Cold Forging

Chapter One – What is Cold Forging and How Does It Work?

Cold forging is a metal shaping technique where metal bar stock is placed into a die and pressed into another closed die at ambient temperature or lower than the metal's austenite temperature.

This process is highly efficient and cost-effective for producing large quantities of components. Cold forging methods can be categorized into cold, warm, and hot forging, and involve tools such as hammers, dies, or presses to shape and deform the metal. It should be distinguished from machining and casting, as it results in a product that is stronger and of superior quality.

Unlike warm or hot forging, cold forging manipulates the metal at room temperature, using localized compressive forces to achieve the desired shape. Depending on the part’s design, the metal may be subjected to multiple dies or repeated strikes to reach the final form.

Chapter Two – How Cold Forging Works?

Cold forging offers significant cost savings primarily because it minimizes labor and eliminates the need for additional processing. Parts can be manufactured at high speeds, up to 1000 units per hour, which reduces the cost per piece. The process involves feeding a metal coil into machines that perform the work quickly and efficiently.

The end products from cold forging exhibit excellent surface quality and enhanced dimensional accuracy, as illustrated in the image below. The various forging techniques contribute to the strength and longevity of the parts, resulting in durable and reliable components.

The Cold Forging Process

Step 1: Lubricant

Before the forging process begins, the workpiece is often coated with a lubricant. This helps to prevent adhesion to the die and maintains a lower temperature during forming, as deformation can generate heat ranging from 250°C to 450°C. The application of lubricants varies by manufacturer and their specific methods, and they are not universally employed in all processes.

Step 2: Feeding the Metal Coil

The metal coil is introduced into the forging machine, positioned above a die that is shaped to form the final part. This die typically consists of two segments: one attached to the hammer, and the other positioned beneath the workpiece. The hammer, which is the upper part of the mechanism, delivers the force necessary to shape and deform the metal.

Step 3: The Stroke

Three primary mechanisms can be used to strike the workpiece: hydraulic, pneumatic, or mechanical. Each method employs a shaft with an attached hammer that descends with significant force onto the workpiece to achieve the intended shape. This process occurs in milliseconds. Occasionally, multiple hammer strikes may be necessary in rapid succession to achieve the precise contour and dimensions required.

Step 4: Part Removal

The method of part removal varies with the specific process used. In contemporary manufacturing, automation often handles this task through conveyors or robotic arms. This approach reduces costs by eliminating the need for manual material handling.

Step 5: After Shaping

The approach to handling parts post-forging varies depending on the complexity of the component. For single-die, single-stroke parts, they are typically trimmed and forwarded to shipping directly. For more intricate components, additional die processes are required to incorporate various features. Generally, the transfer of dies between stations is automated. For larger components, mechanized equipment such as forklifts, hi-los, or cranes is employed for movement.

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Chapter Three –What are the benefits of cold forging?

This chapter explores six key benefits of cold forging, including:

• Cost effective
• Faster production
• Environmentally friendly
• High production output
• Wide choice of metals

Below, you'll find details on the advantages of cold forging and its widespread application. Chapter three provides a comparison between cold forging and hot forging, highlighting the benefits of each process.

Cost effective:

Cold forging avoids the need for pricey heating devices and complex tooling, as well as expensive secondary operations. It offers a 70% reduction in material use compared to machining. In contrast to other metal processing methods that use furnaces, kilns, or electric heating to raise metal temperatures beyond the austenitic phase, which can be costly to operate and maintain, cold forging eliminates these expenses and reduces environmental impact.

With cold forging, the workpiece is finished as soon as it is processed, requiring only minimal additional finishing. This results in significant labor cost savings, which is a major advantage of the cold forging technique.

Faster production:

Cold forging is an efficient technique where the workpiece is directly inserted into the forging press to create a finished component instantly. Contemporary manufacturers employ automation for both loading the workpiece into the press and removing the completed part. As illustrated in the accompanying diagram, the metal is fed into the machine, forged, and ejected within a fraction of a second.

