The clue to which manufacturing process has been used can lie in the number of the particular product being made. Some processes can be used at home and others involve high tooling investment. Low investment processes tend to be craft based and thus slower than high investment ones. Injection moulding is only economically viable if a very high output is required. For example an injection moulding machine can convert plastic granules to a safety helmet in 40 seconds, that is 2160 in 24 hours, 15,120 in a week and 786,240 in a year. The sharing of the tooling cost across so many units results in a relatively low unit price. It is not, however, cost efficient to injection mould small runs (e.g. 5000) of products. On the other hand, casting, fabrication and rotational moulding cost less to set up but are slower in the making. Currently, excluding plastic bags, far more plastic objects are made by injection moulding than by any other process.
Certain processes leave marks behind on the finished product. The most frequently encountered are the marks left by what is now the most widely used process: injection moulding. There are two kinds of marks: that left by the 'sprue', the tail of plastic that is broken off at the point it enters the mould, and the ejector pin marks, smooth and circular, which assist with the removal of the moulding from the mould. For more information please go to what symbols, marks and words are on it?
As certain plastics are only used with certain processes, identifying the process can assist in the identification of the particular plastic. It is helpful to bear in mind when considering manufacturing processes that thermosetting plastics were not injection moulded before about 1960 and they cannot be thermoformed.
The main manufacturing processes are: