One-Die-Two-Pieces Forging of Right-Angle Elbows

Literature Overview

This paper, published in Forging & Stamping Technology (2017, Vol. 42, No. 1, pp. 15–19), authored by Ren Xiaohong, Chen Li, and Gao Zhaoxiang from Sichuan Chemical College and Luzhou Huaxi Machinery Co., Ltd., presents a process innovation in the forging of right-angle elbows. The traditional one-die-one-piece forging method is improved to a one-die-two-pieces configuration, with the aid of Deform-3D finite element simulation for process optimization. The study demonstrates significant improvements in production efficiency, die life, and cost reduction.

Traditional Process Limitations

The conventional one-die-one-piece forging process for right-angle elbows involves placing a single preformed billet into the die cavity, applying forging force, and extracting one finished elbow per cycle. This approach has several inherent limitations:

Low material utilization due to large flash and trimming losses.
Limited production rate, as each forging cycle produces only one component.
Uneven die wear distribution, leading to asymmetric die degradation and reduced service life.
High labor intensity for billet loading and part removal.

The production economics of the traditional method become particularly unfavorable for high-volume manufacturing scenarios where the per-unit cost must be minimized.

One-Die-Two-Pieces Process Design

The improved process places two billets side by side within a single die set, doubling the output per forging cycle. The design of this improved process involves several critical considerations:

Billet Arrangement and Die Geometry

The two billets are arranged parallel to each other within the die cavity, with a carefully calculated spacing between them. The key design parameters include:

Design Parameter	Traditional (1-piece)	Improved (2-pieces)	Design Rationale
Billets per cycle	1	2	Doubled output
Die cavity spacing	N/A	Calculated for even flow	Prevent inter-billet interference
Billet shape	Single preform	Modified preform	Optimized for two-piece filling
Flash distribution	Single flash	Shared flash	Reduced material waste
Forging force per cycle	Baseline	Higher (2× billets)	Requires adequate press capacity

Finite Element Simulation with Deform-3D

The Deform-3D software was employed to simulate the forging process, providing insights into material flow, stress distribution, and cavity filling behavior. The simulation model was constructed with the following parameters:

Material model: Power-law constitutive equation calibrated for the specific steel grade used.
Mesh: Adaptive meshing with refined elements in the deformation zones.
Boundary conditions: Friction coefficient at the die-billet interface set to 0.15–0.25, representing lubricated hot forging conditions.
Thermal analysis: Coupled thermo-mechanical simulation accounting for temperature-dependent material properties.

The simulation results provided the load-stroke curve and equivalent stress distribution at the end of forming, confirming that the cavity was fully filled and the material flow was reasonable throughout the forging process.

Performance Comparison and Results

The quantitative comparison between the traditional and improved processes reveals substantial improvements:

Performance Metric	Traditional Process	Improved Process	Improvement Factor
Production efficiency	Baseline	5×	500% increase
Die service life	Baseline	~2×	100% increase
Cost per 3000 pieces	Baseline	8,230 CNY savings	Significant reduction
Material utilization	Lower	Higher	Reduced waste
Labor requirement	Higher	Lower	Improved ergonomics

The fivefold increase in production efficiency is the most striking result, directly attributable to doubling the output per cycle while maintaining comparable cycle times. The doubling of die life is attributed to more uniform stress distribution across the die surface when two symmetrically arranged billets are forged simultaneously, reducing localized wear patterns.

Engineering Practice Considerations

For engineers considering the implementation of one-die-two-pieces forging for similar applications, several practical considerations must be addressed:

Press capacity: The forging force for two pieces must be verified against the available press tonnage. While the total force is approximately doubled, the force distribution may differ from a simple linear scaling due to inter-billet interaction effects.
Billet heating uniformity: Both billets must be heated to the same forging temperature to ensure uniform deformation behavior. Differential heating can lead to asymmetric cavity filling and dimensional non-conformance.
Die design robustness: The die must be designed to handle the increased forces and the potential for inter-billet material flow interference. Reinforced die geometry and appropriate quench-and-temper treatment are essential for maintaining die life.
Quality inspection: Each forged piece must be individually inspected for dimensional accuracy, as the two-piece configuration may introduce subtle asymmetries that affect fit-up in subsequent welding or machining operations.

Key Reflections and Study Insights

This paper demonstrates the power of process innovation combined with numerical simulation in achieving substantial manufacturing improvements. The concept of increasing the number of pieces per die cycle is straightforward in principle but requires careful engineering analysis to ensure that the benefits are realized without compromising quality. The successful application of Deform-3D simulation in validating the process before production trial is a best practice that reduces the risk and cost of process development.

The 8,230 CNY cost savings per 3,000 pieces represents a compelling economic case for process improvement, particularly in high-volume production environments. For engineers in the pipe fitting manufacturing industry, this work reinforces the principle that incremental process innovations, when properly analyzed and implemented, can yield significant competitive advantages in terms of cost, quality, and delivery performance.