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 system
• Mold system is where the mold is loaded and assembled
• Clamping system gives the packing force for the mold
• Control 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 material
• The melted plastic is ejected into the cavity
• As the screw moves forward continuously, the cavity is packed
• The cavity cools as the gate freezes off
• The screw retracts to get ready for injecting in the next cycle
• The mold then opens and the plasticized parts are ejected by the ejection system
• The mold closes
• The next injection cycle begins 

Commonly used plastic injection molding materials

Polyethylene – The commonly used material for making many products such as grocery bags and water bottles.

Polyethylene Terephthalate or PET - Also used for plastic water bottles, plastic bags and also as polyester fiber in the apparel industry.

Polyvinyl Chloride or PVC - This material has many industrial applications being a cost-effective and durable material.

Polyamide – Known commonly as nylon, polyamide is a flexible and highly durable material with wide ranging applications in climbing equipment such as ropes and cords, clothing and mechanical equipment.

Polypropylene – This type of plastic is typically used to make food containers.

Polystyrene – Polystyrene is commonly used to package other finished products and is also called Styrofoam.

Polyurethane - This flexible plastic is also available as a liquid and is used in adhesives, sealants, and varnishes.

Polycarbonate and acrylic – These highly durable, scratch resistant and transparent plastics find industrial usage and in the construction industry.

How to choose the right plastic injection molding manufacturer?

The major reason for businesses to look for plastic injection molding manufacturers in China is price which can make a huge difference in the bottomline. However, apart from price, there are many factors to look at when choosing a plastic injection molding manufacturer in China such as:

• Is the manufacturer reliable and authentic? - The typical marketplace that most Amazon sellers and companies begin their search is Alibaba. Although the primary marketplace provides comprehensive listing of manufacturers, not every business listed is genuine. Many resellers or trading companies may also pose as manufacturers on the site. Choosing the wrong manufacturer based on the low cost or quote that they offer alone can be disastrous for your business. Some companies that ordered injection molds from a manufacturer in China found that the mold was not a high quality product while the certification the manufacturer provided turned out to be fake. Poor quality molds can wear down in quick time and replacing them can mean higher costs in the long run. Selecting a reliable manufacturer will also involve checking the legitimacy of their licenses, business registration and quality certifications such as ISO as well as samples.
• References - whether they can provide references. A genuine company will be willing to provide references of their past and current customers while a fake company will hesitate or give vague responses.
• Quality Systems - Verify if the manufacturer has stringent quality systems in place for manufacturing.
• Experience - It is important to check how long the company has been manufacturing plastic injection molds and if they have in-depth knowledge of the field and the process. Asking a few technical questions to the supplier will help establish their knowledge and experience.
• Communication - In China, many plastic injection mold manufacturers may have technical sales personnel who have transactional English knowledge. However, when it comes to plastic injection molding, technical knowledge and communication is of utmost importance. They need to understand your product requirements, measurements or dimensions, material requirements and know CAD drawing as well as the mold making process to be able to fully understand your specifications. The manufacturer also needs to be able to explain the molding process, show the 3D drawing and analyze size, material, structure and so on.
• Capability and capacity- Evaluate if the factory’s capacity and capabilities match with your production requirements. Ask if the manufacturer does the entire production in-house or sub-contracts it to multiple other vendors. Check the manufacturing plant’s size and whether it is equipped with state-of-the-art mold processing and injection molding workshops, measuring instrument testing and product assembly services. Also look into whether the factory has other equipment such as CNC machining, milling/grinding, engraving machines, wire cutting and so on that may be required for specific products.

Many manufacturers in China use CAE technology (Computer-aided engineering) which is one of the most effective ways to create mold design, manufacture plastic products and ensure product processing. Compared to traditional mold design, the use of CAE technology has greater advantages in terms of ensuring product quality, improving productivity, cost reduction and reduction in labor intensity.

Evaluating if the manufacturer in China adopts CAE technology to make products is one of the crucial aspects of choosing the right plastic injection molding manufacturer. Traditional ease of injection moulding involves testing several products, finding the problems and then rectifying the process and may also involve modifying mold design and plastic products. All of this boosts production costs, extends the product development cycle and can result in poor quality products.

CAE technology is used before processing in the mold and can accurately predict the injection molding process including packing, melt filling, cooling, stress distribution, deformation or warping, fiber orientation distribution and product shrinkage. With this information on hand, designers can identify problems and rectify the mold design instead of waiting until the mold is made. This avoids mold rework and reduces costs and has considerable economic and technical significance.

Benefits of setting up plastic injection molding in China

Plastic injection molding in China is a flourishing and efficient manufacturing sector. While more than 15,000 plastic manufacturing companies existed in 2016 in China, the total sales had reached US $366 billion. In 2018, plastic parts and products totalling 13.95 million tons were manufactured in the country. The steady growth in the industry is due to rising demand in recent years from downstream industries including computer manufacturing, automobile and household product manufacturing. The industry revenue in 2019 was estimated to be $43.8 billion.

China die-cast and high-end mold products are exported across the world to 190 countries while the exports of more than 700 manufacturers exceed US $1million annually.

This is indicative of the fact that China plastic injection molding manufacturers are competitive in terms of price and can meet the quality standards of European and American markets.

Apart from CAE technology, many manufacturers have adopted advanced technologies such as robotization and automation in the plastics industry.

Injection molding companies are increasingly investing in automated technologies to achieve precise plastic products development, boost product consistency and achieve overall production and quality efficiency.  With automated features, the production line is optimized and enables production of high volume of customized engineering plastics over fewer cycles.

The robotic technology adoption was expected to rise by 75 percent in 2019 while close to 150 robots per 10,000 humans is the expected ratio in 2020.

Here are some of the benefits of setting up plastic injection molding in China:

• Low scrap rates – Many manufacturers use efficient plastic injection molding production where the amount of plastic used is optimized to ensure there is minimal wastage of plastic and residual scrap.
• Cost-effective – The greatest advantage with China is that you can produce a large number of plastic products with less investment. While labor costs less in China, sophisticated technology ensures precision products, less errors in finished products and quicker timelines.
• Repeatable process – As molds are reusable, the same products can be produced repeatedly, saving costs while not compromising quality.

Working with a China sourcing agent who specializes in plastic injection molding in China can optimize these benefits. The sourcing agent will have an office in China and not only can they communicate in Mandarin but they will visit the factory in person to perform an audit and check samples. They can also negotiate the best deals for you once they identify a reliable plastic injection molding manufacturer in China. With communication becoming seamless, you will be able to ensure the supplier in China understands your product requirements fully and is able to execute them without errors. The agent also coordinates with freight forwarders, which makes your process of sourcing plastic injection molding parts from China a hassle free one.

Plastic injection molding methods in China have considerably improved since their inception in the manufacturing world. With the ability of manufacturers in China to make high quality products using the latest technology all while costing less, you will be able to streamline your budget and ensure that you get the best quality of plastic products.

Sourcing Allies is a team of expert China sourcing agents that has helped western customers manufacture and source products from low-cost regions since 2006.

For more on China sourcing visit our website or write to us at info@sourcingallies.com.