This section shares practical case studies of process parameter optimization, focusing on three typical scenarios: general-purpose plastic parts, precision structural parts, and large thick-walled parts. All optimization approaches are actionable on production floor, covering defect identification, parameter adjustment logic, and final results, closely aligned with actual mass production needs.

Background: Product is a control panel housing for a home appliance, with a wall thickness of 1.2mm. Cavity structure contains multiple narrow ribs, it uses general-purpose ABS material. Initial production encountered material shortages at far end of cavity and air marks at gate, resulting in a yield rate of only 75%. Mold lacked a venting design defect, and equipment was a 120T horizontal injection molding machine.
Initial Parameter Issues: Injection speed was high throughout (80mm/s), injection pressure was 120 bar (too high), barrel front temperature was 235℃ (too high), and plasticizing pressure was 30 bar (too low). High-speed mold filling prevented air from escaping quickly at gate, resulting in air bubbles. Furthermore, molten material experienced rapid pressure loss when flowing through narrow ribs, leading to material shortages at far ends.
Optimization Steps
1. Segmented Injection Speed Adjustment: Initial injection (gate section): low speed of 30mm/s to ensure smooth molten material flow and expel air from gate; Mid-injection (cavity body): medium-high speed of 60mm/s to improve molten material flow and cover most of cavity; Late injection (far end ribs): medium pressure and high speed of 70mm/s to fill narrow areas. Adjusting only speed while keeping other parameters unchanged completely eliminated air bubbles and improved material shortages by approximately 50%.
2. Fine-tuning of pressure and temperature: Injection pressure was slightly increased to 130 bar (to compensate for pressure loss at ribs), barrel front temperature was reduced to 225℃ (to prevent ABS thermal degradation), plasticizing pressure was increased to 40 bar (to expel air from barrel and improve uniformity of melt plasticization).
3. Shortening cooling time: Initial cooling was 15 seconds; after optimization, molded parts showed good shaping, and cooling time was shortened to 12 seconds without deformation.
Optimization Results: Molded parts showed no missing material or air bubbles; yield rate increased to 99.2%; molding cycle time was shortened from 38 seconds to 35 seconds, and production efficiency increased by 8%.

 

Background: Product is a small transmission gear with a module of 0.8 and a wall thickness of 2.5mm. It contains metal inserts. Raw material is PA66 + 30% glass fiber (poor crystallinity and flowability). Initially, tooth profile had a dimensional deviation of 0.05mm (0.02mm out of tolerance) and overall warpage of 0.15mm, failing to meet assembly requirements. Mold is a hot runner single-point gate, and mold temperature controller was not initially turned on.
Initial Parameter Issues
Mold temperature: room temperature (25℃); Holding pressure: 80bar (too low); Holding time: 5s (too short); Cooling time: 20s (too short). PA66 + glass fiber crystallizes quickly. Room temperature mold temperature caused uneven crystallization of plastic part, resulting in inconsistent shrinkage in tooth profile. Insufficient holding pressure could not compensate for shrinkage, leading to large dimensional deviations, and insufficient cooling caused warpage.
Optimization Steps
1. Core Mold Temperature Increase: Turn on mold temperature controller and set mold temperature to 80℃ (optimal mold temperature range for PA66 + glass fiber is 70-90℃). This allows plastic part to crystallize slowly, reducing internal stress during crystallization and directly reducing warpage to 0.03mm.
2. Optimized Holding Pressure Parameters: Increase holding pressure to 100 bar (70% of injection pressure) and extend holding time to 8 seconds (until gate solidifies, verified by weighing). This compensates for shrinkage in toothed areas, reducing dimensional deviation to 0.015mm, meeting tolerance requirements.
3. Injection Speed and Cooling Adjustment: Use a medium injection speed of 50mm/s to avoid glass fiber eroding cavity walls (preventing tooth wear). Extend cooling time to 25 seconds to allow plastic part to fully solidify and prevent dimensional springback after demolding.
Optimization Results: Dimensional accuracy and flatness meet assembly standards. Dimensional fluctuations in mass production are ≤0.01mm, and first-pass yield is 100%.

