Feature-based Cnc Programming Environment on the Internet

Effective global manufacturing enterprises require internet-based tools and technologies to virtually integrate the efforts of customers, designers, and manufacturers who work in separate office buildings or on separate continents. We present the framework for an internetaccessible, feature-based, CNC programming environment. The environment empowers users from different geographical sites to control CNC machining processes via real-time simulations, remote access, and remote manipulation. We have implemented an internet-based prototype system for simulating simple turning operations. INTRODUCTION Feature-based design and manufacturing is a popular paradigm in CAD/CAM and is now driving CAD and CAM strategies. Part representation as a collection of features is advantageous when modifying or analyzing a particular feature. Sophisticated algorithms exist to identify the whole made of the part features and to extract part features from the whole. However, difficulties arise when we attempt to redefine the whole in terms of new set of features – like machining features. This is the task of systems that seek to translate design geometry into machining code. Automated generation of machining code is a complex process requiring detailed part geometry knowledge, machining process knowledge, and fluency in the machine programming instructions. The process involves two skills: interpreting part geometry into machining process steps and translating the process steps into machine programming code. These two steps include modeling parts and reasoning about how they should be manufactured, and writing the manufacturing instructions. Current automated systems use feature-based approaches to these tasks. We propose a different basis for feature definition in order to combine the geometrical information and the manufacturing information precisely and efficiently. We present a new type of feature definition called grouped machine features that is the cornerstone of our feature-based CNC programming (FPCP) system. We have implemented an internet-based prototype system for turning operations. Machine features are grouped and the relevant geometrical and machining information is stored in a relational database. This system is built with internet-friendly JAVA applets. This CNC programming system framework represents a step towards the fulfillment of the promise of global manufacturing. GENERATING CNC CODE Features have been studied from different views corresponding to different applications. People have defined sets of feature classes including explicit features, implicit features, functional features, manufacturing features, etc. Each definition only considers some specific type of information. Consider the feature called “hole.” A hole expressed as an explicit feature includes geometric data on the hole location, diameter, and depth. CNC programming instructions require addition information such as tool choice, tool-positioning instructions, operating speed of tool, feed rate of part, and number of cuts. One of the commonly used programming codes is G&M code, a word address programming language. A G code is a command in the program specifying the mode in which a CNC machine moves along programming axes and M codes specify CNC machine functions not related to dimensional or axes movements. In order to generate G&M codes, the user needs to know all the necessary programming commands and should spend a long time on this tedious programming work. Creating a programming environment that can help the users deal with this programming work is difficult. The most direct way to generated CNC code is to write a computer program to output code in response to user inputs. The computational advantage comes in the absence of mistakes in code writing but this simple strategy does not give the designer help in deciding how the part should be manufactured. Another approach is to create post-processing programs for CNC tools. One such CAD/CAM system translates a drawing file directly into APT motion statements. Two problems remain. Motion statements generated in this way don’t always yield feasible tool paths and sitespecific-post-processors have to be developed to translate the APT or CL code into standard CNC language. Holistic approaches aiming at complete automation of the design and manufacturing process must usually restrict themselves to a subset of part types. Many researchers have built feature-based modeling systems and feature-based computer aided process planning (CAPP) systems. Current feature-based systems are mainly concerned with the complete automation of the design and manufacturing process, so they have to simplify the problems down to a set of common features or part types. ICAPP is an early version of an interactive part planning system for prismatic parts. PRISPLAN is a PC-based computer aided process planning system for prismatic parts. By inputting the geometric features, the user can get the proper CNC codes from this system. In the cited implementation the system is available as an add-on to AutoCAD. One of the most promising developments in this area is the use of sophisticated graphical interfaces for CNC code generation. Prasad designed a graphic workstation for generation of CNC profile cutting code. It features a special-purpose graphic editor that allows the user to draw, edit and nest profiles. Providing visual feedback can eliminate some possible mistakes common to manual coding. FEATURE-BASED CNC PROGRAMMING SYSTEM (FBCP) The goal of the FBCP system (Figure 1) is to provide the user with the resource of a machining specialist and a CNC code programmer. The generation of machining code requires interpreting part features into a set of machining operations and translating that set of operations into accurate machining code. Once a designer verifies that the selected set of operations will produce the desired part geometry the translation into machining code is straightforward. The FBCP system provides enough feedback to the user on machining operation choices that the user does not need to be an expert in this area. The FBCP system also splits the CNC code translation into a separate routine with feedback in the form of visual display of code. This relieves the user from the burden of learning CNC programming language, syntax and semantics. As shown in Figure 1, the FBCP creates an interpretation loop that requires only designer knowledge as input and design verification from the user. All other parts of the interpretation and translation are done by the system. The architecture of the FPCP must simplify the interpretation of part features into machining process steps. The FBCP system features four main architectural units: • A feature representation scheme based on the features that are made by machining operations; • A rule-based reasoning system that converts selected machine features into a set of viable machining operations; • A relational database knowledge storage system; and, • A CNC code generation routine. The system isn’t useful until it is wrapped in a user-friendly graphical interface. The details of the user interface will be introduced in Section 4 where the current implementation of the system is introduced. Grouped Machine Features Part features must be interpreted into the series of machining operations that creates them before the machining operations can be translated into machining code. Part features are individual geometric characteristics of a part, such as a hole or a slot. Features can be independent and simple to identify. Some exist as emergent features created from the intersection of the geometry of two or more part features. We define a machine feature as the geometry achieved when one or more machining operations are performed on a piece of machine stock. Some machine features are the straightforward result of a simple operation, such as a cut. Machine feature complexity arises from the manner in which the process is performed. Machine features are affected by the number of CNC Code GMF Selection Part Geometry Display of Machining Feature Results Machining Features (GMF) Machine Operations Reasoning Engine Translation Routine Machining Rules G & M Code RELATIONAL DATABASE Specialist Knowledge