Aluminum Forgings

Chapter 1: What is Aluminum Forging?

Aluminum forging is a technique used to process aluminum alloys by applying pressure and heat to create high-strength, durable products. This process involves pressing, pounding, and squeezing an aluminum billet, workpiece, or cylinder under substantial pressure to produce parts with enhanced strength. The temperatures used in aluminum forging range from just below the recrystallization point to slightly above it, or even at ambient room temperatures.

The forging of aluminum includes all of the different forging processes, such as open and closed die forging and rolled ring forging. The choice of which forging method to use depends on the type of product to be created and how it will be used. In all instances, aluminum is ideal for a wide variety of applications due to its lightweight, strength, toughness, resistance to corrosion, and ability to be forged.

Aluminum alloys are evaluated for forgeability in comparison to carbon steel and low alloy structural steel. At room temperature, aluminum alloys exhibit lower deformation resistance than carbon steel, which has three distinct deformation temperature ranges. Aluminum alloys are notably sensitive to temperature changes, with their deformation resistance varying with increasing or decreasing temperatures.

While casting is a popular method for shaping aluminum, forging offers additional benefits by introducing deformation energy that refines and enhances the alloy's metallurgy. Forging modifies the internal microstructure of aluminum ingots, eliminating voids and porosity through crushing. This process drives recrystallization, improving the durability and toughness of the final forged product.

Chapter 2: What are the different types of aluminum forging?

The selection of the forging process for aluminum aims to leverage the material's benefits, particularly where minimizing weight and mass while ensuring reliability is crucial. Forging is defined as a manufacturing process that shapes and forms metal through compressive forces. The core idea behind forging is to use pressure to mold metal into a precise shape that meets the required dimensions of a component or part.

In general, forging is used to deform metals that have been heated to just above or below their recrystallization temperature or ones that are shaped at room temperature, which are the distinctions between hot and cold forging. From these two general categories, forging breaks into several different methods including drop forging, press forging, upset forging, roll forging, rolled ring forging, and isothermal forging. The choice of method for the forging of aluminum is carefully selected to meet the requirements of the final application and the type of aluminum.

Cold Forging

Aluminum alloys can be easily forged into complex and intricate shapes. The forging process allows aluminum to be shaped without scaling, using lower pressure, and dies at the same temperature as the workpiece. Cold forging utilizes aluminum's plasticity, which is its ability to undergo permanent deformation at room temperature.

While aluminum can be shaped by cutting, this method is time-consuming and generates wasteful shavings. Cold forging, on the other hand, is quicker and produces no shavings. It can create complex designs and intricate shapes in two dimensions without requiring additional processing. Cold forging can form features such as holes, chamfers, pins, fins, and steps in a single operation.

The fundamental principle of cold forging involves deforming an aluminum billet, bar, or workpiece at a temperature below its recrystallization temperature, typically near or at room temperature. This cost-effective method is designed to produce complete aluminum parts that require minimal finishing. Vertical presses, either manual or automatic, apply significant pressure to the workpiece placed between an upper and lower die until it conforms to the die's shape.

Cold forging alters the size and shape of the workpiece, producing a wide variety of aluminum parts such as alternators, gears, starter motors, motorcycle components, hollow shafts, valves, switches, and anti-vibration parts.

The advantages of Cold Forging Aluminum:

• Interchangeability and reproducibility
• Smooth even surface finish
• Precision dimensional control
• Assignment of targeted properties
• Heating is not required.

Hot Forging

Hot forging aluminum enhances its properties, resulting in a strength-to-weight ratio superior to that of steel. Manufacturers often choose hot forging for its ability to produce a range of surface finishes, from very smooth to sharp and uneven, which contrasts with the finishes typically achieved through cold forging. Hot forged aluminum components are favored in various industries for their cost-effectiveness, appealing appearance, and design flexibility.

