*There is not a "single" mold that can be used for injecting molding for "all" plastic materials. Because each plastic has its own chemical, mechanical and thermal characteristics. Therefore, each mold is unique for the material intended to be used. The gate, runner and draft angle may differ from material to material.
Please ask for a quote from Protomold, ICOmold or XcentricMold for finished plastic parts for your own design and get their feedback for your design to see if it even can be molded at all or not. Then please get back to us with your specific mold related questions so that we can reply to your questions intelligently.
Traditionally injection molds have been expensive to manufacture. Molds are typically constructed from hardened steel, pre-hardened steel, aluminum, and/or beryllium-copper alloy. Today, aluminum molds cost substantially less than steel injection molded parts. When higher grade aluminum such as QC-7 and QC-10 aircraft aluminum is used and machined with modern computerized equipment, they can be economical for molding hundreds of thousands of parts. Aluminum molds also offer quick turnaround and faster cycles because of better heat dissipation. It can also be coated for wear resistance to fiberglass reinforced materials. Today's Mold companies use CNC machining and Electrical Discharge Machining (EDM) in the mold manufacturing processes.
Molds consist of two primary halves, injection molds (A plate) and ejector molds (B plate). First, plastic resin enters the mold through a sprue in the injection mold. The sprue bushing is to seal tightly against the nozzle of the injection barrel of the molding machine in order to allow molten plastic to flow from the barrel into the mold, also known as cavity. The sprue bushing directs the molten plastic to the cavity images through channels that are machined into the faces of the A and B plates. These channels allow plastic to run along them, so they are referred to as runners. The amount of resin required to fill the sprue, runner and cavities of a mold is called a shot.
More complex plastic parts are formed using more complex injection molds. These may have sections called slides, that move into a cavity perpendicular to the draw direction, to form overhanging or undercut part features. Some injection molds allow previously injection molded parts to be re-inserted to allow a new plastic layer to form around the first part. This is often referred to as overmolding.
Injection molds can produce several copies of the same parts in a single "shot". The number of "impressions" in the mold of that part is often incorrectly referred to as cavitation. A tool with one impression will often be called a single cavity mold. A custom mold with 2 or more cavities of the same parts will likely be referred to as multiple cavity (family) molds. When you design a mold for more than one parts (multi-cavity), the part distribution should be so balanced that each part is placed at equal distance to the sprue. That allows the mold flow smooth and consistent.
Runner and Gate Design
The runner should be thick enough to carry high amount of plastics without early premature cool down. The gate should be thin enough to have a smooth plastic flow into the cavity.
Wall thickness and design determine if a part would have a sink or wrap after the injection molding or not. Uneven mold wall thickness is always a problem. Certain materials should also have a minimum thickness for a perfect mold-ability.
Here is the video series for Mold Making on Fusion 360: