Injection molding refers to the process of producing plastic injection products – based on thermoplastic and thermostats – materials after being inserted into the hot cylinder, mixing and then spiraling into the mold quench, where the molded piece becomes cold and hard. , Driven.

After a piece is designed by an engineer or industrial designer, the mold is tailored to the piece by the molder.

Injection molds are generally made of steel or aluminum and precision machined to reflect the design features of the component.

Injection molding is used to produce a wide range of products from the smallest objects to the full body of cars.

How did the world of injection molding come about?

In 1868, John Wesley Hyatt, a manufacturer of billiard balls Phelan and Colander, devised a method for making billiard balls from celluloid injection into a mold. By upgrading celluloid, he prepared it for final processing. In 1872, John and his brother unveiled the first injection molding machine that was simpler and less expensive than modern machinery. The device, through a piston, injected the material from inside the hot cylinder into the mold.

As the industry progressed slowly over the years, other products such as shirt collar, buttons and pocket shoulders were developed. In the 1940s, the concept of injection molds grew dramatically due to the widespread demand for cheap and durable products during World War II.

In 1946, James Hendry invented the first spiral injection machine and transformed the plastics industry. In his machine, the piston was replaced by a well-designed drill. The drill guided the material into the cylinder before injection, mixing and then molding. Thus, prior to the injection operation, the possibility of mixing and mixing colored or recycled plastic with raw materials was fully possible.

Today, spiral injection machines make up 95% of the production share of the companies concerned. The injection molding industry has evolved gradually, from the production of combs and buttons to the production of medical, aerospace, toy, packaging, automotive and construction products, over the years.

Injection molding applications

Currently, plastic injection molding is the preferred method of producing plastic parts. Injection molds play a key role in the production of a wide range of products such as home electrical appliances, containers, bottle lids, automotive interior components and most of the plastic products available.

The ability to fabricate multi-component parts and, in fact, co-produce multiple products in a single work cycle, has made injection molding an ideal choice for high volume production. High precision, reproducibility, wide range of consumables, low labor cost, low wastage and the need for low requirements to finalize products after molding are all advantages of plastic injection molding.

Its disadvantages include the high cost of the machine and the need for a prototype (where some complex components may have problems such as twisting or rough surface during the injection process). As a result, precision molding tips must be taken into account when designing plastic injection parts.

Examples of the best polymers suitable for injection molding

Most polymers, including all thermoplastics, some thermostats and some elastomers, can be used for injection molding. In fact, there are tens of thousands of different materials for this purpose and they are increasing every year. Materials can also be mixed with alloys or pre-made compounds.

This feature enables designers to combine materials to achieve the exact specifications of the final product. Consumables are selected depending on their strength and application and therefore their intrinsic properties must be evaluated to achieve the objective. Common polymers such as epoxy and phenolics are two examples of thermostats and nylon, polyester and polyethylene are examples of thermoplastics.

Injection machines

Plastic injection machines consist of feeding funnel, spiral injection drill and thermal unit. The molds are locked in the clamp plates of the machine and then the plastic is sprayed from the inside of the spray into the mold and injection mold.

Injection machines are divided into different tonnages depending on the amount of force applied to their clamp plates. This force keeps the mold steady and idle during the injection process. The tonnage of the device can range between 5 and 6,000 tonnes, though very high tonnages are of relatively less use.

The required grip force is determined by the area depicted in the piece. Then, for each square inch of the area depicted, a coefficient of between 2 and 8 tons is multiplied and the required clamping force is obtained.

As a general rule, 4 or 5 tons per square inch is a numerically acceptable number for most injectable components. If the plastic used is too dry, we will need more injection pressure to fill the mold, and therefore higher clamping force will be required to hold the mold. Also, the grip force required may be determined by the type of consumable material and the size of the piece: Larger plastic parts will require more grip force.

 

Plastic injection machine

At present, the presence of all-electric machines is getting tighter on conventional hydraulic injection machines. Related companies prefer these machines to conventional hydraulic models because of the 80% savings in energy consumption and the nearly 100% reproducibility thanks to the servo motor presence.

While the cost of an electric injection machine is about 30 percent higher than a conventional hydraulic machine, the widespread demand for plastic products is addressing this financial hurdle.

There is speculation that hydraulic injection machines will go down in history for the next 20 years, as more and more companies are moving to the new world of electric machines every day, due to the competitive environment.

The production process cycle

The production cycle in the plastic injection process is very short and usually takes about 2 seconds to 2 minutes. This process involves the following steps:

to close

Before the material is injected into the mold, the first two halves of the mold must be locked together by the clamp unit. Both halves of the mold are attached to the machine, but only one of them can be moved. The clamp unit, relying on hydraulic force, compresses the two halves of the mold and keeps them pressurized during the injection process, with sufficient pressure.

The time required to close and compress the two halves of the mold varies depending on the device used: Large machines (those with higher clamping force) will require more time. This time can be estimated with respect to the timing of the device’s idle cycle.

Injection

Raw plastic materials are usually introduced into the machine in the form of pieces of plastic and driven to the mold by the injection unit. During this process, the material is introduced into the injection mold by application of heat and melting pressure. The accumulation of pressure behind the material will result in a higher density of mold inside the mold.

The amount of material needed to fill the mold space is called a shot. Due to the complex and variable flow of materials in the mold, it is generally difficult to calculate and estimate the injection time. However, this time can be evaluated in terms of the amount of shot required, the pressure, and the power of the injection.

cooling

The molten material inside the mold will gradually lose heat as it contacts the inner surface. At the same time, the material will take shape and shape of the piece in question. However, during this time the phenomenon of fragment shrinkage may also be linked.

The accumulation and flow of more material into the mold during the injection phase can reduce the amount of visible shrinkage. The mold remains locked and idle until the end of the cooling period. Also, the cooling time can be estimated taking into account the thermodynamic properties of the plastic as well as the maximum thickness of the piece.

Exit the piece

After sufficient time, the chilled piece can be removed from the mold by means of an embedded system at the back of the mold. When the mold returns, a special mechanism is applied by pushing the piece out. The need for this pressure is that the piece is absorbed into the core of the mold as it cools down.

Spraying auxiliary elements to the interior of the molding quetta is sometimes used to facilitate the removal of the part, sometimes prior to injection. The time required to open the mold as well as the complete ejection of the piece can be estimated from the device’s cycle time. After removing the piece, the mold is locked again and ready for the next shot injection.

Source: Artak Machine