tolerance of investment castings ISO2768

[246241]

Hi Everybody,

I'm working in a steel foundry in China.
I have a customer in Germany and have some metal parts to be remade by investment casting process. Originally these parts are complete machining parts in Germany.

On the drawing, general tolerance is according to ISO2768 mk. But I suppose it should be machining tolerance, not casting tolerance because it's very tight such as 8+/-0.1mm

Am I right or not? The customer is a trading company and they even don't have an engineer in casting industry.

 

[KENAT]

I believe ISO 2768 does lean toward machining.

I don't have time to look at it now but will if I get a chance at lunch.

KENAT, probably the least qualified checker you'll ever meet...

 

[GMIracing]

a little last I see, but:

First thing I have to ask, is this drawing really a raw-cast/forged part drawing or is it actually a finished component drawing? Do the tolerances on some key features appear to use tolerances only capable by machining? (Controlled independently of the ISO 2768 general tolerance) I ask this cause quite often a customer will send out only the desired finished part and rely completely on the casting/forging company to create the raw/base part as needed to meet the finished part geometry. This is how my company typically works, as it allows much freedom for the casting/forging supplier and also relieves us, the customer, of the responsibility of the entire casting/forging process.

Yes, ISO 2768 mK is used as a general tolerance control on finished/machined parts, with „m“ meaning medium tolerance on Linear and Angular dimensions, and „K“ meaning medium tolerance on geometrical features (straightness, flatness, perpendicularity, symmetry, and runnout) It does not give a fixed +/-0.x dimension, but actually the „implied“ tolerance depends on the size of the feature being controlled. (I also am not a fan of this ISO 2768, as I feel it is used by lazy engineers who do not fully understand the entirely of the Specification… but I don’t want to get into that here)

DIN 1688 parts 1-4 is the normally used in Germany Standard for General Tolerances of different casting methods (Sand, Gravity, Pressure Die). A typical tolerance using this standard usually reads DIN 1688 – GTA 13/5, where the last part is the tolerance grade. (linear and geometrical feature controls)