## 1 Introduction
This has resulted from the increase in low-cost light sources such as UV LCD (liquid crystal display) screens or UV DLP (digital light processing) projectors that allow a complete layer to be cured simultaneously, without the need to scan the photopolymer point by point, as in stereolithography (SAL), making it a much faster manufacturing system [20; 21]. In the case of DLP, the curing process of each layer is performed by projecting a specific section of the layer onto the resin surface, which solidifies due to the photon-activated photochemical reaction. After curing of each layer, the platform is moved upwards, and another section view is projected onto the resin for curing, forming the additional layers. The light distribution and intensity of the light is arbitrarily modulated, as light exposure time is required to cure the resin [22]. Due to the high precision of the process, it is suitable for many applications in the medical and healthcare fields [23; 24; 25; 26]. DLP technology has been widely used for microfabrication applications reaching micrometre accuracies [27; 28; 29]. Several studies have been carried out to observe the accuracy limits offered by this technology, including the study of microstructured surfaces [30; 31]. LCD, on the other hand, is based on the use of LCD screens as a system for generating images of the sections of the part to be manufactured. LCD screens allow UV light to pass through their panels so that it can reach the resin directly, and the corresponding layer of the material is cured. This prevents the light from expanding, and therefore, pixel distortion is less of a problem in this technique compared to that noted for DLP manufacturing. However, the quality is a priori inferior, so efforts are being made to improve this system by using screens with better resolution and light transmission, which improve the efficiency of the system [32]. On the other hand, the low cost of LCD displays makes it a highly interesting process [33]. However, there are limitations in these techniques that must be overcome, such as the force required to separate the cured layer and the transparent film from the tank, since during light-curing, the part remains adhered to the film and can suffer deformations [34; 35; 36; 37]. Another important limitation is the material reloading rate, which is the amount of material that fills the gap in the light-cured resin when it separates from the film. This gap must be filled under vacuum, which can lead to incomplete fills, pores, or cracks [38; 39; 40; 34]. This filling time is directly related to the viscosity of the resin, the size of the part, the pressure gradient, the space between the cured part and the interface, and the part geometry [41; 42]. It is therefore necessary to optimise the reloading time to obtain defect-free parts. In addition to these limitations, it is necessary to optimise the operating parameters of the process to achieve adequate light curing. In this study, a comparison is made between the DLP and LCD VAT photopolymerisation processes (VPP), with the intention of analysing the limits of the technology and how the operating parameters of the process can affect the final result of the parts obtained. We will begin by studying the influence of the discretisation process carried out when exporting the model, establishing the most suitable mesh size and subsequently, analysing the geometric deviations obtained by modifying the different operating parameters of the process. Statistical evaluations will be carried out in order to analyse the influence of the different operational factors, as well as of the technology itself.