Welding Systems -
Capacitor Discharge Welding
As two parts are pressed together with high force, a high current pulse is released through the parts. The projection, critical to the parts weldability, heats to a plastic state and material from both work pieces mix resulting in a diffusion / forge-type bond of fine grain. Parent material strengths are typically achieved without the segregation and re-crystallization problems associated with fusion-type welding processes. The precise charging level provides precise ready-to-assemble parts at high production rates with no part distortion.
During the welding process the high speed pulse plasticizes the material and pushes it out of the weld zone where the material migrates together. The pulse ends and the merged material cools resulting in the diffusion or forge-type weld. A second pulse is used for most high carbon steels. This second pulse produces ultra-fine cementite precipitates from the rapidly cooled BCT Martensitic weld structure and effectively tempers the weld zone.
The Capacitor Discharge welding process (also known as High-Speed Pulse Welding) forms a diffusion or forge-type weld. Rapid metal bonding (approximately 10 ms) causes minimal part heating producing a weld without distortion, discoloration or normalization. Capacitor Discharge welding is similar to resistance welding (AC, spot welding).
Capacitor Discharge welding achieves the diffusion weld using a focused, high current pulse at low voltage. The energy for the pulse is derived from charged capacitors. A precision voltage level controlled to less than 1% variation isolates the welding supply from fluctuations in the power grid. No cover gases are required.
Advantages of CD Welding
- Large assortment of material combinations and Common Coated Materials can be joined
- Welds without distortion, discoloration, or annealing
- Mechanical tolerances are maintained and parts are assembly-ready without cleanup or finish machining
- Process is repeatable, controllable and selective (suspect welds are flagged)
- High production speeds
- Insensitive to oil or other part surface anomalies
- Short welding time localizes heat, allowing CD welds adjacent to heat sensitive parts
- Capacitor discharge welding energies available up to 120 kJ
- Fine crystalline microstructure forms at weld interface
Special Advantages for Powdered Metal Components:
- Significantly higher strength powdered metal joints are possible
- Insensitive to porosity (can weld densities of 6.5 g/cm3)
- Offers an alternative to sinter brazing (due to productivity or geometrical requirements, brazing is sometimes less desirable)
- Localized stress concentrations reduced due to a smoothed density gradient near the weld. Effective weld width is moved deeper into the parent material.
- Retained lubricants are not critical
- Avoids creation, segregation and mixing of unwanted alloys (e.g. copper infiltrated parts are weldable since copper is not drawn into weld)
- Higher carbon (0.8% C) parts can be welded without the detrimental effects of brittle weld structure
- Lower heat input eliminates part distortion
- Materials can be selected regardless of the weld process
- Dissimilar powdered metal materials can be welded to create special function assemblies
- Can create component designs not previously possible and often dismissed by powdered metal part designers