During the hot forging process, aluminum is heated to its recrystallization temperature, ranging from 350°C up to 500°C (662°F up to 932°F). It is then subjected to pressure from forging equipment that pounds and hammers the aluminum workpiece into a die. This process results in a final product with enhanced strength, durability, and reduced grain size. The lightweight nature, high strength-to-weight ratio, and excellent thermal and electrical conductivity of hot forged aluminum make it a popular choice.

Heat and pressure are critical to the hot forging process. High temperatures are maintained throughout to prevent strain hardening during deformation. To ensure consistent high temperatures, forging dies are heated to the temperature of the workpiece or slightly below it. During forging, the aluminum workpiece is repeatedly hammered or stamped until it achieves the desired shape, with the heated dies facilitating the flow of the aluminum.

Drop Forging

Drop forging involves shaping an aluminum workpiece by hammering it between two halves of a die, making it ideal for mass production of aluminum components. The upper die half is attached to a hammer, while the lower die half rests on an anvil. The heated aluminum workpiece is placed in the lower die half on the anvil. Applying continuous pressure compresses the workpiece until it fills the die cavity completely. Excess aluminum, known as flash, is squeezed out through the gaps between the die halves and is later collected for reuse.

Due to its lightweight, aluminum is well-suited for drop forging. This technique primarily utilizes aluminum from the 6000 and 7000 series alloys. After drop forging, the flash is removed from the workpiece, which may then undergo additional treatments.

Drop forging improves the strength, toughness, and fatigue resistance of aluminum. The process ensures precise dimensional accuracy and uniformity. It is a cost-effective method with minimal waste, capable of producing complex and detailed shapes.

Rolled Ring Forging

Rolled ring forging is a process used to create seamless rings from billets or cylinders. The process starts with upsetting the billet, which involves reducing its height while increasing its diameter to the final dimensions required for the ring. This technique uses an open die method, where the billet is heated above its recrystallization temperature.

Upsetting prepares the billet by applying horizontal pressure along its length, causing it to expand beyond the press area. The billet is heated to soften it and make it more ductile, altering the metal’s grain structure in the process.

To produce the ring, the workpiece must be pierced to create a central hole, which is done by punching or shearing. This results in a donut-shaped piece that will fit over a mandrel and be shaped by rollers into the final ring. The term "forging" applies here as the workpiece is reshaped by force rather than being drilled, ground, or bored.

The piercing process creates a hole in the workpiece to fit over the mandrel of the roll forging mechanism. The mandrel, or saddle, is a steel component that must be strong and durable enough to withstand the pressures of the forging process.

To deform the workpiece in rolled ring forging, it is heated to a pliable temperature below its recrystallization point. The workpiece is slowly rotated and pressed against the drive roller, which adjusts the inner and outer diameters (ID and OD) to match the final dimensions. As the workpiece rotates, the mandrel presses against the interior of the donut, squeezing the walls of the ring to reduce their thickness.

The toughness, tensile strength, and fatigue resistance of aluminum make it ideal for rolled ring forging. Unlike many other metals, forged aluminum also provides an excellent surface finish that is smooth and visually appealing. Aluminum rolled ring forgings are used in various applications, including jet engines, turbines, windmills, paper mills, helicopter gearboxes, and tools for hazardous environments.

Open Die Forging

Open die forging shapes aluminum using dies that do not completely enclose the aluminum material. In the open die forging process, an aluminum billet is stamped, hammered, and pummeled until it takes the shape of the die. Since the material is not completely enclosed in the die, completed components receive secondary processing to achieve the desired shape. The process of open die forging is used for the production of discs, sleeves, cylinders, and shafts that are simple and uncomplicated.

Open die forging enhances the grain structure of aluminum components through repeated impacts on the aluminum billet. This method also improves fatigue resistance and strength, adding significant benefits to aluminum products. Like other aluminum forging techniques, open die forging eliminates voids that can compromise a part's effectiveness.

In open die forging, the workpiece is allowed to move freely in the lateral direction, enabling the forging of very large parts weighing several tons. It is well-suited for short production runs and custom products, and is often used for rough shaping ingots for further processing. Additionally, open die forging enhances aluminum's machinability, resulting in components with improved wear resistance and mechanical properties similar to those of machined and cast products.

