## 2 Theoretical Foundation
### Lean Philosophy  
The term Lean Production was first used by [PERSON], a researcher at the International Motor Vehicle Program, according to whom production can be characterized as Lean since it uses less human effort in the factories and, fewer engineering hours for the development of a new product (and in less time) while at the same time keeping a smaller amount of stock, and managing to provide fewer defects and a greater variety of products [6]. Therefore, Lean Manufacturing (LM) prioritizes robust operations that are responsive, flexible, predictable, and consistent, thereby generating production that is focused on continuous improvement through a workforce driven by measures that are production-based, and aligned with customer performance criteria, needs, and expectations [7]. It focuses on a highly responsive approach to customer demand by reducing waste and aiming to produce products and services at a low cost and as fast as required by the customer [8]. The LM is based on the Toyota Production System (TPS), a production system developed by Toyota at a time when the Japanese automotive industry was suffering the consequences of World War II and facing a lack of resources, money, and skilled labor [2]. Toyota was founded around 1918, with the drive and innovation of [PERSON], [PERSON], and [PERSON], as well as [PERSON], a mechanical engineer [9]. [PERSON] contributed by inventing a motorized loom with a specific mechanism designed to stop production if there was a break in the yarn being worked on the loom [10]. This mechanism would later serve as the foundation for Jidoka, one of the main pillars on which the TPS would be built. Jidoka is a concept that features intelligent capabilities where machines automatically stop a process in case of an abnormality, problem, equipment malfunction, or quality problems, among others [11]. Later, [PERSON] realized that it was necessary to create a fast and flexible production process to meet the requirements and demands of customers, with high quality and reasonable price. The idea behind this approach was that, in the market, each customer buys a different car; therefore, in manufacturing, cars should be made one at a time. To do this, [PERSON] began by preparing the system to produce according to a Just-in-Time (JIT) methodology. JIT means being able to purchase products at the right time and quantity to eliminate waste, uneven production, and unreasonableness while improving efficiency [10; 12]. Around the 1950s, [PERSON] became the general director of production and was sent to visit Ford and General Motors, bringing back ideas of implementing mass production for Toyota. However, monetary constraints and the low volume in the Japanese market did not justify large batch sizes. Thus, later, the person who would give a crucial push in the development of TPS and its ability to produce a large variety in small batches economically would be [PERSON]. One of [PERSON]'s most notorious contributions concerns a \"Kanban supermarket\" for controlling material replenishment. The result was a production system able to produce a considerable variety of cars in low volumes and at a competitive cost, changing the conventional mass production way of thinking and a production system that would turn out to be a reference for production all over the world [9]. The TPS was named as the first system to work under Lean guidelines, and as such, LM is considered a successor to TPS, adding some principles to set standards to increase the performance of an organization [10]. Those principles are presented in Table 1. In terms of wastes that affect a productive process, initially, the Lean philosophy identified seven wastes; however, an eighth source of waste is now also considered. These wastes are presented in Table 2.