# Optimization of Brake Calipers Using Topology Optimization for Additive Manufacturing
## 3 Brake Calipers  
A brake system is responsible for the deceleration of a vehicle, and thus is a vital part of driver's safety. The brake system is designed to both slow down and halt a vehicle by transforming its kinetic energy into heat while applying friction forces to the vehicle axles [22]. The most common brake system is the disc brake, which was initially developed in 1951 for racecars application. Just a few years later, in 1955, disc brakes were first used for mass production in the automotive industry, due to their success, on the Citroen DS model [23]. The disc brakes are steadily replacing drum brakes in order to overcome the potential brake power loss of the latter, also known as brake fade [22]. The most crucial component of a disc brake is the caliper that presses a pair of brake pads against the brake's disc, also called rotor, and thus slows down their rotational speed. In the case of hydraulic disc brakes, when the driver pushes the brake pedal, hydraulic pressure is applied by the brake fluid on the caliper's one or several pistons, and these, in turn, force the pads against the disc [24]. Figure 1 depicts a disc brake. The design of calipers is challenging and should be developed with respect to some technical requirements. According to [PERSON], et al. [13], the calipers must be stiff, light, and heat-resistant. Brake calipers require acceptable stresses and deflections under multiple load cases. It is important to mention that any crack on a caliper can lead to an instant brake fluid leak that results in brake malfunction. Thus, a high caliper stiffness provides a uniform pressure distribution on the brake system, which ensures short brake pedal travel, ride quality, and vehicle safety [15]. The term unspruping mass is broadly used to describe the total mass of the suspension, wheels, as well as other components connected to them. On the other hand, sprung mass consists of the supported by the suspension vehicle's body and components. In the case that the vehicle's brakes are mounted outboard, they are considered part of its unsprung mass [12]. As has already been mentioned, a minimization of the vehicle's mass increases its performance. Therefore, the reduction of brake caliper mass is of high importance. The applied friction forces between the brake pads and the rotor result in heat concentration inside the brake system. A low thermal resistance, together with insufficient ventilation of the brakes, increases their thermal deformations resulting in a smaller friction coefficient and, in turn, less braking force [13]. It seems that compliance TO of the brake calipers could reduce their weight while increasing their stiffness. Moreover, the creation of voids in the calipers' structure will increase their ventilation and heat dissipation. A brake caliper is mainly comprised of housing, brake pads, and pistons [12]. The housing is usually made of cast iron, the brake pads of semi-metallic, organic, and ceramic materials, and the pistons of plastic, aluminum, or chrome-plated steel. Generally, there  
Figure 1: A 3D model of a disc brake design in SolidWorks. are two main types of brake calipers: the floating and the fixed calipers [25]. The calipers mostly differ in terms of design, mounting, and operation. On the one hand, the floating calipers move relative to the rotor. Furthermore, they have one or two pairs of pistons only on the inboard side of the rotor. When the brakes are applied, the fluid pressure moves the piston(s), which then pushes the entire caliper creating friction from the brake pads on both sides of the rotor. The floating calipers are prone to sticking failure resulted from dirt or corrosion at their moving components. This can cause extreme heating of the rotor, vehicle's steering vibration, and reduced fuel efficiency [26]. On the other hand, fixed calipers, as their name implies, do not move but are rather fixed with bolts to the caliper bracket. In addition, they have two to six pairs of pistons arranged on opposing sides of the rotor [12].