Injection Molding Process Parameters of ABS+PC Alloy
ABS+PC alloy combines the advantages of ABS such as good fluidity, easy molding and cost performance, as well as PC’s high impact resistance, heat resistance, stable dimensional performance and high hardness. It is widely used in civil plastic parts including electronic and electrical housings, smart home shells, industrial control equipment accessories, general structural plastic parts and protective casings. This material features strong moisture absorption, high sensitivity to molding shear and large internal molding stress with a narrow process window. Improper parameter control will easily cause defects such as silver streaks and bubbles, weld lines, whitening and cracking during ejection, brittle fracture and yellowing carbonization of finished products. Combined with general mass production standards for injection molding, this paper sorts out standardized injection molding process parameters in modules to standardize full-process production technologies.
1 Raw Material Drying Process Parameters
The PC component absorbs water strongly, which is the primary inducement of defective ABS+PC injection products. The moisture content of raw materials must be controlled below 0.04%.
For ordinary natural and black standard ABS+PC: hot air drying temperature 80–85°C, drying time 4–6 h, suitable for mass production of conventional structural parts.
For high-gloss transparent and thin-wall appearance ABS+PC: drying temperature 85°C, drying time 6–7 h to completely remove bound water inside materials.
For flame-retardant modified ABS+PC: drying temperature ≤80°C, drying time 5 h to prevent thermal decomposition of flame retardant additives which would cause mold deposits and black spots.
Supporting hopper constant temperature insulation at 70°C to avoid secondary moisture absorption of materials; extend drying time by 1 hour in rainy and high-humidity environments to eliminate residual water vapor.
2 Barrel Temperature Segmented Process Parameters
Barrel temperature follows the principle of low-temperature melting to avoid thermal degradation. The maximum tolerable temperature of the material shall not exceed 265°C to prevent PC molecular chain cleavage and yellowing & embrittlement of finished products.
General standard ABS+PC (most commonly used)
Feeding section: 200–215°C; melting middle section: 220–235°C; homogenizing front section: 225–240°C; nozzle: 220–235°C
High-flow thin-wall ABS+PC
Increase the overall temperature by 10°C to improve melt fluidity and solve insufficient filling and short shot of thin-wall products; the maximum nozzle temperature shall not exceed 250°C.
Flame-retardant ABS+PC
Reduce the overall temperature by 10–15°C, with the full barrel temperature ≤240°C to lower shear heat and avoid carbonization decomposition of flame retardants.
Shutdown control: keep barrel constant at 200°C for insulation within 20 minutes of shutdown; empty residual materials and cool down to 180°C for storage if shutdown lasts more than 1 hour.
3 Mold Temperature Control Parameters
Mold temperature directly affects the internal stress, surface quality and toughness of plastic parts, divided into three grades according to product structures:
Ordinary matte structural parts: mold temperature 45–65°C to accelerate cooling and molding, shorten production cycles and boost capacity.
High-gloss textured appearance parts: mold temperature 70–85°C to optimize weld lines, improve surface gloss and reduce surface texture defects.
Buckle special-shaped stressed parts: mold temperature 85–95°C to fully release internal molding stress and prevent cracking under assembly stress later.
Production requirement: temperature difference of mold water channels controlled within ±4°C to ensure uniform cooling of plastic parts and avoid warpage, deformation and dimensional deviation.
4 Core Process Parameters of Injection & Packing Pressure
(1) Pressure and Speed
Injection pressure: 80–110 bar for conventional plastic parts, 110–120 bar for thin-wall parts, 70–90 bar for flame-retardant materials.
Injection speed: low-speed filling for thick-wall large parts to prevent gas entrapment and scorching; medium-high speed filling for thin-wall parts to guarantee full cavity filling.
(2) Segmented Packing
Primary packing: 55–75 bar, duration 1.2–2.5 s to quickly compensate melt shrinkage and eliminate surface sink marks.
Secondary packing: 35–50 bar, duration 2–4 s for pressure stabilizing shaping to fix outer diameter and hole position dimensions of products.
(3) Screw Parameters
Screw back pressure: 40–60 bar; raise back pressure for color-mixed products to ensure uniform color matching.
Screw rotation speed: 45–70 r/min for low-shear plasticization to reduce frictional heat and prevent material degradation.
5 Auxiliary Process Parameters of Cooling and Ejection
Cooling time is matched according to wall thickness, with the basic cooling duration of 12–20 s. Extend cooling time by 3 s for every 0.5 mm increase in wall thickness to ensure complete shaping of plastic parts and avoid deformation during ejection. The unilateral draft angle for ejection is set to 1.5°–3°, and increased to 3° for high-gloss appearance parts to prevent ejector pin whitening, cavity scratching and corner chipping. Adjust ejection air pressure and ejection speed to medium-low speed during production to reduce hidden cracks caused by external force.
6 Optimization Points for Common Process Defects
Silver streaks and bubbles on materials: extend drying time, lower nozzle temperature and reduce screw rotation speed.
Obvious surface weld lines: raise mold temperature and slightly increase secondary packing pressure.
Cracking under assembly stress: raise mold temperature and lower injection pressure to release internal stress of plastic parts.
Yellowing and blackening of finished products: reduce overall barrel temperature, clean carbonized deposits inside the barrel and lower shear rate.
In summary, the core principles of ABS+PC injection molding are sufficient drying, low-temperature plasticization, medium-pressure injection and medium-temperature shaping. Fine-tune parameters according to flame retardancy, wall thickness and appearance requirements to stably produce qualified products, suitable for mass processing of various civil plastic parts.
