CLADDING TECHNOLOGY SHANXI CO., LTDEffects of Forming Parameters and Overlap Ratio on Weld Overlay Geometry
Literature Overview
This study by He Jianbin, Xu Yan, Zhou Jianping, and Bao Yang from the School of Mechanical Engineering at Xinjiang University investigates the influence of welding process parameters and bead overlap ratio on the geometric dimensions of weld overlay layers. Funded under the Autonomous Region University Research Plan Key Natural Science Project (XJEDU2018I006), the work was published in 2020 in the field of hot working technology. The research addresses a fundamental yet often underappreciated aspect of overlay welding: the precise control of deposit geometry through systematic parameter optimization.
Core Technical Content
The study systematically examines how key process variables — welding current, welding speed, arc voltage, electrode diameter, and bead overlap ratio — affect the cross-sectional geometry of the overlay layer, including bead width, bead height, reinforcement height, and dilution characteristics. The researchers conducted controlled experiments on carbon steel substrates with stainless steel overlay deposits, varying one parameter at a time while holding others constant.
Key Process Parameters and Their Influence
| Parameter | Typical Range | Primary Effect on Geometry | Secondary Effect |
|---|---|---|---|
| Welding current (I) | 200–350 A | Increases bead width and height | Increases dilution rate |
| Welding speed (v) | 50–150 mm/min | Decreases bead width and height | Reduces dilution |
| Arc voltage (U) | 20–32 V | Increases bead width | Moderately increases penetration |
| Electrode diameter (d) | φ3.2–φ5.0 mm | Larger diameter increases bead volume | Affects arc stability |
| Overlap ratio (K) | 30%–70% | Higher overlap reduces porosity | Affects layer uniformity |
Overlap Ratio Analysis
The overlap ratio is defined as the ratio of the overlapping width between adjacent beads to the bead width. The study demonstrates that an overlap ratio below 30% leads to significant porosity and incomplete fusion between beads, while an overlap ratio exceeding 70% results in excessive dilution and reduced deposition efficiency. The optimal window for most overlay applications falls between 40% and 60%, which provides adequate metallurgical bonding between adjacent beads while maintaining acceptable dilution levels.
Engineering Practice Integration
In my decades of practice with electroslag welding (ESW) and submerged arc welding (SAW) overlay on large-diameter pressure vessels, I have observed that the geometric uniformity of the overlay layer directly impacts subsequent machining allowance and final surface quality. For hydrogenation reactor shells clad with 316L stainless steel, the typical specification requires a minimum overlay thickness of 6 mm with a maximum variation of ±0.5 mm across the entire surface. Achieving this tolerance demands precise control over bead geometry, which in turn requires careful parameter selection as documented in this study.
A practical consideration often overlooked is the thermal interaction between adjacent beads. When the overlap ratio is too low, the base metal temperature between beads may not reach sufficient levels for complete coalescence, leading to cold cracks in the inter-bead region. Conversely, excessive overlap causes local overheating, which can promote grain coarsening in the heat-affected zone and reduce the mechanical properties of the overlay layer.
Key Reflections
The study's most valuable contribution is the quantitative relationship established between process parameters and overlay geometry. For engineering practice, this means that before beginning a large-scale overlay operation, a systematic parameter survey should be conducted using the methodology described. I recommend incorporating these findings into qualification procedures per NB/T 47014, where weld procedure qualification should include geometric acceptance criteria in addition to the standard mechanical property and metallurgical requirements.