Cold Pressure welding

Basel Raafat Radwan Saleh Selim Port Said University

Faculty of engineering

Baselr.saleh@gmail.com

Introduction

All metals are surrounded by surface layers (oxide) which must be disrupted if they are to be welded. Cold pressure welding, carried out at ambient(surrounding) temperature, relies upon the use of high compressive pressure 1400-2800N/mm2

for Aluminium and at least double that value for copper). This provides interfacial deformations of 60% to 80% that break the oxide layers to expose fresh, uncontaminated metal that makes contact. In this state, take over to interatomic forces produce

the weld.

Definition And History • Cold pressure welding is a form of solid phase

welding, which is unique because it is carried out at ambient temperatures. Other forms of solid phase welding are conducted at elevated temperatures

• As early as 3,000 BC, the Egyptians prepared iron by hammering a metal sponge in order to weld the red-hot particles together. Blacksmiths have also hammer welded wrought iron for centuries. This type of welding was always carried out at high temperatures.

• The first known example in Britain of hammer welding at ambient temperatures (therefore true cold pressure welding) dates back to the late Bronze Age, around 700 BC. The material used was gold, and gold boxes made by this process have been found during excavations.

:In Cold pressure welding

• Join metal together using no heat or flux • Pressure brings surfaces together , disrupts surface

films and allows chemical bonding of clean surfaces • Applicable to soft ductile metals , e.g. aluminium• Mainly used for welds in a circular wire section• Used for joining components where heating is not

possible: -Magnets -Butt welding of wires

 How are the two pieces of metal joined?• There have been several explanations as to the actual

mechanism by which a cold pressure weld is obtained (with no flux , heat or electricity). For example, it has been suggested that it happens via recrystallisation, but most explanations have been either experimentally disproved or refuted on theoretical grounds.

• The currently accepted accounts for a cold pressure weld taking place involves the atoms of metals being held together by the metallic 'bond’. The bond can be described as a 'cloud' of free, negatively charged atoms into a unit as a result of attractive forces

Joint types

Lap Joint Butt Joint

• Lap Joint :Where the application demands the joining of lapped sheets to themselves or bars, a series of small welds can be used. When calculating strength, the designer should consider that at least half the thickness of one of the sheets will be lost due to the applied pressure.

• Butt joints: Are primarily used for joining wires and rods in diameters from ~0.5mm up to 12mm

THE ROLE OF DIES

• The dies play an important role in the cold butt weld process. Firstly, they must grip the material firmly and, therefore, the inside of the cavity is either etched or made with an electric pencil

• The gap between the two faces, or noses, of the die is also extremely important. If it is too large, the material will just collapse or bend away. This dimension is taken care of during manufacture and cannot be changed.

• Dies can also be manufactured to suit various profiles, as long as the profile allows the die to be made in two halves.

Advantages

• As the process is performed at ambient temperature, there are no thermal effects on the parts being joined

• The process is fast• It is simple and inexpensive to operate once dies

have been produced.• The ends of the wire or rod need no preparation

to welding and the alignment of the two butt ends is automatic as the material is placed in the die

Disadvantages

• Highly specialized with respect to joint design and materials to be welded (soft iron that has no carbon content)

• welds are made in the 'solid state' they are difficult to inspect

• With the exception of butt welds, or welds where the contact surfaces are sheared together, the thickness of the parts is reduced.

Thank you Caution For scientific integrity …This Information was only combinated and collected by me and I’m not it’s author .