I approached this transmission rear planetary gear carrier as a gear forging project that had to be validated before any hard die was cut. The part supports and locates planetary gears, so it must resist torsion, impact, and fatigue under complex operating conditions. From my perspective, the most economical route for volume production was closed-die gear forging, followed by controlled cooling, heat treatment, and finishing. Because the customer required an early sample and the geometric complexity was high, I used finite-element simulation to evaluate the gear forging process before trial forging. The goal was not merely to predict fill, but to reduce the risk of unsound grain flow, laps, folding, insufficient die filling, and excessive load on the press. The following work summarizes my first-person design reasoning, calculations, simulation setup, results, and conclusions for the gear forging of this rear planetary gear carrier.
Part Function and Material Selection
In my assessment, the rear planetary gear carrier is a structural gear forging. It rotates with the planetary set or can be locked independently, which changes the rotational state of the gear train and ultimately controls wheel motion. The carrier therefore experiences combined bending, torsion, and impact. I selected SAE1020 as the starting material because it is a low-carbon, high-quality structural steel with good ductility and forgeability. In gear forging, SAE1020 is often carburized after forging so that the surface obtains high hardness while the core retains toughness. This combination is well suited to a gear forging that must absorb shock and resist wear at contact regions.
| Property or Element | Typical Value for SAE1020 | Meaning for Gear Forging |
|---|---|---|
| Carbon | 0.18 to 0.23 wt% | Low hardenability, good ductility, suitable for carburizing |
| Manganese | 0.30 to 0.60 wt% | Improves strength and forgeability |
| Phosphorus | 0.040 wt% max | Controlled to avoid hot shortness |
| Sulfur | 0.050 wt% max | Controlled for forgeability and machinability |
| Tensile strength | Approximately 380 to 450 MPa | Low as-forged strength, good plastic flow |
| Yield strength | Approximately 210 to 260 MPa | Allows substantial deformation without cracking |
| Elongation | Approximately 25% or higher | Favorable for gear forging and trimming |
| Forging temperature range | Approximately 1000 to 1200 °C | Defines billet heating and transfer window |
I specified a forged billet rather than a casting because gear forging produces a continuous grain flow that follows the tooth and carrier contour. In a loaded gear forging, grain flow orientation can significantly improve fatigue resistance around the carrier windows and support bosses. For this reason, my material and process route were built around conventional hot gear forging followed by normalizing, trimming, piercing, and sizing.
Forged Part Design and Allowances
I developed the forged part from the customer drawing by adding machining allowance, draft, and forging tolerances. The maximum outer diameter after forging was about 145 mm. The base disk thickness was about 8 mm. The five carrier prongs had a height of about 45.1 mm. The inner wall diameter at the top of the prongs was about 116 mm, and the outer wall diameter was about 141 mm. The estimated forged mass was 1.938 kg. These values guided the billet volume, flash design, die layout, and press tonnage.
| Feature | Forged Dimension | Process Implication |
|---|---|---|
| Maximum outer diameter | 145 mm | Sets die insert size and projected area |
| Base disk thickness | 8 mm | Thin web, risk of distortion during cooling and trimming |
| Carrier prong height | 45.1 mm | Deep features require careful preform volume distribution |
| Prong top inner diameter | 116 mm | Controls mandrel or punch clearance |
| Prong top outer diameter | 141 mm | Affects flash land and die closure |
| Single-side machining allowance | 1.2 mm | Allows finish machining after gear forging |
| Draft angle | 1.5° to 3° | Assists ejection from die cavities |
| Estimated forged mass | 1.938 kg | Used for material utilization and cost |
I used standard shrinkage and tolerance relationships during die design. The die cavity dimension can be expressed as
$$D_d = D_f (1 + \alpha_s \Delta T)$$
where \(D_d\) is the die dimension at room temperature, \(D_f\) is the forged dimension at forging temperature, \(\alpha_s\) is the thermal expansion coefficient, and \(\Delta T\) is the temperature difference. For gear forging, this correction is small but not negligible, especially when the carrier prongs are deep and the web is thin.
The billet volume must satisfy the forged part volume plus flash and scale loss:
$$V_b = V_f + V_{flash} + V_{scale}$$
where \(V_b\) is billet volume, \(V_f\) is forged part volume, \(V_{flash}\) is flash volume, and \(V_{scale}\) is scale loss. I used this relation to check the initial billet size of 60 mm diameter and 101.9 mm length. The billet mass was approximately 2.26 kg, which provided sufficient material for flash and for complete gear forging fill.
