The Ultimate Buyer's Guide for Purchasing Automated vertical casting for metal pipes

Recently, the forging industry has highlighted the advantages of forged products over castings, suggesting that castings are inferior and less reliable. However, in considering casting vs forging, it’s important to recognize that both techniques start in a similar fashion–with raw materials and a design concept.

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Each method has distinct advantages and applications, depending on the requirements of your project. Keep reading to learn more about how we decide between each of these two processes.

What Are the Main Differences Between Casting and Forging?  

When choosing between casting vs forging for metal manufacturing, understanding the key differences is essential to determine which is the best suited to your project. Each method has unique characteristics that influence factors like strength, cost, and performance. 

Here is a breakdown of the key differences between casting vs forging:

• Process: In casting, molten metal is poured into a mold, where it cools and solidifies into the desired shape. With forging, solid metal is shaped under high pressure using presses, dies, and hammers.
• Strength: Forging creates a refined grain structure, making components stronger and less resistant to fatigue than components which have been cast.
• Applications: Casting is preferred for large, complex applications, or where detailed parts are required, such as turbines or medical implants. Forging is ideal for components requiring superior strength, like crankshafts and gears.
• Cost: Forging is more economical for high-volume production of simple shapes, such as bolts and custom fasteners, while casting is more economical for low production runs and intricate designs.
• Material Suitability: While forging is somewhat limited to metals with good malleability, casting supports a wider range of alloys, including work-hardenable metals.
• Precision and Finish: Although both processes often require finishing, there are differences between casting and forging when it comes to surfaces. Casting produces better surface finishes with superior dimensional accuracy, while forging typically requires additional finishing to achieve the desired surface quality and tolerances.

As can easily be seen in this brief comparison, each technique has advantages and disadvantages. Selecting the best process for your application requires deeper knowledge of the processes, which are explored in the following sections.

The Process of Casting and Forging

Most steel components start as castings: metal that has been melted, poured into a mold, and solidified. In the casting process at the foundry, because the mold has the shape of the desired component, all that remains to be done after casting are the various finishing operations.

With forgings, the first shape is an ingot or continuously cast billet. Ingots are large, usually rectangular in form and weigh up to several tons. Ingots or continuously cast billets are forged into shapes by hammers or presses. Extensive machining to final configuration usually is required, and welding also may be necessary before finishing operations can begin.

Table 1 shows typical procedures for casting vs forging for producing a 10-in. valve. Although no two foundries are identical, all would essentially follow the same procedures identified in Table 1.

For forging shops, however, two alternatives are possible: forging two halves and welding them together, or creating the internal channel from a solid billet by piercing and machining. Piercing consists of punching a hole through the piece. The hole then is tapered in shape, but may require extensive machining to bring it into tolerance.

Although there is a substantial area of overlap, forgings tend to be used exclusively in some applications and castings in others. In determining which process to select, the crucial considerations are the ability to satisfy the design criteria and the ultimate cost of the component.

Criteria to Consider

Although castings and forgings share many design criteria, such as the need for generous radii, each process has its own specific design and design modification practices. When changing from one process to the other, the design should be reconsidered and new drawings made, or problems are likely to be encountered.

Casting and Forging Defects

The modification of a design is a different matter. It is often necessary to alter a design by adding a rib or lug, removing a projection, or adjusting its shape. Here, castings provide a distinct advantage, since the modification of a casting pattern or corebox is relatively easy and inexpensive. But the modification of a forging die to accommodate even slight changes is usually difficult, very expensive and new dies may be necessary.

The manufacturing process also places limitations on the shapes that can be produced. Often, foundries must explain to customers that to induce directional solidification and enable the pattern to be removed from the mold, it is necessary to introduce a taper of about 1.5 degrees. According to the Forging Handbook, this magnitude of taper is typically five to ten times greater in forged products.

Mechanical Characteristics

The principal mechanical properties of interest to designers are strength, ductility, and hardness. But how does the user know the mechanical characteristics of a part?

