For everyone who's interested in the whole "cost of aluminum cases vs. plastic cases" argument. (warning, this might be boring to some)
To do injection molding (i'll shorten it to IM from here on in) of plastic is a different process from IM using metal. To get you more aquainted with how the IM process works, here is a great
link. (ah lovely wikipedia).
Two main differences between the two materials are the temperatures that you heat the formed material to, and the materials you need to use to create the molds. For IM of a plastic material, you can get away with an aluminum mold that only requires machining. Since aluminum isn't overly expensive as a mold material and is quite easy to machine, your mold costs will be low. I would estimate that you could probably get molds made for about $1500 USD (these would be known as "tooling" costs). Aluminum is also a lot stronger and more durable than plastic, making it ideal as a mold material.
IM a plastic material will require you to heat it to beyond it's melting point to allow the material to flow into the mold cavity. For plastics, their melting point is anywhere from 200 Celsius to 350 Celsius. Conversely, the melting point of aluminum is 600-700 Celsius depending on what alloy you use.
To answer the question of whether you could use an aluminum mold for making an aluminum case? the answer is no. This is because you don't want to come close to the melting temperature of the mold during IM. Assuming you were making a case out of an alloy that was slightly lower than the mold, you'd still have a soft mold which would gradually warp and weaken over time.
Edit: whoops, I just realized something I didn't mention...and kind of embarrassing I didn't initially clue into this (being a Mech. Eng). Melting an aluminum material inside an aluminum mold will make it impossible to remove. You'll be essentially welding the two together!
To make an aluminum case, you'll now need a mold material that is harder and stronger than aluminum. It will need to have a melting temperature that is higher than aluminum. These materials are usually steels and are
heat treated to make them hard so they will be durable for many IM parts. Heat treated materials are hard and
expensive to machine, driving up the costs of the mold (estimate the mold could now be in the $6,000-$10,000 USD range). Aluminum is also a harder material to
IM properly (more complicated machinery to operate the molds, higher injection pressures, temperatures, etc.) and so the costs for each part will be more expensive. Instead of one plastic part costing $1-$2 to IM, you could be looking at $10-$25 per part, (or much much more) with low volumes such as Pandora.
Only $10 more per part to make them out of aluminum you say? I'll gladly pay the extra you say. Well, it's not that easy because IM costs are closely tied to quantity. There are minimum costs associated to do business and with low volumes for those who want an aluminum case, that means that it's completely unreasonable to make a few hundred aluminum cases. The case will be way more money than the rest of the unit.
If you want an aluminum case, then buy the Pandora with the plastic case and measure it out and have a machine shop make you an aluminum one. There are a few shops out there that I know that will do it for beer
(provided you simplify the part and well, have a good repertoire with the machinist/shop)
I wonder how long before these mods come out.
