Demolding in Injection Molding: Techniques and Best Practices

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Demolding of plastic parts is the last step in the injection molding process. The quality of demoulding will finally determine the quality of plastic parts. When mold is opened, plastic parts must be left on half mold half with a demolding mechanism(usually on moving mold). using a demoulding mechanism to pull out plastic parts.

During the injection molding production process, difficulties in demolding injection molded parts are often encountered. Poor demolding has a significant impact on the quality of injection molded products, and mild demolding may cause surface scratches or patterns on the product. 

Additionally, severe poor demolding can lead to product warping, deformation, and even rupture and damage. So, solving the problem of poor injection molding and demolding affects the quality of the final injection molded product. 

In this article, we will explore all the techniques and best practices for effective demolding in injection molding. Read on to learn more!

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Semi-Manual demolding (Image Source: armorinox)

Understanding Demolding

Demolding is a critical step in the injection molding process where the finished part is removed from the mold cavity once it has solidified. This step is essential to ensure the smooth and efficient production of molded parts.

The demolding process begins after the molten material (polymer) is injected into the mold cavity and allowed to cool and solidify. That said, there are several mechanisms used to facilitate demolding. These mechanisms include: 

  • Ejector Pins: Ejector pins are commonly used in injection molding to push the molded part out of the mold cavity. These pins are typically located on the ejector side of the mold and are activated by hydraulic or mechanical systems. As the mold opens, the ejector pins extend into the mold cavity, pushing the part out of the mold and allowing it to be safely removed.
  • Air Blasts: In some cases, compressed air is used to assist in demolding. Air blasts are directed into specific areas of the mold to help release the part from undercuts or tight features. The force of the compressed air helps to dislodge the part from the mold cavity, facilitating easier removal.
  • Stripper Plates: Stripper plates are another mechanism used for demolding in injection molding. A stripper plate is a movable plate located on the side of the mold opposite the ejector pins. After the mold opens, the stripper plate moves forward to push the part off the core or cavity side of the mold, aiding in the demolding process.

Proper demolding techniques are essential for maintaining production efficiency and achieving consistent quality in injection molding operations. The choice of demolding method depends on the specific geometry of the part, mold design, and material characteristics to ensure successful and smooth demolding of molded components.

Demolding Challenges

Demolding in injection molding can encounter various challenges. For instance, part sticking is a common issue where the molded part adheres too tightly to the mold cavity, making removal difficult. This can lead to surface defects like scratches or marks on the part. 

Additionally, deformation of the part during demolding is another challenge, especially with intricate or delicate designs. These challenges can be influenced by several factors such as:

  • Material properties: Material properties such as viscosity and shrinkage affect how the part interacts with the mold surfaces
  • Mold design: Mold design plays a crucial role in demolding; features like draft angles and surface textures can impact the ease of part removal. 
  • Processing conditions: Processing conditions such as injection pressure and cooling rate can affect how the part solidifies within the mold and consequently how it behaves during demolding. 

Addressing these factors through careful material selection, optimized mold design, and controlled processing parameters is essential for overcoming demolding challenges and ensuring high-quality molded parts.

Innovative Demolding Techniques

Innovative demolding techniques shape plastic injection molding and give manufacturers new ways to demold mass plastic parts. Here are some recent demolding innovations in plastic injection molding that may help your business and make manufacturing more efficient. 

Incremental Cavity Ejection (I.C.E.)

Logic Corp developed the Incremental Cavity Ejection (I.C.E.) technique to address demolding challenges. This innovative method leverages material shrinkage during cooling to aid in part release. As the molded material shrinks, it naturally pulls away from the mold cavity walls, easing the removal process.

I.C.E. allows for partial retraction of the mold core during demolding. Unlike traditional methods where the entire core is pulled back at once, I.C.E. enables controlled, incremental movements of the core. This partial retraction reduces the force required to release the part, minimizing the risk of damage or deformation.

Simultaneous Mold Actions

Simultaneous mold actions involve coordinating core retraction and ejector system movements during demolding. By synchronizing these actions, stress on the molded part is minimized, reducing the likelihood of surface defects like scratches or warping.