For cast steel, it is relatively easy. If the component is made from a standard alloy, the characteristics are given in a standard specification. If it is made from any other alloy, standard foundry tests will provide the answers. The values will apply to that component regardless of the axis along which measurements were made.

Many metal parts are made from rolled products like bars or plates. The rolling process changes the properties of the metal. The major advantage is that the strength is increased in the rolling direction or the longitudinal axis. Both forgings and fabrications have directional properties as a result of the rolling process.

However, tensile strength, elongation and impact properties decrease in the transverse and axial directions. Thus, wrought steel and forgings in particular, are anisotropic (exhibiting different values of a property in different directions). For equivalent alloys, the ductility and impact strength of steel castings generally lie between the longitudinal and transverse values of forgings. In castings, the metal is isotropic, with similar properties in all directions.

With respect to the mechanical characteristics of a forged component, most forging references provide only longitudinal characteristics. To obtain the transverse or axial characteristics, the user will probably have to request them specifically.

Additionally, the service conditions of the components must be carefully evaluated. If the loading is uni-axial along the longitudinal axis, then the directionality of the forging is an advantage. As the stresses increase in any other direction, directionality becomes a problem. Pressure vessels are good examples of applications where stresses are triaxial.

The design code (ANSI B16.34) used by most flow control manufacturers doesn’t indicate that forged products offer any mechanical property advantage over cast products.

In terms of temperature extremes, corrosion resistance and wear resistance, “equivalent” castings and forgings generally perform equally well throughout the temperature range and are generally equally resistant to corrosion and wear.

With regard to corrosion, however, cast stainless steels with controlled amounts of ferrite will probably be superior to their forged counterparts, since ferrite generally increases corrosion resistance. With regard to wear, work-hardenable steels can, for practical purposes, only be obtained as castings.

Fabrication

If two components are to be welded together, it is advantageous to have one or both parts be steel castings. Castings are generally more weldable than “equivalent” forgings. This is true not only of austenitic grades of stainless steel with controlled ferrite but also of plain carbon and low-alloy steels. 

The superior weldability of steel castings was demonstrated in research performed by the University of Tennessee. Five “equivalent” grades of low-alloy casting and forging steels were compared in terms of weldability, or resistance to cold cracking. 

Cold cracking, also known as underbead cracking, occurs after the welded joint has cooled. This can be extremely troublesome since cracks are hidden beneath the weld and aren’t revealed by surface inspection. 

In the University of Tennessee tests, cast and wrought grades of steel plus four other manganese-silicon (Mn-Si) grades were tested to determine the degree of preheating necessary to eliminate underbead cracking.

For each grade, the cast steel required lower preheat temperatures than the wrought steel to achieve crack-free performance. Baseline tests to establish the weldability of the grades without preheating showed the same results. Every cast grade was superior to its wrought “equivalent.”

The problem with the wrought steels has been identified as the elongation of the inclusions. The needle-like inclusions in wrought steels appear to be more likely sites for crack initiation than the round inclusions in casting steels.

Where welding is required, the same considerations apply as previously mentioned. At a given preheat temperature, welds on steel castings tend to be less susceptible to under-bead cracking than welds on steel forgings. Additionally, castings will achieve comparable weld reliability at lower preheat temperatures.

Upgrading

The forging process tends to reduce surface porosity and discontinuities, sometimes closing up small internal cavities. Surface porosity and discontinuities occasionally appear on steel castings and require weld repair. The resultant surfaces meet the same standard requirements as the casting. The cost of this upgrading procedure is usually much less than the cost of additional machining typically required of forging.

Section Thickness and Shape

In forging, metal is moved while it is still in the solid state. Because the forging billet is solid, substantial force is required to change its shape to the desired configuration. Because of this, the required force increases as section size increases. In practical terms, there is a limit on size and section thicknesses produced by forging.

This doesn’t mean that very heavy sections are never forged. But when they are, relatively little deformation or reduction in cross-section occurs. In other words, the surface of the part merely moves from one place to another.

In contrast, in the metal casting process, the metal starts as a liquid and flows into the desired shape. Therefore, it is practical to cast components of large sizes and section thicknesses.

