Plasma welding application prospects while airplanes of mig brand production as one of the methods to reduce welding deformations

Machine-building Engineering and Machine Science

Mechanical Engineering Technology


Аuthors

Pigalova E. A.*, Abramova A. A.**, Kurnikov N. A.***

NAZ “Sokol” - a branch of RAC “MiG”, 1, Chaadaeva str., Nizhny Novgorod, 603950, Russia

*e-mail: ekaterina-pigalova@yandex.ru, e.pigalova@rsk-mig.ru
**e-mail: annakosva@mail.ru
***e-mail: nick.kurnikov@yandex.ru, n.kurnikov@rsk-mig.ru

Abstract

Welding is a complex technological process followed by occurrence of internal residual tensions and deformations of a welded structure.

While producing aircraft It is essential to reduce residual tensions and deformations, since:

– the structure's deformations affect an aircraft external aerodynamic contour reducing its aerodynamic characteristics;

– residual tensions sum up with tensions from external loads on the structure, leading to its destruction;

– residual tensions form volumetric stressed state in separate metal volumes, which complicate plastic deformation of a metal and contributes to its transition to brittle state, leading to local destruction of a structure.

This work is devoted to experimental research on automatic plasma welding application instead of argon-arc welding as one the methods for welding deformations reduction while aircraft structures fabrication.

Plasma welding is the welding performed by directed flow of plasma arc. The plasma arc is characterized by the high temperature (up to 30,000°C), and a wide range of its processing properties. It has much in common with argon-arc welding technology.

The main features that distinguish the plasma arc from the conventional one are:

  • a higher temperature;

  • a smaller arc diameter;

  • cylindrical arc shape (unlike the usual conical shape);

  • the arc pressure on a metal is 6-10 times higher conventional one;

  • the ability to hold the arc at low currents (0.2-30 A).

Conclusion: the plasma arc is more concentrated, powerful and universal source of heating in compared to the conventional one.

The conducted pilot studies consist in comparing parameters of the samples welded by both automatic argon-arc and automatic plasma welding. Based on the performed work, the following conclusions were drawn:

  • the sizes of the weld seam (the width of heat-affected area, the weld seam width, the samples bending angles) made by automatic argon-arc welding exceeded about 1.16 times the sizes of the weld seam made by automatic plasma welding;

  • the width of heat-affected area obtained while automatic argon-arc welding exceeded about 1.2 times the one obtained while automatic plasma welding;

  • the bending angles of the samples with automatic plasma welding are 2-3 times less than with argon-arc welding.

Based on the above said studies at NAZ “Sokol” the decision was made to implement automatic plasma welding. A new installation for sheets butt-joint automatic argon-arc and plasma welding was developed.

The installation consists of:

  • bedplate;

  • beams with clamping push buttons and mechanism for converging these beams;

  • carriages with plasma gun for automatic plasma welding and a burner for automatic argon-arc welding;

  • a mechanism for carriage move along three coordinates: along and transversely to the weld seam axis, as well as up/down;

  • supporting devices for sheet billets.

The interface of control panel software is intuitive and provides the following functionality:

  1. User identification.

  2. Identification of the installation readiness for welding.

  3. Welding programs database (DB) creating and editing.

  4. The ability of welding the parts of various thickness.

  5. Selection the already worked-out and saved welding programs.

  6. Control of welding parameters.

  7. Logging of the welding process.

The effect of implementing the plasma welding instead argon-arc:

1) Higher labor productivity in view of the higher welding speed (by 3-5 times).

2) Time consumption reduction for products leveling after welding (by 50-70%) due to minimal residual deformations in the weld seam due to more concentrated heating source.

3) Time consumption reduction for welding modes testing (by 50-70%) due to the the stored base of welding programs.

Keywords:

automatic plasma welding, automatic argon-arc welding, residual stresses and deformations, control system of the installation

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