Advanced Guide to printing PLA Filament

Author: Matt Tyson/Monday, 21 May 2018/Categories: How To

Advanced Guide to printing PLA Filament

With a variety of blends exhibiting different mechanical properties, wide colour range and excellent resistance to warping; PLA has become one of the most popular 3D Printing materials due to its low printing requirements and excellent dimensional stability.

Contents:

What Is PLA? 
  Regular PLA
  PLA+
  Nano-reinforced PLA
  Filled PLA

Printer Setup
  Loading & Unloading Filament
  Bed Surface
  Bed Leveling & Nozzle Height
  Pre-heating
  Enclosure
  Filament Storage

Printer Settings
  Nozzle Temperature
  Bed Temperature
  Cooling
  Rafts
  Supports
  Dual Extrusion

Post Printing
  Removing a print after completion
  Removing Layer Lines
  Painting
  Joining

Trouble Shooting
  Blocked Nozzle / Filament Jam
  Heat Creep
  Warping
  Poor Layer Adhesion
  Parts difficult to remove from platform

What is PLA?

Regular PLA

PLA (Polylactic acid) is a semi-crystalline plastic and is one of the most popular and easiest materials to 3D print due to its accessible and minimal printing requirements. PLA is a biodegradable and recyclable plastic and PLA filaments are available in a variety of colours including opaque and translucent options.

Regular PLA is a stiff material exhibiting a high stiffness / modulus however its low impact resistance limits its overall applications. One of the advantages of regular PLA is it is easy to 3D Print with near-zero warping, making it the ideal material for large demonstration pieces, architectural models and product design. PLA exhibits a low chemical resistance and low temperature resistance, softening at 60°C (Glass Transition and Vicat temperature).

PLA+

PLA+ materials are modified PLA materials exhibiting improved mechanical performance when compared to regular PLA. Amongst the various PLA+ materials on the market, PLA+ materials generally improve upon the already high tensile strength of regular PLA. 

PLA+ materials exhibit the same low chemical resistance and low temperature resistance with regular PLA materials.

Nano-reinforced / PolyMax™ PLA

PolyMax™ PLA is a nano-reinforced PLA material exhibiting superior impact resistance and ductility when compared with ABS, PLA+ and regular PLA filaments.

With a toughness / impact resistance 20% stronger than ABS and near-zero warping, low odor and low residual stress during printing, PolyMax™ PLA is a suitable replacement for ABS for many applications. Support and raft removal is easier when compared to PLA+ and regular PLA materials.

PolyMax™ PLA exhibits the same low chemical resistance and low temperature resistance as PLA+ and regular PLA materials.

Filled PLA

There are also a wide selection of PLA filaments manufactured with composites and additives. These composites range from glow in the dark, chopped wood or metal and even carbon fibers.

Filaments manufactured with these composites are highly abrasive and will damage the nozzle, extruder and filament detection switch. For most users we recommend avoiding PLA materials that use these abrasive composites and opting for alternative materials. For example printing with a wood-mimic PLA filament that contains no real wood improves user experience and prolongs the life of the 3D Printer or printing with an nano-reinforced PLA instead of carbon fiber filled PLA for a better print quality and reliability.

Printer Setup

Loading and Unloading Filament

Changing between two PLA materials:
If the printer is currently loaded with a different PLA material, unload that material at 200-210°C and extrude your PLA filament at the same temperature. Stop extruding the PLA filament after the previous colour is completely purged.

Changing from a higher temperature material:
If the printer is currently loaded with a higher temperature material (for example ABS), unload that material at its recommended printing temperature, and then load and extrude your PLA filament at that same higher temperature. It is important to load the PLA at this higher temperature so the previous material can be pushed out.  Stop extruding the PLA filament after the previous material has been completely purged.

Changing from a lower temperature material:
If the printer is currently loaded with a different lower temperature material, unload that material  at its recommended printing temperature, and then load and extrude your PLA filament at 200-210°C. Stop extruding the PLA filament after the previous material has been completely purged.

