8 Key Factors in Plastic Injection Molding

Based on Jingsheng's 16 years of injection molding experience, the summary is as follows:

1. 1. Raw Material (Fundamental Basis)

It is not only necessary to select materials such as PP, ABS, PC, PA6, and PPSU, but also pay attention to details:

• ● Modified materials: Adding glass fiber, flame retardant, toughening agent, and anti-UV agent; adding glass fiber will wear the mold and easily cause the product to turn white;
• ● Drying and dehumidification: Nylon, PC, and ABS must be dried; high water content will directly cause silver streaks, bubbles, and cracks;
• ● Color matching/recycled material: Excessive recycled material will lead to unstable strength, appearance, and dimensions; the proportion of recycled material is generally strictly controlled for foreign trade orders;
• ● Fluidity: High-fluidity materials are required for thin-walled products, and low-fluidity materials are selected for thick-walled products to prevent shrinkage.

2. 2. Mold (Key to Shaping)

The shape, precision, and presence of flash of the product all depend on the mold:

• ● Core structure: Cavity (for product forming), runner and gate (injection position), cooling water channel (cooling and shaping), venting (air exhaust to prevent burning and short shot), ejection (demolding without sticking to the mold);
• ● Impact of details: Poor venting → black burning and short shot; poor water channel → uneven cooling, deformation and shrinkage; incorrect gate position → flow marks and watermarks;
• ● Custom foreign trade parts: Mold polishing, mold core hardness, and cavity quantity (multi-cavity mold) directly determine production capacity and appearance grade.

3. 3. Injection Molding Machine (Matching Bearing Capacity)

No matter how good the material and mold are, you cannot produce qualified products if the machine is not selected correctly:

• ● Clamping force: Large tonnage is required for large, deep-cavity, and thin-walled products; otherwise, mold expansion and flash will occur;
• ● Injection volume: The material stored in the barrel must be sufficient for the product + runner; insufficient volume will lead to under-injection and short shot;
• ● Screw configuration: Wear-resistant screws must be used for glass fiber-added materials to prevent wear and impure material mixing.

4. 4. Temperature (Temperature Control Determines Product Quality) Divided into Three Parts

• ● Barrel/nozzle temperature: Melt the plastic into a uniform fluid; low temperature makes it impossible to inject, while high temperature causes yellowing, decomposition, and brittleness;
• ● Mold temperature: High mold temperature → bright product surface and low internal stress; low mold temperature → fast shaping and short cycle, but prone to flow marks and stress cracking;
• ● Sensitive materials: High-temperature materials such as PPSU and PC require extremely high temperature control accuracy.

5. 5. Pressure (MaterialFilling + Dimension Guarantee) Three Key Pressures

• ● Injection pressure: Quickly fill the cavity with material; high pressure is required for thin-walled and slender products;
• ● Holding pressure: Replenish glue when the glue shrinks during cooling; without holding pressure, shrinkage, small dimensions, and surface pits will definitely occur;
• ● Back pressure: Mix evenly during glue melting, making the color matching more uniform, the glue denser, and reducing bubbles;
• ● Clamping pressure: Prevent the mold from being propped open by high-pressure injection to avoid flash.

6. 6. Speed (Controlling Grain + Preventing Defects)

The speed cannot be adjusted randomly; there is logic:

• ● Fast front section of injection: Quickly fill the runner to prevent glue from cooling and blocking the channel;
• ● low speed when passing through the gate and entering the cavity: Prevent jet flow, flow marks, watermarks, and burning;
• ● Slow mold opening/closing and ejection speed: Prevent scratching the product and damaging the appearance surface;
• ● Thin-walled precision parts: Full-speed injection is required; otherwise, it cannot be filled completely.

7. 7. Time (Determining Cycle + Stabilizing Quality)

Poor time adjustment will lead to the collapse of both production capacity and yield:

• ● Injection time: Ensure that the glue can be completely filled;
• ● Holding time: Until the gate solidifies; stopping holding pressure too early will definitely cause shrinkage;
• ● Cooling time: Thick-walled products must be sufficiently cooled; demolding without full cooling → deformation and top whitening;
• ● Cycle time: Compress cooling and mold opening/closing time on the premise of no defects to improve production capacity and reduce unit price.

8. 8. Environment & On-site Control (Preventing Mass Defects with Details)

Many defective products are not caused by machine problems, but by poor on-site management:

• ● Workshop temperature and humidity: In a humid environment, materials absorb moisture, which will definitely cause bubbles and silver streaks;
• ● Raw material storage: Sealed and moisture-proof, classified and placed to avoid material mixing;
• Release agent/oil pollution: Improper use will affect subsequent spraying, silk screen printing, and bonding;
• ● Part taking and placement: Soft glue and bright-surface parts will be scratched if placed randomly, leading to direct scrapping;
• ● Post-process control: Sprue trimming, inspection and packaging to eliminate mixing of impurities and scratches.