DESIGN FOR POROSITY
Massimo Governatori
Supporting Die Casting Companies and OEM Buyers in process improvement, supplier assessment (CQI-27), and product development.
Of the hundreds of millions of Die Cast parts produced around the world every year, most of them contain considerable amounts of porosity.
Despite this, these castings are put to use in a myriad of different applications, where they perform their functions, year after year, without fail, or complaint by the end-users.
In other words, Die Cast parts can contain considerable porosity, and still be fit for purpose.
However, there are some Die Cast parts which, if the contained porosity exceeds a threshold level, will be unacceptable.
The key issues are:
-?????????the type of porosity;
-?????????the location of the porosity;
-?????????the size distribution of the pores;
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-?????????the function of the part;
Therefore, it is very important for Die Casting product designers to have a good understanding of casting porosity, the different types and causes, and whether it will, or will not, have a detrimental effect on the function of the part.
Some product designers attempt to absolve themselves of responsibility by adding a statement to the product specifications such as 'No porosity permitted in this casting'. A statement like this highlights the designer's lack of understanding of the Die Casting process.
What is required is for the product designer, the process designer and the die designer to work together cooperatively, to eliminate any problems that porosity in the casting might cause.
As was described in the topic 'Contraction of the Casting', shrinkage porosity is an inevitable consequence of the solidification of the alloy. It is not possible to wish away the shrinkage. The alloy is going to shrink, whatever the product designer may wish.
As was also described, the cavities and the runners in the die are full of air when the dies close together. So, it is not difficult to see that some of that air could end up in the casting.
The only way to eliminate porosity problems in Die Cast parts is to use a methodical, science-based approach to the design and development of the total project.
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2 年Like that: 'No porosity permitted in this casting'. A statement like this highlights the designer's lack of understanding of the Die Casting process.