Bed Surface

PLA is one of the easiest materials to print, adhering to a variety of printing surfaces

BuildTak™, FlashForge Sheets etc. (Recommended)
These surfaces are an adhesive backed sheet designed to stick onto your printers bed or removable platform. These sheets are our favourite printing surface when printing PLA due to their compatibility with other 3D printing materials, minimizing the need to recalibrate the printers nozzle height when printing multiple materials. It is possible to slice damage these sheets however if you remove the parts gently and set your nozzle height correctly, these sheets will last longer than printing surfaces like blue tape.

Heated Glass Bed (Recommended)
Printing PLA straight onto a heated glass bed is an excellent option if you primarily print PLA. Printing on glass gives the bottom of your prints an incredibly smooth and shiny finish. Of course this requires your printer to be equipped with a flat glass bed and setting your nozzle height correctly is extremely important when printing on glass.

Other surfaces:
When printing PLA you can also print with a variety of other printing surfaces such as blue tape, glue stick and even hairspray (hairspray is not recommended). These surfaces are widely available; offering a fast way to start printing. These surfaces must be replaced often.

Bed Leveling & Nozzle Height

It is important when printing PLA that your first layer adheres to the printing bed. To achieve this it is important to ensure your bed is perfectly levelled and your nozzle height is set correctly.

The ideal nozzle height when printing most materials (including PLA) is a distance of 0.1mm, this is the thickness of two pieces of paper. When changing between bed surfaces, it is important to adjust the nozzle height again to compensate for the added thickness of the bed surface.

Pre-Heating

When printing PLA, pre-heating the heated bed or extruder is not required.

Enclosure

An enclosure is not required when printing PLA.

Printing PLA on an enclosed printer can still be beneficial as the enclosure protects the print from drafts and external temperature changes.

Many enclosed printers have top lids / doors which can be opened or removed. When printing PLA on these printers, we recommend keeping the lid open to prevent the environment getting too hot. This is especially important in summer.

Filament Storage

Like many other plastics, PLA is a hygroscopic material, absorbing moisture from its surrounding environment. When the filament passes through the hot end the moisture rapidly expands creating bubbles in between layers, poor layer adhesion, inconsistent extrusion due to material expansion and thus poor surface quality.
PLA will typically absorb moisture over a period of months however in environments with high humidity (evaporative air-conditioning) this process can take days.

Removing Moisture:
It is possible to remove this moisture by drying the filament. To dry a spool of regular PLA, place it in a pre-heated convection oven at 45˚C for 12-16 hours.

Polymakers PLA materials can be dried at a higher temperature thanks to Polymakers Jam-Free technology which increases the softening temperature of the filament. The majority of Polymakers PLA filaments can be dried at 80˚C for 8 hours while PolyWood™ filament can be dried at 70˚C for 8 hours.

The temperatures listed are for ovens with accurate temperature control. It is important to pre-heat the oven before drying to prevent temperature over shoots. Drying without pre-heating or with higher drying temperatures will cause the filament to fuse together.

Preventing Moisture Absorption:
It is important to store and print your PLA materials in their optimum environment (below 20% humidity) to prevent moisture absorption, as excessive drying will degrade the filament. We recommend storing filaments in a resealable bag with desiccant when not in use and we recommend using a filament dry box like the PolyBox™ when printing. The PolyBox™ is a spool holder / dry box in an environment below 20% relative humidity, preventing moisture absorption.

Printer Settings

Nozzle Temperature

PLA is considered a low temperature material, typically printing between 190°C - 220°C. Of course the optimal printing temperature of a PLA filament will vary depending on which printer you are using and more importantly will vary between filament brands.  

To find the optimal nozzle temperature we recommend starting with a temperature right in the middle of the manufacturer’s suggested settings. If the manufacturer recommends 190°C - 220°C, printing at 205°C is a good starting point. Based on the quality of the print we suggest adjusting ± 5°C at a time.

Troubleshooting Nozzle Temperature
If the nozzle temperature is too hot, you may experience wisps / stringing on the surface of the print, difficult to remove and fused support material , sagging and poor surface quality on overhangs and a noticeable smell during printing.

