3D Printing FDM vs Injection Molding

Can 3D Printing Replace Injection Molding?

Injection molding has been around for a while now. As a result, in the field of manufacturing, it is regarded as a go-to option. However, 3D printing is surging in popularity. The burning question is: will it eventually replace injection molding? This post will explain the two processes and the difference between them.

Table of Contents

What is 3D Printing?

There are many types of processes in 3D printing: FDM, Resin (SLA, SLS, DLP), PolyJet, MJF, etc. To draw a clearer picture in this article, we will focus on the most common process which is FDM. FDM stands for Fused Deposition Modeling. It is the most used 3d printing manufacturing technique. The concept is adding layer upon layer of material until the “structure” finishes.

First, the material is melted to be “squeezed out through a tube.” The material can melt at the glass transition temperature. Without delving into very technical details, the material is in a very “flexible state” at the glass transition temperature. It is at the border between the solid-state and the rubbery state.

Desktop Belt 3D Printer – 3DPrintMill in Action
MP4 Source: Naomi Wu, Creality

This melting occurs as the material filament extrudes through the hot nozzle. Then the material layers are deposited on the print bed. The route depends on the design of the model. With the progressive fusion of layers, the final design is completed.

So basically, FDM is building from the ground up. Like adding bricks on top of bricks to build a house. There are many types of materials available for FDM 3d printing. Popular choices include thermoplastic filaments such as ABS and PLA as well as other materials.

What is Injection Molding?

Injection molding is a process used in manufacturing for high-volume productions. It is trendy for mass production for the primary reason of repeatability. If you wanted to manufacture hundreds or thousands of identical materials, injection molding is the industry’s preferred way to go.

Injection molding is an exciting process. The first step in injection molding is pretty apparent. You make the mold. A mold is designed to match the features of the product precisely. Molds are always made from solid and durable materials such as metal or steel.

Once the mold is in place, the next step begins. The production materials put into a heated barrel, and then heating bands melt it into a flexible consistency. The material consequently becomes molten and flows. The molten material is then fed into the cavity of the mold.

Desktop Injection Molder in Action
MP4 and Photo Source: MicroMolder

Once the molten material is in the cavity of the mold, a couple of things happen. First, the molten material cools. Then it hardens as it cools. More importantly, and the point of the entire process, it takes the mold cavity shape. Of course, the shape of the mold cavity matches the precise shape and features of the products. The finished part is then ejected from the mold.

Materials commonly used for this production process include glasses, metals, plastics, and elastomers.

Difference Between 3D Printing and Injection Molding

Quality of the Parts

Regarding quality, injection molding edges it out over 3d printing as currently used. These are for a couple of reasons. First, injection molded parts are less likely to get delaminated than 3D printed parts. This is due to differences in the production details.

Injection-molded parts are made from homogenous material that cures as a single part. No layering. This is in contrast to FDM-produced materials that construct in layers. Also, 3d printing is mainly used for prototypes than finished products.

3D printed surfaces also tend to have a somewhat rougher surface than injection molded objects because 3d products are assembled in layers, which may give a ridged appearance. However, an extra smoothing finish during 3D printing helps solve the surface issues.

ABS Acetone Smoothing
ABS (Post Processing) Acetone Smoothing – Before – After
(Image: 3DWithUs)

Time

The better option time-wise depends on the intended volume of production. If you want to make only a limited number of copies, then 3D printing is the better option time-wise. The time spent building the mold and its operation is hardly justifiable for small-scale production.

3D printers are very detail-oriented. This allows for detailed creativity and adjustment. But it also takes its toll on the production time. As a result, 3D printers may take more time to produce an object than would be the case for injection molding.

3D printers are, however, more accessible to set up than injection molding equipment. This initial time saving gives 3D printers an edge where small production volumes are involved.

Injection molding is better time-wise for large-scale production. This is so especially in cases where the product is supposed to be the finished version.

Delivery

Delivery in injection molding involves melting down the material, then delivering it still in the molten state into the mold cavity. There it cools and hardens. It has less complicated steps than in 3D printing. It usually delivers the final version of the product at the end.

Delivery in 3D printing involves melting the material but not to a molten state. Then the material is added layer by layer. This is in contrast to injection molding that does not involve a layering process. The product delivered is also not usually the final version; instead, it is typically a prototype.

It is easier to make production adjustments using 3D printers. This is in contrast to injection molding, which has fixed design features of the molds. Therefore 3D printers offer more flexibility in product delivery than injection molding.

3D printing also supports the making of more complicated designs. This more so than feasible with injection molding.

Material Options

Injection molding works well with a broader range of materials, such as nylon, acrylic, polycarbonate, polyoxymethylene, polystyrene, metal, etc.

WRB Cube - Plastic Metal & Wood Composites
WRB Cube – 3D Printed Plastic Metal & Wood Composites (Photo: 3DWithUs)

3D printing also works well with a considerable range of materials. Popular materials used for 3D printing include plastics, resins, and, more recently, metals.

The material options are similar across both modes of production. However, if you are looking for creative manipulation of materials, your better option is 3D printing.

Cost

Whether 3D printing or Injection molding is a better option, cost-wise, depends on some factors. The most important one is the number of parts to be produced. If you intend to make a few copies, e.g., prototypes, 3D printing comes out top.

Injection molding is costly for low-scale operations. This is due to the expense that goes into designing the mold, including its precise cavity. However, at high volume production, e.g., 100+ parts, injection molding becomes the better option cost-wise.

3D printing cost is better for entry-level projects. The cost of acquiring a working 3D printer is nowhere near that of an injection molding setup. Also, open-source software communities and other support networks that help reduce cost are available for 3D printing.

Injection molding is exponentially expensive to operate and run for production. There is also the fact that it allows very room for trial-and-error attempts without the high cost.

Is 3D printing going to replace injection molding?

Injection molding and 3D printing can have complementary uses. 3D printing being better for prototype development and injection molding being better for mass production.

However, 3D printing is rapidly developing with techniques that try to mimic injection molding’s desirable features. As a result, it is becoming more likely that 3D printing will replace injection molding in the future.

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