1. Introduction
1.1 Background of Cylinder Head Integrated Exhaust Technology
The cylinder head integrated exhaust technology is a significant breakthrough in cylinder head casting technology. In traditional engine design, the cylinder head and exhaust manifold are designed separately, resulting in high development costs, complex manufacturing processes, and high waste rates. With the improvement of emission requirements, this integrated technology has become a standard for meeting national six emissions, offering excellent effects on reducing engine cold start emissions and reducing costs.
1.2 Challenges in IEM Cylinder Head Casting
Although the integrated technology has many advantages, its casting difficulty is much higher than that of traditional cylinder heads. The complex waterway structure poses higher requirements for casting processes, especially low – pressure casting. In actual production, various casting defects such as cold shuts, cracks, insufficient pouring, shrinkage cavities, and oxide inclusions may occur. This paper focuses on analyzing the causes of cold shut defects in typical low – pressure casting IEM cylinder heads and proposing preventive and control measures.
2. Product and Forming Process
2.1 Material and Structure
The cylinder head of a certain series of engines in our company is a small cylinder head produced by low – pressure metal mold casting process, using a material similar to AC4B aluminum alloy. The total weight of the casting is about 16Kg, with dimensions of approximately 458 * 288 * 142. The water channels, air channels, and oil chambers are formed by sand cores, and the sand core material is resin sand.
2.2 Forming Process
The product adopts a bottom – injection low – pressure casting process, with upper, lower, left, right, front and rear parting metal molds for forming. The casting pressure, temperature, time, and cooling are all automatically controlled by the pouring machine. After casting, the appearance quality is manually inspected. The waterway sand cores are formed by a hot core box process, and the shooting core temperature, pressure, time, and sintering time are automatically controlled by the core making machine. After sintering, the sintering thickness and sand core appearance are manually inspected.
3. Problems Encountered
During the rapid increase in production volume of the engine, the workshop reported severe cold shuts on the cylinder head, especially at the small end sensor position, with an average rejection rate as high as 1%. This has seriously affected the achievement of workshop quality and cost targets and requires a quick solution.
4. Cause Analysis
4.1 Mechanism Analysis
Cold shuts mainly occur due to poor aluminum liquid fluidity and unreasonable mold temperature during the filling and solidification of the casting, causing the aluminum liquid to be blocked in the cavity. This defect affects the overall strength, machining quality, and product performance of the casting.
4.2 Analysis of Suspected Factors
The project team initially identified factors such as mold differences, equipment differences, labor time, filling pressure – time, cooling time – flow, aluminum liquid temperature, coating shedding status, mold exhaust grooves, and small end structure through brainstorming and further analysis.
4.3 Abnormal Investigation and Verification
- Mold and Equipment Differences: Through statistical analysis and two – factor variance analysis, it was determined that different molds and equipment are not the key factors affecting the cold shut defect rate at the small end sensor outer wall.
- Artificial Time: By comparing the production quality of different pouring machines with different artificial time fluctuations, it was found that artificial time fluctuations are not a key factor affecting the cold shut defect.
- Cooling Time – Flow: CAE analysis showed that changes in cooling – flow near the small end have little impact on the mold temperature field, so cooling time – flow is not a key factor.
- Coating Shedding State: Through double ratio tests on different production periods of a certain pouring machine mold, it was determined that the coating shedding state is not a key factor affecting the cold shut defect.
- Aluminum Liquid Temperature: By setting different aluminum liquid temperatures for production and conducting chi – square tests, it was found that aluminum liquid temperature is not a key factor affecting the cold shut defect.
- Small End Structure: Through small – batch verification of changes to the small end structure, it was determined that the small end structure is a key factor affecting the cold shut defect. Optimizing the structure by adding reinforcing ribs can reduce the cold shut defect rate.
- Mold Exhaust Groove: Through improvement and verification of mold exhaust grooves, it was found that mold exhaust is not a key factor affecting the cold shut defect.
- Filling Pressure – Time: By adjusting the filling pressure and conducting double ratio tests, it was determined that filling pressure – time is a key factor affecting the cold shut defect. Appropriate increase in specific pressure can improve the cold shut defect.
5. Improvement Measures
5.1 Verification of Improvement Measures in Large Quantities
- Filling Pressure – Time: After increasing the specific pressure according to the verification conclusion of small – batch production for half a month, and conducting large – quantity verification, it was found that the cold shut defect rate was significantly reduced.
- Small End Structure: After adding reinforcing ribs to the small end sensor position during a certain period and conducting large – quantity verification, it was found that the cold shut defect rate was reduced, indicating that the improvement measure of optimizing the small end structure is effective.
5.2 Solidification of Improvement Measures
After large – quantity verification, it was determined that the previously analyzed measures are effective. Therefore, the improvement measures were solidified. This includes changing the process and control plan to ensure the consistency of process execution, and making 3D changes to the product and mold to ensure the consistency of product data and on – site execution and the inheritance of experience.
6. Verification Results
The above measures have been implemented on other models of this series and newly developed engines, and the improvement effect is significant. The defect rate has been significantly reduced, and the defects have been basically eliminated.
7. Conclusions
7.1 Importance of Product Design Consideration
During product design, potential problems during casting filling and solidification should be fully considered. Through reasonable design of process structures such as exhaust grooves and reinforcing ribs and the formation of corresponding problem avoidance tables, experience can be accumulated for subsequent models.
7.2 Application of Analytical Tools
In the process of problem analysis and solution, tools such as Six Sigma can be used to systematically analyze and verify causes and problems, which is beneficial for quickly discovering and systematically solving problems…
7.3 Significance of the Research
The research on the cold shut defect of low – pressure casting IEM cylinder heads is of great significance. It not only helps to solve the practical problems faced by the company in the production process but also provides a reference for the industry in dealing with similar casting defects.
7.3.1 Solving Practical Production Problems
In the production of IEM cylinder heads, the high rejection rate due to cold shut defects has a direct impact on the production cost and product quality. By accurately analyzing the causes of the defects and implementing effective improvement measures, the company has successfully reduced the defect rate, improved product quality, and achieved better economic benefits. This has ensured the smooth progress of production and enhanced the competitiveness of the company’s products in the market.
7.3.2 Industry Reference
The methods and processes used in this research can be applied to other similar casting products. The systematic analysis of various factors affecting the cold shut defect and the verification of improvement measures provide a valuable example for the industry. Other companies can learn from this research to better understand the causes of casting defects and take appropriate measures to improve product quality.
8. Future Research Directions
Although significant progress has been made in this research, there are still some areas that can be further explored.
8.1 Optimization of Process Parameters
The current research has identified some key factors affecting the cold shut defect and optimized the corresponding process parameters. However, there may still be room for further optimization of other process parameters. For example, the interaction between different process parameters and its impact on the cold shut defect can be further studied. By conducting more in – depth research on process parameters, it is possible to achieve better control of the casting process and further reduce the defect rate.
8.2 Application of New Materials and Technologies
With the continuous development of materials science and manufacturing technology, new materials and technologies may offer potential solutions to casting defects. For example, the application of advanced ceramic materials or new alloy materials may improve the fluidity of the molten metal and reduce the occurrence of cold shut defects. At the same time, new manufacturing technologies such as additive manufacturing may also provide new ways to optimize the casting structure and process. Future research can explore the application of these new materials and technologies in the casting of IEM cylinder heads to further improve product quality.
8.3 Modeling and Simulation of Casting Processes
Modeling and simulation of casting processes can provide a more accurate understanding of the physical phenomena occurring during casting. By using advanced simulation software, it is possible to predict the occurrence of cold shut defects and optimize the casting process in advance. Future research can focus on improving the accuracy of casting process simulation models and using simulation results to guide the actual production process. This will help to reduce the trial – and – error process in production and improve production efficiency.
9. Discussion on the Relationship between Different Factors and Cold Shut Defects
The occurrence of cold shut defects is affected by multiple factors, and the relationship between these factors is complex. Understanding the interaction between different factors is crucial for effectively preventing and controlling cold shut defects.
9.1 Interaction between Mold Temperature and Aluminum Liquid Temperature
Mold temperature and aluminum liquid temperature have a significant impact on the fluidity of the aluminum liquid. If the mold temperature is too low, the aluminum liquid near the mold wall will cool down quickly, reducing its fluidity and increasing the likelihood of cold shut defects. On the other hand, if the aluminum liquid temperature is too low, it will also lead to poor fluidity and cold shut defects. The interaction between the two temperatures needs to be carefully controlled to ensure the proper fluidity of the aluminum liquid. For example, when adjusting the aluminum liquid temperature, the impact on the mold temperature should also be considered, and vice versa.
9.2 Impact of Small End Structure on Filling Pressure
The small end structure of the cylinder head affects the filling path and pressure of the aluminum liquid. A complex or improper small end structure may lead to an increase in filling pressure and a decrease in filling speed, which in turn may cause cold shut defects. By optimizing the small end structure, such as adding reinforcing ribs, the filling path can be improved, and the filling pressure can be more evenly distributed, reducing the occurrence of cold shut defects.
9.3 Role of Mold Exhaust in the Overall Casting Process
Mold exhaust is an important part of the casting process. Poor mold exhaust can lead to the accumulation of gas in the mold cavity, which affects the fluidity of the aluminum liquid and increases the likelihood of cold shut defects. Adequate mold exhaust can ensure the smooth flow of the aluminum liquid and the normal progress of the casting process. Therefore, in the design and operation of the casting process, attention should be paid to ensuring good mold exhaust conditions.
10. Summary of the Overall Research Process
The research on the cold shut defect of low – pressure casting IEM cylinder heads is a comprehensive process that involves multiple steps and methods.
10.1 Problem Identification
The first step is to identify the problem of cold shut defects in the IEM cylinder heads. This is based on the feedback from the production workshop, where a high rejection rate due to cold shuts was observed.
10.2 Cause Analysis
After identifying the problem, a detailed cause analysis was conducted. This involved analyzing the mechanism of cold shut defects and identifying various possible factors that could affect the defect. Through a series of investigations and analyses, including statistical analysis, two – factor variance analysis, and small – batch verification, the key factors affecting the cold shut defect were determined.
10.3 Improvement Measures
Based on the cause analysis, improvement measures were proposed and implemented. These measures included optimizing the small end structure and adjusting the filling pressure. The improvement measures were then verified in large quantities to ensure their effectiveness.
10.4 Verification Results
The verification results showed that the improvement measures were effective, with a significant reduction in the defect rate. The measures were then solidified to ensure their long – term application in the production process.
10.5 Conclusions and Future Directions
Finally, conclusions were drawn from the research, highlighting the importance of product design and the application of analytical tools. Future research directions were also proposed, focusing on process parameter optimization, new material and technology applications, and casting process simulation.
11. Implications for the Casting Industry
The research on the cold shut defect of low – pressure casting IEM cylinder heads has several implications for the casting industry.
11.1 Quality Control in Casting Production
The research emphasizes the importance of quality control in casting production. By accurately analyzing the causes of defects and implementing effective improvement measures, it is possible to improve product quality and reduce the rejection rate. This provides a model for other casting companies to follow in their quality control efforts.
11.2 Innovation in Casting Technology
The research also highlights the need for innovation in casting technology. By exploring new materials and technologies and optimizing process parameters, it is possible to improve the performance of casting processes and products. This encourages the casting industry to continuously invest in research and development and drive technological progress.
11.2.1 New Materials Exploration
The exploration of new materials such as advanced ceramic materials or new alloy materials can bring new opportunities for improving casting quality. These materials may have better properties such as improved fluidity or higher strength, which can help to reduce casting defects.
11.2.2 Process Parameter Optimization
Optimizing process parameters is an important way to improve casting quality. By studying the interaction between different process parameters and their impact on casting defects, it is possible to find the optimal combination of parameters to achieve better control of the casting process.
11.3 Industry Collaboration and Knowledge Sharing
The research also implies the importance of industry collaboration and knowledge sharing. By sharing research findings and experiences, the casting industry can avoid repeating mistakes and accelerate technological progress. This can be achieved through industry conferences, research collaborations, and knowledge sharing platforms.
12. Case Studies of Similar Casting Defects in Other Products
To further illustrate the universality of the research methods and findings, case studies of similar casting defects in other products are presented.
12.1 Gravity Casting of a Certain Aluminum Alloy Part
In the gravity casting of a certain aluminum alloy part, similar cold shut defects were observed. By applying a similar analysis process as in the IEM cylinder head research, the causes of the defects were identified. These included factors such as improper mold design, low aluminum liquid temperature, and poor mold exhaust. After implementing improvement measures similar to those in the IIM cylinder head research, such as optimizing the mold design and adjusting the aluminum liquid temperature, the defect rate was significantly reduced.
12.2 Low – Pressure Casting of a Steel Casting
In the low – pressure casting of a steel casting, cold shut defects were also a problem. The analysis process revealed that factors such as inappropriate filling pressure and poor mold temperature control…