Since there are fewer parts typically involved and steel castings tend to have better weldability than steel forgings, cast/weld construction is generally preferable to forged/weld construction for extremely large components. 

In the metal forging process, solid metal is forced into the die cavity. In casting, liquid metal is poured into the mold cavity. Liquids can flow almost anywhere. Therefore, as complexity of shape increases, the practicality of forging decreases. Castings can accommodate great complexity of shape.

Material Composition

The question of composition has two parts: what is obtainable from foundries and forging shops, and what is or isn’t castable or forgeable?

Forgings are produced from billets obtained from a steel mill and in compositions produced by the mill. Mills tend to produce limited grades of steel and special orders can be prohibitively expensive. Because steel foundries are more flexible, the number of chemical compositions obtainable from steel foundries is virtually unlimited.

Although a single foundry cannot supply every conceivable alloy, it is always possible to obtain a unique composition to meet a specific requirement from a variety of foundries at lower cost than competitive product forms.

The presence of controlled amounts of ferrite in certain stainless steels leads to increased corrosion resistance, higher crack resistance and better weldability. Ferrite occurs normally in most cast stainless steels, with the ferrite level controllable to produce the desired combination of characteristics. However, ferrite impairs hot working properties and is normally not present in forged components.

The important class of work-hardenable steels also are not forgeable. Work-hardenable steels are generally high-manganese (approximately 13% Mn) alloys that become harder the more they are worked. Thus, they are ideal for dipper teeth, compactor feet and other earth-moving and excavation applications.

Size and Weight

Steel castings are almost always lighter than their forged counterparts and the redesign from forgings to castings usually results in substantial weight savings. For example, a forged muzzle brake for a cannon anti-recoil system weighed more than 600 pounds. The cast version weighed 400 pounds and lasted more than three times longer.

Set-Up and Production Costs

The key to the casting process is the pattern. The key to the forging process is the die. Pattern costs are substantially lower than die costs and can be amortized over shorter runs. With higher runs and with simple component configurations, forged components can become economically converted to equivalent castings. 

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Secondary Operations

The final cost of a part includes its purchase cost plus the cost of performing any necessary additional operations. 

Before assembly operations, for example, it is often necessary to machine the part to the desired shape. This cost can be considerable. When parts are relatively simple, castings and forgings tend to require equal amounts of CNC machining. As parts become more complex, however, castings tend to require less machining.

Industry Applications of Casting and Forging

When it comes to considering casting vs forging and which is better, both play vital roles in manufacturing across a wide range of industries. Each technique offers unique advantages based on the specific demands of the application.

Below are some key industry applications, highlighting the benefits and requirements of casting vs forging:

• Energy: In the energy industry, castings are used for components like pump housings, valve bodies, and turbine blades with complex geometries. In contrast, forgings are ideal for more simple designs, like crankshafts and high-pressure fittings that require superior strength and durability.

• Manufacturing Equipment: When it comes to producing manufacturing equipment, casting is preferred for parts like machine housings, valve bodies, and complex gears. On the other hand, forging is often better suited for high-performance industrial gears and heavy-duty presses. 

• Medical Devices: For medical devices, whether casting or forging is used depends on the application. For example, orthopedic devices that require exceptional strength, such as hip and knee replacement parts, may be forged, while other implants like pacemakers are often manufactured from cast components. The type of metal required for the component will also determine the best metal manufacturing method.

• Consumer Goods: From decorative items to functional hardware, both casting and forging contribute to the production of consumer goods. Tools and miscellaneous hardware are often forged, while components like appliance parts and furniture hardware are often made from castings.

Environmental Impact of Casting vs Forging

The environmental implications of casting and forging varies significantly, with each method presenting distinct challenges and opportunities for sustainability. 

Due to the need to melt metal to high temperatures, casting typically requires higher energy consumption than forging. Increased energy consumption often leads to increased greenhouse gas emissions, especially if fossil fuels are used. Another significant impact is waste material, such as scrap metal and sand. However, recent innovations in casting like 3D printing have made precision casting a more sustainable technique.

