Excavators are indispensable in infrastructure projects, with China’s fleet exceeding 1.3 million units. Bucket teeth endure extreme wear as primary ground-engaging components, creating massive demand for high-performance solutions. While casting traditionally dominated production, inherent defects like shrinkage cavities and environmental concerns necessitated advanced forging alternatives. This research establishes an optimized forging process addressing the unique challenges of bucket tooth geometry through preform innovation validated by simulation and physical trials.
Bucket teeth exhibit complex topology characterized by elongated profiles, concave waist sections, and challenging thin-walled arc protrusions at the crown. Conventional single-stroke forging proves inadequate for such geometry. We implemented a two-stage process: initial preform fabrication followed by final forging. The initial preform design (Figure 2a) yielded incomplete filling at the critical ear-shaped protrusions (Figure 2b), evidenced by depression formation instead of convex geometry. This failure mode indicated insufficient metal flow toward terminal cavity zones during final forging.
Our redesigned preform incorporated strategic curvature at the problematic crown region (Figure 3). This modification provided directional guidance for material flow, reducing forming resistance during terminal operations. The preform mold employed closed-die extrusion with stationary lower punch/die assembly and a moving upper punch. Final forging required a multi-action system: vertically moving inner/outer upper punches combined with horizontally actuated split dies to form the assembly hole and complex sidewalls while preventing flash. The sequence involved:
- Insertion of heated preform
- Horizontal die closure and clamping
- Outer punch descent + constant pressure application
- Inner punch descent to final position (causing outer punch float via counter-pressure)
- Secondary outer punch compression
- Punch retraction + die separation + part ejection
Numerical analysis using Deform-3D quantified process dynamics. The Ø75mm × 162mm billet (1150°C) was meshed with 100,000 elements (minimum size 1.2mm). Key simulation parameters included:
| Parameter | Value |
|---|---|
| Material Type | Plastic (Workpiece), Rigid (H13 Die) |
| Friction Coefficient | 0.3 (Shear Model) |
| Heat Transfer Coefficient | 5 W/(m²·°C) |
| Die Temperature | 300°C |
| Step Size | 0.4 mm |
The optimized preform simulation required 140 steps for 52.5mm punch displacement. Final forging analysis revealed critical insights:
- Equivalent Strain Distribution: Higher strain concentrated at the assembly hole interior walls ($\bar{\epsilon} > 2.5$), while the tooth tip exhibited minimal deformation ($\bar{\epsilon} < 0.8$). The heterogeneous strain field impacts grain refinement and hardness distribution across the bucket tooth.
- Velocity Field Evolution: Metal flow initiated axially downward under the inner punch (Step 30). By Step 164, material encountered die constraints, inducing radial flow toward sidewalls. Step 203 showed upward counter-flow meeting the descending outer punch, creating hydrostatic pressure that filled crown arcs. Final filling (Step 221) demonstrated uniform cavity saturation.
Load analysis proved critical for process optimization. The force-time curve for the inner punch revealed:
- Original preform: Peak load 12.8 kN with incomplete crown filling
- Optimized preform: Peak load 10.2 kN with complete cavity saturation
The 20% load reduction significantly extends die life while confirming improved formability. The governing equation for forging pressure incorporates this efficiency gain:
$$ P = \sigma_f \left(1 + \frac{\mu d}{3h}\right)e^{\frac{2\mu r}{h}} $$
Where $\sigma_f$ is flow stress, $\mu$ friction coefficient, $d$ contact diameter, $h$ height, and $r$ radial distance. Preform optimization directly reduced $\mu$ and $d$ values, lowering $P$.
Production trials on a 500-ton hydraulic press validated simulation accuracy. Key process parameters:
| Stage | Lubricant | Temperature |
|---|---|---|
| Preform | Graphite-based | 1150°C |
| Final Forging | Glass-based | 1150°C |
Resultant bucket teeth exhibited complete cavity filling, smooth hole surfaces, optimized internal fiber lines, and absence of folds/flashes. The optimized preform reduced forming difficulty by 35% while increasing dimensional accuracy to IT11-IT12 standards. This methodology establishes a robust framework for bucket tooth manufacturing, demonstrating that targeted preform geometry directly governs:
- Metal flow vectors during terminal forging
- Strain distribution uniformity
- Tooling load requirements
- Defect suppression capability
The research delivers a validated production solution enhancing bucket tooth durability through controlled microstructure development and dimensional precision.