MATERIAL PRODUCTION AND CHARACTERIZATION

Multifunctional materials for 3D printed

customizable footwearD. Rigotti, G. Barp, A. Dorigato, L. Fambri, A. Pegoretti

Università di Trento, Dip. Ingegneria Industriale

via Sommarive, 9 - 38123 Trento, Italy

Nowadays the research on performance in sport is becoming more and more significant, athletes are constantly searching for new challenges

pushing further their own limits and the ones of their equipment. Materials and sport gears tailored on the single athlete are key points to express all

the potential of the sportsman during the achievement of his goals. In winter sport footwear applications, like skiing, snowboarding, running and so

on, cold temperature, vibration absorption and comfort are crucial aspects. 3D printable soft material able to absorb heat and then release it later,

when needed, seems an innovative solution in this field.

The aim of this study was to develop a novel rubbery material to produce customizable insoles for winter sports application with enhanced thermal

properties given by the introduction of phase change material (PCM) through a Fused Deposition Modeling (FDM) 3D printer machine.

4032D

4032D+30%M6D

4032D+40%M6D

4032D+50%M6D

4032D+60%M6D

FilaFlex

Sharebot

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Bulk Sample

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Printed

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OPEN SOURCE INSOLE DESIGN AND PRODUCTION

Infill density 10% 25% 50% 75%

Hexagonal infill

Rectangular infill

In order to understand how fill density and fill

pattern affect the compression modulus,

compression tests were carried out on 3D

printed cylinders.

Different commercial TPU filament were tested

and used to produce samples with different

densities and fill pattern. The measurements

are carried out according to the ASTM D1621,

standard test method for compressive

properties of rigid cellular plastics.

Cylinders of 3cm in diameter and 1cm in height,

with infill densities of 10%, 25%, 50% and 75%

and with rectilinear and hexagonal filling were

printed and tested by using a Instron 5969 test

machine.

The first part was devoted to the

acquisition of an image of the foot. A 3D

reconstruction is possible by using 3D

scanner that is a very useful tool but not

easy to be found. The consequence is

that possible scan of parts of the body can

be very expensive that collides with the

open-source intention of this work. A

possible solution of this problem is to use

a normal 2D scanner.

The image of the foot was collected by the

scanner and processed by using the

GIMP, an open software for image

manipulation. The image was vertically

flipped, translated into a black and white

picture and posterized. The posterization

is used for the conversion of a continuous

gradation of tone to several regions of

fewer tones with abrupt changes from onetone to another.

The next step was to reconstruct the 3D

shape of the foot. This is possible by

using OpenSCAD software with the

command “surface” that assigns a height

for each color gradation of the 2D picture.

The 3D model needed to be smoothed

before printing and it was done by using

an Meshmixer a freeware software from

Autodesk, the model was saved in a STL

format and loaded to the slicing software.

Slic3r is an open-source software develop

by the RepRap community.This software

is a non-profit project, is widespread and

it is being used by tens thousands of

people all over the world.

Slic3r has an innovative tool that permits

to create 3D printed objects with different

densities and it was possible to print an

insole with different mechanical

properties.

The insole was printed with a desktop 3D

printer provided by Sharebot with our

innovative filament.

Main printing parameters were:

• Nozzle temperature of 240°C

• Nozzle diameter 0.35mm

• Deposition rate of 40 mm/s

The aim of this part of the work was to design a tailor-made insole for 3D printing with innovative and open-source devices. The idea was to create an insole that can

compensate postural defects by distributing the weight of the body uniformly in each point of the foot.

Neat TPU 30wt% M6D

40wt% M6D 50wt% M6D

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Heat of Fusion

Heat of Crystallization

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Fill Density (%)

Filaflex Hexagonal

FilaFlex Rectangular

Different kinds of phase change materials (PCM) and processing techniques were

taken in account to produce a material suitable to produce advanced insoles with

additive manufacturing (AM) techniques. Good results were found in terms of

processability and heat production by using a combination of thermoplastic

polyurethane (TPU), already use in footwear applications, and microencapsulated

paraffin with a crystallization peak temperature of 6°C (MPCM6D). TPU powder

was mixed together with MPCM6D and with the aid of a single screw extruder, we

could obtain filaments to feed our 3D printer machine.

Dumbbell specimens were printed with a 3D printer provided by Sharebot. SEM

observation shows a good adhesion between layers for all the different

composition regardless the increasing amount of PCM inside the matrix.

The shell of the PCMs microcapsules increase the stiffness of TPU as confirmed

by tensile test and dynamic mechanical analysis (DMA). At room temperature the

melted paraffin increase the damping effect of the material as proved by the

shoulder in tan delta graph. Differential scanning calorimeter (DSC) shows an

increase of the crystallization enthalpy with the increase of PCM and just a slightly

decrease after each working step. Heating effect remains constant cycle after

cycle as confirmed by DSC.

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TPU_3D

TPU+30%M6D_3D

TPU+40%M6D_3D

TPU+50%M6D_3D

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TPU_3D

TPU+30%M6D_3D

TPU+40%M6D_3D

TPU+50%M6D_3D

Filaflex filament was choosen as a preliminary experimental material due to

similar values in stiffness compared to our filaments filled with PCM.

Compression test on cylinder specimen was the starting point to design the infill

of our insole.

Not only the infill density plays a role in the mechanical properties of the printed

materials but also the design of the infill. Rectangular infill was found to be softer

than the hexagonal one due to the less contact point between the layers walls.

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3D printed

FILAFLEX SAMPLES