aluminum Ingot vs as cast properties 2

[Schrauben]

I have a customer testing thread rolling and machine screws in aluminum ingots and getting lots of variability in the results. They reported that prior tests conducted in castings (engine blocks) worked well. The material is the same.

Materials are ADC10 (no heat treatment) ADC10-T5 and AC2B-T7 (Customer is in Korea).

I suspect that testing in ingots is not valid, but can't state a definitive reason. I suspect porosity perhaps.

Can anyone state if testing the screws (for torque) in ingots is, or is not, valid and any possible reasons?

Thanks
JR

 

[TVP]

Can you provide some additional information on the ingots, such as the overall dimensions and the casting process that was used? Were the holes already cast into the engine block, or were they machined? What about for the ingots? Porosity would certainly be a concern if a solid chunk (ingot) with a section size of 10-500 mm was tested, instead of a cast engine block with section sizes of 1-10 mm.

 

[Schrauben]

The holes in the ignots were drilled. I am awaiting an answer on the sizing - from the pics in the report the size appears to be 8" x 24" (200mm x 500mm), but it is not entirely clear and the piece may have been cut from a bigger ignot. Thickness and casting process is unknown at this point.

thanks for the response!
John

 

[arunmrao]

A casting like engine block is processed under controlled conditions,while an ingot I gather is not subject to similar process control.

Also as TVP indicated,the section thickness variation in the two will influence shrinkage porosity.

An ingot is cast for eventual forging,rolling or extruding operations. thus gating,feeding techniques and mold quality is not of primary concern. The liquid metal quality may be same as processing conditions are different,the end result is bound to vary.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[CoryPad]

What property is varying? Internal thread stripping strength? If the ingot is much larger in size, especially thickness, compared to the engine block castings, then the material strength will vary a lot.

 

[arunmrao]

What beats me,is the reason for using a cast ingot. Round rods of any size are readily available for the purpose.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[Schrauben]

Corypad - The thread forming torque is varying from 1.6 to 13Nm. The 1.6 value is abnormally low. The strip torque also varies, but not as much. There is so much variation that the -3 sigma values are negative, despite testing 30 pieces (which in my experience has always been enough for statitics with screws)

The size of the ingot is 8" x 16" x 3 1/4". They have agreed that this material is not valid for testing. the worse results were obtained in the middle of the ignot (no surprise there).

Arumrao, I can't answer fully on using round rods, but perhaps they are not available in the cast materials to be used.

Unfortunately, someone did not crunch some number before completeing the tests. If I saw negative - 3 sigma values, I would have stopped all testing. Unfortantely they ran about 400 tests and another facility ran extensive thermal tests

 

[TVP]

Schrauben,

It is clear to me that ingot was a poor substitute for the engine block. The solidication conditions will be completely different for the two, which means that the microstructure will be different, which means the mechanical properties will be different, and the amount and location of porosity also will be different. I also agree with your assessment that testing 30 fasteners should produce a reasonable result, which is an obvious indicator that the ingot was not a suitable sample for evaluation. Good luck.

 

[Schrauben]

Yeah that's pretty clear to me as well - actually as soon as I saw the numbers! I was looking for reasons why to give to my customer. they now accept such. They did experience porosity, but I now suspect that grain from the "solidication conditions" (As TVP stated) is a major reason.

Thanks all.