The starting point of the casting process and metal casting design includes considering the factors that will determine the quality, performance, and manufacturability of the cast part.
The design process itself involves a detailed blueprint that uses various calculations that are dependent upon the requirements of the intended applications of the part.
From the metal’s castability to its machining requirements, there are a host of considerations to ponder over before even considering drafting up an initial blueprint.
In the following sections, 10 of the most crucial metal casting design considerations are listed.
They will give you a better understanding of the metal casting design process and how metal manufacturers use it to ensure the functionality and structural integrity of their metal castings.
Metal castability is the measure of a metal or metal alloy’s ability to be shaped and molded into intricate geometries via the casting process.
The metal’s level of castability directly affects the efficiency of the casting process and the quality of the final product.
The first factor manufacturers look at regarding metal castability is fluidity.
Different metals exhibit varying levels of fluidity when melted.
Metals with low fluidity struggle to reach all corners and crevices of a casting mold, which often leads to incomplete or distorted parts. Conversely, excessively high fluidity can result in turbulence and even mold material penetration.
Shrinkage during solidification is another metal casting consideration manufacturers look at during the design phase.
When molten metal cools and solidifies, it experiences contraction due to volume changes.
Metal manufacturers account for this inevitable shrinkage by calculating the metal’s shrinkage allowance and then incorporating additional volume or tapering in areas where it is needed.
The final consideration is the most obvious, choosing the right metal from a list of the most castable metals.
Several metals possess high castability, so manufacturers don’t have to stray too far and can keep their selection focused on this group.
This list includes:
Since the castability of a metal determines the ease with which it can be melted and poured into a mold, as well as its ability to flow and fill intricate patterns, it is one of the first design factors manufacturers look at during the casting design phase.
The shape, quality, and accuracy of a cast product are directly influenced by the features of the mold, which is why manufacturers look at several mold design factors before designing them.
The first factor manufacturers look at during the mold design phase is the draft angle as it can greatly facilitate the removal of the pattern design from the mold cavity during the design phase.
Altering the draft angle by providing a slight taper to the walls of the mold can reduce the chances of defects like cracks or distortion happening during solidification.
Another mold feature that manufacturers often consider before making the mold is whether or not they should include fillets and radii.
Rounded edges, provided by radii and fillets, help smooth out any uneven corners or sharp angles in the casting.
Not only does including fillets and radii reduce stress concentration points in the mold cavity but they can also increase fluid flow during pouring, resulting in improved mold filling and reduced turbulence.
The gating system design is yet another important feature that is looked at before designing a mold. It is a network of channels through which molten metal flows into the mold cavity.
By accurately designing gates and runners, proper metal flow, minimal turbulence and air entrapment within the castings, and uniform cooling within the mold are achieved.
Some of the other key factors manufacturers evaluate before designing a metal casting mold include:
Considering mold design factors such as draft angles, fillets and radii, and gating system design is essential for successful casting.
Furthermore, continuous evaluation of mold design based on heat resistance, durability, and solidification also helps in optimizing all areas of the casting process, resulting in the most efficient creation of high-quality products in the least amount of time.
Gating is one of the main considerations in mold design, but its importance extends well beyond this single factor.
For example, a well-designed gating system can balance and prevent defects such as misruns and cold shuts from occurring.
Through the strategic placement of gates and runners, casting defects can be reduced to a large extent.
Additionally, well-designed gating systems can have a strong influence on the solidification behavior of cast parts.
For instance, optimized gating systems can assist in controlling factors like cooling rates and directional solidification, which help manipulate grain structure and minimize defects caused by non-uniform solidification.
Gating design modifications like tapering or insulation are often incorporated to promote controlled solidification throughout the casting.
An added benefit of thorough gating design planning is the reduction of casting costs.
Optimizing gating systems for maximum function can lead to lower scrap rates and post-processing requirements like machining or welding.
To achieve the aforementioned benefits, metal manufacturers keep the following design features in mind:
The design of the gating system not only induces proper filling of the mold but helps minimize defects and casting costs.
