Cold Pressure Welding Research Articles

Bond criterion in cold pressure welding of aluminium

Bond criterion in cold pressure welding of aluminium

Bond criterion in cold pressure welding of aluminium

An experimental apparatus to examine a bond criterion is developed. Using this apparatus, it is possible to carry out lap welding using punches that penetrate into strips of the experimental metal; these strips are simultaneously extended in the direction parallel to the bonding surface by bulging. The bond strength is investigated by varying independently the virgin surface ratio α and the normal bonding pressure p. The bond efficiency η, i.e. the ratio of the bond strength to the strength of the base metal, increases with values of α and p. However, when p has a value of 75 MN m−2 the value of η is always 0% at any value of α. It is possible to commence bonding when p=112 MN m−2, a value that is nearly equal to the flow stress of the base metal Y, i.e. p/Y ≍ 1. When p > 225 MN m−2, i.e. p/Y ≥ 2, the value of η does not depend on p, but on α, i.e. bonding commences when α =20% and the value of η reaches 100% when α=55–60%. This means that it is possible to achieve efficient bonding when the value of p is about twice the flow stress of the base metal, i.e. p/Y ≥ 2.MST/889

鉄道における最近の接合技術 電車用架線の常温圧接

鉄道における最近の接合技術 電車用架線の常温圧接

Cold Pressure Welding of Aluminum and Copper by Butt Upsetting

Cold Pressure Welding of Aluminum and Copper by Butt Upsetting

Cold roll and indent vvelding of some metals

The cold pressure welding of copper, brass, aluminium, and stainless steel has been investigated using thin-layer metal sandwiches produced by roll bonding and plane-strain indent welding. Shear tests were carried out to assess the level of bonding and scanning electron microscopy used to examine peeled surfaces from bonded specimens. Welding was found to be initiated by the formation of transverse cracks in the surface layers of the mating surfaces. These cracks coincide on both surfaces and are widened during deformation allowing extrusion of the base material through the cracks until a weld is formed. Extension of the surfaces is necessary for welding and the dependence of threshold deformation on the welding geometry is associated with the different surface behaviour. No recrystallization at interfacial regions was observed.

Cold Pressure Welding of Aluminum and Copper by Butt Upsetting

突合せ冷間圧接を数段階に分けて行う多段圧接法を試み,その利点,すなわち圧接荷重および変形量の低減が示された。さらに接合面における新生面率および面圧を測定し,接合強度におよぼす影響を調べた。その結果,接合強度は新生面率に深い関係があることが示され,この関係から多段圧接の利点も説明された。また新生面率が高い場合には,接合面圧は一体材の引張強さより小さな値で接合が達成されることもわかった。

爆発圧接法によるステンレス鋼／アルミニウム系複合材料の作製と二，三の性質

Two kinds of aluminum base composites, wire-reinforced and multilayered with stainless-steel wire meshes and foils as the reinforcements have been fabricated by means of explosive welding. Explosive welding in a low vacuum with “middle” and “base” plate inserts was examined to solve such problems as poor-bonding and local fracture of the composite constituents. Good bonding was then attained without forming voids or cracks. Electron-probe micro-analysis also revealed no evidence of diffusion of the constitutive elements across the interface. The bonding mechanism of multilayered composites was the same as in the common explosive welding, whereas that of wire-reinforced composites could be attributed to cold pressure welding of the matrix metal extruded through the mesh apertures. The UTS values of the wirereinforced composites were slightly lower than those expected from the so-called rule of mixtures (ROM). Multilayered composites, on the other hand, showed reasonable UTS values compared with ROM predictions. These composites also showed high ductility.

