3D Printed Hooks in Hook and Loop

Hook and Loop Magnified Image (Also popularly known as Velcro)

Hook-and-loop fasteners consist of two components: typically, two lineal fabric strips (or, alternatively, round “dots” or squares) which are attached (sewn or otherwise adhered) to the opposing surfaces to be fastened. The first component features tiny hooks, the second features smaller loops. When the two are pressed together the hooks catch in the loops and the two pieces fasten or bind temporarily. When separated, by pulling or peeling the two surfaces apart, the strips make a distinctive “ripping” sound.

Introduction

Hooks and Loops are widely used in manufacturing industry to provide adhesive property to some part of the product. Few popular applications are in shoes, nameplates etc. But these are used as an add-on on the product and stitched onto it and this bring challenges in adding such texture on surfaces that are not plain. Having a mechanism to 3D print such hooks while printing a 3D printed object can add hook and loops texture on the product itself. Also, it will be easier to perform mass production along with flexibility in the design of such products.

Application

1. Print the 3D object with hook and loop locks printed on it along with the entire printing of the object. Example — Photo frame, name plates etc.
2. Modular prints with customizations of parts.
3. Print acupressure equipment for palm and foot. Example — Acupressure flip flops.
4. Replace parts with wear and tear.

Approach

Step 1 — Get single hook structure

The very first approach in printing hooks is getting a single hook structure printed that mimics the structure of original hooks in hooks and loops. We plan to first extrude more material at the base to enhance the strength of the hook with the base. Then move the extruder upwards and after a certain height, stop the extrusion and move the head to right or left direction. While doing so, the top most part of the 3D print material extruded will be hot enough to bend under gravity and create a downward U like structure on the top.

Step 2 — Print single hook on 3D printed surface to experiment with strength

Once simple hook is printed, next challenge is to test the strength of hook printed on a 3D printed base. To have high strength of hook with it’s base surface, we can increase the temperate on the extruder while printing the lower part of the hook. High temperature will help the extruded material stick properly with the base of same material. Then after waiting for some time and let the material become solid, we can move the extruded upwards to create the hook structure.

Step 3 — Printing multiple hooks on a 3D printed surface

Once a single hook is printed over a 3D printed base, then next challenge is to print the loops on a flat surface like a matrix. This is really challenging because printer head need some space to print and therefore, the hooks printed here will not be very close as seen in commercial hook and loops.

Also, after printing a single loop, the printer head need some space to move to other direction that will make downward loop like structure. Therefore, printer can print hooks in row-wise fashion which will allow it to have space in a direction to move.

Experiment

Experiment Parameters

We experimented on multiple parameters to obtain hook structure. Below are the parameters -

1. Extrusion
2. Speed
3. Height of Hook
4. Cool Off Time
5. Direction of Hook

Experiment Approach

1. Our aim was to get to a suitable hook structure by experimenting iteratively.
2. That would give us most important parameters and an origin to move around.
3. From that combination, we intend to run structured experiments

Experiment 1

1. Material was released from a height Z = 2mm to form base with F = 2700. No wait time for cool off.
2. Print head move upward to Z = 4 and less extrusion with F = 3500
3. Print head moved sidewards to detach the material printed with not much speed.

; previous E25.6039
G0 F2700 X100 Y100 Z2
G1 X100 Y100 E30.60
G1 F3500 X100 Y100 Z4 E32.00
G0 X100 Y105 Z4
G4 P10000
G0 X0.1 Y20 Z0.3 F9000.0 ; Move to start position

Result 1

Initially, material was extruded and print head moved upwards. But when printer head moved sideways, the material was hot enough to be not breakable and the residual material released at the new position and it was released from top. Also, since material was still hot and speed of sideways movement was less, it produced string like long structure.

Since the material was too much to release but there was no time, it was released later. The learning we got here that after releasing the base material, we should wait a little to solidify it and then more further.

Experiment 2

1. Material was released from a height Z = 2mm to form base with F = 2700. Now wait for 10 seconds to release all residual material and let the base cool and become strong.
2. Print head move upward to Z = 4 and moves fast with F = 3500.
3. Print head moved sidewards to detach the material printed with not much speed and keep the head there to let it cool.
4. Move the print head fast to detach it with material.

