Materiali per stampare in 3D: PLA vs ABS

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Aspetti comuni
Molti materiali vengono presi in considerazione per la stampa 3D ma le due palstiche dominanti sono l’ABS e il PLA. Entrambe sono termoplastiche, cioè diventano modellabili quando vengono riscaldate e tornano solide quando vengono raffreddate. Il processo può essere ripetuto infinitamente: il fatto che possano essere rimodellate le ha rese prevalenti nella società odierna ed è la ragione per cui la maggior parte della plastica con cui interagiamo giornalmente sono termoplastiche.

Esistono molte termoplastiche ma solo poche sono usate per la stampa 3D: per essere adattabili alla stampa 3D devono superare 3 test: la possibilità di trasformarle in filamento plastico, la possibilità di distribuirle in varie forme durante il processo di stampa ed infine di essere utilizzabile per le applicazioni finali.

In altre parole devono poter essere usate come “inchiostro” – Filamento Plastico – per le stampanti 3D, devono essere in grado di essere processate in modo ottimale per creare componenti utilizzabili ed infine devono poter essere utilizzare per il loro scopo, in termini di resistenza, durevolezza e aspetto.

Il primo test, quello per la formazione di Plastic Filament di alta qualità è un processo semplice ma che deve essere monitorato con attenzione per trasformare la plastica da un ammasso di palline a una densa, uniforme striscia senza bolle o malformazioni. IN questo caso ABS e PLA si comportano più o meno nello stesso modo; quasi tutte le termoplastiche sono in grado di passare questo test, è solo una questione di tempo e costi.

Stoccaggio
Sia l’ABS che il PLA funzionano negli se prima dell’uso e quando devono essere immagazzinati a lungo, sono sigillati dall’atmosfera per prevenire l’assorbimento di umidità. Ciò non significa che la plastica si rovinerà rimanendo per una settimana sullo scaffale del negozio ma un’esposizione duratura a un ambiente umido potrebbe danneggiare sia il processo di stampa che la qualità delle parti finite.

ABS – Moisture laden ABS will tend to bubble and spurt from the tip of the nozzle when printing; reducing the visual quality of the part, part accuracy, strength and introducing the risk of a stripping or clogging in the nozzle. ABS can be easily dried using a source of hot (preferably dry) air such as a food dehydrator.

PLA – PLA responds somewhat differently to moisture, in addition to bubbles or spurting at the nozzle, you may see discoloration and a reduction in 3D printed part properties as PLA can react with water at high temperatures and undergo de-polymerization. While PLA can also be dried using something as simple as a food dehydrator, it is important to note that this can alter the crystallinity ratio in the PLA and will possibly lead to changes in extrusion temperature and other extrusion characteristics. For many 3D Printers, this need not be of much concern.

Odore
ABS –  While printing ABS, there is often a notable smell of hot plastic. While some complain of the smell, there are many who either do not notice it or do not find it to be particularly unbearable. Ensuring proper ventilation in small rooms, that the ABS used is pure and free of contaminants and heated to the proper temperature in a reliable extruder can go a long way in reducing the smell.

PLA – PLA on the other hand, being derived from sugar gives off a smell similar to a semi-sweet cooking oil. While it certainly won’t bring back fond memories of home-cooked meals, it is considered by many an improvement over hot plastic.

Accuratezza
Both ABS and PLA are capable of creating dimensionally accurate parts. However, there are a few points worthy of mention regarding the two in this regard.

ABS – For most, the single greatest hurdle for accurate parts in ABS will be a curling upwards of the surface in direct contact with the 3D Printer’s print bed. A combination of heating the print surface and ensuring it is smooth, flat and clean goes a long way in eliminating this issue. Additionally, some find various solutions can be useful when applied beforehand to the print surface. For example, a mixture of ABS/Acetone, or a shot of hairspray.

For fine features on parts involving sharp corners, such as gears, there will often be a slight rounding of the corner. A fan to provide a small amount of active cooling around the nozzle can improve corners but one does also run the risk of introducing too much cooling and reducing adhesion between layers, eventually leading to cracks in the finished part.

PLA – Compared to ABS, PLA demonstrates much less part warping. For this reason it is possible to successfully print without a heated bed and use more commonly available “Blue” painters tape as a print surface. Ironically, totally removing the heated bed can still allow the plastic to curl up slightly on large parts, though not always.

PLA undergoes more of a phase-change when heated and becomes much more liquid. If actively cooled, much sharper details can be seen on printed corners without the risk of cracking or warp. The increased flow can also lead to stronger binding between layers, improving the strength of the printed part.

Proprietà generali
In addition to a part being accurately made, it must also perform in its intended purpose.

ABS – ABS as a polymer can take many forms and can be engineered to have many properties. In general, it is a strong plastic with mild flexibility (compared to PLA). Natural ABS before colorants have been added is a soft milky biege. The flexibility of ABS makes creating interlocking pieces or pin connected pieces easier to work with. It is easily sanded and machined. Notably, ABS is soluble in Acetone allowing one to weld parts together with a drop or two, or smooth and create high gloss by brushing or dipping full pieces in Acetone.

It’s strength, flexibility, machinability, and higher temperature resistance make it often a preferred plastic by engineers and those with mechanical uses in mind.

PLA –  Created from processing any number of plant products including corn, potatoes or sugar-beets, PLA is considered a more ‘earth friendly’ plastic compared to petroleum based ABS. Used primarily in food packaging and containers, PLA can be composted at comercial compost facilities. It won’t bio-degrade in your backyard or home compost pile however. It is natural transparent and can be colored to various degrees of translucency and opacity. Also strong, and more rigid than ABS, it is occasionally more difficult to work with in complicated interlocking assemblies and pin-joints. Printed objects will generally have a glossier look and feel than ABS. With a little more work, PLA can also be sanded and machined. The lower melting temperature of PLA makes it unsuitable for many applications as even parts spending the day in a hot car can droop and deform.

Riassumendo
Simplifying the myriad factors that influence the use of one material over the other, broad strokes draw this comparison.

ABS – It’s strength, flexibility, machinability, and higher temperature resistance make it often a preferred plastic for engineers, and professional applications. The hot plastic smell deter some as does the plastics petroleum based origin. The additional requirement of a heated print bed means there are some printers simply incapable of printing ABS with any reliability.

PLA – The wide range of available colors and translucencies and glossy feel often attract those who print for display or small household uses. Many appreciate the plant based origins and prefer the semi-sweet smell over ABS. When properly cooled, PLA seems to have higher maximum printing speeds, lower layer heights, and sharper printed corners. Combining this with low warping on parts make it a popular plastic for home printers, hobbyists, and schools.

Ecco alcuni dati:

Trovate ulteriori informazioni nella Plastic Filament Buyers Guide di Protoparadigm.com