Over the last decade the manufacturing options for plastic products has evolved from simple plastic injection molding being the only option available. 3D printing has become very common, and in some cases, it is a better option to choose. The hardest part is deciding what components should be injection molded, while the rest can be 3D printed. If you’re facing this decision of which process will be better for your product, we’ll discuss each in detail.
What is Plastic Injection Molding?
Plastic resin comes in the form pellets. They are dried to a specific moisture content and then mixed with color pigments that will produce the final color based on the design specifications. Once blended, the raw pellets will be moved into a hopper that will hold and feed the pellets into the heating barrel of the molding machine. The barrel heats the pellets until they are fully molten to form a liquid resin that can be injected into the mold. The liquid resin is forced through the gate in the mold under pressure and then allowed to cool to solidify the part. The mold will lastly open to eject the cooled part and start the complete process over again.
Some Advantages of Plastic Injection Molding
- Plastic injection molding has a vast array of applications and can be done at a lower cost than competing processes and materials. It is the most common way to produce a large volume of finished plastic parts.
- An injection molding tool can last for years or millions of cycles without changing the tolerances of the parts being molded.
- There are thousands of resin options to choose from, each with characteristics to meet the requirements for appearance, strength, dimensional stability and when appropriate, self-lubricating properties.
- The surface quality and individual dimensional tolerances are stable and consistent from part to part over a long period of time, if not the entire life of the project and tooling.
- Different plastics can be insert molded and over-molded for even more design options that can enhance products functionality and visual appeal.
What Is 3D Printing?
You may have heard the term of 3D printing, and you’re probably familiar with some form of printing. Printing on paper, on clothing, or another material. Three-dimensional, or 3D printing, is a rapid prototype process involving manufacturing techniques specialized in making precise physical representations of a three dimensional design or concept. There are many types of 3D printing, one of which is with plastics. The prototypes can be used for improvements with the design, the manufacturability, and with secondary processes. It’s a quick way to generate a sample for testing or as a proof of concept before full scale production begins.
Four Common Types of Plastic 3D Printing
- Stereolithography – Stereolithography (SLA)was one of the earliest adopted processes for 3D printing or additive manufacturing for plastic. It is fast a technique for rapid prototyping, and does allow for complex internal designs features. SLA is an option for low volume production parts that require a quick turnaround prototype. They are made from a bath of photosensitive liquid that is solidified layer by layer with an Ultra-Violet light. The designed part is sectioned into layers by a computer and then these sections are created with the UV light passing through the liquid bath. Stereolithography allows for a finished part with a good quality finish and increased strength.
- Digital Light Processing – Another option using a curing resin is Digital Light Processing. It is comparable to Stereolithography (SLA) prototyping. It passes a more common light source through resin to cure it, but it needs supports and post-build curing where SLA does not. It is a faster option than SLA, and can be less expensive than SLA also. DLP prototypes hold good dimensional tolerances to the initial design with good surface finish quality.
- Fused Deposition Modeling (FDM) – There are many smaller 3D printing options on the consumer market which utilize Fused Deposition Modeling. These are the units you may find with a hobbyist making smaller replacement parts in their home. FDM melts a small plastic filament inside a printing nozzle and the machine deposits the melted plastic systematically layer-by-layer to create the finished prototype. The advantages of using FDM include the low cost, the machines are easy to use, and you can use multiple plastic types and colors in one prototype. The trade-offs are a rough surface condition and lower strength of the finished parts.
- Laminated Object Manufacturing – With Laminated Object Manufacturing, thin laminates are laid layer by layer on a build platform. A cutting device traces out the pattern for the layer and then the platform moves down by the thickness of one layer. The next lamination layer is glued on top, and the process continues until all layers are complete. The finished product should be used for designs that aren’t very complex, but LOM does not cost as much as many of the other options that require critical dimensional tolerances.
What Separates 3D Printing from Injection Molding?
Both injection molding and 3D printing can produce finished plastic parts or components to a complete assembly. The question always comes down to what separates them, and which is the better option in your unique case. That answer requires many variables to be considered before one final decision can be made.
These variables include:
- Cost for the project – 3D printing may cost more per unit produced, but there is no cost for tooling generally. Injection molding requires some form of mold tooling, whether it’s made from aluminum, steel, or another material.
- Volume required – Do you need 10 or 10,000 parts to be produced? 3D printing is a great option for a smaller quantity, and injection molding is perfect for a large run of parts.
- Design flexibility – Do you need to make adjustments to the design? 3D printing allows for adjustments to the design model between each part made. Injection molding requires significant tooling changes.
- Timing – How quickly do you need parts? 3D printing may have parts made in less than 24 hours, while you may have to wait 8 – 16 weeks for an injection molding tool to be completed.
- Scrap materials – Can you afford to lose some of the material in production? Injection molding may have scrap material from gates and runners in the injection mold, while 3D printing may have little to no scrap from producing parts.
- Uniform wall thickness – Injection molding requires a very precise range of wall thickness to ensure the mold tool will completely fill each cavity and cooling does not cause the parts to warp out of tolerance. 3D printing can vary wall thickness easily during printing operations.
Injection molding and 3D printing have distinct advantages, but choosing which option is best for your new project may be hard to decide. If you need advice on a future project, SEA-LECT Plastics is here to help. We have an elite team that designs for injection molding, rapid prototyping, and produces world-class products under the same roof. Give us a call at (425) 339-0288 or email us at info@sealectplastics.com. We look forward to offering support and advice on your next project.
Matthias Poischbeg was born and raised in Hamburg, Germany. Matt moved to Everett, Wash., after finishing his bachelor’s degree in business in 1995 to work for Sea-Dog Corporation, a manufacturer, and distributor of marine and rigging hardware established in 1923.
In 1999, Matt took over the reins at Sea-Lect Plastics Corporation, a sister company of Sea-Dog and a manufacturer of plastic injection molded products with an in-house tool & die shop. Matthias Poischbeg is also a contributor to Grit Daily.