To improve the geometric accuracy of CNC machined parts, dynamic machining errors due to on-line disturbances (tool deflection, tool wear, heat deformation, etc.) should be accounted for in some manner. Unless these on-line disturbances are properly handled, it is obvious that a high degree of geometric accuracy is difficult to achieve. Many attempts have been made to compensate for these on-line disturbances such as the development of engineering models; however, the models are not adequate enough for reflecting the real phenomenon and are dependent on continuous process monitoring using a variety of sensors. Closed-loop process control is a scheme for manufacturing parts and compensating for on-line disturbances and machine tool inaccuracies using error feedback. The goal has been to develop a system that automatically provides dimensional error feedback to the process machine. Closed-loop process control can be achieved before, during (in-process) or after the machining cycle. In-process control is achieved by measuring the part prior to finishing cuts while the part is fixtured to the machine tool. Although the theory behind an automated closed-loop, in-process control system would significantly reduce manufacturing costs, at the present time, machining errors typically are compensated through manual error feedback. This thesis presents a systematic approach for automatically compensating for dynamic machining errors based on a new closed-looped machining scheme. The new scheme incorporates these errors, found through in-process inspection, into a modified CAD model or "Variational Part Model". As a result, the Variational Part Model inherently contains the online disturbances associated with machining. It is important to note that this new scheme assumes the machine tool's static error (ball screw error, joint misalignment, perpendicularity error, etc.) has been addressed by some other compensating method and this scheme only addresses the dynamic machining error. To create the Variational Part Model, the machined part is measured on the machine and compared to the CAD model's theoretical data. The data is then used in conjunction with modeling functions contained in NX's Application Programming Interface (API) to interact with the CAD model and modify its feature geometry. The validity and effectiveness of the methods are presented as well as results from experimental testing. This thesis also presents the methods necessary for automatic CAM process updating to ultimately close the loop between machining and inspection.

Quality control (QC) plan is an important component of manufacturing planning for mass customization. QC planning is to determine the operational tolerances and the way to control process variation for assuring the production quality against design tolerances. It includes four phases, i.e., tolerance stack-up analysis, tolerance assignment, in-process inspection design, and the procedure of error source diagnosis & process control. Previous work has been done for tolerance stack-up modeling based on the datum-machining surface relationship graph (DMG), machining error analysis, and worst-case/statistical method. In this research, the tolerance stack-up analysis is expanded with a Monte-Carlo simulation for solving the tolerance stack-up problem within multi-setups. Based on the tolerance stack-up model and process capability analysis, a tolerance assignment method is developed to determine the operation tolerance specifications in each setup. Optimal result is achieved by using tolerance grade representation and generic algorithm. Then based on a process variation analysis, a platform is established to identify the necessity of in-process inspection and design/select the inspection methods in quality control planning. Finally a general procedure is developed to diagnose the error sources and control the process variation based on the measurements.

On-machine inspection (OMI) via on-machine probing (OMP) is a technology that has the potential to provide a step change in the manufacturing of high precision products. Bringing product inspection closer to the machining process is very attractive proposition for many manufacturers who demand ever better quality, process control and efficiency from their manufacturing systems. However, there is a shortness of understanding, experience, and knowledge with regards to efficiently implementing OMI on industrially-based multi-axis machine tools. Coupled with the risks associated to this disruptive technology, these are major obstacles preventing OMI from being confidently adopted in many high precision manufacturing environments. The research pursued in this thesis investigates the concept of enabling high precision machine tools as measurement devices and focuses upon the question of: “How can traceable on-machine inspection be enabled and sustained in an industrial environment?” As highlighted by the literature and state-of-the-art review, much research and development focuses on the technology surrounding particular aspects of machine tool metrology and measurement whether this is theory, hardware, software, or simulation. Little research has been performed in terms of confirming the viability of industrial OMI and the systematic and holistic application of existing and new technology to enable optimal intervention. This EngD research has contributed towards the use of industrial machine tools as traceable measurement systems. Through the test cases performed, the novel concepts proposed, and solutions tested, a series of fundamental questions have been addressed. Thus, providing new knowledge and use to future researchers, engineers, consultants and manufacturing professionals.

For some time now coordinate measuring machines have been an integral part of the shop floor. The goal has been to make coordinate measuring machines (CMMs) into tools that can easily be used by machinists to improve their manufacturing capabilities. The value of a CMM as a quality control tool is undisputed. Now efforts are being made to further reduce the time and cost of measurement by reducing the physical distance between machining and measuring processes. The ability to reduce that distance to zero and measure a part directly on the chip-making machine has been a goal for many years. Dimensional inspection of parts is primarily conducted by coordinate measuring machines operating on motion instructions from task planning software. The research in direct machining and control (DMAC) at BYU has identified a potential application of CMM technologies on existing machine tools. To prove that a machine tool can be controlled as a CMM with the DMAC controller, this research will integrate the software package PC-DMIS provided by Wilcox Associates, Inc. with a DMAC controller provided by Direct Controls, Inc. to conduct in-process dimensional inspection of parts as they are being machined. This process is referred to as DirectCMM because it will link the DMAC controller directly to PC-DMIS without need for post-processing. This thesis will lay the groundwork for future efforts at developing systems that utilize in-process part inspection to dynamically correct computer aided manufacturing (CAM) process plans. To aid future efforts at dynamic CAM process updating, a software interface specification will be created for passing measurement data between CMM and CAD/CAM software packages. A CMM control specification will also be created to provide a standard method for controlling coordinate measuring machines with the DMAC controller. Possible methods for dynamic CAD/CAM updating will be explored.