Robot-Assisted Shape Deposition Manufacturing

Solid Freeform Fabrication and Shape Deposition are rapid manufacturing processes which build parts by incrcmental material deposition and fusion of crosssectional layers. In Lhis paper, several thermal deposition processes are described for directly fabricating prototype metal shapes using robotically manipulated material deposition systems. A robotic palletizing/part transfer systcm is also described which integrates multiple dcposition and shaping processes into a single facility for rapidly manufacturing functional shapes. Introduction To successfully compete in today’s global markets rcquires the rapid product development and manufacture of new designs to respond to changing market demands. Success requires several innovative manufacturing processes. For one example, computer-aided-design and computcr-aided-manufacturing (CAD/CAM) systems are rcquircd which can quickly produce physical objects dircctly from CAD models. Rapid fabrication is useful for such manufacturing tasks as prototyping, low-volume pars production, and for producing the custom tooling rcquired for high-volume production. Successful automation can reduce fabrication times by efficiently using CAD data and by minimizing human intervention. Convcniional CAD/CAM systems have relied on computer-numerically-controlled (CNC) machinery to hclp build new shapes. Despite efforts to automate CNC opcrations, typical lead times can be long and consequently parts are expensive. There are several fundamcntal technical limitations which account for such dclays. I t is difficult to plan cutting trajectories for complex geometries. Part-specific fixturing must be sclcctcd and often manufactured. Pan-specific cutting proccsscs and tools must be selected (i.e., mills, lathes, drills, EDM, etc.). And, some geomeuies are difficult if not impossible to build. Ultimately. a skilled machinist is nccded to operate the equipment. Although progress has been made toward autonomous planning and cxccution of CNC operations, significant human intcrvcntion is still required. Ncw approaches to shape fabrication are required which do not impose the constraints of conventional CNC cquipmcnt. Solid freeform fabrication processes[ 1,2] such as stcrcolithography. selective laser sintering, and 3D printing, are one such set of emerging technologies which address the challenge of rapid fabrication. In conmast to CNC machining for forming shapes, solid freeform fabrication (SFF) processes simplify process planning and execution by decomposing 3-D geometries into layered 2-D representations and eliminating the need for part-specific tooling and fixturing. These processes build parts by incremental material deposition and fusion of planar cross-sectional layers supported by sacrificial material. Support structures eliminate the need for custom fixturing and permit undercut features to be built up. The planning and execution of SFF processes is independent of the part geometry and therefore relatively quick. Part designers can even operate the equipment. Commercially available SFF processes have been used primarily for those rapid prototyping applications for which plastic, wax and ceramic models and patterns are sufficient. They currently cannot direclly fabricate metal shapes which have superior material properties, good surface appearance and accurate dimensions required for many applications such as the rapid manufacture of production tooling. They can be used indirectly by first quickly creating plastic or wax patterns and ceramic shells from which metal shapes can be cast, however additional machining operations may then be required. The Robotics Institute and The Engineering Design Research Center of Camegie Mellon University (CMU) have been investigating SFF based upon thermal deposition processes as a way to direclfy build metal shapes. Thermal deposition processes, which include thermal spraying (i.e.. arc and plasma) and welding, deposit molten metal and can produce materials with excellent mechanical properties. Robotic manipulation of the thermal deposition torches and robotic parts transfer in a multi-process facility have played important roles in implementing automated systems. This paper describes three such systems developed at CMU. The first system uses stereolithography patterns and thermal spraying for building metal-faced prototype injection mold tools. Another system, called MD*, builds prototype metal shapes directly in layers without the need for preform patterns. The most recent system, called Shape Deposition Manufacturing, is a new fabrication paradigm which uses robotics to integrate SFF and conventional processes into a single system to create functional parts. 1050-4729/94 $03.00