Equipment Selection and Tonnage Estimate
I selected a hot die forging press for this gear forging. Compared with an electric screw press or friction press, the hot die forging press gives a faster and more stable slide motion, shorter contact time between the hot forging and the die, and better potential for automated multi-station gear forging. The shorter contact time is important because it reduces die heating and extends die life. In my view, these advantages are decisive for a complex gear forging with thin webs and tall prongs.
| Equipment Type | Slide Speed | Contact Time | Automation Potential | Suitability for This Gear Forging |
|---|---|---|---|---|
| Hot die forging press | High and stable | Short | High | Preferred |
| Electric screw press | Moderate | Moderate | Medium | Possible but less stable |
| Friction press | Variable | Longer | Low to medium | Less desirable |
| Hydraulic press | Slow | Long | Medium | Not selected for this gear forging |
I estimated the required forging load using the common empirical relationship for hot die forging:
$$P = C K F$$
where \(P\) is the required forging force in kN, \(C\) is a safety factor, \(K\) is the metal deformation resistance coefficient in \(10\,\text{kN/cm}^2\), and \(F\) is the projected area including the flash land. For this gear forging, I took \(C = 1.2\) and \(K = 7\). The projected area with a flash land width of 7 mm gave a characteristic diameter of approximately 160 mm. Therefore,
$$F = \frac{\pi}{4} (160)^2 \frac{1}{100} = 201.06\,\text{cm}^2$$
and
$$P = 1.2 \times 7 \times 10 \times 201.06 = 16889\,\text{kN}$$
This is about 1690 tons. I therefore selected a 2500-ton hot die forging press. The margin between the estimated load and the press capacity accounts for strain-rate effects, friction, flash restraint, die mismatch, and occasional low billet temperature. For a complex gear forging, I prefer this margin rather than operating near the press limit.
| Parameter | Value | Unit |
|---|---|---|
| Safety factor, C | 1.2 | dimensionless |
| Deformation resistance coefficient, K | 7 | 10 kN/cm² |
| Projected diameter including flash | 160 | mm |
| Projected area | 201.06 | cm² |
| Calculated forging force | 16889 | kN |
| Calculated tonnage | about 1690 | ton |
| Selected press capacity | 2500 | ton |
Die Design Strategy for Gear Forging
I considered both backward extrusion and forward extrusion for the gear forging. Backward extrusion would have favored the carrier prong formation if the prongs were placed in the upper die. However, that arrangement would make the upper die cavity very deep and the lower die cavity very shallow. The resulting adhesion force between the hot forging and the upper die would be greater than that in the lower die, so the forging would tend to stick in the upper cavity during ejection. Because the existing press and die set could not easily accommodate an upper ejector, I rejected backward extrusion. I selected forward extrusion with lower ejection, using a lower knockout pin to release the gear forging.
The preforming die was designed as a semi-closed forward extrusion die. The outer contour of the gear forging was rotational, so I could make the semi-closed bridge as a simple rotational body. I set the flash bridge thickness to 2 mm and the flash clearance to 1.5 mm. The preforged part was ejected by the lower knockout pin.
| Die Design Item | Preforming Die | Final Forging Die |
|---|---|---|
| Die type | Semi-closed forward extrusion | Open die |
| Flash bridge thickness | 2 mm | About 2 mm |
| Flash bridge width | Semi-closed bridge | 7 mm |
| Flash clearance | 1.5 mm | Standard clearance |
| Ejection method | Lower knockout pin | Lower knockout pin |
| Main purpose | Distribute volume and pre-shape prongs | Finish fill, control flash, and define final geometry |
To reduce the risk of defects at the top of the carrier prongs during final forging, I added five hemispherical material storage bosses in the upper preforming die at the root positions of the carrier prongs. These bosses gave extra local volume so that the final forging could fill the prong tops without laps or shortness. In gear forging, local volume control is often more important than global volume control, because a small shortage in a deep corner can cause incomplete fill while excess material elsewhere creates excessive flash and load.
I also considered die parting line placement. The parting line must allow the upper and lower dies to close without trapping material, and it must permit the forged gear carrier to be ejected without dragging on deep walls. Because the base disk is thin, I placed the parting line to minimize the depth of the lower cavity while still supporting the prong features. This choice reduced the tendency of the thin web to buckle during ejection.
