Understanding Polycarbonate and ABS Injection Molding
Polycarbonate and ABS are two of the most common plastics used in injection molding. Both offer unique benefits that make them suitable for a wide range of applications. This article provides an in-depth look at polycarbonate and ABS injection molding – from their key properties and advantages to design considerations and applications. ABS plastic is another popular material for injection molded parts and products. Learn about the ABS molding process here. Injection molding with polycarbonate and ABS allows for efficient mass production of plastic components.
An Overview of Polycarbonate Injection Molding
Polycarbonate (PC) is an incredibly versatile thermoplastic polymer. It combines high impact strength, temperature resistance, and optical clarity in one material. This unique mix of properties makes polycarbonate a popular choice for injection molded parts and products. Molding polycarbonate plastics is a common manufacturing technique for durable products. The process involves injecting polycarbonate into molds to create custom shapes. Read more about polycarbonate injection techniques.
Some of the key advantages of polycarbonate injection molding include:
- High impact strength – PC has very high impact and flexural strength. It can withstand high mechanical stresses and impacts without fracturing. This makes it suitable for items that need to endure drops, shocks or vibrations.
- Heat resistance – Polycarbonate has a high glass transition temperature of around 150°C. It can withstand temperatures up to 115°C without deforming. This heat performance allows PC to be used in applications like automotive lenses, lighting, and other products that generate heat.
- Optical clarity – Polycarbonate has high light transmission. It is crystal clear and transparent. This makes it a good choice for applications like lenses, face shields, transparent covers, and machine guards. The clarity also allows colorful molded-in components or backlighting.
- Dimensionally stable – Parts molded from polycarbonate retain their shape well. PC has low creep and deformation tendencies at high temperatures which help molded components hold their form.
- Good electrical properties – Polycarbonate is an excellent insulator and has high dielectric strength. This allows it to be used in electrical and electronic applications.
- UV/weather resistance – PC has moderate UV resistance and weatherability. It can be used outdoors or in lighting fixtures but may yellow or show reduced mechanical properties over time when exposed to UV light.
- Range of processing options – Polycarbonate can be processed on conventional injection molding machines. Film insert molding, co-injection molding, and overmolding can also be used to produce PC parts with unique properties or embedded components.
Polycarbonate’s versatility allows it to be used across a wide spectrum of industries and applications:
- Automotive – Headlamps, instrument panels, bumpers, mirror housings
- Electronics – Laptop bodies, smartphone covers, monitor frames
- Medical – Face shields, medical tools, inhalers, transparent tubes
- Construction – Lighting fixtures, glazing, roofing, sound walls
- Consumer goods – Eyeglasses, sports safety gear, transparent cases
Understanding ABS Injection Molding
ABS (acrylonitrile butadiene styrene) is another widely used engineering thermoplastic in the injection molding industry. It offers an excellent balance of strength, rigidity, durability, and ease of processing. Some of the reasons ABS is popular for injection molded parts include:
- Good impact resistance – The elastomeric properties provided by polybutadiene give ABS resistance to impacts and shocks, even at low temperatures. This makes ABS suitable for protective gear, automotive trim, sporting goods, and other applications subject to occasional impacts.
- Dimensional stability – ABS has relatively low thermal expansion and creep tendencies. It retains its molded shape well without warping or deforming under temperature fluctuations or load.
- Nice aesthetic qualities – Parts molded from ABS have a smooth, glossy look. ABS can be easily colored, painted, plated, or grained for visual appeal. The acrylonitrile component ensures good flow properties and surface finish.
- Economical – ABS is one of the lower cost engineering thermoplastics. The raw material costs less than many other comparable resins. This helps reduce part costs for high volume or large ABS components.
- Recyclable – Pre-consumer and post-industrial ABS scrap can be recycled back into raw material form. This re-grind can be reused in further ABS molding production runs.
- Range of modifications – ABS can be modified with other resins to obtain a range of custom properties. Common examples include ABS/PC for higher temperature resistance and ABS/PVC for increased rigidity.