Eliminates possible negative reactions:

Working with metal can introduce several issues, but cold forging mitigates some of these problems, such as porosity and fatigue, by enhancing the metal's overall strength and ensuring material integrity. However, it is important to note that while cold forging reduces certain drawbacks, it can introduce other challenges in the process.

Increased quality and long life:

Components made through cold forging are designed to endure significant stress. Even when subjected to forces that exceed their yield or elastic limits, these parts maintain their deformed shape without returning to their original form.

Retention of part tolerances:

During a production run, parts can achieve and maintain critical and precise tolerances, provided there is no wear on the die. Each component is manufactured with exacting detail, ensuring that every piece is an exact replica of the initial part.

Design freedom:

Cold forging offers greater design flexibility compared to other methods, enabling the creation of complex contours and shapes in a single step. This contrasts with other processes that often require multiple, expensive secondary operations to achieve similar results.

High production output:

While cold forging methods may vary, this process can achieve impressive production speeds, producing between 50 pieces per minute and over 450 pieces per hour. The primary factors affecting the speed of production are the part's shape and design.

Wide choice of metals:

Cold forging accommodates a diverse array of metals, from hard materials such as carbon steel, alloy steel, and stainless steel, to softer metals including aluminum, brass, and copper.

This image showcases a selection of bolts manufactured through cold forging. Each bolt is crafted from a different type of metal, including copper, brass, aluminum, and steel.

Chapter Four – What are the differences between hot forging and cold forging?

The primary distinction between hot forging and cold forging lies in temperature: cold forging deforms metals at room temperature, creating strain and stress, whereas hot forging involves heating the metals before shaping them.

The critical factor in the temperature range is the austenite stage. Cold forging occurs below this stage, while hot forging involves heating the metal to temperatures beyond the austenite phase.

Choosing cold forging vs hot forging depends on:

• A fabricators equipment and machining: Producers specialize in one process or the other to maximize the use of their equipment.
  
  

  

  
  

  

  
  
• Customer demand: During the design phase of part development, engineers make the decision regarding the best process to produce their designs since cold and hot forging have their limitations.
• Types of part produced: Many times the restrictions regarding the choosing of the right process is determined by the design of the part since specific parts can only be hot forged while others are perfect for cold forging. The designs of cold forged parts are simple without intricate details while hot forging can produce pieces with extremely precise small minute features.
  
  

  

  
  
• Lower cost requirement: Whenever possible, manufacturers choose cold forging since it requires less equipment and does not including heating, which significantly lowers the overall cost of production.

Hot forging

Hot forging is conducted at very high temperatures, which helps prevent strain and hardening while reducing the stress flow and energy required to shape and deform metals. After cooling, the metals retain their new shape. The forming process typically involves hydraulic, pneumatic, or mechanical presses.

Characteristics of hot forging:

Dies or molds:

One of the significant costs associated with hot forging is the production of dies and molds. These are made from high-strength steel designed to endure the extreme temperatures, resist fatigue, and possess the necessary ductility, toughness, and tensile strength.

Forms of hot forging:

While many hot forging techniques are similar to those used in cold forging, additional methods include gas forming, die quenching, draw forming, and isothermal forging.

Temperature of the metal:

The process type determines the metal's temperature during shaping. In certain methods, the metal is fully melted and either poured into a mold or forced through a die. In other processes, the metal is annealed and then shaped under compression and pressure using a die or mold.

Hazardous environmental factors:

The primary drawback of the heating process in forging is the significant amount of pollutants generated, which varies depending on the type of furnace used. This issue has been a persistent challenge since the early days of the industrial revolution and continues to be a concern for manufacturers. The video below illustrates the volume of fumes produced.

Heating metals:

To forge parts, metals must be heated beyond the austenite stage, which typically requires temperatures above 300°F and can reach into the thousands of degrees. Achieving these temperatures necessitates the use of large furnaces or kilns.

Time involved:

Hot forging involves a complex process that includes heating the metal, shaping it, and then cooling it. While the actual stamping, deforming, or shaping may take about the same time as cold forging, the heating and cooling phases require careful management and can extend the overall process duration.

Results of hot forging:

Heating and cooling metals enhance their strength, toughness, and ductility, though they can reduce hardness. During cooling, metals may warp or change shape, and these potential issues should be considered during the engineering phase.

