DESIGN OF GATING SYSTEM ON PISTON OF MOBIL SINJAI WITH GRAVITY DIE CASTING METHOD

Eliminating Shrinkage Defects in Piston Casting: A Gating System Design Breakthrough

This technical summary is based on the academic paper "DESIGN OF GATING SYSTEM ON PISTON OF MOBIL SINJAI WITH GRAVITY DIE CASTING METHOD" by Rizki Yustisiabellah, published by Institut Teknologi Sepuluh Nopember (2015).

Gambar 2.1 Hasil eksperimen dan simulasi (a)Trail 1(b) trail 2 (c) trail 3 (d) trail 4 [4]
Gambar 2.1 Hasil eksperimen dan simulasi (a)Trail 1(b) trail 2 (c) trail 3 (d) trail 4 [4]

Keywords

  • Primary Keyword: Gating System Design
  • Secondary Keywords: Gravity Die Casting, Piston Casting, Shrinkage Defects, Aluminum ADC 12, Casting Simulation

Executive Summary

  • The Challenge: The gravity die casting process for an ADC 12 aluminum alloy piston was producing unacceptable levels of shrinkage and porosity, leading to high scrap rates and the need for costly physical trial-and-error redesigns.
  • The Method: The study utilized advanced casting simulation software to design and validate four distinct gating systems, systematically optimizing riser dimensions and core materials to control solidification.
  • The Key Breakthrough: A simulation-optimized gating system (Type 2) incorporating a 90 mm diameter riser and a cast iron core successfully reduced shrinkage defects to just 0.84% while completely eliminating porosity indications.
  • The Bottom Line: Simulation-driven Gating System Design is a powerful, cost-effective strategy for resolving complex solidification defects, dramatically improving the quality and manufacturability of critical components like aluminum pistons.

The Challenge: Why This Research Matters for HPDC Professionals

In the production of high-performance engine components, consistency is paramount. The subject of this study, the piston for the "Mobil Sinjai," was manufactured using gravity die casting with ADC 12 aluminum. However, the initial process was flawed, resulting in significant shrinkage defects, particularly around the pin area.

Even after an initial redesign that cast the piston with its final valve cutout geometry to avoid machining, the parts were still plagued by surface porosity on the piston skirt—a critical area for load-bearing and stress management. For any casting operation, defects like these reduce mechanical properties and lead to component failure. The conventional path to a solution involves fabricating multiple new dies for trial-and-error testing, a process that is both time-consuming and extremely expensive. This research was initiated to prove that a data-driven, simulation-first approach could solve the defect problem while bypassing the high costs of physical prototyping.

The Approach: Unpacking the Methodology

The study's credibility is founded on a robust simulation methodology that accurately modeled real-world casting conditions to predict and solve the defect issues.

Method 1: High-Fidelity Casting Simulation
The researchers created a 3D model of the piston and its gating system. This model was then subjected to a casting simulation using parameters that mirrored the actual production environment. Key variables included the use of ADC 12 aluminum alloy, a molten metal pouring temperature of 700°C, a pre-heated gray cast iron die at 250°C (or 350°C), and a fill time of 2 seconds. This established a digital twin of the existing, problematic process.

Method 2: Iterative Gating System Design
Four distinct gating system configurations were designed and simulated to isolate the impact of key design features on defect formation:
- Type 1 & 3: These designs represented different part orientations without a riser, serving as a baseline to quantify the initial shrinkage problem.
- Type 2 & 4: These designs incorporated an open riser, a critical feature for feeding molten metal to the casting as it solidifies and shrinks. The diameter of this riser was systematically varied from 50 mm to 90 mm to find the optimal size for defect compensation.

Method 3: Material and Geometry Optimization
Based on the results of the initial simulations, the most promising gating systems were subjected to a final round of optimization. This involved simulating the process with two different core materials (the standard cast iron vs. silica sand) and two different piston head geometries (with the valve cutout vs. a flat top). This allowed the researchers to find the ideal combination that minimized defects while maximizing manufacturability and final part quality.

The Breakthrough: Key Findings & Data

The simulation results provided clear, actionable data demonstrating how specific design choices directly impact casting quality.

Finding 1: The Critical Role of the Riser in Reducing Shrinkage

The data unequivocally proved the necessity of a well-designed riser. As documented in Table 4.2, the baseline Gating System Type 1 (without a riser) produced a massive shrinkage defect of 8.69%. By simply adding a 60 mm riser in the Type 2 design, shrinkage was immediately reduced to 4.86%. This finding highlights that a riser is not optional but essential for feeding the casting during solidification to prevent voids.

Finding 2: Optimizing Riser Diameter is Key to Minimizing Defects

The study further demonstrated that the size of the riser is critical. For Gating System Type 2, simulations were run with riser diameters from 50 mm to 90 mm. As shown in Table 4.3, increasing the riser diameter to 90 mm allowed it to stay molten longer and feed the casting more effectively, reducing shrinkage to a final, minimal value of 0.84%. Similarly, for the Type 4 system, a 70 mm riser was found to be optimal, achieving the study's lowest shrinkage value of 0.54% (Table 4.4).

Practical Implications for R&D and Operations

  • For Process Engineers: This study suggests that adjusting the riser diameter is a primary lever for controlling shrinkage defects in gravity-cast aluminum parts. The data shows a direct correlation between increased riser volume (specifically, a 90 mm diameter for the Type 2 system) and a drastic reduction in shrinkage, from over 8% to under 1%.
  • For Quality Control Teams: The porosity analysis using LCC and Niyama criteria (Table 4.5) provides a powerful predictive tool. The data illustrates that the Type 2 design with a 90 mm riser showed no indications of porosity, establishing a clear quality benchmark. In contrast, the Type 4 system, despite its low shrinkage, showed potential porosity at the pin boss, highlighting a potential failure point.
  • For Design Engineers: The findings indicate that core material selection is critical. Using a cast iron core resulted in superior outcomes (0.84% shrinkage) compared to a silica sand core (1.83% shrinkage) due to its higher thermal conductivity promoting favorable solidification. Furthermore, designing the component with net-shape features like the valve cutout eliminates the need for post-machining, which the paper notes can introduce stress concentrations on thermally critical surfaces.

Paper Details


DESIGN OF GATING SYSTEM ON PISTON OF MOBIL SINJAI WITH GRAVITY DIE CASTING METHOD

1. Overview:

  • Title: DESIGN OF GATING SYSTEM ON PISTON OF MOBIL SINJAI WITH GRAVITY DIE CASTING METHOD
  • Author: Rizki Yustisiabellah
  • Year of publication: 2015
  • Journal/academic society of publication: Institut Teknologi Sepuluh Nopember (ITS) Repository
  • Keywords: Allumunium ADC 12, Shrinkage, Simulation

2. Abstract:

Piston is a component of an engine which function is to foward energy from fuel when expanded into kinetics energy on a cracnkshaft through piston rod. The Piston of Sinjai use allumunium ADC and made by gravity die casting process. Yet, cast products still own a huge defectf so that the gating system need to be evaluated and redesigned. Remake of dies for die casting required a lot of money to spend. Casting simulation have theway to show the casting result and defect without done the experiment. Casting simulation would reduce the cost of trial and error so that will decrease corporates to invest int.o The research start with modeling the casting product as 3D and then run the simulation software with casting parameters which is smilliar with the environment to validate the experiment done before. Allumunium poured at 700° C on dies which already pre-heated at 250 C in2 sec pouring time. Riser added puposely for balancing solidification ratesto prevent shrinkage from happening. To find out what a riser capable of the first and the third gating system was no placed any riser. Riser with diameter of 60 mm added on second and fourth gate system. After simulation of the four gate have been done. Optimazion of casting by variating diameter of the riser. Cast product which has good quality, its gating system will be simulated by replacing gray cast iron as core with silica sand and profilled piston surface to a flat piston. The second gating system which has 60 mm riser lower the percentage of shrinkage to 4,86% from 8,69% which gating doesnt has any riser. The fourth gating with 70 mm riser has sucessfully decrease percentage of shrinkage significanly from 5 % without rise became 0,55%. but, design of the dies based on second gate with rise of 90 mm in diameter. Although shrinkage was higher than the others result was, cast product on tthe fourth was smoother on the surface, easier to be made, and easier to retrieve.

