# Nesting Process Automation in the Footwear Industry: A Hybrid Approach to Minimize Material Waste
## 3 Nesting in the Footwear Sector  
Minimizing material consumption to support green policies is a prominent priority in industry. In the footwear sector, many products are made from leather--an expensive resource that must be used as efficiently as possible. Additionally, leather undergoes chemical treatments that make it challenging to recycle. The footwear industry encompasses a wide variety of shoe types with different assembly methods. The most common and extensively used technique is the so-called 'glued construction', as shown in Figure 3. The sole and cut are impregnated with contact glue, which is reacted by heat or light so that when pressed and joined together, it is sealed. Beyond the conventional construction, there are other manufacturing techniques that, due to their specific characteristics, require distinct methodologies to achieve the desired result. Among the main manufacturing typologies in the market are the'moccasin' or 'Kiowa' type and the 'Strobel' type, which are the focus of the nesting strategies discussed in this paper. Figure 4 depicts a Strobel shoe, while Figures 5 and 6 illustrate a moccasin and a close-up of the assembled shoe. Figure 4: On the (**left**), a scheme of the Strobel construction. On the (**right**), a representation of a sneaker assembled with this type of construction. Figure 3: On the (**left**), a scheme of the “glued” or “conventional” type of assembly seen in cross-section. On the (**right**), shoes mounted with this type of construction. It Is Important to note that moccasins can be further classified Into subtypes, including half moccasins or 'car shoe' style moccasins. Strobel shoes, similarly, can be categorized based on the stitching positioning: on the upper or on the bottom. Unlike traditional or 'cemented' shoes, non-conventional footwear types--such as those discussed in this paper--consist of a reduced number of parts: a single part in the case of Strobel and three or four parts in the case of moccasins. Figure 7 shows the wide variety of parts typically required for traditionally assembled shoes, while Figure 8 highlights the significantly reduced number of parts in Strobel and moccasins. In Strobel constructions, a single part is used to cover the whole upper of the shoe, serving as a base onto which the remaining parts are sewn. The entire assembly is then sewn to the sole using a stitching technique known as Strobel. The main challenge, therefore, is the efficient nesting of moccasin and Strobel shoes as single-part constructions, which constrains the problem's initial characteristics as follows:  
Figure 5: On the (**left**), a scheme of the moccasin construction. On the (**right**), a moccasin. Figure 8: On the (**left**), is an example of the parts of a half moccasin. On the (**right**), is an example of the Strobel cut in a single piece. Figure 6: Close-up view of a moccasin made of leather. Figure 7: Example of parties in traditionally constructed of glue shoes. For moccasins:
* Since these types of footwear are typically made of leather, the available space--or master part to be cut--will be, therefore, irregular in shape. * The parts to be cut are generally large compared to parts used in other types of shoe constructions, except for smaller shoe parts that are occasionally added to these models, which help minimize material waste. * The objective is to place as many complete pairs in one leather, filling any remaining space with as many pieces as possible to optimize material usage. For Strobel, this study focuses on uppers comprised of a single part, which are typically used in sneakers, characterized by their comfort, sporty design, and ability to adapt to different clothing styles:
* These parts are usually made of synthetic material, providing regular, rectangular space. * Each part to be cut is unique; for this study, a 2000 \(\times\) 1000 mm measurement was used as a reference, with mirrored parts required for the left and right feet of each pair.