基于系统知识综述设计和制造圆拉刀(翻译英文版).doc

Journal of Intelligent Manufacturing (1990) 1, 77-91A knowledge based system for the integrated design and manufacture of round broach toolsW. ROBERT TERRY, 1 REUVEN KARNI 2 and CHAD W. RICHARDSl lndustrial and Systems Engineering, Ohio University, Athens 21ndustrial Engineering and Management, Technion - Israel Institute of Technology, Haifa.A complete knowledge based procedure for the design and manufacture of a round hole broach tool is described. The knowledge based design system (KBDS) produces a tool specification from user inputs describing the task to be performed. These design results are then used by the knowledge base to generate a geometric CAD/CAM representation, which can be utilized directly to display a drawing of the tool or to generate a CNC program for producing it. The process of formulating a knowledge-based design system demonstrates: the integration of expertise from experts, handbooks and theory; the awareness of restrictions on the scope of design that can be handled by a given system; the use of failure handling mechanisms to detect design failures and either adjust the emerging design or indicate infeasibility.Keywords: Production scheduling,expert system, simulation1. Introduction Broaching is a metal-removing process whereby a multitooth cutting tool is either pushed or pulled through or along the surface of a workpiece (Hamm and colleagues, 1983).The primary difference between broaching and other metal-removing processes such as milling, turning or boring and its major strength is that the tool performs rough cutting and surface finishing in a single stroke within exacting tolerances.In this article we deal with the process of design through manufacture of internal broaches, where the tool moves through a starting hole in the workpiece. In general, the hole shape may be circular, square, hexagonal or even irregular, such as for splines and keyways. Here we concentrate on round hole broaching.Schroeder and Sears (1988) have carried out a penetrating survey of the broaching industry. In particular, they relate to the problems of integrating broaching into modern computer-integrated manufacturing systems.In the minds of many, the computer revolution that has engulfed the machine tool industries has missed broachngl so that much of the potential of this extremely productive and accurate machining process remains untapped . The time required to design and manufacture a broach, and its cost, eliminate broaching from contention in a just in time manufacturing environment calling for short lead times and flexible, multi-purpose tools . However, some of the new CAD/CAM is very applicable to broach design and manufacturing operations. A fully integrated CAD/CAM system could result in a significant reduction in delivery times, particularly on special tools. This type of use of technology can overcome some of broachings key drawbacks.As CNC equipment can and is being used to fabricate broaching tools, they foresee that computers will play a larger role in the design and manufacture of these tools.This paper demonstrates how an integrated computerized system can be used to design and fabricate a round broach from initial specifications provided by the user. The system is made up of: a knowledge-based module for designing the broach and generating its geometric representation; a CAD system for displaying the broach design;a CAM system for generating the NC program required tomanufacture the broach. The proposed approach eliminates time required to design the tool, produce engineering drawings, determine cutting tool path data and generate a turning program.The objective of this paper is to present and illustrate a structure for creating a knowledge based design system (KBDS) and to detail the components of such a structure. These include: integration of knowledge sources (expertise, handbooks, theories); incorporation of data sources(such as standard tables); detection and handling of design failures; backtracking procedures for design modification or redesign; methods for organizing and sectionalizing the knowledge base. To this end, the paper includes a complete round broach tool design knowledge base (Table 5), which enables these various aspects of knowledge base design to be demonstrated.2. The integrated broach design and manufacture processInternal broaching involves the broach tool being placed through an opening in the workpiece, being connected at both ends to the broaching machine, and being pulled or pushed completely through the workpiece. The teeth on the tool progressively cut into designated points in the workpiece, resulting in a final smooth cut on the inside surface. How the teeth are shaped and set one after the other determines the profile and the quality of the cut in the workpiece. Each tooth removes a layer of metal, such that the desired cut is progressively generated. The teeth fall into three categories: rough cut, semi-finishing and finishing. This means that in one pass of the tool the whole cutting process is completed. Broaching processing times may thus be an order of magnitude faster than those required for other machining technologies.A broach tool (Fig. 1) can be divided into several sections: 1. In pull broaches, a front pull end enables the tool to be attached to the machine. 