No description available.

No description available.

Tese de mestrado integrado. Engenharia Metalúrgica e de Materiais. Faculdade de Engenharia. Universidade do Porto. 2010

The field of numerically controlled (NC) machining has long been interested with predicting and measuring the errors in machining. Creating a simulation of NC machining is one way of achieving this. This thesis presents one such implementation of an NC simulation. It also runs a number of numerical and physical tests to verify the simulation?s correctness. The numerical tests show that the simulator work correctly as well as providing guide lines for appropriate simulation parameters. The physical tests show that the results of the simulation match the results of real NC machines. It is hoped that this thesis can provide a guide for the creation of machining simulators and their verification.

The field of numerically controlled (NC) machining has long been interested with predicting and measuring the errors in machining. Creating a simulation of NC machining is one way of achieving this. This thesis presents one such implementation of an NC simulation. It also runs a number of numerical and physical tests to verify the simulation?s correctness. The numerical tests show that the simulator work correctly as well as providing guide lines for appropriate simulation parameters. The physical tests show that the results of the simulation match the results of real NC machines. It is hoped that this thesis can provide a guide for the creation of machining simulators and their verification.

Machinists often simulate a part program to verify its correctness, since mistakes can cause damage to the part, machine, oneself, or others. A popular approach for part program simulation involves representing the stock (the material the part is being carved from) as a heightmap. Although this approach is computationally fast and memory efficient, only objects that are representable as functional surfaces (e.g., z = f(x, y)) can be machined. This thesis presents a new heightmap-based data structure, called a multidirectional heightmap, that does not have this limitation. A multidirectional heightmap, in response to an overhang, recursively subdivides itself until each piece can be represented by an axis-aligned heightmap. More precisely, a multidirectional heightmap is a kD-tree with the property that all cells are functional: each cell contains a heightmap that represents a functional portion of the stock. To improve accuracy, each regular heightmap can be replaced by a 3-Way Heightmap, a new type of heightmap that samples the tool along all three stock axis directions (three ways) rather than just one. The experimental results herein suggest that the multidirectional heightmap data structure achieves a good level of performance with respect to memory usage, CPU usage, and approximation error.

The main goal of this thesis is to propose a strategy which can integrate the precision hydrodynamic polishing system with an ordinary CNC machine tool. This integrated CNC machine tool is capable of applying the hydrodynamic polishing process, which is a high-precision machining method, to compensate the form error on a work surface to improve its form precision. With such a compensation capability, a low-cost CNC machine tool may play the function of precision machining as well as an expensive CNC machine tool does. It is hoped that with this function equipped in a CNC machine tool the international competition of the domestic machining industry can be enhanced. The complete integrating scheme is composed of three parts. The first part is the hardware of polishing system, which is required to attach to the CNC machine tool. The second one is the software developed in this thesis. It includes the codes to generate the commands to control the CNC machine tool and the attached polishing system. The final one is coordinating system that is to synchronize the actions of the CNC machine tool and polishing system. It is done by requiring the polishing system to match the actions of machine tool through measuring the configuration of machine tool consistently. Because of the first and third parts, no modification to the machine tool is needed and the requirement to read the internal information of CNC controller is waved. This will significantly reduce the complexity in implementing the integrating job. When properly integrated with the required sensors, the software developed in this thesis can harmonize the actions of the polishing system and machine tool to execute the form error compensation task. The software will automatically generate the commands for the polishing system and machine tool based on the geometric and material data of work. It does not require the user to fully comprehend the function of the CAM software and the details of polishing process. This will obviously reduce the skill requirement of operator and facilitate the use of the integrated system. Since the CNC machine tool only plays the function of offering the three translational motions (in X, Y, and Z directions), the application of this strategy to an ordinary CNC machine tool is straightforward.

Machinists often simulate a part program to verify its correctness, since mistakes can cause damage to the part, machine, oneself, or others. A popular approach for part program simulation involves representing the stock (the material the part is being carved from) as a heightmap. Although this approach is computationally fast and memory efficient, only objects that are representable as functional surfaces (e.g., z = f(x, y)) can be machined. This thesis presents a new heightmap-based data structure, called a multidirectional heightmap, that does not have this limitation. A multidirectional heightmap, in response to an overhang, recursively subdivides itself until each piece can be represented by an axis-aligned heightmap. More precisely, a multidirectional heightmap is a kD-tree with the property that all cells are functional: each cell contains a heightmap that represents a functional portion of the stock. To improve accuracy, each regular heightmap can be replaced by a 3-Way Heightmap, a new type of heightmap that samples the tool along all three stock axis directions (three ways) rather than just one. The experimental results herein suggest that the multidirectional heightmap data structure achieves a good level of performance with respect to memory usage, CPU usage, and approximation error.

Former studies have shown that a considerable part of industries’ energy usage can stem from idle times in the production. This thesis, carried out at Siemens Industry sector, evaluates the potential for using the control system to automatically put machines into energy saving mode during idle times. The main part of the thesis consists of a case study performed on machine tools at a Scania production site in Södertälje. Through load measurements the potential for energy savings was determined. The results show that there is a great potential for energy savings during idle times at the site. 20 to 50 percent of the machines’ energy usage can be reduced if they are put into energy saving mode when they are not used. However, the implementation of pause management in an existing control system is often too expensive to be motivated alone. Instead this should be considered before overhauls or rebuilds of machines and production sites. Another way of reducing costs can be to use a standard for pause management like PROFIenergy. A general conclusion is that industries with discrete manufacturing and long pause times have a great potential for energy savings. The same holds for machines with position control, such as robots and machine tools. The thesis also highlights the need for proper energy measurements at a production site in order to evaluate the potential for and results of an energy efficiency measure.

No description available.