Electric heating – Metal heating – For deposition welding
Reexamination Certificate
1999-11-30
2001-08-14
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
For deposition welding
C219S076140, C219S125100, C219S125110
Reexamination Certificate
active
06274839
ABSTRACT:
The present invention is concerned with a method and apparatus for building up a workpiece exclusively or predominately by deposit welding. In particular the invention relates to the method of controlled deposition of metal variously called free-form welding, shaped metal deposition, rapid prototyping by welding or other such names.
An example of a method of controlled weld deposition of metal referred to above is described in U.S. Pat. No. 5,233,150 (equivalent EP-A-0,496,181). There are also a large number of other publications, some of earlier date, which disclose similar methods. The reader will be assumed therefore in the interests of brevity to be familiar with the basic techniques of this process. In summary though, according to such known methods a 3D CAD (Computer Aided Design) model of the workpiece, containing details of its geometry, is produced. This CAD model of the workpiece is then sliced within a computer system into a number of distinct planar layers. For each layer the computer system determines a course of weld runs necessary to form that layer. Typically this comprises an outline of each layer and a pattern of weld runs to fill in the layer. A welding torch, which is carried by a multi-axis robot guided by a computer control system, is then programmed to follow this course of weld runs thereby depositing a layer of the workpiece in metal. The workpiece is accordingly built up in a series of layers, one on top of the other, starting from a first layer which is deposited upon a worktable of the welding robot.
The computer programs for slicing a 3D CAD model into a number of layers for subsequent use in the methods described above are not generally available, and tend to be complex and cumbersome in their practical application to the fabrication of complex practical workpieces and components. The methods of controlling the robot welding equipment associated with prior art methods of deposit welding are also cumbersome and not ideal. Consequently there is considerable complexity and a large manual input is generally required.
It is therefore desirable to provide an improved method and apparatus for controlling and programming a robot used for building up a workpiece by deposit welding which addresses the above problems and/or offers improvements generally.
According to a first aspect of the present invention there is provided 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 so of 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 three dimensional volume model of the article is deconstructed by directing a computer representation of a tool within the algorithm to remove a succession of incremental volume portions from the three dimensional volume model of the article.
Preferably the deconstruction of the three dimensional model is executed using a computer aided machining system. The computer representation of the tool may be a representation of a milling cutter which removes a comparable incremental volume as is deposited by the welding head.
According to a second aspect of the present invention there is provided 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 so of 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.
A fixed plane may be defined within the computer or the control means and the robot is controlled to position the tool within this plane such that the relative x,y,z co-ordinates and relative i,j,k co-ordinates are within this plane. The worktable may be rotated to bring the article within said welding plane.
Preferably the welding head is arranged in use to be substantially vertical during operation of the welding head to deposit a weld bead and the worktable is tilted to provide a required relative tool orientation.
The robot may have more degrees of freedom of movement than are defined by the algorithm that deconstructs the three dimensional volume model of the article, and the method may include the additional step of
executing an interface computer program within a computer which reads the second datafile and performs a further algorithm which uses further user specified constraints on the movement of the robot to alter the second data file before it is used by the robot control means.
Preferably the further user specified constraints specify a rotational position and orientation of the tool about a tool vector. Furthermore the rotational position and orientation of the tool about a tool vector may be aligned with the direction of movement of the tool relative to the article, during at least part of the operation of the robot. Alternatively the rotational position and orientation of the tool about a tool vector may, during at least part of the operation of the robot, be fixed relative to the robot.
The algorithm which deconstructs the three dimensional volume model may define up to five degrees of freedom of movement of the robot.
Preferably the robot has more axes of movement than are defined by the algorithm that deconstructs the three dimensional volume model of the article, and the method includes the additional step of
executing an interface computer program within a computer which reads the second datafile and performs a further algorithm which uses further user specified constraints on the movement of the robot about its axes to alter the second data file before it is used by the robot control means. The robot may have nine axis of movement.
Prefer
Pearce Nigel P
Stone Kevin H
Dunn Tom
Oliff & Berridg,e PLC
Pittman Zidia
Rolls-Royce plc
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