Dimension Stability of Thin-Walled Parts from 3D Printed Composite Materials

Abstract

3D print of composite materials is one of the rapidly developing areas of additive manufacturing technology. This technology is using (instead of advanced FDM or SLA technologies) materials reinforced by short or micro fibres (mainly carbon or glass fibres). These fibres are oriented mainly in direction of filament extrusion. This is causing transverse- isotropic mechanical properties of final part. Composite materials with short fibres has higher modulus of elasticity, higher strength in bending, better thermal stability and higher impact resistance. These properties can be defined by change of volume rate between matrix and reinforcement. It is noticed nowadays, that these materials are more used in automotive and aerospace industry.

Composite materials reinforced by continuous long fibres are on the highest level in area of 3D printed composite materials. These fibres (in direction of extrusion) leads to printing of materials, which tensile strength is at higher level comparing to conventional used aluminium alloys. Orthotropic properties of these materials is the biggest technical problem of this technology. Strength of final material is in direction perpendicular to the extrusion equal only to the strength of matrix (polymer material). This value is much lower comparing to strength of fibres. This disadvantage has to be considered as an input parameter during designing process and product has to be loaded with respect to this property. Orthotropic properties of printed composite material with long continuous fibres has to be taking into account during designing process.

Quality of input material and technological parameters has to be carefully checked during 3D printing process and during replacing of parts made from conventional metal materials also. All these parameters (shape of part, combination of thin and thick walled areas, print axis orientation, print layout and defaults layer thickness) are affecting the heat load in printed composite part.

Internal stress and deformation can occur during printing process and after removing part from printer. These deformations have an undesirable influence on the dimensional accuracy and mechanical properties of final composite part.

Most of 3D printers producers are declaring minimal deformation values, but during experiment described in this article was approved, that specific initial conditions (geometrical properties and process values) can lead to deformations up to order of millimetres. These deformations can occur after print but also after several days (relaxing of material). This paper is dealing with dimensional stability and internal stress of 3D printed parts from composite materials.