## 3 Industrial Applications
### Automotive  
One of the leading industries in the AM market is the automotive industry, with AM average growth of 3.6% in the recent years [5]. The advances in metal AM have provided opportunities for more flexible, optimized, and robust designs; lighter, stronger, and safer products; faster customisation, and reduced lead times and costs. Therefore, different automotive companies are beginning to use metal AM. For instance, Figure 4a shows a 3D printed steering knuckle, also known as an upright. The Formula Student Germany 2012 used EOS DMLS technology to manufacture a light-weighted upright, and the weight of this component was reduced by 35% compared with the existing cast part [68].  
German-based based automotive company, the BMW Group, is a long-standing partner of HP and EOS and uses a variety of AM technologies from these two companies [69]. For instance, BMW fabricated a window guide rail in the i8 Roadster using the HP Multi Jet Fusion metal 3D printer. This AM technology is being used in production to manufacture 100 rails in 24 h [70]. In addition, the i8 Roadster includes another 3D printed component; a fixture for the soft-top attachment, which is made from an aluminium alloy. This component is 44% lighter than the injection-moulded plastic attachment that was originally applied, but is ten times stiffer [69]. BMW is also rolling out an innovative engine, which is a replacement for their S55 engine. This engine consolidates several components, including a cylinder head manufactured using a PBF metal AM printer [71].  
Bugatti, a French car manufacturer, has revealed a range of metal AM components. Figure 4b shows a Bugatti 2.9 kg T16 Al4V brake caliper which was produced in 2018 for future car models. This caliper is one of the largest calipers in the world, and is made using an SLM Solutions SLM 500 multi-laser printer, taking 45 h to print with 2213 layers [72; 73]. According to Bugatti, this caliper has a tensile strength of 1225 MPa. The size of this caliper is 410 \(\times\) 210 \(\times\) 136 mm with a wall dimension that ranges from 1 to 4 mm thick. It is noteworthy that the bracket of the caliper is 40% lighter than the original Aluminium bracket, which weighed approximately 4.9 kg [72]. Clearly, this weight saving comes from Titanium's superior stiffness-to-weight and strength-to-weight ratios compared with aluminium. Figure 4c shows the topology optimised bracket with integrated water cooling circuits, which was developed for Bugatti Chiron and has been used in all series of their cars since its launch [72]. This metal AM product is made of AlSi10 Mg on an SLM 280, manufactured by SLM Solutions. The design of this Bugatti component helps to keep the brake disc temperature at an acceptable level, even under the most extreme weather and operating conditions. Audi, a German automobile manufacturer, is collaborating with SLM Solution Group for producing customised products, spare parts, and parts that are requested rarely [67; 68]. For instance, a water adapter for the Audi W12 engine has been manufactured additively.  
The Honda Motor company, a Japanese automobile manufacturer, is also using metal AM technologies to manufacture the body shell parts of its configurable electric car [5]. German Airbus subsidiary APWorks is using metal AM technologies to fabricate lightweight structures in Scalmalloy, which is an alloy made from Scandium, Aluminium, and Magnesium. Figure 4d shows an AM hollow motorbike chassis structure, which is 30% lighter than the original version using standard materials and manufacturing [74]. Scalmalloy is highly recommended for high-performance applications, and it is strong, corrosion resistant, and light weight with high ductility [75].