Injection molding is a great manufacturing process for large production runs of finalized products. However, producing the steel molds needed for this technology can be expensive.
CNC machining is ideal for rapid prototyping as it has lower initial costs and shorter lead times. It is also compatible with a broader range of materials and tolerates better than injection molding.
Accuracy
CNC machining is an ideal method for manufacturing parts that require beautiful surface finishes and tight tolerances. It’s also an excellent option for projects with limited components needed and offers shorter lead times than injection molding, as complex molds don’t have to be made.
However, regarding volume production, CNC machining for injection molds offers advantages. It involves heating pellets of thermoplastic resin, injecting it into a steel mold to form the desired shape, and then ejecting the molded plastic part. This is a quicker and more efficient process than CNC machining, but it can add to overall lead times for production. Additionally, injection molding can only produce one product per machine cycle. If a project requires the creation of multiple versions with different features, this can become problematic and expensive as it is challenging to adapt and modify an injection-molded design. CNC machining can accommodate these changes with ease, though.
Efficiency
CNC machining is one of the fastest production processes available. It takes hours or less to go from CAD files to a finished, semi-finished product.
The shortened lead time for CNC machining makes it an attractive option for companies looking to get their products into the market sooner than other manufacturing methods. Product developers can also use the process’s speed and accuracy for rapid prototyping, design iteration, and performance testing.
Injection molding may be faster per unit than CNC machining, but it comes with a high upfront cost to create the mold. If minor changes need to be made to a product design, creating new molds can be expensive and time-consuming. Injection molding is best for larger volume production runs. However, if your needs are for smaller quantities, many can offer an on-demand service that keeps costs low using affordable aluminum molds. Learn more about this service here.
Time to Market
Using a digital program to control the cutting of your workpiece, CNC machining can reduce the time needed to go from a product design to a finished part. It can also help speed up the process of injection molding and other techniques that require custom metal tools or dies.
Injection molding requires steel molds to maintain accurate dimensions and inner contours over thousands or even millions of injection cycles. These molds can be costly, which may be prohibitive for developers of new consumer products who are still determining demand.
However, CNC machining can reduce the cost for smaller production runs because it does not rely on expensive steel or aluminum molds. In addition, CNC machining is indifferent to volume; it can be just as efficient in making one part as in making a hundred. This flexibility can be precious for non-consumer industrial products with fluctuating demand and unpredictable supply chain disruptions.
Cost
Injection molding is the dominant method of producing plastic parts. It covers everyday plastics like ABS and nylon to high-performance engineering thermoplastics with customizable shore hardness, thermal and chemical resistance, and more.
However, it is only sometimes the best choice for all products. Injection molds can be expensive, particularly when they require complex design features or tight tolerances.
The injection molding process could be better for products designed with undercuts. Part features cannot be manufactured with a simple two-part mold because the material is in the way when the mold opens or during ejection (such as the teeth of threads or the hook of snap-fit joints). Instead, these part features must be added with inserts. This can add to production costs and lead times. Fortunately, CNC machining can add these undercut features quickly and inexpensively. It is also an excellent option for minor design changes to existing injection molded parts.