ABS injection molded parts span many industries but some common examples include:
- Automotive – Instrument panels, trim, grilles, wheel covers, bumper fascia
- Consumer appliances – Housing, covers, door liners for appliances like refrigerators or dryers
- Electronic housings – For computers, monitors, printers, business equipment, and power tools
- Toys – Lego bricks, action figures, doll parts
- Furniture – Chair armrests and accent pieces
Design Considerations for Polycarbonate and ABS Injection Molding
When designing parts for polycarbonate or ABS injection molding, there are some important design considerations:
- Wall thickness – A general rule is to maintain uniform wall thicknesses between 2-3 mm. Thicker walls may lead to sink marks, voids, and extended cycle times. Thinner walls can warp or lead to breakage. Gradual transitions in wall thickness help the material flow smoother during molding.
- Ribs and gussets – Adding structural ribbing or gussets helps strengthen parts against deflection forces. Uniform thick ribs prevent sinks and improve durability. For ABS, rib thicknesses of 1.5-3 mm are typical. PC can have slightly thicker ribs up to 4 mm.
- Draft angles – Provide draft angles of 1-2° on vertical surfaces to ease part ejection. Polycarbonate generally requires higher draft angles than ABS due to its higher shrinkage.
- Radii and fillets – Generous internal radii reduce stress concentrations in the plastic part. External fillets also help improve part ejection. Minimum inside radii of 2 mm are recommended for both ABS and polycarbonate.
- Textures and surface effects – Molded-in texturing can enhance grip and aesthetics. PC and ABS can replicate subtle textures with steel or epoxy molds. For deeper textures, aluminum or silicone rubber molds may be required.
- Inserts and overmolds – Molded-in threaded inserts allow secure fastening. Use annealed brass or stainless steel for polycarbonate, or harder inserts for ABS. Two-shot molding produces parts with soft-touch overmolds for improved grip and feel.
- Living hinges – These thin flexible hinge sections can be molded into polycarbonate or ABS parts. Typical hinge thickness should be around 0.5 – 1 mm.
Proper mold design is also critical to produce successful ABS and polycarbonate parts with maximum efficiency and minimal issues:
- Polished surfaces – Mirror surface finishes below 0.5 Ra help give smooth glossy molded surfaces
- Venting – Adequate mold venting prevents burn marks and trapped gases
- Cooling – Uniform cooling prevents sinks, warpage, and residual stresses in the finished parts
- Ejection – Generous draft angles, radii, and ejector pin placement prevent sticking
Application Examples of Polycarbonate and ABS Injection Molding
To understand the practical uses of polycarbonate versus ABS injection molding, let’s look at some example applications and see why each material was selected:
Polycarbonate Injection Molded Application – Clear plastic face shields for COVID-19 protection
- High optical clarity allows full visibility of face
- Withstands cleaning/disinfection without damage
- Impact resistance prevents easy breakage
- Heat resistance allows brief autoclaving
ABS Injection Molded Application – White plastic Lego bricks
- Toughness and impact resistance for durability, especially for small thin-walled bricks
- Easy coloring and glossy surface finish for aesthetic appeal
- Good dimensional stability keeps bricks fitting precisely together
- Low-friction surface helps bricks separate after snapping together
- Proven longevity for cherished toys meant to last for generations
Polycarbonate Injection Molded Application – Transparent lids for 5-gallon pails
- Crystal clarity allows easily seeing pail contents
- Strength to withstand rough handling and dropped impacts
- Withstands exposure to many chemicals stored in pails
- Heat resistance to handle hot contents like soups or sanitizing solutions
ABS Injection Molded Application – Black plastic computer monitor housing
- Toughness resists cracking if knocked or dropped
- Nice glossy surface finish looks appealing for home use
- Easy to color match other black computer accessories
- Lower cost than higher performance plastics suitable for home electronics
- Ability to mold large, thin-walled housing parts
This quick comparison shows how the innate material strengths of polycarbonate and ABS make them well-suited for specialized applications across many industries.
Polycarbonate and ABS each offer unique property profiles that make them suitable for a wide range of injection molded plastic parts. Polycarbonate provides extremely high impact strength, heat resistance, and optical clarity whereas ABS offers excellent dimensional stability, aesthetics, and economy. When designing a part, consider the specific needs – from strength and chemistry resistance to visual appeal and planned production volumes. This helps determine if polycarbonate or ABS is the best material choice for maximum performance, quality, and value. With a good understanding of their respective properties and molding behaviors, both these versatile plastics can fulfill their roles in innovative injection molded designs across many fields.