How to determine an extrusion multiplier?

This article explains how to determine a material constant (or a multiplier) that can be used as a material-specific parameter to control your extruder.

1 - Introduction
2 - How to tune for a perfect layer width

1 - Introduction

When adjusting an extruder for the first time or experimenting with new materials, many users observe variations in the extruded material while aiming for consistent bead geometries. These variations can lead to inconsistent wall thicknesses, which is particularly important to address in large-scale additive manufacturing (AM) applications. This article outlines the steps for fine-tuning to achieve the desired bead dimensions. 

But why does this happen?

Thermoplastic composite materials vary in viscosity, fiber content, and thermal conductivity, which can all affect how a material is extruded and deposited onto the next layer. 

As these materials are extruded, the higher viscosity caused by fiber content, such as glass or carbon, makes the flow less consistent compared to pure thermoplastics. The fibers can align with the flow, affecting how the material spreads, while the thermal conductivity influences the cooling rate, impacting how the extruded material settles and bonds with the layer beneath. These factors mean that even with the same extrusion volume, the actual width and quality of each layer can vary. 

2 - How to tune for a perfect layer width

With this procedure, we are going to extrude a theoretical amount of material and adjust using actual measurements. This will probably require two or three iterations before the multiplier is spot on. 

Step 1 - Define a standard test object

For all tests, use an object that is not too complex or too big. CEAD uses a 400x400x400 mm cube with rounded corners (25 mm radius). You can also think about a more complicated object testing other features (e.g. small radii, double bead behavior or overhang). 

Step 2 - Using baseline settings, print your object

Set the layer width in your slicer to a known value and print the test object. 

Example: we will set a bead witdh of 10 mm.

Step 3 - Measure the actual width

Measure the width of a printed bead using a caliper. 

Example: After printing, we measure a 12 mm bead width.

Step 4 - Calculate the extrusion multiplier

Using the formula below, calculate the extrusion multiplier for the first time.

Extrusion multiplier = (Target width / measured width)

Example: Extrusion multiplier = (10,0 mm / 12,0 mm) = 0,833 (or 83,3%)

Step 5 - Set the calculated multiplier and re-print & re-measure

Set the multiplier in your slicing program (usually referred to as a extrusion multiplier, material multiplier or material constant). Reprint the test object using the adapted parameters and remeasure (ideally at the same location for the best results)

Example: After setting an extrusion multiplier of 83,3%, the measured width is 10,3 mm

Step 6 - Calculate the new multiplier

Calculate the new multiplier using the formula below

New extrusion multiplier = old extrusion multiplier * (Target width / measured width)

Example: New extrusion multiplier = 0,833 * (10,0 mm / 10,3 mm) = 0.809 (or 80,9%)

Step 7 - Repeat until satisfactory

Repeat this process until you achieve an accurate-enough extrusion multiplier.

Good to know!

When changing the heatzone setpoints will influence the amount of material being extruded (due to changing viscosity). Therefore, re-tuning your material multiplier after altering these setpoints (for the same material) is recommended. 

Test different bead dimensions and printing speeds (corresponding with your typical printing dimensions and layer times). Since differences in extrusion rate (due to different printing speeds/layer times) can impact the viscosity of the extruded material, this can influence the layer width. 

Due to the abrasive nature of glass- and carbon fibers, nozzles can wear out over time, influencing the flow and pressure on the extruded material and thus influencing the bead width. Make sure to retest/retune the material multiplier over time and replace nozzles when you notice wear.