Horizontal Forming

Horizontal forming (HF) is a recently developed approach to creating overhanging structures using conventional, 3-axis machinery without relying exclusively on direct layering methods. HF is Fleximatter’s method for fabricating hollow objects (Meshorer & Vasilevski, 2017a). HF-based methods were developed especially for medium and large-scale fused granular fabrication (FGF), aiming to simplify and accelerate ME AM processes by cutting the need for support and infill at the manufacturing.

This method was introduced during the praxis with the FLEXIMATER company, working with this method so-called “methods and system for fabricating hollow objects” (Meshorer & Vasilevski, 2017b).

The method comprises the deposition of modeling material in parallel horizontal roads, wherein at least one of the horizontal roads is extruded horizontally above a three-dimensional region devoid of any substantial support. The structure solidifies during the forming process and allows forming of horizontal surfaces in mid-air without any support.

HF roads are generated through the Fleximatter slicer. The layer where the HF is required is manually selected by the user. Then the slicer generates automatic paths for the printer and adds horizontal roads by generating offset contours of the 3d model, in addition to the original model.

Parameters such as forming direction, material volume, overlap, and speed can be defined for HF roads. In this stage, the HF can only generate as an offset of the model in a specific layer. The direction is set from the model contour and can be set in an inside or outside direction (Figure 1).

??Figure 1: HF direction: left: Original model. Middle: Inside from the model contour. Right: Outside from the model contour.

An additional approach was observed in another Israeli 3D printer manufacturer, “MASSIVIT” which applies this method with photopolymer material (Lisitsin et al., 2018).

The literature review searched for topics based on the “method and system for fabricating hollow objects” (Meshorer & Vasilevski, 2017b)?and various common methods such as?“method and apparatus for the manufacture of 3D objects” using pseudoplastic material (Lisitsin et al., 2018) as the research was established based on this methods.?Having no results, the literature review expanded and searched for more extensive keywords and fields in AM (Error! Reference source not found.).

During the additional literature review, the Print on Air (PoA) method was found, to present an approach to forming a horizontal overhang. This method relies on sensing systems embedded into the three-dimensional (3D) printer (e.g., temperature and speed sensors). PoA aims at generating a printing sequence capable of self-sustaining bridge and overhang structures. (Barile et al., 2020). Another interesting example is found on the web without a description or explanation of the method by Babarada Mihai.

??Figure 2: Left: Print on Air (Barile et al., 2020) Right: BABARADA: upside-down printing overhangs

During the literature review, the influence of material volume and overlap were also found in AM technology as SLM (Hirt et al., 2016) and SLS (Chen et al., 2017). Most interesting in these studies is that those technologies are based on powder vat, have support in all printing areas, and hypothetically do not need HF (Figure 3:Right). Although in this manufacturing method, is no need for additional support, the material volume and overlap are essential to get better product quality as the support material can collapse under the overhang structure, causing material deformation (Chen et al., 2017).

For example, Template-Free 3D Micro-printing (Hirt et al., 2016) in selective laser melting (SLM), Hybrid 3d printing (Yoon et al., 2017) in aerodynamically focused nanoparticle (AFN) printing, and Stereolithography SLA (Basile et al., 2016)has a similar approach to form 90 deg overhang. All research mostly focuses on the overlap and material volume to get the required outcome. This method allows the creation of overhanging geometry without reliance on support structures, which are difficult, if not impossible, to remove at some technologies, especially in the micro/nano scales (Yoon et al., 2017).

?Figure 3: Template-Free 3D Microprinting(Hirt et al., 2016) Right: (Chen et al., 2017)

Figure 4: Left: SLA (Basile et al., 2016) Right:(Brant & Sundaram, 2016)

Outstanding gaps

Horizontal forming (HF) is an existing method with the potential to overcome the above-mentioned drawbacks. Therefore, this research focuses on Horizontal Forming (HF), emphasizing the gaps that were revealed in the literature review:

·?????A lack of research on Horizontal Forming (HF):

There are many studies on methods used to overcome overhangs: i.e. support, free-forming, and multi-planar methods. Each one has benefits and drawbacks, and in some cases, multiple methods are required to overcome the overhang. The approach of horizontal forming (HF) is relatively new; the literature provides only a basic understanding of this method, without a study of how the method works and what effect it has on formation quality.

·?????A lack of applications using horizontal forming (HF):

From the literature review and personal knowledge, it seems that horizontal forming?(HF) in thermoplastic materials has existed since 2017 (Meshorer & Vasilevski, 2017b); research on horizontal forming?(HF), in other materials, exists from around the same period. However, there are very few applications using horizontal forming (HF) that could explain the benefits of this method and how it can be used in manufacturing.