Molding Process

Molding is the process of forming parts or components by shaping hot, liquid industrial material (plastic, resin, composite, foam, ceramic, rubber) in a malleable state using a hollowed out block. As the material cools it sets or forms in the shape of the block/mold. Molded components can hold extremely close tolerance and come in almost limitless shapes and sizes making them ideal for almost every industry. The medical device, automotive, aerospace, food, consumer product and many other industries make widespread use of molded materials. Some of the most commonly used molding technologies include:

• Compression Molding: Compression molding is most commonly used for rubber and elastomer component parts. Rubber molding work by placing the material in a heated mold cavity. The male half of the mold closes on the female half containing the material with substantial force pressing the material into shape. Compression molded parts are usually very strong and production runs are usually very high. One of the advantages of compression molding is it can effectively produce intricate parts of both large and small size.
• Dip Molding: Dip molding is a process where the mold is heated to a greater temperature than the liquid material to be molded. The heat from the mold attracts the cooler plastic. The molds are then extracted from the liquid and put through a baking process. After the parts cool they are stripped from the molded and put through secondary operations to form a finished component. Dip Molding is especially effective for applications that need to be turned around rapidly in low or prototype quantity.
• Injection Molding: The injection molding process has the ability to produce an extremely high volume of parts, with exceptional quality, in a very short amount of time. The granules of plastic in the injection molding press are heated until they are soft enough to be squirted into the mold with enough pressure to fill the mold completely. After the work piece cools it is ejected from the mold. Many molding technologies are really derivatives of the injection molding process. They include double shot injection molding, over-molding, insert molding, gas assisted injection molding, reaction injection molding and structural foam injection molding.
• Blow Molding: Blow molding is a process that is commonly used to form containers. Bottles, plastic gas cans, disposable food containers are all made using the blow molding process. At the outset of the blow molding process it resembles injection molding, however the “pre-form” is heated well beyond the temperature in an injection molding press then a high pressure blast of air. The high pressure blast of air causes a hardening of the polymer under stress making the formed bottle very strong. The strength of the bottles formed in this way make them ideal to hold carbonated beverages.
• Spray/Lay Up Molding: Lay-up molding is generally limited to the manufacture of parts with relatively simple shapes that require only one face or side to have a smooth appearance (the other face being rough from the lay-up molding operation). Lay-up molding is recommended for small and medium volumes. Lay-up molding is used by a variety of industries. One of the key benefits to this type of molding is that it can make extremely large parts up to 1600 square feet. This type of molding is fairly inexpensive relative to the simple nature of the parts produced and their size.
• Pour Molding: The technique of pouring liquid resin into a mold or pattern to produce a finished component. The resin can be melted thermoplastic or a mixture of resin and hardener. Producing the molds is low cost at low volumes, but costs can skyrocket if quantities increase because each component take a substantial amount of time to produce. Pour molding is an outstanding technology to produce prototype molded parts and is very effective when producing urethane castings.
• Rotational Molding: Rotational or roto-molding is a process where the mold is heated before the introduction of the polymer. The resin is introduced in powder form and the rotation of the mold attracts the powder and the heat from the mold sets the powdered polymer into shape. For applications that are not completely enclosed a back and forth rolling method is used to agitate the polymer and set it in place within the mold. Some uses for rotational molding would be water tanks, equipment cases, pump housings, plastic seats and port – a – pottys.
• Transfer Molding: Transfer molding is really a bridge between compression and injection molding technologies. There is a piston and cylinder within the mold so the elastomer can be squirted into the mold. The mold then closes using hydraulic pressure and the rubber is forced into the mold cavity. Transfer molding provides more consistency than compression molding but it is poorer than injection molding. Cycle times are shorter than compression molding, but longer than injection molding. Also, unlike most molding technologies, there is a substantial amount of scrap material created using the transfer molding process.