Smart Adhesives in Additive Manufacturing

Presentation by Dr Keith M. Azzopardi about smart adhesives and their role in additive manufacturing at info seminar for Horizon 2020 “How to implement Nanotechnologies, Advanced Materials, Advanced Manufacturing, and Processes, and Biotechnology (NMBP)” On 29th January 2018

Additive Manufacturing

In its broadest sense is creating an item by adding material. In practice this usually involves creating a physical model from a virtual model with the assistance of specific equipment. Material is generally added layer upon layer till the final model/product is achieved. The benefits of this over subtractive manufacturing is that:

• It constitutes a lot less material wastage.
• One can create more complex designs, in one go, allowing for more efficient designs and weight saving.
• Turn around time is generally faster than traditional techniques.

We are seeing that the adoption of 3D printers is being accelerated with an increase in understanding of how this tool can be integrated into day to day processes of companies.

The Hype

The initial hype in the industry, which was embellished by a lot of mainstream media, was that 3D printing will hail a new manufacturing revolution. It was forecasted that 3D printers would become common place in everyone’s homes. Rather than going out to purchase an item you would just download the file and print it at your own convenience. This as we all know has not happened yet. We might still move towards this direction in the future but the industry is not there yet.

Trends

Even though 3D printing has not become a home factory, more and more companies are realising the benefits of having this capability inhouse.

Currently the main drivers to 3D printing adoption are:

• Prototyping – The benefits of using 3D printing in prototyping was realised at the inception of the technology.  This being said, early 3D printers came with hefty price tag and adoption by the masses was not viable. With the expiration of certain patents there was a sudden insurgence of desktop 3D printers, which slashed the cost from something in the 10Ks or 100Ks to a few hundreds or thousands. Once this barrier was removed uptake flourished and the benefits of quick turnaround times and the possibility to iterate cheaply could be  reaped by a much larger sector.
• Production / End use parts
  • Customisation –  The ability to customise and personalise objects, is a highly sought after feature. The new buzz seems to be around ‘mass customization’, which is in effect the bridge between traditional manufacturing and custom fitting. Not surprisingly this is being pushed heavily in the footwear market.
  • Low volume runs using 3D printing have already started to become mainstream. The advantages here are that you do not have to invest large amounts of capital into molds, which can’t be iterated (too much) after being produced. Additionally lead times can go from weeks or months to days. This means that as soon as beta tests are done you can launch soon after. If you get any negative client feedback, it’s much easier and cheaper to iterate and keep your clients happy. As a general rule, a 10 000 pcs as production run is the point to shift back to traditional techniques.
  • Complex designs – Systems such as open cell structures are showing a whole array of new ways to use materials. Before it was very difficult, if not impossible to produce these structures as single item. This was even more so in the case of mass production.

Hurdles of adoption

• Software for design, printing and post processing is in constant development – it requires quite some time to learn how to efficiently design for 3D printing applications, as well as slicing it in a way that eliminates/reducing possible flaws of printing. Soon we can expect to see systems to become smarter with real time sensing and ultimately artificial intelligence applied in this field to eliminate certain level of errors.
• 3D printer hardware is still not plug and play – the printing process requires good level of understanding how to design for 3D printing, what materials to pick and how they perform in printing process. Hardware requires constant calibration and fine tuning. Also the printing speeds are not as fast as industry would like it to be.
• Materials and ease of printing – there is an ever growing number of materials that are introduced to the sector, but even though the R&D and marketing claim that new materials are easy to print with, they still often pose the usual problems of warping and detachment.

No one-size-fits-all solution for material adhesion

The manufacturing industry wants to 3D print with materials it is already accustomed to. Thus, there is a race to adapt the current materials for 3D printing. From a practical perspective the variety in materials is needed because each presents its own beneficial properties, such as the required hardness, durability to wear and tear, robustness, flexibility, temperature durability and chemical resistance. The hard part is that each of the plastics will have different traits and properties as well as would act slightly differently on each 3D printer.

Adhesion challenges

a list of simplified adhesion challenges for each type of plastics:

• ABS – Nitrile groups, unsaturation and triple bonds make it more polar although less so than PLA due to the larger relative amount of carbon atoms. ABS is said to be a mostly amorphous thermosetting polymer and is one of the more challenging material to print with due to warpage. Magigoo helps prevent warpage of the material by helping the print stick to the bed while it is hot and still mouldable.
• PA/nylons – Dominated the the amide functional group, the systems have a degree of polarity. This being said there is a significant amount of variability within this class which make it difficult to come up with a general purpose solution for nylons. Adding to this these materials are also very hygroscopic and require prolonged drying time prior to printing and sufficient storage conditions.
• PP – as well as other polyolefins – are saturated hydrocarbon systems. They have low surface energies which makes them very difficult to adhere. A concept faced through the adhesives industry. Adding to this, it is a semi-crystalline material which makes the warping even more prevalent. This being said engineers and industry has a clear need for this material. As a raw material it is cheap and also has material benefits of chemical resistance and gives the user the ability to create living hinges.
• PC – Is a polar system but now also introduces a significant amount of aromatic character. Here you need to accomodate for these new chemical interactions and be able to compensate for the larger warping forces that it presents.
• PEEK – Is a high performance polymer. Here the aromaticity is even more pronounced. Higher printing temperatures create more of a thermal gradient imposing a new problem. The forces caused during warping in PEEK is also relatively high.

To add the complexity, it is not only required to 3D print the plastic, but the solution has to fit the process, thus be easy to apply, remove and post process. Hence the class of smart adhesives is required to solve the first layer adhesion problem and provide adhesion properties when they are needed, at level they are needed and providing multiple functions in one formulation e.g. first sticking, then stopping/reducing the adhesion when done and be possibly easy to clean as well as environmentally friendly.

Thought3D Lts is a R&D company developing and producing smart adhesives for first layer adhesion in 3D printing. Its first product Magigoo comes in different shapes and forms and works with most common plastics. In 2018 company will release its adhesion solutions for engineering plastics like PA, PP, PC.