Why are injection molded parts prone to cracking?

Why are injection molded parts prone to cracking?

Injection molding, also known as injection forming, is a manufacturing process that involves heating plastic to a molten state, then forcing it into a mold under high pressure, where it cools and solidifies to form the desired plastic products. This process is widely used in the production of various sized and shaped plastic items, such as daily necessities, industrial components, automotive parts, and more.

The main steps of the injection molding process are:

Additives: Place solid plastic particles or powders into the hopper of the injection molding machine. Through heating and stirring, they are melted and transformed into a flowing state of molten plastic.

Ejection: The molten plastic is pushed by the screw of the injection machine and is injected into the cavity of the mold under high pressure, filling the entire mold chamber.

Cooling: The molten plastic injected into the mold cools and solidifies within the mold, forming the desired product shape.

Demolding: After the plastic has cooled and solidified, open the mold and remove the molded plastic product.

Injection molding technology has many advantages, such as:

High precision: The injection molding process can produce parts and products with high precision and consistency.

High production efficiency: The injection molding machine can produce a large number of products in a short period of time, making it suitable for mass production.

Product quality is stable: Due to the injection molding process being able to precisely control every production parameter, the quality of the products is extremely stable.

High plasticity: The injection molding process is applicable to various types of plastics and can produce products with various complex shapes.

During the injection molding process, product cracking is usually caused by the following reasons:

Material selection: Choosing materials that are not suitable for injection molding, or having substandard material quality, will result in product cracking.

Temperature control: In injection molding, it is essential to strictly control the temperature during the heating and cooling processes. If the temperature is not controlled properly, it can easily result in excessive internal stress in the product, causing it to crack.

Pressure issue: Improper pressure control during the injection molding process, especially during the ejection and holding stages, can result in uneven product structure or excessive internal stress causing cracking.

Mold Design: Inadequate mold design or manufacturing quality issues can also cause the product to crack.

Product Design: If the product structure is not designed properly, the wall thickness is uneven, or there are stress concentration areas, it will also lead to cracking problems during the injection molding process or during use of the product.

To prevent the product from cracking, a comprehensive analysis and optimization need to be carried out in terms of material selection, production process, mold design and product design.