Closed Die Forging

The process for closed die forging is very similar to that of open die forging with its variation being the function of the die. While the die in open die forging does not completely close the workpiece, in closed die forging, the die halves completely close and encompass the blank or billet in order to produce the final product. Closed die forging can be completed in a single stage or multiple stages depending on the type of product and its complexity. The types of alloys for aluminum closed die forging are heat treated to different temperatures depending on the type of alloy and its composition.

The closed die forging process involves shaping a billet or blank between the upper and lower halves of a die, with the lower half resting on an anvil and the upper half attached to a hammer. The degree of deformation is precisely controlled to align the grain flow with the direction of stress, breaking down the microstructure of the billet or blank.

Closed die forging is typically used for high-volume production runs due to the significant cost of the dies. This method offers exceptional dimensional accuracy and allows for secondary machining to achieve tighter tolerances. Each product made through closed die forging has consistent dimensional accuracy, which minimizes the need for secondary finishing. The process yields aluminum forgings with excellent mechanical properties and structural integrity.

As an economical choice for large production runs, closed die forging increases cost efficiency by reducing the need for additional machining and enhancing production rates. Like other aluminum products, closed die forged items feature a high strength-to-weight ratio and a wrought structure that is resistant to shock and fatigue. The process eliminates voids and porosity, resulting in a smooth, even surface.

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Chapter 3: What types of aluminum are commonly used for aluminum forging?

The range of aluminum options for forging continues to expand, thanks to aluminum's lightweight nature, resistance to corrosion, and excellent strength-to-weight ratio. However, not all types of aluminum are suitable for forging, making it essential to carefully select the appropriate aluminum alloy for a given project. Among the various aluminum alloys available, the 6000 series and 7000 series are the most commonly used for forging.

Choosing the right aluminum alloy for a project depends on several key factors, including the intended application of the product and the specific properties required. Six critical factors should be considered when selecting an aluminum alloy for forging.

• Cost – Although cost is an obvious consideration, it may not be the most important part of the selection process since the design and nature of a product may require a higher quality of aluminum alloy. Manufacturers work with their clients to assist the clients in selecting an aluminum alloy for forging that is economical and is the best fit for a client’s needs.
• Strength – Forged aluminum parts that will be subjected to stress, heavy loads, and harsh conditions require high strength alloys that are capable of withstanding the load requirements and conditions.
• Corrosion Resistance – All aluminum alloys have corrosion resistance to a certain degree. Although this is true, certain alloys have lower resistance due to the compounds used to produce them. An evaluation of the environment where a product will be used can be a major determining factor when choosing an alloy.
• Weldability – The weldability of aluminum alloys varies from very weldable to unweldable in certain conditions. The factors that make welding aluminum difficult are its oxide layer and thermal conductivity, which influence the level of heat energy necessary to weld aluminum. During the initial selection process, manufacturers learn whether welding will be involved in a project and assist clients in selecting a weldable alloy.
• Machinability – Depending on the forging process and the design of a product, some aluminum alloys may necessitate machining to achieve the required tolerance. There is a wide selection of aluminum alloys that can be machined, to a certain extent. The amount of machining plays an important part in which alloy to choose.
• Thermal Properties – Most aluminum alloys have good thermal conductivity, which is three times greater than that of steel, a factor that makes it an excellent material for cooling and heating applications. Various grades of aluminum alloys are excellent at dissipating heat, making them ideal choices for applications that require the removal of heat.

Aluminum Alloys Used for Forging

Similar to other metals, a variety of aluminum alloys can be selected for manufacturing forged products. Over the 170 years since its introduction, aluminum alloys have become the most extensively used industrial metals, with millions of tons produced annually from both new and recycled sources. Understanding the different aluminum alloys and their properties is essential for choosing the most suitable alloy for a given project.