3. Introduction:

The Mobil Sinjai is a national Indonesian vehicle designed for the agricultural sector, featuring a 650 cc engine. A key component under development is its piston, which is produced by CV. ICCI using a gravity die casting method with cast iron molds. The initial production process yielded pistons with shrinkage defects at the pin section. A redesign of the gating system was performed, including the addition of a riser, which allowed for the production of pistons with two different crown geometries: one flat (requiring machining) and one with an integrated valve cutout. However, the piston with the integrated valve cutout still exhibited surface porosity defects on the piston skirt, a high-stress area. This defect compromises the mechanical properties of the component. This research was undertaken to redesign the gating system using simulation software to mitigate these defects, thereby avoiding the significant costs and time associated with the trial-and-error fabrication of new dies.

4. Summary of the study:

Background of the research topic:

The production of ADC 12 aluminum pistons for the Mobil Sinjai vehicle via gravity die casting resulted in persistent shrinkage and porosity defects. These defects compromise the mechanical integrity of the pistons and necessitate a costly and inefficient redesign process based on physical prototyping.

Status of previous research:

The study references prior work by Hussainy, S. Ferhathullah, et al. [4], which demonstrated the efficacy of using simulation software to identify and eliminate defects in gravity die-cast Al-alloy components. This precedent validates the use of computational modeling as a practical approach to redesigning gating systems and solving solidification-related problems.

Purpose of the study:

The objective of this research is to design a gating system capable of mitigating casting defects, specifically shrinkage and porosity, in the ADC 12 aluminum alloy piston for the Mobil Sinjai, utilizing the predictive capabilities of casting simulation software.

Core study:

The research involved the 3D modeling of the piston and four distinct gating system configurations. A series of casting simulations were conducted using a Rapid Solidification Shrinkage (RSS) model to analyze the casting process. The primary variables investigated were the presence and diameter of a riser (ranging from 50 mm to 90 mm), the material of the core (cast iron versus silica sand), and the geometry of the piston crown (integrated valve cutout versus a flat surface). The performance of each configuration was evaluated based on the resulting percentage of shrinkage (calculated from void volume) and an analysis of porosity potential using the LCC Criterion and Niyama Defect Criterion.

5. Research Methodology

Research Design:

The study employed a computational research design centered on Computational Fluid Dynamics (CFD) analysis of the casting process. A series of simulations were structured to systematically evaluate the impact of different gating system designs on casting defects.

Data Collection and Analysis Methods:

3D geometric models of the piston and gating systems were created in CAD software and exported in STL format. These models were imported into casting simulation software. The analysis involved a multi-step preprocessing phase: defining geometries and materials (ADC 12 Aluminum, Gray Cast Iron), creating a computational mesh, setting boundary conditions (e.g., wall temperatures), and defining metal input parameters. The simulation was run using a solver focused on solidification and shrinkage. Post-processing tools were used to visualize temperature distribution, identify hot spots, and quantify the volume of shrinkage voids to calculate the final shrinkage percentage.

Research Topics and Scope:

The research was focused on the design of a gating system for a gravity die-cast ADC 12 aluminum piston. The scope was constrained by a set of fixed parameters intended to reflect actual production conditions: a pouring temperature of 700°C, an initial die temperature of 250°C (for types 1-3) or 350°C (for type 4), and a pouring time of 2 seconds. The investigation centered on the influence of riser dimensions, core material, and piston head geometry on shrinkage and porosity defects.

