Try this:
AxisY axisY = new AxisY();
axisY.AxisName = "AxisY1";
axisY.Title = "";
axisY.IsZeroBased = true;
axisY.DefaultLabelFormat = "#VAL{P0}";
SellInproductChart.DefaultView.ChartArea.AdditionalYAxes.Add(axisY);
AxisY axisY1 = new AxisY();
axisY1.AxisName = "AxisY2";
axisY1.Title = "";
axisY1.IsZeroBased = true;
axisY1.DefaultLabelFormat = "#VAL{P0}";
SellInproductChart.DefaultView.ChartArea.AdditionalYAxes.Add(axisY1);
objSeriesMapping1.SeriesDefinition.AxisName = "AxisY1";
objSeriesMapping2.SeriesDefinition.AxisName = "AxisY2";