Although forging doesn’t use as much energy, there are still environmental impact challenges related to energy consumption. For example, while both cold and hot forging consume energy, hot forging suppliers typically use a significant amount of energy. Additionally, forging also produces considerable material waste. With closed-loop systems, the use of recycled materials, and other efforts to reduce scrap, forging is becoming more sustainable. 

Ongoing research and technological innovations in casting and forging continue to reduce the environmental impact of metal manufacturing. As demand for green products continues to rise, more companies continue to seek a balance of efficiency and sustainability in their manufacturing choices.

The Competition

To answer the question of casting vs forging, which one is better, ask “what qualifies as large?” and “how do you define complex?” Other considerations include “at what point does a production run become long?” and “what are the required materials?”

These are the gray areas in which neither castings nor forgings show a clear-cut superiority. The solution for the designer is to determine the method of production before finalizing the design. A preliminary design will allow the customer to take advantage of the competitive situation.

Invite bids from reputable foundries and forging shops and decide which process to use on a specific, case-by-case basis. The results may vary in different cases, but the competition can only serve to benefit the customer, user or purchaser.

Future Trends in Casting and Forging

While there are many differences between casting and forging, both are seeing transformative innovations driven by efficiency and sustainability. Each of these trends will continue to shape future practices and expand the capabilities of each technique.

• Additive Manufacturing: Involving complex workflows, this cutting edge technology integrates 3D printing into large, industrial manufacturing processes. Additive manufacturing reduces waste, shortens production timelines, and allows for more complex designs.
• Robotics and Machine Learning: Automation and AI are increasingly used in casting and forging. In casting, robotics improve accuracy and speed up mold pouring, while in forging, robotics are used to handle billets and place dies. Integrating robotics and AI enhances production efficiency, reduces waste, and minimizes downtime.
• Sustainable Material Sourcing: With a shift toward sustainability, many companies are looking for recycled and raw sustainable materials to meet the industry demand for eco-friendly practices.
• Innovative Alloys: Across various sectors, new alloys are being developed and used to expand casting and forging capabilities. Innovative alloys like titanium, aluminum, and superalloys have superior strength and corrosion resistance for a variety of applications, often used by sand casting or die casting suppliers.

As more state-of-the-art metal manufacturing techniques are developed, industries continue to benefit from increased efficiency and expanded design possibilities, and the future of casting and forging is continually being reshaped.

Casting vs Forging: Which is Better?

Clearly, steel castings have and will continue to maintain an important role in manufacturing. Their strength and ability to be produced to the shape required by designers should ensure that their competitive position will be maintained and improved.

Castings will tend to have a definite advantage over forgings when any one of three conditions is met:

• a unique metal composition is required;
• the part is relatively large or complex;
• stresses may be multiaxial

Designers and casting buyers can only obtain the real picture about the performance of either process by developing an open dialogue with their component suppliers. Both parties have the same interest in product design, quality, and cost. This dialogue will ensure that the real problems will be identified and effective solutions found.

Casting is an ancient practice that’s managed to stick around in our lives for the last 7,000 years. As the saying goes, if it’s not broke, don’t fix it—and that can very much be applied to this popular manufacturing procedure today. Even after all these centuries, it’s hard to find a replacement for such a varied and customizable method for making products.  

This is because casting involves adding molten metal to a cavity in the shape of your part. The net shape made with casting may only require light secondary processing. This has advantages over CNC machining where all the features require material removal from a larger metal billet. Also, nearly any metal can be used for casting which opens up an incredible diversity of applications and industries.

Casting can be broken up into several different processes, which we’ve briefly explained below. Each one is a form of casting, but they all involve slightly different materials, tools, machinery, and execution. Here are 14 techniques you can consider for your own parts.

