US Patent 7857615 Injection mold having a buffer region

An injection mold has a plurality of cavities and a runner system for injecting material into the cavities. The runner system includes a main-runner and a sub-runner. The sub-runner interconnects the main-runner and the cavities. The sub-runner includes a first runner and a pair of second runners. The first runner connects the main-runner, and the second runners respectively connects ends of the first runner. A buffer rejoin is formed around a joint of the first runner and each second runner for mixing material when the material flows from the first runner into the second runners to make the material have a symmetric speed distribution in the second runners.