Note: This guide deals with the concepts in a general way and without focusing on a specific brand or model, although they may be mentioned at some point. There may be important differences in calibration or adjustment procedures between different makes and models, so it is recommended to consult the manufacturer's manual before reading this guide.

The printing temperature of a given filament depends not only on the type of material, but also on the printing conditions. Printing speed, nozzle diameter, extruder type or the distance between the extruder and the hotend have a considerable influence on the optimum printing temperature. This is why manufacturers usually provide a temperature range rather than a specific temperature.

The right printing temperature

It is a misconception to talk about the optimum printing temperature for a given filament. Within the range of temperatures that a given material can tolerate, there will be different optimum temperatures depending on the final requirements of the part. For example, the optimum temperature to obtain the best finish for the part may not be the optimum temperature to obtain the maximum mechanical resistance. This is why, in order to determine the optimum printing temperature for a given material, it is necessary to be clear about the final properties required for the part.

How to determine the optimum temperature

When determining the optimum printing temperature, the first thing to do is to define the priority of the final part: aesthetic finish or mechanical functionality.

To determine the optimum temperature prioritising finish quality, it is necessary to print a model that includes at least one bridge and one cantilever at different temperatures and determine the temperature that provides the best finish. There are many examples of models available in online repositories, usually referred to as temperature calibration towers.

Image 1: Example of a temperature tower including bridges, cantilevers and small details. Source: Thingiverse.com

When choosing temperatures, the manufacturer's recommended printing temperature range should be consulted. Ideally, the entire temperature range should be evaluated at 5 °C or 10 °C intervals. In addition, it is also recommended to evaluate 10 degrees above and below the range, due to differences between the manufacturer's and the user's printers.
For example, if for a certain material the manufacturer specifies a printing temperature range between 220 °C and 250 °C, the following temperatures should be evaluated: 210 °C, 220 °C, 230 °C, 240 °C, 250 °C and 260 °C.

Once the samples have been printed, which one provides the best quality and finish should be assessed, paying attention to the following aspects:

• No overhangs on bridges and cantilevers.
• That small details are sharp.
• No curling or lifting at the top corners of the part. To distinguish between curling and warping, it should be taken into account that in the case of warping, the lifting of the corners is greater at the base and decreases with height, while in curling it is the opposite: practically nil at the base and very pronounced at the top of the piece.
• Minimal threads. It should be borne in mind that even at the optimum temperature, threads may appear if the shrinkage configuration is not adequate.

Image 2: Curling or lifting of corners caused by overheating or malfunctioning of the coating fan. Source: Simplify3D.com

When the priority is to optimise the mechanical behaviour of the part, maximum adhesion between layers should be sought. To achieve this, it is necessary to print standardised specimens at different temperatures (as in the previous case) and test them. Generally, higher temperatures will produce better interlayer adhesion, so if it is not possible to test the specimens, it is advisable to work at the upper limit of the range provided by the manufacturer.

On properly calibrated printers, temperatures lower than the range provided by the manufacturer will generally produce a better finish on parts, at the cost of less cohesion between coats. Higher temperatures will ensure optimum intercoat adhesion but will also give a poorer finish, especially on bridges and overhangs.

Many materials will also have a sweet point, i.e. a temperature at which the mechanical properties and surface finish are close to optimum. To determine this temperature, it is necessary to carry out the two previous tests and check if there is a common temperature at which the mechanical properties are close to the maximum value and the surface finish is good.

Effect of temperature on colour and finish

In addition to the aesthetic and mechanical quality of the part, the printing temperature also affects the finish of the part. Both the colour and the finish of the part can vary depending on the printing temperature. Higher temperatures will produce a higher gloss on the surface of the parts, while lower temperatures will produce matt or satin finishes. The higher or lower gloss of the part will also vary the perception of colour.

Main problems resulting from inadequate temperature

As mentioned above, materials do not have a suitable printing temperature, but rather a range of temperatures within which the material can be printed resulting in parts with different properties. However, when the temperature is outside this range, problems start to appear that can lead to printing failures. It is necessary to distinguish between problems caused by over-temperature and under-temperature.

Problems caused by excessive printing temperature:

• Overhangs on cantilevers and bridges: Excessive temperature will cause the plastic not to cool fast enough, so it will collapse under its weight and cause sagging in overhangs and bridges. It should be noted that this can also be caused by poor layer fan performance in materials such as PLA or PETg.
• Curling or corner lifting: This is a phenomenon consisting of a lifting of the corners of the part due to shrinkage of the material during cooling. This effect is more pronounced in the upper layers due to the accumulation of temperature due to inadequate cooling of the previous layers.
• Lack of detail in small elements and edges: Too slow cooling will cause small elements to lose their shape, either due to the plastic's own creep or due to head friction and vibrations.

Image 3: Lack of detail in a vertex due to overheating. Source: simplify3d.com

• Stringing: In certain materials, such as PLA and PETg, excessive temperature will cause stringing in the hotend displacements. This phenomenon depends not only on the temperature, but also on the shrinkage configuration and the thermal performance of the hotend, so excessive temperature can lead to stringing, but stringing does not always imply excessive temperature.
• Difficult to remove supports (in the same material): If the temperature is too high, the adhesion between the workpiece and the supports may be so high that it is impossible to remove them without the use of cutting tools. This is only the case if the same material is used for the part and the supports.
• Inconsistent extrusion: Higher temperature also means lower material viscosity. If the temperature is too high for some materials it can cause the viscosity to be so low that the extrusion is not uniform.
• Heat Creep in the cold zone of the hotend: Certain materials such as PLA can start to creep at temperatures as low as 45°C. Too high a temperature in the hotend can cause the temperature in the cold zone to be high enough to soften the filament, causing clogging. Too high a temperature in the hot end of the hotend can cause the temperature in the cold end to be high enough to soften the filament, causing clogging. This phenomenon is known as heat creep. It is usually caused by inadequate thermal performance of the hotend, aggravated by the use of excessively high print temperatures.

Problems caused by a too low temperature:

• Lack of extrusion and clogging: Excessively low temperature can cause the plastic to not fluidise properly, resulting in lack of extrusion and sometimes clogging.
• Low interlayer adhesion: For good interlayer adhesion to occur, the temperature of the material must be high enough to partially melt the interface with the previous layer. Temperatures that are too low will result in low interlayer adhesion which can lead to delamination or layer separation on shrinkage.

Image 4: Separation of layers. Source: simplify.com

• Poor filler-perimeter bond or gaps in the seam: In general, to avoid material build-up at the end of an extrusion, laminating software sets up a retraction or run-in distance (stops extruding a little before reaching the end of the movement). Too low a printing temperature can result in not enough material being supplied to finish the extrusion, causing gaps between the perimeter and the infill, or in the closing area of the perimeter.