Process Route and Thermal Control
I established the process route as a conventional hot gear forging line with an additional thermal sizing step. The thin base disk of the carrier tends to distort during knockout, piercing, and trimming because SAE1020 is soft at elevated temperature. To control flatness and roundness, I added a hot sizing operation after piercing and trimming. This sizing step is not a cosmetic correction; it is a dimensional stabilization step that improves the final gear forging quality before normalizing and shot blasting.
| Step | Operation | Purpose in the Gear Forging Route |
|---|---|---|
| 1 | Billet cutting | Provide accurate mass and volume for gear forging |
| 2 | Heating | Raise billet to 1160 °C for adequate plasticity |
| 3 | Upsetting | Break scale, distribute deformation, and prepare preform |
| 4 | Preforming | Distribute volume for carrier prongs and reduce final die load |
| 5 | Final forging | Complete gear forging fill and form flash system |
| 6 | Piercing | Remove central web material if required by design |
| 7 | Trimming | Remove flash and define outer contour |
| 8 | Hot sizing | Correct distortion and improve dimensional consistency |
| 9 | Normalizing | Refine microstructure and relieve forging stress |
| 10 | Shot blasting | Remove scale and prepare surface for inspection |
| 11 | Packaging and delivery | Protect finished gear forgings |
I set the billet temperature at 1160 °C. The environment temperature was 30 °C. The heat transfer coefficient was taken as 5 N/(s·mm·°C), including the influence of die lubricant. The convection coefficient was 0.02 N/(s·mm·°C). These values are consistent with a hot gear forging process where the billet is transferred quickly but still loses heat at the die contact surfaces. I used a shear friction coefficient of 0.3 for the simulation. The upper die velocity was 350 mm/s, and the step size was 0.1 mm.
| Simulation Parameter | Value | Unit |
|---|---|---|
| Billet diameter | 60 | mm |
| Billet length | 101.9 | mm |
| Billet mass | 2.26 | kg |
| Mesh count | 102863 | elements |
| Minimum mesh size | 0.68 | mm |
| Mesh ratio | 2 | dimensionless |
| Shear friction coefficient | 0.3 | dimensionless |
| Billet temperature | 1160 | °C |
| Environment temperature | 30 | °C |
| Heat transfer coefficient | 5 | N/(s·mm·°C) |
| Convection coefficient | 0.02 | N/(s·mm·°C) |
| Upper die velocity | 350 | mm/s |
| Step size | 0.1 | mm |
The thermal field during gear forging can be described by the transient heat conduction equation:
$$\rho c_p \frac{\partial T}{\partial t} = \nabla \cdot (k \nabla T) + \dot{q}$$
where \(\rho\) is density, \(c_p\) is specific heat, \(T\) is temperature, \(t\) is time, \(k\) is thermal conductivity, and \(\dot{q}\) is internal heat generation due to deformation. In hot gear forging, the internal heat generation from plastic work can partly compensate for die chilling, especially in the rapidly deforming carrier prongs.
The friction boundary condition was modeled as
$$\tau_f = m k$$
where \(\tau_f\) is friction shear stress, \(m\) is the shear friction factor, and \(k\) is the shear yield strength of the material. I used \(m = 0.3\), which represents a lubricated hot forging condition but still allows realistic flash restraint and die wall friction.
Finite Element Simulation of Gear Forging
I used a three-dimensional finite-element simulation to examine the full gear forging sequence: upsetting, preforming, and final forging. The simulation allowed me to view temperature, effective stress, effective strain, material flow, die load, and filling condition at each stage. For a complex gear forging, this is much more informative than a simple volume or tonnage calculation. I could see whether the preform volume was correctly distributed, whether the prong tops filled before the flash land closed, and whether any region experienced excessive strain concentration.
| Simulation Stage | Key Output | My Interpretation |
|---|---|---|
| Upsetting | Temperature field and billet shape | Heat loss concentrated at die contact surfaces |
| Preforming | Fill, load, stress, strain | Adequate preform distribution, top prongs intentionally not full |
| Final forging | Complete fill, load, stress, strain | Full fill without defects, load close to empirical estimate |
The effective stress and effective strain fields are important for evaluating gear forging soundness. I used the von Mises equivalent stress:
$$\sigma_{eq} = \sqrt{\frac{1}{2}\left[(\sigma_1-\sigma_2)^2 + (\sigma_2-\sigma_3)^2 + (\sigma_3-\sigma_1)^2\right]}$$
and the equivalent plastic strain:
$$\varepsilon_{eq} = \frac{\sqrt{2}}{3}\sqrt{(\varepsilon_1-\varepsilon_2)^2 + (\varepsilon_2-\varepsilon_3)^2 + (\varepsilon_3-\varepsilon_1)^2}$$
These quantities helped me judge whether the gear forging was deforming uniformly or whether local regions were carrying excessive deformation. In a sound gear forging, the equivalent strain should be distributed through the carrier prongs and web without a sharp concentration that could become a cracking or folding site.
