Casting Process: Die Casting vs. Investment Casting
Investment casting and die casting share several similarities, making it challenging to determine the most suitable method for a particular product. Investment casting excels in producing metal parts with exceptional surface finishes, typically in the 125 RMS range, albeit requiring the creation of a new mold for each cycle. On the other hand, die casting proves economically advantageous for non-ferrous parts and large production volumes.
Whether you are working on a new part fabrication and wish to avoid committing to the tooling costs associated with die casting, or you are scaling up production and seeking a cost-effective manufacturing option, the decision-making process can be intricate.
This article delves deeply into the comparison between investment casting and die casting, aiming to provide insights that will help you better understand and evaluate your production options.
Investment casting vs die casting, here are additional distinctions to consider:
Casting Material:
The die or mold used in die casting is typically constructed from stainless steel, a ferrous metal. Consequently, ferrous metals are not suitable for die casting. In contrast, the investment or precision casting technique accommodates both ferrous and non-ferrous metals.
Size of the Part:
Die casting is constrained by the size of the mold and the capacity of the machine, determining the size of the parts produced. In investment casting, the size of parts is not limited by a mold. It proves versatile in casting single or a few large parts cost-effectively.
Surface Finish of the Parts:
Die casting parts necessitate additional finishing efforts to achieve satisfactory surface quality. Conversely, investment casting parts inherently possess excellent surface finishing. Although some finishing work is still required, it is not as extensive as in die casting.
Complex Design:
For intricate product designs, the die casting technique is preferred. This is because the liquid metal may struggle to reach complex areas in the cavity during investment casting. In die casting, various methods such as pressure or vacuum are employed to ensure the molten metal reaches intricate areas effectively.
Investment Casting Process
There are three primary types of presses employed in stamping operations: mechanical, hydraulic, and mechanical servo.
Investment casting, also known as precision or lost wax casting, is a meticulous metalworking process designed to produce precise parts and components with exceptional finishes while minimizing material waste. The name “lost wax casting” originates from the initial stages of the process, where a wax pattern is crafted and then immersed in a ceramic slurry until it solidifies. Subsequently, the wax is melted away, leaving behind a robust mold employed for casting metal parts.
To comprehend its significance in manufacturing, a comprehensive understanding of the entire casting process and the distinctions between investment casting and die casting is crucial.
1. Create Wax Pattern:
• Develop a pattern of the desired part or component through 3D printing or by constructing a wax injection die.
• If a 3D printed pattern is utilized, a CAD model sends product specifications to a printer for production.
• For a wax injection die, an aluminum die is fabricated, which can range from simple single-cavity structures to complex multi-cavity designs based on production volume requirements.
2. Wax Assembly:
• Attach wax patterns to a sprue and organize them into a tree structure.
• Imperfections are meticulously removed from the wax to closely resemble the finished part.
3. Ceramic Coating:
• Immerse the entire assembly in a ceramic slurry, creating a shell around the wax.
• Utilize different ceramic materials with varying properties during coating, preserving intricate details with fine materials and adding hardness and strength with coarser materials.
• Repeat the dipping process until the investment reaches the desired thickness, then allow the mold to set and harden.
4. Dewaxing:
• Invert the cured ceramic mold and subject it to a furnace, where the wax from the initial pattern is melted or evaporated.
• This stage is critical, as ceramic mold failures often occur due to the rapid expansion of wax under heat, placing stress on the mold.
5. Casting:
• Pour or force molten metal into the mold under pressure to create the cast part.
• Allow the mold with molten metal to sit and solidify.
6. Divesting:
• Remove the ceramic shell through vibration, hammering, media blasting, or water ejecting to release the final cast part.
• Clean the part (grinding) to eliminate any remnants of the casting process.
7. Finishing:
• Employ additional grinding techniques to eliminate negatives or impurities, using welding or hand tooling if necessary.
8. Testing:
• Inspect parts for surface or sub-surface defects using visual and fluorescent penetrant inspections.
• Optionally use x-ray inspection for uncovering sub-surface defects.
The entire process is then repeated to cast additional parts.
Die Casting Process
Die casting distinguishes itself from investment casting by utilizing a permanent mold or die that remains unchanged for each casting cycle. This method stands out as the most efficient approach for producing precise non-ferrous metal parts. Two die casting methods, known as the hot chamber and cold chamber methods, exist, differing mainly in machinery and metal, while sharing the majority of the casting process.
In the initial steps, a steel die containing the pattern for a part is crafted. These molds are typically formed in two sections, sometimes more, securely held together on a machine. Molten metal is injected into the die, allowed to cool, and then the die halves are separated to eject the casting. This repetitive process enables manufacturers to swiftly produce numerous parts and components.
The complexity of the finished part determines whether the casting dies will be simple or include cores and movable sides. Dies exhibit durability, enduring 150,000 to over 1,000,000 cycles before necessitating replacement or repairs.
Hot Chamber Method:
In the hot chamber die casting, the same basic steps are followed. This method is suitable for metal alloys with lower melting points. In hot chamber machines, metal is heated in a furnace connected to the machine and delivered to the die through a gooseneck. This process is rapid, with cycle times ranging from under a second for smaller parts weighing less than an ounce to thirty seconds for heavier castings.
Cold Chamber Method:
The primary distinction between cold chamber and hot chamber casting lies in the location of the furnace. Metals with higher melting points demand a robust furnace and more energy to achieve a molten state. Hot chamber machinery would erode at these temperatures, specifically the injection components. Cold chamber machines feature a separate chamber where molten metals are poured. Metal is heated in a furnace apart from the machinery and either poured into the chamber manually or via automatic ladle, making the process less efficient than its hot chamber counterpart.
