Design of Injection Molds for Plastic Bent Tubes

Demolding Methods and Variations for Bent Tube Products

The application of bent tube molds has become increasingly widespread across various industries such as automotive, aerospace, construction, and home appliances. As product designs become more complex, traditional demolding methods may no longer be sufficient. However, it's often impractical to modify the structure of plastic parts, as these specific shapes are essential for the final product to meet mass production standards. For instance, automotive intake manifolds, water pipe elbows, and vacuum cleaner bends require one-piece molding to achieve a satisfactory service life. Therefore, the focus should be on optimizing mold design.

Actually, 80% of bent tube products can be demolded using conventional circular rotational demolding. This is achieved by a hydraulic cylinder driving a rack to rotate a gear for core pulling, or by a slider driving a swing arm to rotate a circular slider for core pulling. The key design points are to accurately locate the center of the arc, ensure proper guide rail guidance, pay attention to mating positions, and set limits for core pulling. However, for the remaining 20% of products, conventional circular rotational demolding is not sufficient. In such cases, alternative solutions must be sought to address the demolding challenge. In recent years, China has developed two sets of demolding solutions to handle these more complex bent tubes: the spine circular core-pulling structure and the circular rotation variable track structure.

While this description might be somewhat abstract without visual aids, we can provide more concrete explanations through images and videos showcasing three different demolding methods for bent tube products.

First, the Conventional Circular Rotational Demolding Structure.

This structure is quite common and can successfully demold many products. It is also relatively stable. Key design points include: accurately locating the center of circular rotation, restraining the rotation center, ensuring proper guide rail guidance on the slider, paying attention to mating positions and post-demolding limits, and calculating the opening and closing stroke.

Please observe the simulated action in the video.

Second, the Circular Rotational Variable Track Core Pulling Structure

Why variable track? This involves a more complex design challenge.

Key design points:?There are two rotation centers: one fixed and one variable. First, draw two circular rotation centers in CAD. Then, draw the guide rail trajectories based on these centers. As shown in the animated video, the slider is initially constrained by the first fixed rotation center as it slides along the first track. When it reaches the second track, the second rotation center on the swing arm of the first center takes over, and the slider follows the second track to rotate and pull the core, avoiding interference with the product and thus achieving demolding.

Advantages:?This structure can solve the demolding problem for bent tubes in constrained positions, and the circular slider can pass through the cooling channels, providing better cooling for the product.

Disadvantages:?The action is more complex, the mold base is larger, and the hydraulic cylinder stroke is longer.

Please observe the simulated action in the video.

Third, the Spine-Type Circular Core Pulling Structure

The circular core is divided into several segments and assembled together. Each segment has an equal arc. Two guide rails are designed to pass through the segments to guide the rotation. In the middle, a spring wire (stainless steel wire) passes through each segment, fixed to the pull plate at the front end. The front end of the pull plate is held by a spring and a limit post.

Advantages:?It can solve the problem of insufficient space and 180-degree bent tubes.

Disadvantages:?It cannot accommodate cooling channels and cannot effectively cool the product. The structure is complex, and mold matching is difficult.

Please observe the simulated action in the video.

These three bent tube structures are widely used in the industry. While all are effective designs, the optimal demolding scheme for a specific application can vary depending on individual design considerations.

This concludes our discussion on bent tube structures. We welcome further input and exploration.

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