Upsetting Stage
During upsetting, the billet lost little heat overall. The temperature remained mostly between 980 °C and 1160 °C. The lowest temperatures appeared at the end faces where the billet touched the dies. This is expected because the die acts as a heat sink. I used this result to confirm that the transfer time was acceptable and that the preform would still have enough plasticity for the subsequent gear forging operations.
| Upsetting Result | Observed Range | Process Meaning |
|---|---|---|
| Overall billet temperature | 980 to 1160 °C | Sufficient for preforming |
| Lowest temperature location | Die contact faces | Expected die chilling |
| Heat loss severity | Low to moderate | Transfer and lubrication acceptable |
Preforming Stage
At the end of preforming, the bottom of the gear forging was well filled, while the tops of the carrier prongs were intentionally not completely filled. The preform volume was designed to be larger than the final forging volume in that region, so the prong height reached approximately 42.4 mm. The temperature range was about 1000 °C to 1240 °C. The required load was approximately 564 tons. This load is modest compared with the final forging load, which confirms that the preforming step primarily redistributes material rather than completing the final gear forging geometry.
| Preforming Result | Value | Comment |
|---|---|---|
| Bottom fill | Complete | Good material distribution |
| Prong top fill | Not complete | Intended because final forging will complete it |
| Prong height | About 42.4 mm | Leaves volume for final fill |
| Temperature range | 1000 to 1240 °C | Good forging window |
| Required load | About 564 tons | Well below press capacity |
The effective stress and effective strain distributions in preforming were relatively uniform and consistent, with no obvious concentration points. This is a favorable sign for gear forging because it suggests that the preform did not create local shear bands or fold-prone flow patterns. I used this result to support the selected preform shape and the hemispherical storage bosses.
Final Forging Stage
At the end of final forging, the gear forging was completely filled with no missing material. The temperature range was about 1020 °C to 1280 °C. The required load was approximately 1540 tons. This value is close to the empirical calculation without the safety factor, which was about 1410 tons. The agreement between simulation and empirical calculation gave me confidence in the selected 2500-ton press and in the die design.
| Final Forging Result | Value | Evaluation |
|---|---|---|
| Fill condition | Complete | No shortage or unfilled prong tops |
| Temperature range | 1020 to 1280 °C | Within acceptable hot forging range |
| Required load | About 1540 tons | Close to empirical estimate |
| Empirical load without safety factor | About 1410 tons | Good correlation |
| Selected press capacity | 2500 tons | Adequate margin |
The effective stress and effective strain distributions in final forging were also relatively uniform and consistent, with no obvious concentration points. This indicated that the material flow was well controlled and that the final die cavity filled in a stable manner. In my judgment, the absence of severe strain concentration is particularly important for a gear forging that will later be carburized and subjected to cyclic torque.
Forging Load, Energy, and Die Stress
I also checked the forging energy and die stress to support the press selection and die material choice. The forging energy can be approximated by integrating the load-displacement curve:
$$E = \int P \, ds$$
where \(E\) is energy, \(P\) is forging load, and \(s\) is slide displacement. Although the exact energy depends on the die elasticity and press characteristics, the simulated load-displacement response showed that the final forging stage consumed most of the energy. This is typical for gear forging, where the flash land closes late in the stroke and the load rises sharply.
The nominal die contact stress can be estimated as
$$\sigma_d = \frac{P}{A_c}$$
where \(\sigma_d\) is die contact stress, \(P\) is forging load, and \(A_c\) is contact area. For the final forging load of about 1540 tons and a representative contact area, the die stress is high enough to require robust die inserts, adequate preload, and good support. I specified die blocks with sufficient hardness and toughness, and I paid attention to fillet radii and die corners because stress concentrations in the die can lead to early cracking.
| Die Stress Consideration | Design Response | Reason |
|---|---|---|
| High final forging load | Use a 2500-ton press | Keeps die stress within a safer range |
| Deep carrier prong cavities | Use generous fillets and polished walls | Improves material flow and reduces stress risers |
| Thin web | Support the lower die and control ejection | Reduces distortion and die deflection |
| Thermal fatigue | Control lubricant and contact time | Extends die life in repeated gear forging |
| Wear at flash land | Select wear-resistant die material | Maintains flash thickness and fill pressure |
I also estimated the die contact time from the slide speed and the deformation length:
$$t_c = \frac{L_s}{v_s}$$
where \(t_c\) is contact time, \(L_s\) is stroke length in contact, and \(v_s\) is slide speed. A shorter contact time reduces heat transfer into the die, which is one reason I preferred the hot die forging press. For this gear forging, the combination of high slide speed and lower ejection risk made the selected press a practical choice.
