Solving Porosity in High-Gastight Die Casting: A Deep Dive into Advanced Mold Design for Automotive Valve Plates
This technical summary is based on the academic paper "Design and Practice of Die Casting Die for High Gastight Valve Plate" by KUANG Xin-wen, ZHANG Zheng-lai, and JIA Zhi-xin, published in FOUNDRY (2019).
Keywords
- Primary Keyword: High-Gastight Die Casting
- Secondary Keywords: Porosity Defects, Die Casting Mold Design, Cooling System, Gating System, Venting System, A380 Aluminum Alloy, Automotive Components
Executive Summary
- The Challenge: To successfully manufacture a complex A380 aluminum alloy automotive valve plate with extremely stringent requirements for internal porosity and gastightness.
- The Method: A holistic mold design optimization was implemented, focusing on a CAE-driven gating and venting system, a nearly integrated core structure for superior thermal management, and an advanced cooling system featuring high-pressure spot cooling and innovative atomized cooling for deep cores.
- The Key Breakthrough: The multi-faceted design approach effectively mitigated porosity defects, achieving a 98% product qualification rate and enabling high-efficiency, fully automated production.
- The Bottom Line: Strategic mold design, particularly in thermal management and gas evacuation, is paramount for achieving high gastightness in complex die-cast parts, directly boosting both quality and production efficiency.
The Challenge: Why This Research Matters for HPDC Professionals
In the demanding world of new energy vehicle components, performance and reliability are non-negotiable. This research addresses the production of a critical A380 aluminum alloy valve plate, a component where internal integrity is everything. The part's complex geometry presents a classic die-casting nightmare:
* Uneven Wall Thickness: Ranging from a thin 2.81 mm to a thick 9.53 mm, creating thermal imbalances and hot spots prone to shrinkage porosity.
* Deep, Slender Cores: Two critical valve holes feature a depth-to-diameter ratio as high as 14, making them difficult to cool effectively and prone to defects.
* Strict Gastightness Requirements: The valve holes, piston bores, and other key surfaces have zero tolerance for porosity that could lead to leakage. Industrial CT scans demand internal pore diameters to be less than 0.3 mm with a total porosity under 5% in critical zones.
For any engineer working with complex, high-performance castings, these challenges are all too familiar. Standard mold design practices are often insufficient, leading to high scrap rates, production bottlenecks, and compromised component reliability. This paper tackles these issues head-on.
The Approach: Unpacking the Methodology
The authors systematically addressed the causes of porosity through a series of intelligent mold design optimizations, validated by CAE analysis and production data.
Method 1: CAE-Optimized Gating and Venting System
To ensure smooth metal flow and efficient gas evacuation, the system was meticulously designed using mold flow analysis. The final design featured four inner gates for balanced filling and eleven overflow runners placed at the end of the flow path. Critically, the venting channels were engineered with a wave-form profile to reduce the impact of escaping gas and prevent blockage, ensuring the cavity is fully purged of air before solidification.
Method 2: Integrated Core Structure for Uniform Thermal Control
Instead of relying on numerous small inserts, which can disrupt heat flow and create thermal inconsistencies, the designers opted for a nearly integrated core structure. This approach ensures that heat from the molten aluminum is transferred away from the cavity more rapidly and uniformly. This stable and balanced thermal field is crucial for minimizing flow resistance, turbulence, and local overheating—all primary contributors to porosity and shrinkage defects.
Method 3: Advanced Cooling System with Targeted Spot Cooling
A sophisticated cooling strategy was implemented to manage the mold's thermal profile. This included:
* Conventional Channels: A network of circular and linear cooling channels provided general cooling to the main areas of the fixed and moving die halves.
* High-Pressure Spot Cooling: A total of 25 high-pressure spot coolers were strategically placed in the fixed die to aggressively cool localized hot spots.
* Innovative Atomized Cooling for Deep Cores: For the challenging deep valve cores, a traditional end-return cooling method was insufficient. The team implemented an advanced "atomized spot cooling" system. This technique ensures the entire length of the core pin is cooled evenly and effectively, preventing the formation of shrinkage porosity deep within the valve holes.
Method 4: Synchronized Ejection for Defect-Free Demolding
To prevent the complex part from deforming or sticking during ejection, the system was reinforced. In addition to standard guide pins and bushings, a high-precision gear and rack mechanism was integrated. This system ensures the ejector plate moves with perfect balance and synchronicity, guaranteeing a smooth, stable ejection cycle and eliminating a common source of production scrap.
