Common Causes and Solutions of Injection Moulding Plastic Deformation

Table of Contents

The common causes for the deformation of injection molded parts are numerous and are caused by a variety of factors. However, solutions usually fall into three main categories: material, design, and process. 

Material problems are the most common cause of distortion and are usually due to the properties of the resin used. For example, if the material has a high shrinkage rate, it is more likely to warp or distort during the cooling process. To solve this problem, it is necessary to use a resin with a lower shrinkage rate or to increase the thickness of the part. 

Design problems are usually related to the geometry of the part. If the part is too thin or has sharp corners, it is more likely to warp during the cooling process. To solve this problem, it is necessary to redesign the part so that it is thicker or has rounded corners. 

Process problems are usually related to the way the part is injected. If the mold is not properly cooled, or if the injection molding pressure is too high, the part is more likely to deform. To solve this problem, it is necessary to improve the cooling process or reduce the injection pressure. 

How do identify the deformation of injection molded parts?

Three main types of deformation can occur in injection molded parts: warpage, sinking, and flying edges.

Warpage is caused by uneven cooling, which may lead to distortion or deformation of the part.

Sinkage occurs when the molten plastic does not fill the mold, resulting in a shallow or sunken surface.

Flashing occurs when excess plastic is extruded from the mold during the injection process, creating unsightly seams.

To identify these injection molding defects, it is important to inspect the part as soon as it is removed from the mold. Any warpage, sagging, or flying edges should be apparent at this time. If these defects are found, they can usually be corrected by adjusting the mold design or injection molding process.

For example, the main causes of the deformation of injection molded parts are improper mold design, the poor performance of raw materials, unsuitable injection conditions, improper operation after injection, etc.

To prevent or reduce the deformation of injection molded parts, it is necessary to analyze the deformation mechanism of injection molded parts and then take corresponding preventive measures.

Molding defects not only affect the appearance and performance of injection molded products but also cause scrap and waste in production.

How to prevent or reduce the defects has been a hot issue in the field of plastic processing. With the development of computer science and technology, CAD/CAE/CAM and other computer-aided technologies have been applied to plastic processing.

Especially in recent years, many new technologies such as CAD/CAE/CAM have been developed. These technologies have greatly promoted the development of the plastic molding industry and provided a powerful means to solve the problems in plastic processing.

The application of these technologies can optimize the design of molds, improve process parameters, and reduce or even eliminate molding defects.

The shape of the injection molded part is similar to the mold cavity but is a distortion of the mold cavity shape

Possible reasons for the problem

1. Bending is due to excessive internal stress in the injection molded part

Bending is a common problem that may occur in injection molded parts. Bending is usually caused by excessive internal stresses on the part. These stresses can be caused by many factors, including uneven cooling, incorrect mold design, or excessive injection pressure.

Bending can also be caused by material selection problems, such as using materials that are too brittle or have poor impact resistance. In most cases, bending can be prevented by careful design of the part and selection of the proper material. However, if bending does occur, it can usually be corrected by heat treatment or other post-molding processes.

2. Slow mold fill rate

Slow mold filling can be caused by many factors. Resin viscosity may be too high, injection pressure may be too low, or gate size may be too small. Slow mold filling can also be caused by an imbalance in cavity pressure.

If the cavity pressure is too high, the molten resin can be pushed out of the gate before it has a chance to fill the entire cavity. Slow mold filling can also be caused by a cold runner system, where the molten resin cools in the runner and gate before reaching the gate. This can cause the resin to solidify before it has a chance to fill the entire cavity.

Slow mold filling can be a big problem because it can lead to premature wear of the mold or defects in the final product. To prevent slow mold filling, injection pressure, gate size, and runner system must be carefully controlled. 

3. Insufficient plastic in the mold cavity

Insufficient plastic in the mold cavity during the injection molding process can lead to several problems. Most notably, it can lead to mold flutter or incomplete filling. In addition, it can lead to warpage or distortion of the part. Insufficient plastic can also lead to poor surface finish and defects in the molded part.

To avoid these problems, it is important to ensure that there is enough plastic in the mold cavity before starting the injection molding cycle. This can be accomplished by carefully measuring the volume of the mold cavity and ensuring that there is sufficient plastic to fill it.

It is also important to monitor the flow of plastic during the injection molding process and make adjustments as necessary to ensure that all parts of the mold cavity are filled evenly.

4. Plastic temperature is too low or inconsistent

Plastic products are often used in applications where high temperatures exist. For example, many foods and beverage containers are made of plastic because they can withstand high temperatures without melting or leaching chemicals into the food. However, if the temperature is too low, the plastic can become brittle and break easily.

