I am investigating cast aluminum for a project. Has anyone had practical experience with cast aluminum?
Specifically, how does it compare with cast magnesium or zinc, or injection molded plastic with a metalic finish (as far as working with the material, how the finished product looks, cost)?
What was the most expensive material and finish you’ve used for product housing?
Would you be interested in cast Aluminum with a nice, consistent finish? How much would you be willing to pay for it?
I believe cast aluminum straight out of the mold will look like mill finish extrusion, like angle, etc. What you do afterwards gives the look. I could be wrong, and I’m sure there is someone out there that can correct me.
Cast aluminum finishes can vary out of the mold depending on what kind of casting you’re doing.
Sand cast will be pocked, dimpled, generally not A-grade cosmetically. Good if you want a raw look. Often there will be a lot of flash on the mold seams.
Die-Cast will have a tighter grain, better surface quality. You can get baby-butt smooth, and I believe you could spec Mold-tech like textures if you wanted to.
To get a metallic finish will require buffing and polishing, and then maybe an anodize process to get a silver (or other color) sheen.
A long time ago I did these speakers: http://www.abtelectronics.com/images/products/l_cls5wh.jpg
which were die-cast aluminum, then powdercoated white or black.
I think magnesium will be even more dull than aluminum. Many cellphone battery covers are molded mag - dull gray finish.
Some die cast parts are also put through a tumbling process. This is another way to finish the surface for the desired result. We have done some die cast parts with good results.
Thanks guys!
A few more questions…
It seems that injection molded plastic with a metalic finish is easier, cheaper, and more common, but it doesn’t look or feel nearly as good. Do you find a large return on investment for the extra effort of using cast metal (ie higher cost, needing to post process)?
Also, I was thinking of using a single cast aluminum part to be both surface treatment and on the other side to have internal structure (ie ribs, standoffs, etc) just like plastic. Would you recommend this? Why or why not?
Thanks so much for your help.
How big is the product?
I’ve never used cast material in a purely aesthetic fashion, it’s always been employed for it’s inherent properties. For the loudspeaker the benefit of die-cast aluminum was it’s ‘dead’ sonic performance, meaning the walls of the speaker wouldn’t resonate. MDF is also used in these applications, as is concrete and corian!
The speaker was two cast parts that were assembled with bolts, so yes you should anticipate ribs and bosses being formed in the aluminum. You will most likely need post-processing in the form of CNC machining to create screw threads, etc…
The weight and feel of die-cast parts is unmistakeable and you’d never get it with plastic, no matter how many lead weights you glue in there. I have a soft spot for cast aluminum cooling ribs like in heat sinks…
I think a great appearance comes from milling off a cast surface to create a polished or grained raised logo e.g. auto engine blocks. You get the contrast from the raw unfinished part and the precision graphic, all in one part.
One of my main avoidences for the vacuume metalized plastics is the scratching and pealing. Also with magnesuim housings you get EMF sheilding as a bonus of the material properties.
make sure about Al pricing. I have heard that prices in China are actually lower than plastic. Mg does not finish well straight from tooling. It has swirls and a dark look that can look cool if you like a raw looking finish. However in most cases Mg parts require an additional aesthetic paint coat.
The first question I would have is: are you looking at castings for a functional or an aesthetic reason? Funtionally, I have used aluminum castings for bases, such as this medical device:
http://www.dobimedical.com/dobisys1.html
It served as the structural foundation for the rest of the components, some of which were very heavy. But manufacturing a casting isn’t as straightforward as injection molding. As some of the other posters have mentioned, you do not get the same type of finish from a cast part that yu get from an extrusuon. You might have to do a significant amount of secondary finishing work to get what you want.
I have also worked with aluminum castings for primarily aesthetic reasons such as this stereo system:
http://www.violalabs.com/spirito.html
In this case, these castings (which were assembled to sustom aluminum estrucsions to form the sides (yes, it was very heavy), had a lot of secondary finishing to get it to look that good.
Compared to plated injection molded parts…it really depends. you can used special injection moldable resins who’s soecific gravity can give them the weight of a metal part. Then you can plate it to further simulate the effect…
Warren
Don’t forget about the environmental and health impacts.
Aluminum is highly recyclable, with a clean manufacturing process. Vacuum-metallizing can be nasty and the parts are not recyclable to my knowledge.
Remember Erin Brockovich? It was about hexavalent-chromium, which is the most commonly used vacuum-metallizing (vapor-chroming) material.
For a more environmentally-friendly effect, this might be an option: http://www.pfonline.com/articles/100604.html
Thanks guys! This is great information.
I think I’m going to go with a cast metal. It’s for a small handheld product, so I’m trying to minimize the number of parts. I’d like to use a single part for both internal structure AND outside aesthetics. Has anyone ever done this?
Aside from the pain of secondary processing, are there any other common issues I should watch for?
Is it worth the post processing hassle?
You might want to look at vacuum process casting. It normally has better surface finish characteristics than straight sand casting. However, if you’re doing a very small part, the minimum wall thicknesses (I think .125 in) might not add up well for you.
My company makes quite large parts using this process (picture a monitor bezel for a 22 inch lcd and you’ll be in our range). While we typically do not add very elaborate internal elements to the casting itself, we can press studs into the castings and add a frame structure to hang everything else on. It powdercoats well, but you do need to watch for surface defects where loose sand might cause surface blowouts.
Good luck.
