Focus of cost reduction and debugging differs for three typical product types: thin-walled parts, deep-cavity parts, and precision gears. Thin-walled parts prioritize speed, deep-cavity parts prioritize stability, and precision gears prioritize precision.
Following explains debugging logic and cost reduction entry points for each type.

Core Challenges: Extremely long flow rate; plastic cools and solidifies before full filling. Main risks are insufficient glue, trapped air, and insufficient clamping force leading to flash.

 

1. Key Points of Process Debugging
· High-Speed, High-Pressure Filling: Thin-walled parts require high speed. Speed typically needs to reach 80%-99% (or even use "acceleration" function), utilizing shear thinning to reduce viscosity. If speed is insufficient, melt will freeze before reaching end.
• Early V-P Switching: V-P switching position should be set when product is just 95%-98% full. Never use holding pressure to fill cavity; otherwise, it will not only be inefficient but also easily generate internal stress.
• High Clamping Force and Mold Rigidity: Thin-walled parts have a large projected area and high cavity pressure. During debugging, low-pressure clamping position must be returned to zero to ensure mold is not stretched open; otherwise, burrs will inevitably occur during high-speed injection.
2. Core Cost Reduction:
• Compressed Cooling Time: Thin-walled parts typically have a wall thickness of only 0.5-1.5mm, resulting in a very short cooling time. During debugging, focus on shortening mold opening and closing time and ejection time, overlapping actions to limit; cycle time can often be compressed to 5-15 seconds.
• Multi-Cavity Balance: Thin-walled parts are often made in multi-cavity molds. During debugging, ensure balanced filling of each cavity; otherwise, if any cavity is not fully filled or overfilled, the entire molded product must be scrapped.
3. Common Problems and Solutions
* Trapped Air and Burning: Due to poor venting. During debugging, use multi-stage injection. In last 5%-10% of stroke, reduce speed to 20%-30% to allow gas to escape, or temporarily use a vacuum cleaner to assist venting on the outside of mold cavity.
* Whitening/Deformation: Due to high residual stress. Appropriately increase mold temperature (e.g., by 10-15℃), or use a push plate to increase stress area.

Core Challenges: Large melt filling depth easily leads to jetting (snake-like) flow, trapped air (cavity bottom), and deformation caused by uneven sidewall pressure.
1. Key Points for Process Debugging
* Multi-stage Slow-High-Speed-Slow Filling: Use a "three-stage injection." The first stage is low speed through gate (to prevent jetting); the second stage is high speed filling middle section (using shear heat to prevent freezing); the third stage is a final deceleration (to prevent trapped air from bursting at cavity bottom).
• Mold Temperature Control: Deep cavity parts suffer from uneven heat dissipation, resulting in a large temperature difference between bottom and top. During debugging, mold temperature needs to be set relatively high (e.g., 80-100℃ for PC deep cavity parts), and a mold temperature controller must be used to ensure even temperature distribution; otherwise, dimensional stability will be impossible.
• Asymmetrical Holding Pressure: Excessive holding pressure can easily cause sidewall bulging. Segmented holding pressure can be used—first apply high pressure to compensate for shrinkage (1-2 seconds), then quickly reduce to low pressure to maintain (preventing mold expansion).
2. Core Cost Reduction
• Reduce Holding Pressure Time: Deep cavity parts typically have gate at the top, with bottom having the thinnest wall thickness. Holding pressure time only needs to ensure no shrinkage marks near top gate; excessively long holding pressure will prolong cycle time and increase demolding difficulty.
• Prevent Sticking (Reduce Scrap): Deep cavity parts have high demolding resistance. During debugging, ejection action should be "slow speed + long stroke," and combined with air blowing assistance to avoid product whitening or deformation due to forced ejection.
3. Common Problems and Solutions
* Spraying Marks (Snake-like Pattern): Initial injection speed is too high. Solution is to reduce initial injection speed to 10%-20% until melt flows through gate and into cavity for about 20mm before increasing the speed again.
* Bottom Air Trapping: Gas cannot escape, causing localized scorching or incomplete filling. Solution is to locate air trapping point, add venting inserts to mold, or reduce final injection speed to 5%-10% during debugging for "overflow venting."

Core Challenges: Extremely high requirements for shrinkage consistency, roundness, and tooth profile accuracy (tolerances are often within ±0.02mm). Main risks are warping and dimensional deviations caused by internal stress.

 

1. Key Points for Process Debugging
* V-P Switching Position Extremely Sensitive: A 0.2mm offset at switching point may cause a 0.05mm change in gear's outer diameter. During debugging, position switching and screw speed closed-loop control must be used to ensure that repeatability of each mold switching point is within ±0.05mm.
• High mold temperature and high material temperature: To reduce internal stress, mold temperature is usually set near material's heat distortion temperature (e.g., 80-100℃ for POM gears, and 150-180℃ for PEEK gears), allowing molecules to relax slowly within mold cavity and reducing orientation.
• Extremely low injection speed and holding pressure: A "low-speed filling + long-term holding pressure" strategy is adopted. High speed will lead to high molecular orientation, resulting in elliptical shapes due to difference in radial and tangential shrinkage rates in gear. Holding pressure must be just enough to compensate for shrinkage until product weight stabilizes, preventing excessive holding pressure from causing internal stress concentration.
2. Core of Cost Reduction
• Yield is cost reduction: Gear scrap rate is high, and primary task for cost reduction is to increase CPK value to above 1.33. Optimal process window is determined through DOE experiments to ensure that addendum circle dimension remains stable despite fluctuations in ambient temperature and raw material batches.
• Automation and Cavity Monitoring: For multi-cavity gear molds, ensure balanced filling in each cavity (flow rate difference <2%). During commissioning, weigh each cavity and install a cavity pressure sensor for real-time monitoring. An alarm should sound and machine should stop immediately if pressure in any cavity becomes abnormal to prevent batch defects.
3. Common Problems and Solutions
• Excessive Ovality: Caused by asymmetrical gate positions or uneven holding pressure. Solution is to use multi-point injection or a ring gate. During commissioning, reduce holding pressure and extend holding time, replacing "high pressure, short time" with "low pressure, long time".
• Inconsistent Tooth Shrinkage: Caused by uneven mold temperature. Solution is to use independent temperature control zones on mold to ensure temperature difference in gear cavity area is controlled within ±2℃.
• Brittle Fracture: Caused by material degradation or excessive internal stress. During commissioning, strictly control residence time (gears often use heat-sensitive materials such as POM, PA, and PEEK). If machine stops for more than 5 minutes, barrel must be emptied and cleaned with PE.
Comparison of debugging priorities for three types of products

During debugging, it is recommended to follow this logic: first ensure product is stable and qualified, then gradually shorten cycle or adjust efficiency.