; previous E25.6039
G0 F2700 X100 Y100 Z2
G1 X100 Y100 E30.60
G4 P10000
G1 F3500 X100 Y100 Z4 E32.00
G0 X100 Y105 Z4
G4 P10000
G0 X0.1 Y20 Z0.3 F9000.0 ; Move to start position

Result 2

Initially, material was extruded and print head stayed there to release all material and also let it cool to become sturdy. But when the printer head moved sideways, it again released some material. Due to residual material still being very soft, pulling the head fast to detach with with material made a string like structure.

The learning we got from here is after forming the base, we should decrease the amount of material released and also, when material is still hot, don’t move the printer head fast, otherwise it will form a string like structure.

Experiment 3

1. Material was released from a height Z = 2mm to form base with F = 2700. Now wait for 10 seconds to release all residual material and let the base cool and become strong.
2. Print head move upward to Z = 3 and less extrusion and F = 100.
3. Print head moved sidewards slowly with no extrusion and after some time, with very high speed it moves in other direction.

; previous E25.6039
G0 F2700 X100 Y100 Z2
G1 X100 Y100 E27.60
G4 P10000
G1 F100 X100 Y100 Z3 E28.00
G0 X100 Y105 Z2
G0 X100 Y20 F9000.0 ; Move to start position

Result 3

Initially, after releasing the base material and waiting for 10 seconds proved fruitful. The base became solid and all material was released. After after a very small increase in height, when printer head was moves sideways slowly, the material was slowly solidifying and after some time, when we moved the head at a very high speed in the other direction, it made a sideways loop.

This loop looks very good but it is not in the desired direction. The learning from this experiment is that we cannot rely on gravity to give us a look kind of structure. Rather, we can move the printer head in such a way that it will form the hook.

Experiment 4

1. Material was released from a height Z = 2mm to form base with F = 2700. Now wait for 10 seconds to release all residual material and let the base cool and become strong.
2. Print head move upward to Z = 5 and less extrusion and F = 100 i.e. very slowly.
3. Print head moved sidewards with decreasing height slowly with no extrusion and after some time, with very high speed it moves in other direction.
4. Here we changed the direction where printer head will move suddenly

; previous E25.6039
G0 F2700 X100 Y100 Z2
G1 X100 Y100 E27.00
G4 P10000
G1 F100 X100 Y100 Z5 E27.00
G0 X100.5 Y105 Z2
G0 X100.5 Y0 F9000.0 ; Move to start position

Result 4

We were thinking of getting similar results like previous experiment but since we changed the direction where printer head will move suddenly, we went very close from the base of hook and thus, it got joined.

Learning from this is to provide some gap between direction of sudden movement and base of the hook.

Experiment 5

1. The experiment was similar to previous one. We just increase the gap between direction where printer head will suddenly move and the base of hook.

; previous E25.6039
G0 F2700 X100 Y100 Z2
G1 X100 Y100 E27.00
G4 P10000
G1 F100 X100 Y100 Z5 E27.00
G0 X100.5 Y105 Z2
G0 X100.5 Y0 F9000.0 ; Move to start position

Result 5

We good really good results with this approach. One biggest advantage to moving downward and also backwards is that we got a hook like structure. It is not exactly what we generally see in velcro, but if printed in matrix fashion, it can work.

Future Work/Improvements

1. More structured experiments to identify ranges of parameters that works.
2. Actual printing using set of parameters from those ranges.
3. Stress testing individual set of parameters to find the best combination

Conclusion

Printing hooks using 3D printing is a tricky task. There are many challenges involved in printing it, like printing a single hook, printing it on a 3D printed base to test it’s strength, printing multiple hooks together and close enough that it’s dense enough to stick properly to loop surface and also not very close that while printing, printer head to touch other printed hooks.

We experimented with multiple ways to print a single hook. The very straight obvious way to depend on gravity to bend the printed material downwards didn’t helped much. We came up with another approach to make sideways hooks instead of downward hooks. The strength of hook printed looks promising and further experiment on its actual application can help in improving this approach in a better way.