Scaling:

Hot forging can result in oxidation, leading to scaling that discolors the metal's surface and complicates finishing processes.

Cold forging

The key difference between cold forging and hot forging lies in the temperature used. Hot forging involves heating the metal above its austenite stage, which alters its microstructure and eliminates internal stress, making it more ductile. In contrast, cold forging does not involve heating, allowing the metal to maintain its original strength and microstructure.

The characteristics of cold forgings are as follows:

Temperature of shaping:

In cold forging, metals are shaped at room temperature, below their austenite stage. This approach reduces costs by eliminating the need for expensive furnaces and heating equipment.

Speed:

Production speeds vary from seven pieces per minute for low-volume machines to up to 400 pieces per minute for high-volume systems.

Equipment:

Cold forging utilizes specialized machines that perform operations such as squeezing, bending, shearing, and drawing. The cost of this equipment varies widely based on its technology and size.

Cost:

Cost savings in cold forging are primarily due to material efficiency and production speed. Material savings arise from minimal scrap production, with reductions of up to 70%. Additionally, the rapid production rate significantly lowers the cost per unit.

Environmental factors:

This machine from Stalcop, shown below, operates with no emissions or pollutants. It is fully enclosed and self-contained, eliminating carbon and other pollutants since heating of the metal is not required.

Results of cold forging:

The diagram below illustrates how cold forging realigns the grain structure of metals to match the flow of the final part. This process reduces porosity fatigue, enhances shearing strength, and minimizes risks to material integrity. While the metal becomes stronger and more resilient through straining, it also loses ductility and becomes more brittle.

Scaling:

Before forging, it is crucial to remove any scaling, such as rust or corrosion, that may have developed during storage. Failure to do so can result in the part exhibiting similar deterioration issues as seen in hot forging.

Finishing:

Minimal finishing is needed with cold forging. Once a part is processed, it is ready for use or shipping with little to no additional work required.

Disadvantages of Cold Forging

Cold forging is not without its drawbacks. As with any production method, it has its own limitations and constraints that should be considered before selecting it for your next project.

• Only simple shapes and designs in high volumes can be produced. Unique, unusual, or intricate patterns cannot be cold forged. Deformation levels and shaping grades are limited, and cold forged metals have less ductility.
  
  

  

  
  
• The alteration of the grain structure of a metal gives it extra strength but may produce residual stress.
• Certain methods of cold forging require heat treatments to eliminate possible cracks or creep hardening.
  
  

  

  
  
• There is a limitation to the types of metals that can be cold forged. Ones with low ductility and sensitivity to strain hardening should not be chosen since they lose their ductility and will break under tensile stress. Only metals with a hardness of HRC 44 on the Rockwell scale can be used.
  
  

  

  
  
• Production processes require a great deal of force to produce the necessary compressive force and pressure. Though the addition of hydraulics and pneumatics has decreased the size of the equipment, it has not eliminated the amount of power the machines consume.
  
  

  

  
  
• Tools, dies, and molds have to be specially designed as well as sturdy and strong enough to be able to endure the constant repetitive force. The beating that cold forging tools endure requires that they be replaced frequently.
  
  

  

  
  

Chapter Five – What are the different processes involved in cold forging?

Technological advancements and progress in metal processing have led to the creation of various cold metal shaping and forming techniques. While each method caters to specific needs, they are all optimized for efficient and rapid production, often eliminating the need for additional finishing steps.

The eight most widely used cold forging methods include:

• Bending
• Cold rolling
• Closed die
• Drawing
• Extrusion
• Open die
• Ring forging
• Swaging

While the following descriptions offer a foundational understanding of the various cold forging methods, it's important to note that other processes exist, which will be covered later in this chapter.

Another crucial factor in cold forging is the type of lubricant used. Common choices include zinc phosphate or various polymer coatings. Despite being performed at room temperature, the bending and shaping actions can raise the metal's temperature. The right lubricant helps prevent errors, reduces the likelihood of the workpiece sticking to the die, and extends the lifespan of the tools.

