The advantages of ABS injection moulding include good mechanical and electrical properties, good surface appearance, excellent chemical resistance, good impact strength, good rigidity and toughness, lightweight, excellent load stability, an ultraviolet light sensitive, etc. However, it has its shortcomings. For example, the sink mark is a headache in ABS injection moulding. So we have to maintain a uniform wall thickness in part design. Also, those bosses incorporated parts have to be appropriately designed to avoid the sink mark. Sharp corners result in stress concentrations and should be avoided.
In the following paragraph, I’d like to talk about ABS injection molding. The fluidity of ABS is between PS and PC, and it has some relationships with injection moulding temperature and injection moulding pressure, which has more influence in this relationship. So a high injection moulding pressure is often adopted to reduce the melt viscosity and improve the cavity filling performance.
ABS injection moulding Process
Pre-treatment for material
The water absorption rate of ABS material is about 0.2% -0.8%. For a standard grade of ABS, it must be dried before processed. The dry temperature is 80-85℃ over 2-4 hours or using drying hopper for baking at 80℃ with 1-2 hours. The regrind material should not exceed 30%, and for Plating Grade ABS, no recycled material should be used
Choose of the injection moulding machine
The screw specifications are as follow: ratio is 20:1; compression ratio greater than 2, the injection moulding pressure is greater than 1500bar, clamping force is between 4700-6200t/m2.
Mould and gate design
Mould temperature set for 60-65℃, channel diameter set for 3mm and thickness is the same as part, less than 1mm gate length, the width of vent hole set for 4-6mm, and thickness is between 0.025-0.05mm
Injection moulding temperature
Suggestions as follow
High impact grade: 220 ℃ -260 ℃, the optimum temperature of 250 ℃
Electroplating grade: 250℃-275℃, the optimum temperature of 270 ℃
Heat-resistant grade: 240℃-280℃, the optimum temperature of 265℃-270℃
Flame retardants grade: 200℃-240℃, the optimum temperature of 220℃-230℃
Transparent grade: 230℃-260℃, the optimum temperature of 245℃
Glass Fiber Reinforced grade: 230℃-270℃
The high melt temperature and moulding temperature are adopted for high demanding product surface.
Injection moulding speed
Slow injection mouding speed applies to flame resistant grade ABS. High speed and multi-stage injection moulding speed applies to production if the high demanding product surface required.
You need to minimize the back pressure as low as possible to avoid wear. Usually should be 5bar.
Uniform mixing can be acquired by high back pressure.
The residence time of ABS plastic is no more than 5-6minutes under 265℃ temperature. The residence time is short for flame retardants ABS grade; you need set temperature as low as 100℃, then clean the barrel with common ABS plastic. The mixture need put into cold water to prevent further decomposition.
You need to use PS, PMMA or PE to clean it if the barrel is moulded by other plastic materials before. There will be some time before the colour change for some ABS after moulded. This may be caused by long residence time or overheating of plastic.
ABS plastic can also be secondary operations, such as ultrasonic welding, decorated mouldings which use hot stamping, pad printing, and laser marking processes.
Several grades of ABS (especially flame retardant) have strong adhesion on the surface of the screw after melted. It will break down after a certain period staying on the screw. So you need to pull out the screw and clean the metering and compression segment, and clean of the screw with PS regularly.
This is all about ABS injection moulding, I hope this can help you a lot, we are making any custom plastic molds and plastic molding parts, please contact and get a quote.