Selection principle of reference level for investment casting

The reference level of investment castingis mainly used as the measurement standard of casting dimension and the positioning standard of machining, and is also used as the reference surface ofpressure profile design. Due to the small machining allowance of investment diecastings, sometimes they can be finished or finished directly without rough machining, so the selection of base level is more important, and the geometricshape, dimensional precision and surface roughness of these faces should be guaranteed from the casting process. The plane, outer circle and inner hole onthe investment mold casting can be used as the reference plane. The following principles should be considered when selecting:

1) Casting reference shall be as consistentas possible with design reference and mechanical process reference.

2) All surfaces to be machined (especiallyimportant surfaces) should be allocated to a necessary and as uniform machining allowance as possible. In general, the important surface with high machiningprecision, high surface roughness and low machining allowance should beselected as the reference surface.

3) When the mutual position accuracybetween the processed and non-processed surfaces is high, this non-processedsurface shall be taken as the reference level. If a casting has more than onemachining surface, the non-machining surface which is close to the machiningsurface and in which the positions of each other are more strict shall be takenas the reference surface.

4) In order to ensure stable positioning,reliable clamping and simple fixture structure during mechanical processing, alarge, smooth, smooth and dimensioned surface should be selected as the baseplane, on which casting flash, burr, cold beans, slope, residual marks ofpouring rising head and parting face are not allowed. As far as possible, thereshould be no ejector bar and free block in the pressure-type part of thecorresponding datum plane.

5) The quantity of base level shall conformto the six-point positioning principle, so that the casting occupies a certainmachining position in the fixture.