Thin Wall Injection Molding

Thin wall injection molding manufacturing and design guide

What is thin wall injection molding?

Thin-wall injection molding is an injection molding technology for manufacturing thin-walled parts.

Thin-wall injection molding technology is also called thin-wall plastic injection molding technology. There are three definitions of it:

① The thickness of the molded product is less than 1 mm, and the projected area of the plastic part is more than 50 cm².

② The wall thickness of the molded product is less than 1 mm (or 1.5 mm), or the t/d (plastic part thickness t, plastic part diameter d, for disc-shaped plastic parts) is less than 0.05. Injection molding is defined as thin-wall injection molding.

③ The flow length L from the main channel of the mold to the farthest point of the finished product, divided by the wall thickness t of the product, is called the flow length/wall thickness ratio. When L/t＞150, it is called thin-wall injection molding. If the thickness of the process is inconsistent, it can be calculated in sections.

The viscosity factor of PP is 1, the flow length of a disposable lunch box is 135mm, the wall thickness is 0.45mm, and the flow length/wall thickness ratio is 300＞150; the viscosity factor of PC is 2, the flow length of a mobile phone battery shell is 38mm, the wall thickness is 0.25mm, and the flow length/wall thickness ratio is 152, multiplied by the viscosity factor 2=304＞150, which is equivalent to that of a disposable lunch box. Both belong to thin-wall injection molding.

What is the principle of thin-wall injection molding?

The mold cavity wall is cold, and when the molten metal fills the mold cavity, the mold cavity wall will form a solidified layer, thereby reducing the thickness of the flow channel. This situation is more serious when the wall thickness is thinner.

The principles of thin-wall injection molding mainly include the following aspects:

1. Fast injection speed:

Thin-wall injection molding requires injecting hot molten plastic material into the mold in a very short time, and usually requires the use of a high-pressure injection machine and a high-speed injection cavity to achieve a fast injection speed.

2. Rapid cooling and solidification:

In order to ensure the uniformity of wall thickness and dimensional stability of thin-wall injection molded products, rapid cooling and solidification are required after injection. Usually, cooling systems and rapid mold opening systems are used to achieve rapid cooling and solidification.

3. Suitable injection molding materials:

Thin-wall injection molding requires the selection of plastic materials with good fluidity and fast solidification properties to ensure that the material can achieve the desired effect during rapid injection and rapid cooling.

Injection Flow Process

1mm wall thickness has a 0.2mm thick solidified layer, and the remaining flow channel is 0.6mm thick. 0.5mm wall thickness has a 0.2mm thick solidified layer, and the remaining flow channel is 0.1mm thick. When the filling is not completed, if the flow channel disappears due to the excessive thickness of the solidified layer, the finished product will not be fully filled.

Therefore, thin-wall injection molding requires it to inject hot-melt plastic material into the mold in a short time, so that it can be quickly cooled and solidified, thereby manufacturing thin-walled plastic products.

Thin-wall injection molding selecting raw materials guide

The principles for selecting thin-wall injection molding materials mainly include good fluidity, high impact resistance, high thermal stability, low orientation and excellent dimensional stability.

Currently commonly used thin-wall injection molding materials are: polypropylene (PP), polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), PC/ABS blends and PA6, etc.

High thermal stability:

Thin-walled injection molded parts often need to be used at a certain temperature, so the raw materials need to have good thermal stability and be able to maintain stable physical and chemical properties in high temperature environments to avoid deformation or aging.

Low Directivity:

Thin-walled injection molded parts have lower requirements on the directionality of raw materials to ensure consistent performance of the product in different directions and avoid uneven performance due to directional differences.

Excellent dimensional stability:

The raw materials should have good dimensional stability to ensure that the thin-walled injection molded parts have small dimensional changes during processing and use and meet the precision requirements.

Flowability:

Thin-wall injection molding requires the raw material to have good flowability in order to fill thin walls. Materials with good flowability can ensure that thin-walled plastic parts are fully filled during the injection molding process to avoid voids or incomplete filling. The melt index (MI) of PP plastics is as high as 60 (g/10min), such as Basell’s Moplen RP1086. The reason why many finished products use PS/ABS is that they require the toughness of PC and the flowability of ABS, which is also suitable for thin-wall injection molding.