Lubricant manufacturers offer a variety of products to fit each type of cold forging process. Pictured are graphite lubricants, but graphite free types are available as well as calcium aluminate, aluminum fluoride, and phosphate coatings.

Common cold forging methods:

Bending

Bending involves using a press and die to force the workpiece against a shaping tool, a process also known as pyramid rolling. This method is sometimes employed to prepare a piece for subsequent cold forging processes. The workpiece is deformed along a single axis to achieve the desired angle.

Cold rolling

Rolling is a forming process where metal is passed through a pair of rotating rollers for plastic deformation caused by compressive force. The compressive stresses produce friction between the rolls and the metal stock‘s surface. It is commonly used for the processing of steel.

Closed Die

In closed die forging, the workpiece is shaped by successive mechanical blows after it has been placed between two die halves. Since the hammer strikes the workpiece multiple times, some producers refer to closed die forging as drop forging. As the metal is struck, it flows into the cavities of the die changing it to the shape of the die.

Drawing

Drawing involves pulling the workpiece through a die using tensile force applied at the die's exit. This process reduces the cross-sectional area of the workpiece while increasing its length. The resulting metal components achieve tighter dimensional tolerances compared to those produced by rolling.

Extrusion

In cold extrusion, a billet or slug is pushed through a die under compressive force that shapes it into the profile of the final part. After extrusion, the piece is cut to the desired length and either prepared for shipment or sent for additional processing. The compressive force in cold extrusion can reach up to 20,000 kN (approximately 2007 tons), and the process can be performed in forward, backward, or both directions.

Forward extrusion involves pushing the metal forward through the die.

Backward extrusion involves pushing the metal into the die in reverse, creating holes or cups with a thicker bottom compared to the sides.

Lateral extrusion applies force sideways, perpendicular to the extrusion direction, to add a secondary feature to the profile.

Open Die:

Open die forging uses two flat dies that lack a pre-cut profile. The workpiece is progressively shaped through multiple processes, allowing for a wide variety of shapes and sizes. This method is commonly used for large metal components that demand high structural integrity. Deformation is achieved by repositioning the workpiece throughout the process.

Squeezing, or sizing, is a specific type of open die forging where force is applied over a short distance to achieve precise dimensional finishes.

Ring forging

Ring forging involves creating a circular workpiece with a central hole, resembling a donut shape. As the pierced piece is rotated, it is hammered and compressed. This process results in seamless rings with precise diameters and excellent strength.

Swaging

Swaging, also known as radial forging, involves deforming a workpiece to ensure that two parts fit together precisely. It is an automated and highly reliable process. There are two main types of swaging: tube swaging and radial swaging. Tube swaging resembles extrusion, where the workpiece is pushed through a die. Radial swaging, on the other hand, uses a hammer to press the workpiece through two or more dies.

When searching for a cold forging manufacturer, you'll encounter more methods than the seven discussed here. Understanding these basic methods will enable you to engage knowledgeably with producers and interpret industry terminology effectively.

As with any advanced production technique, cold forging continues to evolve with the development of new methods and technologies. Automation and robotics are increasingly significant factors, transforming the industry rapidly. Consulting a forging specialist can help you identify the process that best meets your requirements.

Chapter Six – What types of equipment and machines are used in cold forging?

Cold forging equipment is available in three main types: hydraulic, pneumatic, and mechanical. While some suppliers focus on just one variety, most offer a range of options based on price and operational needs. Modern machines often incorporate technology and automation, as illustrated by the servo cold forging press from Marvel Machinery shown below. Part designs are typically created using engineering software like CAD.

There are requirements that machines must meet in order to be used for cold forging.

• Force - Cold forging processes depend on a tremendous amount of force. The equipment connected with it must be capable of absorbing that force and dissipating it.
• Balance - Machines have to be statically and dynamically mass balanced to reduce vibrations and enhance performance.
• Endurance over time - Regardless of the method of cold forging, each requires powerful repeated force. For a machine to last, it has to be able to endure that force.
• Multiple operations - Modern cold forging or forming machines, called headers, complete one to several operations during one process. This is necessary since there is a limited amount of deforming that can be performed with one stroke.

