Your Source for GD&T Training and Materials
Software Support - a tolerance capability expert system (TCE)
Excerpt of Process Capable Tolerancing (PCT) article
written by Don Day, Tec-Ease Inc, USA, Martin Raines and Ken Swift, CapraTechnology Ltd, UK
Excerpt of Process Capable Tolerancing (PCT) article written by Don Day, Tec-Ease Inc, USA, Martin Raines and Ken Swift, CapraTechnology Ltd, UK One software tool that is now available to design teams is TCE. This user friendly package provides a straight forward, rapid and consistent way of allocating process capable limits to design dimensions. The expert system runs on a PC under the Windows® operating environment. The memory and processor requirements are modest and the expert system can be used in either a stand-alone mode or integrated with a suite of engineering tools. The expert is coded in C++. This is a powerful general purpose programming language, whose object-oriented nature enables the creation of a system that readily facilitates incremental expansion in the range of manufacturing processes available to the user.
The analysis begins with the selection of a manufacturing process to be investigated for the design characteristic in question and the determination of the 'ideal' or 'best achievable' value of Cpk for a given tolerance. As necessary the user can then consider the effects of design geometry and material type on process capability. (It is not always necessary to consider material effects since many of the maps have been derived for particular material types). The user is guided through a series of questions (in a wizard format) to enable the influence of geometry and material on variability to be enumerated.
Consider the Aluminum Bronze component case study (Fig. 11). The analysis on the 21.46mm critical characteristic is shown in Fig. 12. The main screen in Fig. 12 is where the user can select processes to be investigated, machining in this case. Tabs are provided to move from one process group to another. Clicking on a process displays the appropriate capability map. Double clicking the process brings up the process setup screen where the characteristic dimension and its tolerance can be entered and assessed. Note that the predicted Cpk is consistent with the shop floor value. Selecting the 'Summary' button on the 'process setup' screen gives access to the results obtained, and enables a user to derive an appropriate (Cpk) target. The failure severity rating from the FMEA can be entered and an appropriate process capability target can be obtained using coded data from the Conformability Map (Fig. 10). If the engineering requirement is not met, the software can be used to explore the effect of design changes. Changes in geometry, material, process and tolerance can be rapidly investigated.
(3)Courtesy CapraTechnology Limited
Learn more about this software package
