Injection Molded Acrylic vs. Fabricated Acrylic: What’s the difference?
May it be the display case at your local bakery or the window on your next airline flight – acrylic is everywhere. This is because an acrylic sheet’s easy formability and fabrication-friendly qualities allow it to be formed into nearly any shape, curve or sharp angle, an ideal choice for craftsmen and artists. However, it is important to note that with all different types of acrylics out there, each type has its advantages and disadvantages.
|Injection Molded Acrylic||No yellowing; some blue haze when removed from mold||Medium||Yes||Limited scratching; usually can be buffed out||$$|
|Fabricated Acrylic||Extremely clear; no yellowing or blue haze||Medium||No||Limited scratching; usually can be buffed out||$$$|
Injection Molded Manufacturing
Injection molding is the most common modern method of manufacturing acrylic parts; it is ideal for producing high volumes of the same object. In the retail display world, injection molded items are less expensive than fabricated or hand-crafted acrylic displays due to being produced in large quantities.
An injection molding machine consists of four major components. Within in the Injection Unit portion lives three: The Base, Hopper, and Barrel. The fourth being The Clamping Unit, which is home to many more essential parts.
The Base: Supports all the other components, as well as the electronics for all the control systems needed to run the machine.
The Hopper: The area where the plastic material (commonly referred to as pellets, resins, granules – see photo below) is poured into the machine before the injection molding process can begin. From the Hopper, the pellets are poured into the next major component – the Barrel.
The Barrel: This part heats the pellets into a molten state. This allows the pellets to flow through the barrel, where the screw inside the barrel injects the acrylic into molds or cavities in the Clamping Unit.
The Clamping Unit: Within the clamping unit, there are two large plates that hold the actual mold. A mold consists of two steel parts that are fastened to each of the large plates on the clamping unit. When the injection molding machine is ready to inject molten pellets into the mold or cavity, the clamping unit closes the two independent plates and allows the material to flow into the cavity to create the part. The acrylic part is then cooled into a solid. Once the acrylic piece is cool, the clamping unit simply opens the mold and the piece falls out, to be collected in a bin.
Although manufacturing high quantities provides a less expensive unit cost, it can be very expensive to accumulate the machinery and the mold itself.
Acrylic Fabrication: Cut, Bend, Glue, Polish!
Fabricating acrylic is a very clean, detailed oriented, way of manufacturing acrylic. There are virtually no defects due to manufacturing. Fabricating acrylic by hand will eliminate the relief marks and/or blue haze you would get injection molded pieces.
Cut: First, a sheet at the desired thickness must be cut by a CNC (Computer Numerical Control) machine into appropriately sized pieces to complete a project. A CNC machine is a high precision tool that’s computer-controlled and makes repeated, accurate movements cutting through the sheet of acrylic. It takes the digitized data entered and cuts the acrylic into the appropriate size.
Bend: If the cut sheet needs to be bent it is brought over to industrial strip heaters. The now cut piece will sit hovering a few inches above a heat strip for the appropriate time to become malleable. Once heated, the acrylic is bent and is left to cool usually using a jig or clamp to ensure the bends stay in place.
Glue: Now that the acrylic piece is cooled, its time to glue. Unlike injection molding, joints are bonded by hand using solvent agents that “melt” the material together. Cement-based solvents are commonly used when gluing acrylic pieces.
Polish: After the gluing process and necessary drying time, it is time for the acrylic piece to be flame polished. Flame polishing is a method of polishing, usually used for thermoplastics or glass, by exposing it to a flame or heat. By slightly melting the surface of the material, surface tension smooths the surface of the acrylic out. When done properly, flame polishing produces the clearest finish. Lastly, a scratch remover can be used as finishing touches to a perfect polish!
Although, both processes differ greatly, understanding them should make it easier to choose which will be better for your needs.