The process of injection molding manufactures large quantities of parts. It is mainly used in situations where thousands or even millions of the same parts are produced at the same time. One major advantage of using injection molding is able to produce in large quantities. After paying the initial cost, the process’s per-unit prices will be very low. The prices are reduced even more as higher quantities of parts are produced. The following are some of the other major advantages that the injection molding process offers:
Is Repeatable and Low Scraps are Produced
When compared to CNC machining and other similar manufacturing processes, scraps are produced at a very low rate with plastic injection molding. CNC is well-known to cut high percentages off of the original plastic block. Injection molding, however, also cannot be compared to processes such as 3D printing that has even lower amounts of scraps. Plastic injection molding services produce waste from four main areas: the runner system, ejector pins, gate locations, and the sprue. The part called the sprue takes the molten plastic and guides it from the injection molding machine’s spout to the injection molding tool, while the runner is comprised of channels that join the sprue.
Their purpose is guiding the molten plastic into the cavities inside of the plastic injection molding tool. The gate comes after the runners that lead into the party cavity directly. Once the injection process is complete, solid pieces are left along the gates, runners, and sprue by the cooling plastic, if it is not contained properly. Once the first part is produced, the second and others that follow are nearly identical in part size and shape. This is a great characteristic, particularly when attempting to keep up with high volume parts production and brand consistency.
What Are the Disadvantages of Injection Molding?
This process tends to a very high upfront cost due to the design, testing, and tooling requirements. Once the parts look the same as the first one that is produced, then you will need to ensure that the first part is right when you are producing them in high volumes. If not, then the following process will be very messy and include thousands of flawed parts. In order to get the first part just right, you will need to do the following:
– Designing and prototyping the actual part according to specifications. A 3D printer is first used to design the prototype using ABS plastic and various materials.
-Designing an injection tool to be used in the initial production process – It is necessary to generate 300 to 1,000 prototypes using the production materials.
– Refining all of the injection molding tool’s surface finish before mass production begins.
The injection molding process requires a wall thickness that is uniform. For example, cutting a cross-section would show a 2-3mm wall thickness. That prevents uneven colling and the deformation of strength, wall thickness, and part shapes. Some potentially negative aspects associated with injection molding include the following:
Long lead times and high tooling costs
Tooling is a major process and only one phase in the entire molding process. The long time and high cost that is required due to first needing to having to produce a prototype part prior to producing the actual molded part. Once the prototype is produced and perfected, then you will need to produce the perfect mold tool to produce duplicates of the parts with zero errors in high volumes. As you can see now, both money and time are required to getting the prototype right and a molding tool with all of the fine details needed for mass production.
Harder to make changes
Typically these tools are made out of steel, so it can be a big hassle to make changes. In situations where plastic needs to be added to a tool, larger cavities can always be made by cutting the aluminum or steel away depending on what the tool is made out of. If the plastic needs to be taken out of the metal, you will need to reduce the size of the mold cavity by metal being added to it.
Material Suited for Injection Molding
One of the most critical factors that need to be considered in the injection molding process is the kinds of materials that are used. Those plastic materials have a direct effect on the molding manufacturing process and also performance. In order to select the right materials, its environment and function need to be considered. Other factors that need to be considered in thermoplastic include cost, color, durability, flexibility, and material strength. The following is a list of the materials that are most commonly used:
Nylon
Due to nylon’s high melting temperature and toughness, it is mainly used for producing plastic products such as bearings and gears. It is most well-known for resisting wear and tear and chemicals and is also cost-effective.
Acrylic
The material is used for producing transparent parts such as walls, window panes, and lighting equipment. Due to acrylic’s tensile strength, it is used frequently in place of glass. It is scratch-resistant as well. One of its most common uses is creating food containers. That is due to its odorless and tasteless nature which makes it ideal for food storage and preparation.
Polyoxymethylene
This material is often used to make parts that would be made out of metal and is used for producing hardened plastic parts. Polyoxymethylene’s chemical compound makes it very tough, rigid, and strong. It is commonly used to make ball bearings, gears, and knife handles.
Conclusion
Whether a material is suitable or not to use in an injection molding machine will depend on what is being produced. The materials that are used need to meet all of the property requirements and also be resistant to the application’s environment. For example, parts that are frequently used in moving mechanisms or the kitchen need to use Polyoxymethylene due to clamping and extreme heat. Places in need of translucent walls or lighting such as public offices need the material to be acrylic for construction purposes. Many other things need to be considered throughout the injection molding process which depends on what the purpose is of the parts that are being produced.