Common Items in Casting

Regardless of the casting method, there are common factors that will help you navigate the processes below. These include:

• The Pattern or Master Pattern is a reusable or sacrificial shape of the final part used to form the cavity where the molten metal will pour. Most processes, such as sand casting and investment casting, require a pattern. The exception is when a tool or die is used.
• Die Tools are reusable metal portions common in processes like die casting. These are akin to the tooling that can be used in our injection molding services, only designed for liquid metal versus thermoplastic.
• Gates, sprues, and vents are channels where molten metal flows into the cavity. They may also be strategically placed where an air pocket would occur within a cavity. Adding exit holes in these locations will allow for the metal to fill that cavity and flow into the sprue, being trimmed after casting.
• Flash is the excess metal that seeps into the areas where a core, cavity, or die interacts. It can be ground off or trimmed after casting.
• Net shapes are the outcome of most casting processes due to the metal’s shrink rate and cavity surface. Critical surfaces, details like threaded holes, sealing surfaces, and tightly toleranced features are typically added via secondary machining.

Now, on to our types of casting!

1. Sand Casting

Sand might seem fragile and crumbly, but with the right type, it can form quality, single-use molds that allow you to create all kinds of castings. You’ll find that sand casting is mainly used for forming hot liquid metal or alloys into intricate objects. The molds are made of sand and are typically use multiple halves or cores. Sand molds look like impressions of parts from different angles, and when combined make the final shape of the part. Features are added to allow molten metal to be poured in as well as flow through the designs. It’s an enticing choice for manufacturers because you can shape alloys with high melting temperatures, like steel, nickel, and titanium, which often can’t be cast with other methods. Sand casting is not limited to high temperature metals, however, and can be applicable for softer alloys like aluminum, bronze, or zinc.

The sand used in sand casting is slightly different from the kind you’d find on the beach; it is made of silica (a popular casting sand), chemically bonded sand, or green sand. After casting, the mold may be reused or destroyed depending on the design created. The metal shape can then be post processed through grinding and machining to remove sprues, flashing, and add details or tightly toleranced features. You can use sand casting for all kinds of products at medium to high volumes, such as marine flywheels and engines, barbecue grills, skin fittings for ships, and jewelry.

To learn more, see our guide on Sand Casting Manufacturing.

A sand casting diagram is below:

2. Die Casting (Metal Die Casting)

While sand casting can melt alloys with high melting temperatures, you can look to die casting for forming metals that have lower melting points. Once you’ve turned your materials from solids to hot, molten liquids, you can inject them into long-life die-casting molds made of hardened steel. These tools consist of a cavity, core, and sometimes inserts. Unlike plastic injection molding, it is sometimes more feasible to machine side features after casting versus using a side action. Die casting traces back to the 19th century. Since its arrival on the manufacturing scene, there have been two types of procedures developed that you can use. The first is hot chamber, which features a built-in furnace within the machinery that melts the materials. If you use the cold chamber process, the second procedure, you’ll melt materials in a separate furnace and then move the molten material into the injection chamber afterward. You can implement die casting to make aerospace and automotive components in high quantity production, as well as toys, furniture, and electronics. Die casting is offered through Xometry’s core services and quotes can be created through the Instant Quoting Engine.

To learn more, see our guide on What is Die Casting Used For.

3. Investment Casting

We’re not talking about financial investments here, but rather the older term for the word that means covering up or putting on clothes. This is where investment casting gets its roots, harkening back to the Bronze Age, but it still remains a popular technique today if you want to make a wide range of products, including MRI machines, jewelry, and gas turbines. It’s a great choice, too, if you want to create near-identical copies at a large scale. Investment casting works by using wax patterns that are enveloped in ceramic. The ceramic takes on the surface and shape of the wax pattern (with added features for material or treeing). Afterward, they get pushed into a sand and slurry mix. At this point the wax has done its job and will be evaporated via heat, then molten metal is poured in to create the finished products. Like sand casting, investment casting can use a variety of materials. You can see how the process works in the image below.

In prototyping or low volumes, an investment pattern can be made using 3D printed wax or low-ash polymers. Low-ash is important because any remaining ash in the cavity may cause blemishes or defects on the cast component. In production, injection molding is used to rapidly create wax patterns that can be treed together to build multiple components at once. Like other metal casting processes, parts go through secondary trimming and finishing before completion.
To learn more, see our guide on What is Investment Casting.

