Transmission Housing

I. Core Advantages and Features of the Transmission Housing

The transmission housing serves as the "protective shell and load-bearing framework" of the transmission system, simultaneously bearing gear impact, sealing hydraulic fluid, and accommodating complex transmission components. Its advantages stem from the in-depth integration of aluminum alloy material properties with die-cast structural design. Specifically, they are as follows:

1. Lightweighting and Vehicle Energy Efficiency Optimization: Greater weight reduction advantages compared to traditional materials.

● Weight Breakthrough: Transmission housings made from die-cast aluminum alloys (ADC12, A356-T6) are 30%-40% lighter than cast iron housings of the same size. For example, the 7DCT transmission housing for passenger cars (420mm long, 280mm wide, and 190mm high) weighs only 8.5kg as a blank, compared to 14.2kg for a cast iron housing. This directly reduces the vehicle's unsprung mass, helping to lower fuel consumption by 0.2-0.4L/100km. AMT transmission housings for commercial heavy-duty trucks (larger in size) are die-casted using aluminum alloy, reducing weight by 25-30kg per unit, thereby minimizing power loss. 

● Scenario Adaptation: Passenger cars pursue low fuel consumption (for example, hybrid vehicle transmission housings must balance lightweighting and sealing), while commercial vehicles prioritize a balance between load-bearing and weight reduction (for example, heavy-duty truck housings have wall thicknesses of 8-12mm, 3-5mm thinner than cast iron while still meeting strength requirements).

2. High Structural Integration: Reducing Parts and Assembly Costs

● Complex Structures: The die-casting process allows for direct integration of bearing seats, shift mechanism mounting holes, hydraulic oil channels, cooling ribs, and other components, eliminating the need for subsequent welding or machining. For example, a die-casting process integrates 12 bearing seats (with a bore diameter of 35-60mm) and 8 cross-oil channels (with a minimum bore diameter of 8mm). This reduces the number of parts from 18 in a cast iron housing to 1, reduces the number of assembly steps from 22 to 8, and reduces the assembly time per unit from 40 minutes to 12 minutes, increasing annual production capacity to 500,000 units.

● Guaranteed Dimensional Precision: Key assembly surfaces (such as the flange surface connecting to the engine) meet tolerances of GB/T 6414 CT7, with a flatness of ≤0.1mm and a bearing hole roundness of ≤0.005mm. This allows for direct, gasket-free precision fit with gear shafts and bearings, reducing transmission clearance and lowering NVH (noise, vibration, and harshness) (measured transmission noise is 3-5dB lower than that of a cast iron housing).

3. Excellent Sealing and Heat Dissipation: Ensures long-term, stable transmission operation.

● High Airtightness and Anti-Leakage: The die-cast housing has no weld seams (eliminating the risk of leakage at welds in cast iron housings). The sealing surface utilizes a "stepped groove + fluororubber sealing ring" design, coupled with a high-vacuum die-casting process (porosity ≤2%). At 0.8MPa hydraulic oil pressure, leakage is ≤3mL/24h, significantly lower than the industry standard (≤10mL/24h). This design is suitable for hydraulically driven transmissions such as automatic and continuous transmissions, preventing shifting failures caused by oil leakage.

● Efficient heat dissipation and temperature control: The thermal conductivity of aluminum alloy (ADC12: 105W/(m・K)) is 2.3 times that of cast iron (45W/(m・K)). Combined with the integrated "wave-shaped heat dissipation ribs" (12mm high, 10mm apart) on the outer surface of the housing, the heat dissipation area is increased by 60% compared to a smooth housing. This stabilizes the transmission operating oil temperature at 80-100°C (cast iron housings can easily exceed 110°C, requiring an additional cooler), extending the life of the hydraulic oil and friction plates by 20%-30%.

4. Impact and Corrosion Resistance: Suitable for Complex Operating Conditions

● Impact Strength: After T6 heat treatment (solution treatment + aging), A356-T6 aluminum alloy achieves a tensile strength of ≥310 MPa and a yield strength of ≥280 MPa. It can withstand radial impact forces during gear transmission (e.g., impact loads of 800-1200 N during rapid acceleration) without cracking or deformation in the housing. A gearbox housing for an off-road vehicle survived 100,000 impact tests (load of 1000 N) and maintained its sealing performance.

● Environmental Adaptability: The aluminum alloy surface naturally forms an oxide film (Al₂O₃). After powder coating or anodizing, the salt spray test life reaches 500-800 hours (compared to 200-300 hours for galvanized cast iron housings). This makes it suitable for humid (e.g., mountain roads during rainy season) and dusty (e.g., construction sites) operating conditions, preventing strength degradation due to housing corrosion.