High impact resistance:

Thin-walled plastic parts usually have higher requirements for impact resistance, so it is necessary to choose materials with high impact resistance to ensure that the product can resist external impact without breaking or being damaged during normal use.As the wall thickness decreases in thin-wall injection molding, plastics with better physical properties are needed to maintain the strength of the product.

Thin-wall injection mold manufacturing guide

In the process of making thin-wall injection molds, the following points should be noted:

Mold Steel Material Selection

In the production process of thin-wall injection molds, it is necessary to select materials with high strength, high rigidity, high wear resistance and corrosion resistance. Commonly used materials include high-quality alloy steel, stainless steel, etc.

Mold Structural Design

The structural design of thin-wall injection molds should be reasonable, just like the template of the injection molding machine. The template of the mold should be thick to reduce deformation. High-speed injection molding requires good exhaust. Sufficient exhaust grooves, breathable mold steel and vacuuming are all methods.

Mould Processing Technology

The processing technology of thin-wall injection molds must be fine to ensure the dimensional accuracy and surface quality of each component. The processing accuracy of the mold must be very high to achieve uniform thickness of the circumference or four walls.

Mould Assembly and Debugging

The assembly and debugging of the mold is one of the key links in the production of thin-wall injection molds, and the requirements for multi-cavity molds are higher. The molds are equipped with ejection and blowing devices to accelerate the fall of the finished product after demoulding and close the mold immediately.

Why use thin-wall injection molding？

The cost of plastics usually accounts for a large proportion of the finished product cost, such as 50-80%. Thin walls can help reduce this proportion. As consumer electronic devices such as mobile phones, digital cameras, and handheld computers become smaller and lighter, the plastic parts are designed to be thinner.

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① Weight reduction: Thin wall injection molding allows for the production of lightweight parts with reduced material usage, making it ideal for applications where weight is a critical factor, such as in the aerospace, automotive, and medical industries.

② Cost savings: By using less material, thin wall injection molding can help reduce production costs, which can be significant for high-volume productions.

③ Increased production speed: Thin wall injection machines can produce parts at a faster rate than traditional molding machines, making it an attractive option for high-volume productions.

④ Improved part consistency: Thin wall injection molding ensures consistent part quality and reduces the risk of shrink, which is critical for applications where part consistency is essential.

What are the applications of thin-wall injection molding？

Thin-wall injection molding technology is widely used in many fields. Here are some common applications of thin-wall injection molding:

① Food packaging
Thin-wall injection molding technology is widely used in the field of food packaging. Thin-wall injection molding can be used to produce food packaging containers with good sealing and preservation properties, such as plastic bowls, plastic boxes, etc. The fast production speed and high efficiency of thin-wall injection molding make large-scale production possible, which can meet the requirements of the food packaging industry for production efficiency and product quality.

② Electronic product housing
Thin-wall injection molding technology is also widely used in the manufacture of electronic product housings. Thin-wall injection molding can be used to produce thin, strong electronic product housings, such as mobile phone housings, TV housings, etc. The high precision and dimensional stability of thin-wall injection molding can meet the requirements of electronic product housings for appearance quality and dimensional accuracy.

③ Auto Parts
Thin-wall injection molding technology has also been widely used in the field of auto parts manufacturing. Lightweight and high-strength auto parts, such as auto interior parts and auto lamps, can be produced through thin-wall injection molding. The rapid cooling and curing and high efficiency of thin-wall injection molding can improve the production efficiency of auto parts and reduce production costs.

④ Medical devices
Thin-wall injection molding technology also has important applications in the field of medical device manufacturing. Thin-wall injection molding can be used to produce medical devices with good biocompatibility and easy cleaning, such as syringes and infusion sets. The high precision and dimensional stability of thin-wall injection molding can meet the requirements of medical devices for appearance quality and dimensional accuracy.

Thin-wall injection molding technology is an important injection molding technology for manufacturing thin-wall parts. It produces thin-wall plastic products with excellent performance through fast injection speed and rapid cooling and solidification. Thin-wall injection molding technology is widely used in food packaging, electronic product housings, automotive parts, medical devices and other fields. With the advancement of science and technology and the improvement of processes, thin-wall injection molding technology will be applied in more fields and contribute to the development of various industries.

Thin Wall Injection Molding

Thin wall injection molding manufacturing and design guide

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What is thin wall injection molding?