What is injection molding?

Injection molding is a method of producing plastic parts.This is done with an injection molding machine. The shape of the part to be injection molded controlled by the geometry of the injection mold. The injection molding machine has two basic parts; the injection unit, which melts the plastic and then injects or moves it into the mold, and the clamping unit, which holds the injection mold. The unit clamps the mold in a closed position during injection, opens the mold after cooling, and ejects the finished part.

Injection molding is a commong method of producing intricate plastic components in high volume.

Injection molds are made from hardened tool steel, although aluminum may be used for some low volume applications of injection molding. Injection molds can vary from simple open-shut injection molds, single cavity injection molds to complex multi-cavity injection molds with moving cores, stepped shut-offs, unscrewing devices. Due to the tonnage used in this high pressure process, proper materials , supports, parting line locks etc. must used to ensure the life of the mold. Cavities may be polished or textured to achieve a desired finish on the injection molded part.

Injection molding is perfromed by companies called molders. Some molders also design and build injection molds. The most common materials injection molded are plastic (plastic injection molding) and rubber (rubber injection molding).

Metal can also be injection molding. This is known as metal injection molding (MIM). Metal inection molding is relatively new but has gained popularity quickly. Metal injection molding produces intricate metal injection molded parts very economically.

What is compression molding?

Compression molding was specifically developed for replacing of metal components with composite parts via compression molding. The compression molding process can be carried out with either thermosets or thermoplastics. However, most applications today use thermoset polymers. In fact, compression molding is the most common method of processing thermosets. Although many industries utilize compression molding, the automotive industry is the biggest user of compression molding technology. The advantages of compression molding are short cycle time, high production rate. Excellent surface finishes result from compression molding.

What is dip molding?

Dip molding is a process where a mold or part is dipped into a polymer for dip molding or dip coating a part. This dip molding process is used to make items such as surgeons gloves and hand tool handles. Plastisol is the most common dip molding material. But latex, neoprene, urethane, and other materials are also used in dip molding.

What is insert molding?

Insert molding is an injection molding process whereby plastic is injected into a cavity and around an insert piece placed into the same cavity just prior to molding, thus the term insert molding.. The result of insert molding is a single piece with the insert encapsulated by the plastic. The insert can be made of metal or another plastic. Insert molding was initially developed to place threaded inserts in molded parts and to encapsulate the wire-plug connection on electrical cords. Insert molding is also used quite extensively in the manufacture of medical devices. Typical applications of insert molding include insert-molded needle hubs and luer fittings and bifurcations, as well as encapsulated electrical components and threaded fasteners. There are few design limitations or restrictions on material combinations.

What is layup molding?

Lay-up molding may is used for the production of parts of all sizes, for example technical parts with a surface area of a few square feet, as well as swimming pools as large as 1600 square feet can be produced by lay-up molding. Lay-up molding is generally limited to the manufacture of parts with relatively simple shapes that require only one face 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.

What is porous media molding?

Porous media molding refers to the molding of porous plastic or other media such that when the component is molded it has "pores". Porous molding is used to produce nib (example: end of a highlighter) that allow ink to flow through the porous plastic. Cosmetic and reconstructive surgery implants such as chins, noses and cheeks can be made from porous plastic via porous media molding, the fact that the part is porous plastic allows the tissue to bond to it is a advantge that porous plastic has over other materials.

What is pour molding?

Pour molding as the name implies, is the process of pouring a liquified material into a mold that is the inverse of the desired part geomerty. Pour molding is not suitable for high volume or highly intricate components. Pour molding is primarily used for decorative components with limited function.

What is reaction molding?

Reaction molding, also referred to as reaction injection molding (RIM). The low pressure method of reaction molding involves mechanical mixing often with plural component dispensing equipment rather than by impingement and immediately injects the mixture into a closed reaction mold cavity. The reactive polymer resins such as polyols, isocyanates, polyurethanes, and polyamides provide fast reaction molding cycles well suited for automotive and furniture applications. Common reaction injection molded parts include automotive bumpers, fender and panel components, appliance housings, and furniture components. When short fibers or flakes are used to produce a more isotropic product, the process is called reinforced reaction injection molding (RRIM). Many hybrids such as polyurethane/urea, polyurethane/polyester hybrid systems are currently being used as well as those for RIM already mentioned.

What is rotational molding?

Rotational molding is a highly versatile manufacturing option that provides many design possibilities at low production costs. The rotational molding process starts with a mold that is placed in a rotational molding machine that has a loading, heating, and cooling area.

Several rotational molds may be placed on the rotational molding machine at the same time. Pre-measured plastic resin is loaded into each mold, and then the molds are moved into the oven where they are slowly rotated on both the vertical and horizontal axis, thus the term rotational molding.. The melted resin adheres to the hot mold and coats every surface evenly. The rotational mold continues to rotate during the cooling cycle so the parts retain an even wall thickness.

Once the parts are cooled, they are released from the rotational mold. The rotational speed, heating and cooling times are all controlled throughout the process.

Rotational molding offers design advantages over other molding processes. With proper design, parts that are assembled from several pieces can be molded as one part, eliminating expensive fabrication costs.

Rotational molding has a number of inherent design strengths, such as consistent wall thickness and strong outside corners that are virtually stress free. If additional strength is required, reinforcing ribs can be designed into the part to be rotational molded.

What is structural foam molding?

Structural foam molding is a derivative of the injection molding process. Large structural parts often require thicker walls than standard injection molding can produce. Structural foam molding allows for the injection molding of thick wall parts through the addition of a foam agent, thus the term structural foam molding. Any injection moldable thermoplastics can be structural foam molded. To produce the thicker wall part, a small amount of nitrogen or chemical blow agent is introduced into the plastic material. Under pressure inside the injection screw, the foaming agents do not expand. When the melted plastic enters the mold cavity, foaming occurs. As the foaming plastics fill the foam mold cavity, the wall of the part solidifies against the cold mold wall. A thin layer of plastic solidifies without foaming along the mold wall. This thin layer forms a skin structure over the foamed inter core. The thin solid wall is supported by the interior cellular foamed structure. A part produced this way results in a heavy cellular structure similar to wood products. Structural foam molding is a common process.