Journal of Mechanical Working Technology最新文献

Tool wear measurements are a significant factor in the operation of an automation machine tool installation. This paper reports four methods for detection of tool wear: cutting force, chip direction, temperature rise and acoustic emission signal. The simple combined measurement method will be used to indicate ceramic tool wear or breakage. Ceramic inserts on a lathe single point cutting were used in the tests at high cutting speed. The true root-mean-square, RMS, of the acoustic emission signal measured at the base of the insert is shown to be the most sensitive to tool wear.

In recent years, there have been tremendous amount of interest in manufacturing automation and Computer-integrated Manufacturing (CIM). To attain a high level of automation in CIM, there has been relentless effort in trying to integrate the islands of automation in manufacturing. These are often fraught with much frustrations and difficulties. The main clamity in integration is due to the mismatch of information available from the CAD system and that required by CAPP system. The geometric information generated by the solid modellers in most CAD systems are low level whilst the CAPPs will operate efficiently only at a higher level of abstraction. CAPP systems thrives on feature information but such information in CAD databases are rather implicit and at times not even available. Although there has been much research and development work in making these feature information in CAD databases more explicit through feature recognition and extraction, this is really a regressive step. A much better approach is to define features as they exist right at the start at the modelling stage and store these feature definitions in a feature database which can be assessed directly by CAPP. In this way the likelihood of making errors in interpretation is minimized as the feature information are derived at source.

This paper describes the prototyping of a feature-based modelling system in an AI logic language, Prolog. Feature hierarchy depicting the part-feature relationships can be defined by the designer when he is making the design of the part. By defining features as objects and through object oriented programming, generic and specialized feature properties can be defined or inherited through a child/parent relationship. These constituent features are composed semantically and meaningfully through a bottom-up strategy based on feature composition rules and feature primitives. The result of the parsing exercise is a solid representation of the global model depicted as a CSG tree of features. This solid model will ultimately be translated into solid modeller specific commands and further evaluated to give active boundaries representing geometric and topological information for rendering.

In this paper, a simulation based scheduling algorithm for the performance evaluation of Batch Job Shop Flexible Manufacturing Systems (BJSFMS) has been developed. The simulation experiments have been conducted for a system with six machines processing six different type of jobs whereas the system performance has been evaluated on the basis of Maximum Makespan and Average Machine Utilization.

Models for the system performance indices have been developed by the use of multiple regression analysis technique. It has been concluded that processing time of jobs and their transportation times are interdependent operating parameters and the average machine utilization becomes virtually constant when the transportation time exceeds the processing time.

In this paper, a detector to measure the chucking force of the collet chuck holders used in machining centers has been developed, and various kinds of chucks are tested. The chucking pressure distribution is corresponding to the deformation of chuck's bore and the mean chucking pressure has a good agreement with the estimated value from the maximum chucking torque.

This paper presents the concepts of integrating a solids and surface modeler database with a manufacturing postprocessor in the production of complex shapes and geometries encountered in high technology manufacturing. The postprocessor translates information between a standard IGES file and the solid modeler to be fed to a 5 axis CNC machine. This process is demonstrated through an example which generates the mold cavities of an injection molding toll. IGES surface entities are created individually for each face of the solid model and the postprocessor creates a CNC program based on ruled surfaces corresponding to the IGES surface information. A second method is presented in the transfer of information between a surface modeler, a design database and the postprocessor. The design database provides information for blade shapes which are altered periodically. The surface modeler builds the complete impeller shape based on cross sectional geometries, overall design dimensions and number of blades on a given impeller. The postprocessor transfers the geometrical data from the surface modeler into a 5 axis CNC machine to manufacture the impeller blades. Blades are exclusively defined by ruled surfaces, so, the tool design and dimensions are critical to the success of the machining operation.

Many manufacturing systems can be modeled as a hierarchical, distributed control structure in which each level of the hierarchy represents a different level of information abstraction. Tasks passed to each level from the previous levels are decomposed into a set of simpler tasks. If these simpler tasks are within the conceptual domain of the current level of the hierarchy, they are acted upon. If not, they are decomposed further to be passed onto the next lower level of the hierarchy. The decomposition of tasks frees the upper levels of the hierarchy to make global decisions about the manufacturing process. With the advent of the personal computer, microprocessor-based hierarchical distribution has become a reality upon the factory floor.

Today personal computers, PCs, account for the vast majority of cell controller installations. Among the reasons for this dominance are low cost, ease of programming, and the ability to combine the capabilities of third party products. Adding these capabilities to the manufacturing system increases flexibility creating an intelligent, closed loop environment. Within this environment, the PC takes on many roles. One of these roles is as a front-end controller. The front-end controller provides two basic functions for the manufacturing environment. First, the front-end controller provides a “plug” for systems integration. Equipment and software manufacturers have not yet agreed upon standards for system interfaces. That is, they cannot be plugged together as home stereo components can be; they are not “plug” compatible. The front-end controller provides this plug by creating an interface that allows previously incompatible systems to work together. Secondly, the front-end controller provides a local processing node within a level of the distributed manufacturing environment. The manufacturing environment needs this because much of today's equipment and software are underdeveloped. They lack the processing power to formulate the kinds of environment-based decisions necessary to achieve the implementation of the unmanned machine cell. The front-end controller bridges this gap enhancing the existing capabilities of equipment and software while adding new capabilities. Some of the new capabilities may be low level error recovery, a local database for equipment or tool histories, a local user interface, and data acquisition, assimilation, and management.

In a program sponsored by the National Institute of Standards and Testing Automated Manufacturing Research Facility (NIST AMRF), the University of Kansas (KU) has been developing work station level rules for a vertical machining work station. The vertical machining work station at KU consists of an American Robot, a Hurco KMC-3P Three Axis Vertical Milling Machine, an automated fixture, and a Sun Microsystems 4/260 work station controller. The architecture of the work station is based on the five level control system under implementation at the AMRF