3.1
Preparation before welding
3.1.1
Bevel form and positioning welding
In selection When choosing the form and size of the groove, minimize the number of welding layers and the amount of filler metal to reduce the accumulation of welds and prevent the plasticity of the joint from decreasing
. When the welding thickness is less than
2.5mm
, there is no need to make a bevel and a butt joint is used, and no filling wire is required. When the thickness is large, a slope opening must be made, and flat welding is generally used.
Tack welding is one of the main measures to reduce welding deformation. Generally, the spacing between welding points is
100mm
～
150mm,
The length is about
10mm
～
15mm
.
The welding wire,
welding parameters and shielding gas conditions used for position welding are the same as those for formal welding.
When the arc is stopped at each positioning welding point,
The argon gas should be turned off with a delay.
3.1.2
Mechanical cleaning
For weldments that do not require high welding quality or are difficult to pickle, you can use emery cloth or stainless steel wire brush to wipe them, or Use a carbide scraper to scrape
- 3 -
the welded edge and scrape
0.025mm
to remove the oxide film. Then use solvents such as acetone, carbon tetrachloride or methanol to remove fingerprints, organic matter and oil stains on the surface of the welding wire on both sides of the groove.
3.1.3
Chemical cleaning
If the titanium plate has been pickled after hot rolling and a new oxide film is formed during storage, the mass fraction can be The mass fraction of
HF
is
2
～
4
30
～
40
HNO
3
Soak in H
2
O
solution
15min
～
20min
Then rinse with clean water and dry.
Titanium plates that have not been pickled after hot rolling have thicker oxide films and should be washed with alkali first, rinsed and then pickled, and then separated with hot and cold water. Rinse and finally wipe dry with a white cloth.
3.2
Selection of welding methods
The welding methods that can be used for titanium and titanium alloys include tungsten arc welding, melting arc welding and vacuum electrons Beam welding, resistance spot welding, brazing, diffusion welding, laser welding and other welding methods can also be used. Only the welding process of tungsten arc welding is studied here.
Welding using DC reverse connection method
TA1
When using pure titanium, although there is "cathode broken
"
Function
,
However, due to the small current required, productivity is limited.
The allowable current of AC tungsten arc welding is between the direct current connection and the reverse connection.
At the same time, there is another half cycle when the workpiece is the cathode
"
Cathode fragmentation
"
Function
,
Comprehensive
It has the advantages of DC forward and reverse connection, so using AC tungsten arc welding
TA1
industrial pure titanium can achieve more ideal results.
3.3
Selection of welding materials
Titanium and titanium alloys are not sensitive to welding hot cracks,
welding
TA1
You can choose a filler metal with the same composition as the base metal,
The welding wire is supplied in a vacuum annealed
state,
The surface shall not have defects such as burnt skin,
cracks,
oxidation color,
metallic or non-metallic inclusions, etc.
The commonly used welding wire diameter is
φ
0.8
～
φ
4mm