Influence de l'etat de surface et du serrage sur les outils assembles par frettage

Shrink-fit assembly is a solution adopted for tool-toolholder interface, it consists in heating the holder by means of a specialized heater. At normal temperature, the holder bore is slightly undersize compared to the tool shank. Heating the holder opens this bore, allowing the tool to be inserted. When the holder cools, the bore shrinks around the tool shank to create a rigid clamp. Shrink-fit presents no connection element between the two parts to assemble such as bolts, keys or others. It allows easy achievements, without unbalance or overall eccentricity.; The qualities sought for the interface tool-toolholder are minimum run-out, rigidity, balance, vibration damping of use and less cost. The shrink-fit solution is considered as valuating the investment for very fast HSM processes and very committed HSM users, it offers superior concentricity, balance and ease of use. Its main default is the low capacity of vibration damping. The behaviour of the shrink-fit assembly in machining at high speed still remains to be studied and we are convinced that there are potentials to arise at end to better control this method.; Shrink-fit is an important process in machine manufacture however the design of these connections is not sufficiently precise due to lack of knowledge regarding the effects of many parameters. Control of the friction coefficient is a determining criterion which directly affects the reliability and operational safety of these assemblies. This is why the work presented here was undertaken.; Designing an optimum structural joint giving rise to desired damping, which is involved in our case of study, is possible if all surface topography factors are understood. Damping in structural joints is associated with frictional losses caused by slip or small relative interfacial movement of component parts on one another. When unlubricated joint surface are involved, this damping mechanism is called frictional damping. Damping in unlubricated joints might be due to three of interactions: macro- and micro-slip and cyclic deformation of the asperities. For our research which is a case of machine tool joints, cyclic plastic deformation of asperities would appear to be the most significant when the magnitude of the interface pressures involved is high.; A better understanding of the effects of roughness and interference on friction, torque capacity and damping of shrink fits is achieved. A statistical design of experiments is used. Results show the existence of correlation between dependent parameters and roughness and interference. The interaction between roughnesses of mating surfaces has a main effect on friction coefficient. The application of the results for tool and holder interface confirm for us that one can optimise the surface roughness and interference in order to obtain desired torque without losing any damping or repeatability capacity. Results can be useful for similar shrink fit applications such as machines joints.; Lame formula for interference fits, largely used, does not consider the roughness of contact surface. We show that roughness has main effect on friction and torque capacity. The relation between maximum torque and surface roughness is parabolic and show a minimum for average asperities sizes. Indeed, for smooth surfaces the bearing area is larger and so the contact pressure. This pressure decreases when asperities sizes increase until a certain minimum where a second phenomenon starts to dominate which is the overlapping of the asperities. This phenomenon makes possible to obtain higher maximum torque with lower contact pressures.; A new method for computing effective interference taking into account micro- and macro-structure is proposed using the surface bearing ratio parameters which can give a good estimation of the radial deflection of the contact interface and the contact area.