How to parameterise and optimise a resin

One of the most complex tasks when working with resins is correctly adjusting the printing parameters. Achieving optimal values is usually a simple task but requires multiple iterative printing tests.

The Parameters

When calibrating a resin, it is important to know the available parameters and their influence. The most common ones are:

• First Layer Exposure: This is the time that the first layers will be exposed, i.e., the time the LEDs will remain on. It should be higher to ensure adhesion to the build platform.
• Exposure Time: The time that the rest of the layers will be exposed. Excessively long exposure time can cause dimensional errors and loss of resolution, while too short a time can cause parts not to cure properly.
• Delay Time: This is a waiting time from when the LED turns off until the platform moves. It allows the part to cool before starting the next layer. Usually set to zero, except for resins that require very long exposure times or for the first layers.
• Lift Height: The height the platform lifts at each layer change. If the platform does not lift enough, the part will not detach properly from the tank bottom, and subsequent layers will fail, but large lift heights increase print time. The ideal value is the minimum required to allow the part to separate, but slightly higher lifts are always advisable.
• Lift Speed: The speed at which the platform raises and lowers between layers. High speeds reduce printing time but increase the risk of failure, especially in supports.

The Calibration Model

The first thing needed to parameterize a resin is to have a validation model. This is a model that includes various different details and sizes and is used to evaluate the quality and dimensional accuracy of the print.

There are multiple models available in the most common file repositories, such as this model.

Image 1: Resin Calibration Matrix. Source: Thingiverse.

Correct parameters will provide a quality print, where all details are visible, and with precise dimensions.

Optimization

The most important thing when parameterizing a resin is to determine the correct exposure values. To do this, several iterations should be done varying these values. The process is as follows:

Step 1: Determine the correct exposure:

1. Select high exposure values. As a starting point, you can select double the exposure of another similar resin that has already been optimized or from a predefined profile in the software for similar materials.
2. Print the test model and evaluate it.

Image 2: Model with excessively long exposure times (left) and model with optimal exposure times (right).

3. If the part has failed or not cured properly, increase the exposure time by 50%; if the time is excessively long, halve it.
4. Print again and evaluate as many times as necessary until the correct exposure is determined.

Image 3: Diagram.

Step 2: Determine the correct first layer exposure:
To determine the correct exposure for the first layers, you should print a part with little contact surface with the platform and progressively reduce the exposure of the first layers until the first layers do not adhere. Once determined, it should be increased by 50% for the final value.

Step 3: Lift Height and Speed:
Generally, these parameters are affected by the type of resin, but also by the type of part. To determine the optimum values, you should start with large heights and slow speeds. First, progressively reduce the height until the part fails, and increase that value by 50% for the final value. Once the height is determined, increase the speed until the part fails, and reduce the value by 25% for the final value.

In parts that require tall supports, it is advisable to reduce lift speed by half to avoid failures in the supports.