# Towards Machine Learning for Error Compensation in Additive Manufacturing
## 2 Advancements in Additive Manufacturing
### Transformations from Conventional Manufacturing  
One of the biggest advantages that additive manufacturing has got to offer over traditional manufacturing approaches is that no special new tooling is required in additive manufacturing in creating a part. This would highly improve the turnaround time in rapid prototyping other than reducing resources that would be normally allocated in tooling [68]. In addition, preparation of the production line and getting an assembly process set up could be potentially avoided. Conventional manufacturing comprises formative manufacturing which involves techniques like injection moulding [69]; a process that removes material from a larger piece of material employing standard machining processes such as milling and lathing until the prototype part is created. Additive manufacturing has a clear advantage in rapid prototyping which is a speedy process of creating a three-dimensional model of a physical part or product before being manufactured in higher quantities [70]. Currently, prototypes are usually done by layered manufacturing technology in the likes of polymers and various metal types [71]. Figure 2: Smart factories schematics with general properties in Industry 4.0. One of the known perks of additive manufacturing over conventional manufacturing processes is the lean nature of the source required in printing the product [72]. In additive manufacturing like polymer extrusion, only material intended to be in the exact representation of the CAD model is estimated beforehand and fully utilised with minimal waste. In injection moulding, the use of extra material is required in order to fill the mould [73]. In sheet metal assembly, a by-product in the form of scrap metal will be produced [74]. The scrap metal is often recyclable, but it would involve an upfront cost for the material to be salvaged. In most instances, additive manufacturing will produce almost zero material wastage in rapid prototyping process when a correct process configuration is followed. The types of additive and conventional manufacturing types are described in Figure 3.  
However, additive manufacturing is rather less efficient in the post prototyping phase. Albeit the unnecessary and irrelevant retooling, the rate at which the printer could complete a whole assembly of a finished product leaves much to be desired if we were to compare to the most conventional manufacturing process like CNC milling and moulding. This is because only a single layer will be laid out or fused together at one time to accommodate the customizable nature of the process. Although additive manufacturing has a much shorter lead time in prototyping tasks, with the current technology available, it cannot sustain the rate that is required to be used for a full-fledged manufacturing line [75]. So, when it comes to making a limited-run prototype of a part, 3D printing has a clear edge over the traditional method of tooling an entire production line but not suited for a high output production. All in all, although additive manufacturing has a very short turnaround, it is only suitable to cater to the need of a manufacturing process like the prototyping phase due to the intricate steps involved and the resolution of details it can offer. To justify the cost of tooling, manufacturers do not require to produce as much of the volume required due to the high rate of reproduction of a single design. Traditional manufacturing like machining and casting provides high quality level parts, good surface finishing, and very high dimensional accuracy for all sorts of materials. Nonetheless, 3D printing technologies like Aerosol Jet has recently made significant gains against traditional manufacturing processes by offering better material selection, ranging from ceramics to dielectric adhesives [76; 77]. However, when it comes to making a limited-run prototype of a part, 3D printing has a clear edge over the traditional method which requires tooling for the entire production line.