If the mold temperature is inconsistent, the plastic can warp or deform. Therefore, it is important to maintain a stable temperature when handling plastic products. Otherwise, the product may not meet its intended purpose.

5. Injection molded parts are too hot during ejection

Injection parts can become too hot during ejection, causing various problems. The heat can cause the material to deform and make it difficult to remove the part from the mold.

In addition, heat can cause the material to become brittle and break. In severe cases, the heat can even cause the material to catch fire. To prevent these problems, it is important to cool the injection molded parts as soon as it is ejected.

There are several ways to do this, including using a blast of cold air or immersing the part in a cooling pool. By taking these steps, you can help ensure that your injection molded parts are cooled quickly and safely.

6. Inadequate cooling or inconsistent temperatures in the moving and fixed molds

Inadequate cooling or inconsistent temperatures between the moving and fixed molds can cause a variety of defects in the molded part. If the moving mold is not properly cooled, the molten plastic material will solidify before it reaches the cold slug well. As a result, the material will not fill the mold cavity, resulting in a short shot.

In addition, if the dynamic mold is not cooled uniformly, the plastic material will solidify at different rates, causing warpage. Similarly, if the fixed mold is not properly cooled, the material will solidify before it reaches the end of the mold cavity. This can result in depression marks or voids.

To prevent these defects, it is important to ensure that both the moving mold and the stationary mold are cooled uniformly and consistently.

7. Poorly constructed injection molded parts

An ill-constructed injection molded part can lead to manufacturing difficulties, increased scrap rates, and reduced production yields.

In some cases, it can also lead to poor product quality and function. When designing injection molded parts, it is important to consider the manufacturability of the part and the impact of the design on the overall production process.

By considering these factors, you can minimize the likelihood of problems during manufacturing and ensure that your part meets all specifications.

The solution to the deformation of injection molded parts

Solving the deformation problem of injection molded parts is a major challenge for many industries, especially the automotive and aerospace industries, which have extremely demanding product performance and safety requirements. During or after the manufacturing process, injection molded parts may be deformed for several reasons.

In some cases, the material used to make the part is not compatible with the molding process or the molding conditions are not ideal. In other cases, the geometry of the part dictates that it is prone to distortion during cooling.

Regardless of the cause, addressing the deformation of injection molded parts is a critical issue that must be addressed to ensure product quality and safety.

There are many ways to address the deformation of injection molding plastic parts, depending on the specific needs of the application. In some cases, parts can be redesigned to reduce their susceptibility to distortion.

In other cases, it may be necessary to modify the materials used to make the part or to change the molding conditions. Regardless of the method used to address the formation of an injection molded component, it is important to ensure that it is compatible with the overall manufacturing process and does not adversely affect product quality or safety.

Distortion of the injection molded part is a common problem that can occur during the manufacturing process. There are several potential causes for this problem, including poor material selection, incorrect mold design, or poor manufacturing conditions. However, several solutions can be used to correct this problem.

For example, the size and shape of the part can be adjusted to compensate for the distortion. The choice of material can also be changed to a more appropriate choice.

In addition, the mold can be redesigned to prevent the problem from occurring in future runs. By following these steps, it is possible to solve the deformation problem of injection molded parts and produce high-quality parts.

1. Reduce injection pressure 

Injection pressure is one of the main causes of the deformation of injection molded parts. By reducing the injection pressure, the deformation of parts can be greatly reduced.

In addition, using lower injection pressure can also help improve the surface finish of the part and reduce the risk of warpage. Ultimately, reducing injection pressure is a simple and effective way to improve the quality of injection molded parts.  

2. Reduce screw forward time

Reducing screw advance time can be achieved by reducing the speed of screw advance, or by increasing the back pressure. By reducing the screw advance time, the material has less time to cool and shrink before solidifying.

As a result, the finished part is less likely to deform. In addition, this technique also helps to improve the surface finish of the part. By reducing the time the screw advances, the material has less time to cool and shrink before solidifying, resulting in a smoother surface finish.

3. Increase the cycle time, especially the cooling time

Immediately after ejection from the mold (especially for thicker injection molded parts) immerse the injection molded part in warm water (38°C) to allow the part to cool slowly

One potential solution to the deformation of injection molded parts is to increase the cycle time, especially the cooling time. Immersing the part in warm water immediately after ejecting it from the mold allows the part to cool slowly and reduces the risk of distortion.

This is particularly effective for thicker parts that are more prone to distortion. However, it is important to note that this solution may not work for all types of distortion.

