Therefore the runner is usually designed so as to have the same length from the sprue to each cavity. Use of reprocessed materials. Sprues and runners among moldings are not products. These portions are sometimes discarded, but in other cases they are finely reground and reused as materials for molding. These materials are called reprocessed materials. Reprocessed materials are not solely used as materials for molding but usually used after blending with virgin pellets, since there is possibility of deterioration in various characteristics of the plastics because of the initial molding process.
For the properties when reprocessed materials are used, please refer to "reprocessing capability" in the plastic data base. Molding condition means cylinder temperature, injection speed, mold temperature etc. Depending on the conditions selected, the appearances, dimensions, and mechanical properties of the molded products change considerably.
Therefore, well-tried technology and experience are required to select the most suitable molding conditions. The standard molding conditions for our materials are shown below. Please click the mouse at the following names of plastics. The injection molding process requires the use of an injection molding machine, raw plastic material, and a mold.
The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part. The steps in this process are described in greater detail in the next section. Injection molding is used to produce thin-walled plastic parts for a wide variety of applications, one of the most common being plastic housings.
Plastic housing is a thin-walled enclosure, often requiring many ribs and bosses on the interior. These housings are used in a variety of products including household appliances, consumer electronics, power tools, and as automotive dashboards. Other common thin-walled products include different types of open containers, such as buckets.
Injection molding is also used to produce several everyday items such as toothbrushes or small plastic toys. Many medical devices, including valves and syringes, are manufactured using injection molding as well.
The process cycle for injection molding is very short, typically between 2 seconds and 2 minutes, and consists of the following four stages:. After the injection molding cycle, some post processing is typically required. During cooling, the material in the channels of the mold will solidify attached to the part. This excess material, along with any flash that has occurred, must be trimmed from the part, typically by using cutters. For some types of material, such as thermoplastics, the scrap material that results from this trimming can be recycled by being placed into a plastic grinder, also called regrind machines or granulators, which regrinds the scrap material into pellets.
Due to some degradation of the material properties, the regrind must be mixed with raw material in the proper regrind ratio to be reused in the injection molding process. Injection molded part. Injection molding machines have many components and are available in different configurations, including a horizontal configuration and a vertical configuration. However, regardless of their design, all injection molding machines utilize a power source, injection unit, mold assembly, and clamping unit to perform the four stages of the process cycle.
The injection unit is responsible for both heating and injecting the material into the mold. The first part of this unit is the hopper, a large container into which the raw plastic is poured. The hopper has an open bottom, which allows the material to feed into the barrel. The barrel contains the mechanism for heating and injecting the material into the mold. This mechanism is usually a ram injector or a reciprocating screw. A ram injector forces the material forward through a heated section with a ram or plunger that is usually hydraulically powered.
Today, the more common technique is the use of a reciprocating screw. A reciprocating screw moves the material forward by both rotating and sliding axially, being powered by either a hydraulic or electric motor. The material enters the grooves of the screw from the hopper and is advanced towards the mold as the screw rotates.
While it is advanced, the material is melted by pressure, friction, and additional heaters that surround the reciprocating screw. The molten plastic is then injected very quickly into the mold through the nozzle at the end of the barrel by the buildup of pressure and the forward action of the screw. This increasing pressure allows the material to be packed and forcibly held in the mold. Once the material has solidified inside the mold, the screw can retract and fill with more material for the next shot.
Injection molding machine - Injection unit. Prior to the injection of the molten plastic into the mold, the two halves of the mold must first be securely closed by the clamping unit. When the mold is attached to the injection molding machine, each half is fixed to a large plate, called a platen. The front half of the mold, called the mold cavity, is mounted to a stationary platen and aligns with the nozzle of the injection unit. The rear half of the mold, called the mold core, is mounted to a movable platen, which slides along the tie bars.
The hydraulically powered clamping motor actuates clamping bars that push the moveable platen towards the stationary platen and exert sufficient force to keep the mold securely closed while the material is injected and subsequently cools.
After the required cooling time, the mold is then opened by the clamping motor. An ejection system, which is attached to the rear half of the mold, is actuated by the ejector bar and pushes the solidified part out of the open cavity. Injection molding machine - Clamping unit. Injection molding machines are typically characterized by the tonnage of the clamp force they provide.
