Keys To Successful 3D FDM / FFF Printing

FDM / FFF 3D printing is one of the most widely used processes in additive manufacturing, whether to produce prototypes, tooling, or finished parts. Now compatible with a wide variety of thermoplastics, it makes it possible to design more or less complex components by adding successive layers of material on a printing plate.

Keys To Successful 3D FDM / FFF Printing

Better design to better print

When it comes to 3D printing, modeling is a crucial step; Volumic recalls: designing a model for FDM 3D printing involves quite significant changes compared to traditional manufacturing techniques. It will make it possible to optimize the printing time and the rendering and the material consumed (for the supports, for example), and the post-processing time.

Indeed, a part requiring supports will necessarily have a post-production time and maybe much less clean than one without support. In all cases where there is support, surface degradation is more or less severe depending on the technique used but always present.

It is, therefore, necessary to adopt new reflexes by trying to eliminate any surface with more than 45 to 55 ° of inclination compared to the base. In the end, it is often relatively easy to make a 45 ° chamfer rather than a shoulder—direct, which will require supports.

The hollowing out of the volumes is not necessarily a good thing either in FDM, according to the manufacturer, because the filling of the part can be chosen, unlike injection, for example, and hollowed out areas will often require supports by degrading the components.

Surfaces and consuming material that we were trying to save. The constraints in injection are not the same as in printing: you have to think differently, which is very important from the modeling stage.

The material, a choice not to be overlooked

More and more different materials are available to meet the maximum number of applications in all sectors of activity. Not all subjects require the same level of experience and attention. The main point that will make the material easier or more capricious to print remains the adhesion to the plate.

This point should not be neglected because, in addition to a failed impression, it can also generate quite significant machine breakdowns due to collisions of an object that has taken off. You can have direct collisions with the print head, which could be damaged and cause breakages on other parts of the printer.

The so-called “Standard” materials (PLA, PETG) are stabilized to provide excellent adhesion so that prints go smoothly, even if the machine’s calibration is not perfect. Additives are added to optimize adhesion and facilitate the printing process. 

On the other hand, more technical materials will have much less grip on the one hand, and very often a fairly significant shrinkage that risks generating warping, further reducing the surface area on the plate, and further increasing the risk of detachment.

Therefore, it is essential to prepare the printing surface well about the material to be printed, as there is no “universal” solution. For example, for printing technical fabrics with a high-temperature plate (110/120 ° C or more), Dimafix type lacquer will be more effective than 3DLAC. The latter is more suitable for standard materials and more economical.

It may also be necessary to use unique platen coverings. A PEKK will be able to print on a Vitro + Dimafix tray as a rule, but a PEEK or a PEI will be much more finicky and will require a PEI coating on the tray as well as lacquer. For this type of material, it is also advisable to set the machine zero point low enough (distance between the nozzle and the plate), to crush the first layer and increase adhesion properly.

Multiplying contours on the first layer to extend the surface to the plate are often of great help and generate relatively little post-processing. By sticking the part to its outline in this way, beyond properly arming the nozzle, the part will be held much better on the plate, even if initially its contact surface with the latter was small.

For materials that tend to delaminate upwards, a shield of one or two walls around the object over its entire height can also help keep more heat inside and prevent or reduce this kind of phenomenon.

How to properly prepare your 3D file

The STL model you have is very important for a quality result. Very often, the model created on a CAD software like SolidWorks, for example, is exported in STL with the software’s default parameters. This parameter should be adjusted according to your objects to generate a model with enough faces to have perfect quality curves and shapes. 

The resolution of the STL model is often wrongly underestimated because even if the faces are not seen as such on the printed model, this will generate noise on the surfaces, especially on precise machines like the Volumes, which will transcribe all those thousands of little movements.

Better a model a little heavy than not enough. Do not choose too fine a resolution if it is not really essential, the thinner the layers, the more likely they are to generate micro-collisions which will give you a worse result or cause your print to fail. The larger the object, the higher the mesh resolution should be. 

