Industrial manufacturing is an extremely demanding process and requires highly durable machinery. One way to make sure this machinery continues to function properly is by implementing industrial plastic parts. These parts are commonly used because they are durable, temperature-resistant, chemical-resistant, and less prone to corrosion than their metal counterparts. Here, we will explore how industrial plastic parts are made and what polymers are generally used.
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In order to machine industrial plastic parts, CNC machining is generally used. CNC (Computer Numerical Control) machining uses pre-programmed computer software to guide the machines and tooling during the production process. Since the production is run by a computer system, the CNC machining processes are highly precise, allowing for the creation of intricate parts and products with little to no error and easy repeatability. Numerous CNC machining processes can be used to create industrial plastic parts.
There are many polymers used to create industrial plastic parts. Each of these polymers reduces the weight of the machines and does not corrode like metal parts do, allowing the machine to run longer without the need for costly replacements and repairs.
Picking an appropriate manufacturing method for a new product is often easier said than done. CNC machining and plastic injection molding are both commonly used and cost-effective ways to produce parts. While both methods are similar in those regards, they are completely different fabrication methods. CNC machining is a subtractive manufacturing process that uses metal cutters to remove material from a workpiece to create the final part shape. Plastic injection molding forces liquid plastic to conform to the shape of a mold to make the finished part. Three major differences exist between the two methods. These are materials that can be used, the volume of production that can be attained, and part dimensional tolerances and precision.
These differences lead to significantly different costs for the two processes. In this article, we discuss everything there is to know about CNC machining vs. plastic injection molding, including the advantages and disadvantages of each, and process alternatives to both.
CNC machining is a subtractive manufacturing process that uses machines like mills, lathes, drill presses, and saws, to make highly precise parts. Computer-Aided Design (CAD) data is developed during the product design phase. This CAD data is then used as the basis for programming and optimizing the machine tool sequences and paths. The material is then processed using cutters, such as end mills and drill bits to create the parts. Auxiliary machinery, including honing, hobbing, or grinding machines, may also be needed to complete parts to customer specifications.
While manual machining of parts has existed since BC, CNC machining wasn’t developed until the mid-s. The first control mechanisms that eventually were used on CNC machines were used to punch code tapes as a way of communication. In , the first experimental 3-axis milling machine was created to make helicopter blades and stiffer skin for various aircraft. In the s, CAD and CAM software began to be integrated into CNC systems. Now, CNC machining is one of the most widely used manufacturing methods in the world. It is used to make products for several industries, from automotive to agriculture. CNC machining is often preferred to injection molding due to the ability to easily accommodate product design changes, its ability to produce tight tolerance parts, and the possibility of using several different materials.
To learn more, see our guide on What is CNC Machining.
Listed below are some advantages of CNC machining over injection molding:
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Listed below are the disadvantages of CNC machining vs. injection molding:
Plastic injection molding is a manufacturing method that uses an injection molding machine (IMM). These machines contain components such as injection screws, injection barrels, and fabricated molds. Plastic pellets are fed into the barrel and are melted through the rotation of the screw and heater bands. The molten plastic is injected into the mold and formed into the geometry of the part. The IMM holds pressure on the mold until products have been properly formed and cooled. The completed parts are ejected and the cycle restarts.
Brothers Isaiah and John Hyatt developed injection molding in and used it to mold hair combs, buttons, and other small items. In the 150 years since that first machine, injection molding has blossomed into a multi-billion dollar global industry. Injection molding is considered a more cost-effective and efficient way to make plastic parts than CNC machining.
For more information, see our guide on what is plastic injection molding.
With CNC machining, tighter-tolerance parts can be made from a wider range of materials than with injection molding. However, injection molding can produce parts at a much more rapid pace without the need for post-processing - making it ideal for high-volume production. While injection molding is ideal for higher volumes, a large upfront investment must be made to fabricate an injection mold. However, injection molds will pay for themselves once a sufficient amount of parts are produced and sold.
Tooling costs for CNC machining are significantly less than for injection molding. CNC machining costs are associated with the fabrication of fixtures and jigs and the procurement of raw materials and tools. Molds for injection molding can cost a few thousand dollars for single-cavity and low-cavitation molds and up to hundreds of thousand dollars for multiple-cavity molds. An injection mold will pay for itself when its cost is spread over a sufficiently high production volume. Assuming you have the necessary machinery to make parts and only need to make arrangements for tooling like molds, fixtures, and jigs, upfront costs on CNC machining are lower.
Both CNC machining and injection molding are notable for their ability to rapidly produce parts. For small-volume runs, CNC machining is often preferred. Injection molding is preferred for larger runs because multiple-cavity molds can rapidly produce parts and reduce per-piece cost. Taking into account the lead time for mold production, it takes longer to start series production using injection molding than using CNC machining. Consider using CNC machining for small production runs and injection molding for large runs.
Injection molding can both produce more parts per base machine and more parts per dollar invested compared to CNC machining. Molds used in injection molding can have multiple cavities - from one cavity to several hundred. Hence, injection molding can quickly produce large numbers of parts. In CNC machining, parts are generally made one by one. While CNC machining is fast at producing parts, injection molding is even faster.
A broader range of materials can be used in CNC machining processes than in injection molding. CNC machining is capable of producing parts from certain plastics, but also from metals, like aluminum and steel. Many thermoplastics, thermosets, and elastomers are too soft to be CNC machined. However, they can easily be fabricated into parts using injection molding machines.
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