When becomes additive manufacturing profitable?

In this first blog in a series on design in additive manufacturing we discuss the use, advantages and limitations of additive manufacturing and compare the technology to traditional manufacturing techniques.

With additive manufacturing (AM), it is said that you can make any geometries. So designers naturally propose amazing geometries and are often disappointed by the results they received concerning the part quality. The part can be distorted, with a local bad surface quality, not as clean as expected or out of tolerances… To face those problems, designers can make their parts much easier to produce with some basic considerations. If it is easier, the final quality will be improved, and sometimes even the cost will be decreased for the same function fulfillment.

Why use additive manufacturing?

Using traditional or conventional technologies such as machining and injection moulding has a lot of advantages. All the subtractive technics (EDM, turning, milling,…) can provide a mirror-like surface aspect, and be accurate down to the micron, on almost all materials available. Injection moulding is quite long to setup but, once it is fixed, the production volume (i.e. parts production per time unit) will be very high, which is commonly the only way to reach mass production.

But industrials challenges become more and more complicated, to such an extent that sometimes the geometry to face a given challenge is just not feasible by conventional technics. Sometimes, it is because of tool accessibility in machining or due to the fact that the mould has to be opened in injection moulding to retrieve the part without damaging it, or just because the production is too small (one single prototype) to be cost-effective and justify the tooling cost required to make it.

Those quite strong limitations mentioned above may prevent a part to be made lighter, more efficient or get early prototypes much sooner to quickly iterate and improve it. In addition, the capabilities of traditional technologies, related to the cost, can be summarised roughly in a single picture, in which appear the opportunities linked to additive manufacturing:

Cost effective opportunities (green areas) for AM compared to conventional manufacturing

In the figure you can see what is preferably to do with conventional manufacturing (CM) and what is economically more interesting to do with additive manufacturing (AM).

By looking at the number of parts produced in the traditional way, it is well known that the more identic parts are produced by a machine, the lower the batch costs are. If the batch size is too small, the tooling cost can become prohibitive for the production, which can become unprofitable. This is represented by the blue curve, with the dotted line being the limit when the number of part produced gets too small.

In terms of geometrical complexity related to cost in conventional machining, the tendency is more like the red curve. Low complexity means low cost, and if the part is too complex for the technology, the part becomes just too expansive or there is even no possibility to produce the part for technical reasons. This limitation is represented by the red dotted line.

If AM is considered (green dotted line), the first entry point is that AM is currently quite expensive (so located on the right side of the graph), but we can also say that this high price will not change so much with the number of parts produced or the complexity of the parts.

Assuming that, two regions in the graph appear to be profitable with AM compared to conventional manufacturing:

  • making very complex parts…
  • …which are needed in small quantities.

Which also means that, if the part chosen is located elsewhere in the graph (cheaper to manufacture, not too complex, quite high quantities), i.e. outside of the green areas, then AM should not be preferred to manufacture that part, as money will be lost or more risk related to current AM uncertainties will be taken.

Advantages to AM

Additive Manufacturing (AM) can have many advantages:

  • With an optimised design, much less material waste will be generated compared to machining.
  • Thanks to the layer-by-layer approach, the inside of a part becomes easily accessible, this allowing the designer to make much more complex designs (internal cavities, light weight structures, channels,…) than conventional technics.
  • Single-step-manufacturing gets rid of tooling during the manufacturing step. No need of a mould or special device to position the part in a machine.
  • A wide range of materials is already available in polymers, metals and ceramics.
  • Roughly, one could say that geometrical complexity does not increase the cost. In other words, making a part very light, made of a 3D mesh, with channels and hinges integrated, would roughly cost the same as a cubic block with the same height and same material volume. It is absolutely not the case for conventional technologies.
  • It becomes feasible to produce very different parts (in size, complexity,…) in a single run when a mould can only make the model it had been designed to produce. Particularly interesting for medical applications such as customised implants…
  • Some AM technologies can produce parts constituted of different materials in a single run.
  • Some functionalities (springs, hinges, gears, rotative shafts,…) can be integrated in the design to manufacture. This will not require post-assembly steps, but will be ready coming out of the AM centre.
  • The delay to produce a standard volume (300 x 300 x 400 mm³) is usually less than a week from scratches and CAD to the final part ready to be used. Very convenient even for the early iterative development of a product which should be finally made by injection moulding for mass production.
  • Customisation, labelling, texturing, conformal cooling channels, weight reduction,… become much more affordable.

Limitations to AM

But there are, of course, some limitations to be aware of:

  • The best geometrical accuracy achievable is 0.1 mm on standard AM machines, for a part smaller than 100 mm. Above this length, 0.1% should be considered. This value can even reach 0.3 %, depending on material, technology and part bulkiness/massivity. This is the reason why post-processing is often needed locally.
  • The maximum part size limitation can prevent the designer to make big parts such as car bumpers or tables in a single run on standard technologies. In average, nowadays, the maximum size achievable on industrial-grade machines is around 800 mm. But some out-of-standard technics can make a mould in sand with the dimensions 4,000 x 2,000 x 1,000 mm or even houses with concrete walls, or a small car hull from a “polymer + carbon fiber” extruder moving along XYZ.
  • Plenty of AM technologies will require a support structure. Roughly said, this structure connects the part to the build platform. It will prevent the parts from moving during manufacturing and keeps them fixed. It is built by the machine at the same time as the parts themselves. Unfortunately, this structure has to be remove after manufacturing and thus will require a post-processing step to detach the support from the parts.
  • Just after manufacturing, the raw material is everywhere, all around the parts, inside any cavities, gaps, channels, holes,… And, if the design doesn’t take that fact into consideration, this raw material can be very difficult to remove, specially in narrow places.
  • Some technics produce part with anisotropic mechanical properties, especially in cheap machines and at a “huge” layer thickness (> 100 µm). But for the majority of AM technologies, this mechanical anisotropy is not strongly marked.

A good designer is the most valuable resource in the AM world. He will be able to optimise the shape of the part to meet the requirements, but also take all the factors to ease the manufacturing and the post-processing steps into account. Efficient and 'easy-to-produce' design is the single way to make AM profitable.

Sirris offers you support in design for AM. Together with you we check the technical and/or economical feasibility of your idea. Curious to know if your products are suitable for (re)design for AM? Contact us or attend one of our future masterclasses!

This blog was written in the framework of the Cornet project AM 4 Industry.