The Breakthrough: Key Findings & Data
The implementation of this advanced mold design yielded exceptional results in a real-world production environment.
Finding 1: High-Efficiency, Automated Production Achieved
The robust and thermally stable mold design enabled a fully automated production cell. The process was so efficient and reliable that it achieved a production rate of 600 qualified parts per 8-hour shift, demonstrating a significant improvement in productivity.
Finding 2: Superior Product Quality and Mold Longevity
The primary goal of achieving high gastightness was met with outstanding success. The finished castings consistently met the stringent internal quality standards, resulting in a product qualification rate of 98%. Furthermore, the durable and well-engineered mold demonstrated excellent longevity, reaching a service life of 150,000 cycles. Figure 8 in the paper shows the final machined valve plate, a testament to the quality achieved.
Practical Implications for R&D and Operations
- For Process Engineers: This study suggests that adjusting cooling strategies for deep-core or thick-section features can yield significant returns. The success of atomized spot cooling (Figure 5) demonstrates that targeted, high-efficiency cooling is a powerful tool for reducing or eliminating shrinkage porosity.
- For Quality Control Teams: The data in Table 1 of the paper, which specifies different porosity limits (PC1, PC2, PC3) for different functional areas of the part, illustrates the importance of location-specific quality criteria. This approach, verified by CT scanning, can help focus quality efforts where they matter most.
- For Design Engineers: The findings indicate that the fundamental structure of the mold core (integrated vs. insert-heavy) has a profound influence on thermal management and defect formation. This suggests that prioritizing uniform heat transfer in the early mold design phase is a critical step toward first-time-right production of complex components.
Paper Details
Design and Practice of Die Casting Die for High Gastight Valve Plate
1. Overview:
- Title: Design and Practice of Die Casting Die for High Gastight Valve Plate
- Author: KUANG Xin-wen, ZHANG Zheng-lai, JIA Zhi-xin
- Year of publication: 2019
- Journal/academic society of publication: FOUNDRY
- Keywords: Die casting; Gas hole; Die casting die; Cooling system
2. Abstract:
The causes of gas hole formation in die castings were analyzed. According to the structural characteristics and high gastightness requirements of an aluminum alloy valve plate, the die casting mold was optimized through the rational design of the core structure, gating and venting system. The cooling for the high-gastight holes was enhanced and an air blow and spray coating structure was implemented. The mold temperature was monitored and controlled by combining water channels with high-pressure spot cooling. This approach ensures the quality of the product and improves the service life and production efficiency of the mold.
3. Introduction:
This study focuses on a valve plate component for new energy vehicles, as shown in Figure 1. The part has a single-piece weight of 2.1 kg, is made of A380 aluminum alloy, and has dimensions of 280 mm × 170 mm × 53 mm. As a plate-shell type part, it has a complex structure and is prone to deformation during ejection. The part's structural characteristics include: (1) highly non-uniform wall thickness, ranging from a minimum of 2.81 mm to a maximum of 9.53 mm, with multiple hot spots that are highly susceptible to defects such as gas holes, shrinkage porosity, and cracks; (2) two valve holes with a diameter of 9.1 mm and depths of 130 mm and 80 mm respectively, resulting in a high depth-to-diameter ratio of up to 14, which requires a rational deep-hole core-pulling structure; (3) two piston holes on each side with a depth of 120 mm, requiring side core-pulling; (4) stringent porosity requirements for the valve core holes, piston holes, valve plate face, and battery cell holes. The two valve holes, in particular, have strict internal quality requirements verified by industrial CT, with internal gas and shrinkage pores required to be less than 0.3 mm in diameter and a porosity rate of less than 5%. The main difficulties with this die casting are the strict gastightness requirements (Table 1) and the high propensity for deformation during ejection.
4. Summary of the study:
Background of the research topic:
The production of complex, high-performance components for the new energy vehicle industry, such as this valve plate, demands advanced die casting solutions that can reliably meet stringent standards for low porosity and high gastightness.
Status of previous research:
The paper acknowledges established knowledge regarding the causes of porosity in aluminum die castings. These causes are categorized as: (1) poor melt quality due to inadequate refining and degassing (hydrogen porosity); (2) improper mold venting leading to entrapped air; (3) incorrect die casting parameters (e.g., excessively high filling speed) causing gas entrapment (blowholes); (4) volumetric shrinkage during solidification (shrinkage porosity); and (5) porosity resulting from large variations in wall thickness, which creates isolated hot spots.
