PLA plastic is one of the most popular materials used in 3D printing today. This filament is easy to use, odorless, non-toxic, and made from renewable resources. Thanks to its technical characteristics, it can be used to print 3D volume models of various types, but only if the technological nuances are respected. Otherwise, the product can become deformed and the plastic can shrink.
Causes of deformation of PLA models
PLA plastic is a polylactic acid, that is, thermoplastic polyester, extracted from corn starch, tapioca roots or sugar cane. This material is widely used in manufacturing, including food production. PLA-plastic has a relatively low melting point – only 80 ° C, so in the manufacture of filament other plastics are added to the material, which makes it fully suitable for use in 3D-printers.
PLA plastic has minimal shrinkage parameters, the filament made of this polymer is more rigid, less subject to wear and tear, and models printed with this filament have a smoother and more beautiful surface.
The increased hardness and stiffness make the material quite brittle. Therefore, PLA is not suitable for printing those parts that will be subjected to serious mechanical stress in the process of use.
Also PLA is not suitable for high temperatures – due to the low melting point already after 70 °C the product will lose its rigidity, will give shrinkage and deform.
Also shrinkage may occur directly in the process of printing due to the difference in temperature conditions inside the product and on its surface. A sharp difference will cause the edges of the model to rise and deform the entire product.
The shrinkage effect can be caused by too much free space in the print box. The problem occurs when the table is not powerful enough to sufficiently heat the heat box space throughout the entire volume of the model being printed.
Shrinkage can occur because the part does not adhere well enough to the table surface. If there is not enough adhesion, the internal stress (shrinkage) will overcome its forces and the product will lose its shape.
PLA shrinkage can also occur because of the low sinterability of the layers. If the internal stress exceeds the sintering strength of the layers, a tear will occur and cracks will appear on the surface of the model.
The 3D printing process can also be hindered by the unscrupulousness of the filament manufacturer. Due to the effect of liquation, i.e. heterogeneity of the chemical composition formed during crystallization, the model will not lose its visual appeal, but its final performance characteristics will fall markedly. Most often, chemical heterogeneity occurs when the manufacturer does not control the purity of the plastic formula.
Why does shrinkage occur in PLA plastic?
Shrinkage is the property of polymer material to decrease in volume during the curing process. The effect is expressed as a percentage and directly depends on how pure the chemical composition of the filament is, as well as the melting temperature of the polymer and the temperature in the thermal box during 3D printing.
IMPORTANT: as a rule, high-quality materials have a shrinkage not more than 0,5 %, low-quality materials – up to 4-5 %.
It is worth noting that the first layers of the product are subjected to shrinkage to a greater extent, as this zone is subjected to constant heating due to the energy transmitted by the printer’s table and the corresponding difference between the temperatures of the subsequent layers.
How to avoid shrinkage?
In order to avoid shrinkage and deformation of the PLA model, it is recommended to follow the rules listed below.
- Increase adhesion. How firmly the first layers of the model are bonded to the work surface, directly affects the final quality of the product. Adhesion can be increased by changing the material of the work table – there are surfaces made of aluminum, glass, basalt, titanium, etc. Also a popular means to increase adhesion is a special polyamide film, which is applied to the working table before starting printing. In some cases, such a film is additionally treated with sandpaper – the sanded surface will increase adhesion to the plastic. Also, adhesion can be increased by applying a special spray adhesive or hairspray.
- Reducing print speed can also reduce deformation. This will increase the time cost, but will result in evenly cooled layers, reducing the likelihood of excessive material shrinkage. This rule is extremely important for printing with PLA plastic because polylactide has a long cooling time and the lower layers can be deformed by the pressure of the layers applied on top if they do not pass the glass transition point.
- In order to avoid shrinkage, it is necessary to get rid of possible drafts. If they occur, the part will cool unevenly and shrinkage will occur at different rates, leading to a skewed model. You can avoid negative effects by purchasing a printer with a closed chamber or by isolating the room in which the device is located by tightly closing doors and windows. The model must be cooled quickly and evenly, so printers are equipped with additional fans on the extruders
- Reduce the print temperature. It is optimal to set a temperature that is only slightly higher than the glass transition temperature of the plastic used. In this way extrusion will proceed correctly and the layers will fuse with each other quickly. Excessive temperature leads to longer cooling times and therefore the possibility of excessive shrinkage of the product.
- Reduce the print density. Optimal is to choose a printing model that is filled inside with a mesh or honeycomb of plastic threads. This option is the most advantageous, because in this case not only reduces the consumption of material, but also reduces the likelihood of deformation due to the sufficient rigidity of the structure and a relatively smaller volume of plastic in the upper layers, which minimizes the pressure created.
Printing mistakes and how to avoid them
When printing PLA plastic, errors can occur that will eventually lead to shrinkage of the finished model.
The most common are:
- Insufficient adhesion of the first layer of the product. If this indicator is insufficient – the model may shift due to the first layers peeling from the surface of the heating table. To solve the problem, you can increase the temperature of the platform heating or cover the table with a special composition or film, which will mechanically increase the adhesion. Polyamide film, aerosol adhesive, PLA and solvent suspension, as well as regular hairspray and glue stick have proven to be good. It is also recommended at the 3D model design stage to increase the contact area of the part with the surface by adding a raft – an extended first layer.
- Appearance of threads, shaggy, cobwebs. The effect occurs when the material does not match the temperature settings of the printer. It is recommended to decrease the temperature of the extruder and use the retraction function – retracting the filament in the opposite direction if the extruder head hangs up.
- Deformation of the product. Shrinkage in this case occurs because the printed layers do not have time to harden and cool completely. To avoid this phenomenon, it is necessary to reduce the printing speed and reduce the temperature of heating the plastic. It is also recommended to set the airflow so that the air is not blown onto the extruder.
- Over-shrinkage can also occur if the layer thickness and fill percentage of the part are set incorrectly. If problems occur, it is recommended to change these settings according to the manufacturer’s requirements.
PLA plastic is a material widely used in 3D printing. It is easy to use, and products printed with this filament have high performance characteristics. However, printing with this plastic requires compliance with a number of requirements for temperature conditions and printing speed. If these rules are not followed, the product may deform.
