Design freedom through software?
While the market for 3D printing could potentially be huge, industrial additive manufacturing (AM) machines, especially those working with metals, require further development to make them truly production machines. This was one of the talking points during a panel discussion on 3D printing at Photonics West (for a report on the panel discussion, see page 10). Still, there are a number of systems now available, and the breadth of possibilities made available by AM can be seen at the LIA’s Laser Additive Manufacturing (LAM) workshop from 4-5 March 2015 in Florida, USA (for more on the conference, see the LIA news on page 35).
In order to make the most of the AM process chain there needs to be a change in mindset of the designers and engineers creating parts to be made with additive processes. Optimisation of the process chain was called for in May 2014 at the AKL International Laser Technology Congress in Aachen, Germany, where a number of speakers voiced concerns that industry was trying to force a new, disruptive technology into an industry that was designed for more conventional, reductive manufacturing processes, and that this partly is what is hindering the integration of AM into large-scale production.
Speaking to Laser Systems Europe, Michael Anton, materials business manager EMEA at 3D printing system provider Stratasys, noted: ‘We are getting more and more requests to help with optimisation of design software for the design stage. I am currently working on a presentation talking about design for AM because unfortunately there is not much written material available on this.’
Anton said that until recently, designers have been thinking in prototypes that mimic the final parts manufactured in traditional ways. He commented: ‘A lot of designers today are still following a list of rules to make parts producible through traditional manufacturing. This means we need to change the way designers think about the process and start making them think outside the box.’
Anton believes this is a change that will be seen over the next few years because ‘now, with the background of additive manufacturing we can think about “what can we do better, what can we do differently? Where do we need to increase wall thickness and where do we need to make things a little thinner?” We have to split our thinking; it is absolutely a change in the mindset of the designer.’
In order to assist the designer in this changeover process the software they use is key, and automated or suggestive functions will help make the mental switch easier. Stratasys provides its own system-software for 3D printing.
Anton explained: ‘This is print preparation software. The Objet Studio allows you to load STL files and prepare a job for production. You place the part into the build envelope, can change the scale as required, you can choose the material, create hollow parts or an overmoulding, and choose the support styles, and more.’
For Stratasys’ fused deposition modelling (FDM) systems, there are different kinds of software available for different machines. Anton said that some are just ‘green flag’ programs for simpler tasks which are chosen for design approval before processing, but there is also software that offers more options for more demanding high-end applications.
Anton explained: ‘The easier applications allow you to place the parts, make copies and adjust scale, as well as being able to alter the build supports; this is what we mean by green flag software. For really professional work, you can adjust each layer of the design, adjust wall thickness, control the supports; there are a few dozen parameters that can be used to produce the best working part with the desired properties. It is very important to control, for example, the wall thickness to avoid air gaps, set the right raster tolerance, or repair some STL issues. A lot more parameter settings are available with the Insight software.’
Katrien Lenaerts and Tim Van den Bogaert, both product managers in Materialise’s software division have also noted the increasing demand for optimised AM software. Belgium-based Materialise have offered software to users of AM for 20 years but the spokespeople told Laser Systems Europe in a statement: ‘Today we experience a tendency of optimising existing product designs with the help of additive manufacturing. In this case, often the initial product has been designed in conventional CAD and we will use tools like 3-maticSTL to revise and optimise the design for AM.’
Even though there are a variety of methods for AM, from stereolithography through to direct metal deposition, the first few processes are the same from the software’s perspective. From the initial CAD model of a design, Lenaerts and Van den Bogaert explained that before the build can take place the design file must be converted into STL (Standard Tessellation Language) format, (see panel).
The designer must then ensure that the file is watertight so that it can be built, but the closer the process gets to the machine the more specific functions must be, depending on the technique being used. Materialise’s product managers said: ‘Those specific functions are in order to be able to actually build the part and to utilise the machine as efficiently as possible. In a laser sintering machine you can stack parts on top of each other and the more parts you can manage to squeeze into the build area, the more efficient the working. Doing this by hand takes a long time and it is incredibly hard to reach the same results as software algorithms doing the work for you.’