Factors such as metal flow and temperature control, as well as efficient metal addition are all carefully considered when designing a metal casting gating system that is both efficient and cost-effective.
Parting lines serve as the boundary between the two halves of a die or mold.
They are where the stationary half (also referred to as the cope) and the moving half (also known as the drag) of the die or mold join together.
During the design and engineering phases, determining the location of the parting line is of utmost importance.
This is because its positioning will designate which side of the die will be the cover and which side will function as the ejector.
The die cover serves as a protective shell that encloses the cavity where the molten metal is poured and the die ejector is a mechanism for removing the final cast piece from the mold once it has solidified.
Since the quality of a metal cast part is heavily influenced by the placement of the parting line, a well-thought-out parting line location needs to be identified so that defects in the finished product will not appear.
The proper alignment and tight sealing of the die halves can effectively prevent leaks and flash formation during the casting procedure.
Moreover, a precise parting line location and shape will limit detrimental effects on part functionality.
Internal features such as ribs, bosses, and undercuts can all be enhanced by proper parting line locations.
The complexity of the parting line geometry is also a key consideration as this factor often dictates how easily molds can be separated during the demolding process.
Faster and more efficient demolding processes lead to lower production costs and faster cycle times.
Manufacturers and engineers often identify the most optimal parting lines through various means, the most common of which include:
Aside from parting line location, manufacturers also take into account several other features to improve aesthetics
These features include:
Parting lines help prevent leakage and ensure proper alignment of mold halves, resulting in precise and accurate castings.
Through careful analysis, manufacturers can design and place these lines in the right location, facilitating easy removal of the casting from the mold and reducing the risk of damage or distortion to the final product.
Part design influences various aspects of the casting process, from mold filling to machining operations.
A part should be designed in such a way that it can be easily and efficiently produced through the casting process.
The initial part design will have a substantial impact on not only the casting process but also on subsequent machining operations.
Designing parts with the correct wall thicknesses allows for easier removal of excess material during machining, reducing both time and costs.
One of the first considerations manufacturers look at when designing a metal part is the material they are going to use—different metals have varying properties and characteristics that can greatly impact the final product.
For example, if a casting requires high strength and resistance to wear and tear, then materials like carbon steel or stainless steel are often the best choice.
Another consideration is the complexity of the shape of the part.
Metal castings can offer great design flexibility, yet intricate shapes (e.g., concave shapes) can present a variety of challenges during the casting process.
Factors such as parting lines, draft angles, and undercuts all need careful consideration during the part design process to ensure successful casting production.
Part designers and manufacturers must also think about wall thickness and uniformity when coming up with a design.
As was mentioned earlier, wall thickness can affect both the cost and quality of the casting.
Thick walls may lead to longer solidification times and potential defects like shrinkage porosity or hot tears, while thin walls are prone to distortion and warping during the cooling phase.
Generally, manufacturers follow several steps when designing a cast part.
First, the manufacturer has to conceptualize the part. This includes understanding the part’s function, performance requirements, and operating environment.
Next,someone designs the part. This can be done using CAD software. A 3D model of the part is created, which includes all features of the final part: size, shape, and surface finish.
Since the part design will be highly influenced by the casting method used (e.g., sand casting, die casting, investment casting), it’s important to devise the right design process.
This decision will depend on factors like the part’s complexity, required precision, production volume, and cost considerations.
Creating the pattern follows. The pattern is a replica of the final part, taking into account the shrinkage that occurs when the metal solidifies.
After that, the mold is designed to have a cavity that is a negative of the pattern. It may also include cores if the part has internal features.
Finally, there’s creating a prototype of the part, as well as testing it to ensure it meets all functional and performance requirements.
A metal casting part design requires a good understanding of the part’s requirements, capabilities, and limitations regarding the different casting processes that can be used.
With a thorough understanding of the part design process and continuous improvement efforts, manufacturers, engineers, and foundry managers can achieve efficient and reliable casting production.
The solidification pattern in casting dictates the transformation of materials from a liquid to a solid state.
