When specifying and purchasing metal castings, there are several important considerations to keep in mind. First and foremost, it is crucial to ensure that the casting meets the necessary requirements for the intended application. This includes factors such as size, shape, and material composition.
Another important consideration is the quality of the casting itself. This can be influenced by a variety of factors, including the casting process used, the skill and experience of the manufacturer, and the quality of the raw materials used. It is important to work with a reputable manufacturer who has a proven track record of producing high-quality castings that meet the necessary specifications.
Finally, the cost is also an important consideration when specifying and purchasing metal castings. While it is important to ensure that the casting meets all necessary requirements and is of high quality, it is also important to keep costs in mind and work within a budget. By carefully considering all of these factors, it is possible to ensure that the metal casting procured is of the highest quality and meets all necessary requirements for the intended application.
Material Selection Considerations
When specifying and purchasing metal castings, material selection is a critical consideration. The choice of material will affect the performance, durability, and cost of the casting. Here are some factors to consider when selecting a material:
- Strength and Hardness: The strength and hardness of the material should be appropriate for the application. For example, if the casting will be subjected to high stress or wear, a stronger and harder material may be required.
- Corrosion Resistance: If the casting will be exposed to corrosive environments, a material with good corrosion resistance should be selected. This can help to prevent degradation and prolong the life of the casting.
- Temperature Resistance: If the casting will be exposed to high temperatures, a material with good temperature resistance should be selected. This can help to prevent deformation or failure of the casting.
- Machinability: Some materials are easier to machine than others. If the casting will require machining after casting, a material with good machinability should be selected.
- Cost: The cost of the material should also be considered. While it may be tempting to select a high-performance material, it may not be cost-effective for the application.
Overall, the material selection should be based on careful consideration of the application requirements, performance needs, and cost constraints. By selecting the right material, the casting can provide optimal performance and durability.
Design Considerations
When specifying and purchasing metal castings, design considerations play a crucial role in ensuring that the final product meets the required specifications and performs as intended. Here are some key design considerations to keep in mind:
1. Material Selection: The choice of material is critical in determining the performance and durability of the metal casting. Factors to consider include the mechanical properties of the material, its resistance to corrosion, and its ability to withstand high temperatures.
2. Part Complexity: The complexity of the part will impact the casting process and the final product’s quality. More complex parts require more intricate casting processes, which can increase production costs and lead times.
3. Wall Thickness: The thickness of the walls in the casting can affect the part’s strength and durability. Thicker walls can provide greater strength, but they can also lead to issues such as shrinkage and warping during the casting process.
4. Draft Angle: A draft angle refers to the taper applied to the walls of the casting to aid in its removal from the mold. A sufficient draft angle is necessary to ensure that the casting can be removed without damaging it.
5. Surface Finish: The surface finish of the casting can impact the part’s aesthetics, functionality, and durability. The desired surface finish should be specified early in the design process to ensure that the casting process can achieve the desired results.
In summary, when specifying and purchasing metal castings, careful consideration of design factors is critical. Material selection, part complexity, wall thickness, draft angle, and surface finish are all key factors to consider to ensure that the final product meets the required specifications and performs as intended.
Manufacturing Considerations
When specifying and purchasing metal castings, it is important to consider the manufacturing process. The quality of the final product is dependent on the manufacturing process, and any errors or issues during production can result in defects or failure of the castings.
One important consideration is the type of casting process used. Different processes, such as sand casting, investment casting, or die casting, have their own advantages and disadvantages. For example, sand casting is a low-cost method that can produce large parts, but may have a lower surface finish and dimensional accuracy compared to other processes.
Another consideration is the material used for the casting. The properties of the material, such as strength, corrosion resistance, and thermal conductivity, can affect the performance of the final product. It is important to select the appropriate material for the intended application.
The design of the casting also plays a crucial role in the manufacturing process. The design should be optimized for the selected casting process and material, taking into account factors such as wall thickness, draft angles, and fillets. A well-designed casting can reduce the risk of defects and improve the overall quality of the product.
In addition, the manufacturing facility should have appropriate quality control measures in place to ensure consistent and reliable production. This can include inspection and testing of raw materials, monitoring of process parameters, and inspection of finished castings.
Overall, considering the manufacturing process when specifying and purchasing metal castings can help ensure a high-quality final product that meets the intended requirements.