Applications of Investment Casting Compared to Die Casting
The versatility of investment casting is evident across various industries, answering the common question of what types of parts can be investment cast. Its applications span nearly limitless possibilities, with numerous sectors benefiting from this intricate process.
Investment Casting Applications:
• Power Generation and Aerospace: Employed for crafting turbine blades featuring intricate shapes and complex cooling systems.
• Firearm Manufacturing: Utilized to produce precision parts like hammers, triggers, and other components.
• Oil and Gas Industry: Applied for creating pressure relief and safety components for equipment.
• Automotive: Widely used for various automotive components.
• Food Service: Found in components for food service industry applications.
• Defense: Significant in crafting parts for defense equipment.
• Medical: Utilized in the production of critical medical components.
• Agriculture: Benefits from investment cast parts in specific applications.
Die Casting Applications:
• Automotive Industry: Integral for transmission, engine components, GPS, and entertainment system housings.
• General Motors Innovation: Pioneering techniques like the Acurad method, with applications in the defense sector.
• Recreation and Landscaping: Used in crafting RV chassis, outboard gear cases, hydrostatic axles, and marine undercuts.
• Healthcare Sector: Essential for life-sustaining hospital equipment such as blood analysis machines, peristaltic pumps, surgical devices, and controls.
Both investment casting and die casting find their places across a multitude of industries, providing tailored solutions for specific needs with efficiency and accuracy.
Advantages and Disadvantages of Die Casting:
Advantages:
• Cost-Effectiveness: Economical for higher production volumes.
• Near-Net-Shape Parts: Capable of producing parts with minimal secondary machining.
• Rapid and Consistent Production: Efficiently produces reliable and consistent parts.
• Excellent Dimensional Tolerance: Die-cast parts exhibit superior dimensional accuracy.
Disadvantages:
• High Porosity: Susceptible to high porosity, making it less suitable for parts requiring high hardness.
• No Heat Treatment: Inability to undergo heat treatment due to porosity.
• High Cost for Smaller Runs: Costly for smaller production quantities.
• Challenges with Core-Casting: Difficulty in casting parts that necessitate cores.
• Limited to Non-Ferrous Metals: Constrained to non-ferrous metal applications.
Advantages and Disadvantages of Investment Casting:
Advantages:
• Complex Geometries: Ideal for parts and components with intricate geometries.
• High Tolerances: Achieves high tolerance levels in parts and components.
• Superior Surface Finishes: Provides excellent surface finishes without requiring additional operations.
• Economical Production: An economical solution for parts that typically require welding or secondary processes.
• Versatility in Metal Casting: Capable of casting both ferrous and non-ferrous metals.
Disadvantages:
• Longer Cycle Times: Requires longer cycle times for creating new ceramic molds, contributing to overall costs.
• Challenges with Core-Casting: Similar to die casting, faces challenges in casting parts that demand cores.
• Costly Binders and Refractory: Involves expenses related to binders and refractory materials for mold creation.
Is Investment Casting More Costly than Die Casting?
The production cost comparison between investment casting and die casting hinges on several factors. When dealing with large production volumes, creating parts through investment casting tends to be more expensive than die casting. This is primarily due to the manual nature of investment casting, which results in a slower production pace. Manufacturers can generate a greater quantity of die casting parts within a given timeframe.
In essence, manufacturing investment casting parts requires more time, necessitating additional labor, thereby elevating overall production costs. Conversely, for small volume production, die casting proves to be more expensive. The substantial expense of die casting machines, coupled with insufficient production volume to offset the costs, contributes to this scenario.
The overall cost also relies on the tooling and machining aspects of the parts. Investment casting parts involve lower tooling costs but more machining than their die casting counterparts. Consequently, in cases of small production volumes, investment casting is preferable due to the significant savings in tooling costs outweighing the machining expenses. However, in large volume production, the higher machining costs make investment casting more expensive than die casting.
Choosing the Right Casting Method for Your Parts
When determining the optimal casting method for your specific production needs, take the following variables into consideration:
Material:
Both investment casting and die casting are suitable for non-ferrous metals. However, if your preference is copper or stainless steel alloys, investment casting emerges as the superior choice.
Budget:
The labor-intensive nature of investment casting can elevate costs, primarily attributed to tooling expenses. Die casting, with its greater need for tooling and frequent reliance on secondary machining processes, proves to be more cost-effective for longer production runs.
Design Complexity:
Investment casting offers unparalleled flexibility in handling intricate designs and incorporating changes to a part. It allows for easy integration of product numbers and logos, a level of detail that die casting cannot match.
Part Size:
Investment casting has size limitations due to the repeated dipping required for creating a ceramic mold from the wax pattern. It accommodates parts ranging from one ounce to about 200 pounds. Die casting, while generally less restrictive, follows the principle that larger parts incur larger tooling costs.
Cycle Time:
Die casting takes the lead in cycle time efficiency, boasting the capability to produce over 45 shots per minute. Additionally, die casting can be fully automated, unlike investment casting, which demands additional labor.
Surface Finish:
Investment cast parts exhibit superior finishes compared to die casting, with a standard of 125 micro finish.
Tolerance:
Tolerance levels are contingent on both the part’s shape and material. In general, die cast parts up to 25mm begin with a tolerance of +/- 0.050mm, increasing with larger sizes. Similarly, investment cast parts of the same size commence with a tolerance of +/- 0.250mm, scaling with the part’s dimensions.
Conclusion: Making Informed Casting Decisions
Determining the optimal casting process for your part involves navigating through various trade-offs associated with each method. Allow our experienced team to assist you in gaining a comprehensive understanding of your options and identifying the ideal manufacturing partner capable of delivering high-quality parts at competitive prices.
