Precision Forging Machine Hammer Head Machining and Surfacing Process Research

Literature Overview and Industrial Context

This paper by Xin Zhijie, Cao Minman, and Liu Fang from North University of China, published in Forging and Stamping Technology in 2013, addresses the manufacturing and repair challenges associated with hammer heads used in precision forging machines. Precision forging hammers are critical equipment in the production of high-quality forged components such as automotive axles, aerospace structural parts, and industrial tooling. The hammer head is the most heavily loaded and wear-prone component of the forging machine, subjected to repeated impact loading, high temperatures, and abrasive contact with die surfaces. The researchers investigated both the initial machining process for manufacturing hammer heads and the surfacing process for repairing worn hammer heads, with the goal of reducing dependence on imported hammer heads and extending service life through repair.

Hammer Head Machining Process Design

The machining process for the hammer head was designed to minimize material waste, ensure dimensional accuracy, and optimize material flow. The key steps include rough machining, semi-finishing, and finishing operations, with careful consideration of the forging sequence, heat treatment schedule, and final machining allowances. The researchers developed a rational forging and machining process that effectively reduces the cost associated with imported hammer heads. The process design incorporates principles of cost-effective manufacturing, including the selection of appropriate forging methods, heat treatment cycles, and machining strategies.

Process Step	Description	Key Parameters
Material selection	High-strength alloy steel	Appropriate grade for impact and fatigue resistance
Forging	Multi-stage forging to achieve near-net shape	Temperature control, reduction ratio
Heat treatment	Quenching and tempering for strength and toughness	Quenching medium, tempering temperature
Rough machining	Removal of excess material	Cutting speed, feed rate
Semi-finishing	Dimensional refinement	Tolerance control
Finishing	Final surface preparation for surfacing	Surface roughness, cleanliness
Surfacing	Wear-resistant overlay deposition	Welding parameters, filler material

Surfacing Process for Hammer Head Repair

The surfacing process for repairing worn hammer heads involves the deposition of a wear-resistant alloy layer on the worn surfaces. The researchers developed a surfacing process that can restore the hammer head to serviceable condition after wear. The surfacing material is selected to provide adequate hardness and wear resistance while maintaining sufficient toughness to withstand impact loading. The welding process parameters are optimized to ensure good fusion, low dilution, and minimal residual stress. The repaired hammer head is then subjected to a post-weld heat treatment to relieve residual stresses and stabilize the microstructure.

The experimental validation of the combined machining and surfacing process demonstrated that hammer heads manufactured and repaired according to this process were capable of forging approximately 2000 axles over a 13-day production period. After this service, the hammer head surface exhibited only fine cracks with no significant cracking or wear damage. This performance meets the production requirements for the specific application.

Quality Assessment and Defect Analysis

The quality of the surfacing layer is assessed through multiple criteria:

Assessment Criterion	Acceptance Criteria	Testing Method
Hardness	Meets specified range for wear resistance	Vickers or Rockwell hardness test
Surface integrity	No cracks, porosity, or lack of fusion	Visual inspection, MT, PT
Bond strength	Adequate adhesion to base metal	Microtensile or bend test
Wear resistance	Sufficient service life for target application	In-service performance monitoring
Residual stress	Within acceptable limits	X-ray diffraction or strain gauge method

The fine cracks observed after 13 days of service are a concern that requires attention. These cracks likely originate from thermal stress during the surfacing process or from cyclic thermal and mechanical loading during forging. While they do not represent immediate failure, they indicate a potential degradation mechanism that could lead to progressive crack growth and eventual failure if not monitored. Engineers should consider implementing a crack monitoring program for repaired hammer heads and establishing replacement intervals based on service history.

Study Insights and Reflections

This research is practically oriented and addresses a real industrial need: the reduction of dependence on expensive imported hammer heads and the extension of hammer head service life through effective repair. The combined approach of optimized machining and surfacing repair is a cost-effective strategy that aligns with the principles of sustainable manufacturing and resource conservation. For engineers involved in forging equipment maintenance, this literature provides a concrete example of how surfacing technology can be applied to restore worn components to functional condition. The key lesson is that surfacing repair is not merely a surface treatment but a comprehensive process that requires careful consideration of the base material condition, welding parameters, post-weld treatment, and service life prediction. The observation of fine cracks after extended service highlights the importance of long-term durability assessment and the need for periodic inspection and maintenance of repaired components. Future work should focus on developing more durable surfacing materials that can withstand extended service without crack initiation, and on establishing predictive maintenance models based on service data.