Quality Considerations
When specifying and purchasing metal castings, quality is of utmost importance. The following are some quality considerations that should be taken into account:
- Material selection: The choice of material used for the casting will have a significant impact on the quality of the final product. It is important to select a material that is appropriate for the intended use and that meets the required specifications.
- Surface finish: The surface finish of a casting can affect its performance and appearance. The desired surface finish should be specified upfront, and the casting process should be optimized to achieve the desired result.
- Tolerances: Tolerances refer to the allowable variation in dimensions and other properties of the casting. It is important to specify the required tolerances upfront and to ensure that they are met during the casting process.
- Testing and inspection: Quality control measures such as testing and inspection should be in place to ensure that the casting meets the required specifications. This can include non-destructive testing, dimensional inspection, and material testing.
- Traceability: Traceability refers to the ability to track a casting back to its source material and manufacturing process. This is important for quality control and for identifying any issues that may arise.
By considering these quality factors when specifying and purchasing metal castings, the end result will be a high-quality product that meets the required specifications and performs as intended.
Cost Considerations
When specifying and purchasing metal castings, cost is a major consideration. It is important to balance cost with quality and performance requirements. Here are some factors to consider when evaluating the cost of metal castings:
- Material costs: The cost of the raw materials used in the casting process can vary widely depending on the type of metal used. For example, aluminum is generally less expensive than bronze or iron.
- Production volume: The cost per unit of a casting can vary depending on the volume of production. High volume production typically results in lower costs per unit.
- Design complexity: The more complex the design of the casting, the more expensive it will be to produce. This is because more intricate designs require more time and skill to create.
- Tooling costs: Tooling costs can be a significant factor in the overall cost of a casting. The cost of tooling will depend on the complexity of the design and the volume of production.
- Post-processing costs: Depending on the requirements of the final product, post-processing may be necessary. This can include machining, finishing, and coating. These additional processes can add to the overall cost of the casting.
It is important to work closely with the casting supplier to understand the cost implications of each of these factors and to find the right balance between cost and quality.
Metal casting is a complex process that requires numerous considerations when purchasing, including casting design, the metal casting process to be used, and quality control factors. Ultimately, there are many considerations in metal casting and there is no “one size fits all” solution. Therefore, we developed an outline of the various considerations when a customer selects a metal casting solution. Before reviewing important considerations in metal casting, let us review MetalTek’s metal casting processes.
Materials Used By Metal Casting Process
Sand Casting Materials
The sand casting process produces metal components of all sizes and shapes with exterior detail and inner passages using cores (if needed). Almost any alloy can be sand cast. In sand casting the “purchased tool” is a pattern that replicates the part to be cast. Patterns are usually hardwoods, polyurethane, or other durable material. The non-reusable sand mold is created by inserting the pattern into a bed of sand, compressing the sand, and removing the pattern. This leaves a cavity in the shape of the part.
Molten metal is poured into this cavity by a series of hollow pathways called risers and runners. After metal solidification, all previously hollow areas (risers, runners, and the cavity made from the pattern) are solid metal. The risers and runners are removed, leaving a metal part resembling the pattern.
Investment Casting Materials
In investment casting, the tooling is a die with an inner cavity that resembles the part. Wax is injected into this cavity to create a wax pattern. The wax pattern is assembled onto a “tree” with other patterns, which is dipped into a ceramic material to create a shell. The wax pattern is melted away, resulting in a hollow shell into which molten metal is poured.
After solidification, the shell and tree are removed. Relative to other metal casting processes, the final part can have a smoother surface, higher dimensional precision, and thinner walls. This results in cost savings due to lower part weight and less post-cast processing. With investment casting, there is a large selection of alloys during the material selection process.
Centrifugal Casting Materials
With centrifugal casting, the basic tooling is typically a steel die into which molten metal is poured. Dies are rotated around a vertical axis (for “ring” shapes) or a horizontal axis (for “tube” shapes). This metal casting process uses centrifugal force to cause heavier material (metal) to move toward the outside diameter (OD) of the ring, and lighter material (oxides and other impurities) to migrate toward the inside diameter (ID).
The metal will solidify from the OD towards the ID, leaving the purest metal on the outside of the metal casting and pushing the less pure elements toward the center. The ID is machined to remove impurities, leaving a solid ring or tube of the highest casting quality.
