3D Printing vs. Injection Molding

One of the biggest developing technologies emerging in the modern era is 3D printing, an additive form of manufacturing that seeks to alter the way companies go about producing new products and possibly even manufacturing itself. As like any other new technology, as it develops, the overall usage price drops to a point of commercial viability. Today, 3D printing has found itself a market where it can be used appropriately to facilitate prototyping and even reduce lead times. It has the potential to accelerate production and improve productivity. However, the question remains as to whether this technology can replace current conventional manufacturing methods. To explore this idea, 3D printing will be compared to a conventional manufacturing method, injection molding.

Injection Molding and 3D Printing in Manufacturing

Injection Molding plays a big role in producing parts in large volumes and moving a product into mass production. This process has been a staple in the industry for its ability to reduce waste when compared to CNC machining – a process where a block of metal is cut away to create a product. When running an injection molding process, the only waste obtained would be from the runner, sprue, and gates. If a company uses a slightly more expensive thermoplastic material, then this waste can be remelted and reused for other injection molds. Overall, by reusing and reducing waste, this can serve to reduce overall material costs.

However, it must be understood that the mold presents itself as a high entry cost to this manufacturing method. Creating the mold can range anywhere in between $1,000 to an excess of $80,000, depending on the complexity of the model. Before any kind of injection molding can be done, the mold must be manufactured. This alone can lead to long lead times and could delay company productivity until the model can be made. However, this process becomes more economically efficient as production is increased. As economies of scale take its effect, this process gradually reduces the cost per part manufactured. This makes this manufacturing methods ideal for large production companies and for those can afford to pay the high barrier to entry.

The benefits from economies of scale can be amplified for more complex products. With injection molding, a more complex part is coupled with a more complex mold, this of course, causes the cost to rise. Meanwhile, 3D printing has no added costs associated with increasing complexity but lacks the benefit of cost reduction per part as manufacturing increases. As we can see in the infographic below, injection molding proves to be more cost effective in large scale operations. It can also be noticed where the cross over point is for the two processes, showing at what cost per part and what production level the two processes are equal. It can also be concluded that 3D printing is more cost efficient at lower levels of production. This case uses polylactic acid (PLA) as an analysis.

Rex Plastics, an American plastic manufacturer has put together a graph detailing the cost estimates for each mold. Rapid prototyping tooling is a fast and cost-efficient way to carry out low-volume injection molding for several types of plastic parts. Insert tooling combines metal and plastics, or multiple combinations of materials and components into a single mold. This improves wear resistance, tensile strength, conductivity, and allows for tighter tolerances. High production tooling allows for molds to be specifically designed for high production. This means tighter tolerances, endurance, high automated wear maintenance provisions, and process control capabilities. Cost estimates for the three options are listed below.

For smaller companies, 3D printing can serve as a good alternative. By either outsourcing or purchasing your own 3D printing machine, the product needed can be printed in a matter of a day or two and can quickly be rushed into production or to wherever needed in the logistics train. Additionally, this process is known for its very low waste turnover with each product manufactured. 3D printing is an accurate form of manufacturing a product, however it does run with a higher risk of failure. Certain estimates place this at around 20%. Due to the high rate of failure, there is a risk of wasting material and time.

A Cost Analysis: Car Frame
Based upon market prices for common materials used for 3D printing and injection molding, we can obtain a preliminary estimate for the cost of materials. Listed below is the cost for each material in terms of euros per metric ton.

Using a cost calculator from Xometry, a company focused on the production of products, we can determine a general estimate for how much a part would cost for both injection molding and 3D printing. For this analysis, a car fender with a 1643.32 cm3 volume will be analyzed with three separate manufacturing techniques – HP Multi Jet Fusion, SLS 3D printing, and injection molding.

SLS printing is a technique that uses a laser as the power source to sinter powdered material such as Nylon or Polycarbonate, often resulting in a rougher but stronger part. HP Multi Jet Fusion is relatively newer way to 3D Print. For this process, printing is done layer by layer as a fusing agent is added with each pass. For both 3D printing studies below, Nylon 12 30% Glass Filled is used as the base material, resulting in 3.22 kg of material used. The results are listed below.

Conclusion

Overall, there are more than just cost factors to consider when deciding to use either 3D printing or injection molding. These factors include time, finish, accuracy, and quantity. It is up to the company to determine what methodology is best in producing what they need. However, the question of whether a company can substitute either forms of manufacturing is clear. 3D printing can serve as a good compliment rather than a substitution. It can be well-used for rapid prototyping or low-scale production levels. It can serve as a proper bridge between the two and ultimately optimize the production cycle of a company.