If one considers the everyday things we take for granted you will be amazed at how many of them are products of plastic injection molding in one way or another. The plastic bottles we use for drinks, the model kits we built as kids. The mobile phone, that we all carry, have their bodies molded, and so it goes, all forms of plastic container, plastic garden chairs. These are all things we take for granted. The packaging industry depends on the plastic injection molding process for just about everything they do like the boxes and blister packs that are used to enclose the products actually for sale.
Then there are a huge number of products that we probably never think about; the lenses in the explosion of digital cameras and the cameras on mobile phones are all products of molded plastic. Fiber optic cable is obviously an extrusion from a mold. The material that is used to actually make these represents a massive advance in plastic technology to the material used to make the cheap plastic forks and plastic juice containers that all of us use once and throw away.
Within plastic injection molding there are a whole range of factors that one never thinks about, but the technology is advancing inexorably on two fronts. The first is the range of materials that can be molded. Space age materials for use in the shuttle and for panels and fenders of automobiles are such products. The limitations are materials development, which continues apace, and mold design.
The other is the machines themselves and the molds that fit in them. If one designs a moldable product then one has to ensure that a machine can clamp the mold inject the material with sufficient force to fill the mold, eject the air and cool fast enough so that the mold can be opened and a virtually finished product ejected.
Molds are themselves extremely expensive to make and the old way of machining molds was limited in that there were many areas of design impossible to machine, so a process of electro spark erosion which allowed pre-hardened steel to be eroded and shaped precisely and not need re-hardening. Molds themselves have to be constructed so that the various parts can be fitted, the air escape as the material is injected and then a coolant allowed to flow through to bet the entire mold down to a temperature to cool the product efficiently so that it hardens sufficiently to be removed and stay in shape. Thus once a mold is made the limitations are the injection and the cooling as to the number of products that can be produced. Obviously the unit cost per product is massively reduced the longer the run as molds may wear over time but usually will last for long runs of many tens of thousands of products before needing maintenance.
High precision plastics molding for items such as lenses and fiber optics require specialized machinery and molds. There are not many of them around.