Benefits of Polycarbonate and ABS Injection Molding for Manufacturing

Injection molding is a common manufacturing process used to produce parts and products from thermoplastic materials. Two of the most popular thermoplastics used in injection molding are polycarbonate and ABS (acrylonitrile butadiene styrene). Both offer unique benefits and are suitable for a wide range of applications.

What is Polycarbonate Injection Molding?

Polycarbonate injection molding is the process of injecting polycarbonate resin into a mold to produce plastic parts. Polycarbonate is an incredibly versatile thermoplastic known for its high strength, durability, and transparency. It has excellent impact resistance, dimensional stability, and temperature resistance, making it ideal for applications like machine components, automotive parts, transparent enclosures, and safety equipment. Polycarbonate injection molded parts maintain their properties in temperatures from -100 to 280°F.

Some of the key benefits of polycarbonate injection molding include:

• High tensile strength – Polycarbonate has very high impact strength and tensile strength, even at low temperatures. This allows it to withstand high mechanical and physical stresses.
• Transparency – Polycarbonate is optically clear and transparent. It maintains transparency even after secondary operations like painting or metallization.
• Heat resistance – With a heat deflection temperature of 270°F to 330°F, polycarbonate retains its stiffness, shape, and strength in hot environments.
• Dimensional stability – Polycarbonate exhibits low creep and shrinkage. Molded parts maintain precise dimensions and shape over product lifetimes.
• Flame retardant – Polycarbonate grades are naturally flame resistant and meet UL94 V-2 ratings for flammability without additives.

Applications of Polycarbonate Injection Molding

Some of the most common applications of polycarbonate injection molding include:

• Automotive – Headlamps, tail lamps, instrument clusters, bumpers, radiator fans
• Consumer goods – Transparent housings, handheld devices
• Medical – Face shields, medical equipment housings
• Construction – Skylights, lighting fixtures, transparent roofing
• Electronics – Computer housings, precision components

The clarity, impact resistance and heat properties make polycarbonate the material of choice for safety goggles, riot shields, automobile headlamps, and other transparent items that must withstand high impact. Polycarbonate is also easy to mold and an exceptionally versatile material for designers.

What is ABS Injection Molding?

ABS injection molding involves injecting ABS (acrylonitrile butadiene styrene) resin into a mold tool to produce molded plastic parts. ABS is an engineered thermoplastic terpolymer made up of acrylonitrile, butadiene, and styrene monomers. ABS combines the strength and rigidity of acrylonitrile and styrene polymers with the toughness of polybutadiene rubber. The result is a durable plastic with properties that make it suitable for a wide range of applications.

Some of the key properties and benefits of ABS injection molding include:

• High impact strength – The rubbery butadiene components give ABS excellent impact resistance and toughness, even at low temperatures.
• Dimensional stability – ABS exhibits relatively low creep and warpage. Molded parts maintain shape and precise dimensions.
• Thermal stability – ABS retains stiffness, strength and hardness in temperatures up to 185°F. It has a heat deflection temperature of 199 to 221°F.
• Chemical resistance – ABS offers good chemical resistance, especially to aqueous solutions of salts, acids, alkalis, oils and hydrocarbons.
• Ease of fabrication – ABS is simple to machine, drill, glue and coat with finishes. ABS thermoplastic has low melting temperature for easy injection molding.
• Electrical insulating properties – ABS is non-conductive and shows high electrical resistivity. It does not easily ignite and is self-extinguishing.

Applications of ABS Injection Molding

Due to its all-around mechanical properties and chemical resistance, ABS injection molded parts are found in nearly every sector. ABS is commonly used to make:

• Automotive components – Wheel covers, dashboards, bumper fasciae, interior trim components
• Appliances – Refrigerator liners, microwave oven cavities, vacuum cleaner components
• Consumer goods – Toys, musical instruments, sporting goods, luggage shells
• Electronics – Computer keyboards, telephones, monitors, printers, electronic enclosures
• Medical devices – Medical tool housings, prosthetics

ABS offers an excellent balance of affordability, strength, rigidity, toughness, and manufacturability. It can be modified with ABS/PC blends or impact modifiers to further improve specific properties. ABS injection molded parts require minimal finishing and coat easily for aesthetics.

Key Differences Between Polycarbonate and ABS

While both polycarbonate and ABS are widely used in injection molding, there are some important differences between the two thermoplastics:

Strength and Impact Resistance

• Polycarbonate exhibits extremely high strength across all temperatures. It maintains glass-like clarity even on impact.
• ABS offers high impact strength, especially at room temperature. Impact resistance decreases at lower temperatures.

Heat Resistance

• Polycarbonate retains stiffness and tensile strength at temperatures exceeding 220°F.
• ABS loses stiffness and tensile strength above 185°F but offers moderate heat resistance.

Chemical Resistance

• Polycarbonate has poor chemical resistance, compared to other plastics. It dissolves in chlorinated and aromatic hydrocarbons.
• ABS offers good resistance to aqueous acids, alkalis and salt solutions. It has moderate resistance to oils, greases, alcohols and solvents.

Price

• Polycarbonate is more expensive than ABS resin. Parts also require higher molding temperatures increasing production costs.
• ABS is one of the lowest cost engineering thermoplastics. It is easy to process and mold with short cycle times.

For applications requiring optical clarity, extreme impact resistance, and higher heat resistance, polycarbonate is the better choice. ABS provides the best balance between cost and mechanical properties for more consumer-focused products not requiring transparency.

Injection Molding Process

While polycarbonate and ABS have different properties and applications, the basic injection molding process used is similar for both plastics:

1. Clamping – The two halves of the injection mold are securely clamped together to prevent leakage during injection.
2. Injection – Plastic pellets are gravity fed from a hopper into the injection barrel where they are heated to reach a molten state. A reciprocating screw piston then forces the molten plastic at high pressure into the mold cavity.
3. Cooling – Cooling channels circulate water to cool and solidify the molded parts. Polycarbonate typically requires higher melt and mold temperatures than ABS.
4. Ejection – After adequate cooling time, the mold opens and parts are ejected by ejector pins. The mold closes and the process repeats.

Precisely controlling variables like melt temperature, injection rate, pressure, and cooling time is key to producing high quality, consistent parts with fast cycle times. The mold tool is also carefully designed with draft angles and ejector pin placement to optimize flow and part ejection.

Conclusion

Polycarbonate and ABS both offer unique benefits making them highly versatile materials for injection molding. Polycarbonate provides optical clarity, extreme strength and heat resistance needed for specialty applications. ABS delivers a winning balance of strength, rigidity, impact toughness, and affordability ideal for mass-produced consumer products. With sound mold design and control of key process parameters, manufacturers can leverage polycarbonate and ABS injection molding to efficiently produce high quality plastic components.