Two slider (slide) structures that are not conducive to injection molding production
In injection mold design, the slider (or runner) is a critical component for creating undercuts or convexities on plastic parts. The rationality of its structural design directly impacts mold life, production efficiency, and part quality. However, certain slider designs can exhibit numerous issues in actual production, hindering smooth injection molding operations and potentially leading to production interruptions or product scrap. The following analysis examines two slider structures that pose challenges for injection molding production, exploring their underlying issues and potential improvements.
The first type of slider structure that is unfavorable for injection molding production is a slider structure without a guide device. This slider lacks effective guidance and positioning during movement, relying primarily on the fit between the slider and the guide rail for sliding. Due to the vibration and impact generated by the mold during the injection molding process, the clearance between the slider and the guide rail gradually increases after long-term use, resulting in unstable slider movement, offset, or jamming. When the slider is offset, its molded portion does not accurately match the undercut or undercut structure of the plastic part, resulting in defects such as dimensional deviation, flash, and even strain on the plastic part. Jamming is even more serious and may prevent the slider from returning to its original position. Forced production can damage the mold’s core, cavity, or slider itself, resulting in increased mold maintenance costs and production downtime. In addition, the uneven force applied to the slider during movement without a guide device can easily lead to increased local wear, shortening the service life of the slider and guide rail, and increasing the frequency and cost of mold maintenance.
The second type of slider structure that’s detrimental to injection molding production is one with insufficient locking force. When the mold is closed, the slider must withstand the lateral pressure generated by the melt filling process. If the locking mechanism’s locking force is insufficient and unable to resist this lateral pressure, the slider will retreat during the injection process, resulting in flash or dimensional deviations on the molded part. Common causes of insufficient locking force include improperly designed locking block angles, insufficient contact area of the locking surface, and excessive clearance between the locking block and slider. For example, if the locking block angle is greater than the slider’s tilt angle, the locking force will be insufficient, preventing the slider from being effectively locked. If the contact area of the locking surface is too small, excessive local pressure will result, causing the locking surface to wear rapidly, further reducing the locking effect. This structure not only affects the quality of the molded part, but also can cause collisions and wear on internal mold components due to abnormal slider movement, shortening the mold’s lifespan and increasing the risk of failure during production.
Slider structures without guides can also negatively impact production efficiency. Due to the slider’s unstable motion, it can become stuck or deflect during each mold opening and closing process. Operators must frequently check the slider’s position and status, and even manually adjust it. This inevitably increases production support time and reduces production efficiency. On automated production lines, sliders with this structure are more prone to failure, leading to interruptions in automated production and requiring manual intervention, defeating the purpose of automated production. Furthermore, due to the slider’s unstable motion, the mold’s opening and closing speeds cannot be increased, as this exacerbates slider vibration and deflection, further limiting production efficiency. In contrast, slider structures with guides (such as guide posts, guide sleeves, and guide keys) ensure smooth and accurate slider movement, reducing the risk of failure and improving production efficiency.
A slider structure with insufficient locking force can increase the defective rate of plastic parts and production costs. Flash generated by the slider’s retreat during the injection process requires subsequent trimming of the plastic part, increasing process and labor costs. For parts requiring high precision, flash can lead to the direct scrapping of the product, increasing the scrap rate. Furthermore, the wear and damage to the mold caused by insufficient locking force requires frequent repairs and part replacements, increasing mold maintenance costs and delaying production schedules due to downtime for repairs, impacting delivery times. Furthermore, to compensate for insufficient locking force, operators may resort to measures such as reducing injection pressure or slowing down the injection speed. While this can reduce lateral pressure, it can affect the filling and holding pressure of the melt, resulting in other defects such as underfill and sink marks in the plastic part, creating a vicious cycle that further reduces product quality and production efficiency.
Improving the two disadvantageous slider structures mentioned above is crucial for improving the stability and economic efficiency of injection molding production. For slider structures without guides, appropriate guides should be added, such as guide grooves and keys on the slider’s base, or guide posts and sleeves installed on the slider’s sides. This ensures smooth movement of the slider in a fixed direction during motion and reduces deviation and sticking. For slider structures with insufficient locking force, the locking block design should be optimized, with a properly defined angle (typically 1°-2° larger than the slider’s inclination angle), increasing the contact area of the locking surface, and reducing the clearance to improve locking force and stability. Furthermore, auxiliary locking devices, such as locating pins or springs on the slider, can be added to enhance the slider’s positioning in the closed mold state. These improvements can effectively address the issues associated with the slider structure, improve mold reliability and service life, reduce production costs, ensure consistent part quality, and thus facilitate smooth injection molding production.