Material Flow and Defect Prevention in Gear Forging
In gear forging, the most common defects are incomplete fill, laps, folds, scale pits, cracking, and excessive flash. I evaluated each risk against the simulation results. The prong tops were the most critical fill region because they are deep and require material to flow upward while the flash land restricts lateral escape. The hemispherical storage bosses provided local volume, and the final simulation showed complete fill. The thin web was the most critical distortion region, so I added hot sizing after trimming. The base disk was the most critical cooling region, so I specified normalizing before finish operations.
| Potential Defect | Risk in This Gear Forging | Preventive Action |
|---|---|---|
| Incomplete fill at prong tops | High without preform volume control | Added five hemispherical storage bosses |
| Lap or fold at prong roots | Moderate | Optimized preform shape and radii |
| Excessive flash | Moderate | Controlled billet mass and flash bridge |
| Web distortion | High because web is thin | Added hot sizing after piercing and trimming |
| Scale defects | Moderate | Controlled heating and descaling during upsetting |
| Die wear at flash land | Moderate to high | Selected wear-resistant die material and lubrication |
| Thermal cracking of die | Moderate | Reduced contact time and controlled preheating |
The material flow in the final forging was generally radial and axial, filling the carrier prongs from the root toward the top. This flow pattern is desirable because it promotes grain flow along the prong direction. In a gear forging, grain flow continuity around the carrier windows can improve fatigue strength. I also checked that the flow did not create a sharp dead zone in the web or a fold at the inner corner. The simulation showed no such defect.
Microstructure and Post-Forge Heat Treatment
After gear forging, I specified normalizing to refine the grain structure and relieve internal stresses. Because the material is SAE1020, the forged part is relatively soft and ductile. For final service, carburizing can produce a hard surface and a tough core. This heat treatment strategy is common for gear forgings that must resist wear at contact surfaces while tolerating impact loads.
| Post-Forge Operation | Expected Effect | Reason for Gear Forging |
|---|---|---|
| Normalizing | Refines grains and relieves stress | Improves dimensional stability before machining |
| Shot blasting | Removes scale and improves surface | Prepares forging for inspection and machining |
| Carburizing | Hard surface and tough core | Enhances wear resistance and fatigue strength |
| Finish machining | Final dimensions and surface finish | Meets transmission gear carrier tolerances |
I also considered grain flow relative to the final part. A well-designed gear forging should not cut through the flow lines during machining if it can be avoided. For this carrier, the machining allowance was 1.2 mm per side, which is modest. I therefore kept the forged contour close to the final contour so that the beneficial grain flow remained near the surface after machining.
Simulation Validation and Decision
I used the simulation results to decide whether to proceed with die manufacturing before trial forging. The final forging fill was complete, the load was within the selected press capacity, the effective stress and strain distributions were acceptable, and the temperature field remained in a forgeable range. The preforming stage successfully prepared the volume distribution, and the final stage completed the gear forging without defects. Based on these results, I concluded that the gear forging process was feasible and that the die could be manufactured for sampling.
| Decision Criterion | Result | Decision |
|---|---|---|
| Complete die filling | Achieved | Proceed |
| Forging load within press capacity | Achieved | Proceed |
| No severe strain concentration | Achieved | Proceed |
| Temperature within forging window | Achieved | Proceed |
| Defect risk controlled | Achieved | Proceed with die manufacturing |
| Sampling schedule | Improved by simulation | Start die making early |
From my perspective, the greatest value of the finite-element simulation was not only the confirmation of fill. It was the ability to test the gear forging sequence before committing to steel, machining, and heat treatment of the dies. By predicting temperature, stress, strain, and load, I could optimize the preform, flash, and ejection strategy. This reduced the probability of multiple trial rounds and shortened the sample delivery time.