The required clamp force is determined by the projected area of the parts in the mold and the pressure with which the material is injected. Therefore, a larger part will require a larger clamping force. Also, certain materials that require high injection pressures may require higher tonnage machines. The size of the part must also comply with other machine specifications, such as shot capacity, clamp stroke , minimum mold thickness, and platen size.
Injection molded parts can vary greatly in size and therefore require these measures to cover a very large range. As a result, injection molding machines are designed to each accommodate a small range of this larger spectrum of values.
Sample specifications are shown below for three different models Babyplast, Powerline, and Maxima of injection molding machine that are manufactured by Cincinnati Milacron.
Injection molding machine. The injection molding process uses molds, typically made of steel or aluminum, as the custom tooling. The mold has many components, but can be split into two halves. Each half is attached inside the injection molding machine and the rear half is allowed to slide so that the mold can be opened and closed along the mold's parting line. The packaging industry uses plastics to pack foods such as salads, meats, chips etc. In addition to that, cosmetic items like shampoo, facial creams, and make-up boxes also come enclosed in plastics.
In the automotive components, plastic injection moulding products such as bumpers, dashboards, wipers, etc are used. CDs and DVDs are normally made from plastic parts. The outer and inner surfaces of the vending machine, battery casing and electrical switches are produced in high volume using moulded plastics. The plastic injection moulding process is fast and can produce identical objects in large amounts with high precision.
Manufacturing plastic products are easy to use, lightweight and are making everyday life easier. Let us see some commonly used plastics products made by injection moulding. Plastic injection moulding process, as opposed to injection moulding using other materials such as metal or glass, has many advantages, not least the versatility of the plastic itself, which can come in almost any colour, and be moulded into any shape or size.
Plastic is durable, hygienic and easy to get hold of. Many types of plastic can also be recyclable, such as thermoplastics, making them a great option for many sustainable projects too. Alternatively, a pre-moulded form can be put inside a larger mould to have molten plastic poured in around it to form the next stage in a more complex production cycle. This process is known as insert moulding and is useful for producing plastic parts that have protruding metal bars or screws attached, for example, or for attaching plastic films to plastic food containers.
Choosing whether or not to use plastic injection moulding in a manufacturing process is a decision that must be based on the individual project requirements.
There are both advantages and disadvantages to the process. Plastic as a product has many advantages. It is durable, flexible and very easy to shape into the exact form that is required. Many thermoplastics can be recycled, and plastic products can usually be strong enough to be reused many times over, even if they cannot be fully recycled.
Getting the design right includes:. Before you endeavor to produce a part via injection molding consider a few of the following things:. Typical parts you might want to injection mold include joints, brackets, or housings. One of the most obvious advantages to injection molding is that the housing serves multiple purposes.
First, it serves as a handle for the end user to interact with. It also acts as a receptacle for the battery and motor as well the location of various screw bosses that will be used to fasten the device together once the internal parts are assembled. In other words, injection molding is extremely effective when you need to organize a lot of internal parts within a housing. Of note, this part is also an overmolded part. For more on this process read here.
Some of the other reasons that injection molding is a good fit for this example include the fact that t he drill is being produced in large volume. That is, Panasonic is creating a large number of copies of the same drill handle.
Injection molding is wonderful for this kind of high volume production because the high initial costs pay the manufacturer back over time with low per unit costs. For this same reason injection molding can be a poor choice for low volume production. Additionally of note, there are some design constraints if using injection molding. For example, the part has nearly uniform wall thickness which is important in order to avoid defects , and the part is made with a thermoplastic material allowing for solid plastic stock to be repeatedly melted for the procedure.
If you were designing a part with a thermoset material then injection molding would be more nuanced. You can injection mold a thermoset material but you can only do it once. Trying to melt a thermoset plastic a second time will result in burning the material. Similarly, a part with varied wall thickness would require more attention in the mold tool design to ensure uniform cooling and to avoid defects during production.
Injection molding is a great technology for finished production on a massive scale. Prior to this late stage in production, however, 3D printing is much more affordable and flexible for products in the early stages of design. Our expertise and unique collaborative process alleviates your stress and helps take your Design, Engineering and Prototyping process to the next level. Home About Contact Blog. Email: info creativemechanisms. Call Now: What is Injection Molding: Injection Molding is a manufacturing process for producing parts in large volume.
Why Use Injection Molding: The principal advantage of injection molding is the ability to scale production en masse.
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