Factors Affecting SLA 3D Printing Accuracy

Factors Affecting SLA 3D Printing Accuracy makenica.com/factors-affecting-sla-3d-printing-accuracy February 26, 2021

Accuracy is one of the core features you expect from SLA 3D printing, especially SLA printers renowned for their high precision level. If an SLA printer cannot replicate a model with adequate precision, its primary mission has failed.

However, obtaining a very high degree of precision is not straightforward. Several minor considerations can all add up to manufacturing a component that is a long way from the original model.

Accuracy vs. resolution of SLA 3D Printing Let's quickly clear up just what we mean by accuracy before we get started and separate it from a similar resolution definition. The accuracy of SLA 3D printing explains how much a component varies from its intended form. This could be the cumulative discrepancy over the entire portion or the point at which the discrepancy was maximum.

E.g., a printed component may be scanned and found to have an average dimensional deviation (physical variation from the original model) of 0.050 mm and a maximum deviation of 0.15 mm. This varies from the resolution, which defines the level of detail that a printer can potentially generate based on the specification.

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High resolution does not necessarily translate into high accuracy, and results can also be misleading. It is not rare for high-resolution devices to generate extremely inaccurate pieces. That is why experienced manufacturers value accuracy even more than resolution, particularly in industries where detail is crucial.

Let's take a closer look at ten of the primary inaccuracy sources in SLA 3D printing Bangalore.

1. Mechanical Control Perhaps the most significant determinant of accuracy is the degree of mechanical control the printer provides. This relates to the precision of the different mechanisms' actions, including the mirrors, the galvanometer, and the platform.

If any of these do not move in complete correspondence with the software requirements, the discrepancy will result. From the user's point of view, there's not anything that can be said with this. The precision of the movement comes from the consistency of the pieces and how well they were assembled.

Desktop printers are failing terribly in this respect of SLA 3D Printing Bangalore, and there's nothing like the consistency you get in high-end commercial printers. Low-cost industrial printers can commonly save on prices by using inexpensive materials. Having low-grade components doesn't only mean that mechanical control is weakened from the start but that the pieces' wear will also decrease over time.

Any inaccuracies in the modules or assembly of the printer shall be transferred to the printed pieces.

The exact form of the inaccuracy depends on which part of the problem occurs. E.g., the zaxis errors vary in origin from the x-y axis errors. Errors on the x-y axes are typically due to problems with the scanning mirror (that directs the beam to a specific point on the layer). This part is vital to consistency, and the slightest mistake in movement will create significant inconsistencies.

The accuracy of the z-axis depends primarily on the movement of the build platform as it descends (or increases in desktop models) layer by layer.

The build platform's movement is managed by a long screw, which needs to be turned precisely to make the platform move at the same layer height, typically about 0.1 mm.

Minute problems in the construction standard of this screw will be passed on to the printed part, typically in surface roughness. It is also important that the build platform stays completely parallel at all times. Any minor tendency can lead to inaccuracies, often in the form of a slanting impact in the component.

2. Material Deformation Since SLA 3D Printing uses resin and not molten thermoplastics, the effect of material shrinkage and warping is far less significant than in filament-based printing techniques.

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However, it doesn't mean that SLA 3D Printing isn't without its deformation problems.

Resin-based SLA 3D printing Bangalore is typically influenced by a certain degree of sagging. While the resin is cured by exposure to the laser, it does not become wholly cured in a brief period. The material can only achieve maximum strength when it is put in a UV curing oven during post-processing.

That's not to suggest that it's just not up to the full load-bearing state until the material is weak or uncured. This is not a problem for well-supported areas of the portion, but if there are long, thin, or deficient parts in support, any sluggishness can occur.

This sagging is typically microscopic, but since one layer arises at a time, the phenomenon can be cumulative, resulting in visible dimensional inconsistencies. The use of the resin influences this effect. Some more substantial materials may not suffer from this, but flexible materials are especially vulnerable to the problem.

This is why the support material is so critical in SLA 3D Printing Bangalore. If the software does not position the support most optimally, its accuracy will be severely compromised.

Supports are typically created at an angle of 45° to the component 3. Computer Modeling If the printer's mechanical control was flawless and the materials were perfect, the pieces would still not be created 100% accurate. This is because the practicalities of CAD modeling impose constraints on how accurate a component can be. STL modeling uses a finite number of triangles to construct the shape of a component.

This approach poses few challenges when recreating flat surfaces, but some curves are physically challenging to depict. Many pointed triangles are used to approximate the curve as best as possible, but it is not smooth at the microscopic level.

