## 1 Introduction  
Single point incremental formation (SPIF), patented by [PERSON] in 1967 [1] and later developed by Prof. [PERSON] [2] and [PERSON] et al. [3], consists of the progressive deformation of a metal sheet by means of a steel punch at the top of a machining center or robot. The forming is done in such a way that neither presses nor dies are necessary [4]. The SPIF technique enables the manufacturing of prototypes from sheet materials. By means of SPIF, forming can be done to all types of metals and alloys: aluminum, steel, stainless steel, tin, copper, titanium, among others [5; 6]. Polymers can also be worked with [7]: polyamide (PA), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), polycarbonate (PC), polyethylene terephthalate (PET). The advantages and disadvantages of the process are summarized in Table 1.  
As well as prototypes, with SPIF, it is also possible to obtain short manufacturing series at low cost. [PERSON] et al. [8] determined that SPIF technology is more profitable than deep drawing up to a batch size of 600 pieces. [PERSON] et al. [9] affirm that SPIF is a more efficient process than deep forming processes which produce cuttings and scrap metal. The process has evolved in recent years [11], and its use has increased in different sectors, such as automotive [12; 13; 14; 15; 16], medicine [17; 18; 19], energy [20], architecture [21], and art [22]. One of the least explored uses of this process is in the manufacturing of molds. [PERSON] et al. [23] have proposed the use of molds made by means of SPIF directed at compound material sheeting. [PERSON] et al. [24] and [PERSON] et al. [25] have considered its use in thermoforming operations. Recently, it has been tested in rotomolding processes, and in other polymer processing techniques [26]. In most cases, for the demolding process, it is desirable for the mold to have a non-stick coating. These coatings may be of several types, although the most common are those made with resins that are rich in fluoropolymers [27]. Such resins may be applied to the metal sheets before forming, so that the manufactured piece is the final one. However, until now the friction between the tool and the sheet complicated the forming process with pre-coated SPIF sheeting [28]. In order to avoid direct contact between the tool and the coating, in this study, the dummy technique [29; 30] has been used: a dummy sheet is placed over the sheet to be formed, and the punch simultaneously forms both sheets, without any direct contact with the lower pre-coated sheet. This novel method enables the application of the SPIF process to sheets pre-coated in resins rich in fluoropolymers, and thus, among other applications, directly manufacture prototypes or short series of non-stick molds. The aluminum-magnesium alloy EN AW 5754 H32 is commonly used to manufacture molds in the food industry, as it comes into contact with food and has good formability [31]. The incremental forming of this material has been studied previously by [PERSON] [32], [PERSON] [33], and [PERSON] [34]. For the industrial use of SPIF, it is imperative to reduce springback and achieve good geometrical accuracy [10]. There are previous studies that have analyzed this matter with aluminum alloys. [PERSON] et al. [35; 36] focused on the improvement of the dimensional accuracy of truncated cone pieces from sheets of EN AW 1050-O. [PERSON] et al. [37] advanced in the accuracy reached using SPIF in two-slope cones manufactured in EN AW 3003. However, no previous studies have been found in the literature concerning the geometrical accuracy reached using SPIF with sheets of EN AW 5754 H32, nor authors who have approached this subject using the dummy method. This work has two main aims. The first is to present and describe the use of the dummy method in incremental forming for the direct manufacturing of prototypes or short series of molds.