Will Additive Manufacturing replace Subtractive Manufacturing?

Additive Manufacturing(AM) or 3D printing as it is commonly called, is a manufacturing technology wherein parts are fabricated layer by layer. Since the material is added layer by layer, it is called Additive manufacturing. Essentially, you start with nothing and end up building a part bottom up as opposed to Subtractive(traditional) manufacturing wherein you start with a chunk of material and machine it to achieve the desired shape. Since you remove (subtract)the material, it is called as Subtractive manufacturing. Traditional manufacturing results in material wastage. Whereas, in AM, apart from the support structures that are generated, there is little or no material wastage.

DMLS technology in Additive Manufacturing. Image Source: Schivo3d

Since AM is not governed by the traditional design rules associated with tooling and molding, it gives designers an unprecedented design freedom. This helps the designers to actually design the parts for function and efficiency without having to worry about undercuts and draft angles.

Also, AM facilitates topology optimization — wherein a part is subjected to boundary conditions, and the geometry is modified in successive iterations by removing material from less critical areas, and strengthening the critical ones. This results in a structure that is not only optimized for weight but also for performance. The output(3D CAD design) that comes out of the Topology optimization software is unconventional, modern-esque, bionic form that can only be fabricated by AM.

Topology Optimization. Image Source: SolidThinking

Another way to reduce part weight is to incorporate lattice structures within the part geometry.

Lattice structures in DMLS technology. Image Source: Renishaw

The disadvantage of AM is that, the technology hasn’t reached a stage wherein it can fabricate highly precise parts with tight tolerances. The average tolerance in AM is around (+/-)150–200µm. Although this may work for most of the regular applications, such a loose tolerance would render the parts inoperable in critical, engineering applications of aerospace and automotive industries.

Subtractive manufacturing on the other hand can produce really precise parts with very tight tolerances, but it doesn’t offer the design freedom and other offerings of AM viz. part consolidation, expedited timelines etc.

Subtractive Manufacturing. Image Source: Smith Industries Ltd.

Many people are of the opinion that, Additive Manufacturing is going to replace Subtractive Manufacturing. But that’s not true. AM will aid subtractive manufacturing rather than replace it.

This is where the concept of Hybrid manufacturing comes into picture.

In hybrid manufacturing we combine best of both the worlds. We basically design a part for AM — which is optimized and efficient — and while designing the same, we give some stock(allowance) on critical areas. These areas are later machined using conventional fabrication techniques, thereby producing a part that adheres to the high precision requirements of the industry with an accelerated time-to-market and state-of-the-art, efficient design.

Many people are of the opinion that, Additive Manufacturing is going to replace Subtractive Manufacturing. But that’s not true. AM will aid subtractive manufacturing rather than replace it. At the end of the day, we need both the methods to fabricate precise, optimized and efficient parts. Hybrid manufacturing is the need of the hour; the sooner we embrace it into our manufacturing processes the better!

Spider Bracket: Topology Optimization + Lattice structures. Image Source: Renishaw, Altair, and Materialise

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