Short shot (also known as short fill or incomplete filling) is one of the most common defects in injection molding, where the molten plastic fails to completely fill the mold cavity. This results in parts with missing sections, thin walls, or incomplete features, often occurring at thin walls, deep cavities, or flow path ends. It not only affects product appearance and structural strength but also increases scrap rates and production costs. Preventing short shots can significantly improve injection molding quality, efficiency, and cost-effectiveness.
Main Causes of Short Shots
Short shots typically stem from excessive flow resistance or premature solidification of the melt, including:
- Gate/runner design too small, too long, or unbalanced, causing high pressure loss.
- Poor mold venting, where trapped gases compress and block filling.
- Insufficient injection pressure/speed, or inadequate holding pressure.
- Low melt or mold temperature, leading to high viscosity and poor flowability.
- Inadequate material drying (excess moisture/volatiles) or improper machine selection (insufficient shot size).
How to Effectively Prevent Short Shots
- Optimize Mold Design — Use balanced runners and larger gate sizes; position gates at thicker wall areas. Add venting slots (depth 0.02–0.04 mm), vents, or cold slugs to eliminate air traps.
- Adjust Process Parameters — Increase melt and mold temperatures to extend flow time; boost injection pressure/speed and holding pressure/time. Reduce injection speed if needed to minimize resistance.
- Material Management — Select high-flow, low-viscosity resins; rigorously dry materials to remove moisture/volatiles; avoid excessive lubricants.
- Equipment Maintenance — Choose machines with shot size at least 120% of part + runner weight; regularly check heating systems, screw/barrel temperature uniformity, and ensure no blockages in gates.
- Early Validation — Follow DFM (Design for Manufacturability) principles for uniform wall thickness and avoid sharp corners; conduct “fill-only” trials during mold testing for gradual optimization.
By implementing these systematic measures, most short shot issues can be avoided or quickly resolved. As a professional injection mold manufacturer, ATC-Mould specializes in high-precision mold design and process optimization, helping clients eliminate short shot defects from the source for stable mass production. If you’re facing short shot problems or need custom injection molding solutions, contact us today for a free DFM analysis and trial mold support! Our expert team will help boost your product yield and reduce costs.