Injection molded parts are among the most common you’ll find in your day-to-day life, and there are plenty of reasons why they’re so popular. First of all, they’re cheap to produce due to their high volume requirements, and they’re also both strong and flexible.
Because these parts are molded as opposed to machined, injection molded parts require minimal material and few individual components, making them a cost-effective option that can still be used in a variety of applications.
Processes Include in Plastic Parts Manufacturing!
To learn more about injection molded parts in particular and manufacturing plastics in general, keep reading!
Raw Material Processing
The raw material is usually purchased in bulk and then prepared before being added to the molding machine. The material is typically processed in an extruder, which may be heated or cooled, depending on what type of plastic is being used.
The molten plastic is fed into a large barrel with a screw at its base that pushes it through small holes where it’s forced into a large vat known as a hopper. This process can produce long strands of a material called polymer strands. These strands are chopped up and moved through a series of rollers until they reach consistent thicknesses; thicker areas get wider rollers, thinner areas narrower ones.
After making their way through these rollers, polymer strands are wound onto spools and can be stored for future use. Later, when designing your part you should select from two different types of materials: thermoplastics (materials that can repeatedly soften and return to their original shape) or thermosets (materials like epoxy and polyurethane resin).
Once ready to create your injection molded part, you’ll need to choose between two different manufacturing methods: direct or indirect molding.
Mixing – Continuous and Batch
Once your plastic is melted and mixed, it is ready to be injected into an injection molding machine. For our purposes, we will focus on continuous mixers. Two key components determine quality control: gate location and wall thickness. It is important that these parts do not have small or large gates as well as that their walls meet specific guidelines; you can see a visual representation of gate location and wall thickness here. Having strong materials: Materials used in injection molded parts need to be strong enough to withstand wear and tear over time.
Compression Molding
From Raw Material to Functional Part In a compression molding process, plastic pellets are heated until they melt and then injected into a closed steel mold cavity. Once cooled and solidified, these injection molded parts can be removed from their molds to complete their manufacturing process.
The advantage of using compression molding is that it can create large volumes of parts at once; however, it requires expensive tools. Moreover, compressed-molded parts often have seams in which pieces were fused together during cooling. These seams must be ground or sanded down for smoothness and aesthetics.
For example, ice cube trays utilize a compression molding process to create identical trays that interlock when frozen. Another application might include medical equipment such as kidney jars.
Materials like polycarbonate resin (PCR) are preferred over acrylonitrile butadiene styrene (ABS) because PCR has better heat resistance than ABS allowing containers holding boiling liquids to withstand high temperatures without warping.
Blow Molding
In blow molding, plastic pellets are melted in a large extruder and forced into a heated, shaped mold. The empty mold is placed on top of a container (blow mold) filled with cold air. As air from the mold is forced into the blow-molded part, it cools quickly and shrinks to create a tight fit between your two products.
Blow-molded items are usually made from low-density polyethylene or LDPE. Common containers include bottles and jugs used for water and other liquids. Commonly blow-molded objects include toys, caps, bags, lids, wheels, and games like Beanie Babies.
When an item becomes too dirty or worn to use any longer you can always recycle these items instead of throwing them away because they are made out of recyclable material such as plastic. Check out your local recycling center for more information on recycling plastics!
Extrusion Blow Molding (EBM)
Extrusion blow molding, or EBM, is a plastic manufacturing process where plastic is heated up and extruded into a large tube. This tube is usually hollow and has an inner pressure, then cooled to create a semi-solid piece of plastic. The semi-solid tube is formed into whatever shape you need via extrusion blow molding and then it’s trimmed, painted, texturized, or whatever you like.
All sorts of materials can be used for EBM including polypropylene, polyethylene terephthalate (PET), polystyrene, polycarbonate, and glass-filled polycarbonate. How do you make any one of these items? It depends on what material your project needs in order to be successful.
Injection Blow Molding (IBM)
First, plastic pellets are mixed with a resin and heated to a molten state. The melted plastic is then loaded into a hot barrel (sometimes called a hopper) that’s inside an injection molding machine. The plastic is injected under high pressure into the mold cavity, where it cools and solidifies after moving through an injection tunnel.
This can be done multiple times at once on multi-cavity molds, which are more common for larger parts like car body panels and computer cases. The molded part is ejected from its mold and placed onto a conveyor belt.
When all of the finished products have been molded, they’re collected in a bin before being sent off to another processor packaged for shipping. Some IBM processes even feature equipment capable of producing hundreds of thousands of plastic parts per hour!
Other Processes
Several plastic manufacturing processes can be used to create plastic parts. Molding is one of those processes, and it’s arguably one of the more popular choices among manufacturers and consumers alike. There are two main types of molding – injection molding and extrusion. Both manufacturing processes will be detailed here.
Before we get into specific details about how these molding methods work, it’s important that you understand what a mold is and how it operates.
So let’s talk about molds first. What Is a Mold? A metal or polymer part is molded by filling a mold with heated liquid plastic (also known as resin) over an object called a pattern; that molded object then cools and hardens into shape.
The exact process involved in creating a molded object depends on the type of mold chosen by a manufacturer. Molds can be open or closed, and they are made from different materials depending on several factors. The two primary considerations when choosing what material to use for your mold are speed and temperature sensitivity.