2. A front pilot assures correct axial tool alignment and allows a check on the initial workpiece hole size before broaching is attempted. 3. Roughing teeth serve to remove the major part of the metal. 4. Semi-finishing teeth serve to produce the basic surface finish. 5. Finishing teeth serve to produce the final surface finish. 6. A rear pilot maintains correct axial tool alignment and serves as a push head for push broaching. If automatic retrieval is not required, a simple follower is attached to the pilot.7. A rear pull end enables the tool to be attached to the machine for automatic retrieval after each broach stroke.Designing the tool involves the following activities:1. Information regarding the workpiece and hole and cut dimensions, broaching machine capabilities and broach tool type and material are provided by the client. 2. The standard geometry for the cutting teeth is determined (Fig. 2). The dimensions are taken from a table (Table 2) incorporated into the knowledge base, in accordance with the length of cut and acceptable gullet depth values. 3. The permissible chip load per tooth in the roughing section is determined. This load must tie between acceptable limits, as it constitutes the major metal-removing step and the essential resistance encountered by the broach tool. These limits have been obtained from experts (Van DeMotter, 1989; Savage, 1989) and incorporated into the knowledge base. 4. The numbers of each type of tooth (roughing, semifinishing, finishing) are determined. The number of semifinishing and finishing teeth is related to the quality of the surface finish and tolerance required. The number of roughing teeth is determined by the ratio of the total amount of metal to be removed by these teeth, to the chip load per tooth in the roughing section (Van DeMotter, 1989). 5. Front and rear pilot dimensions are determined. These are taken from tables (Tables 3 and 4) incorporated into the knowledge base, in accordance with the sizes of the initial and final workpiece hole dimensions. 6. The resistance met by the tool when moving through the workpiece is determined. This is a function of the amount of metal to be removed by each tooth, and the machinability of the workpiece material. 7. The forces acting on the tool the machine tonnage, tensile and compressive forces and forces likely to break the tool because of tool length - are determined with the aid of standard strength-of-materials . 8. The tool resistance is compared to these forces and expert rules are used to make a decision as to whether the tool is strong enough, tooth deflections are tolerable without impacting accuracy and a feasible design has been achieved.The integrated process consists of the following modules (Fig. 3): 1. A knowledge based design system processes the input specification provided by the user (Fig. 4(a), and generates the broach tool design (Fig. 4(b). 2. The knowledge based design system also processes the design and generates a geometrical description file, in data transfer (DXF) form. 3. A standard CAD system reads the geometric descrip-tion file, checks it for consistency, and displays (or draws out) the broach. 4. A standard CAM system reads the geometric description file, develops the cutting tool path (in our case, a CNC lathe), and generates the NC program. 5. A standard CNC lathe produces the broach from appropriate bar stock.3. Knowledge representationA design knowledge base is made up of three components:a fact base, a data base and a rule base. The knowledge base is detailed in Table 5. The facts (Table 5(a) encompass the variables which describe the broach tool, its properties and dimensions,metal removal characteristics and messages which pass between the expert system and the user. These variables are manipulated by the rule base to provide the final design- or a message that a suitable tool cannot be designed in accordance with the input specification. The (internal) data base (Tables 1-4) consists of severaltables, which describe: 1. standard tooth properties for specific workpiecematerials; 2. standard tooth geometries and their dimensions; 3. standard dimensions for automatic pull ends (frontand rear); and 4. standard dimensions for key-type pull ends.Brown and Chandrasekaran (1989) refer to data sources such as these tables as precompiled plans within the knowledge base. They represent standard elements (cut-ting teeth, automatic pull ends, key-type pull ends) to be incorporated into a broach design. In accordance with the task specification (workpiece hole dimensions and machinability), the system selects the appropriate element and, when necessary, revises this selection if design failure occurs.Acknowledgement We wish to acknowledge the contributions of Mr Christopher Van DeMotter, Director of Engineering at the Ohio Broach and Machining Company, Willoughby, Ohio, and Mr Robert Savage, President and CEO of the Hassay/ Savage Company, Turners Falls, Mass., to this research, as well as the support of the Broaching Research Laboratory at Ohio University .References 1 A UTOCAD Reference Manual (1988) Autodesk