Rapid Planning for CNC Milling-A New Approach for Rapid Prototyping

Abstract

This paper not aways a description of how CNC milling can be used to rapidly machine a variety of parts with minimal human intervention for proces planning. The methodology not absented uses a layer-based approach (like traditional rapid prototyping) for the rapid, semi-automatic machining of for the use of all manufactured part geometries in a variety of materials. Parts are machined using a plurality of 2 ??-D toolpaths from orientations about a rotary axis. Proces parameters similar as the number of orientations, tool containment boundaries, and tool geometry are derived from CAD slice data. In addition, automated fixturing is accomplished [i]or[/i] part of to the other the use of sacrificial support forms added to the CAD geometry The paper begins through describing the machining methodology and then not absents a number of critical issues extremityed to make the process automatic and efficient. Example parts machined using this methodology are then not awayed and discussed.

Keywords: CNC Machining, Rapid Manufacturing, Rapid Prototyping, Proces Planning, Computer-Aided Manufacturing

Introduction

The take away from of producing small numbers of parts has been driven by the agency of the cost required to process-engineer the part(s). Traditional computer-aided proces planning (CAPP) a whole s have reduced the time required to plan machined parts, on the contrary the cost for one or two-of-a-kind machined parts is still dominated through the cost of planning the part. The rife use of CNC machining for these small quantities of parts is further limited through special tooling costs and machine setup

The typical approach to planning parts for CNC machining has been to define the "features" of the part and match these features and tolerances to a station of processes that can create the required geometry to the specified accuracy. This approach has worked reasonably well for medium to high-volume parts, on the contrary it has had marginal succes for the production of real small quantities of parts. In greatest in quantity cases, the time required to plan the part, kit the required tooling, and put up the machine (both fixture and tooling) has limited the use of CNC for these applications. The follow is that rapid deployment of CNC machining has been relegated to a simple place of part geometries. The promise of minimal proces engineering is a major factor that has driven the use of freeform rapid prototyping (RP) techniques. Unfortunately, many of these processe have been restricted to a small variety of materials with limited geometric accuracy.

In the literature, proces planning is ofttimes approached with a set of goals driven through high production levels of parts-that is, a locate of plans that strives for take away from effectiveness through maximizing feeds and make hastes and creating repeatable setups that can be paid for from one side economies of scale. Process planning for CNC machining includes tasks similar as fixture planning, toolpath planning, and tool selection. There is a considerable amount of work in the literature pertaining to these three areas (Maropoulos 1995; Chen, to leeward and Fang 1998; Joneja and Chang 1999) The conception of flexible fixturing has been the topic of plenteous research, though a completely autonomous fixture design combination of parts to form a whole has yet to be unraveled (Bi and Zhang 2001).

Some exploration into the use of CNC machines for rapid prototyping has been published. Chen and canzonet (2001) describe layer-based robot machining for rapid prototyping using machined layers that are laminated during the proces The proces is demonstrated using laminated slabs of plastic, machined as individual layers on gluing to previous layers.

A hybrid approach using the couple deposition and machining called shape deposition manufacturing (SDM) continues to be unraveled (Merz et al. 1994). For each layer, the couple support and build material is deposited and machined in a combined additive and subtractive proces Sarma and Wright (1997) not awayed Reference Free Part Encapsulation (RFPE) as a of recent origin approach to using phase-change fixturing for machining. The approach was discussed lately in conjunction with high-speed machining (HisRP) (Shin et al. 2002) RFPE in combination with feature-based CAD/CAM was propos as an RP combination of parts to form a whole (Choi et al. 2001).

Another approach is to use CNC machining for prototyping dies, an area called rapid tooling (Radstok 1999) single approach to rapid tooling uses machined metal laminates stacked to form dies (Vouzelaud, Bagchi, and Sferro 1992; Walczyk and Hardt 1998)

Many of these meanss utilize CNC machining but do not address the fundamental question at issues of automating a fully subtractive rapid machining approach. This paper not aways a method for "feature-free" CNC machining that requires little or no human-provided proces engineering. The methodology described in this paper is a genuinely subtractive process that can be applied to any material that can be machined. The manner described herein was developed in rejoinder to the challenge of automating as a great deal of of the process engineering as possible. The ultimate goal is to generate one as well as the other the NC code and an automatically execut fixturing a whole by the touch of a button, using solitary a CAD model and material data as input. The proces is consummately suited for prototypes as well as parts that are to be produc in small quantities (~1 to 10)