Five Tips to Consider when Turning to Injection Molding from 3D Printing

There are currently several manufacturing techniques for manufacturing plastic parts. All over the world, injection molding machines, 3D printers, and CNC machines are cutting, extruding, and injection molding plastics into usable parts. All these machines have their unique advantages.

Ⅰ. The difference between 3D printing and injection molding

Injection molding injects liquid plastic into metal molds is the most widely used process for manufacturing plastic parts, but alternatives such as vacuum casting and 3D printing provide different advantages and provide designers and manufacturers with great flexibility. After all, different projects may require different types of machines.

However, in many cases, different technologies are used in different manufacturing stages. For example, 3D printing is usually preferred for prototyping because it is simple, easy to carry, and has a very low start-up cost. And injection molding is usually the first choice for a large number of end-use parts because it is fast and highly repeatable. 3D printing prototyping service serves the research and development stage, while injection molding is responsible for production.

Ⅱ. Five key skills for the transition from 3D printing to injection molding

What happens when a 3D printed prototype is created and needs to be produced by injection molding? Given the fundamental differences between the two manufacturing technologies, how to ensure that molded parts meet the specifications of their printed counterparts? How to plan ahead to ensure the success of prototype design and production?

1. Design injection molding as much as possible

Thinking ahead is not always easy. When the first task is to make a 3D printed prototype, the natural instinct is to create the best printed part, which means applying DFM (design for manufacturing) principles to the 3D printing process.

But if the plan is to eventually switch from 3D printing to injection molding, the 3D printed prototype must be designed to be not only printable, but also moldable.

In practice, this means following the design principles of injection molding-even in the 3D printing stage. The draft angle should be included, overhang should be avoided, and sharp corners should be rounded. In addition, since the mold cannot replicate those complex filling patterns, complex filling patterns (which can actually increase the strength and efficiency of 3D printed parts) should be abandoned to support simple ribs.

Designing injection molding from the beginning reduces the need for drastic changes before production and simplifies the transition from one process to another.

2. Use production materials to print

A useful prototype is not necessarily one that meets the highest standards in appearance and performance. On the contrary, a useful prototype is the one that best represents the end-use part, including its advantages and disadvantages.

This may mean making certain compromises, including material selection.

Injection molding is a highly flexible process that is compatible with various plastics, while 3D printing is more limited in terms of available materials. But when designing a 3D printing prototype, it is important to choose materials that match or at least imitate the materials used in the production process.

Importantly, this may not be a natural choice for successful 3D printing jobs. Some effective molding materials are actually difficult to 3D print, requiring additional time and more thorough post-processing. However, choosing representative materials will produce prototypes that more faithfully represent the final part, allowing a smoother transition to production.

3. Polishing the prototype refers to the "molded" surface treatment

For mechanical or aesthetic parts, it is important to create a prototype with the surface finish of the final part. Mechanical components may require a certain degree of friction or smoothness, so prototypes with completely different textures will not be particularly useful. (In addition, professional-looking prototypes can help marketing or promoting products.)

Fortunately, surface treatment can be applied to transform the appearance of 3D printed prototypes. Through professional polishing, using cloth or polishing wheels, the surface roughness of the printed parts can be significantly reduced, and even a mirror-like gloss can be produced.

The result is that the 3D printed part has no layer lines and rough textures, and actually looks like a molded part.

4. Beyond FDM

FDM (Fused Deposition Modeling) 3D printers are a very popular choice for prototyping. It is cheap, easy to use and compatible with a variety of plastic filaments, many companies only need to install them in the office.

Having said that, the parts produced by FDM 3D printing are quite different from the molded parts. The structural composition and engineering surface finish are also completely different, so prototypes made by FDM are not easily converted into molded parts. On the other hand, more high-quality FDM alternatives can produce more shaped parts.

5. Seek expert advice

Obviously, one of the easiest ways to ensure a smooth transition between the 3D printed prototype and the injection molded final part is to discuss the entire project with an expert.

If you plan to order a prototype through a professional service provider, be sure to let them know that the end-use part will be injection molded. It's even better to use the same service provider for prototyping and production, allowing them to use their expertise to link the two processes.