AIM Processing Small Plastic Parts Blog

In plastic injection molding, the process of demolding a part is as important as creating the mold design and forming the part. Successful demolding is essential for maintaining part quality, reducing mold damage and minimizing cycle times. To optimize the process, here are three crucial tricks to enable a clean release from the mold without creating defects in the part. These recommendations will generate more consistent and efficient demolding.

Trick 1: Optimize the mold design

A well-designed mold is the foundation for successful demolding. Key design features include draft angles, the ejection system, parting lines and smooth mold surfaces. Each of these design techniques plays an important role in ensuring the part releases cleanly without damage.

• Using core features on the ejection side: In a typical two-part injection mold, the ejection takes place on the moving side of the tool. In order for that to happen, we need to ensure that the part moves with the moving side of the tool at mold opening and doesn’t remain stuck in the stationary side. The optimal way to ensure that the part follows the moving side is to have mold features for the part to shrink around, often called “cores”.
• Draft angles: The sides of the mold cavity should have a slight taper or draft angle, allowing parts to slide out easily during ejection. For most parts, a draft angle between 1°-2° is adequate. Textured surfaces may require a draft angle of 3°-5°.
• Ejection system: The placement of ejector pins, sleeves and lifters should allow part ejection with an even distribution of force across the part. A more uniform force distribution avoids pressure spots that could damage the part. Strategically placing these components in structurally strong or non-visible areas helps maintain part aesthetics and structural integrity.
  Ejector pins are cylindrical rods used to push the structurally strong areas of a molded part out of the mold. Ejector sleeves are hollow cylindrical tubes that operate like ejector pins. The ejector sleeves push hollow portions of a part from the mold to avoid deformation and marks. Lifters are sliding or angled components that help to release parts with complex geometries, such as angled features that would be difficult to eject without damage if using a perpendicular force.
• Parting lines and smooth surfaces: Smooth mold surfaces and correctly placed parting lines reduce friction and sticking, which enables easier release of the part. Precise alignment of parting lines can prevent micro undercuts in the part that will cause it to stick to the mold.

Trick 2: Control cooling time and temperature

The mold temperature and cooling time are the critical operating parameters for ensuring parts retain shape, rigidity and quality during demolding.

• Cooling time: Allow the part sufficient cooling time within the mold to avoid warping or deformation during ejection. Cooling times will vary based on the part’s thickness, material type and the mold’s cooling system. Rushing this process often results in defects, particularly with thicker or more complex parts. Cooling time also enables the part to shrink onto the “core” features on the moving side, so that the part will not get stuck in the stationary side to the tool when the mold opens.
• Temperature control: Effective temperature control maintains uniform cooling across the part to minimize warping and shrinkage that can also cause sticking. Mold cooling channel designs should keep the molded part at a uniform temperature, aligned with the material’s requirements, as an uneven temperature profile can lead to adhesion issues and uneven shrinkage.

Trick 3: Optimize material selection and use mold release agents

• Material Selection: Each plastic has unique demolding characteristics based on its shrinkage rate, rigidity and temperature tolerance. For example, polyolefins generally release better than soft thermoplastics, which can stick without extra draft or cooling time.
• Mold Release Agents: If permitted by the application, mold release agents can be a quick fix for improving demolding. However, they should be used sparingly to avoid buildup, which can compromise part quality and lead to frequent mold cleaning. When used correctly, these agents are ideal for helping parts with complex shapes or sticky materials release smoothly.

By focusing on these three tricks, enhancing mold design, managing temperature and cooling time and careful material selection, your plastic injection molder can maintain high part quality throughout the demolding process and can minimize cycle times.

AIM Processing incorporates these tricks in the manufacturing of all parts

AIM Processing engineers will recommend a mold designer based on the type of part that needs to be molded. AIM engineers also will recommend an appropriate plastic that will meet the specifications for the part and ease the mold release process. Their knowledge of the material and their expertise with AIM’s injection mold machines, will allow the engineers to select the optimum injection molding machine and the optimum operating parameters for successful demolding and the most efficient cycle time.

Let AIM Processing partner with you to help you define the important considerations for your part and make the high-quality, efficiently demolded injection molded part you need. Contact AIM Processing at Contact AIM Processing.