Plastic is a versatile material that can create various parts, including power tool components, innovative armchair designs and prosthetic limbs. Regardless of what product you want to produce, it is essential to establish the proper manufacturing process for your parts.
When producing plastic parts, you can explore different options, including injection molding, extrusion molding, CNC machining, vacuum forming, urethane casting, 3D printing, and roto-molding. Below is a comparison between producing a CNC mold and injection molding.
What is injection molding?
Injection molding is a manufacturing process primarily used in mass production whereby the same part has to be created thousands or millions of times. The process involves injecting molten materials into a mold, where it hardens or solidifies, taking the shape of the cavity and then being ejected out of the machine.
Before that, the material, which can be plastic, glass, aluminum or any other, is fed into a barrel where it is subjected to high temperatures. The most common type of plastic that most manufacturers use for this process includes thermoplastic and thermoset resins. The molten material is fed into a mold cavity using a helical screw, where it hardens to the configuration of the cavity.
What is CNC machining?
CNC machining is a manufacturing process whereby the movement of production equipment is controlled by pre-programmed software and code control. The process involves combining different elements, including technical drawings, mechanical design, mathematics, and computer programming skills to produce various metal or plastic parts. Unlike the previous NC machines, which operators would manually control with hand wheels or levers, most CNC machines are automated.
Since the dimensions of a specific part are set into place with computer-aided design software, the process allows for consistency in parts production, which would be difficult to replicate manually.
Differences between injection molding and CNC machining
The difference between the two manufacturing processes begins in the production phase. The initial design of the two processes takes on a similar method. For the initial setup of both processes, a manufacturer takes a design to the plastic production firm to ensure it is correctly crafted so that the end product serves its purpose. Once the plastic production firm goes over the design to ensure it is perfect, a 3D design is created using CAD software (Computer-aided design). The 3D design allows the manufacturer and the production company to know what the final product will look like.
The design is a crucial process since it allows you to detect any faults or anything that needs adjustments. Having a bad design usually results in high production costs since you may re-do the entire process. For this reason, you want to ensure you get the design right before starting production. Therefore, the initial design is crucial for both plastic injection molding and CNC machining.
It is in the production that the two start to differ. With injection molding, you require first to create a mold. It is a cavity where the liquid plastic or metal is injected, allowing the molten material to take its shape after cooling or hardening. After the material has solidified, it is quickly ejected from the molding machine, and the process repeats itself. However, for CNC machining, the product design is fed into a computer and broken down into a series of commands fed into one or several tools. Unlike injection molding, which is about filling in, CNC machining uses a subtractive fabrication method. The machine receives a plastic or metal block and cuts it down until the final shape is attained.
Due to its action method, CNC machining produces more waste than injection molding. CNC machining cuts away a substantial amount of material, which can either be scrapped entirely or melted and formed into another block. However, this costs more production time and energy, making it not cost-effective. Setting up the initial mold for injection molding might take longer, but there is little to no waste once complete. The process involves filling the liquid into a mold and not cutting away a block into a particular shape.
Injection molding produces parts quicker, and it is also the best manufacturing method for high volume production. But for fewer parts, approximately less than a hundred, CNC milling is less expensive.
It is best to work with a professional when choosing the proper manufacturing process since you need to consider various variables, including the volume of products and type of material.