The design drawings of customized aluminum alloy forgings must be closely integrated with the forging process characteristics to avoid forming difficulties, mold loss or performance defects caused by unreasonable structural design. The following is an analysis of the structural elements, dimensional tolerances, process identification and other dimensions combined with the aluminum alloy forging characteristics:
I. Process adaptability of structural design
1. Avoid extreme structural features
| Taboo structure | Risk manifestation | Improvement plan |
| Deep hole (hole depth / hole diameter > 5:1) | Punch is easy to bend and break, and the hole wall is not fully filled | Use stepped hole segmented forming to reserve subsequent drilling allowance |
| High rib (rib height / wall thickness > 3:1) | Metal flow is blocked, and the rib part is lacking in filling | Stepped rib design to increase the transition slope |
| Thin wall (wall thickness < 2mm) | Fast cooling during forging, easy to fold | Partial thickening to 3-4mm, subsequent machining thinning |
Case: The design drawing of an aluminum alloy motor housing has a Φ10mm deep hole (hole depth 55mm). The punch was severely worn during forging, so it was later changed to a Φ10mm×30mm blind hole +Φ8mm×25mm stepped hole. The forming qualification rate was increased from 40% to 92%.
2. Differentiated design of draft angle
Corresponding angles of alloy series:
6 series (6061/6082): outer wall 5°-7°, inner wall 7°-10° (good plasticity, slightly smaller angle);
7 series (7075/7A04): outer wall 7°-10°, inner wall 10°-15° (strong quenching tendency, angle needs to be increased to prevent jamming);
2 series (2024/2A12): outer wall 6°-8°, inner wall 8°-12° (avoid demoulding cracks caused by too small angle).
Structural optimization: For deep cavity structures (such as battery housings), variable angle design is adopted: 10° for the upper section, 8° for the middle section, and 5° for the lower section, with ejection mechanism to assist demoulding.
3. Mechanical matching of fillet radius
Calculation of minimum fillet radius (Rmin):
Rmin = 0.2× wall thickness + 2mm (applicable to 6 series);
Rmin = 0.3× wall thickness + 3mm (applicable to 7 series / 2 series).
Example: For 7075 forgings with a wall thickness of 5mm, the corner R should be ≥0.3×5+3=4.5mm to avoid stress concentration cracking when R＜3mm.
Treatment of special parts: Elliptical transition is used at the connection between ribs and webs (the long axis is along the metal flow direction), such as the design of R8×R12 elliptical fillet at the connection of the ribs of a certain bracket to reduce the risk of forging folding.
II. Dimensional tolerance and machining allowance design
1. Forging process adaptation of tolerance band
Linear dimension tolerance (refer to GB/T 15826.7-2012):
| Size Range (mm) | 6 Series Normal Accuracy (mm) | 7 Aeries Precision Grade (mm) |
| ≤50 | ±0.5 | ±0.3 |
| 50-120 | ±0.8 | ±0.5 |
| 120-260 | ±1.2 | ±0.8 |
Geometric tolerance control: flatness ≤ 0.5mm/100mm, verticality ≤ 0.8mm/100mm, thin-walled parts (wall thickness < 5mm) need to be tightened to 1/2 standard value.
2. Three-dimensional distribution of machining allowance
Radial allowance: 3-5mm (free forging), 1.5-3mm (die forging) for outer cylindrical surface; 4-6mm (free forging), 2-4mm (die forging) for inner hole surface.
Axial allowance: 2-4mm is left on each end surface. For shaft parts with aspect ratio > 3, 1-2mm anti-warping allowance needs to be added in the middle section.
Allowance compensation: For 7 series forgings, due to the large quenching deformation, the key size allowance needs to be increased by 20%-30%, such as the inner diameter allowance of a 7075 flange increased from 3mm to 4mm.
III. Process identification and special requirements
1. Mandatory marking of fiber flow direction
Marking method: Use arrows to indicate the fiber direction in the cross-sectional view. The angle between the fiber direction and the principal stress direction is required to be ≤15° in the key stress-bearing parts (such as the hub bolt hole area).
Prohibited design: Avoid the stress direction of the forging being perpendicular to the fiber direction (such as when the gear tooth direction is perpendicular to the fiber, the bending strength decreases by 30%).
2. Design of parting surface and process boss
Parting surface selection principle:
Located at the maximum cross-section of the forging to avoid misalignment caused by asymmetric parting;
The roughness of the parting surface of the 7 series forgings is Ra≤1.6μm to prevent burrs caused by tearing of the flash.
Process boss design: For asymmetric forgings (such as L-shaped brackets), a Φ10-15mm process boss needs to be designed for positioning. The boss is subsequently machined and removed, and the position is selected in the non-stress area.
