Injection Molding
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Underfilling/Short Shot of Block Copolymer Polypropylene Injection Molded Products
Problem Phenomenon
The product fails to completely fill the cavity, with material-missing parts, incomplete edges, or local voids.
Short shot directly leads to product scrapping, and usually occurs first in parts with long flow distance, thin walls, or poor venting.
Cause Analysis
（1）The injection pressure is insufficient or the injection speed is too slow, and the melt solidifies prematurely during mold filling
（2）The barrel temperature is too low (below the 200-270 lower limit), the melt viscosity is high, and the flowability is poor
（3）The mold temperature is too low, the melt cools rapidly after contacting the mold wall, and the flow distance is shortened
（4）The gate size is too small or the runner is too long, and the melt flow resistance is large
（5）The cavity venting is poor, and the trapped gas hinders the melt filling
Solution
（1）Increase the injection pressure to 80-150MPa, increase the injection speed, and shorten the mold filling time
（2）Increase the barrel temperature to a higher value within the 200-270 range to reduce the melt viscosity
（3）Increase the mold temperature to a higher value within the 40-90°C range to delay melt cooling
（4）Increase the gate and runner sizes, shorten the runner length, and reduce the flow resistance
（5）Check and improve the mold venting, and add vent grooves or vent pins at the filling end
Key Takeaway
Short shot is the result of insufficient melt flowability or excessive mold filling resistance, and needs to be solved by increasing the temperature, pressure, and improving the gating and venting system.
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