Aluminum Alloy 6061

Aluminum alloy 6061 is part of the 6000 series of aluminum alloys that have the number 6 indicating that the primary alloys in the series are magnesium and silicon, which are present in greater quantities than the other alloying elements. The composition of 6061 is 98% aluminum, 1% magnesium, 0.6% silicon, 0.28% copper, and 0.2% chromium with an assortment of small quantities of other elements.

Aluminum 6061 is known for its weldability, machinability, corrosion resistance, and workability. This alloy comes in various tempered grades, including 6061-O, 6061-T4, and 6061-T6. The designation following 6061 specifies the tempering treatment the alloy has undergone. The letter 'O' indicates that the aluminum has been annealed, while T4 and T6 grades denote higher yield strength due to their specific heat treatments and aging processes.

Aluminum Alloy 6063

Aluminum alloy 6063 is a medium-strength alloy renowned for its architectural applications due to its suitability for intricate and complex designs. Like 6061, alloy 6063 comes in T4 and T6 tempered grades. Being part of the 6000 series, it primarily contains manganese and silicon, with manganese enhancing strength and silicon lowering the melting point.

Alloy 6063 is ideal for applications requiring both lightweight properties and strength. Its low density allows for the formation of complex shapes without adding excessive weight, contributing to its widespread use. Additionally, 6063's lack of copper content provides superior corrosion resistance compared to other aluminum alloys. It also boasts excellent weldability.

Known as architectural aluminum, 6063 can be soft anodized to achieve a visually appealing colored finish, making it popular for building applications. Its resilience to harsh weather conditions further supports its use in demanding environments.

Aluminum Alloy 6082

Aluminum alloy 6082 is a medium-strength alloy, notable for its superior structural strength compared to other 6000 series alloys. This exceptional strength is attributed to the high manganese content, ranging from 0.4% to 1%, which influences the grain structure and enhances the alloy's ability to withstand higher stress levels. This increased strength also improves its machinability.

Despite its high structural strength, alloy 6082 is not typically used for architectural or aesthetic applications due to its poor anodizing qualities. Instead, it is favored for construction purposes, including scaffolding, bridges, transportation, and engineering applications. Like other 6000 series alloys, 6082 is available in various tempering grades, including O, T4, and T6.

Alloy 6082 is valued for its weldability, brazability, corrosion resistance, formability, and machinability. It is commonly used in forms such as rods, bar stock, and machining stock. Though relatively new, the T6 variant of alloy 6082 is widely used in the automotive, aviation, and high-speed rail industries. Its properties make it particularly suitable for hot forging, allowing the production of aluminum products with diverse dimensions. The alloy's excellent processing performance, corrosion resistance, dimensional stability, ease of coating, and effective oxidation further contribute to its versatility.

Aluminum Alloy 7075

Aluminum alloy 7075 is coveted as the highest strength alloy of all the aluminum alloys. Unlike 6000 series aluminum alloys, alloy 7075 has zinc, copper, and magnesium as alloying elements to create strength of 83,000 psi and resistance to stress corrosion cracking, which makes alloy 7075 an excellent material for use in high stress structural applications. Its forgings have superior static strength for use in airframe construction and stressed aircraft parts. The tempered series of alloy 7075 are T6, T651, T7351, and T76.

Alloy 7075-T6 is known for its highest strength among aluminum alloys, though it has lower toughness and resistance to stress corrosion cracking, making it unsuitable for cryogenic applications. Alloy 7075-T73, while offering improved resistance to stress corrosion and exfoliation, sacrifices some of the strength found in the T6 temper. The high strength, low density, excellent thermal properties, and ability to achieve a polished finish make alloy 7075 particularly popular in mold tooling applications.

The 7000 series aluminum alloys, including 7075, are extensively used in transportation applications due to their exceptional strength. Alloy 7075 was originally employed in the construction of fighter jets, contributing to their superior maneuverability. Its high strength has led to its adoption in various products, such as rock-climbing gear, bicycle components, skate frames, lacrosse stick shafts, and hang glider frames. Additionally, alloy 7075 is utilized in the military sector for manufacturing the M16 and AR-15 rifles.

