Considerations for Manufacturing Plastic Prototypes

Understanding whether CNC machining, 3D printing, or injection molding is the most suitable method for your plastic prototype manufacturing.

Planning and producing multiple iterations of any product is the most effective way to reduce overall project costs. It also helps mitigate long-term risks and provides optimized part designs wherever possible. For instance, medical device manufacturers must assess the ergonomics and functionality of their surgical instruments before presenting them to surgeons. Commercial drone designers may conduct dozens of test flights in wind tunnels to determine the airworthiness of their aircraft, while robot manufacturers wish to understand the efficiency of their latest robot designs in executing specified tasks. Each of these activities requires a prototype (or more likely, multiple prototypes). This is particularly true for plastic parts, as what better way to avoid costly design errors before finalizing product design than by using prototypes? Manufacturers from various industries often evaluate their latest metal creations through 3D printing, machining, or plastic molding. This is the most effective way to reach the finish line.

Within the product development process, plastic prototypes have different use cases:

Conceptual Prototype: Typically, the first batch of parts produced during the product lifecycle. It is intended to showcase the visual appearance of the part or product. At this stage, factors such as material strength and surface finish quality are less of a concern. 3D printing technologies such as SLA and FDM are typical manufacturing methods for conceptual prototypes.

Functional Prototype: Functional prototypes allow the design team to test the shape and fit of the part. At this stage, accurately representing the material properties of the final part may be particularly valuable, hence CNC machining or 3D printing technologies such as SLS or MJF are often used.

What are the manufacturing options for plastic prototypes?

Fortunately, there are several options available for prototyping plastic parts. Each has its own unique advantages and limitations, which may determine which one is most suitable for your products.

3D Printing:

Benefits of 3D printing:

More cost-effective: Because there are no fixed or cutting tools for 3D printing, part costs are typically lower. This includes only raw materials, machine time, and any necessary post-processing.

Rapid delivery cycles and quick iteration: Similar to injection molding, eliminating tools and traditional "setups" means fast turnaround times. Additionally, many printers have enough build volume for designers to generate multiple iterations within the same build.

Fewer design constraints: The 3D printing community extensively discusses its "infinite design freedom." While somewhat exaggerated, the fact remains that many manufacturers use it to produce complex components in a single print, reducing part count and simplifying the supply chain. As mentioned earlier, ensuring designs can transition to injection molding for large-scale production is crucial if this is the ultimate goal.

3D Printing Challenges:

Mechanical performance: The resins and powders used in 3D printing machines are "like" materials. They approximate counterparts of molding and machining, although many are suitable for final use, they are not direct substitutes.

Surface finish: Due to the layer-by-layer construction process, almost all 3D printed parts will exhibit some degree of "stepped" texture. Using polishing or sanding to remove these imperfections is a popular choice, but it adds to the project's time and cost.

Limited color choices: Typically, 3D printing offers parts in white, black, gray, or translucent. We're happy to dye or paint them post-completion, but this is an additional post-processing step.

CNC Machining:

Due to ZONZE's continuous focus on rapid turnover, we have developed standardized toolsets that allow us to deliver customized machined parts within one to two days. The delivery time frame is similar to 3D printing, and the prices won't be significantly higher (depending on the geometry of the parts, quantity, and other factors). However, there are still some differences between machined parts and those manufactured through 3D printing:

Benefits of CNC Machining:

Final use materials: Sometimes it's crucial to use actual production materials for prototyping. Perhaps the parts will undergo functional testing and validation, or the client wants to see and touch prototypes that closely resemble the final design as possible.

Production quantity: Generally, as the quantity increases, the cost-effectiveness of 3D printing decreases. With the emergence of new technologies like PolyJet, this decades-long status quo is starting to change, but in terms of manufacturing speed, machining almost always emerges as the winner, with installation costs easier to amortize.

Rapid delivery cycles and quick iteration: CNC machining is as fast as 3D printing, and in some cases, even faster. Parts can turn around as quickly as within one working day.

Challenges of CNC Machining:

Part geometry: As mentioned earlier, 3D printing reigns supreme in complexity. Machining shops face features such as undercuts unreachable by cutting tools, thin walls that may induce vibrations, extreme aspect ratios in drilled holes, and other part characteristics that are no big deal for 3D printers.

Multi-part assemblies: Machined parts typically integrate into a single assembly, and connecting these components often means bolting or welding them together, increasing costs. If what would typically be a multi-part assembly can be 3D printed as a single piece, the entire project would achieve significant victories. However, similarly, as long as you ensure that with increasing quantities, you can economically produce 3D printed parts.

Injection Moulding for Plastic Prototyping

The terms "plastic injection molds" and "prototype design" have long been at odds with each other. This is because the mass production tools required for manufacturing most plastic parts are both expensive and require months of development time. At ZONZE, we've changed this paradigm with rapid aluminum machining molds, which can produce hundreds of prototype parts, typically delivered in about a week.

There's no need to list a long string of pros and cons here because this decision tree has only one or two branches. If you need a hundred or more injection molded prototypes for functional testing, rapid machining tools can provide customers with parts made from real materials, at very high speed, and with almost the same tolerances and surface finishes as production tools. Rapid turnaround molds can also serve as bridge tools until production molds are completed or for trial runs to test molded part designs.

It's important to note that this takes time. Time for designing the molds, time for machining, testing, and final approval. It's still much faster and significantly less expensive than the "steel molds" described earlier, but costs may be prohibitive when 3D printing or machining can address immediate needs. As mentioned before, there are many factors to consider, so give us a call or send your part design to our contact email (info@zonzescm.com) for an evaluation of options and to receive Design for Manufacturability (DFM) feedback.