The commonly used welding processes in the wire harness industry include diffusion welding (too high cost), high-frequency welding (high welding temperature), cold pressure welding (high pressure required) and ultrasonic welding. However, due to the limitations of the first three welding methods, they can not be used on a large scale. Only ultrasonic welding has become the mainstream welding method in the wire harness industry because of its unique simplicity and economy.
Ultrasonic welding uses high-frequency vibration waves to transfer to the surfaces of two wire harness workpieces to be welded. Under pressure, the surfaces of the two wire harness workpieces rub against each other to form the fusion between molecular layers. It has the advantages of fast, energy saving, high fusion strength, good conductivity, no spark and close to cold processing; The disadvantages are that the welded metal parts cannot be too thick (generally less than or equal to 5mm), the welding spot cannot be too large, and pressure is required. The following are two forms of ultrasonic welding, bilateral welding and unilateral welding.
Unilateral welding
Ultrasonic welding in the wire harness industry is divided into the following three welding processes according to the location of ultrasonic wave: pre assembly welding, line edge welding and on-line welding; Next, we will introduce the advantages and disadvantages of these three welding processes:
The first is pre assembly welding. As the name suggests, it is a process of welding wires in the pre assembly area. Its feature is that the original line is directly sent to the pre assembly area for ultrasonic crimping after opening. The advantage is that the transportation distance of the original line is close. At the same time, because it is in the pre assembly area, it corresponds to all items in the general assembly area, so centralized production and mass production can be realized; With sufficient materials and inventory, uninterrupted production can greatly improve the utilization rate of equipment; However, there are also great disadvantages. The disadvantage is that in the pre assembly area, the demand information for final assembly is seriously delayed, resulting in the need to adopt the production mode dominated by plan. In this way, there will be a large number of WIP materials placed in the material temporary storage area. Once there are order fluctuations or process parameter errors, a large number of crimping Kanban will be scrapped.
The second type, line side crimping, means line side crimping on the final assembly line. The difference between it and pre crimping is that the crimping equipment is moved from the pre assembly area to the final assembly area. The production mode is also changed from planned production mode (push type) to pull type production mode. The change of production mode leads to a large reduction of WIP between stations. However, due to the reduction of WIP Kanban, it must be in the design of production line, Reserve a certain lead time for the ultrasonic station to prepare materials, otherwise there will be the risk of delayed material supply and sluggish shutdown.
Production process: the final assembly production line produces according to the production order. In the process of production, the demand for crimping Kanban is generated on the assembly line. At this time, the pull Kanban is transmitted to the sonic production area. The production personnel give the demand for wire pulling Kanban according to the pull Kanban information, take the single line Kanban from the wire temporary storage area, and then send the single line Kanban to the final assembly ultrasonic crimping area. The single line becomes a crimping Kanban after ultrasonic crimping, The crimped Kanban is then sent to the required position on the final assembly line. The third is online welding. Online welding is divided into kit station online welding and assembly station online welding. No matter which station is welded, its production mode is driven by the demand of the production line to achieve zero inventory. However, the biggest disadvantage of this production mode is that the utilization rate of equipment is relatively low (as shown in the figure below, the man-machine analysis of ultrasonic station), and the utilization rate of equipment cannot reach 100%, As shown in the following example, according to the man-machine analysis of the station, the equipment utilization rate of online sonic is only 54%.
Man machine analysis of ultrasonic station
Nevertheless, we still use ultrasonic crimping in the actual production process. It is generally used in the body line, instrument line, front cabin line and other large lines. Because of its many circuits, it is easy to have stranded wires. Now ultrasonic can solve this problem well.
Therefore, in the actual production process, we will choose the ultrasonic process according to different situations. For the harness with many circuits (body wire, instrument wire and front cabin wire), we usually use online ultrasonic crimping; For medium wire harness (door line, seat line) or small wire (ceiling line, middle air line), we usually use line edge ultrasonic crimping; When the output of the project is relatively low, the ultrasonic Kanban of multiple projects can be integrated and crimped on the same equipment, and the pre installed ultrasonic crimping can be selected.