6. Key Results:

Key Results:

  • The inclusion of a riser in the gating system was found to be critical for reducing shrinkage. Gating system type 2, with a 60 mm riser, decreased shrinkage from 8.69% (type 1, no riser) to 4.86%.
  • An increase in riser diameter generally leads to a decrease in shrinkage. For gating system type 2, the optimal diameter was 90 mm, which resulted in 0.84% shrinkage. For gating system type 4, a 70 mm riser was optimal, resulting in 0.54% shrinkage.
  • The use of a metallic (cast iron) core resulted in significantly lower shrinkage compared to a sand (silica) core. For the optimized type 2 system, the cast iron core produced 0.84% shrinkage, whereas the silica core resulted in 1.83% shrinkage.
  • Analysis using LCC and Niyama criteria indicated that the gating system type 2 with a 90 mm riser was free from porosity indications. In contrast, the type 4 system showed potential for porosity formation in the pin boss region.
  • The final proposed design, based on a holistic review of shrinkage, porosity, and manufacturability, was gating system type 2 with a 90 mm riser, a cast iron core, and an integrated valve cutout profile.

Figure Name List:

Gambar 2.2 Simulasi untuk optimasi hasil coran dengan riser berbentuk silinder (a) riser 30 mm (b) riser 35 mm [4]
Gambar 2.2 Simulasi untuk optimasi hasil coran dengan riser berbentuk silinder (a) riser 30 mm (b) riser 35 mm [4]
Gambar 2.3 Piston
Gambar 2.3 Piston
  • Gambar 1.1 Piston dengan matrass datar
  • Gambar 1.2 Piston dengan matrass berpola
  • Gambar 2.1 Hasil eksperimen dan simulasi
  • Gambar 2.2 Simulasi untuk optimasi hasil coran dengan riser berbentuk silinder
  • Gambar 2.3 Produk setelah perancangan ulang
  • Gambar 2.4 Piston
  • Gambar 2.5 Dua tipe mesin die casting
  • Gambar 2.6 Bottom-gated permanen mold
  • Gambar 2.7 Salah satu contoh bagaimana pengecoran dengan metode die casting didesain ulang
  • Gambar 2. 8 Cawan tuang
  • Gambar 2.9 Bentuk sprue
  • Gambar 2.10 Bentuk saluran turun dasar
  • Gambar 2.11Perangkap kotoran
  • Gambar 2.12 Saluran Masuk
  • Gambar 2.13 Jenis Riser
  • Gambar 2.14 Area sprue
  • Gambar 2.15 Gate dan runner area
  • Gambar 2.16Wall base area
  • Gambar 2.17 Penambah untuk paduan alumunium
  • Gambar 2.18 Cacat rongga udara
  • Gambar 2.19 Cacat surface crack
  • Gambar 2.20 Cacat penyusutan
  • Gambar 2.21 Ilustrasi terjadinya cacat penyusutan
  • Gambar 3.1 Flowchart Penelitian
  • Gambar 4.1 Model Piston Sinjai
  • Gambar 4.2 Bottom Gating Sistem 1 saluran
  • Gambar 4.3 Penampang runner
  • Gambar 4.4 Rancangan sistem saluran baru
  • Gambar 4.5 Rancangan Sistem Saluran dengan Penambah Atas
  • Gambar 4.6 Model 3D yang digunakan untuk simulasi
  • Gambar 4.7 Geometry Interpretation
  • Gambar 4.8 Solid Object
  • Gambar 4.9 Pengaturan Meshing
  • Gambar 4.10 Boundary Condition
  • Gambar 4.12 Metal Input
  • Gambar 4.12 Metal Parameter
  • Gambar 4.13 Heat Transfer Coefficient
  • Gambar 4.14 Solver Parameter
  • Gambar 4.15 Advanced Option
  • Gambar 4.16 Post Processing
  • Gambar 4.17 Model 3D gating system tipe 1
  • Gambar 4.18 Shringkage pada simulasi sistem yang ditunjukkan dengan void volume
  • Gambar 4.19 Temperatur pada kondisi logam
  • Gambar 4.20 Model 3D Gating system tipe 2
  • Gambar 4.21 Shrinkage pada simulasi
  • Gambar 4.22 Temperatur. pada kondisi
  • Gambar 4.23 Model 3D system gating system tipe 3 pada simulasi
  • Gambar 4.24 Shrinkage pada simulasi
  • Gambar 4.25 Temperatur logam pada kondisi
  • Gambar 4.26 Model 3Dgating system tipe 3
  • Gambar 4.27 Shrinkage pada simulasi
  • Gambar 4.28 Temperatur pada kondisi logam
  • Gambar 4.29 Cacat Shrinkage tampak atas dalam bentuk cube view
  • Gambar 4.30 Cacat shrinkage tampak samping dalam bentuk cube view
  • Gambar 4.31 Perbandingan persentase shrinkage dengan berbagai ukuran diameter pada dua jenis gating system
  • Gambar 4.32 Hasil simulasi gating system tipe 2 dengan riser 90 mm (a)Inti cast iron (b) inti pasir silica
  • Gambar 4.33 Gambar Hasil simulasi gating system tipe 4 dengan riser 70 mm (a)Inti cast iron (b) inti pasir silica
  • Gambar 4.34 Hasil simulasi gating system tipe 2 dengan riser 90 mm (a) piston memiliki valve cutout (b) piston dengan permukaan rata
  • Gambar 4.44 Gambar Hasil simulasi gating system tipe 4 dengan riser 70 mm (a) piston memiliki valve cutout (b) piston dengan permukaan rata
  • Gambar 4.45 Perencanaan Gating System untuk Piston Sinjai Dengan Gravity Die Casting