Purpose of the study:
The objective was to develop a comprehensive die casting mold design and an associated production process capable of manufacturing a complex A380 aluminum alloy valve plate that meets strict gastightness requirements, achieves low internal porosity, and allows for high-efficiency production.
Core study:
The study centers on a multi-faceted optimization of the die casting mold for the valve plate. The core technical contributions include:
1. Optimization of the gating and venting system using CAE analysis to ensure balanced filling and complete evacuation of cavity gases.
2. Adoption of a nearly integrated mold core structure to promote uniform heat transfer and minimize thermal imbalances.
3. Implementation of an advanced, digitally controlled cooling system that combines conventional cooling channels with high-pressure spot cooling.
4. Development of an innovative "atomized spot cooling" method specifically for the deep valve cores to ensure uniform cooling and prevent shrinkage.
5. Integration of an inner spray and air blow structure on the sliders for the long core pins to reduce friction and prevent galling.
6. Use of a gear-and-rack synchronized ejection system to ensure stable, deformation-free part removal.
5. Research Methodology
Research Design:
The research followed an applied engineering design and case study methodology. It began with a systematic analysis of the root causes of porosity defects common to such castings. Based on this analysis, a series of targeted design solutions for the mold's structural, thermal, and mechanical systems were proposed and implemented. The efficacy of these design solutions was then validated through industrial production trials and rigorous quality inspection of the resulting parts.
Data Collection and Analysis Methods:
CAE mold flow simulation was utilized in the initial design phase to optimize the gating and venting system. For quality verification, industrial CT (Computed Tomography) scanning was employed to inspect the internal porosity of the castings, with results compared against the quantitative requirements outlined in Table 1. Performance of the overall solution was evaluated by collecting production data, including cycle time, qualified part output per shift, and total mold service life.
Research Topics and Scope:
The research is narrowly focused on the die casting mold design for a specific high-gastight A380 aluminum alloy valve plate intended for use in new energy vehicles. The scope of the investigation covers the analysis of porosity formation mechanisms and the detailed design of the mold's key subsystems: the gating system, venting system, core structure, cooling system, and ejection system.
6. Key Results:
Key Results:
- The optimized mold design and process enabled fully automated, continuous, and efficient production.
- A high production rate of 600 qualified parts per 8-hour shift was achieved.
- The castings successfully met all specified gastightness requirements, resulting in a final product qualification rate of 98%.
- The mold demonstrated excellent durability, achieving a service life of 150,000 casting cycles.
Figure Name List:
- 图1 车用铝合金阀板
- 图2 浇注系统、排气系统设计以及液压抽芯机构
- 图3 动、定模芯设计
- 图4 定模芯冷却水道和点冷布局
- 图5 型芯处加强冷却
- 图6 滑块上设计内置喷涂和吹气结构示意图
- 图7 顶出系统齿轮齿条机构
- 图8 加工后的阀板压铸件
7. Conclusion:
This paper presents the mold structure developed for producing a new energy vehicle valve plate, with a primary focus on measures to reduce porosity. The combination of cooling channels and high-pressure spot cooling, particularly the enhanced cooling and air-blowing structure for small core parts, along with a rational design of the gating and venting system, allows for effective monitoring and control of the mold temperature. This comprehensive approach ensures the quality of the product while improving both the service life of the mold and the overall production efficiency.
8. References:
- [1] 潘宪曾. 压铸模设计手册 [M]. 北京: 机械工业出版社, 2006.
- [2] 崔黎明, 姚三九, 苏建磊. 铝合金泵盖压铸件气孔缺陷分析及对策[J]. 铸造技术, 2007, 28 ( 12) : 1662-1665.
- [3] 徐义武, 詹凤伟. 压铸件气孔缺陷分析及解决方案[J]. 特种铸造及有色合金, 2013, 33 ( 2) : 151-154.
- [4] 历长云, 王有超, 许磊, 等. 铸造工艺参数对ADC12铝合金支架压铸件缺陷的影响[J]. 特种铸造及有色合金, 2010, 30 ( 12) : 1120-1122.
