Modeling the sole hardness

With the 3D models of out feet and clay prints from the last post, we were one step closer to our goal. Now we need to determine the required hardness of the final sole. We decided the best way to do this is to compare the model of our feet without a load (in mid-air) and our feet when a load is applied (in clay).

3D model of one of our feet

To make a good comparison we only needed the underside of our feet. This meant we could clean up our models and remove a lot of unnecessary data points from the .STL files. After cutting and trimming we are left with the bottom 20mm or so of the shape of our feet.

After trying some different programs we finally found a CloudCompare, a good package for comparing two similar 3D models. The program also contained an option for aligning the models as closely as possible. This is done by choosing recognisable points on both models, which CloudCompare then used to find the orientation which yields the lowest total distance between the points. This is followed by a cloud registration which does the same, but with every single point on the meshes.

With the models of the loaded and unloaded foot matched as closely as possible, the cloud/mesh distance is calculated. This assigns a value to each mesh depending on the distance to the corresponding mesh of the reference mesh.

Cloud/mesh distance in colour scale

Cloud/mesh distance in 8-bit grayscale

By comparing the two models the change is a measure of how much the tissue in the foot compresses. For practical purposes, the values are converted to an 8-bit grayscale. This is done to properly define the various hardnesses we hope to achieve in the final product.

Foot scanning

In the past week we have been in contact with Bertus Naagen who is a staff member at TU Delft and has a lot of experience with 3D scanning. He introduced us to the 3D scanner Artec Eva which is a scanner that is used for small objects.

We made a mold out of Clay and scanned each of our feet:

Bertus Naagen scanned the Clay mold:

Foot scanning

 

We also did a 3D scanning of the food itself:

The scanner created 12 STL files for each of our feet.

Compression Test 2

After the first compression test, we did a second one. This time we chose a 50% infill for all the printed cubes, but with different pocket sizing. The pocket sizing starts at 0 mm and ends at 2 mm, with increments of 0.2 mm over a total of eleven cubes. In the pictures below, you can see the different pocket sizes. The numbers indicate the pocket sizes of the cube.

Printed cubes with different pocket sizing

The pocket sizing of 1.2mm

Pocket sizing of 2.0mm

Looking at a different pocket size is rather interesting because you will create the same infill percentage with a different pocket size. In the pictures below you can see how the pocket size influences the pattern. It seems logical that a bigger pocket size means more area to move into when it gets compressed. Conducting this test will show us whether that is true and how the difference in pocket sizing will influence the printed products.

0 mm pocket size

1.5 mm pocket size

The cubes have been tested by the same machine, as the last post with the same load range. First test round was done with a load of 0-2000N and the second with a load of 0-4000N.

Timelapse compression test

The results of the test can be seen below.

Graph for 4,000N test.

In the 4,000N test, you can see that the pockets for 0.0mm – 0.6mm has little influence on the compression. The 0.4 mm is hidden behind 0.6mm line. Starting from 0.8mm it starts to have some influence. While the pockets are bigger, the amount force that is needed also increases. 1.0mm becomes a less curvy line, meaning that the cube becomes stiffer.
From 1.2mm there is something weird happening, it is the most flexible cube together with the 1.4mm cube. The odd thing is, that 1.0mm is pretty rigid but if you increase the cube by 0.2mm it loses a lot of its stiffness.

The cubes become more rigid from 1.6mm till 2.0mm. A possible reason why the cubes become stiffer from 1.6mm till 2.0 mm pocket sizing is the internal structure. The cubes get a new structure when you increase the pocket size to more than 1.6mm. Cura also does not recommend the user to go above this threshold number, in this case 1.0mm. The new (extra) structure might distribute the force more evenly and results in less compression.

The cubes gets deformed quite a bit after each test, they do get their shape back after a few minutes, we have not measured this yet. Measuring the deformation might give us rather useful data. Especially for insoles as they will be loaded at all times when they are in use.

Deformed Cube

Testing the material

To make the insoles, we will need some hand-on experience with the material. Together with Ph.D. Tim Kuipers we decided to print cubes of 20x20x20 mm with the following infill: 6%, 9%, 12.7%, 18%, 25.3%, 35.7%, 50%, 70.9% and 99%. We chose these odd numbers since Cura generates the patterns with an angle of sqrt(2) radians and hereby we can calculate the specific infill for Kuipers. The specific pattern will change gradually as the cube gets build up. Cura has a function where it is possible to see the inside of a cubes infill as it builds up:

Cura layers

After the cubes were printed we used a compression machine to test the load of the interval from 0-2000 N and 0-4000 N. The test was made to determine if there was a relation between infill percentage and flexibility. Here is the result:

Compression test 1

Compression test graph

 

 

We found out that:

  • The infil is inversely correlated to the compression
  • There appears to be signs of fatigue in the material. This can be derived form the horizontal translation of the second graph of each cube.
  • The infill density best suited for use in shoe soles appears to be closest to the cube with 50% infill.