Cold Pressure Welding—The Mechanisms Governing Bonding

Investigations of the bonding surface in scanning electron microscope after fracture confirm the mechanisms of bond formation in cold pressure welding to be: fracture of work-hardened surface layer, surface expansion increasing the area of virgin surface, extrusion of virgin material through cracks of the original surface layer, and establishment of real contact and bonding between virgin material. This implies that normal pressure as well as surface expansion are basic parameters governing the bond strength. Experimental investigations of pressure welding Al-Al under plane strain compression in a specially developed equipment allowing independent variation of normal pressure and surface expansion confirm this. Based upon a slip-line analysis of the extrusion through cracks of the surface layer and upon the establishment of real contact between virgin material, a theory for the bond strength as a function of surface expansion and normal pressure is developed. The theory is in good agreement with the experimental results.

Interfacial conditions and bond strength in cold pressure welding by rolling

AbstractA re-evaluation has been made of the mechanism of bonding in cold pressure welding by rolling. In the experimental work, composites of commercially pure aluminium have been rolled to deformations of up to 75% and two testing methods have been used to measure the ultimate shear strength of the formed welds. Metallographk observation has shown that below the threshold deformation the unwelded surfaces consist of the original scratch-brushed areas and regions of the underlying base metal which are revealed but cannot weld, owing to the presence of contaminants. A major feature of the bonding mechanism described in this paper is that such contaminated areas remain unwelded even at the higher rolling deformations so that the final weld strength is a function of(lie metallic area revealed after the threshold deformation. The area welded has been calculated from this proposition and the results compare well with the proportion of welded area measured from micrographs of the fracture surfaces. A general e...

Production of stainless steel wire-reinforced aluminium composite sheet by explosive compaction

Composite sheet material has been produced by explosively compacting stacks of alternately placed stainless steel wire meshes and aluminium foils. It was found that stacks could be satisfactorily bonded by using an aluminium driver plate which was prevented from bonding to the stack by interposing a polythene sheet. Stacks containing six or seven layers of mesh and having a wire volume fraction of up to 0.24 could be bonded when the driver plate kinetic energy exceeded 120 J cm−2. It is concluded that the bonding mechanism involves cold pressure welding of the matrix metal by extrusion through the mesh apertures, and the aperture size is a controlling factor in bonding. No evidence was found of strong bonding between the wires and the matrix. In the production of larger sizes of composite sheet, (300 mm×500 mm), blistering and tearing occurred due to the presence of excess air in the stack, a consequence of bowing of the foils by the springy and curved pieces of mesh. This difficulty was overcome by enclosing the stack in a polythene envelope, which was evacuated before detonation of the charge, so that the stack was compressed by atmospheric pressure. Tests have shown that tensile and fatigue properties of the composites compare favourably with other aluminium matrix composites and with high strength aluminium alloys.

Cold pressure welded copper-constantan thermocouples

Cold pressure welding has been used to produce a lap junction between 0.15 mm thick strips of copper and constantan which had been plated with 2 mu m of nickel. The junction thickness after welding was 0.10 mm, and after further cold rolling to 0.06 mm a thermocouple performance within the requirements of BS 1041 (1966) was obtained.

Compatibility of Gold Deposits for Connector Contacts

A forty way, two part, printed circuit board connector has been the test vehicle for the evaluation of wear of a number of gold deposits in similar and dissimilar combinations. The proprietary electrolytes, from four suppliers, consisted of four acid cyanide types (cobalt or nickel hardened) two noncyanide (sulphite) and two neutral cyanide organically hardened golds. Assessment of wear was made by scanning electron microscope examination of wear tracks and by changes in contact resistance when the connectors were subsequently exposed to a corrosive environment. The acid Cyanide deposits exhibited least wear, the sulphite types wore excessively by cold pressure welding to produce platelets of debris, and the neutral cyanide golds were of mixed extent of wear. A hypothesis involving a polymer lubrication mechanism is proposed to explain the Iow wear of the acid golds. Scanning electron micrographs support this pro- posal.

