What is plastic injection molding

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. This website uses cookies. What is injection molding Injection molding machine Mold Moldings Use of reprocessed materials Molding condition 1. What is injection molding?

You can change a plastic mold in two different ways. First, you can make the mold cavity larger by cutting away parts of the metal mold. This process adds plastic to the part. Removing plastic from the part can prove more challenging. In some cases, you can weld metal into the cavity, but that sometimes may not be possible, and a new cavity or an entirely new mold might be required. That could mean going back to the design phase.

Plastic injection molding relies on heating and cooling plastic. If a mold shape causes the plastic to cool in an inconsistent manner, your plastic part will be vulnerable to defects. You can limit this risk by making sure the mold walls are uniform in size, so your part solidifies evenly. Keep in mind that the thicker the wall, the longer each cycle will take. If you need to produce large single plastic parts, injection molding has its limitations. While there are injection molding machines large enough to produce boat hulls, the molding scenarios discussed in this article are for smaller parts, three pounds or less.

If you are in need of a larger part, lead times and costs can increase exponentially. You may be able to get around this limitation by using a number of injection molds to create multiple parts of a large product and assembling it as a secondary operation. Recently, we had an entrepreneurial client come to us with an idea for a plastic part. He had jury-rigged an innovative gutter cleaner from parts he bought at a local hardware store.

On his own, he produced about a dozen gutter cleaners. But he needed to scale his production to make the product commercially viable. He came to our team at Rex Plastics to find out whether plastic injection molding was right for his design. After reviewing the hand-made prototype, we recommended that he use injection molding for the following reasons:.

We were able to design a mold for the gutter cleaner, build a prototype, tool the mold, and begin production in just a few months. Today, the client purchases thousands per year, and order quantities for his gutter cleaner are climbing steadily.

Watch out how we helped Big Blok redesign their injection molded lids:. Injection molding manufacturers range in capabilities and services.

Some companies only work with a pre-existing design while others offer support throughout the entire product development process. As a full-service plastic injection molding manufacturer, Rex Plastics offers a complete range of mold making and producing capabilities.

From consultation to product distribution, our clients benefit from our long list of in-house capabilities including:. Rex Plastics is a second-generation, family-owned and operated full-service plastic injection molding contract manufacturer.

We are based right here in the US in Vancouver, Washington and work with large corporations and startups. Moulding costs correlate with the number of cavities in a mould.

Fewer cavities require less tooling work, which lowers the manufacturing costs to create an injection mould. Added details such as these will increase the cost, as they require more tooling. The most cost-effective type of injection moulding is rubber injection moulding, which produces a high yield of durable products. In addition, consistent vulcanisation processes with precise temperature controls can lower costs by reducing waste material.

While the mould tools have a high cost, the actual injection moulding production has a relatively low cost. With over 85, commercial plastic material option available and 45 polymer families, there is a wealth of different plastics that can be used for injection moulding.

Of these, the polymers can be broadly placed into two groups; thermosets and thermoplastics. Polyethylene offers a number of advantages including high ductility levels, good tensile strength, strong impact resistance, resistance to moisture absorption, and recyclability.

This tough, impact-resistant plastic is widely used across industry. With good resistance to acids and bases, ABS also offers low shrinkage rates and high dimensional stability. This strong, impact resistant plastic has low shrinkage and good dimensional stability.

A transparent plastic that is available in different optically clear grades, PC can provide a high cosmetic finish and good heat resistance. There are many different types of PPA or nylons , each of which has its own advantages. Generally-speaking, nylons offer high strength and temperature resistance as well as being chemically resistant, apart from against strong acids and bases.

Some nylons are abrasion resistant and offer good hardness and stiffness with good impact strength. Commonly known as acetal, this plastic has high hardness, stiffness, strength and toughness. It also has good lubricity and is resistant to hydrocarbons and organic solvents. Good elasticity and slipperiness also provide advantages for some applications. PMMA, also known as acrylic, provides good optical properties, high gloss and scratch resistance. It also offers low shrinkage and less sink for geometries with thin and think sections.

This inexpensive resin material delivers high impact resistance in certain grades but can be brittle in cold temperatures in the case of propylene homopolymer. Copolymers offer greater resistance to impact while PP is also wear-resistant, flexible and can provide very high elongation, as well as being resistant to acids and bases. Good electrical properties makes PBT ideal for power components as well as automotive applications.

The strength ranges from moderate to high depending on glass fill, with unfilled grades being tough and flexible. A dimensionally stable material with high toughness, temperature and heat resistance, PPSU is also resistant to radiation sterilisation, alkalis and weak acids.

This high temperature, high-performance resin provides heat resistance and flame retardancy, excellent strength and dimensional stability, as well as good chemical resistance. Typically, quality control departments will limit the amount of regrind that is allowed to be placed back into the press. Some performance properties of the plastic can degrade as it is molded over and over. Or, if they have a lot of it, a factory can sell this re-grind to some other factory who can use it.

Typically regrind material is used for low-quality parts that don't need high performance properties. Up front costs tend to be very high due to design, testing, and tooling requirements. If you are going to produce parts in high volumes you want to make sure you get the design right the first time. That is more complicated than you might think. 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.