Acrylic is a versatile thermoplastic material used for various applications due to its optical clarity, UV resistance, lightweight yet durable properties and ease of fabrication. But many wonder – can acrylic be injection molded?
The short answer is yes. Acrylic, also known as PMMA (polymethyl methacrylate), can absolutely be injection molded to create high quality parts and products.
In this complete guide, as a professional plastic injection molding manufacturer, we’ll cover everything you need to know about acrylic injection molding, including:
- What is acrylic and its properties
- The benefits of acrylic injection molding
- acrylic injection molding process
- Design considerations and specifications
- Applications
So if you’re exploring using acrylic in your injection molded parts or products, read on.
What is Acrylic Plastic?
Acrylic plastic, also referred to as acrylic or PMMA, is a clear thermoplastic material that resembles glass but is less prone to shattering.
With good weatherability, optical clarity and lightweight yet durable properties, acrylic serves as an excellent glass substitute in products where impact resistance and transparency are beneficial but weight is a concern.
Acrylic offers manufacturers advantages in injection molding including:
- Optical clarity – acrylic can achieve light transmission over 90%
- Dimensional stability
- High rigidity and tensile strength
- Weather and UV light resistance
- Low moisture absorption rate
- Ease of fabrication including thermoforming
These well-balanced performance attributes make acrylic a versatile option suitable for injection molding a wide range of parts.
Benefits of Acrylic Injection Molding
There are several key advantages to using acrylic plastic in injection molded components and products:
Optical Clarity
With light transmission exceeding 92%, acrylic offers exceptional optical clarity making it useful in applications like lenses, light fixtures, and transparent enclosures. The material retains this clarity over time without yellowing.
Lightweight
Weighing half as much as glass, acrylic’s lower density allows substantial weight savings which is beneficial in transportation applications. Less material is also required to produce acrylic parts.
Durability
Acrylic combines high rigidity and tensile strength with good impact resistance allowing acrylic injection molded parts to withstand rugged use. Exposure to sunlight and moisture has minimal effect on mechanical performance.
Dimensional Stability
The dimensional stability of acrylic is much less affected by moisture absorption compared to other plastics. Parts maintain accuracy and shape over a wide temperature range as well.
Ease of Fabrication
In addition to injection molding, acrylic sheeting can be easily machined and thermoformed providing additional manufacturing flexibility at minimal expense. The moldability of acrylic also facilitates intricate part geometries.
Economical Production
Favorable flow properties permit acrylic to be processed on conventional injection molding equipment without excessive pressure requirements. Short cycle times coupled with lower material usage compared to metals or glass lead to economical part production.
The well-balanced performance properties of acrylic coupled with design freedom in injection molding make it an economical, versatile material suitable for producing durable and functional components.
Can Acrylic be Injection Molded? Acrylic Injection Molding Process
Yes, acrylic can absolutely be injection molded. The acrylic injection molding process involves heating acrylic plastic until it liquefies and injecting it under pressure into a steel mold. Here are the basic steps:
1. Dry the Acrylic Resin
Like other amorphous plastics, acrylic resin absorbs ambient moisture. To avoid defects caused by moisture evaporating into steam during melting, acrylic pellets must first be thoroughly dried.
A dehumidifying hopper dryer is typically used to reduce moisture content below 0.02% prior to molding. Insufficient drying can cause small bubbles in parts compromising clarity.
2. Melt & Inject Acrylic
Next, plastic pellets move from the hopper into the injection molding barrel to be melted by heat and shearing forces. A reciprocating screw feeds the now molten plastic forward where an injection ram forces it at high pressure into the mold cavity.
Peak injection pressures typically range from 12,000-18,000 psi depending on part size and complexity. Holding pressure is maintained to compensate for material shrinkage as the acrylic solidifies.
3. Cool Acrylic Under Pressure
While constrained in the mold, cooling fluid circulates through channels to solidify the acrylic part from the outside-in. This is necessary to establish sufficient rigidity so the part will retain its shape once ejected.
Sufficient pack & hold times of 3-8 seconds allow inner material to cool properly reducing residual stresses in thicker sections that might otherwise warp upon ejection.
4. Open Mold & Eject Part
As soon as the acrylic part has adequately hardened, the two mold halves separate allowing ejector pins to push the finished component from the cavity. Some minor flash trimming along mold parting lines may be required to finish the part.
The mold then closes and the injection molding process repeats continually producing acrylic parts of consistent quality with tight dimensional tolerances.
Acrylic Injection Molding Design Considerations
Several factors need consideration when designing parts intended for acrylic injection molding:
Uniform Wall Thickness
As with other amorphous plastics, keeping wall thickness uniform optimizes flow and cooling. Abrupt changes in thickness often create non-fill or warp in parts. Diffuser ribs help transition areas needing heavier cross-sections.
Generous Radii & Draft Angles
Sharp corners act as stress concentrators leading to cracking. Maintaining radii >20% of nominal wall thickness enhances durability. Draft angles of 1-2° also aid part ejection.
Gate Location
Gate position influences orientation of molecular chains frozen-in during filling. Locating gates to minimize visible weld lines optimizes clarity and mechanical performance.
Ribs & Gussets
Supplementary ribs or gussets placed in less visible regions reinforce large flat areas prone to warpage while minimizing sink marks. This strengthens parts without compromising aesthetics.
Proactive design for molding is essential to realize optimal performance and appearance in acrylic parts. Experienced molders can advise part geometry and gate location recommendations.
Acrylic Injection Molding Specifications
When preparing to produce injection molded acrylic components, adhering to several processing specifications is vital:
- Melt Temp – Acrylic should be processed within the range of 420-500°F (215-260°C) with tighter control near the low end. Overheating causes burning.
- Mold Temp – Steel mold surface temperature ideally around 185-200°F (85-93°C) produces best results. Cooler molds increase cycle times while warmer molds reduce clarity.
- Injection Pressure – Given its higher viscosity, fast injection rates between 15,000-30,000 psi help acrylic completely fill thin ribs and complex geometries.
- Back Pressure – 50-100 psi assists mixing and minimizes trapped gases that could form bubbles in parts.
With processing knowledge acquired from experience, acrylic injection molding easily produces transparent parts completely free of visual defects.
Acrylic Injection Molding Applications
The optical clarity, rigidity and durability possible with injected acrylic parts lends itself well to products where visibility or impact resistance are important.
Typical applications of acrylic injection molding include:
- Lenses, globes, light covers
- Instrument cluster lenses
- Medical equipment guards
- Transparent machine guards
- Skylights, sunroofs
- Display cases
- Decorative accessories
In markets like automotive and medical, acrylic injection molding offers a cost-effective method to manufacture transparent components able to withstand harsh environmental conditions across long service lives.
The versatility of acrylic plastic makes it a valued material for injection molding innovative new products as well.
Can Acrylic be Injection Molded? Absolutely Yes.
In summary, acrylic or PMMA plastic is an exceptional material that can absolutely be injection molded to create rigid, crystal clear parts even with complex shapes.
Acrylic combines optical transparency and durability in injection molded applications like instrument cluster lenses, transparent machine guards and skylights. It serves as an economical alternative to glass, polycarbonate or other clear plastics.
With proper adhesion to processing guidelines and mold design considerations, acrylic injection molding is an easily mastered, value-creating manufacturing process. Replacing higher cost materials with injected acrylic parts frequently produces welcome cost savings as well.
So in answer to the initial question “Can acrylic be injection molded?” – acrylic injection molding readily creates flawless, resilient transparent components able to fulfill demanding application requirements across prolonged service lives.