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Analysis and Countermeasures for Short Shots in Injection Molding – A Case Study of PC+ABS
By AriApril 3rd, 202666 views
In injection molding production, a "short shot" refers to the incomplete filling of the mold cavity by the melt, resulting in partial or unclear contours of the product. It is a common quality defect. This article takes PC+ABS plastic products as an example to analyze the causes of short shots and propose corresponding solutions.
The PC+ABS alloy combines the rigidity and heat resistance of polycarbonate with the good processability of ABS, but its melt fluidity is relatively poor and sensitive to processing conditions. The main causes of short shots can be summarized in two aspects:1. Low mold temperature reduces melt fluidity PC+ABS is sensitive to temperature changes. When the mold temperature is too low, the melt cools rapidly during cavity filling, its viscosity rises sharply, and flow resistance increases. This prevents the melt from reaching the far ends or thin-walled sections of the cavity, resulting in a short shot. This problem is particularly prominent in winter or when the cooling channel design is inadequate.
2. Insufficient holding pressure or holding time leads to inadequate packing During the injection process, after cavity filling, a certain holding pressure and time are required to compensate for cooling shrinkage. If the holding pressure is set too low or the holding time too short, not enough melt can be pushed into the cavity to compensate for volumetric shrinkage, ultimately causing local short shots.
Solution: Optimize process parameters – adjust injection speed To address the above causes, process parameter optimization should be the primary approach. First, appropriately increase the mold temperature (recommended range 70–90°C) and ensure uniform temperature distribution to improve melt fluidity. Second, adjust the injection speed reasonably – adopt a “high-speed filling” strategy so that the melt fills the cavity quickly before cooling, while avoiding jetting or thermal degradation. At the same time, appropriately extend the holding time or increase the holding pressure to ensure adequate packing.
In summary, solving short shot problems requires a systematic analysis of the synergistic effects of mold temperature, injection speed, and holding pressure parameters. Through fine-tuning of these parameters, the molding integrity of PC+ABS products can be effectively improved and the reject rate reduced.
1. Low mold temperature reduces melt fluidity
