Setting up Plastic Injection Molding in China

Plastic items such as toys, utensils, medical devices, water bottles, food containers and other devices have become indispensable in our daily lives. Most other components and products used in various industrial, automotive and construction sectors also involve many plastic parts.

While plastic has continued to be a popular material that finds numerous applications, the process of manufacturing plastic has improved over time. Most plastic components are made using plastic injection molding and China is a preferred destination for setting up plastic injection molding due to the cost advantages it offers.

The process involves heating the raw plastic material, injecting it into the mold, cooling the plastic and creating the desired end product. The creation of mold prototypes is as much a science as it is an art. Comprehensive technical expertise and utmost attention to detail are required to design, manufacture and finish custom plastic parts. Minor errors can lead to repetition of manufacturing procedures from scratch, that extend lead times and boost up cost of manufacturing.

To set up plastic injection molding in China, it is important to have a fundamental knowledge of the plastic injection molding process and know how to select the right manufacturer in China.

Plastic injection molding process

The first step in manufacturing plastic injection molding in China is to create the design of the mold. This task is taken up by design engineers who use their specialized design and computer skills to craft mold designs. Based on the product requirement, they also add elements of texturing such as logos, patterns, gloss finishes, matte finishes, layered textures, graphics and gripping surface.

The next step is to transfer the design to a plastic injection molding machine which then carves out the precise product using the design. These molds when made out of high strength steel can withstand the stress of mass production.

Creating a digital model helps the manufacturers in determining the precise shape and scale of the mold. The design has to achieve maximum precision as even minor errors in this stage can impact the entire production and can lead to product recalls. After finalizing the mold design, the next stage is to select the material that needs to be molded in the plastic injection molding machine.

The plastic injection molding machine has these basic components: 

The injection system that feeds raw material (plastic) into the cylinder, heats and melts the plastic and pushes the melted plastic into the cavity through the vertical passage (spure)The hydraulic system provides the force for injection systemMold system is where the mold is loaded and assembledClamping system gives the packing force for the moldControl system enables controlling of heating and cooling system.

The process of plastic injection molding starts with gravity feeding of raw materials into the injection system of the molding machine. The raw material melts due to the applied heat and pressure and the material is then injected into the mold under high pressure. Once the material enters the cavity, pressure is maintained until the raw material cools and solidifies. When the temperature of the plastic part is lower than the distortion temperature of the material, the mold opens out and the plastic product is ejected.

The entire production process is known as the molding cycle while the time lag between injection of the melted raw material into the cavity and the opening up of the mold is referred to as the clamp close time.

The time taken for the injection cycle is the sum of clamp close time and time needed to open the mold, eject the part and close the mold.  

The cycle of plastic injection molding has these steps:

The mold closes while the screw of the injection system begins moving forward to inject the material while heating the materialThe melted plastic is ejected into the cavityAs the screw moves forward continuously, the cavity is packedThe cavity cools as the gate freezes offThe screw retracts to get ready for injecting in the next cycleThe mold then opens and the plasticized parts are ejected by the ejection systemThe mold closesThe next injection cycle begins