Pierre Lagarrigue

Calculation of tool paths for a torus mill on free-form surfaces on five-axis machines with detection and elimination of interference

Within the framework of a study carried out in cooperation with the Sapex Company, we sought to develop an overall machining program for free-form surfaces on a 5-axis NC machine tool. This program comprises a certain number of general cases that will then have to be adapted to specific situations. In this paper, we present the algorithms allowing the following cases to be dealt with:Positioning a torus mill at a given point on the surface with automatic search for interference between the end of the tool and the surface.Angular correction or the raising of the tool to avoid interference.Calculation of trajectories for a “rolling” torus mill on a ruled surface resting on a free-form surface of the NURBS (Non Uniform Rational B-Splines) type.The latter can be broken down into two parts:Seeking the axis position on the adjusted surface.Determination of the tools point of contact on the freeform surface.

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.

Compensation for machining defects due to spindle dilatation

Defects are a common occurrence in industry when it comes to prolonged machining tasks (machining moulds, series of work-pieces, etc.). The relatively long machining time is generally what gives significant value added to the work-piece. We therefore need to avoid having to produce test work-pieces as much as possible [NC Machines, Hermes Paris (1997)]. This article considers dispersions introduced by dilatation of the spindle during machining on NC machine tools. Such dispersions are obviously prejudicial to obtaining accurate dimensions along the Z-axis of the machine. Firstly, we introduce the context of the study and the problem we had to confront. Secondly, the experimental study enabled us to highlight those parameters having an influence and quantify defects. By expressing dilatation and relaxation in the form of an equation, we were then able to calculate defects at a given instant. This enabled us to generate an algorithm for processing of the N.C. program so we could correct errors by compensating for defects during machining. We completed the study by machining a series of work-pieces using the programme integrating compensation for dilatation so as to validate the approach.

Influence of dry plunge-milling conditions on surface integrity of magnesium alloys

Plunge milling is a machining process used to remove material rapidly in roughing operations. It is known to offer significant increases in productivity as compared with conventional milling, especially in the case of deep milled workpieces. However, this improvement of productivity also entails the increase in machining conditions so it could be harmful to surface integrity. In this study the authors consider the case of a dry plunge milling process applied to two wrought Mg-Zr-Zn-RE alloys and one cast Mg-Zr-Zn-RE alloy with two different types of inserts. First, the study involves obtaining surfaces through experimental designs. Second, plunge milling conditions are correlated with surface integrity factors, such as roughness, microstructure and microhardness. This study suggests plunge milling conditions to offer a trade-off between surface integrity and chip flow.

Communication system and team situation awareness in a multiplayer real-time learning environment: application to a virtual operating room

Digital multi-player learning games are believed to represent an important step forward in risk management training, especially related to human factors, where they are trusted to improve the performance of a team of learners in reducing serious adverse events, near-misses and crashes in complex socio-technical systems. Team situation awareness is one of the critical factors that can lead the team to consider the situation with an erroneous mental representation. Then, inadequate decisions are likely to be made regarding the actual situation. This paper describes an innovative communication system designed to be used in digital learning games. The system aims at enabling the learners to share information and build a common representation of the situation to help them take appropriate actions, anticipate failures, identify, reduce or correct errors. This innovative system is neither based on voice-chat nor branching dialogues, but on the idea that pieces of information can be manipulated as tangible objects in a virtual environment. To that end, it provides a handful of graphic interactions allowing users to collect, memorize, exchange, listen and broadcast information, ask and answer questions, debate and vote. The communication system was experimented on a healthcare training context with students and their teacher. The training scenario is set in a virtual operating room and features latent critical events (wrong-patient or wrong-side surgery). Teams have to manage such a critical situation, detect anomalies hidden in the environment and share them to make the most suitable decision. Analyzing the results demonstrated the efficacy of the communication system as per the ability for the players to actually exchange information, build a common representation of the situation and make collaborative decisions accordingly. The communication system was considered user-friendly by the users and successfully exposed lifelike behaviors such as debate, conflict or irritation. More importantly, every matter or implicit disagreement was raised while playing the game and led to an argued discussion, although eventually the right decision was not always taken by the team. So, improving the gameplay should help theplayers to manage a conflict and to make them agree on the most suitable decision.

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.

3D Real-Time Collaborative Environment to Learn Teamwork and Non-technical Skills in the Operating Room

Risk-management training in the operating room (OR) can be achieved by involving learners in a simulated risky situation. The task is particularly complex because most of the time, the causes of an accident or an adverse event imply a large variety of contributing factors that are (i) difficult to combine artificially and (ii) even harder to detect and evaluate in a dynamic training context. This paper describes a model for specifying pedagogical objectives that has been integrated and used in a 3D virtual operating room project designed to train medical staff on risk management, particularly risks linked to communication default. Training sessions organized with trainers, student-anesthetist-nurses, student-operating-nurse and student-anesthetists show how teamwork efficiency in critical situations may be evaluated in a collaborative environment.

Tool flank wear influence on workpiece heating in dry machining

Following a lathe turning operation modification in order to work in dry machining condition, it appears that new tools and cutting condition modifications where insufficient to recover surface quality previously obtained with cutting fluid. Indeed, workpiece temperature evolutions produced with a single tool insert have conducted preventive replacements but no law where found for this substitution. Some responses have been found in literature review, especially on cutting zone temperature estimation in orthogonal and dry cutting with a new tool. But no solutions are provided to avoid production drop due to the important temperature raise in the cutting zone. The aim of this paper is to study tool flank wear influence on workpiece temperature distribution during dry cutting operations. The first part stands up a new analytical model, which takes account of tool wear and elastic deformation of the workpiece in heat generation in the cutting zone. The second part shows by an experimental procedure that temperature growth in cutting zone during machining process is dependant on the tool flank wear evolution.

The configuration of a machining centre and its influence on accuracy

The aim of the paper is to provide an experimental method for revealing systematic defects in a machining centre. The problem is first analysed by comparing results from two different machining operations carried out on the same unit. The machining unit as a whole is then studied in order to obtain maximum precision on each axis, and to determine the influence of machine layout on accuracy. Finally, the best possible layout is chosen in terms of optimum precision.