This invention concerns techniques for manufacturing assemblies of molded parts.
Recent trends particularly in the auto industry have been to manufacture many parts from molded plastics in order to reduce weight and costs. The engine air intake system is one example in which the intake manifold and air induction ducts and air flow throttle valve are now commonly constructed of molded parts, whereas formerly those parts were constructed of cast and machined metal.
This trend is continuing and as a further development, efforts are being made to mold complete assemblies as of the air flow throttle body and the intake manifold as one molded part.
Air flow valves include a flow control blade or disc fit into a bore in the throttle housing body defining the air flow passage. The disc is pivoted on a shaft to open and close the flow passage, and must fit accurately to be able to rotate between a closed position allowing a low flow of air and open positions. With machined or stamped metal parts, a sufficiently accurate fit has been obtained by a technique of centering the disc at assembly.
The centering of the disc within the bore has in the past been accomplished during assembly by rotating the disc to a closed position to center the disc in the bore, and then fixedly attaching it to the mounting shaft as with screws or by a staking operation.
However, where the valve body and the valve disc are both molded, a difficult manufacturing problem is encountered due to the close tolerances required for a proper fit.
Precision molding techniques have been developed for this purpose, but are only marginally economic.
Advances in plastic molding technology have included techniques for molding assemblies including moving parts. In U.S. Pat. Nos. 5,421,718 and 5,304,336 there is described a process for molding the movable valve disc inside the valve body, using the throttle body bore to size the disc.
A complex mold configuration is required involving movable inserts, etc., as well as multistaged molding steps.
The efforts to achieve an integrated molded manifold and air flow throttle body have involved quite complex mold configurations, such that it does not appear feasible to also mold the disc into the air flow valve body at the same time that the manifold and throttle body are molded.
It is the object of the present invention to provide a manufacturing process for molding an accurately fitted valve disc of an air flow valve which can be carried out without a complex mold configuration such as to be able to be applied to the manufacture of integrated manifold and throttle body components.