Cold Pressure Welding

Cold pressure welding is the establishment of an atom-to-atom bond between the two pieces to be joined through intimate contact between oxide-free areas achieved under pressure and without the formation of a liquid phase. So as to develop this bond, surface films have to be removed or at least reduced in amount. Surface films fall into two categories: - Oxide film: All metals except gold possess an oxide film at room temperature. In most metals, the oxide film reaches a limiting thickness in the range 20-100 angstroms at room temperature. - Contaminant film: This film consists of a thin layer of moisture and greases. The best technique, which has proved to be successful in reducing these films, is a combination of chemical and mechanical cleaning. Then, the welding method contains two stages. The process of welding consists of the formation of overlapped oxide-free metallic areas; this is controlled by:

(a) the difference on a micro-scale of the local plastic strain occurring on matching opposite faces of the weld interface

(b) relative hardness of the metal and its oxide film, and

(c) mechanical properties of the oxide.

The second stage involves: 

(a) plastic flow of the metal to the over-lapped areas; the stress at which this can take place is influenced by the stacking fault energy of the metal

(b) some relative shear displacement at the points where metal cleaned of oxide comes into contact; this is influenced by surface roughness Cold pressure welding is used for joining of aluminium cables, various kitchen furniture, electrolysis cells, communication lines, for joining wires and rods, production of heat exchangers at coolers and application of joining different materials nowadays. Various researchers carried some of the studies about cold pressure welding out: gave knowledge about investigations on pressure welding and cold pressure welding. [3] Investigated the mechanism of solid-state pressure welding. Examined the bonding mechanism of cold pressure welding. [5] Investigated cold pressure welding of aluminium and copper by butt upsetting. [6] Investigated effects on welding strength of process parameters in cold pressure welding of aluminium. [7] Obtained the surface roughness depending on welding strength in cold pressure welding of aluminium. [8] Directed the process parameters optimization for obtaining high weld strength in cold solid-state joining of sintered steel and copper powder metallurgical performs. The knowledge about the cold pressure welding method and the developments in its applications were given in this study. Then, as for example, cold pressure welding was applied on commercial purity aluminium alloy sheets as lap welding. 150 metric ton hydraulic press was used for the welding process. Before welding, the wire-brushing process was applied for preparing aluminium sheets, which are test parts, the roughness was determined with surface roughness equipment and afterwards, deformation was applied at different deformation ratios. Then, the microstructure of the welded parts at a given welding deformation was examined, and it was researched that whether joints were properly obtained or not. Then, the results were commented.