Molding

Molding

Process ofmanufacturingby shaping pliable raw material using a rigid frame or model called apattern.Amoldormouldis a hollowed-out block that is filled with a liquid likeplastic,glass,metal, orceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape. 3A mold is the counterpart to acast. The manufacturer who makes the molds is called themoldmaker. Arelease agentis typically used to make removal of the hardened/set substance from the mold easier. Typical uses for molded plastics include moldedfurniture, moldedhousehold goods, moldedcases, and structural materials.

Types of molding include:

Blow molding(BrEmoulding) is a manufacturing process by which hollowplasticparts 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 begins with melting down the plastic and forming it into a parison or preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass.

Typologies of blow moldingExtrusion blow molding

Inextrusion blow molding(EBM), plastic is melted and extruded into a hollow tube (a parison). This parison is then captured by closing it into a cooled metal mold. Air is then blown into the parison, inflating it into the shape of the hollowbottle, container, or part. After the plastic has cooled sufficiently, the mold is opened and the part is ejected.Continuous and Intermittent are two variations of Extrusion Blow Molding. In Continuous Extrusion Blow Molding the parison is extruded continuously and the individual parts are cut off by a suitable knife. In Intermittent blow molding there are two processes: straight intermittent is similar to injection molding whereby the screw turns, then stops and pushes the melt out. With the accumulator method, an accumulator gathers melted plastic and when the previous mold has cooled and enough plastic has accumulated, a rod pushes the melted plastic and forms the parison. In this case the screw may turn continuously or intermittently

Injection blow molding

The process ofinjection blow molding(IBM) is used for the production of hollowglassandplasticobjects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve bottles. The process is divided into three steps: injection, blowing and ejection.

Stretch blow molding processIn the stretch blow molding (SBM) process, the plastic is first molded into a "preform using the injection molding process. These preforms are produced with the necks of the bottles, including threads (the "finish") on one end. These preforms are packaged, and fed later (after cooling) into a reheat stretch blow molding machine. In the SBM process, the preforms are heated (typically using infrared heaters) above their glass transition temperature, then blown using high pressure air into bottles using metal blow molds. The prefrm is always stretched with a core rod as part of the process. In the single-stage process both priform manufacture and bottle blowing are performed in the same machine. The stretching of some polymers, such as PET results in strain hardening of the resin, allowing the bottles to resist deforming under the pressures formed by carbonated beverages, which typically approach 60 psi. The main applications are bottles, jars and other containers.

12Compression moldingis a method ofmoldingin which the molding material, generally preheated, is first placed in an open, heatedmoldcavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, whileheatandpressureare maintained until the molding material has cured. The process employs thermosettingresinsin a partially cured stage, either in the form of granules,putty-like masses, or preforms. Compression molding is a high-volume, high-pressure method suitable for molding complex, high-strengthfiberglassreinforcements. Advanced compositethermoplasticscan also be compression molded with unidirectional tapes, woven fabrics, randomly oriented fiber mat or chopped strand. Injection moldingis amanufacturingprocess for producing parts by injecting material into a mold. Injection molding can be performed with a host of materials, including metals,glasses,elastomers, confections, and most commonlythermoplasticandthermosettingpolymers. Material for the part is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity.After a product is designed, usually by anindustrial designeror anengineer, molds are made by amoldmaker(or toolmaker) from metal, usually eithersteeloraluminum, andprecision-machinedto form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest components to entirebody panelsofcars.

Matrix molding

is a technique often used duringmolding. The person doing the assembly will first create the rigid outer shell, then introduce the softer and more fluid molding material between the shell and theprototype. This process is often used for complex shapes usingcompositessuch as withglassandglass/ceramiccomposites.Rotational Molding involves a heated hollow mold which is filled with a charge or shot weight of material. It is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to 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. The process was applied to plastics in the 1940s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.

Transfer molding

likecompression molding, is a process where the amount of molding material (usually athermosetplastic) is measured and inserted before the molding takes place. The molding material is preheated and loaded into a chamber known as thepot. Aplungeris then used to force the material from the pot through channels known as asprueand runner system into the mold cavities. The mold remains closed as the material is inserted and is opened to release the part from the sprue and runner. The mold walls are heated to a temperature above themelting pointof the mold material; this allows a faster flow of material through the cavities.Plunger moldingis a variation on transfer molding, where an auxiliary ram exerts pressure on the material being molded. This approach often performs better in fully automatic operation.

Rotational Molding) involves a heated hollow mold which is filled with a charge or shot weight of material. It is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to 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. The process was applied to plastics in the 1940s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.

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