Analyzing this pattern offers valuable insights into the behavior and formation of metals and other materials during the casting process.
Several factors influence the solidification pattern: the cooling rate, material composition, and the presence of impurities.
Therefore, manufacturers must consider and comprehend these various factors to accurately predict how patterns will arise and react during casting,
By carefully considering the appropriate patterns, the mechanical properties and overall quality of castings can be improved, while simultaneously minimizing defects such as porosity or cracks.
One commonly observed solidification pattern is known as columnar (dendritic growth).
This pattern occurs when crystals begin forming at multiple nucleation sites within the molten material.
Columnar crystals grow in distinct directions until they collide and merge, resulting in larger grains which help increase strength, fatigue resistance, and dimensional accuracy in castings.
Another noteworthy solidification pattern is equiaxed (granular growth).
In this scenario, nucleation takes place randomly within the molten material leading to the formation of spherical shaped grains.
Granular growth is frequently observed in castings subjected to rapid cooling.
To achieve the desired solidification pattern, manufacturers consider the following options while designing the solidification process.
First, there is the rate of cooling, which needs to be controlled. The better the thermal conductivity and the greater the latent heat of crystallization of the casting alloy, the stronger the ability to cast to a uniform temperature and the smaller the temperature gradient.
Avoiding shrinkage defects during solidification can be accomplished by using risers.
Then, there are directional solidification and unidirectional solidification.
The first one is a fast solidification process where cooling starts from the bottom of the mold and reaches the top. This type of solidification results in higher impurity removal.
The latter, on the other hand, is a slow solidification process where cooling starts from top to bottom, resulting in a smoother surface.
The casting shape also needs to be considered. The time of solidification is directly proportional to the volume of surface area.
Therefore, the shape of the casting can greatly influence the pattern which is produced during solidification.
A well-controlled solidification process can lead to a casting with a better surface finish, less shrinkage and distortion, and more structural cohesion.
Controlling the cooling rate and ensuring more uniform solidification makes it possible for metal manufacturers to achieve the microstructure patterns and mechanical properties the metal casting will need to fulfill its application requirements.
Section changes refer to the fluctuation in thickness of a cast part.
They are significant because they can alter the properties of the final product quite drastically.
The rigidity of a section serves as a governing factor when determining the minimum thickness that can be designed for a section.
Thinner sections tend to cool and solidify at a quicker pace compared to their thicker counterparts.
Consequently, this disparity in cooling rates can lead to inconsistencies in the microstructure of the metal, resulting in defects, particularly shrinkage.
To ensure the proper changes in thickness during casting, manufacturers give careful consideration to the avoidance of sudden transitions and sharp corners within the sections.
The presence of sharp edges in a cast increases the likelihood of hot tears, shrinkage, and cracks during solidification.
Combating sudden transitions during solidification necessitates gradual transitions between sections to facilitate a more even distribution of stress.
Rapid fluctuations in section thickness can result in variations in cooling rates during solidification that can introduce internal stresses that compromise the integrity of the component.
During the design phase, manufacturers incorporate well-thought-out section changes into their metal casting design by following these guidelines.
While the above guidelines help manufacturers maintain a smoother surface change rate, close cooperation between the customers’ design engineers and the foundry’s casting engineers will still be necessary to optimize the casting design in terms of cost and performance.
Dimensional tolerance is the permissible deviation in dimensions of a cast product in relation to its desired or specified measurements.
Precise dimensional tolerance almost guarantees proper fitment, assembly, and interchangeability of components.
Achieving the desired dimensional tolerance requires careful control of various variables throughout the casting process.
The first step is paying close attention to mold design accuracy.
The mold serves as the blueprint for the cast metal, and therefore any deviations or inaccuracies in its design can directly impact the dimensional tolerance of the final product.
The second variable that must be considered is the selection and preparation of the material.
Different metals possess different characteristics, like thermal expansion coefficients and shrinkage rates.
