Drawing specification for alu/zinc cast

[recho2000]

Help,
I am new to the casting world. I would like to complete my details drawing and add specification to ensure that the manufacturer will provide a good casting.
I put all the dimension tolerance that I need.
I am not sure of the specification that are regonize for :
Crak
Gas hole
porosity ASTM E155 etc.. 5% etc..
DO you have standard note applicable to drawing to specify the requirment of the material and surface finish quality..

 

[swall]

Do you know what specific alloy you will be working with? As to your other questions on specification issues, most answers are contingent upon the end usage of your part. Specs for critical safety items are more stringent than for example, specs for castings to be used in lawn sprinklers.

 

[recho2000]

The end application is a shield for RF noise on a printed circuit board. The mechanical property for strenght are not critical. However the surface finish finish of the parts needs to be good to allow dispensing of silicon.
The design is very much like a chocolate box with thin walls. The top of the walls will have the gaskets. These walls need to be very good finish and flat top edge. The beading is about 1.35mm high and the compression is 30%. a compression of 10% will reduce the shield effectiveness. This is the main constraint for flatness tolerance and no craks or gas hole on the top of the walls.

 

[swall]

If this will be a high volume part, magnesium die casting would be a good candidate. Mag has good RF shielding properties.Suggest alloy AZ91D and talk to a diecaster about the surface finish and flatness tolerances.

 

[TVP]

I agree with swall. You should also investigate semi-solid cast Mg alloy AZ91. This process is also called semi-solid molding or thixocasting. Contact Thixomat or Phillips:

http://www.thixomat.com/

http://www.phillipsplastics.com/capabilities/metals/magnesium_injection.html