What is the relationship between plastic injection mold and shrinkage rate?

The relationship between plastic injection mold and shrinkage rate is complex and influenced by several factors, including:

1.Material type: Different plastics have different shrinkage rates, which can range from 0.5% to 2% which have a significant impact on the dimensional accuracy and quality of the final parts. Here are a few examples of plastic materials with their typical shrinkage rates:

2.Polyethylene (PE): PE has a low shrinkage rate of 0.5% to 1%. This makes it well-suited for applications where dimensional stability is important, such as packaging and consumer goods.

Polypropylene (PP): PP has a moderate shrinkage rate of 0.8% to 1.5%. This material is widely used for a variety of applications, including household goods, packaging, and automotive parts.

Acrylonitrile-Butadiene-Styrene (ABS): ABS has a moderate shrinkage rate of 1% to 1.5%. This material is commonly used in applications where impact resistance, toughness, and dimensional stability are required, such as toys, electronics, and automotive parts.

Nylon (PA): Nylon has a relatively high shrinkage rate of 1.5% to 2%. This material is often used in high-stress applications, such as gears and bearings, and in applications where dimensional stability is not a critical factor.

2, Wall thickness:
Wall thickness is one of the key factors that can affect shrinkage in plastic injection molding. Here’s how:

Thicker walls tend to have higher shrinkage rates, as more material is needed to fill the mold, resulting in a higher degree of contraction. The thicker the wall section, the more time it takes for heat to dissipate, which can result in a slower cooling rate and higher shrinkage.

Uneven wall thickness can result in uneven shrinkage, as different parts of the part will cool and solidify at different rates. This can result in warping, distortion, and other dimensional inaccuracies in the final part.

To minimize shrinkage and achieve consistent, high-quality parts, it is often necessary to optimize the wall thickness distribution and to use process control techniques such as temperature control, slow injection speeds, and balanced filling of the mold cavities. Additionally, simulation tools, such as finite element analysis (FEA), can be used to predict shrinkage and to optimize the mold design to minimize its impact on part quality.

3, Part geometry:
The geometry of a plastic part can have a significant impact on shrinkage because it affects the way that the plastic flows, cools, and solidifies within its mold.

Complex geometries: Parts with complex geometries, such as undercuts, deep pockets, and curves, can result in areas where the plastic is trapped and cannot shrink evenly. This can result in higher shrinkage rates in these areas and can cause warping, distortion, and other dimensional inaccuracies in the final part.

Material flow: The way that the plastic flows into and fills the mold can also be affected by the part geometry. If the plastic does not flow evenly into all areas of the mold, it can result in higher shrinkage rates in certain areas.
Cooling rate: The cooling rate of the plastic is also affected by the part geometry. In areas with complex geometries, the plastic may take longer to cool and solidify, which can result in higher shrinkage rates.

4,Mold temperature:

The temperature of the mold affects the rate at which the plastic cools and solidifies. Higher mold temperatures can result in slower cooling rates, which can increase shrinkage. Conversely, lower mold temperatures can result in faster cooling rates, which can decrease shrinkage but may also result in increased warping and other dimensional inaccuracies in the final part.

Xiamen Ruicheng has a rich experienced engineer team on the injection mould techniques that involves using process control techniques, such as temperature control systems and mold temperature sensors, as well as optimizing the mold design and processing conditions to ensure uniform cooling and consistent part quality.

Xiamen Ruicheng note: the careful prototyping and testing can help to identify potential issues and to optimize the mold design for consistent, high-quality parts.