Background: Product is a 20L chemical drum body with a maximum wall thickness of 8mm and a thin-walled sealing surface at the opening. Raw material is HDPE (highly crystalline). Initial production resulted in shrinkage cavities at thick-walled bottom of drum body and flash at the opening, requiring manual trimming and leading to high raw material consumption. Equipment was a 500T large injection molding machine, and mold used a multi-point needle valve gate.
Initial Parameter Issues: Injection pressure was 140bar throughout (too high), holding pressure was 100bar (too high and without segmentation), holding time was 10s (too short), and mold temperature was 30℃ (too low). High pressure caused flash on thin-walled sealing surface at the opening, and insufficient holding time at thick-walled area resulted in insufficient melt shrinkage, leading to shrinkage cavities.
Optimization Steps
1. First, resolve flash by reducing high-pressure parameters: Reduce injection pressure to 120bar and holding pressure to 80bar. Flash at the opening was completely eliminated, and shrinkage cavities showed no significant change.
2. Segmented pressure holding + extended holding time to solve shrinkage cavities: A stepped pressure holding method is used, with first segment at 80 bar (holding for 10 seconds), second at 60 bar (holding for 15 seconds), and third at 40 bar (holding for 5 seconds). This gradual reduction in pressure avoids stress concentration in thick-walled areas, extending the total holding time to 30 seconds. This stepped pressure holding method ensures continuous shrinkage compensation in thick-walled areas, completely eliminating shrinkage cavities.
3. Increased mold temperature + optimized cooling: Mold temperature is increased to 50℃, allowing for uniform crystallization of HDPE in thick-walled areas and reducing internal shrinkage. Cooling time is adjusted from 60 seconds to 70 seconds to ensure complete solidification in thick-walled areas, resulting in no deformation after demolding.
4. Fine-tuned injection speed: Multi-point gates simultaneously fill mold, using a medium injection speed of 40 mm/s to ensure uniform flow of molten material in cavity and avoid excessive local pressure.
Optimization Results: Barrel body is free of shrinkage cavities and flash at the opening, eliminating need for manual trimming. Raw material consumption per unit area decreased by 3%, and product qualification rate increased from 82% to 99.5%. Batch production saw no repeated defects.

Background: Product is a food-grade transparent PC water cup with a wall thickness of 3mm. Requirements are a surface free of silver streaks and white marks, with a light transmittance ≥90%. Initial production resulted in silver streaks on the cup surface and white marks at the bottom gate. PC raw material was dry, but effect was unsatisfactory. Equipment was a 200T injection molding machine with a point gate mold.
Initial Parameter Issues: Raw material was left for too long after drying (moisture reabsorption); barrel temperature was 260℃ (too low, resulting in insufficient PC melting); initial injection speed was 70mm/s (too high); and plasticizing pressure was 25bar (too low). Moisture absorption by PC caused silver streaks at high temperatures. Low-speed melting combined with high-pressure, high-speed mold filling led to excessive shearing of molten material at the bottom, forming white marks.
Optimization Steps
1. Secondary Raw Material Drying + Process Humidity Control: Re-dry PC raw material at 120℃ for 4 hours. Immediately after drying, load material into machine to prevent moisture re-entry. This is fundamental to resolving silver streaks; eliminate raw material issues before adjusting process.
2. Increase Barrel Temperature and Optimize Plasticization: Adjust barrel temperature to 280℃ (optimal melting temperature for PC is 270-290℃), increase plasticizing pressure to 40 bar to improve uniformity of melt plasticization and eliminate hidden silver streaks caused by uneven melting.
3. Low-Speed Injection, Medium-Speed Mold Filling: Initial injection (gate section): low speed of 20mm/s to reduce melt shear and eliminate white marks at the bottom; mid-injection (body section): medium speed of 50mm/s to ensure melt flow and avoid material shortages; no high speeds throughout to prevent PC degradation due to shear heat.
4. Fine-tuning Mold Temperature and Cooling: Mold temperature was set to 80℃ to allow PC to cool slowly, improving its transparency. Cooling time was adjusted from 40s to 45s to ensure complete shaping of plastic part and prevent stress cracking after demolding.
Optimization Results: Cup surface was free of silver streaks, and bottom had no white marks. Light transmittance reached 92%, meeting requirements for food-grade transparent plastic parts. Mass production showed no appearance defects.

