There are several factors that can cause weak infill in 3D prints, such as:

• Infill density: This is the percentage of material used to fill the interior of a 3D printed object. A higher infill density means more material and stronger infill, while a lower infill density means less material and weaker infill. A general rule of thumb is to use at least 20% infill density for most prints.
• Infill pattern: This is the shape of the material used to fill the interior of a 3D printed object. There are many types of infill patterns, such as grid, honeycomb, triangular, gyroid, etc. Some infill patterns are stronger than others, depending on how they distribute the material and how they connect with the outer shell of the object. For example, honeycomb and triangular patterns are stronger than grid and lines patterns.
• Infill speed: This is the speed at which the nozzle moves while printing the infill. A higher infill speed means faster printing time, but it can also cause under-extrusion, which means not enough material is extruded from the nozzle. Under-extrusion can result in weak and stringy infill, as well as poor adhesion between the layers. A lower infill speed means slower printing time, but it can also ensure better extrusion and stronger infill.
• Infill line width: This is the thickness of the material used to print the infill. A higher infill line width means more material and stronger infill, while a lower infill line width means less material and weaker infill. The optimal infill line width depends on the nozzle size and layer height you are using. A general rule of thumb is to use an infill line width that is equal to or slightly larger than your nozzle size.

How to Fix Weak Infill?

If you have diagnosed that your 3D prints have weak infill, you can try some of these solutions to fix it:

• Increase your infill density: This is the easiest way to improve your infill strength. You can adjust your infill density in your slicer software before printing. As mentioned earlier, a minimum of 20% infill density is recommended for most prints.
• Change your infill pattern: This can also make a big difference in your infill strength. You can choose a different infill pattern in your slicer software before printing. As mentioned earlier, some patterns are stronger than others, so you may want to experiment with different options and see what works best for your print.
• Lower your infill speed: This can help prevent under-extrusion and improve your infill quality. You can adjust your infill speed in your slicer software before printing. A good way to find the optimal speed is to start with a low value and gradually increase it until you see signs of under-extrusion or poor quality.
• Increase your infill line width: This can also help increase your infill strength by using more material. You can adjust your infill line width in your slicer software before printing. As mentioned earlier, a good way to find the optimal value is to use an online calculator or a test print.