A forming device includes a blow-forming die and a shielding member. The blow-forming die includes a first die that protrudes from a first die holder towards a second die holder and a second die that protrudes from the second die holder towards the first die holder. The shielding member is configured to extend from the first die holder to the second die holder before the blow-forming die commences forming a flange part of a pipe in a sub-cavity part. The sub-cavity part is between a main cavity part and the shielding member. The shielding member is separated from the first die and the second die.