What Is Injection Molding And Why It Is Important
What is Injection Molding?
Injection molding is a manufacturing process widely used for the production of articles of plastic toys and trinkets for automotive body panels, water bottles and cell phone cases. A liquid plastic is forced into a mold and cured - it sounds simple, but it is a complex process. The fluid used will vary from hot glass to a variety of plastics - thermosetting and thermoplastic.
History
The first injection molding machine was patented in 1872, and celluloid was used to produce simple everyday items like hair combs. Just after World War II, an improved injection molding process much - ' screw injection ' was developed and is the most used technique today. Its inventor James Watson Hendry, later developed ' blow ' which is used for example to produce modern plastic bottles.
Types of plastic
The plastics used in the injection molding are polymers - Chemistry - either thermosetting or thermoplastic. Thermosets are set by the application of heat or through a catalytic reaction. Once cured, they cannot be re-melted and reused - the curing process is chemically irreversible. Thermoplastics, however, can be heated, melted and re-used.
The thermosetting plastics include epoxy, polyester and phenolic resins, while thermoplastics include nylon and polyethylene. There are almost twenty thousand compounds available for plastic injection molding, which means that it is not a perfect solution for almost any requirement molding.
Glass is not a polymer, so that does not conform to the accepted definition of thermoplastic - even though it can be melted and recycled.
The Mold
The mold manufacturing has historically been a highly skilled art ( "die - making" ) . A mold is usually in two main sets fastened together in a press. Make a mold often requires a complex design, multi-function machine and a high degree of skill. The tool is generally of steel or beryllium copper, which is used for the manufacture of the mold requires a heat treatment to harden it. Aluminum is cheaper and easier to machine, and can be used for the production of the shorter term. Today, milling techniques discharge machining ( " EDM " ) enabled computer control a high degree of automation of the process of mold manufacture.
Some molds are designed to produce several related parties - for example, a model airplane kit - and these are known as family molds. Other mold designs can have multiple copies ( ' impressions ' ) of the same article produced in a ' shot' - that is, one injection of plastic into the mold.
How Injection Molding Works
There are three main units make up an injection molding machine - the feed hopper, barrel heater and the ram. The plastic in the hopper is in granular or powder form, although some materials, such as silicone rubber may be a liquid and may not require heating.
Once hot liquid, the ram ( ' screw ' ) causes the liquid in the mold and the liquid held firmly sets. More viscous molten plastic required higher (and higher loads press ) pressure to force the plastic in every nook and cranny. The plastic mold is cooled as the metal conducts heat and then the press is cycled to remove the trim. However, for thermosetting plastics, the mold is heated to secure the plastic.
Advantages of Injection Molding
Injection molding allows complex shapes to be manufactured, some of which could be almost impossible to produce economically by other means.
The wide range of materials allows almost exact coincidence of the physical properties required by the article, and multilayer molded allows the adaptation of the mechanical properties and visual appeal - even a toothbrush.
In volume, this is a low-cost process, arguably, with minimal environmental impact. There is little scrap created in this process, and waste that is produced, and to be re- ground and reused.
Disadvantages of Injection Molding
Investing in tools - make the mold - usually requires large production volumes to recover the investment, although this depends on a particular object.
The output of the tool takes development time, and some parts do not easily lend themselves to a practical design mold.
The Economics of injection molding
A mold of high quality, although relatively high cost, will be able to produce hundreds of thousands of "impressions." .
The plastic itself is pretty cheap, and despite the energy required to heat the plastic and press cycle (to remove each print ) the process can be economical, even for the most basic products, such as bottle caps.
With several hundred new plastic compounds being developed every year, and techniques of modern molds, injection molding is safe to continue increasing use in the next fifty years. Although thermosets cannot be recycled, its use, especially for high-precision components, is also destined to grow.