Manufacturing Quality Control for Gear Forging
I defined quality control points for the gear forging process. Billet mass and heating temperature are checked before forging. Die temperature and lubrication are monitored during forging. Forging load, fill, flash thickness, and surface condition are checked after final forging. After trimming and sizing, the flatness, outer diameter, prong height, and inner diameter are inspected. After normalizing and shot blasting, the parts are inspected for cracks, scale, and dimensional deviation.
| Control Point | Check Item | Target or Method |
|---|---|---|
| Billet preparation | Diameter, length, mass | Match simulated billet |
| Heating | Temperature and atmosphere | 1160 °C target, controlled scale |
| Upsetting | Shape and scale removal | Visual and dimensional check |
| Preforming | Fill and prong height | Verify preform volume distribution |
| Final forging | Fill, flash, load | No shortage, stable load |
| Piercing and trimming | Hole position and flash removal | Dimensional gauge |
| Hot sizing | Flatness and roundness | Control web distortion |
| Normalizing | Hardness and microstructure | Meet specification |
| Final inspection | Cracks, dimensions, surface | Visual, gauge, and non-destructive if required |
I also considered the importance of die maintenance in gear forging. The flash land is a high-wear region. If the flash land wears, the restraint changes and the fill may become incomplete or the flash may become too thick. I therefore specified periodic inspection of the flash land, prong corners, and punch edges. In my experience, a stable gear forging process depends as much on die maintenance as on the initial die design.
Economic and Production Advantages
I selected gear forging because it offers an excellent balance of strength, productivity, and cost for this rear planetary gear carrier. A forged carrier has better mechanical properties than a casting and can be produced at a much lower cost than a fully machined part. The simulation-driven approach further reduced cost by lowering the risk of trial-and-error die modification. In my evaluation, the main economic benefits were shorter sample lead time, fewer trial forging rounds, higher material utilization, and more predictable die life.
| Economic Factor | Effect of Simulation-Led Gear Forging |
|---|---|
| Sample lead time | Reduced by avoiding repeated die trials |
| Die cost | Lower risk of premature redesign |
| Material utilization | Optimized billet mass and flash |
| Press utilization | Load matched to 2500-ton press |
| Scrap rate | Reduced by defect prediction |
| Production stability | Improved by controlled preform and flash |
The simulation also helped me communicate the process plan to the manufacturing team. Instead of relying only on experience, I could show the temperature field, load curve, and strain distribution. This made the die design review more objective and helped the team agree on the preform shape, flash dimensions, and ejection method.
Summary of Key Parameters
For clarity, I summarized the main parameters that governed this gear forging project. These values formed the basis of the die design, simulation, and process control plan.
| Category | Parameter | Value |
|---|---|---|
| Material | SAE1020 | Low-carbon carburizing steel |
| Part | Rear planetary gear carrier | Gear forging |
| Forged mass | Final part | 1.938 kg |
| Billet | Diameter and length | 60 mm × 101.9 mm |
| Billet mass | Initial charge | 2.26 kg |
| Maximum outer diameter | Forged | 145 mm |
| Web thickness | Base disk | 8 mm |
| Prong height | Carrier features | 45.1 mm |
| Draft angle | Die design | 1.5° to 3° |
| Machining allowance | Single side | 1.2 mm |
| Press | Hot die forging press | 2500 tons |
| Final forging load | Simulated | About 1540 tons |
| Preforming load | Simulated | About 564 tons |
| Billet temperature | Heating | 1160 °C |
| Friction | Shear friction coefficient | 0.3 |
| Flash bridge | Final die | 7 mm wide, about 2 mm thick |
| Ejection | Lower knockout | Selected to avoid sticking |
Conclusion
I concluded that the proposed gear forging process for the transmission rear planetary gear carrier is feasible. The finite-element simulation showed complete final fill, acceptable temperature distribution, uniform effective stress and strain, and a forging load that matches empirical calculation. The preforming stage successfully prepared the material volume, and the hemispherical storage bosses helped fill the carrier prong tops. The selected 2500-ton hot die forging press provides sufficient capacity, and the forward extrusion die arrangement with lower ejection avoids the risk of sticking in the upper die.
For me, the most important lesson is that gear forging is not only a shape-forming operation. It is a thermo-mechanical process in which die design, billet volume, flash restraint, friction, temperature, and ejection all interact. Simulation allows these interactions to be examined before the first hammer blow. By using the results presented here, I can proceed with die manufacturing, trial forging, and sample delivery with much greater confidence. The gear forging route is therefore approved for the next stage of process development and production preparation.