Abstract
In an attempt to find a solution similar to the FDM 3D printers which would allow cost-effective and reliable additive manufacturing of metal components, this paper proposes a three-axis WAAM system capable of reliably printing small, near-net-shape metal objects. The system consists of gas metal arc (GMA) process equipment, a three-axis CNC positioning system, the interpass temperature control and forced cooling of the base plate and the deposit. The main challenge addressed is the minimisation of shape distortions caused by excessive heat accumulation when printing small objects. The interpass temperature control uses an IR pyrometer to remotely measure the last deposited layer and a control system to keep the interpass temperature below the predefined value by stopping the deposition after each layer in order to allow the deposit to cool. This results in a stable and more repeatable shape of the deposit, even when the heat transfer conditions are changing during the build-up process. The combination of adaptive interlayer dwell time and forced cooling significantly improves system productivity. Open-source NC control and path generation software is used, which enables fast and easy creation of the control code. Different control methods are evaluated through the printing of simple walls, and the printing accuracy is evaluated by printing small shell objects. As the results show, the interpass temperature control allows small objects to be printed at near-net shape with a deviation of 2%, which means that successful printing of 3D shapes can be achieved without trial and error approach.
Highlights
Technical improvements, low investment costs and the availability of many open-source solutions have led to a widespread use of additive manufacturing technology with polymer-based materials [1], and an FDM printer is an invaluable part of many workshops
In an attempt to find a solution similar to the FDM 3D printers, this paper proposes a three-axis CNC-based wire arc additive manufacturing (WAAM) system
The results show that the greatest deviation from the net shape is in the humps on the top of the object, which are caused by the beginning and end of the weld cladding process
Summary
Low investment costs and the availability of many open-source solutions have led to a widespread use of additive manufacturing technology with polymer-based materials [1], and an FDM (fused deposition modelling) printer is an invaluable part of many workshops. Yang et al [8] performed a thermal analysis for thin walls made of low carbon steel using infrared thermography They found that longer interlayer dwell times lead to a decreased mean temperature of the part and a smaller high temperature area, while the temperature gradient and the cooling rate of the deposited part increased, resulting in improved surface quality and a reduction in total height difference. Montevecchi et al [15] proposed a cooling system where a coolant hose is attached to the welding nozzle and conveys the air jet on the deposited surface a few layers below the point of the deposition The effectiveness of their method was assessed using a finite element thermal model of the WAAM of structural steel walls. The effectiveness of the proposed system was not evaluated experimentally and might not even constitute a viable solution, since cooling with high-pressure air during the deposition process, proposed by Montevecchi et al, could disturb the shielding gas atmosphere and lead to porosity problems
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