What is Hot Stamping Process? Benefits and Limitation of ...

What is Hot Stamping Process?

If you want to learn more, please visit our website MK.

Hot stamping, also known as hot forming or press hardening, is the technique of forming metal when it is extremely hot (above 900 degrees C) and then quenching (fast cooling) it in the die. The method transforms low-tensile-strength metal into steel with extremely high tensile strength (150 to 200 kilopounds per square inch) (KSI).

Body pillars, roof rails, rockers, bumpers, and door intrusion beams are just a few of the structural vehicle components that can be made by hot stamping. The hot stamping method ensures that these components are both sturdy enough to handle a heavy load and light enough to increase fuel efficiency.

HSS hot stamping technology, which combines classic hot forging and cold stamping technology, is a novel production technology that has emerged in recent years.

It's a manufacturing method that combines high-temperature steel stamping with die forming and quenching. Hot Forming, Hot Stamping, Hot Press, Press Hardening, and Die Quenching are all terms for the same thing.

The procedure can also reduce the cost of producing a part, which is especially useful in the production of traditional rear frames and other components that require robust and light materials.

In the automotive industry, the manufacture uses this technology to make stronger, lighter components, which enhances vehicle fuel efficiency and safety. Manufacturers can use hot stamping to create relatively complex parts in a single step. A multi-component, near-net-shape item is created, which is stronger than a welded steel part. Hot stamping is an important procedure for the manufacture of automobiles because it reduces the weight and increases the rigidity of high-strength steel parts.

Why Hot Stamping is Needed?

On the surface, the hot-stamping method appears straightforward: heat a steel blank until it is red-hot, press it into a die cavity, and leave it there to cool for a few seconds. 'High Tensile Strength' inspires images of a blacksmith welding a hot blank over an anvil with a sledgehammer and a quench bucket by his side ' Modern hot stamping allows for the formation of relatively complex pieces in a single step die.' The end result is a complicated, near-net-shape part with yield strengths that are many times higher than those of mild steel.'

Consumers are constantly concerned about safety and fuel economy, even when fuel costs are quite low. In fact, according to a Consumer Reports poll, >50% of car owners expect their next vehicle to get greater fuel efficiency. According to a study, if a vehicle's weight is lowered by 10%, its fuel efficiency can improve by 6 to 8%. Suppliers in the automotive industry have constantly sought ways to lower the weight of the vehicles they create in response to consumer demand for greater fuel mileage.

Some of the other reasons for use of the Hot Stamping Process

2. Complicated Products: Because hot stamping permits complex parts to be made in a single stroke, multi-component assemblies can be redesigned and formed as a single component, obviating the need for downstream joining operations like welding.
3. Springback: After its strengthening capabilities, maybe hot stamping's most significant advantage is its stress-relieving capability, which eliminates spring back and warping issues, which are frequent when forming high-strength steel (HSS) and advanced high-strength steel (AHSS).

Cold-stamped AHSS parts have a tendency to bounce back, which is one of the challenges of stamping AHSS.

History of Hot Stamping in the Automotive Industry

Hot stamping was invented and patented by the Swedish company Plannja in , particularly for the production of saw blades and lawnmower blades. When they created a hardened boron steel component for their Saab in , Saab Automobile AB became the first in the automotive industry to use hot stamping. More automakers have moved to hot stamping in the decades since to reduce car weight and increase fuel efficiency.

Volvo Car Company conducted research into the use of hot stamping parts in one of its car models, and additional hot stamping parts have been employed in automobile body manufacture since . In , the overall quantity had surpassed 100 million.

How does Hot Stamping Process Work?

In the first stage of the press line, the press-hardenable material'boron steel or aluminized steel'is heated to over 900 degrees in an oven to an austenite temperature.

The material is promptly moved to a press, where the part is created while still hot. The part is then quenched by being held in a water-cooled die cavity for a few seconds at the bottom of the stroke, which causes the grain structure of the material to change from austenitic to martensitic.

