3D Printing Shrinkage Compensation

When 3D printing, the size of the object highly matters, but at times, it does not. The three highly used materials in 3D printing are PLA, ABS, and Nylon. ABS is slightly flexible and stronger, while the PLA plastic comes in several colors and it is biodegradable. But there is a big difference between the three types of 3D printing materials – the shrinkage factor. The shrinkage occurs as the material transition from the liquid state after melting to the solid state when in the curing process.

The shrinkage arises in the thermosets as the material changes from liquid to a solid state when in the curing stage. Some printers have features that allow the users to compensate for natural shrinkage of material to ensure the accuracy of every part. Mostly, the machines set the values automatically for the material combination but additional calibration and measurements might be necessary with some geometry. The number of loops needed to attain the desired accuracy highly varies depending on the geometry, general settings of the machine and the post-processing. The user can complete the process in various modes to understand how each part behaves in particular modes.

How Much Does PLA Generally Shrink?

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3D PLA Filament Shrinkage (source)

PLA, known as the Polylactic Acid, has many benefits because it is biodegradable, unlike some other materials like ABS. The manufacturers use renewable raw materials like corn-starch to make PLA. PLA is among the easier materials to print but it has a tendency of shrinking slightly after the 3D printing. You will not require a heated printing platform during the printing, which is the case to expect with ABS material. PLA also prints at a lower temperature that ranges between 190 degrees Celsius and 230 degrees Celsius.

PLA is a difficult material to manipulate because the cooling and solidification speed is very high. Moreover, the models can deteriorate after they get into contact with water. Nevertheless, the PLA printing material is simple to use, consistent and it is available in several colors. The features make it ideal for FDM 3D printing. The shrinkage rate of PLA is between 2.0-2.5 percent. That is considerably lower considering that the shrinkage of ABS is 8 percent.

How Much Does 3D Print Nylon Shrink?

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3D Nylon Filament Shrinkage (source)

Most manufacturers from different parts of the world use nylon (polyamide) to complete their 3D printing projects. That is because it has a high strength-to-weight ratio, it is flexible, corrosion resistant and has impressive flexibility. The material can withstand mechanical stress and therefore it is a good choice when printing 3D tools, end-use parts, and functional prototypes.

From making simple prototypes to designing complex aerospace component, engineers embrace nylon. Manufacturers from different parts of the world also find it a better choice for applications that need abrasion and impact resistance. The material is made to resist humidity. It is also highly flexible, durable and stronger than other materials, which makes it a choice for end-use parts. The shrinking rate of nylon stands at 1.7 percent, which is considerably lower than that of PLA and ABS.

How Much Does ABS Generally Shrink?

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3D ABS Filament Shrinkage (source)

Most individuals use ABS filament when completing their 3D printing projects. ABS is also highly used in parts of appliances, cars and mobile phone cases. The thermoplastic has a base of elastomers, which the manufacturers base on polybutadience to make it more resistant to shocks and flexible.

In 3D printing, ABS has to be heated to a temperature between 230 degrees Celsius and 260 degrees Celsius to make the objects. The material is tough and can easily withstand temperatures between -20 degrees Celsius and 80 degrees Celsius. Moreover, the material’s high strength makes it reusable and the users can weld it with some chemical processes.

However, the ABS material shrinks when it gets into contact with air and it is not biodegradable and therefore the 3D printing platform has to be heated to eliminate chances of warping. Moreover, experts recommend the use of closed chambers in the 3D printer to eliminate the chances of particle emissions during the printing process. People mostly use ABS in fused deposition modeling technology. Producers also provide the ABS material in liquid form for use in PolyJet and steerolithography processes.

The ABS material is the commonest 3D printing material in the industry. Electric flapper, mouse and appliances shell are made from ABS. One of its characteristics is a high melting point and stronger stability. The shrinkage rate of the material is over 8 percent.

Is Shrinkage a Huge Problem in 3D Printing?

