mold before injection and open the injection mold after injected parts solidified; and the injection unit includes an injection cylinder, the injection cylinder is connected with the feeding channel of the plasticizing unit, and a verticallyreciprocating plunger is provided in the injection cylinder, which can expel air above the molten material in the injection cylinder by its upward advancement and then push the molten material into the injection mold. The design that the injectioncylinder is positioned vertically and the plunger can inject the molten material upwards can expel air above the liquid column of molten material in the injection cylinder to eliminate air entrapment before the molten material is being push into themold.

According to the invention, it is preferred that the injection machine further comprises a pressure sensing apparatus, which is provided near to the top of the injection cylinder to measure the pressure of the molten material to be injected. During the upward advancement of the plunger the pressure profile measured by the pressure sensing apparatus is used to compute in real-time the amount of upward advancement of the plunger required to inject the precise amount of molten material into the injection mold and control the movement of the plunger accordingly in real-time. In fact, the pressure sensing mechanism through the injection process will provide an effective way of avoiding damage to the mould when some solid is blocking the mouldand more importantly the signature of the pressure variations will provide an effective means of calculating and controlling the exact amount of material to be injected.

The vertical injection machine process occurs cyclically. The vertical injection machine cycle of the micro vertical injection machine according to the invention is divided into five stages. The first is the feeding stage, the second is the stage for shuttingoff the feeding channel by advancement of the plunger 41, the third is the injection stage, the fourth is the molding stage and the fifth is the removing stage.