At present, the electrical contact tips are generally made of silver alloy plate through the roll mill rolled into a very thin strip, and the strips are then punched into small electrical contact tips according to the required shape by a punch press. Due to the poor wettability between the silver metal oxide material and solder as well as the copper alloy contact bridge, it is necessary to compound a layer of pure silver on the welding surface as a transition layer in the process of contact processing to improve the welding strength and welding area between the contact and the contact bridge.
There are currently four silver cladding processes that have been mass-produced in the industry: powder hot-pressed silver cladding, hot-rolled silver cladding, extrusion silver cladding, and cold heading silver cladding. The silver layer fluctuation range that these processes can usually achieve is about 5% to 20% of the contact thickness. In addition, the advantages and disadvantages of the above four processes are as follows:
1. Powder hot-pressed silver cladding,
① The contact area between the working layer and the silver layer is large, and the bonding strength is excellent;
② High material utilization rate and low manufacturing cost.
① Narrow scope of application, only suitable for powder metallurgy process materials;
② The thickness of the silver layer is thick, and the distribution of the silver layer is uneven, resulting in high material cost;
③ During the processing, it is easy for the working layer powder and the silver layer to be doped with each other.
2. Hot-rolled silver cladding/ extrusion silver cladding
① The process is a thermal diffusion composite with high composite strength;
② The thickness distribution of the composite silver layer is relatively uniform and the thickness is controllable;
③ It can be used to prepare contact tips of most specifications.
① The interface cleanliness before cladding is very high, and local impurities and foreign matter on the surface of the composite material have a serious impact on the composite strength;
② Circular contacts, special-shaped contacts and some square contacts can only be processed by stamping and blanking after the strip is silver-cladded, which results in low material utilization and high manufacturing costs;
③ Using the stamping processing method, the flatness of the welding surface is poor, which affects the welding quality.
3. Cold heading silver cladding
① High material utilization rate and low manufacturing cost;
② The cladding process belongs to the cold pressure welding forming of the fracture position of the wire material segment, and there are few factors that affect the composite strength;
③ The welding surface has good flatness, which is conducive to welding.
① The process is cold composite, and the composite strength is low;
② Sufficiently thick silver layer thickness must be required to complete cold heading; poor uniformity of silver layer distribution; high silver content in contacts of the same material and specification;
③ Compared with the contact tips processed by the thermal cladding process, the silver layer is thicker and the thickness of the working layer is relatively thinner, which theoretically decreases the electrical life of the contact material to a certain extent;
④ There are certain limitations on the specifications that can be processed, and not all specifications can use this production process. It is only suitable for producing contacts with circular or square rounded corners, and contacts that are too thin cannot be produced;
⑤ The plasticity requirements of materials are high, and materials with poor plasticity are prone to cracks during the cold heading forming process.
——The content of the article comes from the Internet