Cold forming is a forming technique commonly used in machine and plant engineering. The process is automated on special forming presses. These presses often interwork with other machines.
What is cold forming?
Cold forming in accordance with DIN 8580 solidifies metals at temperatures well below the recrystallization temperature. They are made more resilient by means of large forming forces (compressive forces, tensile forces). The unintended deformation of metal parts is called cold deformation. It occurs in impact accidents on vehicles or in industrial production if the parameters are incorrect. The industry uses cold forming to increase the strength of metallic materials and to achieve good surface properties and low dimensional tolerances. Cold forming serves the purpose of changing the properties of the raw material but not its shape. The machines used for cold forming are presses with a high component throughput. They process 150 to 300 pieces per minute.
As the deformation most often cannot be achieved by a single procedure, several procedures are applied in a row. Cold forming of wire, for example, is carried out on horizontal presses. The fed copper wire is first cut to the correct length and then formed by several punches and shaping dies. Depending on the application, work hardening is distinguished between sheet metal and cold massive forming. Sheet metal forming processes include deep drawing, cold rolling, bending, edging and spinning. Cold massive forming includes, among others, cold drawing, cold forging, cold swaging and cold extrusion.
Cold forming is suitable for all fields of application where harder metals and higher yield strengths are required: mechanical, plant, and apparatus engineering, automotive engineering and electrical engineering. All non-brittle metals and alloys that are unsuitable for hot forming can be used for cold forming. Whether cold forming is performed at room temperature or after a slight warm-up depends on the recrystallization temperature of the respective metal. Warm forming and hot forming differ from the work hardening in that these forming techniques use temperatures above the recrystallization temperature. Cold forming can be reversed by recrystallization annealing.
How do the materials behave during cold forming?
During cold forming, the crystal lattice changes. The dislocation density increases as a result of motion. The dislocations rub against each other and interfere with each other. Therefore, work hardening is often followed by a heat treatment. The industrial user must apply higher compressive stresses to increase the hardness and yield strength. The use of cold forming reduces the ductility, initial permeability and electrical conductivity of the workpiece. Cold forming can also increase the magnetizability. A side effect of the increased dislocation density is an increase in the energy stored in the crystal lattice. If the cold deformation is carried out longer than required for the solidification, the metal will crack. The characteristic feature of sheet metal forming is that the material thickness remains largely the same. Massive cold forming, on the other hand, causes large cross-section changes.
What are the advantages and disadvantages of cold forming?
The key benefits are:
- tighter dimensional tolerances and thus more precise processing
- the fiber course is not interrupted
- permanent hardening of the material
- better material utilization compared to machining processes
- suitable for large batch sizes
- short processing times
- good surface quality
- energy-efficient production
- further processing in form of hardening is usually not necessary
- higher workpiece load capacity
A major disadvantage is that a quite high mechanical effort is required. A tensile test shows when the component breaks.
Quality assurance through optical measurement technology
Work hardening can cause defects such as wrinkles, duplication, material thinning and cracking. They are often discovered only at the finished part. Modern methods such as high-frequency pulse measurement check the forming tools and parts after production. In addition, the entire cold forming process can be monitored with their help. Cracks in components caused by changes in parameters lead to increased amplitudes in the image. Automated 3D optical measuring systems ensure consistently high quality. This also makes it easy to determine sheet metal properties and check initial samples. For more information on quality control in sheet metal forming, go to: www.gom.com/knowledge-day.