3. Heat treatment status and flaw detection requirements
Status identification: The drawing title bar must indicate the status of T6/T74/T651, etc. For example, when the 2024 forging requires the T4 status, it must be marked as "solution treatment + natural aging".
Non-destructive testing terms:
Important parts (such as chassis parts): 100% ultrasonic flaw detection (acceptance level ≥ GB/T 6462-2017 II level);
Aerospace-grade forgings: Add fluorescent penetration testing (sensitivity level ≥ ASME V 2 level).
IV. Typical failure cases and improvement plans
1. Case: 6061 automobile control arm cracking
Original design problem: The wall thickness of the web in the middle of the arm body changes suddenly (from 8mm→3mm), the transition radius is R2mm, and cracks at the sudden change after forging.
Improved design: The wall thickness changes gradually (8mm→5mm→3mm), and the transition zone is set with an angle of R8mm+45°, and the cracking problem disappears.
2. Case: 7075 aviation joint size out of tolerance
Original tolerance setting: diameter Φ50mm±0.3mm (die forging), the out of tolerance rate due to quenching shrinkage in actual production reached 50%.
Improvement plan: mark "4mm machining allowance after hot forging, fine turning to Φ50±0.05mm after quenching", and the qualified rate is increased to 98%.
V. Design tools and standard references
1. CAE simulation-assisted design
Use Deform-3D to simulate metal flow and optimize draft angle and fillet: For example, the simulation of a complex shell shows that the metal flow rate difference at the R5mm fillet of the original design is 20%, and the flow rate difference is reduced to 5% after changing to R8mm.
2. Industry standard references
Domestic: GB/T 15826-2012 "Machining allowance and tolerance of steel die forgings on hammer";
International: ISO 8492:2011 "Aluminum and aluminum alloy forging tolerances".
In summary, the design of aluminum alloy forging drawings needs to deeply couple material properties (such as quenching sensitivity of the 7 series), forging processes (such as metal flow laws of die forging) and structural functions, and ensure the manufacturability and performance of forgings through reasonable draft angles, fillet radii, allowance allocation and process identification. It is recommended to collaborate with forging manufacturers in the design stage and avoid process risks in advance through DFM (design for manufacturability) analysis.
Email: cast@ebcastings.com
The design drawings of customized aluminum alloy forgings must be closely integrated with the forging process characteristics to avoid forming difficulties, mold loss or performance defects caused by unreasonable structural design. The following is an analysis of the structural elements, dimensional tolerances, process identification and other dimensions combined with the aluminum alloy forging characteristics:
I. Process adaptability of structural design
1. Avoid extreme structural features
| Taboo structure | Risk manifestation | Improvement plan |
| Deep hole (hole depth / hole diameter > 5:1) | Punch is easy to bend and break, and the hole wall is not fully filled | Use stepped hole segmented forming to reserve subsequent drilling allowance |
| High rib (rib height / wall thickness > 3:1) | Metal flow is blocked, and the rib part is lacking in filling | Stepped rib design to increase the transition slope |
| Thin wall (wall thickness < 2mm) | Fast cooling during forging, easy to fold | Partial thickening to 3-4mm, subsequent machining thinning |
Case: The design drawing of an aluminum alloy motor housing has a Φ10mm deep hole (hole depth 55mm). The punch was severely worn during forging, so it was later changed to a Φ10mm×30mm blind hole +Φ8mm×25mm stepped hole. The forming qualification rate was increased from 40% to 92%.
2. Differentiated design of draft angle
Corresponding angles of alloy series:
6 series (6061/6082): outer wall 5°-7°, inner wall 7°-10° (good plasticity, slightly smaller angle);
7 series (7075/7A04): outer wall 7°-10°, inner wall 10°-15° (strong quenching tendency, angle needs to be increased to prevent jamming);
2 series (2024/2A12): outer wall 6°-8°, inner wall 8°-12° (avoid demoulding cracks caused by too small angle).
Structural optimization: For deep cavity structures (such as battery housings), variable angle design is adopted: 10° for the upper section, 8° for the middle section, and 5° for the lower section, with ejection mechanism to assist demoulding.
3. Mechanical matching of fillet radius
Calculation of minimum fillet radius (Rmin):
Rmin = 0.2× wall thickness + 2mm (applicable to 6 series);
Rmin = 0.3× wall thickness + 3mm (applicable to 7 series / 2 series).
Example: For 7075 forgings with a wall thickness of 5mm, the corner R should be ≥0.3×5+3=4.5mm to avoid stress concentration cracking when R＜3mm.
