Abstract: A mold device includes first and second molds matched and engaged with each other at first and second curved major surfaces thereof to define a cavity between first and second matched portions. The molds respectively have first and second step portions surrounding the matched portions and spaced apart from the major surfaces in a height direction so as to define an air venting channel that is in air communication with the cavity and the ambient air. With such construction, the mold device is easy to fabricate and has a fewer number of components, thereby simplifying the manufacturing process and reducing the manufacturing cost.