Why IGLU Reduces warping

This blog post will explain succinctly the mechanics behind FDM print warping and why IGLU helps to reduce it.

During extrusion, the thermoplastics (filaments) which move through the printer nozzle must cool from their printing temperature (200-300°C) to the temperature of the part being produced. In the initial layer, this temperature will match that of the bed (60-100°C in most cases) and will grow cooler with each additional layer until the temperature of the layer is consistent with the temperature of the printer chamber.

This cooling causes a problem: Warping!

Warping occurs due to dimensional contraction which almost all materials experience when cooled. This morphing occurs in every material you see at all times. Your world is literally expanding and shrinking before your eyes, you just can’t see it until it causes your 3D print to peel from the bed…

We can calculate a theoretical approximation for this contraction by using material properties and a change in temperature:

Take two 100mm lengths of ABS being cooled from 110 to 60°C and 45°C respectively (I’ve chosen these values for a specific reason which we’ll discuss soon). ABS has a thermal expansion coefficient of 9x10^-5 mm/mm°C. That means for every 1mm length of material, it will grow or shrink by 0.00009mm for every degree of temperature change. A 10mm piece of material expand or contract 10x as much as a 1mm piece of material per degree.

We can take these example situations and plug it into a simple formula:

   Change in length = Expansion Coefficient x Length x Temperature change

So, we can calculate our contraction when cooling from 110°C to 45°C case as -0.585mm. (negative indicating that it grows smaller).

and in the 100°C case: -0.09mm.

110 degrees is the glass transition temperature of ABS, where it is soft and malleable. Above this region, the polymer chains which make up the material can slide past each other, and the impact of shrinking is easily overpowered by the stiffness of the build plate. Shrinkage has the largest effect on prints once the material has solidified but continues to shrink.

From this when can see that there will be more shrinkage when the material is cooled to 45°C (like in the upper layers of a stock printer with a 45°C chamber temperature) then in the 100°C case (such as layers that are in close proximity to a 100°C bed). This imbalance causes that dreadful peeling.

Now there’s more at play than just this shrinkage, the rigid bed helps to resist this bending, carbon fibre reinforcement resists the contraction in -CF materials, the young’s modulus of thermoplastics decreases as temperatures increase and much more. All of these factors change the warping characteristics of a specific print.

IGLU helps to solve the expansion issue for each print by increasing the chamber temperature within the printer, thereby reducing the contraction of subsequent layers as you move away from the bed.

Using the same formula as earlier but at 60°C (which is an achievable chamber temp with IGLU but not for a stock printer in ~20°C ambient conditions). We can calculate a new shrinkage value of -0.45mm, a 23% decrease.

Therefore, each layer is theoretically contracting by 23% less than in the example 45 case. By reducing this retraction, we immediately release some of the pressure from the build plate and bed adhesion, keeping our prints straighter. While this doesn't seem like much, it makes a big difference. Check out our polycarbonate test prints in the cover photo. Identical G-codes and set up process. One with IGLU, one without.