7. Conclusion:

Based on the research conducted, several conclusions can be drawn. First, an open riser can significantly reduce shrinkage when added to the gating system. Second, the analysis of LCC and Niyama defect criteria for the gating system type 2 with a 90 mm riser shows no indication of porosity defects. In contrast, the type 4 system with a 70 mm riser indicates potential porosity on the piston pin surface. Finally, the study resulted in a proposed design for gating system type 2, which utilizes a metallic core, a 90 mm riser, and a mold shape that includes the valve cutout profile. This design was selected based on considerations of no porosity indication, ease of mold manufacturing, and the ability to retrieve the cast part without the need for an ejector.

8. References:

  • [1] Surdia, Tata. 2006. Teknik Pengecoran Logam. 9th edition. Jakarta: PT. Pradnya Paramita.
  • [2] Flemings, Merton C. 1974. Solidification Processing. USA : McGrawhill
  • [3] Krar, Steve F. 1999. Illustrated Dictionary of Metal Working and Manufacturing Technology. USA : Mc Graw-Hill.
  • [4] Hussainy, S. Ferhathullah. 2015. A Practical Approach to Eliminate Defects in Gravity Die Cast Al-Alloy Casting Using Simulation Software. MJCET, Telangana, India.
  • [5] Resources, Tools and Basic Information for Engineering and Design of Technical Applications. (http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html) 7 Mei 2015.
  • [6] Alumunium Die Casting Manufacturer From China. (http://www.aludiecasting.com/support-data.php) 29 April 2015.
  • [7] H.H Doehler. 1951. Die Casting. USA : McGraw-Hill
  • [8] P.R. Beeley. 1972. Foundry Technology. USA : Buttertworth (Publisher) Inc
  • [9] Chidasama, Bhupendra J. 2013. Solidification Analysis and Optimization Using Pro Cast. S.P.B Patel Engineering College, Mehsana, India.
  • [10] Prayuga, Bayu. 2015. Rancang Bangun dan Analisa Simulasi Sistem Saluran terhadap cacat penyusutan (shrinkage) pada Pembuatan Kepala Silinder (Cylinder Head) Sinjai (Mesin jawa timur) 650 cc material Alumunium ADC 12 dengan Pengecoran Pasir Sand Casting).Institut Teknologi Sepuluh November, Surabaya.
  • [11] Stefanescu, D.M. 1988. ASM Handbook Volume 15 Casting. USA: ASM International
  • [12] Kurniawah, Moch. Wahyu. 2014. Analisis Kekuatan dan Deformasi Piston Mesin Bensin-Bio Etanol dan Gas Dengan Injeksi Langsung Untuk Kendaraan Nasional Dengan Simulasi Numerik).Institut Teknologi Sepuluh November, Surabaya.