Press and Tooling Needed for Hot Stamping Process

• System of Heating: To heat the blank to roughly 960 degrees C, an oven or inductive heating system must be installed before the forming station in the press line.
• System of Cooling: A cooling system with a large number of variably controlled cooling circuits is also required for the press.
• An Automated Handling System: Because the heated part is extremely hot to the touch, the system must include an automated part handling system, such as a shuttle or robot transfer system.
• Dwelling Capacity: To maintain tonnage at the bottom of the stroke while the component is quenched, a hydraulic or servo press with dwell capability is necessary.
• Safety: For a hot operation, the press system must meet all safety standards.
• Tooling: The hot-stamping die is a single-step die with internal cooling channels that must be constructed of thermal shock-resistant tooling materials.

Limitations of Hot Stamping Process

Laser Trim: Because the part is too hard to cut using standard steel trimming dies once it has been press-hardened, the final trim must be done with a laser.

Reforming Can't Be done: Because the material is hardened, hot stamping is a one-step process'in reality, numerous procedures, such as further draws or flanging, are not possible.

Slower Forming: The process of hot forming is slower than that of cold stamping. It takes roughly 15 to 20 seconds to go from one stroke to the next.

Material Cost: Boron steel is more expensive than low-carbon materials.

Material Availability: Only boron materials can be hot-stamped; galvanized or prepainted steel cannot be used in this method. Boron is the element that allows the material to transition from a regular to a martensite state when it cools.

Conclusion                                                                                                                

The demand for high-strength steel (HSS) auto parts has risen in recent years as automobiles have become lighter. Many corporations and research institutes in the United States, Europe, Japan, and China have committed significant resources in the development of modern automobile HSS forming technology. Despite its high strength, HSS has significant drawbacks, including poor forming performance, unpredictable spring back, and the ability to shatter during the forming process. As a result, applying typical cold stamping technology to create complicated auto parts, where hot stamping technology is required, is problematic.

PS:  What do you think about the benefits and challenges of using HSS. Share your view on the process in the comment section.

Related Articles

1. What Is Hot Stamping

In its simplest definition, hot stamping, also called hot forming or press hardening, is the process of forming metal while it is very hot (in excess of 900 degrees C) and then quenching it (cooling it quickly) in the die. The process converts low-tensile-strength metal to a very high-strength steel (150 to 200 kilopounds per square inch (KSI).

2. How Does the Process Work?

The press-hardenable material'boron steel or aluminized steel'is heated to more than 900 degrees to an austenite temperature in an oven in the first stage of the press line. The material is transferred quickly to a press, and the part is formed while the material is very hot. Then the part is quenched'by being held in a water-cooled die cavity for a few seconds at the bottom of the stroke, which is when the material's grain structure is converted from a austenitic state to a martensitic state.

3. Why Hot Stamp?

"On the surface, the hot-stamping process sounds rather simple'heat a steel blank until it is red-hot, press it into a die cavity, and keep it there for a few seconds while it cools. The whole process conjures up visions of a blacksmith working a hot blank over an anvil with a sledge hammer and a quench bucket by his side," said Rich Marando, president of Graebener Group Technologies, Napoleon, Ohio.

High Tensile Strength."In the case of modern hot stamping, relatively complex parts can be formed in a single-step die," Marando continued. "The result is a complex, near-net-shape part with yield strengths many times stronger than a mild steel part."

Boron steel, in its original state, has tensile strength of around 50 KSI but is about 200 KSI after it is hot-formed.

Want more information on Hot Foil Stamping Machine For Sale? Feel free to contact us.

Complex Components. Because hot stamping allows the forming of complex parts in one stroke, multi-component assemblies can be redesigned and formed as one component, eliminating some downstream joining processes such as welding.

No Springback. Perhaps hot stamping's most significant advantage, after its strengthening capability, is its stress-relieving capability that resolves problems with springback and warping, a common problem when forming high-strength steel (HSS) and advanced high-strength steel (AHSS).

Cosma International Inc., Troy, Mich., a division of Magna International, designs, develops, and manufactures automotive systems, assemblies, modules, and components. The Tier 1 supplier relayed its experiences with hot stamping in "Hot forming: Strong meets light; Caught between NHTSA and CAFE," published in the May issue of The FABRICATOR®.

One of the challenges inherent in stamping AHSS is that cold-stamped AHSS parts have a tendency to spring back. This interferes with fit-up and causes difficulties during welding and assembly, said Swamy Kotagiri, director of R&D.

It becomes really difficult to cold-stamp complex, angular parts or parts with a 3-D twist when they are made with very high-strength materials'150 to 200 KSI.

