5 Ways to Make Things from Plastic
Rotational Molding - is a molding process for creating many kinds of mostly hollow items, typically of plastic. The process heats finely ground plastic resin in molds that are spun on two axes while being baked in large ovens. Centrifugal force pushes the molten plastic against the walls of the mold. In order to maintain even thickness throughout the part, the mold continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase. Diverse products like kayaks, fuel tanks and children's play balls are created. Rotational molding offers tool designers the flexibility to make molds that include inserts, curves and contours as well as logos and slots for plastic or metal inserts to be placed. Tooling costs are lower with rotational molds than injection or blow molds. The results are lower start-up costs and cost-effective production runs even when producing as few as 25 components at one time.
Injection Molding - is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Molten plastic is injected at high pressure into a mold, which is the inverse of the desired shape. The mold is held closed under high pressure and cooled so that the molded product solidifies. Once the plastic has cooled, the mold is opened, usually automatically, and the finished product is removed. The mold is made from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Injection molding is used to create many things such as wire spools, bottle caps, automotive dashboards and most other plastic products available today. Injection molding is the most common method of part manufacturing. It is ideal for producing high volumes of the same object. Some advantages of injection molding are high production rates, repeatable high tolerances, the ability to use a wide range of materials and low labor cost. Some disadvantages of this process are expensive equipment investment, potentially high running costs, and the need to design moldable parts.
Blow Molding - is a manufacturing process by which hollow plastic parts are formed. In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and stretch blow molding. The blow molding process is a well-developed molding technique, used mainly with products that have a uniform wall thickness and where the shape will be important. First, plastic granules are fed into a hopper and then heated to form a molten plastic. The material is blown to the shape of the mold. Once the plastic has cooled and hardened the mold opens up and the part is ejected. Blow molding processes generate, in most cases, bottles, plastic drums, and fuel tanks. There are many types of materials to choose from and the tooling is less expensive than injection molding, but higher than rotational molding. Although blow molding has been automated and can produce mass quantities of products, the process is largely limited to hollow forms. These forms are delicate and contain various thicknesses which must be precise, which often results in wasted material in the process of arriving at containers with proper dimensions and specifications.
Extrusion Molding - is a manufacturing process by extruding melted plastic through a die that provides the correct profile shape. Manufacturing companies employ extrusion molding to make products with a consistent cross-section. Common items found in a home made by this process include PVC pipe, rain gutters and even straws. Extrusion molding has a low cost relative to other molding processes. This stems, in part, from the efficiency of the process. Most extrusion molding uses thermoplastics, which can repeatedly undergo melting and hardening. Leftover materials, normally discarded as waste in other processes, can be reused. The nature of the extrusion molding process places limits on the kinds of products it can manufacture. For example, plastic soda bottles narrow at one end to accommodate a cap, which normal extrusion molding cannot achieve. When the hot plastic exits the extruder, it frequently expands. The expansion of the plastic at this stage of the process is called die swell. Predicting the exact degree of expansion remains problematic as it arises from different factors in the process.
Thermoforming - is a manufacturing process of heating and molding temperature-sensitive material. It uses sheets of a polymer called thermoplastic, which is extruded in varying levels of thickness, depending on its intended purpose. Thermoforming uses several different types of molds and processes in order to achieve the final product. Thin-gauge thermoforming is primarily the manufacture of disposable cups, containers, lids, trays, blisters, clamshells, and other products for the food and general retail industries. Thick-gauge thermoforming includes parts as diverse as vehicle door and dash panels, refrigerator liners, utility vehicle beds, and plastic pallets. Thermoformed products are more precise to design specifications, compared with those produced by molding together multiple parts. Because it uses low pressures, it requires a smaller quantity of less sophisticated tools, which also means that molds can be produced from relatively inexpensive materials. A second benefit is that large parts can be produced.
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