Expert Q&A: Your Top Questions Answered

Q1: Why was the Type 2 gating system chosen as the final design when the Type 4 system achieved a lower absolute shrinkage value (0.54% vs. 0.84%)?

A1: The decision was based on a holistic assessment of quality and manufacturability. While the Type 4 system showed slightly lower shrinkage, the porosity analysis in Table 4.5 revealed it had a potential for porosity defects at the pin boss. The Type 2 system showed no such porosity risk. Furthermore, the conclusion on page 81 states the Type 2 design was easier to manufacture and allowed for part retrieval without a complex ejector system, making it the superior choice for production.

Q2: What is the practical significance of using a cast iron core instead of a silica sand core for this application?

A2: The study found that the cast iron core significantly reduced shrinkage compared to the silica sand core (0.84% vs. 1.83% for the best Type 2 design). This is because the metallic cast iron core has much higher thermal conductivity, which draws heat from the molten aluminum more quickly, promoting directional solidification and reducing the formation of isolated hot spots that lead to shrinkage voids. The paper also notes that metal cores generally yield better surface quality and mechanical properties in the final casting.

Q3: The paper recommends casting the piston with the integrated valve cutout rather than machining it later. Why is this important?

A3: The introduction on page 19 explains this rationale. Machining the piston crown creates a surface with different mechanical properties compared to the as-cast material beneath it. When the piston is subjected to the high thermal stresses of engine operation, this difference in properties can lead to stress concentrations, potentially causing material failure. Casting the valve cutout as a net-shape feature creates a more homogenous material structure, improving the component's durability and fatigue life.

Q4: How were the initial parameters for the simulation, such as the 700°C pouring temperature and 250°C die temperature, determined?

A4: These parameters were chosen to create a "digital twin" that accurately reflects the actual industrial process being studied. The abstract states the simulation was run with casting parameters "which is smilliar with the environment to validate the experiment done before." This ensures that the simulation results are not just theoretical but are directly applicable to solving the real-world production problem.

Q5: The study focuses heavily on shrinkage. How did the final recommended design address the other key defect, which was porosity on the piston skirt?

A5: The final design addresses porosity through multiple factors. The optimized Gating System Design ensures a controlled, non-turbulent fill, which prevents air entrapment. More importantly, the porosity analysis using the LCC and Niyama criteria (Table 4.5) for the final recommended design (Type 2 with a 90 mm riser) showed no indications of porosity formation anywhere in the casting. This predictive analysis confirmed that the design which solved the shrinkage problem also inherently solved the porosity problem.

Conclusion: Paving the Way for Higher Quality and Productivity

The persistent challenge of shrinkage and porosity in aluminum casting can lead to significant production losses and compromise component integrity. This study provides a clear and powerful demonstration that a simulation-led Gating System Design process is the most efficient path to resolving these complex solidification issues. By systematically modeling, testing, and optimizing the gating system in a virtual environment, the researchers were able to reduce shrinkage defects by over 90% and eliminate porosity, creating a robust, production-ready process without the immense cost of physical tooling iterations.

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 OF GATING SYSTEM ON PISTON OF MOBIL SINJAI WITH GRAVITY DIE CASTING METHOD" by "Rizki Yustisiabellah".

Source: https://core.ac.uk/display/80761229

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