Key Point One: Material Handling – “Drying is the lifeline”

This is the most crucial first step. The slight hygroscopicity of ABS is sufficient to ruin the entire production batch.

It must be thoroughly dried: ABS particles will absorb moisture from the air during storage and transportation. Before injection molding, a dehumidifying dryer must be used to continuously dry at a temperature of 80-85℃ for 2-4 hours. It cannot be simply replaced by a common hot air oven.

Consequence: Incomplete drying can lead to silver streaks (silver threads), bubbles, foggy surface, and material degradation on the product surface, resulting in a significant reduction in strength.

Judgment: A simple verification method is to perform an “air injection”. If the molten material strip injected from the nozzle is smooth and bright, without bubbles or crackling sounds, it indicates that the drying effect is good.

Key Point Two: Injection Molding Process – “Artistic Control”
Process parameters are the “steering wheel” for controlling product quality. The process window of ABS is relatively wide, but precision determines quality.

Temperature control

Barrel temperature: The typical processing temperature range for ABS is 190-250℃. It is recommended to set it in sections from back to front to avoid excessively high temperatures.

Rear section (feeding area) : 160-180℃ (To prevent caking at the hopper opening)

Middle section (compression zone) : 180-220℃ (main plasticizing zone)

Front section (metering area) : 210-240℃ (to ensure uniform melt)

Nozzle temperature: 200-230℃ (slightly lower than the front section to prevent salivation)

Mold temperature: Mold temperature has a significant impact on the appearance and internal stress of ABS products. It is recommended that the mold temperature be controlled between 50 and 80 degrees Celsius.

The benefits of high mold temperature (60-80℃) :

Enhance the surface gloss, make the parts more lustrous, and have a stronger ability to replicate the surface details of the mold.

Reduce the weld line, make the weld line less obvious and have higher strength.

Significantly reduce internal stress, enhance the dimensional stability of parts and their resistance to environmental stress cracking.

The disadvantages of low mold temperature (<50℃) : It may lead to poor surface gloss, obvious weld marks, large internal stress, and increased product brittleness.

Pressure and Speed

Injection speed: Medium or high injection speed is often used to achieve a bright surface. However, if the speed is too fast, it may cause jet streaks (the melt shooting into the cavity like a snake) or trapped gas. For complex or thin-walled parts, a multi-level injection control of “slow-fast-slow” can be adopted.

Holding pressure and duration: This is the key to controlling shrinkage (depression).

Holding pressure: Usually 50% to 80% of the injection pressure. Sufficient holding pressure needs to be applied to compensate for the shrinkage of the plastic during cooling.

The holding pressure time mainly depends on the freezing time of the gate. Too short a time can cause internal contraction (shrinkage) of the product, especially in the tendons and thick-walled areas. If the time is too long, it will increase internal stress, reduce toughness and waste the cycle. It needs to be optimized through practice.

Key Point Three: Mold Design – “Details Determine Success or Failure
The mold directly determines the shape, appearance and precision of the parts.

Gate design: Select based on the appearance requirements of the product. For parts with high appearance requirements, latent gates or needle valve hot runners can be adopted to obtain fine and aesthetically pleasing gate marks.

Exhaust system: Adequate exhaust is essential. Poor exhaust can lead to defects such as charring (brown or black stripes appearing on the surface of parts) and incomplete filling. Exhaust slots are usually located on the parting surface and at the fit of inserts, with a depth of 0.02 to 0.03mm.

Cooling system: Uniform and efficient cooling is of vital importance. Uneven cooling can cause warping and deformation of parts.

Demolding slope: The shrinkage rate of ABS is approximately 0.4% to 0.7%. It is necessary to ensure a sufficient demolding slope (usually above 1° to 1.5°) to facilitate ejection and prevent surface scratches.

Key Point Four: Product Design – “Inherent Advantages
Excellent design is the prerequisite for successful production.

Uniform wall thickness: This is the most important design principle. Uneven wall thickness is the main cause of shrinkage, warping and internal stress. It is recommended that the wall thickness be 2.0-3.5mm.

Rounded corner transition: All the junctions of inner and outer corners should be changed to rounded corner transitions. This can greatly reduce stress concentration, improve plastic flow, and enhance the strength of parts.

Reinforcement rib design: The thickness of the ribs should not exceed 50%-60% of the wall thickness at the attachment point to prevent shrinkage marks on the back.

Point Five: Post-processing
Annealing treatment: For parts with significant internal stress or extremely high dimensional accuracy requirements, annealing treatment can be carried out. Place the parts in a hot air circulation oven and heat them at 70-80℃ (below the heat distortion temperature of ABS) for 2-4 hours, then cool them slowly to room temperature. This method can effectively eliminate internal stress, improve dimensional stability and chemical resistance.