3D printing VS. injection molding: technologies for success. Part 1

Review

In industries, the majority of plastic items are created through injection molding. However, with the advancement of additive technologies, it has become more cost-effective to utilize 3D printing not only in the early stages of development but also in prototype or small-scale production. The development of an apparently basic enclosure or component for a new device involves high labor costs as the moment the design of the part is finished, technological setup, tool manufacturing, and production startup begins. To avoid these costs, electronics designers, for example, may frequently try to locate a suitable purchased case, drill holes in it for mounting the board and outputting connectors, and use the device. This technique is efficient for the initial product prototypes. Later on, when the project expands, you’ll need your own enclosure.

Manufacturing technology impacts everything – from a product’s appearance to production costs. In this article, we’ll contrast the most widely used additive fusion technologies with injection molding.

Fused Deposition Modeling (FDM) and Stereolithography are the most common  3D printing techniques which allow for comparatively low equipment costs and  a wide range of materials with various characteristics. FDM technology is better suited for manufacturing enclosures since the final product will be stronger than when printed on an SLA printer. At the same time, the parts obtained by SLA and FDM methods are less durable than those by injection molding. This is due to the 3D printer’s layer-by-layer construction method. The joints of the layers are not homogeneous and when loaded, the part is more likely to break in layers. Later, we’ll discuss ways to prevent this. 

Injection molding is a technique for creating plastic parts by injecting polymer melt into a mold and then cooling it. Parts are typically produced at pressures between 80 and 140 MPa. The most precise transfer of the product's portion dimensions is made possible by high pressure. The choice of the necessary pressure depends on the polymer viscosity, mold, melt mass, etc. With a slight allowance for material shrinkage, the mold cavity is identical to the finished product. When compared to 3D printing, the mold production process is expensive, time-consuming, and lengthy. It is determined by the distinctiveness of each individual mold, the repetitive use of intricate geometric shapes for metal products, high-quality surface treatment (thermal treatment, grinding, and polishing) in the mold, and other factors.

Naturally, each technology is characterized by pros and cons. In this series of articles, we will discuss how to pick the appropriate technology. We singled out 3 core points to go through while developing the enclosure. They are:

• The problem statement; 
• The technology selection;
• Enclosure design.

This article will focus on the first 2 points 

PROBLEM STATEMENT

The problem statement stage is a pivotal part in enclosure development as it provides the scope of work, as well as aids in reducing the costs by reasoning out the most efficient technology. To state the problem, one must bear in mind the sub-stages which smooth up unevenness during the development of a physical part. They are:

• Defining enclosure functions
• Durability features
• Appearance and post-processing

Defining enclosure functions

The first and probably the most crucial stage of designing a plastic product is to formulate an answer to the questions "What do I need the enclosure for? How and who will use it? And what is required of it?" The answers to these questions will help you understand what direction to go in next. There may be more questions, of course. For example, what batch of enclosures is required at this time? How significant is the device's current design to you? How and at what temperatures will the gadget function?

Once you have answered these questions for yourself, try to draw the enclosure yourself, on a sheet of paper. Consider what it should be, what design standards you want to adhere to. Start with the dimensions of the case and then try to draw its individual elements, such as buttons, screen, ports, outputs, and so on.

Durability features

In comparison to similar products manufactured with an FDM printer, injection molded products are more durable. This is caused by the layered structure of the printed product. Basically, the 3D printed product disintegrates into layers. This is due to the fact that the autogeneity of the layers of the printed product does not give the same strength as the cast product. To minimize the difference in durability, the product should be printed so that the layers are parallel to the load and work in tension. Another disadvantage of 3D printing is that it is very difficult to perform strength calculations and modeling. The material's heterogeneity is to blame for this. Therefore, don't rely on simulations to ensure the strength of your enclosures if you are making a small series. To verify that your SLA or FDM enclosure can resist a drop or other excessive load that may occur during use, it is preferable to conduct field tests. Here is a table comparing ABS plastic's durability metrics, one of the most widely used thermoplastics for printing and molding.

The layers of the 3D-printed samples were stacked at a 45-degree angle to the direction of load. The performance of the molded ABS samples varies because they are unique from one another. The majority of the time, samples are produced in small batches that do not adhere to all technological requirements. For instance, the first and last samples have different characteristics as the temperature of the mold increases with each sample produced. By modifying the machinery and technological procedure before putting the item into production, it is possible to think of the durability of the molded ABS plastic as being equivalent to the range's upper bounds.

Appearance and post-processing

Most of the time, post-processing is not necessary for injection molded items as they appear uniform and homogeneous. Post processing may be necessary when wood needs to be metalized or dyed, or when polymers require UV protection.

Post-processing is usually necessary with additive manufacturing to give the result a pleasing appearance. When printing, support structures are used, which must be taken down after printing is finished. Once removed, they leave behind minor inconsistencies that need to be mechanically eliminated.

To enhance the surface quality, coatings are used. They are thin layers of material of a different nature or structure that provide unique characteristics to the surface.Coatings can be ornamental, protective and chemically resistant once. The most common reason for applying paint and lacquer coatings is to offer the product’s surface decorative or protective-decorative features. The steps involved in applying paintwork often include surface preparation, priming, puttying, dying, varnishing, polishing, and drying. Take a look at the way we dyed Smart Cup and AirZen prototypes. Although labor-intensive, it would be ideal for marketing campaigns.

Batch cost

The use of additive technologies is profitable for no more than 100 pieces. While the price of an injection-molded enclosure will be in the range of $1 to $2, the price of a similar 3D-printed enclosure can range from $60 to $90, depending on post-processing. The production and development of the mold account for a sizable portion of the cost of injection molding. Purchasing a long-lasting mold may be more expensive than utilizing a 3D printer if the product has a short lifecycle or a tiny market. Also keep in mind that a mold cannot be changed once it has been made. 3D printing is a preferable choice if your product is still in the testing and initial prototyping stages and has not undergone a final design decision.

When launching the final product, you need to consider the volume of a batch. If you manufacture 50 – 200 items annually, then 3D printing is the best option. As manufacturing quantities rise, you might consider transitioning to injection molding. Entry-level injection molds cost around $10,000. In a batch of 200 pieces every year, at a cost of $50 – $60 per enclosure manufactured on a 3D printer, we would spend $12,000 in total. Since the cost of the enclosure made via injection molding will be between 3 and 5 dollars, we should start thinking about a mold at this time. It will be possible to recuperate the cost of the tooling in a year with improved production volume.  

Conclusion

Thus, EnCata’s team assists the customer in establishing the goals for the plastic product during the initial stages of part development. This is required to modify the product design for the particular technological process. Additionally, we always take into consideration the cost of the preproduction process because purchasing injection molding tooling will prove to be a costly fad if your batch size is under 100 pieces. The part's shape plays a crucial role as well. In the following section of the article, we will discuss the intricacies of designing using the technologies mentioned.