If the distortion is due to incorrect mold design or material selection, then increasing the cycle time will not alleviate the problem. In this case, it is necessary to consult with an expert to determine the root cause of the problem and find an appropriate solution.

4. Increase injection speed  

One way to increase the injection speed is to use a higher melt temperature. This will reduce the viscosity of the molten plastic and make it flow more easily. In addition, using a higher melt temperature can help prevent the formation of defects, such as weld lines and dimple marks. Another way to increase the injection speed is to increase the screw speed.

This will also reduce the viscosity of the molten plastic, making it easier for the screw to push the plastic through the nozzle. In addition, increasing the screw speed can help prevent material from bleeding out at the edges of the screw threads.

Finally, injecting at a higher pressure will also help increase the injection speed. This will force the molten plastic into the mold cavity faster, reducing the overall cycle time. By implementing these solutions, it is possible to increase injection speed without sacrificing quality or performance.    

5. Increase plastic temperature 

To address the deformation of the injection molded part, increasing the plastic temperature will help to reduce the amount of deformation that occurs during the cooling process. In addition, it is important to ensure that the mold is properly ventilated so that air can escape freely.

Finally, it may be necessary to use a higher injection pressure or speed to prevent the plastic from cooling too quickly. By following these simple steps, it is possible to significantly reduce the amount of deformation in the injection molded part.

6. Use of cooling equipment

The use of cooling equipment greatly reduces the risk of deformation during the plastic injection. By using cooling equipment, the plastic is cooled more evenly and quickly, thus preventing it from deforming during the cooling process.

In addition, the cooling equipment ensures that the plastic is cooled to the proper temperature, which further reduces the risk of deformation. Therefore, the use of cooling equipment is an important part of ensuring that the injection molded part is properly cooled and not deformed.

7. Increase the cooling time

Improve the cooling conditions to ensure that the mold temperatures of the moving and fixed molds are as consistent as possible

Solve the problem of deformation of injection molded parts. Increase the cooling time or improve the cooling conditions to ensure that the mold temperature of the moving and fixed molds are the same as far as possible.

The deformation caused by different mold temperatures leads to the poor dimensional accuracy of the injection molded parts, especially when the cooling rate of the moving mold is faster than that of the fixed mold.

Deformation also causes surface defects, such as warpage and dent marks. When the mold is opened, the molded part will shrink and deform due to its high temperature, which also affects the dimensional accuracy.

To solve this problem, it is necessary to increase the cooling time or improve the cooling conditions so that the temperature difference between the moving mold and the fixed mold is minimized and the mild temperatures of the two molds are as close as possible to achieve good dimensional accuracy of the injection molded parts.

In addition, it is also necessary to select suitable molding materials and injection conditions to further reduce dimensional tolerances.

8. Improve the structure of the plastic part

To improve the structure of the plastic part, it is necessary to increase its stiffness and strength. One way to do this is to increase the uniform wall thickness of the part. Another way to improve the structure of the plastic part is to add reinforcement. Reinforcement can be in the form of fibers, particles, or sheets.

The reinforcement can be oriented in various ways to achieve the desired properties. The type of reinforcement and the orientation will depend on the specific application. To successfully improve the structure of the plastic parts, it is important to consider all aspects of the design.

The main causes of the deformation of injection molded parts are residual stress, dimensional accuracy, and warpage. To solve these problems, the following points should be noted in the design, molding, and post-treatment of plastic parts.

1. Use symmetrical or near-symmetrical structures as much as possible

2. Minimizing the mold wall thickness of the part and making the thickest wall thickness as uniform as possible

3. the use of ribs or tabs where re Selectinforcement is required

4. Select CNC machining processes when high dimensional accuracy is required.

5. Select an appropriate cooling system and cycle time.

6. Avoid sudden changes in section dimensions.

7) Use preheating before welding.

8) Pay attention to the surface treatment after welding.

9) Select the appropriate packaging method.

Trial production should be conducted according to the above principles to verify the rationality of the design and avoid the potential risks of mass production.

Conclusion

There are many reasons for the deformation of injection molded parts, but most solutions fall into three main categories: material, design, and process. Material problems are the most common cause of distortion, usually due to the properties of the resin used.

For example, if the material has a high shrinkage rate, it is more likely to warp or distort during the cooling process. To solve this problem, it is necessary to use a resin with a lower shrinkage rate or to increase the thickness of the part.

Design problems are usually related to the geometry of the part. If the part is too thin or has sharp corners, it is more likely to distort during cooling. To solve this problem, it is necessary to redesign.

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