# Dimensional Errors Due to Overhanging Features in Laser Powder Bed Fusion Parts Made of Ti-6 Al-4V
## 1 Introduction  
Additive Manufacturing (AM), colloquially known as 3D printing, is a rapidly evolving group of fabrication techniques that are currently revolutionizing design and production pracises across industries [1]. They have displayed potential to disrupt and beneficially affect globally established process chains and business models [2; 3]. Their main advantages include an increased design freedom, shortening of lead times, and reduction in material usage [4]. Additionally, combined with their ability to print on demand, AM techniques align well with today's industrial trends of digital manufacturing and mass customization [5; 6]. Therefore, this combination of competencies that AM offers and modern trends has allowed AM to arrive as a unique solution for current and future demands. Laser-based powder bed fusion (L-PBF) is one of the AM techniques that is gaining an increased market acceptance and penetration, particularly in a wide range of industrial applications that include automotive, aerospace, medical/dental, and robotics industries [4]. In addition to all the advantages mentioned above, the availability of printable super-alloys, such as Ti-6 Al-4V, allows metal products with superior properties to be produced, i.e. high strength-to-weight ratio and corrosion resistance, which were not easily obtainable using conventional manufacturing methods [7; 8; 9]. This makes AMtechniques prime candidates for applications where low-density and excellent corrosion-resistant materials are required, such as in the aerospace industry [10]. However, the L-PBF process still faces some technological challenges that need addressing in order to improve the robustness and repeatability of the parts produced. In particular, when compared to other conventional manufacturing technologies, AM, and L-PBF in particular, lags behind when it comes to being able to predict different quality-based performance indicators of the parts produced, such as the dimensional accuracy and surface quality. Therefore, a significant portion of current AM research is focussed on investigating these different aspects of precision, namely the repeatability, predictability, and robustness of the process. Various approaches have been employed for this purpose, including investigating the design for precision AM using topology optimization [11], computational modeling of the L-PBF process [12], and statistical process optimization studies [13]. These methods are also complemented by studies on improving methods for the finishing of parts [14], as well as for metrology [15]. In particular, [PERSON] et al. compared two topology optimization (TO) techniques--one based on commercial software and another based on an in-house developed TO method that also compensates for localized overheating caused during part manufacturing. This work discusses the precision benefits that are achieved when manufacturing constraints are included within topology optimization, rather than just purely geometric constraints [11]. [PERSON] et al. developed a multi-physic numerical model of the L-PBF process, which was then used to track the formation of porosities that cause imprecision while printing. Their results indicate that porosities are largely caused due to the improper fusion of particles between tracks [12]. [PERSON] et al. investigated the effects of process parameters on the surface texture of a down-facing part and showed that the interaction and interdependency of process parameters have the greatest effect on the surface roughness as they directly affect the degree of cross formation due to the various levels of energy density applied to the powder [13]. [PERSON] et al. investigated improving the precision of AM-produced surfaces by carrying out a subsequent laser polishing step after printing. This early study investigated the various process parameters and discussed their effect on the achieved surface.