 

Background: Product was an automotive door panel interior part, 500*300mm in size, a thin-walled, large-area plastic part with a wall thickness of 2mm. Raw material was PP (low crystallinity, prone to warping). Initially, plastic part warped by 3mm, making it impossible to fit properly. Furthermore, cooling time was 40s, and molding cycle was 75s, resulting in low production efficiency. Mold used a large gate with uniform cooling water channels.
Initial Parameter Issues: Mold temperature was at room temperature (20℃), cooling time was too long, injection speed was medium throughout (50mm/s, resulting in inconsistent filling speeds across cavity), and holding pressure was 70 bar (too high). Room temperature mold caused significant differences in cooling rates across different parts of plastic part, leading to warping. High holding pressure increased internal stress, further exacerbating warping.
Optimization Steps
1. Uniform mold temperature to reduce cooling differences: Turn on mold temperature controller and set mold temperature to 40℃ to ensure uniform cooling across plastic part, reducing warping to 1mm.
2. Optimize injection speed for balanced filling: Use multi-stage speeds: 30mm/s at gate, 60mm/s at large cavity surface, and 40mm/s at edges. This allows molten material to flow evenly within large cavity area, reducing localized cooling rate differences and further reducing warping to 0.5mm, meeting assembly requirements.
3. Reduce holding pressure to minimize internal stress: Reduce holding pressure to 50 bar (60% of injection pressure) and shorten holding time to 8 seconds to avoid internal stress caused by high-pressure holding, ensuring warpage is stabilized within 0.5 mm.
4. Gradually shorten cooling time to improve efficiency: Starting from 40 seconds, reduce cooling time by 2 seconds each time until slight deformation occurs after demolding. A final cooling time of 25 seconds is determined, resulting in well-formed parts without deformation.
Optimization Results: Part warpage ≤ 0.5 mm, meeting automotive interior assembly standards. Molding cycle time reduced from 75 seconds to 50 seconds, production efficiency increased by 50%, and mass production stability is high.
Core Summary of Case Optimization
1. Eliminate non-parametric factors first: In all cases, ensure mold (no venting, water channel defects), raw materials (dry and plasticized), and equipment (mold closing accuracy, pressure stability) are functioning correctly before adjusting process parameters, avoiding "compensating for mold/raw material defects with process improvements."
2. Single-variable adjustment as a foundation: Adjust only one core parameter (e.g., speed, holding pressure, mold temperature) at a time, clarify causal relationship between defects and parameters, then perform multi-parameter synergistic optimization.
3. Different core optimization points for different materials: For crystalline plastics (PA66, HDPE, PP), prioritize optimizing mold temperature and holding pressure to solve shrinkage cavities and warpage caused by uneven crystallization; for non-crystalline plastics (ABS, PC), prioritize optimizing speed and temperature to solve surface defects and mold filling problems; for glass fiber reinforced materials, control injection speed to avoid glass fiber erosion of mold cavity.
4. Thick-walled parts emphasize holding pressure, thin-walled parts emphasize speed: For thick-walled parts, core solution is to solve shrinkage cavities through segmented holding pressure and extended holding time; for thin-walled parts, core solution is to solve mold filling and surface defects through segmented speed, while also considering pressure compensation.