*Linear Friction Welding (LFW) is a uniquely important manufacturing process because it allows welding of dissimilar materials without filler material.* *LFW is a solid-state joining process that utilizes friction heat to soften the workpieces and bonding by applied pressure. In this study, bi-metallic Ti6Al4V-CoCrMo joints were manufactured using LFW process and analyzed the weldability and bonding strength. Ti6Al4V and CoCrMo cylinders were manufactured to a standard size of tensile specimens and cut into two identical pieces. The surfaces to be welded were polished and cleaned before performing welding. During the friction welding, CoCrMo cylinder was oscillated and Ti6Al4V cylinder was pushed to obtain axial shortening. Pressures were administered at 62 MPa to apply initial friction force and increased to 110 MPa to join the plasticized workpieces. The experimental thermal data was recorded with an IR camera.*

*Two numerical models to simulate heat flow during friction welding process were created. A simple one-dimensional thermal flow was attempted and two-dimensional heat flow was approximated using a combined effect of radiation and convection through the cylindrical surface. Secondly, most of the plasticizing and expulsion of flash were produced in a direction of oscillation and forging after in-plane shearing at the weld interface. In the thermal stress simulation model, the temperature-dependent thermal properties of Ti-6al-4V were used. The thermal properties of CoCrMo were assumed constant due the fact that CoCrMo does not change phase until it reaches its melting temperature. Since the weld cycle was 1.8 s and the temperature remained constant at 20 mm from the weld interface, the dimensions of each workpieces 12.7 mm by 20 mm for the model. The heat losses due to radiation was different for each workpiece because both materials had a different emissivity and the heat loss by convection is a function of the surface temperature by natural convection. The left boundary of the Ti-6Al-4V and the right boundary of the Co-Cr-Mo workpiece were constrained at a constant temperature of 45°C. The heat input is assumed to only occur at the weld interface.*

*The majority of plasticization would occur on Ti6Al4V. The forged Ti6Al4V surrounds the joint area and then solidified. This prevents two materials from mixing to form strong bond. Tensile test results describe a large-scale plastic strain and catastrophic failure of the weldment. The maximum deformation of the simulation model is 4.1 mm which is well matched with the measured data of 4.3 mm within 5% error.*


Thermal Stress Simulation Model of Dissimilar Linear Friction Welding (Lfw) Technology for Manufacturing of Bi-Metallic Biomedical Implants

Division / Sponsor: 
Manufacturing Engineering Division (MED)

International Manufacturing Science and Engineering Conference - Paper Proceedings: https://asmedigitalcollection.asme.org/MSEC/MSEC2020/volume/84256

JSME 2020 Conference on Leading Edge Manufacturing/Materials and Processing - Paper Proceedings: https://asmedigitalcollection.asme.org/lemp/LEMP2020/volume/83624

MSEC2020 - Virtual Conference, LEMP2020 - Virtual Conference

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