Stirring head for welding metal and thermoplastic polymer and welding method

Abstract

The invention provides a stirring head for welding metal and a thermoplastic polymer and a welding method, and belongs to the field of new material connection. The stirring head is characterized by a concave shaft shoulder and an inverted-tower-shaped stirring needle with a multi-stage flow blocking circular truncated cone structure of the stirring head. The welding method is characterized in that friction stir lap welding is completed by heating the two sides of the upper surface of a welding seam through a resistance type auxiliary heating strip, and an auxiliary heat source can provide the effects of preheating before welding and slow cooling after welding for a welded plate. According to the stirring head for welding the metal and the thermoplastic polymer and the welding method, the flow choking appearance design of the stirring head can inhibit the overflow of a thermoplastic polymer material and improve the surface quality of the welding seam; and the welding auxiliary heating process for the metal and the thermoplastic polymer material is based on the thoughts of isothermal peak rotation speed reduction and stress reduction anti-pulling-off, the rotation speed of the stirring head is reduced under the condition that the same welding temperature is guaranteed, and therefore joint surface forming is improved, internal defects are eliminated, the interface structure is optimized, and the quality of a heterogeneous joint is comprehensively improved.

Description

technical field [0001] The invention belongs to the technical field of friction stir welding, and relates to a stirring head for welding metal and thermoplastic polymer and a welding method. Background technique [0002] Thermoplastic polymer materials have high specific strength, high specific modulus and excellent corrosion resistance, so they have broad application prospects in aerospace, wind power, transportation and other fields. In some industrial manufacturing fields, the wide application of thermoplastic polymer materials inevitably leads to connection problems with traditional metal materials such as steel, aluminum, and magnesium alloys. At present, most of the connections between thermoplastic polymer materials and metals are adhesive bonding and mechanical connections (riveting and bolting), but problems such as joint aging or stress concentration are unavoidable. [0003] Friction Stir Welding (FSW) is a new type of solid-phase joining technology, which uses a...

AI Technical Summary

Problems solved by technology

However, in the friction stir welding technology, the problems of poor weld formation quality, many internal defects in the joint, and low mechanical properties caused by the welding of metals and thermoplastic polymer materials have not been effectively solved.

[0004]In particular, in the process of Friction Stir Lap Welding (FSLW), which relies on material migration at the lap interface to form an effective connection, the cone The flow-promoting stirring head represented by the shape needle drives the surrounding materials to make axial and radial three-dimensional flow, resulting in overflow of thermoplastic polymer material and poor forming quality of weld surface

However, the window of process parameters in the connection of metal and thermoplastic polymer materials is narrow, and the speed of the stirring head has a direct impact on heat input and material flow, and has a greater impact on joint formation

Excessively high speed can easily cause excessive heat input, resulting in the following problems: due to the poor compatibility of the two materials and the large difference in melting point, the viscoelastic polymer material overflows the surface of the weld when heated, affecting the forming of the joint; due to the thermal expansion of the material With different coefficients, hole defects are prone to appear in the joint; the material "pull-off separation" defect caused by the large stress in the interface will further deteriorate the mechanical properties of the joint

However, this technical solution is only applicable to the overlapping form of the polymer material on the top and the metal material on the bottom, and the problem of hole defects caused by the low thermal conductivity of the polymer is improved by the auxiliary heat of the polymer.

However, for the overlapping form of the metal on top and the polymer on the bottom, static shoulder heating will not improve the problem of large temperature gradients on the polymer side, but will also bring Due to the softening of the metal, it is impossible to seal the overflow of the polymer material of the lower plate, which exacerbates the current situation of difficulty in joint forming and low mechanical properties

Therefore, this solution is no longer suitable for lap joints with metal on top and polymer material on the bottom

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