The more triangles used, the greater the detail, which can cause challenges in file sizes and processing time. New technologies and applications handle this problem even better than in the past, a very significant drawback in SLA computing power's early days.

The further triangles used in the STL file, the smoother curved surfaces can be re-created.

4. Orientation Print orientation is critical in SLA 3D Printing, as discussed in this article comparing desktop printers to commercial printers. In most SLA desktop machines, the part is printed upside down, ensuring that most of the part is hanged during the build process.

This can be countered to some degree by extra support material, but there would also be some material drooping due to gravity. However, it is not only the direction in which the part is printed that is relevant. The orientation of the part inside the building chamber is also a consideration to remember.

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First of all, there's the problem of over-exposure to contend with. This is because the laser light beams into the present coating. And even partly cures some of the resin behind it.

This effect in SLA 3D Printing is significantly more significant if translucent or semitransparent material is used.

It is also the case that certain colors absorb UV light more than others, meaning that parts using blue, green, or yellow products will suffer less, and other colors such as red or gray will suffer more. This problem can be resolved to some degree by placing the component strategically in the built-in chamber. This is done by concerning the laser so that the beam does not shine through other uncured materials so much.

In addition to the light that shines through, there is a further question of light bending across the component as it is printed. This can also allow UV light to enter areas where it is not meant to cause overexposure. Calculating how best to orient a component to mitigate this effect is incredibly difficult, but it cannot be overlooked if the highest precision is sought.

Orientation influences both print accuracy and speed.

5. The thickness of the layer Generally, the thinner's thickness, the better, as thin layers provide higher resolution.

However, this is not always the case to a certain extent. Some SLA 3D Printing Bangalore experiments have found that thinner layers will contribute to a lower precision for layer sizes below 0.1mm. This is because of a variety of reasons.

For most pieces, moving below 0.1mm does not provide any particular benefit in terms of precision and merely raises the number of layers. More layers imply more mechanical activity, meaning that any changes in motion are exacerbated.

Thinner layers are often somewhat more likely to warp, and the longer the build time, the longer the component can be entirely cured by the UV oven. The inaccuracies caused by these variables are minor, but they may understand why the use of a layer size of 0.05 mm often creates a less reliable component than the use of 0.1 mm layers. That said, the use of layer sizes considerably wider than 0.1 mm would undoubtedly contribute to a less precise portion, creating noticeable stairs.

6. Diameter of beam As one would imagine, the smaller the beam, the higher the degree of detail. A wide beam can result in quicker printing times but at the expense of precision and accuracy. The tradeoff was so plain in the past, but today there are SLA printers that accommodate more than one beam size during the same construction. You can customize two spot sizes, one small and one large.

The larger spot size is used for areas where the detail is not essential, thereby speeding up the operation, and the small spot is used for areas such as corners or curved surfaces. This way, at least to some degree, it is possible to get the best of all worlds.

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Without this capability, any specificity will eventually be sacrificed. And whether or not the equipment accepts variable beam sizes, it is essential to choose the required beam diameter for each design.

Judging the optimum beam size based on the part's specifications requires expertise and detailed technical knowledge. Having this parameter incorrect would undoubtedly result in a lack of accuracy.

7. Temperature and environment Maintaining a controlled environment is of the utmost importance in industrial SLA 3D printing. As described above, warping and drooping is a matter of SLA 3D printing, which is aggravated by heat and humidity. Any variations in these during the printing process can influence how the component is made.

Resin is extremely temperature-sensitive and, for SLA 3D printing purposes, the viscosity must be as minimal as possible. The higher the temperature, the less dense the resin, so for this purpose, it is essential to keep the resin wet (and at a constant temperature).

It cannot be too warm, though, because it would make the component too soft and fragile.

The sweet spot is usually about 38 degrees, and any deviation from that would influence the component's shape. It is also essential that the resin surface stays utterly flat at all times. If there are any vibrations or even the slightest movement, the equipment's performance would be seriously compromised.

The resin surface must stay completely smooth at all times.

8. Scanning pitch Scanning pitch refers to the distance between the center of each laser spot. The beam does not move in continuous motion but shines at particular points along the course at specific intervals. Usually, there is a degree of overlap between each of these spots. Otherwise, there will be wide gaps between each cured region. The scanning pitch defines the degree of overlap, which profoundly impacts both accuracy and speed.

If the scanning pitch is low, there will be less uncured resin around the edges, and the surfaces will be much smoother. This will, of course, result in longer printing times, as each scan will take longer. On the other side, making a wide scanning pitch would be easy but will result in rough edges that need a lot of sanding down.

Read More : Frequent issues with SLA 3D printing – troubleshooting guide

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