Method and apparatus for building up a workpiece by deposit welding

A method of forming an article comprising in combination the steps of:

• constructing in a computer memory or equivalent data storage means a first datafile which is a definition of a three dimensional volume model of an article;
• executing a computer program, within a computer, which reads the first datafile and performs an algorithm which deconstructs the three dimensional volume model defined by the first datafile and produces a second datafile comprising a string of sequential relative spatial co-ordinates describing a tool path through the three dimensional volume model of the article;
• operating a multi-axis welding robot comprising a worktable, worktable drive means, robot arm, welding head disposed on said robot arm, and control means that are arranged to control the movement of the welding robot and the welding head relative to the worktable, the control means utilising said second datafile to position the welding head relative to the worktable such that the relative movement follows the path defined by the second datafile, the operation of the welding head also being controlled to deposit a weld bead as it follows at least a part of the path to build up a solid representation of the three dimensional volume model of the article;
• characterised in that the second datafile comprises a string of x,y,z co-ordinates representing the relative position of the tool along the path and for each x,y,z, co-ordinates a corresponding set of i,j,k co-ordinates which together with the respective x,y,z co-ordinates define a tool vector which represents the relative spatial orientation of the tool at a particular tool position along the path.