II. Die-casting Technology Features for Transmission Housings

Transmission housings have stringent requirements for cavity complexity, strength uniformity, and sealing accuracy, requiring targeted die-casting process design. The core technical features are as follows:

1. Precise Matching of Material and Die-casting Parameters: Balancing Formability and Strength

● Aluminum Alloy Selection: Differentiated material selection based on transmission type

● Passenger Car DCT/AT Housings: Choose ADC12 (excellent fluidity, suitable for molding complex oil passages and cooling ribs, and low cost);

● Commercial Vehicle and Heavy-Duty Truck AMT Housings: Choose A356-T6 (higher strength, excellent impact resistance after T6 heat treatment, suitable for heavy loads). Key Process Parameter Control:

● Clamping Force: Small passenger car bodies use a 1200-1600T cold chamber die-casting machine, and large commercial vehicle bodies use a 2000-2500T die-casting machine (to avoid flashing at the parting surface and ensure uniform wall thickness);

● Injection Speed: 5-7m/s during the filling phase (to quickly fill complex oil passages and prevent material shortages); 1.0-1.5m/s during the holding phase (to reduce shrinkage and ensure bearing hole density);

● Mold Temperature: 200-240°C (ADC12), 220-260°C (A356-T6). "Zone Temperature Control" (mold temperature in the bearing hole area is 5-10°C higher) is used with a mold temperature controller to prevent localized shrinkage cracking. 

2. High Vacuum Die Casting: Solving Porosity and Sealing Challenges

● Vacuum System Design: To meet the "high-pressure sealing" requirements of transmission housings, we utilize a "multi-point vacuum extraction + cavity zone sealing" technology. Six to eight vacuum extraction holes are located in the mold at key locations, such as the housing oil passages and bearing holes. Combined with the integrated vacuum valve, this technology maintains cavity vacuum at ≤4 kPa, minimizing air entrainment during aluminum molten filling and maintaining internal casting porosity at ≤2% (≤1% in the stressed area). This prevents hydraulic oil leakage caused by porosity.

● Actual Results: After high-vacuum die casting, the airtightness qualification rate of an AT transmission housing increased from 82% with traditional die casting to 98%. Subsequent repair welding and hole plugging were eliminated, reducing unit costs by 15%. 3. Complex Cavity Molding Optimization: Overcoming Oil Channel and Bearing Hole Challenges

● Mold Runner and Venting Design: To address the "air trapping" problem of intersecting oil channels (such as "L-shaped" and "T-shaped" channels), a "circular runner + latent gate" design is adopted. Auxiliary gates are installed at the oil channel entrances to ensure simultaneous aluminum filling of the oil channels and the main cavity. Wedge-shaped venting grooves (0.2mm width, 0.15mm depth) are also installed at the ends of the oil channels and at the bases of the heat dissipation ribs to expel trapped air and prevent oil channel blockage or material shortages.

● Bearing Hole Precision Control: Bearing holes are produced using a combined "mold insert + post-processing fine boring" process. During die casting, high-strength alloy inserts (HRC50-55) are used to ensure initial hole formation. Subsequently, CNC fine boring (tolerance ±0.005mm) ensures hole roundness and coaxiality (coaxiality of multiple bearing holes ≤0.01mm), meeting the precise fit requirements of the gear shaft. 4. Intelligent Process Control and Post-Processing: Stable Batch Quality

● Real-time Parameter Monitoring: The MES system links the die-casting machine, vacuum valve, and mold temperature controller to collect real-time data on 15 key parameters, including injection force (±5% tolerance), molten aluminum temperature (675-695°C, ±5% tolerance), and vacuum level (≤4kPa). Automatically shut down and issue an alarm if deviations occur, preventing batch defects. (For example, one factory has used this system to control the batch defect rate to below 0.5%). Integrated post-processing: After die-casting, the system integrates a "T6 heat treatment (A356-T6 aging temperature 170°C x 4 hours, 30% strength increase)" + robotic deburring (for gate and parting surface residue, accuracy ±0.1mm) + airtightness testing (0.8MPa pressure hold for 5 minutes) + three-dimensional coordinate measurement (full inspection of key dimensions)" production line, achieving a one-stop "die-casting - molding - testing" production process. This reduces the single-piece production cycle from 60 minutes with traditional processes to 25 minutes.

III. Typical Application Cases

7DCT transmission case for a passenger car (for a joint venture automaker): Made of ADC12 material, using a 1600T die-casting machine with high vacuum technology, it integrates 8 oil passages and 10 bearing seats. The blank weighs 8.2kg, with airtightness leakage of ≤2mL/24h. The annual production capacity is 600,000 pieces, with a 98.5% pass rate. Commercial vehicle and heavy-duty truck AMT transmission housing (for a domestic automaker): Made of A356-T6 material, molded on a 2500T die-casting machine, 10mm wall thickness, tensile strength ≥320MPa, no deformation after 100,000 impact tests, suitable for heavy-duty conditions (maximum load 1500N).