There were a few requirements that the material for my product needed to fulfill in order to be suitable for my project. Those being:

• Must be able to be injection moulded due to the complicated shape of the otter and the fur texture all around its body.
• Should be a semi decent thermal insulator as wireless charging can sometimes produce a lot of heat in the charging base. (The rock base)
• Must have good impact ressistance in case the otter is dropped as it is being carried around the house.

What Material was Chosen: 

Polyvinyl chloride (PVC) was chosen as the material for the otters body as well as the casing for the charging base (rock base). This is becasue firstly;

Thermal Insulator:

• Heat stabilisers are added to PVC when it is manufactured which mean that its maximum operating temperature is high enough that there is not a risk when the induction charging process is taking place between the otter and the charging base. The specifics are that the maximum operating temperature of PVC is 60ºC and the maximum temperature reached by induction charging is 30.5ºC. This means that it can be used for both the otters body as well as the charging base.
  

  Melanie Loveridge, Chaou Tan, Faduma M. Maddar, Guillaume Remy, Mike Abbott, Shaun Dixon, Richard McMahon, Ollie Curnick, Mark Ellis, Mike Lain, Anup Barai, Mark Amor-Segan, Rohit Bhagat, Dave Greenwood (April 2019), ‘Temperature Considerations for Charging Li-Ion Batteries: Inductive versus Mains Charging Modes for Portable Electronic Devices.’

Impact Strength

• PVC also has good impact strength at cool temperatures meaning that if the product is dropped from waist height (the most comfortable position for it based on wrist postion when holding it) the product should not break with the only possible exception of that being if it lands on it’s tail, however this could be an issue with any material due to the design. To test this a simulation was run on solidworks with a model of the otters tail:

• The maximum stress exerted was 0.228MPa and as the Yield Strength of PVC is 53.1MPa (taken from CES edupack) that means that the maximum force than can be applied in complience with a saftey factor of 2.05 using the the Pugsley method = 114N. 

Mass of Tarka = 2.35Kg, Speed of Tarka when dropped from waist height (average) = 4.25 m/s ∴ Kinetic Energy of Tarka when dropped = 21.22 J

∴ Impact Force = KE/d = 21.22/0.92 = 23.07N  (In reality this would be even lower as Tarka would be lighter than specified as the calculations here are for a solid block of PVC in the shape of Tarka)

• Therefore PVC is more than suitable as the force exerted from dropping the otter would be 23.07N and the maximum force that can be exerted on the weakest point of Tarka (the tail) is 114N. 

Injection Moulding

• PVC is able to be injection moulded however as there is chlorine in the material it makes it more difficult, due to the gas given off being toxic and corrosive when melted, so in order to stop this shops that use the process need to have sufficient ventilation systems.

 

Injection Moulding Process

• The reason that PVC was chosen as the material for Tarka was I wanted a texture covering the body that looked like fur, but wasn’t soft like a fluffy toy as users had agreed that would have been to disturbing. There is a company called Funko POP! who do injection moulded small figurines, some of which have detailing and hair which both looks, and feels the same as what I would want my product to look and feel like. An example of one of thier products is shown below:

The Process: Two Shot Injection Moulding

Two shot injection moulding means that multiple components of different colours can be moulded at the same time. This means that the otters main body as well as its underbody could be moulded at the same time in one manouver, in different colours to clearly show what areas need to be painted what colour.

The otters body would be moulded in two halves, with the split line down the length of the otter, this is so the electronics could be mounted inside and then the otter could be closed together to give the final product. The charging rock base would also be done this way, however the split line for that would be around the perimiter so that there is a large area to access to insert the components before it is closed together.

The disadvantages of using this method however are the tooling costs and machine costs. That being said this process is the best process available for coveying the idea of a otter as it can produce the level of detail required for the otters fur.

Finishing the Product:

The otters body and would then be spray painted with a matte finish so that the product had the correct colour scheme of a dry otter and not one that has just gone for a swim in a river. The rock would also be spray painted so that it looked like a rock that you might find in the otters natural habitat.

Advantages: 

• Speed and efficiency
• Smooth and even finish that can withstand wear and tear

Disadvantages: 

• More waste due to overspray