Manufacturing Processes: Learn the Basics about Injection Molding and 3D Printing

The advancement in manufacturing processes, specifically injection molding and 3D printing (additive manufacturing), is creating an opportunity for product designers to manage projects more effectively and produce higher quality parts. It is also true that with more processes to select from, there are more questions as to which process should be used and for what purpose.

Engineers are building their own roadmaps to create viable paths so they can produce their designs and deliver products to market in a timely manner. Based on what the engineer has been exposed to, their path may not always be an optimal one.

The purpose of this blog is to provide designers and engineers with a grounded approach to determining which process type should be considered and why.

Manufacturing Processes: Injection Molding and 3D Printing

No matter what new processes and technologies are introduced, there is always room for recalling fundamentals. In fact, revisiting the the basics will help you to make more informed decisions when choosing between injection molding and additive manufacturing.

Know Your Part: How the part is used can determine which manufacturing process you choose

How will the part be used? This is the most important question you can ask yourself. Whether you choose injection molding or 3D printing, understanding how the part will be used can help to mitigate risk.

Concept or Final Production

One end of the continuum demands that you are in pilot mode manufacturing multiple prototypes to determine the best design. On the other end of the continuum, the demand is for  efficient manufacturability and alignment with the intent to flawlessly go-to-market. Materials testing, form-fit-function, tolerances, design iterations, production part quantity all take on a different meaning based on which end of the continuum defines your scope.

Simple or Complex Parts

Regardless of which end of this continuum defines your part, there are many manufacturability compromises that could derail your intended design. One way to help mititage risk is to apply specific measures based on whether the part is simple or complex.

Simple Does Not Mean Easy

A simple part is designed using one type of material and requires little to no special considerations during production. Just because it is a simple part doesn’t mean it will be easy to manufcture.

Therefore, build a list of non-negotiables that the manufactgurer must follow to help achieve your design intent.

Complex Part Designs

In contrast, a complex part design may require overmolding to add a soft grip to your part. Or it could include undercuts which require special accommodations during production to assist with ejection from the mold.

Whether using plastic injection molding or 3D printing, involve your manufacturer early when producing complex parts. This will help to improve your design’s manufacturability. Also, it can help mitigate risk and eliminate unnecessary production costs.

Optimize the Product Development Cycle, Mitigate Risk when Choosing a Manufacturing Process

The process for launching a product that includes manufacturing processes like injection molding and 3D printing has been continuously developed for decades. The time, energy, and cost required to make changes increases as you progress through the process. At the very least, factors to consider when optimizing your desing for production should include time-to-market and process integration.

Time-to-market

Understand where you have the most leniency and where there is little to no compromise. Once you know your strategy, you can leverage key constituents such as the right manufacturing process and manufacturer to achieve your design intent.

For example, Microsoft develops a strategy to introduce products to market knowing that “version 1.0” will be swiftly iterated and followed by the launch of “version 1.1.”  The question you need to answer is, “What’s my project’s strategy?”.

Process Integration

It is becoming more and more clear that reliance on one manufacturing process may not always be ideal. As an example, reaching an aggressive time-to-market with a new product introduction containing complex parts requiring iterative testing as to form-fit-function is a reality for many engineers. This requires inexpensive prototype testing providing the most speed prior to moving into a mid-volume production environment.

Beginning with a 3D printed part to validate your design while you are tooling-up for mid-volume injection molding runs may be the best time-to-market solution to reduce your risk and predict your outcome. This approach also suggests that you involve yourself earlier in the design process with a manufacturer who will understand your strategy and align processes to fit.

Know the basics of the 3D printing and injection molding manufacturing processes

When designing plastic parts, think of 3D printing and injection molding as manufacturing processes that are on the same team with different roles. They each provide unique value, but can also complement each other to produce your product.

Here is an overview the 3D printing and plastic injection molding processes.

3D Printing Manufacturing Process

Consider the following 3D printing technologies and how they could apply to your project. While this is not the full comprehensive list of technologies available, it does represent the majority.

3D Printing Technologies

Stereolithography (SLA) – Available since 1989, SLA uses an ultraviolet laser to cure parts one layer at a time in photo-reactive epoxy resin. It is one of the most accurate 3D printing technologies and ideal for fine detailed, small featured parts as fine as .002” layer thickness. SLA is capable of producing large parts as well.

Fused Deposition Modeling (FDM) – FDM extrudes thermoplastics layer by layer, with a variety of thicknesses as fine as .005” per layer. FDM uses real engineering grade thermoplastics, functional parts that can withstand rigorous testing, and creates end-use production parts with a variety of color options. It has excellent tensile strength, flexibility, high melting points and chemical resistance, and UV resistance.

Selective Laser Sintering (SLS) – SLS uses engineering and high-performance, powder-based materials activated by thermal energy of a laser in the Z axis to build one layer at a time. SLS uses real thermoplastic base materials producing robust parts, end-use aerospace applications. Accurate fine features and complex geometries, and fire retardant plastic materials, UL 94 V0 are standard. Popular uses also include living hinges and high-flex snaps.

PolyJet – This technology is similar to inkjet printers where jets layer a liquid photopolymer that is instantly cured with UV lights attached to print heads. It produces fine layer high resolution parts. PolyJet is high speed, fine detail and smooth surfaces directly off the machine, and can print at 16 microns. Uses include living hinges, overhangs, and complicated geometries without needing to be assembled. There are multiple color options, multiple materials, and durometers in one print.

Injection Molding Manufacturing process

Injection molding offers a predictable and scalable process for both rapid prototyping and production. Its ability to produce parts from multiple materials with a high degree of consistency and tight tolerance makes it a proven approach to manufacture parts.

Here are a few popular plastic injection molding procesess to consider.

There are a number of best practices to consider including material selection, wall thickness, draft, runners and gates, ribs, bosses, corners and transitions.

Beyond best practices, injection molding offers several key features that can transform your design including overmolding, insert molding, and undercuts. Tolerances are ± .005” and can reach ± .001” with tooling. 

 

Injection molding processes

Overmolding  is a 2-part plastic injection molding process. It uses hard and soft plastic resins to optimize the function and structure of a part. Overmolding is often used to create a soft grip, add rubber-like grips to clips designed to grab inanimate objects, and achieve better color contrast.

Insert Molding is the process of injection molding molten thermoplastic around pieces placed in the injection molding cavity. Doing so results in a strong bond between integral pieces of your final part. Accurate mold design and construction is essential to insert molding to not only maintain part tolerances but also assure the tooling reliability.

Undercuts – An undercut is any indentation or protrusion that prohibits the ejection of a part from a mold. Undercuts can be used to carry out complex forms of molding such as the overmolding process and insert molding process. Undercuts are used to create interlocking or snap and latch features, allowing for clamshell or housing designs to come together for quick and easy assembly, or capturing holes or ports for wiring, button features or assembly, and vertical threads and barb fittings typically used in medical device products.

Conclusion

Relying on the fundamentals of manufacturing processes like 3D printing and injection molding can help to mitigate risk. Thinking through how your part will be used and what non-negotiables drive your design cycle will lead to the most successful project outcome.

Also, consider whether you are best served by a single process type, integrating processes, or integrating manufacturers to reach a viable conclusion to your project. Regardless one fact remains – thinking about manufacturability earlier in the design cycle to properly select and leverage the 3D Printing and Injection Molding processes is essential to your success.

Interested in obtaining more advice? Reach an Application Engineer at sales@xcentricmold.com, or call (586) 589-4636

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