我是这样打开的
procedure Tform_main.sb_plateClick(Sender: TObject);
begin
    Form_plate:=TForm_plate.Create(Application);
    Form_plate.showmodal;
    form_plate.Free;
end;然后是这样关闭的
procedure TForm_plate.BitBtn1Click(Sender: TObject);
begin
    close;
end;