BRepFeat_SplitShape

Try any of these functions to see if it works on your sample, the AddNewSplit(TopoDS_Shape Stock, gp_Pln plane1) is more efficient than AddNewSplit(TopoDS_Shape Stock, TopoDS_Shape Tool)

you could either do :

TopoDS_Shape result = AddNewSplit(aFace2,aFace1);

or since you already have the plane:

aPlane = GC_MakePlane( gp_Pln( gp_Ax3( gp_XOY() ) ) ).Value()
TopoDS_Shape result = AddNewSplit(aFace2,aPlane);

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// split stock with tool

TopoDS_Shape AddNewSplit(TopoDS_Shape Stock, TopoDS_Shape Tool)
{
TopoDS_Shape nullshape;
BRepAlgoAPI_Section asect(Stock, Tool,Standard_False);
asect.ComputePCurveOn1(Standard_True);
asect.Approximation(Standard_True);
asect.Build();
TopoDS_Shape R = asect.Shape();

if (!asect.ErrorStatus()== 0) return nullshape;
BRepFeat_SplitShape asplit(Stock);

for (TopExp_Explorer Ex(R,TopAbs_EDGE); Ex.More(); Ex.Next()) {
TopoDS_Shape anEdge = Ex.Current();
TopoDS_Shape aFace;
if (asect.HasAncestorFaceOn1(anEdge,aFace)) {
TopoDS_Face F = TopoDS::Face(aFace);
TopoDS_Edge E = TopoDS::Edge(anEdge);
asplit.Add(E,F);
}
}

try
{
asplit.Build();
}

catch(...)
{
return nullshape;
}

if(!asplit.Shape().IsNull())
{
return asplit.Shape();
} else {

return nullshape;

}

}

// split stock with plane

TopoDS_Shape AddNewSplit(TopoDS_Shape Stock, gp_Pln plane1)
{
TopoDS_Shape nullshape;
BRepAlgoAPI_Section asect(Stock,plane1,Standard_False);

asect.ComputePCurveOn1(Standard_True);
asect.Approximation(Standard_True);
asect.Build();
TopoDS_Shape R = asect.Shape();

if (!asect.ErrorStatus()== 0) return nullshape;

BRepFeat_SplitShape asplit(Stock);

for (TopExp_Explorer Ex(R,TopAbs_EDGE); Ex.More(); Ex.Next()) {
TopoDS_Shape anEdge = Ex.Current();
TopoDS_Shape aFace;
if (asect.HasAncestorFaceOn1(anEdge,aFace)) {
TopoDS_Face F = TopoDS::Face(aFace);
TopoDS_Edge E = TopoDS::Edge(anEdge);
asplit.Add(E,F);
}
}

try
{
asplit.Build();
}

catch(...)
{
return nullshape;
}

if(!asplit.Shape().IsNull())
{
return asplit.Shape();
} else {

return nullshape;
}

}

Are you using python? Your function looks very similar to mine. I wonder if there are differences in C++ version versus Python version.

Try specifying a point to the plane constructor, just to make sure both planes have the same origin.
even if the gp_XOY() and gp_YOZ() planes have the same origin try this:

PL1 = gp_Pln( gp_Pnt(0,0,0),gp_Vec(0,0,1));
PL2 = gp_Pln( gp_Pnt(0,0,0),gp_Vec(0,1,0));

Also when you display the result of the split using :

display.DisplayShape(aSplit.Shape())

does it display something?

if it does display something, check that the result contains more than one face, because BRepFeat_SplitShape simply segments the object, you have to do a topological exploration against the faces of aSplit.Shape() that you want to keep.

if nothing is displaying than commentoff the code for splitting and display aface1 and aface2 in the viewport using the parameter values you have specified above, and visually inspect that the two surfaces are actually touching each other. If they are not touching change the parameters until they do and rerun the splitting.

if it still is not working... post your results...