The accuracy and fine resolution of laser technology makes it ideal for creating high quality products from a variety of source materials via additive manufacturing (AM).
However, this intense heat can create challenges for manufacturers. For example, in metal processing, a rapid cooling in the material can generate unintended residual stresses, which can ultimately impact product performance.
Of particular concern in AM is the ablation mechanism, where the irradiation of the laser beam causes an instantaneous material sublimation and subsequent solidification that can result in a ‘cloud’ of emissions known as ‘condensate’ or ‘plume’.
Should this settle on the inside of the machine, it can lead to machine durability issues as well as obstructing the laser optics, resulting in beam scattering and reduced build quality.
It is for these reasons – product quality, materials stability and equipment performance – that the AM environment needs careful management – this is where effective filtration and atmosphere management are critical. For example, in metal AM, which commonly involves aluminium and titanium, unwanted oxidation can lead to unbonded material, so chambers are kept inert through the use of nitrogen or argon. Maintaining a stable chamber temperature is also critical for process integrity.
A further challenge resulting from the process is managing the flammable material collected through the filtration system, because exposure to oxygen during the exchange process could result in a thermal event. To help address this challenge, Bofa has developed a filter exchange system for its AM 400 unit that creates a seal around the filter housing, enabling removal and exchange quickly and in a controlled manner. This also helps minimise the escape of nitrogen or argon during the process. The system also offers high air flow potential up to a maximum of 190 cubic ft/min and a maximum pressure generation of 250mbar, with low leakage at <30ml/min at -10mbar.
High temperature atmosphere control
In AM processes, the quality of the finished product is directly proportional to the accuracy of the thermal control. AM requires the application of high temperatures to join the materials. This can create challenges in conventional chemical absorption filtration because the higher energy can impact the ability to bind emissions to filtration media.
This can be addressed using a process ‘loop’ to remove particulate through active convection and pressure differentials. A purge process can also be used to remove residual chemicals at lower temperature once the AM process is complete. Such technology can be found in Bofa’s 3D PrintPRO HT system, which also uses active convection to help ensure that key components are kept free from dust and particulate.
Process emissions settling inside an AM machine can affect its durability, obstruct the laser optics, and ultimately reduce build quality
These advances in high temperature atmosphere control are enabling manufacturers to leverage the cost, speed and customisation benefits of AM technologies – and take advantage of the evolution of functional materials that have the potential to open up AM benefits across an ever-wider market spectrum.
Of course, effective filtration also relies on accurate control, so alongside air management innovation, Bofa has also introduced ways to help protect system electronics and safeguard the performance of the multi-stage filtration system, for example by using specialist glues and gas filters.
Here, scientific resources play a key role in emissions that need to be filtered, whether by reference to safety data sheets or analysis of particulate/gases that result from lasering combinations of materials. This research enables chemical reactions to be specified that can form part of the filtration system in a high temperature environment – it is a specialism that is growing in importance with the rapid proliferation of AM across a wider range of industry sectors.
Bofa’s AM 400 enables easy management of the flammable material collected through the filtration system, which if exposed to oxygen during the exchange process could lead to a thermal event
It is also important that the filtration system does not inadvertently lead to a reduction in process critical temperatures across the laser bed, or disturb the materials being worked (powder, for example). This temperature control is particularly important with polymers, where the bed is preheated, and the laser power is significantly lower than that in metal.
Understanding all these challenges – temperature, the mass and makeup of emissions – is key when specifying the appropriate extraction system set-up and filtration media. And, of course, the greater the mass, the more energy/airflow needed to remove it, so pipes, hoses and pumps need to be sized to maintain an environment that helps protect the laser operation while capturing and filtering emissions.
As 3D printing technology matures and adoption rates increase, the requirement for greater understanding of the profile of emissions being generated by these processes also grows, particularly with the trend towards the development of more functional materials. BOFA is working closely with OEMs to ensure that filtration technology not only keeps pace with developments in the space but anticipates the evolution of AM.
Joshua Evans is an applications engineer and head of Bofa Academy at Bofa International