During demolding, the mold’s core retracts gradually while the ejector system applies controlled force to push the part out. This coordinated approach ensures smooth and uniform part release. By minimizing stress on the part, simultaneous mold actions contribute to producing high-quality molded components with precise details and minimal defects.

Technical Aspects of Effective Demolding

Implementing advanced demolding techniques often requires specific technical setups and modifications to injection molding machines. Let’s explore some of them below!

Linear Transducers

Integrating linear transducers into the molding machine allows for precise measurement and control of core movements during demolding. These devices provide real-time feedback on core positions, enabling accurate and controlled retraction to optimize part release.

Optical Comparators

Optical comparators are used to inspect part features and mold surfaces for quality assurance. They can be integrated into the demolding process to monitor part release and detect any issues such as sticking or deformation. This real-time feedback helps in adjusting demolding parameters for optimal results.

Machine Modifications

To accommodate new demolding strategies, injection molding machines may require modifications. This can include adding additional actuators or sensors for precise core movements, upgrading control systems to incorporate advanced demolding techniques, or retrofitting with specialized tooling and fixtures.

Guidelines for Implementation

When implementing advanced demolding techniques, it’s essential to follow specific guidelines. These guidelines include:

  • Conduct thorough feasibility studies to assess the compatibility of new techniques with existing machine setups.
  • Collaborate with equipment manufacturers or specialists to customize machine configurations for optimal demolding performance.
  • Train operators on new demolding procedures and monitor process parameters to ensure consistent part quality.

Material Considerations

The physical and chemical properties of materials play a crucial role in determining adhesion, demolding force, and demolding difficulty in the injection molding process. Below is how different factors affect the demolding process. 

Melt Fluidity

The melt fluidity of a material affects how well it can fill the mold cavity and how it interacts with mold surfaces during cooling. Materials with high melt fluidity may exhibit better mold filling but could also result in increased adhesion to the mold.

Thermal Deformation Temperature

Materials with higher thermal deformation temperatures can withstand higher mold temperatures without deforming, reducing the risk of sticking to the mold surface during demolding.

Surface Energy

Surface energy influences the interaction between the material and mold surface. Higher surface energy materials are more likely to adhere strongly to the mold, increasing demolding difficulty.

Thermal Expansion Coefficient

Materials with higher thermal expansion coefficients may experience greater dimensional changes during cooling, impacting their ability to release from the mold.

Tips to Optimize Demolding

When selecting and adjusting process parameters for specific materials to improve demolding outcomes in injection molding:

  • Choose mold release agents based on material surface energy to enhance part release.
  • Adjust mold temperature according to material thermal properties to prevent sticking.
  • Optimize injection pressure and speed for proper mold filling without causing excessive stress.
  • Implement appropriate cooling time to ensure sufficient solidification and minimize part adhesion to the mold.
  • Use mold surface treatments such as coatings or textures tailored to the material’s characteristics to facilitate easier part release and reduce demolding force. 

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Demolding Wedges (Image Source: Fiberglass Warehouse)

Optimizing Mold Design for Easier Demolding

Mold design plays a critical role in ensuring efficient demolding in injection molding processes. Properly designed molds not only facilitate smooth part release but also help minimize the risk of part damage and production delays. If you aim to optimize your mold design for easier demolding, you can do it through the tips below!

1. Include Draft Angles

Including draft angles in mold design is essential. These angled surfaces on the mold walls allow for easier removal of the molded part by reducing friction between the part and the mold. Typically, draft angles of 1-2 degrees per side are recommended to prevent sticking and enable smooth demolding.

2. Ensure Smooth Surface Finish

A smooth surface finish on mold cavities and cores is vital for easy demolding. Polished or textured finishes can reduce adhesion between the part and mold surfaces, promoting a smoother release of the molded part.

3. Facilitate Adequate Venting

Proper venting within the mold is crucial to release trapped air and gases during injection molding. Inadequate venting can lead to air pockets or vacuum effects, causing part sticking or incompletely filled mold cavities.