If the nozzle temperature isn't hot enough, you may experience compromised mechanical properties due to the poor layer adhesion, under-extrusion (uneven / rough surface quality) and if the filament is not melting fast enough; nozzle blockages.  

Bed Temperature

PLA can be printed without a heated bed, however success without a heated bed is dependent on your printing surface, printing environment and model size.

A heated bed can be used when printing PLA (up to 60°C). It is important your heated bed isn’t set above the materials glass transition temperature, which for PLA is 60°C.

Cooling

When printing PLA it is best to print with the cooling fan on. The cooling fan solidifies the plastic which helps to prevent the model fusing to supports. 

Adequate cooling is also important when printing complex models with unsupported overhangs. To improve overhang print quality you can orientate the model so overhangs are facing the cooling fan.

Rafts

A raft is not required when printing PLA materials however if the printing bed is not perfectly levelled, a raft can be used to compensate and improve bed adhesion. When printing both the raft and model in PLA, the raft is harder to remove than ABS however should still peel away.

Supports

When printing both the supports and model in PLA, supports will be harder to remove than ABS but should still peel away cleanly.

If supports are fusing to the model, try decreasing the printing temperature by -5°C adjustments or increase the distance between the model and supports.

If your supports are failing / collapsing during the print, try increasing support density and printing with a raft , this will improve adhesion for the supports.

Dual Extrusion

Support & Raft:
Dedicated support and raft materials compatible with PLA include PolySupport™; an easy peel support material, PolyDissolve™ S1; an optimized water dissolvable support material and PVA.

Dual Colour / Material:
In most cases, PLA filaments will stick to other PLA based materials; ideal for dual colour printing.

Post 3D Printing

Removing a print after completion

Once your 3D Print has completed, it can be removed from the build plate. The best method to remove your PLA 3D Prints will depend on your build platform with some of these methods specific to removing PLA prints. 

Rigid Build Platform
On rigid build platforms like glass or aluminium, a sharp paint scraper can be used to easily remove the model.

Some printers are designed so the platform can be removed from the bed while other printers the build platform may be fixed in the printer. If the platform is fixed, we recommend supporting the platform with your second hand to prevent uneven pressure on the bed which could affect your bed leveling.

Flexible Build Platform
Some printers on the market print on flexible build plates. With these platforms users can flex the plate to remove prints.

Click here if you are having issues removing prints from the build platform.

Removing Layer Lines

ABS like other materials can be post-processed after printing to remove layer lines and achieve a smooth surface. ABS is considerably easy to sand for professional applications. In addition printing with finer resolutions and using a filler primer can drastically cut down on sanding / post-processing time.

PLA also be chemically smoothed however the chemicals involved for this process are incredibly dangerous and known carcinogens. The process of chemically smoothing PLA is not recommended by 3D Printing Solutions and should only be investigated by industrial clients prepared to follow all strict safety precautions. 

Painting

PLA plastics can be easily painted with acrylic and enamel based paints. Removing layer lines and model clean up are recommended before painting.

Joining

Parts printed in PLA can be joined with a variety of techniques

Glue
Gluing parts printed in PLA is simple, with your choice of CA, Super Glue, Guerrilla Glue and Two Part Epoxies. Two part epoxy is in our experience the best glue for PLA. We also recommend sanding contact surfaces with a coarse sandpaper to increase the surface area for the glue, this will result in a stronger join.

Friction Welding

Friction welding is the process of welding two 3D Printed parts together using a short length of PLA filament and a rotary dremel tool. This technique is incredibly simple and an effective way to create strong joins between your printed parts.

1. Cut off a short piece of PLA filament and load the filament in the rotary dremel tool. 
2. Turn on the rotary dremel tool and feed the spinning filament where your two parts meet.
3. The friction from the rotating filament will cut a deep channel between the seam and melt; fusing the two parts together.
4. Continue this process with a new cut of PLA filament and experiment with different directions, pressures and speeds to find the optimal technique for your tool.

Both 1.75mm and 2.85mm filament can be used to friction weld however this will depend on the rotary dremel tools chuck. Using 2.85mm filament is ideal for this technique as the thicker diameter will allow you to cut longer rods of filament, speeding up the process. 1.75mm filament can also be used however shorter rods will need to be cut to avoid snapping the filament.

