This is one of the simplest and most economical methods of producing a tool for the injection molding of thermoplastic parts.

It consists of mounting a pattern within a mold box, setting up a parting line, and then painting and later pouring resin over the pattern until there is sufficient material to form one half of the tool. After completing the first half, the process is repeated for the other half of the tool. There are many tooling resins available with different mechanical and thermal characteristics – with epoxy being one of the most popular. The resins are often loaded with aluminum powder or pellets to improve the thermal conductivity and compression strength of the tool and to reduce the cost of the resin. Cast resin tools are usually used for 100 to 200 molded parts, although it’s possible to get up to 1,000 parts – depending on the material being molded.

The advantages of this process are that it’s fast, relatively simple, and can be used to mold common thermoplastics such as polypropylene and ABS. A disadvantage is the low mechanical strength of the molds, especially when the mold includes small thin features. For this reason, this method of rapid tooling is only suitable for relatively simple shapes. Also, the low thermal conductivity of the mold material lengthens the molding cycles times.