Blow molding is similar to injection molding except that hot liquid plastic comes out of a barrel vertically, in a hollow molten tube or "parison." The mold close on it and compressed air blows up the parison like a balloon, forcing it outward to conform to the inside shape of the mold. After cooling, a hollow part emerges. Typically used for jars, bottles, containers etc.
Part prices are generally higher than injection molded parts, but lower than rotationally molded parts. Tooling costs are moderately expensive.
Compression molding presses a slug of hard plastic between two heated mold halves. Generally, compression molding uses vertical presses instead of the horizontal presses used for injection and blow molding. After formation, parts are air-cooled. Prices for both tooling and part pieces are moderate.
Dip molding is similar to hot dip coating, in which the finished product is the fused plastisol stripped from the dipped mold. Dip molding is used to produce such parts as gloves, grips, and protective caps.
Film insert molding (FIM) permanently embeds an image beneath the surface of a molded part. A material such as film or fabric is inserted into a mold. Plastic material is then injected.
Gas assist molding or gas injection molding (GIM) is used to produce plastic parts with hollow interiors. A partial shot of plastic is followed by high-pressure gas to fill the mold cavity with plastic.
Reaction injection molding (RIM) mixes two or more reactive chemicals at a high speed as they are injected into a mold. Typically, this low temperature process typically takes less than a minute to complete including time for mixing, curing, and demolding.
Resin transfer molding (RTM) is a liquid molding process that is commonly used in the aerospace and automotive industries. In the RTM process, a resin is mixed with a hardener and then injected at low pressure into a mold containing dry fibers. The part must cure for several hours at room temperature before it is removed from the mold.
Hollow molds filled with powdered plastic are secured to pipe-like spokes that extend from a central hub. The molds rotate or tumble on separate axes at once. The hub swings the entire mold into an enclosed furnace room that causes the powder to melt and stick to the insides of the tools. With the molds still tumbling slowly, the tools swing into a cooling room where sprayed water causes the plastic to harden into a hollow part. This technique is also known as rotomolding.
Low tooling costs and high piece prices are typical of this process. Cycle times average around 40-45 minutes.
Structural foam molding is a type of injection molding process commonly used for parts that require thicker walls than standard injection molding. Introducing a small amount of nitrogen or chemical blow agent into the plastic material allows for the creation of the thicker walls. Foaming occurs as the melted plastic material enters the mold cavity. A thin plastic skin forms and solidifies along the mold wall and supports the interior cellular foam on the inside. Structural foam molding can be used with any thermoplastic that can be injection molded.
Thermoplastic injection molding is the most widely used plastic processing method. The injection molding machine reduces pelletized raw material and colorant to a hot liquid. This "melt" is then forced into a cooled mold under tremendous pressure. After the material solidifies, the mold is unclamped and a finished part is ejected. Injection molding offers the lowest piece prices available; however, tooling prices are usually the highest.
Thermoset polymers decompose rather than melt when heated and, once set into a final shape, do not flow. Because this class of materials does not shrink significantly during molding, large cross sections can be molded without causing warping or sinking problems, as occurs in thermoplastic molding. In the thermoset cast molding process, liquid material is poured into an open mold.
Thermoset injection molding is similar to thermoplastic injection molding except for how uncured thermoset resins are mixed, injected, and held in the mold until cured. After the material solidifies, the mold is unclamped and a finished part is ejected. Injection molding offers the lowest piece prices available; however, tooling prices are typically the highest.
In thermoforming, sheets of pre-extruded rigid plastic are heated horizontally and sucked down into hollow one-piece tools. After the hot plastic solidifies again, its shape conforms to that of the mold. Trimming is usually necessary to put the part in final form.
Vacuum forming is done at atmospheric pressure (14.2 psi). A variation of this process, pressure forming, incorporates the use of a pressure box built around the tool which increases the pressures far beyond atmospheric. Greater surface definition in parts can therefore be achieved.
Tooling costs are generally low and piece prices can vary depending on machinery.
Vacuum assisted resin transfer molding (VARTM) is an infusion process where a vacuum draws a resin into a one-sided mold. A cover, or bag, is placed over the top of the resin to form a vacuum-tight seal. Then the vacuum is applied, drawing the resin into the mold. This method is also referred to as vacuum infusion process (VIP) molding.
Vacuum bag molding or bag molding is a process in which a sheet of flexible transparent material (bag), bleeder cloth, and release film are placed over the lay up on a mold and sealed on the edges. The vacuum is applied between the sheet and the lay up, removing the trapped air. The part is then cured with temperature and time.