In the compression test 1 we tested each cube with the same infill two times. The first time with a load of 2,000N and the next with 4,000 N. When comparing the first and second test it seems that the second test is almost always weaker (comparing from force 0 to 2,000N). We want to see if there is a connection between the number of times a cube is loaded with force and it’s strength.
We chose to work further on the cube with 50% infill, since this cube seems to have the best properties when it comes to flexibility and compression and since the compression travel is almost linear to the amount of force the cube is exposed to.

Fatigue Test 1

We want to make a fatigue test to see if the material gets weaker the more it is used. This is important when working with shoe insoles, since the insole is constantly exposed to varying forces.

Repeated test

On the graph we can see that the further the material has travelled down the softer/ weaker it gets.

If we take a closer look at the maximum travel distance (see graph), we can see  that the cube is strongest the first time it gets compressed, but then it gets weaker.  After the first test the cubes travel distance is in a somewhere random order, but overall the trend line is declining so the material gets more fragile the more it gets compressed. But since we only conducted 10 test results we cannot say for sure that there is a coherence between the travel distance and the number of times force is loaded on the material. We will have to do more and longer tests.

Pull test
Parallel to the compression test we are planing on making a pull test, so we started the print this afternoon.
With Cura 3.0 it is possible to monitor the print from your computer:

The very first test

For our project, we are tasked with developing an insole for shoes that are 3D printed form Ultiamker’s TPU 95A filament. This has the compression characteristics of a rubber but the hardness of a plastic. To become familiar with the material we decided we needed some samples as soon as possible.

 

 

 

 

 

The above cubes were the very first prints we made with the new filament. These are 20*20*20mm cubes printed on an Ultimaker 3. The infill pattern is Cross 3D, which is available in the 3.0.0 Beta version of Cura, printed at 25, 20, 15 and 10 percent infill. The cubes only show the infill itself, as the cubes were printed with 0mm wall thickness. Straight away we could feel there was a large difference in compressibility between the cubes.

The only problem we have encountered so far is that the print quality is greatly reduced at the lowest infill. This can clearly be seen in the rightmost cube.

This first week has given us an insight into what we can come to expect from this project for the coming weeks and we are excited to start developing customisable soles from 3D printed pliable filament.

This is what we want to end out with:

The pictures above are prints where Cura have generated the infill out of a black/ white image. This is also something we want to achieve with the final shoe sole.

Project introduction   

The additive manufacturing technology 3D-printing is a rather old technology first introduced in 1980s, but in the recent years the technology is becoming more and more known and easier to use. The technology favour rapid prototyping and custom design rather than mass production. This makes it suitable for manufacturing of individual design.

We know that every person has a specific way of working and a specific need of support in their feet. As it is today, we buy sneakers or running shoes that are designed to fit the typical “normal person”. But wouldn’t it be better if we made individual shoes or shoe insoles?

This is what we are going to experience with in the next 4 weeks. We have been fortunate to work with the new 3D-printer Ultimaker 3 and have been introduced to Ultimakers new material TPU 95A and a beta version of the program Cura 3.0. TPU 95A is a filament that is flexible and tear resistance and with Cura 3.0 it is possible to generate patterns in the material depending on the infill percentage which makes the material more flexible. Adidas recently released their new shoe that is partly 3D printed with Carbons 3D-printers:

So it has been possible to print flexible structures for a while but only with powder based 3D-printers. With Ultimakers new material TPU95A it is now possible to print flexible structures with a regular FDM-printer, which is a more common and cheaper printer compared to the powder based printers. The flexibility is especially important when working with shoe insoles since the footwear needs to be more stiff certain places and more soft other places for an optimal support for the feet.

We believe that people in the future will get more customized footwear, so that less people will get injured from running or walking in their everyday life. As 3D scanners and 3D printers gets increasingly popular, it is easy to imagine a scenario in the future where costumers will get their feet scanned in a shop and hereafter get an insoles printed directly in the store and hereby optimized the properties of their individual foot.