CNC-RP: A Technique for Using CNC Machining as a Rapid Prototyping Tool in Product/Process Development Matthew Frank Graduate Student mcf113@psu.edu Drs. Sanjay B. Joshi and Richard A. Wysk Department of Industrial and Manufacturing Engineering The Pennsylvania State University University Park, Pennsylvania 16802 sjoshi@psu.edu rwysk@psu.edu Abstract A technique for using CNC machining as a Rapid Prototyping (RP) tool is presented. A 3-Axis machine and a programmable or indexable 4th axis is used to create complex shapes that would otherwise require 5-axis machining. The method involves a novel approach of slicing the part geometry and then fixturing through the use of a temporary feature added to the solid model. Multiple 3-axis NC programs are generated for the various rotations about the axis of the temporary feature (cylinder) used for fixturing. Similar to the support structures that are used in other rapid prototyping systems, the cylinder is removed after processing. Although a complete system has yet to be developed, the method presented herein will make automation of NC rapid prototyping straightforward. Keywords CNC Machining, Rapid Prototyping, CAM 1. Introduction Rapid Prototyping (RP) has been described as a technology for producing accurate parts directly from CAD models(typically in a few hours), with little need for human intervention [1]. According to Webster’s dictionary, a prototype is “a first full-scale and usually functional form of a new type or design of a construction (as an airplane)”[2]. Many of the current RP methods fall short in their ability to create models that can be tested for the true functional requirements of a prototype [3]. When the part being modeled requires rigorous performance and failure testing, creating a part in the appropriate material is critical. Many of today’s free form RP methods are very limited by both material and accuracy. We propose using CNC machining as a rapid prototyping tool. In this paper, we illustrate the development of a novel technique called CNC-RP. CNC machining can create parts in a wide array of the most widely used materials to a very high accuracy. Rough machining to +/- 0.002” is typical, while finish machining can achieve +/- 0.0005”, a combination which isnot readily seen in other commercial RP processes. On the other hand, current CNC machining is limited to a simplerset of part geometries. Unlike other RP methods, CNC is a subtractive process, which requires a line of sight for the cutting tool. Hollow parts are impossible and undercuts require specialized tools and/or numerous re-fixturing operations. Small inside corner radii also pose a problem for machining without the use of specialized tools. Process planning for CNC machining requires a lot of work from a highly skilled technician, including developing a process plan, making tooling decisions, and designing a fixture scheme. Although CAM software makes the process faster and easier for a machinist, it is often not readily usable by engineers and other designers. This is one of the most significant hurdles that has kept CNC from serious consideration as an RP tool. Those who use RP technology typically desire “Turnkey” applications that nearly eliminate the need for user intervention. The methodology outlined in this paper is easily systemized, and can be implemented in computer software. Although a software system has not yet been developed, we envisage that the application described herein can be encapsulated within a software system. Wang, et al, (1999) suggested that an automated machining process could be a viable rapid prototyping process. They contend that complex fixture and process planning are major factors in making traditional CNC machining slower than typical RP methods [4]. With CNC-RP, the goal was to find more automated ways to do these two tasks. Suh and Lee (1998) developed a CAM method to use 3-axis machining in conjunction with a rotary-tilt type