In our experience gluing two parts together and then friction welding the surfaces results in the strongest join, these welding marks can be later sanded down and any pits in the surface can be filled with plasti bond.

Trouble Shooting

Blocked Nozzle / Filament Jam

When 3D Printing it is possible to encounter filament jams or nozzle blockages, these blockages can be caused due to a variety of reasons.

Causes and Steps to Prevent Nozzle Blockage and filament jams.
In all of these cases if the filament cannot pass through the extruder, the extruder gear will continue to try push the filament and will eventually 'chew out' the filament. If you hear a clicking or clunking sound coming from the extruder, this is a good sign that the filament is jammed or will be if ignored. 

  • If your extruder temperature is too low during printing, the PLA filament will not flow and will have difficulty extruding. Printing with the correct nozzle temperature will solve this issue.
  • If the filament is softening in the hot end, the extruder will 'chew out' the filament, causing a nozzle jam. This issue is known as heat creep, click here to learn more about this issue.
  • If there is too much friction on the filament, the extruder may have difficulties feeding the plastic. Try feeding the filament with a spool holder in different positions (above, beside, behind the printer).
  • If the nozzle height is set too close to the bed, the filament will have difficulty feeding through the nozzle eventually causing a filament jam. When printing at finer layer heights (0.1 and 0.05mm) the correct nozzle height is even more important. To prevent this issue it is important to print with the bed leveled and the correct nozzle height.
  • If the part is warping or lifting off the bed, the part will be pushing against the nozzle limiting extrusion and material flow, in this case it is important to prevent the part from warping.
  • Filled PLA materials (CF, Metal-filled etc.) are commonly known to cause nozzle blockages. Printing with a different PLA material or cleaning and keeping some spare nozzles is recommended.
  • Nozzle Blockages can occur more commonly with finer nozzles. The majority of 3D Printers are equipped with 0.4mm nozzles, it is important when printing or experimenting with a smaller nozzle (0.2mm) to adjust printing speed and extrusion settings 
  • If the filament is of poor quality is oval shaped or manufactured with an inconsistent diameter, this can cause the filament to jam in the extruder. The industry standard for filament tolerance is ± 0.05 mm. If the filament is 1.75mm an acceptable diameter variance would be between 1.70 - 1.80mm. Premium and higher quality brands can offer ± 0.02 mm tolerance. If you have difficulties printing PLA with only specific brands of filament this could signify issue with their quality control or could also be related to heat creep.

Cleaning a PLA Nozzle Blockage
If the nozzle is blocked with PLA one of the most successful solutions is to feed a tougher / harder and higher temperature material (for example PC-Max) through the extruder. In most cases, the properties of the tougher material and its higher printing temperature help to purge and remove the clogged PLA plastic. It is important when feeding the tougher material at its required printing temperature, for PolyCarbonate (PC) this is 250°C and to push the filament into the extruder during this process.

If you cannot remove the blockage of PLA plastic from the nozzle, we recommend swapping to a spare nozzle.

Heat Creep

What is heat creep?

Some users have difficulty printing PLA due to a problem known as heat creep. In essence this issue is caused when heat creeps up the extruder to the extruder gear and softens the filament. Rather than the gear gripping and pushing the filament through the hot end, it will chew the filament out.

Heat creep affects lower temperature materials like PLA due to their low softening temperature of 60°C and the issue is more prominent on printers designed to print high temperature materials, dual extruder printers where a section of filament sits idle for long times or cheap 3D printers with poorly designed extruders.

Solutions to preventing heat creep.

The first step is to make sure the extruder fan is and cooling the extruder as intended and if the printer is enclosed, printing with all front doors and top hatches open may help to prevent the filament from softening near the extruder gear.

This issue is also more common when printing parts models with retraction. The filament will feed past the extruder gear multiple times with each retraction, this makes it far easier for the extruder gear to ‘chew out’ the filament. Printing simple parts with little or no retraction are more likely to be successful as the filament will only be passing the gear once.

