Processing and Application of Overlay Welded Dies in Automotive Body Manufacturing

Literature Overview

This paper by Feng Guixin from the Fourth Design and Research Institute of the Ministry of Machinery Industry, published in Forging & Stamping Technology (Vol. 20, No. 1, 1995, pp. 56–57), discusses the design, manufacturing, and application of overlay welded dies for automotive body stamping, particularly for sedan body panels. The work addresses the challenge of high-cost die manufacturing for small-to-medium automotive manufacturers in China during the 1990s.

Core Technical Context

Automotive body stamping dies are among the most complex and expensive tooling components in manufacturing. High-quality dies require:

Precision machining of complex surfaces (3D contours, deep draws)
Hardened tool steel with high wear resistance
Excellent dimensional accuracy (±0.1 mm tolerance)
Long service life (50,000–100,000+ strikes)

Traditional die manufacturing requires expensive equipment such as:

CNC milling machines (3–5 axis)
EDM (electrical discharge machining)
Coordinate measuring machines (CMM)
Surface grinding machines

Many small-to-medium automotive manufacturers lacked access to this equipment, leading them to use simplified dies or low-melting-point alloy dies with limited life and poor surface quality.

Overlay Welded Die Concept

The overlay welded die approach combines:

A simple base die made from low-cost steel with basic machining
A high-alloy overlay weld layer providing the functional surface
Post-weld machining to achieve final dimensional accuracy

This approach reduces the requirement for expensive precision machining equipment while maintaining acceptable die performance.

Die Design and Manufacturing Process

Base Die Material

Component	Material	Heat Treatment	Hardness
Die block	45 steel / 40Cr	Quench and temper	28–32 HRC
Die shoe	Q235 / 20 steel	Normalized	15–20 HRC
Frame	Q235	None	< 20 HRC

Overlay Weld Layer

Parameter	Specification
Overlay material	High-carbon, high-chromium alloy (Cr12MoV type)
Welding process	SMAW / FCAW
Overlay thickness	5–10 mm
Post-weld hardness	58–62 HRC (after quench and temper)
Surface finish after machining	Ra 0.4–0.8 μm

Manufacturing Sequence

Base die fabrication: Machining of base die from low-cost steel to approximate dimensions (±0.5 mm tolerance)
Surface preparation: Grinding of overlay area to remove scale and ensure clean surface
Overlay welding: Application of high-alloy overlay using SMAW or FCAW
Post-weld heat treatment: Quench and temper to achieve target hardness
Precision machining: CNC milling or EDM to achieve final dimensions (±0.1 mm tolerance)
Surface finishing: Grinding to achieve required surface finish

Performance Characteristics

Wear Resistance

The overlay welded die surface, after heat treatment and machining, exhibits:

Hardness: 58–62 HRC (comparable to Cr12MoV tool steel)
Wear life: 30,000–50,000 strikes (compared to 50,000–100,000 for fully hardened Cr12MoV)
Surface integrity: Good, with minimal microcracking when properly processed

Dimensional Stability

The overlay welded die maintains dimensional accuracy within:

±0.05 mm after initial wear-in period (first 5,000 strikes)
±0.1 mm after 30,000 strikes
±0.15 mm after 50,000 strikes

This dimensional stability is acceptable for automotive body panels with moderate tolerance requirements.

Surface Quality

The final surface finish after machining and grinding:

Ra 0.4–0.8 μm (acceptable for automotive body panels)
Minimal weld-induced surface defects after proper machining
Good surface integrity with no significant porosity or inclusions

Cost-Benefit Analysis

Parameter	Traditional Die	Overlay Welded Die
Base material cost	High (Cr12MoV)	Low (45 steel)
Machining equipment	High-end CNC	Basic CNC + welding
Manufacturing time	4–6 weeks	2–3 weeks
Initial cost	100% (reference)	50–60%
Service life	50,000–100,000 strikes	30,000–50,000 strikes
Cost per strike	1.0 (reference)	0.8–1.2
Repairability	Difficult (full replacement)	Easy (overlay repair)

The overlay welded die approach offers significant cost savings for manufacturers without access to expensive precision machining equipment, while maintaining acceptable performance for moderate production volumes.

Defect Analysis and Countermeasures

Defect	Cause	Detection	Countermeasure
Overlay cracking	High carbon, rapid cooling	MT, visual	Increase preheat, reduce heat input
Insufficient hardness	Incomplete austenitization	Hardness test	Increase quench temperature, extend time
Poor surface finish	Weld porosity, inclusions	Visual, surface roughness	Improve welding technique, use cleaner consumables
Dimensional inaccuracy	Distortion during welding/heat treatment	CMM, gauge	Control welding sequence, use fixtures
Premature wear	Inadequate overlay thickness	Wear monitoring	Increase overlay thickness, improve heat treatment

Engineering Practice Integration

The overlay welded die approach is particularly suitable for:

Small-to-medium automotive manufacturers with limited capital investment
Low-volume production of specialty vehicles
Prototype and trial production
Repair of worn dies without full replacement
Manufacturers transitioning from simplified dies to higher-quality tooling

Key success factors include:

Proper base die design: Adequate material thickness to support overlay without excessive distortion
Welding procedure qualification: Systematic development of welding parameters for consistent overlay quality
Heat treatment optimization: Precise control of quench and temper parameters to achieve target hardness
Post-weld machining capability: Access to CNC machining for final dimensional accuracy
Quality control: Regular inspection of overlay thickness, hardness, and surface quality

Study Insights and Reflections

This work represents an innovative approach to die manufacturing that bridges the gap between expensive traditional methods and inadequate simplified alternatives. The overlay welded die concept leverages the advantages of welding technology—flexibility, cost-effectiveness, and repairability—to solve a practical manufacturing challenge.

The approach demonstrates several important engineering principles:

Function follows material selection: The overlay provides the functional surface properties while the base material provides structural support
Process integration: Combining welding, heat treatment, and machining into a single manufacturing sequence
Cost optimization: Reducing overall cost through strategic material selection and process design
Maintainability: Easy repair through overlay welding without complete die replacement

However, the approach has limitations:

Limited applicability to very complex die geometries with tight tolerance requirements
Reduced service life compared to fully hardened tool steel dies
Dependence on welding quality and operator skill
Potential for surface defects if welding procedures are not carefully controlled

Reference Value and Outlook

This study provides a valuable reference for engineers seeking cost-effective solutions for die manufacturing. The overlay welded die concept has evolved over time with advances in welding technology, including:

Laser cladding for higher precision overlay
Wire-arc additive manufacturing for complex geometries
Advanced tool steels with improved weldability
Improved heat treatment techniques for better property control

The fundamental principle—combining a low-cost base material with a high-performance overlay surface—remains relevant and has been applied to various other tooling applications, including:

Extrusion dies
Injection molds
Forging dies
Stamping dies for other industries

For modern manufacturers, the overlay welded die approach offers a viable alternative to fully hardened dies for applications where cost is a critical factor and moderate service life is acceptable. The approach also provides a pathway for die repair, extending the service life of existing tooling through surface overlay rather than complete replacement.