# How to identify die casting vs CNC?



## NGrimberg (Jun 6, 2018)

Hello! How do you know if a product was made using CNC machining or die casting? For example, a phone back cover. The Google Pixel 2 has an aluminum chassis. How can I tell if that was made using CNC or die casting? Any input would be appreciated!


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## rgray (Jun 6, 2018)

I'm thinking something like that is stamped.
Looking closely at cast parts you can see the parting line if they haven't gone to the trouble to remove it.
Cast aluminum is somewhat brittle so thin parts are likely not cast.


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## Asm109 (Jun 6, 2018)

Casting requires draft. ie angles on vertical surfaces so the part slips out of the die easily.  Requires a gate where the metal was injected.
Good design strives to keep the wall thickness constant. CNC machining has no such requirement.
Machining leaves cutter marks.  Dead sharp inner corners are much more difficult to make No draft required.
Close visual examination will tell you what process made the part.
It could also be a combo.  Casting with a bit of machining to hold a critical dimension or two.


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## derf (Jun 6, 2018)

Look at the cost. In the case of a phone back, it's a high volume part. That means it will be manufactured the most cost effective way....die cast.


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## RWanke (Jun 6, 2018)

Depends on the phone. I phone X sells for $1000. Supposedly all machined aluminum. Maybe that's why.


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## Downunder Bob (Jun 7, 2018)

Machined parts will usually have some visible mahine marks, unless they have been very well finished. Also virtually impossible to have square internal corners.

Die cast will usually have visible draft, also you can often see the marks left by ejection pins and sometimes sprue gates, and part lines are visible. However if the part is extensively machined after casting, not always easy to tell. A toolmaker who is familiar with die casting dies can usually tell. but for the novice not always easy.

If it's important to know can you post some very clear close up photos from various angles. We might be able to help.


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## mws (Jun 10, 2018)

Most all small metal electronics cases, particularly phones these days, are machined. The tolerances are such that it doesn't pay to cast such a small part which will then need to be machined anyway. So they just start with a punched blank and CNC the rest, and changes are easy if they need clearance for a different component.


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## Downunder Bob (Jun 11, 2018)

mws said:


> Most all small metal electronics cases, particularly phones these days, are machined. The tolerances are such that it doesn't pay to cast such a small part which will then need to be machined anyway. So they just start with a punched blank and CNC the rest, and changes are easy if they need clearance for a different component.



High pressure die casting can achieve some pretty good tolerances. Back in the mid 60's when I was working as a toolmaker we made some dies that produced precision parts for a customer that did not require machining.

many said it couldn't be done. but we did it. What they meant was, that they'd never seen it done, afraid to stretch the envelope. Fear is always the biggest hurdle for achievement. I admit however, that nowadays, with high speed CNC it's probably just cheaper.


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## mws (Jun 11, 2018)

Downunder Bob said:


> High pressure die casting can achieve some pretty good tolerances. Back in the mid 60's when I was working as a toolmaker we made some dies that produced precision parts for a customer that did not require machining.
> 
> many said it couldn't be done. but we did it. What they meant was, that they'd never seen it done, afraid to stretch the envelope. Fear is always the biggest hurdle for achievement. I admit however, that nowadays, with high speed CNC it's probably just cheaper.



Indeed! I suppose, given some of the external features I've seen on some cases that might be an option.  All the ones I've opened show milling marks internally with no ejection pin marks. No doubt, the volume of these throw away phones produced would cover the price of a few moulds in short order.   There's a fellow, Paul Hamler, on you tube that does some pressurized lost wax casting "at home".  It's pretty neat. Where's there's a will...


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