Bonded joints and non-destructive testing: Problems in methods for the control of quality of butt welds made by the friction, cold pressure and flash welding processes

Traditionally ndt of fusion welded joints for critical weldments is conducted during the final stages of fabrication on the basis of 100% inspection. The Author has long maintained (and it may be regarded by some as self-evident) that ndt serves industry better in circumstances where it can be used to monitor quality during production thus avoiding the production of expensive scrap.Unfortunately ndt methods, with few exceptions, cannot be considered particularly useful in either role when it comes to the control of quality of friction, pressure and flash welds. In this article an attempt is made to explain why this is so and why it is necessary to resort to sampling techniques and destructive tests to assess quality on the basis of circumstantial evidence. Recent trends have been towards the monitoring of process parameters in two of these processes and some measure of success has been achieved.

冷間圧接の研究(第1報)

A method enabling metals to be welded at room temperature, called cold pressure welding has recently been developed.This unique welding process without the use of heat or electricity, requiring only the simplest tools and permitting the use of unshilled operators, is evoked considerable interst thronghout industry.The writers' study herein introduced, aimed at the cold pressure butt-welding for aluminium used for electrical industry.The results of the experiment are summarized as follows :(1) For the pressure welding, a cleaning method of the surface to be joined is most important. According to our experiments, the motor-driven rotary wire scratch-brushing treatment is most suitable for this purpose.(2) The breaking strength of the butt-joint is depend upon the working degree of the specimens prepared for, that is, joint efficiency of cold pressure welding for annealed material is over 100%, but for cold drawn one is not so good. For example, the efficiency for 67% cold drawn specimen is about 97%.(3) The "Figure of Merit" used to classify weldability for aluminium to aluminium is about 30. This values are same order to A. B. Sowter's data obtained from lap welding, reported in the Materials and Methods, Nov., 1948.(4) The distance from sleeve end to the cleaned surface to be joined is affected on the breaking strength of the welded specimen for tension or torsion test. It was found that the longer distance is necessary to be obtained stable and complete welding and the suitable distance is about similer to the diameter of specimen.(5) Distribution of micro-hardness of cold butt welds is measured. In case of cold drawn meterials, the hardness value of the portion separated 2-3 mm from the weld interface is lower than the value of specimen itself. It is thought that the cause of this phenomena is related to the "Bauschinger Effect".

Tools for the Workshop

This new welding tool is intended for butt‐welding wires, particularly aluminium and copper, from 0·036 inches to 0·064 inches in diameter. It is a recent addition to the range of equipment made by the General Electric Co. Ltd., for cold pressure welding. With this technique, which was developed at the G.E.C. Research laboratories, aluminium and copper wires can be welded by pressure alone, no heat being required; the joints obtained have a mechanical strength and an electrical conductivity equivalent to those of the parent wire. Certain aluminium alloys such as Silmalee can also be welded in this way. The technique was developed by the G.E.C. as a convenient method of joining aluminium conductor which is now being used on an increasing scale. A second welding tool covers the welding of wires from 0·080 to 0·144 inches.

Cold pressure welding

Cold pressure welding

Adhesion of solids and the effect of surface films

Earlier experiments have shown that the friction between metals is due to the shearing of junctions formed by adhesion or welding at the points of intimate contact. This suggests that when the load is removed the junctions should remain and an appreciable normal force should be needed to separate the surfaces. Experiments show that with clean hard surfaces in dry air the adhesion is negligibly small. In moist air appreciable adhesion may be observed, and it is shown that this is due to the surface tension of a thin film of adsorbed water. The surface-tension forces due to thin films of liquid trapped between solid surfaces may be very large. Under certain conditions the viscosity of the liquid may also be important. The absence of adhesion between clean hard surfaces is not due to the non-formation of metallic junctions. Experiments show that it is due to the released elastic stresses which break the junctions one by one as the load is removed. With very soft metals, such as lead or indium, where the effect of released elastic stresses is very much less important, marked adhesion is observed in air, if the surfaces are freed of grosser contaminants. This adhesion provides direct evidence for the formation of metallic junctions by a process of cold welding or pressure welding at the points of Contact. If the surfaces are covered with oxide films of appreciable thickness, the amount of metallic interaction is diminished with a corresponding reduction in the adhesion. Lubricant films have a similar effect, and in general those materials which are most effective in reducing the adhesion are also most effective, as boundary lubricants, in reducing the friction.