The four aluminum alloys discussed are just a small selection of the numerous alloys available for aluminum forging. These alloys are among the most commonly used due to their essential properties, including strength, durability, corrosion resistance, toughness, and ductility. Their characteristics make them particularly suitable for various forging applications.

Chapter 4: What are the benefits of aluminum forging?

Forging is an ancient metalworking technique that has been utilized for centuries to create items ranging from weapons and cutlery to cookware, jewelry, and structural supports. Originally, the process involved hammering metal on an anvil with heat to shape it. While modern forging methods have become technologically advanced, they still incorporate some of the fundamental techniques used by early metalworkers.

Surface Finish

A key advantage of using aluminum for manufacturing components is its smooth, even, and attractive finish, similar to polished silver. While the forging process often yields products with this desirable finish, it can also produce surfaces with sharp serrations and jagged peaks. These variations may necessitate additional finishing or be integral to the product’s intended function and use.

Design Flexibility

The outcome of aluminum forging is heavily influenced by the design and configuration of the die used in production. Aluminum design engineers take client specifications to create dies with precise dimensions and configurations for forging the desired products. The main constraint of the process is the manufacturability of the design. Computer-aided design (CAD) technology allows for pretesting of designs before actual production begins, ensuring feasibility and precision.

Strength

Aluminum forging creates components, parts, products, and instruments that exhibit superior strength compared to those produced through casting and machining. The forging process aligns the grain structure of the component with its shape, thereby enhancing its strength and durability. Forged aluminum is particularly well-suited for applications that demand high resistance to repetitive loading, frequent impact, and harsh conditions, thanks to its exceptional impact resistance and strength.

Cost

Aluminum forging is typically less expensive compared to other manufacturing processes when factors like material cost and lead times are equal. The tooling required for aluminum forging is generally more affordable than that for aluminum die casting, and the process yields a higher production rate.

Mechanical Properties

Forging enhances the mechanical properties of aluminum alloys by altering their microstructure. This results in increased tensile strength, yield strength, toughness, and fatigue resistance.

Durability and Reliability

Unlike other aluminum forming methods that may produce products with porosity and voids, aluminum forging utilizes compressive forces to eliminate these imperfections. This results in increased durability, performance, and reliability of the final products.

Dimensional Accuracy

Aluminum forging avoids issues with shrinkage by heating the metal to just below or above its recrystallization point. The billet or workpiece is processed in its solid form, ensuring precise dimensional accuracy and integrity.

Property Reliability

One of the key advantages of aluminum forging is the retention of aluminum's exceptional properties. Despite the shaping and manipulation involved, the forging process does not compromise any of aluminum’s beneficial characteristics.

Material Waste

Modern manufacturing emphasizes reducing waste, and aluminum forging supports this goal. The flash produced from open and closed die forging can be easily reused and recycled, minimizing waste. Aluminum is highly recyclable and can be processed repeatedly without loss of quality.

High Volume Production

Aluminum forging excels in high-volume production, efficiently creating thousands of complex and intricate shapes in a short period. The timeline from design introduction to finished product delivery can be as brief as two months or less, with minimal waste generated despite large production quantities.

Conclusion

• Aluminum forging is a process that places aluminum alloys under pressure to form high strength, durable parts. The process of aluminum forging involves pressing, pounding, and squeezing an aluminum billet under great pressure to create parts that have high strength.
• The choice of the forging process for aluminum is to ensure that components have all of the positive properties of aluminum where weight and mass must be minimized and reliability is a necessity.
• In general, forging is used to form metals that have been heated to just above their recrystallization temperature and metals that are shaped at room temperature, which are the distinctions between hot and cold forging.
• It must be understood that not all aluminums can be used for forging, which necessitates careful selection of the type of aluminum to be used for a project.
• In the 170 years since its introduction, aluminum alloys have become the most widely used industrial metal with several million tons of it being used every year including new and recycled aluminum.

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