Yann Landon

Kinematic modelling of a 3-axis NC machine tool in linear and circular interpolation

Machining time is a major performance criterion when it comes to high-speed machining. CAM software can help in estimating that time for a given strategy. But in practice, CAM-programmed feed rates are rarely achieved, especially where complex surface finishing is concerned. This means that machining time forecasts are often more than one step removed from reality. The reason behind this is that CAM routines do not take either the dynamic performances of the machines or their specific machining tolerances into account. The present article seeks to improve simulation of high-speed NC machine dynamic behaviour and machining time prediction, offering two models. The first contributes through enhanced simulation of three-axis paths in linear and circular interpolation, taking high-speed machine accelerations and jerks into account. The second model allows transition passages between blocks to be integrated in the simulation by adding in a polynomial transition path that caters for the true machining environment tolerances. Models are based on respect for path monitoring. Experimental validation shows the contribution of polynomial modelling of the transition passage due to the absence of a leap in acceleration. Simulation error on the machining time prediction remains below 1%.

Study into causes of damage to carbon epoxy composite material during the drilling process

There is increasing interest from industry in the machining of composite materials, especially the drilling of thick composite panels and of multi-material assemblies. Damage to laminates due to drilling has an influence on the resistance of plates to the various stresses applied to the structure. The present paper aims firstly to highlight the different defects generated by drilling thick carbon epoxy plates at the entry, on the wall and on the whole exit. Following this, the main aim of this work is the observation in the real time of the initiation and the propagation of such defects. This enables to understand and to show the causes of these defects and then allow operating procedures to be proposed that are likely to reduce such damage.

Characterization of the Surface Quality of Holes Drilled in CFRP Laminates

Assembling composite structures requires a significant number of drillings. During machining, defects appear on the surface of the drilled hole. This paper outlines that the criterion Ra is not adapted to reliably characterize the surface quality on composites. In particular, various tests have shown significant variations of the value of Ra according to the angular position of measurement, as well as the filtering artefacts. This study puts forward a new methodology to characterize the surface quality of a composite hole. To this end, a study of sensitivity of the various criteria proposed by standard ISO4287 was conducted. Various geometries of tool are also tested in the experimental phase. The impact of cutting parameters and tool wear are analyzed based on this new methodology.

Study of Manufacturing Defects and Tool Geometry Optimisation for Multi-Material Stack Drilling

In the aeronautic industries, composite materials are increasingly being used for structural parts. Carbon Fibre Reinforced Plastics (CFRP) are often used in combination with metallic materials, mostly aluminium alloys. This raises new problems in aircraft assembly when it comes to machining the holes for thousands of fasteners. The preferred method for this is a one-shot drilling-reaming-countersinking operation usually using a power tool and with the need to respect tight dimensional and geometric specifications. The solutions proposed so far with existing cutting tools, involving reduced feed rate, are unsatisfactory from an economic point of view. This study first focuses on identifying machining defects and difficulties encountered during drilling of aluminium/CFRP stacks. Then, based on the results of different works on drilling [1,3], an experimental study is proposed to define the critical macro-and micro-geometric parameters of a carbide drill. The criteria relate to the fragmentation of the metallic chips, burr avoidance and zero damage to the CFRP. The first results obtained with the new generation cutters developed show the importance of a constant axial rake angle and of the tool point angle in the chip fragmentation phenomenon but also in preserving the health of the CFRP material. The influence of the constant rake angle on the axial forces generated is also shown. Finally, an optimal combination of the tool geometrical parameters is achieved in order to obtain the expected results.

Drilling thick composite materials using large diameter drills

Composite materials are widely used in aeronautical structures. Assembling the various parts involved requires machining operations, especially drilling. When drilling, a number of defects that diminish the structure breaking strength are propagated. Delamination on hole exit is considered to be the main such defect, this being directly related to the drilling axial force. Determining the drilling critical thrust force at delamination is thus crucial. A number of studies have been conducted into this question but are only applicable to small diameter drilling operations cases. This paper proposes an orthotropic analytical model with the aim of calculating the drilling critical thrust force with a large diameter drill. New assumptions are then proposed. The plate element located under the cutter is broken down into a number of zones in relation to the cutter different active parts. A digital model is developed to validate analytical modelling. Punching tests were also conducted to validate the choices of boundary conditions.

Method for rapid characterisation of cutting forces in end milling considering runout

Pocket machining is currently performed by moulds and dies manufacturers as well as in the aeronautical industry. The good prediction of cutting forces during end milling is so required in order to determine the behaviour of the tool and the workpiece that are the cause of a large number of defects and breakages, or to effectively size the clamping system. Cutting forces depend on a large number of factors, because of cutting parameters and runouts. This study proposes a new method for rapid characterisation of the cutting forces during end milling for a given tool/material couple, from a unique reference test using a single-tooth milling cutter. The variations in forces due to changes in cutting conditions, as in the corners of pockets, as well as axial and radial runouts of the teeth, are integrated in order to effectively predict the instantaneous cutting forces. The comparison between predicted and measured forces is presented. This approach is validated through a milling operation.

A decision support model in mass customization

Abstract Mass customization (MC) is one of the leading strategies used in production industries in today’s market filled with competition. MC is an oxymoron of controlling production costs and satisfying customers’ individual requirements. It is well known that economy of scale and economy of scope is a pair of conflicts, and how to get the balance between them is the key issue to promote enterprises’ competition. By analyzing and processing information of customer preference, product features and cost, this paper proposes a decision support model in mass customization to obtain the optimized production solution. Genetic algorithm is used for optimization, and the results of an illustrative example show that the model is efficient in production industries.

Low-frequency chatter genesis during inclined surface copy-milling with ball-end mill: Experimental study

ABSTRACT In this study low-frequency chatter during machining of inclined surfaces with ball-end mills is experimentally investigated. An explanation of genesis of low-frequency vibrations have been proposed for various conditions: cutting direction, lead angle values, spindle speed, depth of cut. As a result, it has been proven that low-frequency chatter has more significant effect on machined surface than usual chatter. Low-frequency chatter occurs during downward milling, rather than upward milling, especially when lead angle increases. Furthermore, low-frequency chatter takes place in the beginning of cutting process, thereafter develops into steady state of usual chatter, which has no such significant effect on machined surface, as it has been shown. The results are in line with the supposition that low frequency vibrations are caused by sudden and irregular nature of shearing process, when magnitude is small.

Tool/Material Interferences Sensibility to Process and Tool Parameters in Vibration-Assisted Drilling

Vibration-assisted drilling is a critical process applied on high-value products such as aeronautic parts. This process performs discontinuous cutting and improves the drilling behavior of some materials, including chip evacuation, heat generation, mean cutting force. Several research papers illustrated the differences between vibration-assisted and conventional drilling, hence demonstrating that conventional drilling models may not apply. In this process, the cutting conditions evolve drastically along the trajectory and the tool radius. The tool/material interferences (back-cutting and indentation) proved to significantly contribute to the thrust force. A method properly describing all rigid interferences is detailed. A local analysis of the influence of the tool geometry and process parameters over interferences is presented. Interferences distribution on the tool surfaces are highlighted, and the presence of back-cutting far away from the cutting edge is confirmed. A comparison is performed in conventional drilling between the predicted shape of the interferences on the tool surfaces and the real shape of a used tool. The most interfering areas of the tool surfaces are slightly altered to simulate a tool grind, the interference results are compared with the original tool geometry, and significant interference reduction is observed.

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.