This issue can also sometimes be overcome with a different PLA material. All Polymaker PLA based materials (PolyLite™ PLA, PolyMax PLA, PolyWood™) are manufactured with an innovative Jam-Free™ technology which improves the heat stability of the PLA filament. As a result Polymakers PLA filaments exhibit a high softening temperature of more than 140 °C, so while printing, the filament will never soften in the “cold end” and can melt rapidly once entering the heating zone. It is important to note parts printed in Polymaker PLA filaments still exhibit the same heat resistance as other PLA materials

Warping

PLA materials are considered one of the easiest materials to print exhibiting near-zero warping and excellent dimensional stability. In some rare cases it is possible for PLA materials to warp or lift, lets look at why PLA shouldn't warp and what can cause PLA prints to warp or lift off the bed.

Simply put warping is caused by internal stress in the 3D printed part; this internal stress can be created in two ways for semi-crystalline materials.

1. As the filament is extruded through the small diameter of the nozzle, the polymer chain of the filament is stretched and will want to return back to its ‘normal’ state, much like a stretched elastic band will go back to its position when it is released and will curl / warp. At temperatures moderately close to the materials glass transition temperature (tg), the polymer chain will 'relax', releasing the internal stress and preventing warping. Due to the low (tg) temperature of PLA (60°C), PLA should print with minimal / near-zero internal stress at room temperature.

2. PLA like many other plastics (for example Nylon, PEEK) is a semi-crystalline plastic. Internal stress can be created specifically due to crystallization behaviour during printing, causing warping and cracking. When it comes to printing PLA at room temperature, internal stress caused by crystallization behaviour should be minimal due to how the material crystallizes. 

So if PLA materials generally print with low residual and internal stress, why can they warp?

Preventing warping.

  • The most common reason for PLA parts to warp or lift during the print is due to insufficient bed adhesion or an incorrect nozzle height. If the first layer of extruded plastic is not sticking to the bed, a small amount of small residual stress will be enough to lift the part off the bed. It is important to ensure your nozzle height and bed is leveled correctly, you are using the correct printing surfaces for PLA.
  • Drafts, cool air from air conditioners and low environmental temperatures in winter can cause the material to behave differently and will print with internal stress. An enclosure with a closed front door can help to maintain the right printing environment for users having difficulty with parts warping.
  • Printing with a heated bed at 60°C  can help to heat up the surrounding environment and improve bed adhesion and printing consistency.

Poor Layer Adhesion

Causes and steps to improve poor layer adhesion.

  • If the filament is under-extruding during printing there will be inconsistencies and gaps between the layer, compromising  mechanical strength and layer adhesion. It is important to ensure you are printing the PLA filament at the right nozzle temperature to ensure consistent flow and to minimize drag or tension which may prevent the filament from feeding.
  • Poor layer adhesion can also be caused when printing with a PLA spoiled with moisture. When the filament passes through the hot end, the moisture erupts creating bubbles in the extruded plastic, compromising  the parts mechanical properties. If a spool of filament has absorbed moisture, it can be dried however it is important to store the PLA correctly and prevent this issue from occurring.

Parts difficult to remove from platform

While excellent adhesion between the bed and part is important to achieve a successful print, sometimes it can be difficult to remove models if your adhesion is too good.

Causes and steps to improve print removal experience

  • Some print surfaces specifically manufactured for PLA materials are designed to maintain adhesion with the part when the bed is heated and self-release when the part is cool. Try removing the models when the heated bed is hot or cold to see what method best suits your printing surface.
  • Your heated bed may be operating too hot or your nozzle temperature may be too close to the bed. You can try making slight adjustments to the heated bed temperature or nozzle height if this improves your user experience. Of course this is a fine balance as adhesion between the print and platform is important to achieve successful prints.
  • While not required, in some cases with other materials, some users will use Glue stick on top of their print surface to act as a release agent for part removal.

 

Filament Links

PolyLite™ PLA Introduction
Buy PolyLite™ PLA

PolyMax™ PLA Introduction
Buy PolyMax™ PLA

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