Types of cold forging equipment:

Hydraulic die forging hammer

The hydraulic die forging hammer is engineered to deliver maximum force with minimal investment. It can create a diverse range of impressions using various dies. This hammer operates on hydraulic principles, where an incompressible liquid is housed in a cylinder. When the liquid is compressed by a piston, it drives a shaft with the die attached downward onto the workpiece.

Screw press

The screw press is suited for large deformations due to its slow pressing speed. It is effective for flashless dies and long rod forgings. Its design accommodates single-slot dies for bending and final forging operations. An electric motor drives the screw, which presses the die onto the workpiece.

C Frame High Speed Press

The C-frame design is ideal for forming, punching, bending, and multi-pressing applications. Available in single or double crank configurations, these presses offer punch forces ranging from 110 to 400 tons and slide strokes between 110 and 280 mm. They can accommodate die heights from 435 to 600 mm and are suitable for producing small parts.

Pneumatic power press

The pneumatic-powered press is capable of handling all die pressing functions. It features a pneumatically operated friction clutch and brake. The press's power is generated by an air compressor, which uses air pressure in a cylinder with a piston to drive the forging hammer onto the workpiece.

Mechanical cold press

Among the various cold forging machines, mechanical presses are becoming less common due to their need for substantial size to generate the required force. They use a flywheel to store energy from a motor. When activated, the flywheel drives the hammer or ram onto the die. Although it can deliver power over multiple rotations, the press must pause to allow the motor to recharge the flywheel before resuming its cycles.

Among the various types of cold forging equipment, hydraulic and pneumatic presses are the most prevalent due to their compact size, adjustable force capabilities, and programmability. When evaluating production options, it's important to consider the types of equipment available from a producer, as modern and well-maintained equipment is more likely to yield higher-quality parts.

Chapter Seven- Who are the leading manufacturers of cold forging machines?

Numerous machines are available for cold forging, and they play a crucial role in modern industry. Cold forging allows for the cost-effective and efficient production of high-strength metal components used in sectors such as automotive, hand tools, and military hardware. Below, we highlight some prominent brands of cold forging machines used in the United States and Canada:

Hatebur - Model: HF-series

Hatebur's HF-series machines are renowned for their high-speed precision forging, advanced automation, and multi-station design. These features enable the efficient production of complex metal components with exceptional accuracy.

Sakamura USA - Model: SACMA Cold Formers

Sakamura USA provides SACMA Cold Formers, known for their versatility, precision, and high productivity in cold forging. These machines offer precise control over forging parameters and can produce a diverse range of components efficiently.

National Machinery - Model: FORMAX Plus

National Machinery's FORMAX Plus machines are distinguished by their advanced servo-driven technology, rapid tool change capabilities, and energy-efficient operation. These features enhance precision and productivity in cold forging applications, ensuring high-quality component manufacturing.

Carlo Salvi - Model: CF-Series

Carlo Salvi's CF-Series machines are renowned for their high-performance cold forging capabilities. They provide exceptional control over force and displacement, feature rapid tool change systems, and incorporate advanced monitoring and control technologies.

Nakashimada Engineering Works - Model: NBF-series

Nakashimada Engineering Works offers the NBF-series machines, which are celebrated for their sophisticated cold forging technology, accurate parameter control, and rapid production speeds. These attributes ensure both high efficiency and dependability in the manufacturing of components.

Keep in mind that details such as specific models, features, or components may have changed since my last update. For the most current information on the latest cold forging machines and their capabilities in the United States and Canada, it’s best to check with the manufacturers or relevant industry resources.

Chapter Eight– What are the different types of forged metals?

Cold forging offers a wide array of choices when you are choosing a metal for a project. The different varieties include hard metals such as carbon steel, alloy steel, and stainless steel. Aluminum, brass, copper, silicon, and magnesium are soft metals that can be used. The one requirement for any metal is that it has a hardness of 44 HRC or lower on the Rockwell scale.

Copper

Copper is highly suitable for cold forging due to its excellent ductility and malleability. It can be easily shaped, bent, or stretched with minimal force, resulting in components that are resistant to corrosion and rust.

