How to achieve a good looking aluminium die casting?

  • Thread starter Thread starter GarethW
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Rumbling has principally been used for many years to remove burrs from components which in itself can be a very time consuming and therefore costly process.
 
In the US I think this process is called tumbling and it is done usually in a plastic tank with a vibratory action that causes the media in the tank to circulate in a circular pattern from center up and moves to outer edge then back down. Parts are placed in this bowl submerged by the media flowing and vibrating around it. The pieces to be deburred or polished are also caught up in this circulation pattern. Thus tumbling. The finish this produces and amount of deburring will depend on the time as mentioned and the media.
This also typically is done wet, so a slurry of media and soap and water is used.
For Aluminum parts the surface oxidizes leaving a grey finish if water and soup are used. If dry it might be more polished but the tank will have to be cleaned and media washed to keep up the appearance as more aluminum particles contaminate the tank.

This will tend to round off sharp edges , usually desirable but maybe not. Soft media will do less material removal than hard media.
The same goes with media shape. Ceramic triangle for example are most effective for deburring quickly. Small Stainless Steel sheet metal parts for example.
Screw holes may be affected if large compared to media size and not if small compared to media size.

This is a cheap process in that the labor content is low and the equipment is relatively inexpensive to purchase.
However if the purpose for using this process is to get a specific cosmetic finish, it may require some experimenting to get a desired finish. Media type and lubricant fluid and tank contamination are factors to name a few.
 
If you want to get beautiful Al diecasting surface, I think you can:

1. polish your die (so the parts will be smooth) or sand paint on your die(so parts have a rough feeling if you want);
2. Only polish the necessary surface of your diecasting parts;
3. pay attention to your release agent and the water, the best is to use pure water, any salt will lead to parts dark and look a lots of spots on parts; and blow the die clean after agent sprayed.
4. Sand spraying, a very soft way, just like powder coating.
 
Hey!!! It is very nice thread as I have really learned newer and more effective ways for achieving a good looking aluminium die casting.
 
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Stainless steel and aluminum if your anodizing ?

AndrewR said:
I have seen very good results achieved with blasting using Stainless steel bead, it imparts a great looking finish that is partially corosion resistant without any further threatment.
Click to expand...
This is new to me recently I was alerted to an issue blasting aluminum with the same media that is used for stainless steel, that the cabinet has to be cleaned and the blasting media fresh. I am not sure if this applies with stainless steel beads? Basic concern as stainless steel is a harder medal that burs can imbed in your aluminum and if this happens and you are planning on anodizing that aluminum, the small flacks of steel with leave black burn marks in your aluminum during anodize process, as I said this may be different with Steel beads? It was something I was wholly unaware of and was glad that it was brought to my attention sooner than later. Just a note for those clear anodizing any aluminum.

I am trying to find the perfect media to blast aluminum to match the look and feel of the MacBook, as we make MacBook Hardware. any advice would be appreciated.

Thanks
Craig
 
From my understanding, it depends on how strict your requirements are. Do you need EMI shielding? What metal material is being used?

Copper-nickel plating would be my first bet off the top of my head. It is used in die cast electronic components and also protects against corrosion. I know my company uses this finish in a part that is in a PCB board, with critical contact points to complete the circuit.

I want to provide you with a guide my company offers for free that may be able to help you with the process.. this guide includes what to expect for cost with each finishing. Here is the link: www.cwmdiecast.com/documents/SurFinQckGd.pdf

Let me know if you have any other questions.
 
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