Benefits of Improved Demolding Techniques

Improved demolding techniques offer several important benefits in manufacturing processes. Some of the benefits include the following:

Faster Cycle Times

Advanced demolding methods, such as using specialized coatings, optimized mold designs, or mechanical assists like ejector pins, enable quicker and smoother part release from molds. This reduces the overall cycle time per part, increasing production efficiency and output.

Reduced Part Defects

By minimizing stresses and improving part release, advanced demolding techniques help to prevent defects such as cracks, warping, or surface imperfections. This leads to higher-quality finished products with fewer rejects or rework requirements.

Lower Production Costs

Faster cycle times and reduced part defects directly contribute to lower production costs. Shorter cycle times mean more parts can be produced in less time, optimizing equipment utilization and reducing labor costs. Additionally, fewer defects mean less material waste and lower expenses associated with rework or scrap.


Efficient demolding methods lead to reduced energy consumption due to shorter cycle times and less material waste. This contributes to a more sustainable manufacturing process by minimizing resource usage and environmental impact.

Case Studies of Real-Life Application of Demolding Strategies

Demolding is widely used in real-world scenarios. Below are a few companies that use innovative demolding techniques in their production processes. 


Toyota has been making use of advanced demolding strategies in their production processes. By incorporating specialized mold coatings and utilizing robotic demolding systems, Toyota will achieve significant reductions in cycle times and minimize part defects. This optimization results in improved production efficiency, lower costs, and enhanced product quality across their vehicle assembly lines.


Spigen, a prominent manufacturer of smartphone cases, makes use of innovative demolding techniques utilizing vacuum-assisted systems. This implementation streamlines part release and reduces defects like surface imperfections and scratches. 

As a result, Spigen has managed to enhance customer satisfaction with higher-quality products. This has also helped the company achieve increased production efficiency and reduced waste in its consumer electronics manufacturing.

Johnson & Johnson

Johnson & Johnson is a leading medical device company. For the past decade, this company has massively adopted precision demolding technologies featuring robotic arms in their manufacturing processes. 

The approach, which ensures gentle and precise part removal, results in product integrity and consistency which is vital for medical equipment. By minimizing damage during demolding, Johnson & Johnson reduces waste, improves product quality, and upholds stringent regulatory standards in medical device production.

Maintenance and Troubleshooting

Troubleshooting and maintaining mold components ensures that you achieve consistent demolding performance. However, the whole process requires diligent care and attention to detail. Here is how you can ensure proper mold troubleshooting and maintenance to optimize demolding:

  1. Regular Cleaning and Inspection: After each production run, thoroughly clean molds to remove resin residues and inspect for wear or damage. Use appropriate cleaning agents and tools to ensure molds are free from contaminants that can affect demolding performance.
  2. Lubrication and Mold Release: Apply suitable mold release agents or lubricants to mold surfaces to facilitate smooth demolding. Ensure even and adequate coverage to prevent sticking or friction during part ejection.
  3. Temperature Control and Monitoring: Maintain consistent mold temperatures within specified ranges to prevent thermal stress on parts and ensure uniform material flow during injection molding. Use temperature monitoring devices to detect and adjust deviations promptly.
  4. Storage and Handling: Store molds in clean, controlled environments to prevent contamination and damage. Use protective covers or storage racks to minimize the risk of physical wear and maintain mold integrity between uses.
  5. Scheduled Maintenance and Component Replacement: Implement a proactive maintenance schedule to replace worn components such as ejector pins, slides, and mold inserts. Regularly inspect mold cavities, cores, and runners for signs of damage or fatigue, and address issues promptly to prevent demolding problems.

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Demolding (Image resource: Researchgate)


Efficient demolding is vital for maintaining high-quality production standards in injection molding. Adopting advanced demolding techniques is essential for enhancing production efficiency, reducing defects, and achieving overall manufacturing excellence. 

You can address your demolding challenges with innovative solutions and process control. This will help you optimize your injection molding operations and promote the delivery of superior products to the market. 


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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