5. Continuous Casting

This process gets its name from the steady flow of molten metal you’ll control going in and out of the molds and the continuous metal products it produces, like tubes, slabs, and bars. You can get high-quality shapes with this type of casting because of the quick cooling process and low risk of contaminants getting in. Like gravity die casting, you’ll notice that continuous casting also uses gravity to keep a steady flow of material coming. Continuous casting has a very high upfront cost and setup, making it ideal for producing high volumes of raw materials but not for any low volume applications.

6. Shell Molding

You know of sand casting, but we can keep the beach theme going with shell molding, which has some similarities to the former. Its name points to the process, which involves molding a silica sand and resin shell around a heated metal pattern. You can then remove the shell, and pour molten metal into the cavity. You might be curious why you’d choose this over sand molding, especially seeing that it’s more expensive in some instances. Shell molding can give you more accurate dimensions on products, nicer finishes, and larger quantities with less labor.

7. Lost-Foam Casting

Foam and molten metal don’t sound like they could mix, but this relatively newer process shows it’s possible to a certain extent. With lost-foam casting, you’ll inject molten metal into a foam mold that’s surrounded with support sand. The polystyrene foam will burn away and gas will disperse through the sand, leading to a cooled, formed shape. It’s a fantastic option if you need thin-walled products or items that are more intricately shaped. You’re not limited by industry, as this method works for creating all kinds of things like art sculptures, automotive parts, and circuit boards.

14. Plaster Casting

Another form of casting you can consider is one that sits under investment casting - plaster casting. Plaster casting may remind you of the Plaster of Paris molds kids use to create fake fossils or toys, and it’s made of the same thing, gypsum. At the manufacturing level, you can use this method to create prototypes, gears, ornaments, and valves. To plaster cast, you’ll coat a rubber or metal pattern with adhesive then pour in the materials that will set, cool, and be removed.

How Casting Works

Casting is a type of manufacturing process that forms materials into different shapes through hot materials and molds. Each casting process has its own unique steps and details that make it stand out from others, but in general, you’ll find that any type of casting involves the pouring or injecting of molten materials into a mold, which then cools and hardens into a finished product.

When it comes to producing intricate goods or large quantities of them, you’ll probably investigate casting as an option. It’s used across many different industries, whether you’re after extremely complex aerospace parts or basic toys. 

Xometry Senior Solutions Engineer Jake Thompson says he helps clients choose the right type of casting process by asking the following questions: "1) What is the alloy? 2) What is your volume? 3) What is the part size? 4) Is there a tooling budget we need to stay under?"

Materials Used in Casting

It all depends on the type of casting you’re looking to do, but these are the most common materials you’ll use when it comes to these casting methods:

• Metals: Certain casting methods will be able to accommodate metals you want to melt, such as iron, aluminum, copper, and zinc.
• Alloys: Whether you use sand casting or metal die, all kinds of alloys like bronze and brass can be melted and molded. 
• Ceramics: These materials are popular for pottery applications and can include clay or porcelain. 
• Plastics: These bendable materials can be molded through casting, too.
• Composite materials: Resin and fiber mixtures and other composites are another suitable choice you can use in casting processes.
• Rubber: For parts with elasticity and flexibility, you can use rubber in casting. 
• Glass: If you need artistic objects or thin-walled items, glass can be funneled into certain casting processes.
• Concrete: This is a common choice when you’re making architectural products and decorative castings. 

Xometry offers the following metals for its die casting production services:

• Aluminum alloys: A360.0, A380.0, A383.0 (ADC12), and A413.0
• Zinc alloys: Zamak-2, Zamak-3

Summary

As you can see, casting isn’t limited to just one methodology or industry. With these 14 processes, you can cover a wide range of industries and make a series of precise, intricate products in a slew of materials.

Xometry provides a wide range of manufacturing capabilities, including casting and other value-added services for all of your prototyping and production needs. Get a free, no-obligation quote today.

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

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