Important Considerations When Selecting A Casting Process
Choosing The Right Alloy For The Operating Environment
There are important considerations in casting that customers need to be aware of before choosing the specific metal casting type (centrifugal casting, investment casting, or sand casting). For example, what is the operating environment? Will the component experience high heat? High wear? Both? Will the component need to stand up to corrosion from saltwater?
Once the specific operating environment is defined then the appropriate alloy can be chosen. Alloy selection mirrors environmental factors, as various alloys hold up better in extreme temperature conditions, under high wear, or in corrosive environments.
Optimizing The Manufacturing Process
Any engineer designing a part has a primary objective for the function of the part in question. This objective is subject to a variety of competing constraints. We have already discussed the operating environment, which helps determine a minimum baseline for the material/metal used.
Optimizing the manufacturing process involves identifying and prioritizing all competing constraints. It is imperative to recognize that these competing constraints typically require the customer and metal casting supplier to determine the optimal balance of cost, quality requirements, and speed to market. The next section provides a deeper look into the primary considerations for each major metal casting process.
Balancing Cost, Quality Requirements, And Speed To Market
Presuming that the geometry, metallurgical requirements, and total quantity of parts validate the use of metal castings, here are some general considerations among MetalTek’s three major metal casting processes:
Sand Casting
Sand casting benefits:
- Lower piece price, tool cost, and lead time
- Broad range of geometries, including holes/passages not machinable
- Near-net shape to reduce machining costs
- Minimal size constraints
- Custom metallurgical compositions
Sand casting limitations:
- Dimensional tolerances (per ISO 8062 CT10 to CT12) not typically as tight as investment casting
- Cast thickness of 1/4″ to 3/8″ for limited distances; typically minimum of 1/2″ for larger parts
- Machining required to improve as-cast surface finish (250+ RMS)
- Air-melted alloys
Sand casting best fits:
- Low (single piece) to very high production volume
- Need to eliminate machining and/or fabrication
- Wide range of metallurgical compositions (heat, corrosion, and wear-resistant alloys)
- Use of additive manufacturing/3D printing for sand molds or tooling to reduce cost
- Custom and/or complex geometries
Investment Casting
Investment casting benefits:
- Higher metallurgical quality
- Tight dimensional control
- Smoother surface (80-125 RMS)
- Minimal metal waste in casting
- Little or no machining
- Can use with vacuum-melted alloys and air-melted alloys
- Broader range of geometries, including tighter dimensions and tolerances
Investment casting limitations:
- Higher piece price, tool cost, and lead time
- Size limited to 40” cube
Investment casting best fits:
- Medium to very high volume
- Expensive or exotic alloys
- Part weight restrictions (e.g., aerospace applications)
- Extreme heat in operating environment
- Many working surfaces or flow paths
Centrifugal Casting
Centrifugal casting benefits:
- Directional solidification provides the highest metallurgical quality and superior machinability
- Minimal or no tooling costs for most tube or ring geometries
- Can cast tubes and machine into multiple ring shapes
- Lower costs and lead times than rolled-ring forgings
- Could utilize sand, investment, or other material molds to increase quality in those geometries
Centrifugal casting limitations:
- Geometries are somewhat limited to rings and tubes (which can limit production lot sizes)
- Used primarily with air-melt alloys, with limited size availability for vacuum alloys.
- Must machine ID (it is the riser for the casting)
- OD usually requires machining to remove “orange-peel” surface.
Centrifugal casting best fits:
- Ring or tube geometries competing against forgings
- Some shaped geometries (extra tooling) where higher metallurgical quality is mandatory
How Does Hengke Metal Meet Quality Requirements?
Hengke Metal carefully reviews quality requirements from drawings and specifications prior to accepting an order. We comply with all industry standards for allowable tolerances in the various metal casting processes, documented by all required/agreed-upon certifications. In process, we go one step further to ensure compliance with metallurgical requirements.
Hengke Metal uses a solidification modeling program to simulate the flow of molten metal into a mold and analyze the predicted solidification as the mold cools. This model will help in the tool design, including locations for gates and risers, to ensure a metallurgically compliant part.
Hengke Metal’s Advantages
Hengke Metal strives to build a collaborative relationship with every customer, to best meet both technical and commercial requirements. The customer’s engineering personnel are the experts in the design of their part, and Hengke Metal is the expert in alloys and metal casting processes.
We can leverage our wealth of technical expertise and vast industry experience to help your company choose the optimal product design and manufacturing process to meet your objectives.
Contact us and let us help you with your next project.