Simple injection molding machine structure and injection method for the same

A simple injection molding machine structure, comprising:

• a stationary platen mounted with a first mold core;
• a movable platen corresponding in position to the stationary platen, the movable platen being movable freely relative to the stationary platen and mounted with a second mold core corresponding in position to the first mold core, wherein the first and second mold cores engage with each other to enclose a mold cavity;
• and
• an injection unit disposed on the movable platen and including an injection barrel, a heating member, a screw rod, and a driving member, the screw rod having an end coupled to the driving member and another end extended into and received in the injection barrel, the heating member being disposed on the injection barrel, the injection barrel having an injection nozzle penetrating the movable platen to communicate with the mold cavity;
• said driving member including a variable frequency motor coupled to said screw rod for controlling the rotational speed of the screw rod in a manner whereby the force of pressurizing a molten plastic being delivered to said mold cavity substantially equals a back pressure produced in the mold cavity as the molten plastic is inserted into the mold cavity.