A fairly frequent source of error on the impressions also lies in the fact that the model which will be sliced ​​must be free from any mesh error (open faces, which overlaps …) because this risks being misinterpreted by the slicer and generate motions or extrusions which will cause the printing to fail. Always check the model for face errors; most slicers moreover have built-in verification functions.

There are more and more regarding these slicers, and software like the Adobe suite and Fusion are starting to integrate this. The cutting performance is now of good quality on most software (which was not necessarily the case a few years ago), the biggest differences will lie in the positioning assistance features, for example, settings for optimized printing and rendering, or personalized media handling, which can make all the difference. 

Volumic chose to work with Simplify3D because its slicing quality coupled with very efficient optimization parameters and its manual media management make it a simple and powerful tool at a very reasonable cost.

Finally, a good habit is to always monitor the start of your print and the status of the first layer infill. This will show you a good or bad calibration quite clearly.

The machine characteristics of the 3D printer

The essential points for printing are of course the temperatures of the nozzle and the plate in relation to the material. The impression profiles and the indications given by the manufacturers remain general. This therefore does not necessarily mean that it will be suitable in all circumstances, and may need to vary depending on the ambient temperature, for example, or the type of nozzle fitted. We very often underestimate what 5 ° C more or less at the nozzle can change!

The ventilation of the object is also very important for a good rendering, but can also reduce the bond between layers of the object if it is too important.

Concerning the speed , it will play a very important role in the final quality of the object, and more especially the relative speeds according to the zones. For example, increasing the print speed of the infill will save a lot of printing time without compromising on quality. On the other hand, increasing the speed of the walls will generate more and more artifacts and ghosting on the surface of the room. The speed of each zone has a very different impact and should be changed independently of the others for perfect optimization.

The plate’s temperature will condition the object’s adhesion, which is, therefore, more than essential. As a general rule, the ideal plateau temperature for a given material is, as far as possible, that of the Tg of the material in question.

Another essential point, which is surely the most important of all, is the cooling of the print head.. A badly cooled head will generate all kinds of malfunctions, but mainly filament blockages. For example, a change of 2 ° C in the head cooling body is sufficient to cause a PLA print to fail.

The filament must remain as cold as possible throughout the head to liquefy suddenly over the shortest possible distance before the nozzle (hence the thermal barrier), and especially not to heat gradually, otherwise, the filament will systematically hang. A nozzle and thermal barrier in good condition, and changed regularly, will give you quality objects and repeatability of prints. Volumic recommends changing the nozzle after 800 hours of printing on average. You can also use a purge filament which will dislodge the impurities. Moreover,

The type of nozzle used depends mainly on the printed material. Printing of loaded materials, even weakly, must be done with a hardened steel nozzle, otherwise, it will wear out very quickly and cause all kinds of problems and drop in quality.

On the other hand, a nickel-plated copper nozzle will give better results (due to its thermal performance) in rendering and speed on uncharged materials. Therefore, there is no “universal” nozzle that will give the best results in all circumstances.

Post-processing methods to go further

The post-processing can sometimes be tedious. This is why the placement of the supports must be done with care and without zeal. Proper substrate preparation can be a huge time saver in post-processing, don’t underestimate this step.

Always use safety gloves when working on the supports, even without tools, they can cut or scratch. The spatula remains a good tool to take them off, especially on large flat surfaces. Moreover, always peel off the supports in the direction of the filament of the layer in contact, this will have less resistance than in other directions.

A fairly effective option to facilitate the removal of supports is to configure a few “dense” layers in contact with the object for slicing. This will on the one hand improve the surface finish of the part at the location of the supports, but will also create a more solid support surface which will tend to be less fragmented on shrinkage.

Some materials will give very good results with substrates, like the Universal ULTRA, which will provide very clean surfaces after removal and come off much more quickly than other materials. Conversely, PETG, because of its excellent bond between layers, will be quite difficult to clean.

A deburring tool kit can be a big help and small flat screwdrivers and needle nose pliers (electronic type) for cleaning hard-to-reach parts. Ultrasonic cutters are also very powerful tools for this kind of work, a little expensive but very effective.