Preventing warping and improving adhesion of high temperature pla, Exercícios de Design e Aplicações de Lógica Digital. Universidade Paulista (UniP)
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vinicius_marion15 de Julho de 2015

Preventing warping and improving adhesion of high temperature pla, Exercícios de Design e Aplicações de Lógica Digital. Universidade Paulista (UniP)

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Preventing warping and improving adhesion of high temperature

PLA: A practical guide

By Razzak Al-Gurnawi (razzak.algurnawi@gmail.com)

Introduction

In the 3d printing community, PLA has traditionally been regarded as a material that allows

easy and trouble free printing. Its properties allow it to adhere to a variety of surfaces at a

relatively low temperature. While this is generally true, it is not always the case. Many users

in the 3d printing community have experienced problems with first layer adhesion and

warping, which are issues usually associated with ABS.

While this guide attempts to address some of the issues encountered with bed adhesion and

warping, it is by no means a complete guide. It is worthwhile noting at the outset that there is

no substitute for proper calibration of the printer, especially ensuring the level of the printer

bed relative to the nozzle is appropriate and consistent.

PLA types

It is important to note at this stage that PLA comes in several variants. For the purpose of

this discussion I will be focusing on the NatureWorks brand PLA. Most popular in the 3d

printing world seem to be the following variants:

Natureworks Ingeo 4 Series 4043D:

Natureworks Ingeo 4 Series 4032D:

The two products have some very important differences in properties which must be

considered carefully before printing. The major differences between the two materials lie in

their thermal properties. The 4043D plastic has a melting point of 145°C-160°C, while the

4032D plastic has a melting point of 155°C-170°C, making the latter more suitable for higher

temperature applications which traditionally have been the realm of ABS.

Problems encountered

This increased temperature resistance of the 4032D plastic raises several problems when it

comes to 3d printing. The two major ones are:

• Poor bed adhesion

• Warping of printed parts

These require higher extruder and heated bed temperatures, which in themselves cause

additional problems.

Poor bed adhesion

The 4032D plastic will not adhere to the printing surface as easily as the 4043D plastic. A

plain glass sheet may not be sufficient as the surface is too smooth for the plastic to bond to.

A part printed on a glass sheet typically seems to detach itself with minimal lateral loads

(poking with the finger).

There are many documented ways to overcome this poor bonding of the first layer:

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• Sandblasting the glass bed

• Using painters tape on the printing surface

• Using glue sticks

• Applying hairspray to the printed bed

• Using watered down PVA glue

• Lemon juice (I assume this has to do with keeping the surface free from oil?!)

• etc

Your mileage may vary with any of these techniques and many of them will work better than

others. They are all generally inexpensive and experimenting with what works is

encouraged. I personally have found the PVA glue technique to be excellent. Adhesion has

been so good, I accidentally broke a slender piece while removing it.

To apply this technique, mix a quantity of PVA with water. 2 parts water to 1 part PVA works

very well. Apply this to the printing surface using a brush. The heated bed will dry this layer

very quickly as it heats up. To decrease adhesion, simply add more water.

I have found that a heated bed at a temperature of 90°C works very well. It is possible to go

lower, but I have suffered poor results at anything below 70°C. Nozzle temperature can vary,

but 220°C +/- 10°C seems to be the optimal range. This avoids the filament rolling over the

surface and sticking to the nozzle.

Warping

Once good first layer adhesion was achieved, catastrophic warping of the plastic part is

usually experienced, an example of which can be found in Fig. 1.

Fig. 1 – Catastrophic warping

After an extensive review of online material, consultation of the material data sheets and the

material vendor, the reason for warping is believed to be due to the steeper temperature

gradient experienced by the part in the Z direction. This temperature gradient crosses the

glass transition temperature of PLA. Crossing this critical temperature threshold is believed

to cause the warping problems experienced with high temperature PLA (4032D). This does

not usually occur with regular 4043A PLA which is usually printed at bed temperatures

around 50 degrees.

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Glass Transition Temperature

Wikipedia defines the glass transition temperature as the reversible transition of an

amorphous material from a hard and relatively brittle state into a molten or rubber like state.

When undergoing this phase transition, the material experiences a large change in material

properties. This change in material properties also affects the expansion coefficient of the

material as shown in Fig. 2. While the material experiences one rate of expansion between

points A and B, once it goes through the transition (the region between points B and C) its

rate of expansion changes to the rate between points C and D.

Fig. 2 – Thermal expansion vs. temperature

Temperature gradient across the printing Z axis

A 3d printed part can typically be assumed to experience a temperature gradient as shown

in Fig. 3. If we heat the print bed to approximately 90°C, the lower layers (left hand side of

the graph) will be above the transition temperature of the material, while the upper layers

drop below it (right hand side of the graph). In practise, this means the part expands at

different rates across its Z axis. This causes the layers to curl on one another.

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Fig. 3 – Hypothetical temperature distribution across the Z axis of a printed part

Conclusion

Based on the analysis above, it would be prudent to print the part in question using a

temperature which is below the material’s glass transition. This however is in direct conflict

with the adhesion problem faced earlier, where it is established that it is important to print

the heat resistant PLA at higher temperatures to improve adhesion.

The solution to this is to use a high temperature to apply the first layer of plastic and get a

good level of adhesion. After the first layer is printed, the temperature is dropped below the

glass transition point (around 50°C -55°C). This allows the print to experience the same

lower rate of expansion (Fig. 2 region A to B) across its entire z depth. Curling is not

experienced at the first layer due to this temperature as the material layer is thin enough to

accommodate expansion and contraction.

This has indeed been tested successfully several times using a Printrbot LC v2 with a

heated bed and a glass sheet. The results are very consistent. An example of this is shown

in Fig 4.

Fig. 4 – Successful printing run

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