Treatment of special parts: Elliptical transition is used at the connection between ribs and webs (the long axis is along the metal flow direction), such as the design of R8×R12 elliptical fillet at the connection of the ribs of a certain bracket to reduce the risk of forging folding.
II. Dimensional tolerance and machining allowance design
1. Forging process adaptation of tolerance band
Linear dimension tolerance (refer to GB/T 15826.7-2012):
| Size Range (mm) | 6 Series Normal Accuracy (mm) | 7 Aeries Precision Grade (mm) |
| ≤50 | ±0.5 | ±0.3 |
| 50-120 | ±0.8 | ±0.5 |
| 120-260 | ±1.2 | ±0.8 |
Geometric tolerance control: flatness ≤ 0.5mm/100mm, verticality ≤ 0.8mm/100mm, thin-walled parts (wall thickness < 5mm) need to be tightened to 1/2 standard value.
2. Three-dimensional distribution of machining allowance
Radial allowance: 3-5mm (free forging), 1.5-3mm (die forging) for outer cylindrical surface; 4-6mm (free forging), 2-4mm (die forging) for inner hole surface.
Axial allowance: 2-4mm is left on each end surface. For shaft parts with aspect ratio > 3, 1-2mm anti-warping allowance needs to be added in the middle section.
Allowance compensation: For 7 series forgings, due to the large quenching deformation, the key size allowance needs to be increased by 20%-30%, such as the inner diameter allowance of a 7075 flange increased from 3mm to 4mm.
III. Process identification and special requirements
1. Mandatory marking of fiber flow direction
Marking method: Use arrows to indicate the fiber direction in the cross-sectional view. The angle between the fiber direction and the principal stress direction is required to be ≤15° in the key stress-bearing parts (such as the hub bolt hole area).
Prohibited design: Avoid the stress direction of the forging being perpendicular to the fiber direction (such as when the gear tooth direction is perpendicular to the fiber, the bending strength decreases by 30%).
2. Design of parting surface and process boss
Parting surface selection principle:
Located at the maximum cross-section of the forging to avoid misalignment caused by asymmetric parting;
The roughness of the parting surface of the 7 series forgings is Ra≤1.6μm to prevent burrs caused by tearing of the flash.
Process boss design: For asymmetric forgings (such as L-shaped brackets), a Φ10-15mm process boss needs to be designed for positioning. The boss is subsequently machined and removed, and the position is selected in the non-stress area.
3. Heat treatment status and flaw detection requirements
Status identification: The drawing title bar must indicate the status of T6/T74/T651, etc. For example, when the 2024 forging requires the T4 status, it must be marked as "solution treatment + natural aging".
Non-destructive testing terms:
Important parts (such as chassis parts): 100% ultrasonic flaw detection (acceptance level ≥ GB/T 6462-2017 II level);
Aerospace-grade forgings: Add fluorescent penetration testing (sensitivity level ≥ ASME V 2 level).
IV. Typical failure cases and improvement plans
1. Case: 6061 automobile control arm cracking
Original design problem: The wall thickness of the web in the middle of the arm body changes suddenly (from 8mm→3mm), the transition radius is R2mm, and cracks at the sudden change after forging.
Improved design: The wall thickness changes gradually (8mm→5mm→3mm), and the transition zone is set with an angle of R8mm+45°, and the cracking problem disappears.
2. Case: 7075 aviation joint size out of tolerance
Original tolerance setting: diameter Φ50mm±0.3mm (die forging), the out of tolerance rate due to quenching shrinkage in actual production reached 50%.
Improvement plan: mark "4mm machining allowance after hot forging, fine turning to Φ50±0.05mm after quenching", and the qualified rate is increased to 98%.
V. Design tools and standard references
1. CAE simulation-assisted design
Use Deform-3D to simulate metal flow and optimize draft angle and fillet: For example, the simulation of a complex shell shows that the metal flow rate difference at the R5mm fillet of the original design is 20%, and the flow rate difference is reduced to 5% after changing to R8mm.
2. Industry standard references
Domestic: GB/T 15826-2012 "Machining allowance and tolerance of steel die forgings on hammer";
International: ISO 8492:2011 "Aluminum and aluminum alloy forging tolerances".
In summary, the design of aluminum alloy forging drawings needs to deeply couple material properties (such as quenching sensitivity of the 7 series), forging processes (such as metal flow laws of die forging) and structural functions, and ensure the manufacturability and performance of forgings through reasonable draft angles, fillet radii, allowance allocation and process identification. It is recommended to collaborate with forging manufacturers in the design stage and avoid process risks in advance through DFM (design for manufacturability) analysis.
Email: cast@ebcastings.com