Selecting a metal or alloy with a similar coefficient to that of the desired dimensions will minimize any potential dimensional variations caused by thermal effects from occurring.
Aside from the previously mentioned guidelines, there are two other guidelines manufacturers tend to follow to ensure proper dimensional tolerances.
These include tolerance and machining allowance grades, as well as allowances.
Following a set standard such as The International Standard ISO 8062 provides a system of tolerance grades and machining allowance grades for cast metals and alloys that can be systematically employed.
On the other hand, there are the allowances.
The shapes of cast metal components reflect not only the functional requirements of the component but also the manufacturability requirements dictated by the casting process.
For instance, castings must incorporate the proper draft allowances for successful mold-making and machining.
Manufacturers oftentimes use technologies such as computer-aided design (CAD) software and non-destructive testing (NDT) methods to help predict potential dimensional discrepancies before the actual casting process begins.
Precise measurements and tolerances can be predicted by controlling variables such as mold design accuracy, material selection and preparation, and utilizing advanced technologies.
With careful consideration and implementation of such factors, the metal casting will produce parts with accurate dimensions that fulfill their desired requirements.
A good surface finish enhances the overall visual appeal and functionality of the end product.
The term “surface finish” encompasses the quality and texture of the outer layer of a cast metal component.
The surface finish does not necessarily have to be smooth or rough for that matter as surface texture will entirely depend on the design requirements.
An impeccably smooth and glossy metal surface tends to exude a sense of opulence and precision, while a rough or textured surface can offer improved grip or enhanced adhesion for specific applications.
One influential factor that affects surface finish is the chosen casting process. For instance, in sand casting, the quality of the mold plays a crucial role in determining the final surface finish.
A mold containing fine sand grains facilitates the achievement of a smoother surface compared to one constructed with coarse sand particles.
In addition to casting process considerations, material selection also has a notable impact on surface finish.
Different metals have different degrees of hardness and grain structure.
By consciously selecting the materials suitable for casting purposes, manufacturers can achieve not only visually appealing finishes but also add functional improvements like corrosion resistance to their end product.
There are a few other important considerations manufacturers look at to ensure a good surface finish for metal castings.
These include:
When metal manufacturers pay careful attention to intricate details such as grain size in molds and the choice of post-processing treatments, they can design a casting process that has the potential to create beautifully finished and functionally optimized cast components suitable for various applications.
Choosing the correct machining option will provide for tighter tolerances, smoother surface finishes, and complex shapes that cannot be achieved through casting alone.
However, excessive machining can result in increased production time and costs, so finding the right balance between casting dimensions and machining allowances is crucial for efficiency.
One strategy manufacturers use to minimize machining requirements is to optimize the casting design before machining ever takes place.
Incorporating features such as uniform wall thickness, fillets, and radii at critical areas can decrease the need for extensive material removal during machining operations.
Manufacturers also give careful consideration to draft angles during the design process as they can reduce undercuts, which will simplify subsequent machining operations.
Integrating core pins and slides into the design can also aid in creating internal features that do not require additional milling or drilling operations.
Aside from the above, manufacturers also consider the following factors for their machining operations:
Addressing the machining requirements during the design phase of metal casting can save time and costs while achieving the highest quality standards.
Optimizing casting geometry for minimal post-casting machining operations and making informed choices in material selection are effective strategies to achieve this end goal.
Metal casting design is a complex process that requires careful consideration of various factors that play crucial roles in casting success.
Manufacturers plan part design, solidification pattern, and section changes ahead of time to achieve dimensional accuracy and a high-quality surface finish for their cast parts.
However, navigating these considerations can be challenging without expert advice.
Perfect casting design requires informed decisions that balance design complexity, production efficiency, and overall cost.
Consulting with a custom metal manufacturing company is essential as their expertise can help simplify the metal casting process by ensuring that the most important factors about casting design are taken into account.
From a contract manufacturing firm, BuntyLLC evolved into a full service custom machined, forged and cast metal parts fabrication enterprise. We supply global solutions from our headquarters in Greenville, South Carolina.
Get A Quote