Application of Submerged Arc Surfacing Technology in Hydraulic Cylinder Manufacturing

Overview and Background

The paper by Liu Tiejun and colleagues from Sany Heavy Equipment Co., Ltd., published in Coal Mine Machinery in 2012, presents a novel manufacturing approach for hydraulic cylinder piston rods using submerged arc surfacing (SAS) technology. Hydraulic cylinders are critical components in hydraulic supports used in underground coal mining operations, where they must withstand extreme cyclic loading, abrasive environments, and high-pressure hydraulic fluid. The traditional manufacturing route for piston rods involves machining large-diameter solid steel blanks, which results in significant material waste and high machining costs, particularly for large-diameter cylinders common in mining applications.

The authors propose an alternative strategy: starting with a smaller-diameter base rod and building up the required dimensions through controlled SAS deposition. This approach fundamentally changes the manufacturing philosophy from subtractive to additive material processing. The study demonstrates that SAS not only improves material utilization but also significantly reduces the subsequent machining allowance, offering a viable and economically attractive process alternative for large-diameter hydraulic cylinder production.

Technical Process Description

The submerged arc surfacing process described in this paper follows a systematic methodology suitable for production environments. The base rod is typically made from a medium-carbon or low-alloy steel that provides adequate strength and weldability for the underlying structure. The surfacing layers are deposited using a consumable electrode wire with a flux cover, which provides both the arc shielding and a source of alloying elements to tailor the surface properties.

The process involves multiple passes of surfacing to build up the required diameter incrementally. Each pass is carefully planned to ensure uniform coverage and to avoid excessive heat accumulation. The flux acts as both a protective barrier against atmospheric contamination and as a source of alloying elements such as manganese, silicon, and carbon, which can be adjusted to achieve desired surface hardness and wear resistance.

Material Utilization and Economic Analysis

One of the most compelling aspects of this study is the economic argument for adopting SAS in hydraulic cylinder manufacturing. Traditional machining from solid bar stock for a large-diameter piston rod (e.g., 200 mm or more) can result in material utilization rates as low as 30-40 percent, with the remainder removed as chip waste during turning operations. By contrast, the SAS approach starts with a smaller base diameter and deposits only the material needed for the functional surface layer, potentially improving material utilization to 60-75 percent.

The reduction in machining allowance is equally significant. When a piston rod is machined entirely from solid stock, the final grinding and polishing operations must remove substantial material to achieve the required surface finish and dimensional accuracy. With SAS-built-up rods, the surfacing pass itself produces a relatively smooth and uniform surface that requires less subsequent machining. This translates directly into reduced machine time, lower tool wear, and decreased energy consumption in the finishing operations.

Quality Considerations and Defect Prevention

Submerged arc surfacing, while advantageous in terms of material efficiency, introduces specific quality challenges that must be addressed. The primary concerns include porosity from flux contamination, undercut at the bead edges, incomplete fusion between layers, and potential cracking due to hydrogen embrittlement or high cooling rates. The authors emphasize the importance of maintaining proper flux drying procedures and ensuring adequate gas shielding during the early stages of arc ignition.

Residual stress from the multi-pass surfacing is another critical factor. Each deposited layer experiences rapid cooling and contraction, creating tensile residual stresses in the newly deposited metal and compressive stresses in previously deposited layers. For piston rods subjected to cyclic bending and axial loading, these residual stresses can reduce fatigue life if not properly managed. Post-weld stress relief annealing or controlled cooling rates can mitigate this issue.

Engineering Practice Insights

From a practical standpoint, the SAS approach for hydraulic cylinder manufacturing aligns well with modern lean manufacturing principles. It reduces raw material inventory requirements, decreases machining cycle times, and generates less scrap waste. However, the process requires careful qualification and ongoing process monitoring. Weld operators must be trained in SAS-specific techniques, and flux handling procedures must be rigorously enforced to prevent moisture-induced defects.

The integration of SAS into hydraulic cylinder production also opens the door to hybrid material strategies. Different surfacing layers can be deposited with varying alloy compositions to create gradient properties — for example, a harder, more wear-resistant outer layer over a tougher, more ductile inner layer. This capability is particularly valuable for piston rods operating in abrasive mining environments where surface durability is paramount.

Key Reflections and Implications

This study represents an early but significant contribution to the application of additive manufacturing concepts in heavy equipment production. The fundamental insight — that building up material through controlled deposition can be more efficient than removing material through machining — has since been validated and expanded by numerous subsequent studies. The SAS technology described here is a mature, well-understood process that can be implemented with relatively modest capital investment compared to more advanced additive manufacturing systems.

The study's emphasis on material utilization and machining reduction speaks to a broader manufacturing philosophy: optimizing the entire process chain rather than optimizing individual operations in isolation. For engineers evaluating manufacturing routes for large-diameter cylindrical components, the SAS approach warrants serious consideration, particularly when material costs and machining capacity are limiting factors. The key to successful implementation lies in thorough process qualification, rigorous quality control, and a clear understanding of the metallurgical consequences of multi-pass surfacing on the final component performance.