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Shrinkage a Huge Problem in 3D Printing (source)

During 3D printing, the size of the object might be important but at times it might be irrelevant. When the size is important, the printing material shrinkage can be a huge issue. Nylon, ABS and PLA are the three highly used materials in personal 3D printing projects. ABS is stronger and more flexible while PLA is biodegradable and the producers offer it in various colors.

When cooling, ABS shrinks by around 8 percent, but that highly varies depending on the use and some other conditions. PLA has lesser shrinkage, which stands at 2.5 percent and that of Nylon stands 1.7 percent. That means that apart from warping, the printed material will not be of the desired size. A 50 mm print might be a 46 mm after the printing.

At times, the difference might not be important. For example, when printing a scanning bust of someone, the fact that the bust will be 82mm instead of 92mm will not make a huge practical difference. The printing is better with PLA and Nylon which people believe that they do not shrink at all. That is the main reason most 3D operators and printers use the two materials. However, both PLA and Nylon shrink, but not much. PLA will shrink by around 2 percent while Nylon will shrink by around 1.7 percent. That depends on the species of Nylon or PLA used.

A quick example, a printed iPhone might not fit into its case because of the slight shrinkage. If something has to fit together precisely, the sizing has to be exact. That is not possible with 3D modeling dimensions. Some people start by measuring the shrinkage and resize their model to a slightly larger size. Therefore, after printing the model, it resizes to the target size. That might not be adequate.

How to Compensate Shrinkage in 3D Printing

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3D Printing Shrinkage Compensation (source)

Material shrinkage is common in thermosets and arises during the transition from liquid to the solid state – after printing. When the ABS material shrinks uniformly, it will only get a little smaller. However, when only a part of the model shrinks, that will be a big problem because the model will get warped. A warped model will bend up from the printer’s build plate, crack or deform. Several factors contribute to the warping of a model but improper cooling is the commonest problem.

That happens after the printing material cools down rapidly or when the temperature surrounding the print model is uneven. An air conditioner inside the room is more likely to cause this problem. The other possible reason is placing the 3D printer near your open windows. That is the key reason why most 3D printers’ manufacturers design their products to deal with both warping and shrinkage.

Hot ABS filament gets through the nozzle of the 3D printer and cools down to 80 degrees Celsius. The printing chamber maintains the temperature at 80 degrees Celsius throughout the printing process. After the printing ends, the printer will cool the temperature further. That way, every layer cools down simultaneously. Moreover, the printing chamber remains sealed from the environment. When the temperature reduces uniformly across the whole build space, it eliminates the chances of material warping.

Even though PLA filament nearly has no shrinkage, ABS is stronger and it will endure most post-processing techniques. When printing with PLA or nylon, you will not need any enclosure to prevent warping. ABS warps due to shrinking at different temperatures. That is the key reason why PLA and nylon are becoming a popular choice in 3D printing.

Before you start printing, you should do several things to reduce the chances of warping. If you have a compatible printer, remember to use MK8. MK8 prevents the plastic from staying in the melted form for a long time because it might degrade. The MK8 nozzle holds similar plastic the other nozzles hold, but much of the plastic stays in solid form. Therefore, PLA will rarely degrade.

Even though the 3D printer takes into account the material shrinkage when printing, if you realize a problem, you should start compensating for it. As the printing involves thermal steps, you should scale your desired models by 2 percent for PLA, 1.7 percent for nylon and 8 percent for ABS. The upscale will compensate for any shrinkage and the result will be dimensional accuracy of + or – 1 percent. Dimension accuracy is not related to the model’s details and it is hard to guarantee it.

Conclusion

Managing shrinkage is among the complicated tasks in the 3D printed world, considering the many involved factors and how each of them affects the others. Shrinkage exists in two forms – linear and volumetric. Volumetric shrinkage results from thermal contraction and affects every type of polymer and crystallization for the semi-crystalline polymers. It describes the changes in volume when the material changes from liquid to solid state.

Generally, plastics can shrink by around 25 percent and the shrinkage affects all the dimensions. To reduce the chances of warping associated with shrinkage, you should maintain a uniform temperature around the printer. You should compensate for the shrinkage when printing by scaling your desired model upwards.

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