- [5] 张正来, 贾志欣. 具有深孔抽芯的壳盖压铸模设计[J]. 铸造, 2018, 67 ( 8) : 688-691.
Expert Q&A: Your Top Questions Answered
Q1: Why was a nearly integrated core structure preferred over a design with many separate inserts?
A1: According to the paper, a structure with numerous inserts can lead to poor thermal conductivity across the assembly, resulting in an uneven mold temperature field. This can cause increased flow resistance, turbulence, and local overheating, all of which contribute to the formation of porosity and shrinkage defects. The nearly integrated structure was chosen to ensure rapid and uniform heat transfer, creating a stable thermal balance that is conducive to producing a sound casting.
Q2: What was the specific innovation in the cooling of the deep valve cores, and why was it necessary?
A2: The innovation was the use of an "atomized spot cooling" system. Traditional end-return spot cooling primarily cools the tip of the core, leaving the rest of the pin hotter and causing uneven cooling, which leads to shrinkage porosity. The atomized cooling method, as detailed in Section 3.3.2 and Figure 5, ensures that the entire forming section of the core pin is cooled effectively and uniformly, which was critical for eliminating defects deep within the high-L/D-ratio valve holes.
Q3: How did the mold design address the evacuation of air and gas from the cavity during the fast filling process?
A3: The design used a CAE-optimized gating and venting system. To ensure complete gas evacuation, 11 overflow runners were placed at the final filling points of the cavity. Furthermore, the venting channels connected to these overflows were designed with a wave-form shape. This specific geometry, as mentioned in Section 3.1, is designed to reduce the impact force of the exiting gas, preventing premature blockage of the vents by solidified metal and ensuring a clear path for air to escape.
Q4: What specific mechanism was used to prevent part deformation during ejection?
A4: While standard guide pins and bushings were used, the design was enhanced with a gear and rack mechanism. As described in Section 3.4 and shown in Figure 7, four sets of gears and racks were installed around the mold base. This system mechanically synchronizes the movement of the ejector plate, ensuring it advances with exceptional balance and stability, thereby preventing the complex part from being twisted or distorted during ejection.
Q5: The paper mentions an "inner spray and gas blow structure" on the slider for the long core pins. What was its purpose?
A5: This structure, shown in Figure 6, served a dual purpose for the long core pins that form the valve holes. During the mold open sequence, it first sprays a layer of lubricant directly onto the surface of the core pin. It then blows compressed air to evenly distribute the lubricant and cool the pin. This process significantly reduces friction between the core pin and the solidified aluminum casting, preventing galling and sticking during core retraction.
Q6: According to the paper, what are the primary causes of porosity in aluminum die castings like this one?
A6: The paper outlines five primary causes in Section 2. These are: 1) Poor refining and degassing of the molten aluminum, leading to dissolved hydrogen being released during solidification. 2) Inadequate mold venting, which traps air inside the cavity. 3) Improper die casting parameters, such as excessive fill speed, which can cause the liquid metal to fold over and entrap gas. 4) Volumetric shrinkage as the aluminum solidifies, creating shrinkage porosity. 5) Large variations in the part's wall thickness, which creates isolated hot spots that are the last to solidify and are prone to porosity.
Conclusion: Paving the Way for Higher Quality and Productivity
The successful production of this complex valve plate underscores a critical principle in modern manufacturing: achieving success in High-Gastight Die Casting is not about a single solution, but a holistic, intelligent approach to mold design. By systematically analyzing the root causes of porosity and implementing advanced, targeted solutions for thermal management, gas evacuation, and mechanical stability, the authors transformed a challenging component into a high-volume, high-quality success story. The key breakthrough—combining CAE-driven design with innovative cooling and ejection systems—provides a clear roadmap for overcoming similar challenges in other critical automotive and industrial components.
At CASTMAN, we are committed to applying the latest industry research to help our customers achieve higher productivity and quality. If the challenges discussed in this paper align with your operational goals, contact our engineering team to explore how these principles can be implemented in your components.
Copyright Information
This content is a summary and analysis based on the paper "Design and Practice of Die Casting Die for High Gastight Valve Plate" by "KUANG Xin-wen, ZHANG Zheng-lai, JIA Zhi-xin".
Source: This paper was published in the journal FOUNDRY, Vol. 68, No. 8, 2019.
This material is for informational purposes only. Unauthorized commercial use is prohibited.
Copyright © 2025 CASTMAN. All rights reserved.