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UVA Joint_V1

A project log for UVA

High-power ultraviolet flashlight for curing UV adhesive (https://bit.ly/FldRdy-DB)

Miguel FernándezMiguel Fernández 07/18/2020 at 12:330 Comments

To achieve a multi-tool kit it is necessary to understand the parts of it. This system is composed of two main elements: The battery pack and the Instrument or tool (in this case the ultraviolet light for curing adhesives).

It's a simple idea based on one challenge, the joint. This is also the most important mechanical part of the design because it is the starting point for the development of different tool-heads. The UVA joint has to achieve 4 principles:

  1. Simplicity (to encourage people to develop new tools)
  2. Durability (It has to resist the wear of daily connection/disconnection and also the falls and shocks)
  3. Reliability (the user should be confident that the electrical and mechanical joint wouldn't fail and the tool will work as it is expected)
  4. Replaceability (The modular design of the UVA system allow to replace the chassis where the joint is build in without affecting the electronics).

With these bases in mind, we design a rotational joint that is structured by three different connections: the snap-fit cantilever, the electrical contact and the Locks. It is necessary to leave some tolerance (in our case 0.4mm) because FDM prints are not 100% accurate. Calibration, environmental conditions and human interaction could affect the quality of the finished pieces. We need a tight fit because we have to prevent movement between the battery pack and the tool, but also we need to prevent the plastic to fail, crack or to not fit at all.

To fit the part it is necessary to make a 28 degrees rotation in the longitudinal axis. It will snap by this rotation and do not return to the starting point without some force. Every connection has its mission to constraint the parts together.

  1. Snap-fit cantilever: this part is the most complex to design and is the one that ensures that the UVA joint will keep together the battery pack and the tool. It makes a restriction in the rotation after the snap. This rotation restriction could be broken after applying some force to unlock the uva joint.
  2. Locks: This connection is responsible for avoiding the movement in the vertical axis. The locks will help to reduce or eliminate the forces over the snap-fit cantilever after the snap, increasing the quality of the joint and the durability of the connections.
  3. Electrical connection: This part is under development. It will be the mechanism responsible to transmit the electricity between the battery pack and the tool.

The joint was modeled with Autodesk Fusion 360, here the link to the model: https://a360.co/2OywktE

We are going to be using this software because it is free and tremendously good for mechanical design. It can also be use to simulate electrical circuits. 

Here some information that we used to design the UVA joint:

About conections:

https://www.3dhubs.com/knowledge-base/how-design-snap-fit-joints-3d-printing/

https://drive.google.com/file/d/1E7P1v8KytKME5-KJwtn3b6-2PuZkFO8J/view?usp=sharing

https://drive.google.com/file/d/1D9oW7FTgxugsrYvvysp96yshwzoi6t6p/view?usp=sharing

Snap-fit design calculator:

https://plastics-rubber.basf.com/northamerica/en/performance_polymers/services/service_calculation_programmes.html

About PLA:

friction coefficient: 0.492

 https://www.researchgate.net/publication/330003074_Wear_and_coefficient_of_friction_of_PLA_-_Graphite_composite_in_3D_printing_technology

Secant modulus: 3300 Mpa

http://www.matweb.com/search/DataSheet.aspx?MatGUID=ab96a4c0655c4018a8785ac4031b9278

Allowable material strain: 3%

https://www.researchgate.net/publication/257608973_Enhanced_ductility_of_polylactide_materials_Reactive_blending_with_pre-hot_sheared_natural_rubber

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