René Mayer

Application of fuzzy knowledge base for corrected measured point determination in coordinate metrology

This paper describes an application of fuzzy logic for corrected measured point determination in coordinate metrology. The correction method works on a series of indicated points obtained by contact scanning of the measured surface with a spherical tip probe. The outline of the probe ball defines an arc for each measured point, each such arc being delimited by the points of intersection with the preceeding and the following arcs. As a first approximation the corrected measured point is estimated as the mid-point of the arc. The refinement to the method consists in determining an angular compensation to be applied to the mid-point estimation and calculating the associated indicated measured point coordinate values. To determine an angular compensation a rule-based approach to decision making using fuzzy logic techniques is proposed. In this approach, we consider imprecise vague knowledge as a set of rules linking a finite number of conditions with a finite number of conclusions. The representation of such imprecise knowledge by means of fuzzy linguistic terms makes it possible to carry out quantitative processing in the course of inference based on the compositional rule of inference that is used for handling uncertain (imprecise) knowledge, often called approximate reasoning or fuzzy reasoning. Such knowledge can be collected and delivered by a human expert (e.g., decision maker, designer, process planner, machine operator, etc.). For our case, this knowledge is expressed by a finite number of heuristic fuzzy rules of the Multiple Input Single Output type (MISO). The paper will include a brief discussion of a new compensation procedure of probe radius tip and related test results of the same probe head carried out on a fixed bridge Mitutoyo Legex 910 CMM equipped with a MPP-300 scanning probe in the continuous scanning mode.

Chaotic Tool Wear During Machining of Titanium Metal Matrix Composite (TiMMCs)

The initial tool wear during machining of titanium metal matrix composite (TiMMCs) is the result of several wear mechanisms: tool layer damage, friction - tribological wear, adhesion, diffusion and brace wear. This phenomenon occurs at the first instant and extends to only ten seconds at most. In this case the adhesive wear is the most important mechanism while the brace wear is considered as a resistance wear layer at the beginning of the steady wear period. In this paper, the effect of the initial tool wear and initial cutting conditions on tool wear progression and tool life is investigated. We proposed herein a new mathematical model based on the scatter wear and Lyapunov exponent to study quantitatively the “chaotic tool wear”. The Chaos theory, which has proved efficient in explaining how something changes in time, was used to demonstrate the dependence of the tool life on the initial cutting conditions and thus contribute to a better understanding of the influence of the initial cutting condition on the tool life. Based on the chaotic tool wear model, the scatter wear dimension and Lyapunov exponents were found to be positive in all case of the initial cutting conditions such as initial speed, feed rate and depth of cut. The initial cutting speed appears however to have the most significant impact on tool life. In particular, the mathematical model was successfully applied to the case of machining TiMMCs. It was clearly shown that changing the initial cutting speed by 20 m/min for the first two seconds of machining instead of keeping it constant at 60 m/min during the whole cutting process leads to an increase in the tool life (up to 24%).Copyright

Identification and Compensation of Dynamic Scale Mismatches in High-Speed End Mill Boring Trajectory on CNC Machines

During high-speed end mill boring, dynamic scale mismatch originates from the difference in the dynamic response of each axis and, at high feedrates, causes a trajectory ovalization along the axis with the fastest dynamic response. To investigate this error, an experimental approach is used at different feedrates and trajectory radii for a high-speed machine tool with linear motor drives. Results show that dynamic scale mismatch causes out-of roundness and radius size errors. A simple second order model is used successfully to predict the dynamic scale mismatch and a strategy is proposed and tested to compensate it at the G-code level. An experimental trial reveals the usefulness of the approach.

IMPROVEMENT TO HIGH-SPEED END MILL BORING ACCURACY BY A SIMPLE COMPENSATION STRATEGY

The present study aims to establish a compensation strategy to improve the accuracy of the end mill boring in order to replace the boring bar method to machine a hole. First, an experimental approach based on KGM circular tests is used to investigate the main sources of errors which affect circular contouring accuracy at different feed rates and trajectory radii for two types of machine tool. Then, boring of aluminum parts is performed on a Mitsui Seiki HU40-T five-axis machining centre using two different processes, boring with a boring bar and boring with a high-speed end mill. Next, a simple experimental model based on statistical tests is developed and used to predict the radius size errors. Finally, a compensation strategy is applied to improve the accuracy of the end mill boring process. KGM circular tests results show that the machine exhibits radius size errors that are significant. It also shows that backlash and reversal spikes are important sources of error which affect out-of-roundness. After applying the compensation strategy, machining results show that bores machined through high-speed end mill have a quality similar to those machined with the boring bar while maintaining the high feed rates and thus high productivity.

Teaching Tolerances: A Comparison between the Conventional and Reverse Engineering Approaches

Over the last decade Geometric Dimensioning and Tolerancing (GD&T) has gone from black art to the forefront of computer aided design research. Despite a prominent position in industrial and academic research, GD&T is seldom taught at university level. This paper offers a glimpse at two of those courses, and compares the pedagogy adopted to introduce the fundamental concepts. The conventional approach taken to tolerance education at the Ecole Polytechnique of Montreal is integrated through the curriculum in a two course sequence, respectively as required sophomore and elective senior courses. An elective senior design course at Rensselaer Polytechnic Institute introduces GD&T by way of reverse engineering of existing mechanical systems. Both approaches are presented and a comparison is drawn from the point of view of course contents and integration within a Mechanical Engineering curriculum. To illustrate the two different approaches, concrete examples taken from the course contents are included.

Blank design for the stretch forming of aircraft skin

In this article, a new approach is proposed for the manufacture of aircraft skin. Based on the optimal designed flatten blank with pockets pre-machined, stretch forming process is employed to form the designed aircraft skin. This approach relatively increased the accuracy of pockets shapes and thickness value and reduced the machining difficulty on the curved surface compared with the traditional method that the pockets are machined after the blank deformed. To study the feasibility of this method, FEA software was used to conduct the numerical simulation to obtain CAD data of the deformed part. Then the profiles of the pockets were dispersed with numerous points and the correspondence relationships were set up among the designed pockets on flat blank, formed pockets and the target pockets. To improve the blank design, shape sensitive method was employed by evaluating the offset influence of two designed blanks on the formed pockets profiles. It could decrease the numbers of iteration in blank design and reduce the shapes deviations between the formed pockets profiles and the target pockets profiles.