Method of forming a shaped article

A method of forming a shaped article wherein said article comprises at least two parts which are bonded, the method comprising:

• assembling at least two parts in a cavity of a tool to form an assembly of the at least two parts, wherein the cavity is adapted to receive the assembly of at least two parts in the form of the shaped article;
• sealing the cavity of the tool to contain the assembly of the at least two parts inside the cavity and inhibit leakage from the cavity;
• wherein the tool comprises tool parts that define the cavity, and the tool parts comprise materials with different coefficients of thermal expansion such that the step of sealing the cavity of the tool is reversibly achieved by relative expansion of the tool parts in a heated configuration, whereby a sealed pressurised environment is created and the tool parts are fixedly fastened together and material flow is inhibited to preserve the geometry of the shaped article;
• and
• melting the assembly of at least two parts to bond the at least two parts together to form the shaped article.