Surfacing Process for Blanking Die Manufacturing

Literature Overview

This 2006 paper by He Bolin and Yu Yingxia from East China Jiaotong University, published in Hot Working Technology (Vol. 35, No. 15, pp. 26-28), presents a systematic study of the surfacing process used to manufacture blanking dies for cold stamping operations. The work was supported by the Ministry of Machinery Industry Research Fund (95251214). The classification TG455 confirms the welding technology focus. The paper addresses a practical manufacturing challenge: producing high-hardness cutting edges on cold work dies through surfacing rather than traditional methods such as full die hardening or replacement of the entire die block.

Core Technical Content

The fundamental approach involves using 42CrMo steel as the die body substrate and depositing a high-hardness alloy layer on the cutting edge area through surfacing welding. This replaces the conventional manufacturing process where the entire die block is hardened, which is energy-intensive and can cause distortion. The surfacing approach allows the bulk of the die to retain its toughness while providing a hard, wear-resistant cutting edge.

The research systematically investigated the effects of welding process parameters on the microstructure, hardness, and wear resistance of the surfacing layer. The following parameter optimization results were obtained:

Parameter	Optimized Value	Effect on Overlay
Welding Current	180-220 A	Controls dilution rate and dilution of substrate into overlay
Arc Voltage	22-28 V	Influences penetration depth and bead geometry
Travel Speed	5-8 cm/min	Balances deposition rate with heat input
Number of Layers	2-3 passes	Builds required thickness, improves hardness uniformity
Post-Weld Treatment	580-620°C tempering	Achieves target hardness while maintaining toughness

The surfacing layer achieved an average hardness exceeding 57.5 HRC, which is well within the required range for cold blanking die applications. The metallographic examination confirmed the absence of porosity, cracks, and other welding defects in both the overlay metal and the transition zone. The weld bead geometry was uniform and well-formed, indicating good process control.

Process Analysis and Defect Prevention

The selection of 42CrMo as the substrate is notable. This low-alloy quenched and tempered steel offers good weldability, moderate hardenability, and excellent toughness, making it an ideal base material for cold work tool applications. The surfacing alloy must be carefully selected to provide the required cutting edge hardness while maintaining sufficient toughness to resist chipping and fracture during stamping operations.

The paper emphasizes several critical process control points. First, the substrate must be preheated to 200-300°C to reduce the risk of hydrogen-induced cracking in the transition zone. Second, the welding sequence must be planned to minimize distortion of the die geometry, which is critical for maintaining dimensional accuracy in the stamped parts. Third, the interpass temperature must be controlled to prevent excessive grain growth in the overlay and to maintain the desired microstructure.

Common defects in cold work die surfacing include:

Defect Type	Root Cause	Countermeasure
Cracking	Excessive residual stress, high carbon content	Preheating, controlled cooling, proper filler selection
Porosity	Gas absorption, contaminated filler	Clean filler, proper shielding, dry storage
Delamination	Poor wetting, thermal mismatch	Surface preparation, optimized heat input
Hardness variation	Inconsistent dilution rate	Parameter control, multi-layer approach

Field Application and Study Insights

The paper reports successful field application of the surfaced blanking dies, with the surfacing layer remaining intact during service and achieving a service life equal to or exceeding that of traditionally manufactured dies. This is a significant practical result, demonstrating that the surfacing approach is not merely a laboratory exercise but a viable manufacturing technology.

The broader implication is that surfacing welding offers a flexible and economical approach to tool and die manufacturing. Instead of producing an entire die block from expensive tool steel, a lower-cost structural steel substrate can be used with a hard alloy overlay applied only where needed. This approach also facilitates repair of worn dies by re-surfacing the cutting edges, extending the service life of die blocks and reducing overall manufacturing costs. The paper provides a valuable reference for engineers developing surfacing-based manufacturing processes for cold work tools and similar applications.