Actually building the part is one of the less familiar aspects of AM when transferring from conventional processes. Due to the layer-by-layer approach, supports are crucial in the build stage to ensure the part doesn’t fail and the requirements of the structures depend on the materials used. Without support structures on a stereolithography machine the build will likely fail. In most metal technologies support structures are even more important and are typically much stronger and more numerous. The ideal support structures will vary so Materialise and Stratasys offer specific software tools for different materials or process types.
Stratasys’ Anton explained the physical problem: ‘There must be supports for every wall with even a very small negative angle. Only positive and right angle walls do not need support. With the PolyJet technology, any overhanging geometry needs a supporting structure. For the FDM software there is more freedom to create a support; you don’t need support for an overhanging side wall of up to 45° for some cases. This means for low angle side walls, you don’t need supports which makes the job cheaper, quicker, and easier.
From the software’s perspective Van den Bogaert and Lenaerts explained that the user must distinguish between the plastic technologies, such as stereolithography or FDM, and metal technologies. ‘The plastic technologies have been in the market for a much longer period and thus the processes are much better known. This allowed us to fully automate the generation of supporting structures for these technologies, while also optimising material consumption, part quality and minimising finishing operations.
‘For metal technologies we do offer a very extensive toolkit and also an automated suggestion. However, a skilled person is still involved in order to tweak the supporting structures with the tools available in the toolbox. At this point in time a fully automated solution is not desired by the users.’ They concluded that given the typical applications for metal AM, users more often want to have control over balancing part quality, production speed, and finishing processes.
One way to improve the speed of the build is to reduce the amount of material required and less material offers other benefits as well. It reduces part costs, which is good for prototype design; a lighter part that maintains its strength can be helpful if the part is designed to be functional as well. This lightweight construction – typically using lattice or honeycomb structures – is one of the main selling points of additive manufacturing.
Implementing a lattice structure is very hard if not impossible to do in traditional CAD, according to Lenaerts. On STL it is still cumbersome given the sizes of the dataset generated, she said, so automating the process would help the user.
Van den Bogaert and Lenaerts explained: ‘On the one side we have an R&D tool called 3-matic which has a large automated toolset to start from any geometry and introduce porous structures in it by clicking some buttons. This is a balance between giving the user enough freedom to experiment and to completely automate.
‘If one of our customers wants to fully automate a certain workflow which they find suitable for their application then we will go into a development project for them and automate everything. However, the application is then typically so specific that it becomes a custom development for our customer which is not useful to the general market.’
Whether these features are automated or not, the user must still be educated in how to get the most out of the software and the amount of pre-required knowledge from the user depends on the system. Anton explained: ‘For entry-level systems, the operator needs to be able to use windows, a mouse, and a keyboard; it’s really easy to use and easy to learn. The training provided with the system installation to use the software properly takes around a day; there are no hidden functions so it’s very much a “plug and play” system.’
After the easy things are running and the operator has worked for a few weeks with the standard level functionality, Stratasys offers an advanced training course to speed up the operator’s knowledge. This would let the operator work using all of the available parameters and opens more possibilities to produce high-level parts, noted Anton.
As mass additive manufacturing comes to fruition, it is important to monitor all aspects of the build. Van den Bogaert and Lenaerts explained: ‘Especially if we are talking about the industrial laser technologies, there is an evolution going on towards mass manufacturing of final components. In these environments the management of the production process, feedback from the machines on performance, traceability of each component produced, things like this are at least as important.
‘For this reason Materialise offers an entire platform of software solutions, both covering the data processing originating from a wide variety of applications up to the wide variety of printing technologies and at the same time supporting the manufacturing process from order intake up to shipment of the produced components.’
Tom Eddershaw is a technical writer for Electro Optics, Imaging & Machine Vision Europe, and Laser Systems Europe.
You can contact him on email@example.com or on +44 (0) 1223 275 478.