Florent Eyma

Machinability and surface quality during high speed trimming of multi directional CFRP

In this paper, high speed trimming of a multidirectional CFRP using unused and used burr tools is considered in order to investigate the influence of the machining parameters (e.g., feed speed, cutting speed and cutting distance) on the cutting forces, machining temperature, and the machined surface quality. To estimate the effect of the tools’ wear and cutting parameters on the cutting forces and surface roughness, a statistical method (ANOVA) has been used. When considering an unused tool, the recorded temperatures were below the glass transition temperature of the composite material (Tg). In the case of used tools, these temperatures were mostly higher than the Tg. Furthermore, SEM observations of the machined surface showed damaged areas. These areas were wider when the cutting distance increased. Statistical analyses have shown that the machining parameters have a significant influence on the variation of the machined surface quality and the cutting forces.

Strains and cutting forces involved in the solid wood rotating cutting process

Abstract Today, for wood industries, a better knowledge of material behaviour during machining is needed for economical and productive reasons: with equipment adapted to manufacturers’ needs. Woodworking machinery and tools manufacturers, as well as their users, urgently require reliable information on the main factors influencing wood cutting and above all on the magnitude of the force required to separate a chip, i.e. the cutting force and its variations in different cases. This is the main aim of this work. This investigation deals with the study of 14 wood species in the following cutting process: routing, i.e. peripheral milling parallel to the longitudinal direction. The influence of main mechanical characteristics was studied and a formulation was obtained which allowed us to estimate more precisely strains involved and the general behaviour of wood during machining.

Wood peeling process monitoring: a comparison of signal processing methods to estimate veneer average lathe check frequency

Experienced peeling operators are able to adjust the settings of their device by hearing the sound coming from the process. Based on this idea, a research program was undertaken to evaluate the possibility of using acoustic or vibration measurements supplying a support decision system to assist untrained operators.The present paper deals with lathe check phenomenon which is one of the most critical defects of veneer (leading to handling difficulties, excess of glue consumption, poor veneer surface quality, etc.). Several signal processing techniques giving a spectral representation of sensors measurements are compared. Finally, an original procedure based on Power Spectral Density ratio is proposed to measure the average lathe check frequency of the veneer during the process.ZusammenfassungErfahrene Schälmaschinenführer können die Maschineneinstellungen nach Gehör vornehmen. Davon ausgehend wurde ein Forschungsprogramm initiiert, in welchem untersucht werden soll, ob Schall- oder Schwingungsmessungen als Entscheidungshilfe für unerfahrene Arbeiter genutzt werden können.Die vorliegende Studie beschäftigt sich mit Schälrissen, einem der kritischsten Mängel bei Furnieren, die zu Schwierigkeiten bei der Bearbeitung, wie z. B. übermäßigem Klebstoffverbrauch oder schlechter Qualität der Furnieroberflächen führen können. Verschiedene Signalverarbeitungsverfahren, die eine spektrale Darstellung der Sensormessungen liefern, werden verglichen. Abschließend wird ein neues Verfahren zur Messung der mittleren Rissfrequenz bei Furnieren vorgeschlagen, das auf dem spektralen Leistungsdichteverhältnis (PSD) basiert.

Surface Quality and Dust Analysis in High Speed Trimming of CFRP

In this work, high speed trimming of a multi directional carbon fiber reinforced plastic using a tungsten carbide burr tool is studied. The influence of the machining parameters on both the dust size and surface quality is investigated. A high percentage of dust is found under the theoretical chip size and the surface quality is found to be affected by the cutting parameters. The percentage of inhaled dust reaching the pulmonary alveoli is quantified and found to be very high, it is also found that this percentage is affected by the cutting conditions.

Influence of Tool Geometry and Machining Parameters on the Surface Quality and the Effect of Surface Quality on Compressive Strength of Carbon Fibre Reinforced Plastic

In this chapter the influence of tool geometry and cutting conditions on cutting forces, surface defects and the percetage of dust generated durring trimming and reaching the pulmonary alveoli is investigated. The surface defects were analysed using a scanning electron microscope and diferent surface roughness measurement devices. It was observed that these leters were highly depend on the cutting condition and the tool geometry, and more important that the effect of cutting parameters can be completely diferent from a tool to an other or even when considering different ranges of cutting parameters (standard cutting speed and high cutting speed). The compressive strenght after machining is also investigated. It is observed that whatever tool geometry, cutting conditions, surface roughnesses (defects) are, the response still the same for all the composite samples except for those machined at cutting temperatures higher than the glass fiber transition.