Vacuum forming begins with a thermoplastic sheet that is heated to form a drape and is then drawn over or into the mold, assisted by vacuum holes in the mold, to impart the desired shape of the part. Vacuum assisted resin transfer molding (VARTM) is an infusion process where a vacuum draws a resin into a one-sided mold. A cover, or bag, is placed over the top of the resin to form a vacuum-tight seal, and then the vacuum is applied, drawing the resin into the mold.
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Micro molding uses special miniature molding machines to produce very small parts that typically weigh less than two grams. Micro molding serves a variety of industries and is used in medical, automotive, and consumer electronics applications.
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Suppliers can mold-in or mold-on graphics such as company logos, warning labels, and instructions. Mold-in graphics incorporate a decal into a molded part. The decal is applied to the mold surface and becomes integral to the molded component. Mold-on graphics can be applied after the part is molded.
Two-shot injection molding produces a part with two different raw materials or colors in a single operation. Molding machines have two injection units: one vertical and one horizontal. By using a rotating mold, the machine automatically produces a substrate of one resin or color and overmolds the part with the second resin or color.
Suppliers provide secondary operations and assembly services such as electro-mechanical assemblies, ultrasonic and heat welding, printing, painting, bonding, and machining.
Suppliers provide packaging and shipping capabilities including bulk shipments for further processing or final packaging and shipping of products or devices directly to the individual end customer.
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Some of the considerations for raw material selection include impact strength, high and low temperature characteristics, warpage, resistance to ultraviolet light and the friendliness of the material to printing or adhesives.
Aside from the below breakdown, plastic resins are also broadly classified as either thermoplastic or thermoset. Thermoplastic resins can be remelted after processing. Flash and rejected parts can be reground and added to virgin resin for reprocessing. Thermoset plastics, typically used in compression molding and SMC molding, cannot be remelted. Once processed, if they are reheated, they simply burn up and disintegrate. Thus, rejected parts and flash cannot be reused.
Commodity grade resins are used more widely than other graded resins. This category includes polyethylene, polypropylene, polystyrene and polyvinyl chloride (PVC).
Engineering grade resins are more difficult to process than other graded resins, but have characteristics that make them desirable for specialized use. Commonly used engineering grade thermoplastics include acetal, acrylonitrile butadiene styrene (ABS), nylon, noryl, and polycarbonate.
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AS 9100 is an expanded, international version of AS 9000, a standard which defines quality system requirements for suppliers to the aerospace industry. AS 9100 was developed by major aerospace manufactures in conjunction with the ISO Aerospace Technical Committee (TC) 20, and published by the Society of Automotive Engineers (SAE).
ISO 9001:2000 establishes requirements for company quality management systems. Standards range from manufacturing to services such as design, development, production, and installation.
ISO 13485:2003 specifies quality management system (QMS) requirements for organizations that need to demonstrate their ability to provide medical devices and related services that consistently meet applicable customer and regulatory requirements. ISO 13485:2003 contains specific requirements for medical devices and excludes non-applicable requirements from ISO 9001. Consequently, an organization with a QMS that conforms to ISO 13485:2003 cannot claim to conformity to ISO 9001 unless the QMS meets all of ISO 9001’s requirements.
ISO 14001 specifies the actual requirements for an environmental management system. It applies to those environmental aspects, over which the organization has control or influence. ISO 14001 was first published in 1996 and is the only ISO 14000 standard against which it is currently possible to be certified by an external certification authority.
ISO/TS 16949:2002 is an ISO Technical Specification that aligns existing American (QS-9000), German (VDA6.1), French (EAQF) and Italian (AVSQ) automotive quality systems standards for the global automotive industry.
QS 9000 is a quality standard for suppliers of DaimlerChrysler Corporation, Ford Motor Company, and General Motors Corporation. QS-9000 is based on the 1994 edition of ISO 9001, but contains additional requirements that are particular to the automotive industry. Specifically, QS 9000 applies to suppliers of production materials, production and service parts, heat treating, painting and plating, and other finishing services.
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Companies are located in the Northeast United States, namely Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island and Vermont.
Companies are located in the Southern United States, namely Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, Washington D.C., and West Virginia.
Companies are located in the Midwest United States, namely Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Nebraska, North Dakota, Ohio, South Dakota and Wisconsin.
Companies have facilities in South American countries such as Argentina, Brazil, or Chile; or in Central American countries such as Costa Rica, Honduras, Panama, etc.
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