Aluminum

Aluminum is a lightweight, non-ferrous metal with a low density. It melts at approximately 1220°F and is known for its malleability, as well as its resistance to rust and corrosion.

Carbon steel

Carbon steel is an iron-carbon alloy, with its various grades determined by the carbon content. It is known for its outstanding strength and ductility.

Stainless steel

Stainless steel is widely used for its corrosion resistance, aesthetic appeal, and strength. While the term "stainless steel" broadly refers to steel with these properties, it actually encompasses a range of grades, each defined by its specific alloy composition.

Steels used for cold forging

Low carbon steels with a carbon content of 0.1% to 0.25%. Cold forging improves strain hardening in steel removing the need for austenitization, quenching, or annealing.

Metals Suitable for Cold Forging

Data from website https://www.deringerney.com

Suitable Alloy	Cold Formability Characteristic
Copper	Excellent
Gold, Silver and most of their Alloys	Excellent
Brass- Cartridge Brass	Good
Platinum, palladium, tantalum, and their alloys	Most are cold formable.
Titanium and its alloys	Pure Ti and alloys with high ductility, yes, but alloys like 6-4 are only hot head able.
Nickel and its alloys	Pure Ni yes, alloys with room temperature elongation of 20% or more, yes.
Iron and steels	Pure iron, yes. Steels, depends on the steel. Many are cold formable.

Considerations when choosing a metal:

When selecting a metal for a project, thorough research is crucial. Different metals respond to plastic deformation and shaping in various ways. The chosen metal should meet the final use requirements and desired strength. Consulting with a forging expert can provide valuable insights to help you make an informed decision.

Chapter Nine – What are the applications of cold forging?

Cold forging is capable of producing components of various sizes with exceptional dimensional precision and structural accuracy. Its cost-effectiveness and rapid production speed have made it a preferred method in manufacturing.

Cold forging meets the demands of modern industries because it:

• Maximizes the use of raw materials: A key investment for any operation is raw materials, which is an essential and important element of cold forging and is carefully monitored.
• Reduces costs: Since parts are rapidly produced, the cost per unit is very low making the final products more profitable and less expensive to produce.
• Produces high quality parts: Cold forging increases the strength and durability of parts and products guaranteeing that they will last longer. The structure and characteristics of a shaped piece does not change providing excellent dimensional accuracy.

Applications where cold forged parts are used:

Automobiles

Cold forging's exceptional strength, reliability, and cost-effectiveness make it highly appealing for the automotive industry. Cold forged components are used in high-stress areas due to their superior shock resistance. Parts such as drive trains, drive shafts, and struts or shocks benefit from this process. The diagram below illustrates various undercarriage components of a car that are manufactured through cold forging.

Hand Tools and Hardware

Connectors like nails, bolts, rivets, and nuts have long been manufactured through cold forging. The process is favored by hand tool producers due to its ability to achieve tight tolerances and high dimensional accuracy, making it preferable to machining and other methods.

Military

The military adheres to stringent specifications for hardware, often opting for cold forging in the production of shell casings, bullets, and other military equipment. This method ensures high reliability and performance under demanding conditions. The precise tolerances and strength of cold forged components make them ideal for military applications.

Gear Production

Cold forging is used for gear production because it eliminates the need of cutting in gear shaping. Gears can be produced from billets that are less than 50 mm or shaped using coiled wire. Some annealing may be necessary to remove residual stress and work hardening. An important benefit of cold forged gears is how smoothly and quietly they intermesh.

Conclusion

• Cold forging produces metals with low tolerances and high dimensional accuracy at very low cost and high volumes.
• Cold forging quickly and rapidly creates finished parts immediately available and complete.
• Manufacturers will offer you a wide selection of processes to produce exactly and precisely the part you need using the most up to date and technically advanced equipment.
• You will have a wide array of metals to select for the completion of your project from hardened steel and stainless steel to copper and aluminum.
• You will find very few limitations to the number of products that you can have produced from stress withstanding components for your car to rivets, gears, and work tools.
• When you compare cold and hot forging, you will find that cold forging takes less time and produces stronger and longer lasting parts and products.

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