Characterization and Comparison of Defects Detection Limits of Ultrasonic Non Destructive Techniques

This work deals with the Liquid Resin Infusion (LRI) process developed within the research program “FUSelage COMPosite” of DAHER SOCATA. This manufacturing process enables the realization of complex composite structures or fuselage elements in a single phase (mono-material), which considerably reduce connections and relative difficulties. The concern here is the investigation of non destructive testing (NDT) methods that can be applied to LRI-structures in order to define their capacities for defect detection, and especially their associated critical defect size. In aviation industry, the AITM standards require the ultrasonic testing as NDT for composite materials. Therefore the aim of this work is to characterize and compare three different and complementary ultrasonic techniques on composite specimens. Such analysis allows to define the NDT application field of each method in term of defect detection.

Moisture content monitoring in glulam structures by embedded sensors via electrical methods

In recent years, an increasing number of glulam structures have emerged in civil engineering, but their development is limited by durability issues. Degradations related to excessive moisture content (MC) or wetting/drying cycles were observed and can lead to severe structural damages. As a result, the development of continuous monitoring techniques of wood MC becomes essential. Currently, the mostly used MC control methods are based on electrical measurements (resistive or capacitive). Nevertheless, existing solutions are not practical to conduct measurements inside every lamella of glulam. In the light of these observations, it is proposed to transform glulam into “smart material” by embedding the MC monitoring system either inside or between lamellas, considering the major constraints of fabrication of this material (the small glue line thickness, the important bonding pressure, etc.). To achieve this, 4 measurement configurations using “pin-type” or “surface” electrodes were investigated with the following steps. First, a feasibility study was conducted to make sure of the good functionality of the measurement configurations. Thereafter, the selected configurations were used to monitor the MC variation (10–70%) in glulam specimens. At the same time, the influence of electrode spacing and bonding pressure on the electrical measurements was also investigated. Results show that the selected configurations are operational for the local MC measurement in the lamellas of glulam, regardless of the types of sensors used or the measured physical quantities (electrical resistance or capacitance). This study aims to provide valuable information for the future development of embedded MC monitoring system in glulam structures.

Effects of machining parameters on raised grain occurring after the application of water-based finishes

The application of water-based finishes to wood surfaces is known to increase surface roughness by raising the grain. This phenomenon is detrimental in the appearance of the finished wood surface. To eliminate it, light denibbing is needed prior to applying the second coat of finish. The objective of this study is to optimize wood machining to minimize raised grain caused by water-based coatings and to avoid, or at least, to minimize the sanding operation between each coat of finish. Experiments were done on beech samples. Complete experimental design was defined to generate several surface qualities from “smooth” to “rough” which are linked to the average thickness of the removed chips. The planing parameters were the cutting mode, cutting direction, feed speed, and rotation speed. To compare with existing practices in joinery industries, specimens were also sanded. Two layers of water based coating were applied. Half of the samples were sanded after the first coat and the other half were not. Following each coat, surface roughness was measured and raised grain was evaluated through tactile tests. Results show that sanding operation is responsible for more raised grain than planing. Whereas for planing, high chip removal thickness gives more raised grain after coating application. The effects of the other parameters on raised grain occurence are not found to be statistically significant. The average roughness (Sa), quadratic mean roughness (Sq), reduced peak height (Spk) and the material volume of the peak section (Vmp) are the roughness parameters best correlated with tactile evaluation of grain raising, but the correlations are weak.

Comparative Study of Tools in Drilling Composites T700-M21 and T800-M21

The drilling of composite materials can produce, around the hole, defects and damages which decrease the mechanical resistance of the drilled workpiece. This study shows the influence of several tools (drill, mill and reamer) on the hole quality obtained, in the context of reference parts where surface integrity is a priority. An experimental study is suggested and the criteria used to assess the hole quality are defined. Results show the behavior of each type of cutting tool and their influence on the defects generated. Finally, this study helps creating a scale of recommended cutting conditions to reduce the tool wear and improve the hole quality.