Additive vs. Subtractive Manufacturing

All too many people are unfamiliar with the advantages and disadvantages of additive manufacturing vs. subtractive manufacturing, and when to use one or the other. Subtractive manufacturing has historically been more commonly used than additive manufacturing. However, in recent years, interest, and confidence in the abilities of additive manufacturing have grown to a point where industries as large as automotive, aviation, and furniture have started to utilize it.

Additive manufacturing, commonly referred to as 3D printing, is the process in which material is added to initially nothing to form a part. Common types of additive manufacturing include fused deposit modeling (FDM), selective laser sintering (SLS), stereolithography (SLA), and many more. These processes build a part layer by layer, and in recent years, accomplish sufficient surface finish and mechanical properties. Subtractive manufacturing, exactly the opposite of additive manufacturing, is the process in which material is removed from what is initially a bulk of the material. Common types of subtractive manufacturing include milling, turning, laser cutting, and water jet cutting. Such processes triumph for their commonplace in manufacturing, mathematical models exist to purely optimize these processes for efficiency.

When choosing a manufacturing process, specifically additive or subtractive manufacturing, one must consider the requirements of the part in question, quantity, the desired material, and lastly the design. The function and part requirements of a product are established before the design of a product are begun. The part in question will have several functional requirements that it must meet. These functional requirements can depend on a lot of things such as geometry, surface finish, physical and mechanical properties, cost, and so on. It is important to keep in mind that accomplishing these requirements will depend on the process used to produce the part. Comparing the differences between additive and subtractive manufacturing, it is apparent that additive manufacturing can achieve more complex geometries than subtractive manufacturing. On the other hand, subtractive manufacturing can achieve a better surface finish without any post-processing than additive manufacturing. Typically, subtractive manufacturing can produce much larger parts than additive manufacturing, but additive manufacturing can achieve more complex inner geometry. On the other hand, one must consider if the part is to be produced in low or high volumes. Additive manufacturing presents little setup time to begin processing whereas subtractive manufacturing requires more. However, processing time in additive manufacturing is slow compared to subtractive manufacturing that has been optimized by mathematical models. Both can achieve tight tolerances, but this very much depends on which process is being used. Some of the tightest tolerances can be achieved with CNC but SLA is also promising. One must weigh these possibilities and decide which requirements hold the highest importance.

The next step in choosing either additive or subtractive manufacturing is what kind of material is of interest. If from establishing the functional requirements it was determined that the part must be made of metal, then the part will most likely need to be made with subtractive manufacturing as a range of metals are available for selection with this process, and metal 3D printing is still a young technology, but with a very bright future. However, if a part crosses into the world of polymers, this is where the selection between additive and subtractive manufacturing may become challenging. Historically, most types of polymers can be processed with subtractive manufacturing but in recent years, additive manufacturing has seen dozens of new types of polymers available for selection. ABS, PET, CE, PE, PU, and several other polymers have become available for additive manufacturing. Say a material was chosen for a specific part that could be produced with either additive or subtractive manufacturing, one must revisit the tradeoffs of the importance of the part requirements.

The last obstacle pertains to the final stages of conceptualizing a part, design. Design is the last phase that will determine how a part is produced. When a product reaches its final stages of design, it is designed for manufacturing and assembly if applicable. The part could be designed for turning, milling, injection molding, 3D printing, etc. Many make the mistake of submitting a part for quoting with both additive and subtractive manufacturing but do not realize that the design is biased to one or the other process often discouraging one process from another. A part designed for additive manufacturing is completely different than a part designed for subtractive manufacturing. Either process holds advantages and disadvantages different from the other. So, when designing a part, a designer must consider if the part should be produced via additive or subtractive manufacturing and carry out the design of the part to be optimized for such processes.

In conclusion, both additive and subtractive manufacturing present a wide range of advantages and disadvantages to one another. When considering which process will be used to produce a part, the importance of part requirements, materials, and design comes into question.

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