Abstract: With deepening development of automotive lightweighting technology, structural complexity and dimensional specifications of large die castings have significantly increased, their gating and drainage system designs have become more refined. Traditional edge-cutting mold removal processes, when faced with multi-layered slag pockets, complex venting branches, and thick-walled ingates, reveal problems such as low automation, high labor intensity, and high risk of casting damage. Taking die-cast housing of a heavy-duty truck transmission as research object, a combined automated removal scheme of "shear-bump-knock-saw" is proposed. Through coordinated operation of hydraulic shearing, robotic arm bumping, pneumatic hammer striking, and precision sawing, efficient removal of complex gating and drainage systems is achieved, providing an innovative approach for post-processing of similar complex die castings.
Die casting, as a core technology in the field of liquid metal forming, occupies an important position in automotive parts manufacturing due to its high precision, high efficiency, and ability to form complex structures. Die casting technology, as an important process in production of aluminum alloy parts, has high forming accuracy, production efficiency, and excellent surface quality, making it suitable for mass automated production and occupying an increasingly important position in casting industry. "China Die Casting Industry Development Report (2024)" shows that global die casting market has exceeded 800 billion yuan, with automotive die castings accounting for over 65%. With advancement of "dual carbon" target, aluminum alloy die castings, due to their low density (2.7g/cm3) and high specific strength (≥200MPa), have become a key technological path for automotive lightweighting. Taking heavy-duty truck transmissions as an example, aluminum alloy housings reduce weight by up to 40% compared to traditional cast iron parts, improving fuel efficiency by 5%-8%.
Gating and venting system, as "circulatory system" of die casting mold, has core function of guiding molten metal to fill mold smoothly, expelling gases from cavity, and collecting cold material. Modern die castings commonly employ multi-layer slag pockets (such as 3-5 layers of three-dimensional distribution) and mesh-like venting branches to address defects such as porosity and cold shuts. A study of 67051015-1DC transmission die casting housing shows that its gating and venting system includes 9 thick-walled ingates (5.7mm thick), 40 three-dimensional slag pockets, and 4 interconnected venting branches. However, removal of gating system for this shell presents three major challenges: (1) 40 three-dimensional slag bales are distributed across three height layers and interlock with each other, resulting in a low one-time collision and positioning rate for robotic arm; (2) traditional edge-cutting mold process suffers from a high failure rate due to process positioning deviations; (3) manual removal of nine thick-walled inlets is labor-intensive and poses a dust hazard. To address these issues, author proposes a combined automated removal scheme of "shear-bump-knock-saw" to handle this complex structure.

1.1 Casting Technical Parameters
Target casting is housing of an AMT heavy-duty truck transmission, with external dimensions of 520mm * 420mm * 325mm, an average wall thickness of 7mm, and a weight of 33kg. It is die-cast using ADC12 aluminum alloy, and its structural characteristics include:
(1) Multi-directional concave-convex features: internal cavity contains complex gearbox cavities, sensor mounting holes, and other features.
(2) Thin-walled to thick-walled transition: Flange connection area has a wall thickness of up to 15mm, forming a significant thermal point with thin-walled area.
(3) Three-dimensional gating network: Gating system is radially distributed, with slag pockets arranged in three layers along casting axis. Venting branches connect upper and lower slag pockets through ϕ8mm channels, as shown in Figure 1.

 

1.2 Key Design Considerations for Gating System
Gating system design for this casting follows principle of "sequential filling - gradient venting - efficient slag collection".
(1) Ingate design: Nine fan-shaped ingates, 25-30mm wide, are used to increase contact area and reduce scouring speed of molten metal, controlling it at 30-40m/s to reduce risk of air entrapment.
(2) Slag Pack Layout: ① Top-level slag pack: Located at the edge of top flange of casting, used to collect cold material that first enters cavity; ② Middle-level slag pack: Distributed on both sides of inner cavity, connected to outside through ϕ10mm venting branches; ③ Bottom-level slag pack: Located at the bottom boss of casting, combined with a blind hole structure to enhance slag collection.
(3) Venting System: A combination of "main venting channel + branched venting branches" is adopted. Cross-sectional area of main venting channel is 50mm², and cross-sectional area of venting branches is 10-15mm², ensuring rapid discharge of gas from cavity.
1.3 Limitations of Traditional Processes
(1) Trimming Die Process: Slag packs need to be removed beforehand by a robotic arm. However, with 40 slag packs distributed across two ends and inner cavity of casting, spanning three height layers and interlocking with each other, robotic arm's one-time collision accuracy is only 85%. Furthermore, uneven force during collision process (peak load reaches 500N) leads to positioning deviations, with errors ≥2mm, resulting in a trimming die failure rate as high as 15%.
(2) Manual Processing: Removing a single casting slag bale takes 200 seconds, and sawing gating system takes an additional 300 seconds. Furthermore, dust concentration exceeds standard, measuring 8.5 mg/m³, which is 4 mg/m³ higher than national standard limit. Daily labor intensity for workers is equivalent to handling a 1.5-ton heavy object.

