3D Printing vs. Plastics Injection Molding

3D printing has been available for decades. There are several reasons it has only begun to gain traction. In this article, we will explore some reasons why has there been so much interest in 3D printing in recent years and how it compares with injection molding.

3D printing began as a method of creating a prototype part that could be physically observed in form, fit and sometimes even functionality before large cash investments were made in the manufacturing process. The methodology of 3D printing started as a simple layering process with either a liquid or powder polymer-based medium.

In the infancy of 3D printing the quality of the printed item commonly could not be utilized as a production part because it had inherent deficiencies. For example, the quality of the adhered layers of the part were weak, making the part susceptible to breakage. In addition, the part was also very porous and could not be used in applications where porosity was not acceptable. Thus, the market for this technology primarily remained in the pre-production hemisphere. Yet, with the advent of material suppliers creating new polymers and polymer blends, the quality of 3D printed parts has significantly improved. The improvements gained include increased bond strength and decreased porosity.

Bond strength of the layers in 3D printing has increased effectively enough so that parts can actually be used for their intended purpose as long as they meet the mechanical demands of the product.

Unfortunately, the 3D layering process creates ‘weld lines’ (an injection molding term) between layers which is essentially two layers of polymer that meet. The problem with ‘weld lines’ or ‘layers’ is that the polymer sits upon itself and has no way of physically mixing. This lack of mixing doesn’t allow the molecules to intertwine and entangle, creating a strong bond. Thus, the actual layering process has an inherent flaw.

However, additional processes have been employed in order to further strengthen the part such as the inclusion of inserts, fiber in the material, and post printing sintering. These additional processes raise the quality of the part up to a level where it can almost compete with the traditional injection molding process. Unfortunately, the combined time to 3D print a part and the implementation of the post molding process translates into a long cycle time for each part. Manufacturers try to overcome this hurdle by purchasing multiple 3D printers which all print the parts simultaneously. This is an additional expense that must have a primary benefit to provide a good ROI.

Another improvement to 3D Printing is decreased porosity. Material suppliers have been working with polymers and polymer blends which decrease porosity. While the porosity has decreased in the evolution of 3D printing, it still remains as it is a bi-product of the ‘layering’ process. A porous plastic does not have any barrier protection and will allow unwanted materials to enter and flow through the pores rendering it useless in many applications. The combination of layering (weld lines) and porosity results in a part with poor mechanical strength regardless of the quality of the material being used as the substrate.

Nevertheless, an outstanding benefit of 3D printed parts is 3D printing can create features both on and within the part. This attribute is, in most cases, impossible for the injection molding process to produce. This is where 3D printing shines. It is this characteristic that has opened the door to the world of 3D printing. That along with the ability to design something and print it immediately is a big factor. There is no waiting for a mold or tool to be built before parts can be generated.

Conversely, the injection molding process is very different from 3D printing. An injection molding machine screw thoroughly mixes the polymer and then injects the polymer into a mold where the polymer is homogenous, thus creating a part with uniform and high mechanical properties. The weakest regions of an injection molded part are high stress zones and weld line regions. Both can be combatted with the use of pre-molding simulation.

Injection molding does have limitations such as creating complex features within a part that cannot be produced due to tool design limitations. These complex features can be cored out regions of the part or internal geometry that cannot be produced in a one-part design or even a multi-part design. Sometimes the ‘lost core’ method (an older method) can be utilized in injection molding in order to create internal cavities within a part that cannot be tooled. However, tool design has come a long way and many creative techniques can now be utilized to accomplish this task. Not all tool and/or part designers may be aware of these techniques so it is important for them to consider using injection experts such as the team at Bozilla Corporation to evaluate the design.  

3D printing vs. Plastics injection molding

When comparing a 3D printed part to an injection molded part, there are definitive differences that make one process better suited than the other when deciding which process to use for manufacturing. 3D printed parts can make very complex parts but concessions will have to be understood such as material porosity, loss of mechanical properties and long cycle times. Alternatively, traditional injection molding can produce less-complicated parts with quick cycle times that have high durability and better overall properties.

Plastics injection molding optimization


However when utilizing the appropriate simulation expertise, building tools with complicated geometry can bring the injection molding process to the next level. Having a clear understanding of the limitations of each process is critical when deciding which technology to utilize on a project.

Contact Bozilla Corporation today and let’s discuss how we can successfully contribute to your project. Bozilla Corporation’s Injection molding Team has over 20 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting and Autodesk Moldflow software training. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com
About Bozilla Corporation: https://youtu.be/HIUfzwf1x90



About the Author:

Chris Czeczuga is a Plastics Engineer, Injection molding expert, Military Veteran and the President of Bozilla Corporation. He has proven success with many Fortune 500 companies throughout the injection molding industry. A graduate from UMass Lowell, he is Expert Certified with Autodesk, has 20+ years of field experience, intimate knowledge of injection molding part, tool and feed system design. Bozilla Corporation’s success is built on providing the highest level of injection molding simulation and consulting advice to businesses who have short lead times, require an efficient, cost-effective molding process, and desire to produce a correct part the first time.