# Optimization of Brake Calipers Using Topology Optimization for Additive Manufacturing
## 4 Methodology
According to Low [32], the main part of the generated heat, approximately 90-95%, is absorbed by the brake disc, and the rest 5-10% is distributed among the pads, the pistons, the brake fluid, and the caliper housing, assuming little to no heat dissipation. It is clear that the energy transferred during braking is highly related to the thermal resistance of the pads and the disc surface. Hence, the calipers also should be heat-resistant, and this is something that was taken into consideration in the choice of their production material. The maximum allowed pressure on the brake master cylinder, according to their technical specifications, is 20 MPa. A pressure test was conducted at the ISR calipers, using an in-house test jig, and the maximum displacement in the y-direction of the front and the rear caliper, at 20 MPa, found 0.5 mm and 0.4 mm, respectively. In consequence, these were the maximum allowed displacements for the in-house developed calipers too. After the analysis of the vehicle and the ISR calipers, an optimization procedure of the calipers for their weight reduction was implemented on three levels, based on the [PERSON], et al. [2] guidelines: downsizing of the vehicle, use of lighter materials in manufacturing, and removal of unwanted material from vehicle components. At level one, new design concepts of the calipers were developed in SolidWorks by using reverse engineering of the commercial ISR calipers. The main goal at this point was either the reduction of the calipers' components or their downsizing. Thus, several design concepts were created and validated with respect to the ISR calipers' initial designs, the weight trade-offs among their components, and their interaction with the car's rim and upright. A crucial decision was to decrease the number of pistons from four to two in the front caliper. On the one hand, a four-piston caliper has an increased piston area and, thus, a reduced hydraulic pressure compared to a dual-piston caliper. However, the use of more pistons increases the risk of seal failure as well as the maintenance time. On the other hand, a dual-piston caliper could result in smaller design space and a less complex assembly due to the reduction of its components, but it contains a heavier housing to support its increased hydraulic pressure. Thus, there is a trade-off between the weight of the housing and the weight of the other caliper's components. The authors decided to develop a design concept of a dual-piston front caliper reducing its complexity and overall volume. Hence, both front and rear will be fixed dual-piston calipers. Furthermore, the initial design space of their housings was expanded as much as possible, with respect to the spatial placement of the wheel components, in order to increase the design flexibility for the TO algorithm. These design concepts, \"design space assemblies\", were validated in ABAQUS for the same load case and boundary conditions with the conducted physical test of the ISR calipers. At the second level of optimization, an exploration of the material choices for the calipers was conducted. All the materials of the calipers' components, except the housings, were kept the same, thus from this point, the optimization focus was on housings only. It was decided that the optimized housings will be 3D printed using SLM. Hence, material research was done among the available 3D printing materials. Three were the predominant materials: AlSi10 Mg, Steel MS1, and Ti6 Al4V. On the one hand, the AlSi10 Mg was the lightest material with the lowest specific gravity (2.7 g/cm\({}^{3}\)) compared to the other two available options, the Steel MS1 (8.1 g/cm\({}^{3}\)) and the Ti6 Al4V (4.4 g/cm\({}^{3}\)). Concerning the used case study in this paper, every gram counts in the development of calipers for a racecar. However, the calipers of a racecar are exposed to high braking forces and temperatures. Hence, the Ti6 Al4V with an exceptional yield strength (1147 MPa), even at 500 \({}^{\circ}\)C (890 MPa), was considered an excellent choice [33].