Based on characteristics of casting and processing difficulties, and considering limitations of traditional processes, an innovative combined removal scheme was proposed. This scheme fully considers difficulties and drawbacks of traditional removal methods, such as robotic arm's single-hit-and-place rate being only 85%, cutting die failure rate being as high as 15%, and high labor intensity for workers. Innovations are mainly reflected in process route design and equipment used.
2.1 Process Route Design
Targeting structural characteristics of this casting, an innovative four-step process chain of "shear-bump-knock-saw" was proposed. Through modular equipment integration, the entire process from venting branch shearing to gating system sawing is automated. New process flow is shown in Figure 2.

 

2.2 Key Equipment and Process Parameters
2.2.1 Hydraulic Shearing Technology
Equipment Selection: YJ-160 hydraulic shears are used, as shown in Figure 3. Maximum shearing force is 160kN, blade width is 40mm, suitable for 8-12mm venting branches. Working state is shown in Figure 4.

 

Process Parameters: Shearing speed 50mm/s, single shearing time 2.5s; for 4 venting branches, 8 cuts are used, total time 20s.
2.2.2 Robotic Arm Collision Process
Tool Configuration: Collision fixture is shown in Figure 5, collision state is shown in Figure 6.

 

Actuator: ABBIRB4600 robotic arm, load 110kg, repeatability ±0.06mm.
Motion Trajectory: A composite motion of "vertical oscillation + horizontal rotation" is used, oscillation frequency 2Hz, rotation angle ±45°, single collision cycle time 3s.
Results Data: The average removal time for 32 outer slag blisters was 96 seconds, with impact force controlled at 200-300 N, and surface impact deformation of casting ≤0.1 mm.
2.2.3 Pneumatic Hammering Process
Tool Configuration: Ingersoll Rand 2130Ti pneumatic hammer, impact frequency 2000 bpm, impact force 50-150 N, equipped with a 300 mm extension rod, as shown in Figure 7. Working status is shown in Figure 8.

 

Path Planning: 8 slag blisters were treated in a "side first, then inner cavity" sequence, with each strike taking 3 seconds, for a total of 24 seconds.
Process Optimization: For sensitive areas <5 mm from casting body, segmented striking was used, with each impact stroke lasting 5 mm to avoid stress concentration and localized deformation.
2.2.4 Precision Aluminum Cutting Process
Equipment Configuration: Band saw adopts a double-column structure, with a saw blade linear speed of 20m/s, equipped with a servo feed system, and a feed accuracy of ±0.05mm, as shown in Figure 9.

 

Jig Design: A three-point positioning fixture is used, with casting fixed by a pneumatic pressure plate. Clamping force is 8kN, angle between sawing path and inner gate axis is controlled at 5-8°, as shown in Figure 10.
Quality Control: Residual gate thickness after sawing is ≤1mm, and surface roughness Ra is ≤6.3μm.

3.1 Efficiency Comparison
To verify efficiency improvement of combined removal scheme, 10 shifts of 67051015-1DC shell castings were continuously produced on same die-casting island using three processes: traditional edge-cutting mold, manual, and combined automated scheme. Processing time, failure rate, and daily production capacity of each casting unit were statistically analyzed for each process. Average value of 10 shifts was taken, and results are shown in Table 1.
Table 1. Production Efficiency Comparison

3.2 Actual Quality Improvement
Traditional edge-trimming dies utilize a edge-trimming machine to provide pressure and remove sprue from casting using a cutting edge. This method results in chipping issues in casting, requires a large safety margin, and leads to a large amount of residual sprue. Manual removal uses a hand saw, which causes inconsistent sprue height and damage during casting handling. Combined removal method allows for precise control of residual sprue height and eliminates chipping and damage issues. Table 2 shows results of statistically analyzing residual sprue height and number of damaged or dented castings under each of three process methods.
Table 2. Comparison of Casting Quality

As shown in Table 2, using traditional edge-trimming die, manual, and combined automated methods, average residual sprue height decreased from 3mm to 1mm; casting damage rate decreased from 3% to 1.2%, and there were no visible dents in the areas affected by impacts or knocks.
Furthermore, working environment was improved, significantly reducing labor intensity of workers.

4.1 Technological Innovation
(1) Process Integration: Through modular combination of "shear-knock-knock-saw," limitations of traditional single processes are overcome, achieving fully automated processing of complex gating systems.
(2) Flexible Design: Configuration of robotic arms and replaceable tooling makes this solution applicable to multiple types of castings with similar structures (such as different models of gearbox housings), with a changeover time ≤30min.
(3) Quality-Efficiency Co-optimization: Processing cycle is highly matched with die-casting machine cycle time (195s vs 200s), achieving seamless connection between "die-casting and gating removal."
4.2 Development Prospects
Intelligent Upgrade: An AI vision inspection system can be introduced to identify residual defects in gating system in real time and trigger automatic reprocessing, increasing yield rate to over 99%.
Green Manufacturing: A cutting fluid recycling system (recovery rate ≥95%) and a centralized waste chip treatment device can be developed to further reduce environmental impact.
Multi-axis linkage technology: Exploring application of six-axis robotic arms in processing of complex internal cavities to achieve "dead-angle" dewatering and drainage, and expanding scope of process applicability.