Trimming aluminium die cast parts 1

[SarahEmery]

We die cast our own parts and break them off the shot in a press. We have a problem with some parts where the gate shears and tears into the part as it is broken off and we are not really sure what is causing this. We have tried different kind of edges on the die block and fiddled in other ways without much success. Is there anyone out there who has experience of this that knows what causes it? We have gates 2mm thick that shear just fine and gates 1.7mm thick that don't unless you get the part perfectly in the right place on the die block.

 

[CoryPad]

Fracture follows a path of largest stress and least resistance. Stress is applied by the press, and resistance is determined by geometry (sectional area and stress concentration) and material strength. The crack path exits the gate area and enters the bulk material because this path has the highest stress/least resistance. Factors that influence this include:

1) gate geometry - Is it uniform? Is there a section change to constrain the fracture to the gate?

2) shear blade/die geometry - Is it uniform? Is there excessive gap that allows the stress to be applied outside the gate area?

3) material strength - Is there large porosity (shrinkage or entrapped gas) or inclusions near the gate? They can significantly reduce strength and cause fracture.

 

[ornerynorsk]

Can you check to make sure your holding fixture is not interfering with the part coming into complete contact with your shearing points. It sounds like the part is not sitting all the way down on your trim die.

 

[gbent]

I think you answered your own question. "Unless you get the part perfectly in the right place on the die block."
Figure out what the conditions are for clearance when the part is perfectly placed.
Also, what is the clearance for the trim die? I have seen many trim dies that were made to print, and then the edges had to be blacksmithed to match the part. Some areas were to loose, and other areas were to tight.