4. Which Components Are Hot-Formed?

Simply put, hot stamping is best-suited to form components that must be both lightweight and very strong. Hot stamping's most prevalent application has been for structural automotive components such as body pillars, rockers, roof rails, bumpers, and door intrusion beams that must be strong enough to withstand a large load with minimal intrusion into the passenger compartment during a rollover and impact.

Hot stamping's most prevalent application has been for structural automotive components such as body pillars, rockers, roof rails, bumpers, and door intrusion beams.

Cosma sought ways to meet the National Highway Traffic Safety Administration's (NHTSA) structural requirements for increased vehicle safety. The requirement to reduce the roof intrusion into the compartment area in a rollover has become even more demanding.

"The roof crush standards are based on gross vehicle weight [GVW]," Kotagiri said. "Basically, the standard is saying that if a vehicle's GVW is 4,000 pounds, it has to withstand a force of up to 1.5 times that 4,000 pounds, or 6,000 pounds, in a roof crush test intended to simulate a rollover incident. New rules require the vehicle to be 2.25 to 2.5 times the GVW."

To meet those requirements, the components' material must be stronger'normally achieved by increasing in thickness and weight.

In an apparent contradiction, the components also have to be engineered to be as light as possible to meet increasingly stringent corporate average fuel economy (CAFE) standards for lower emissions, he said. "So the objective is to get the required structural performance, but add as little weight as possible," said Kotagiri.

5. What Are the Unique Press and Tooling Requirements?

Heating System. An oven or inductive heating system must be installed before the forming station in the press line to heat the blank to about 960 degrees C.

Cooling System. The press also must be equipped with a cooling system with a high number of variably controlled cooling circuits.

Automated Handling. Because the heated part is very hot to the touch, an automated part handling system, such as a shuttle or robot transfer system, must be integrated into the system.

Dwell Capability. A hydraulic or servo press with dwell capabilities is required to maintain tonnage at the bottom of stroke while the part is quenched.

Safety. The press system must conform to all safety requirements for a hot operation.

Tooling. The hot-stamping die is a single-step die with internal cooling channels, and it must be made of tooling materials that are resistant to thermal shock.

6. How Does It Affect Downstream Processes?

Because deep forming can be done in one hit, multipart assemblies can be formed as a single complex component.

"In the past, to beef up the safety performance of side-impact beams, the solution has been to add parts'to add more metal into the body side. In many cases, with hot stamping we're able to eliminate the need for additional parts," Kotagiri said in the article.

"Let's say you have a body side B pillar inner, B pillar reinforcement, and a B pillar outer. If I use hot-formed components in that assembly, now I'm able to eliminate the reinforcements. In roof crush case studies where conventional stampings and reinforcements have been substituted with hot-stamped components, the mass is reduced by roughly 30 to 40 percent," he said.

Scale. After forming, the part may need special treatment to remove scale and improve rust resistance. Uncoated boron steel requires a nitrogen-rich (or other inert gas) atmosphere in the furnace; otherwise, once it is exposed to the atmosphere, it develops a scale on it that must be removed by shot peening or sandblasting. Aluminum silicon-coated boron steel does not require scale removal.

7. What Are Other Capability Considerations?

Lower Tonnage Requirement. Kotagiri said the tonnage requirement to hot-form a high-strength steel part is substantially lower than is needed to cold-form it. Hot forming the draw portion of a B pillar requires only 30 percent to 40 percent of the tonnage needed to cold-form it using a similar-strength material, he said. So the part, which requires 1,000 tons to be cold-stamped, needs only 300 to 400 tons to be hot-formed, he said.

Complex Part Features. Hot forming can achieve very complex geometries at high strengths that cannot be cold-formed. "Honestly, there is not one other process today where you can form a part like an A pillar at the same strength, because of springback and because tonnage and strength requirements," Kotagiri said.

8. What Are Hot Stamping's Limitations?

Laser Trim. The final trim must be done with a laser because once the part is press-hardened, it is too hard to be trimmed using traditional steel trimming dies.

Material Cost. Boron steel costs more than low-carbon materials.

Cannot Be Re-formed. Hot stamping is a one-step process'in fact, multiple processes, such as additional draws or flanging, cannot be performed'because the material is hardened.

Slower Forming. The hot-forming process is slower than cold stamping. From stroke to stroke, it takes about 15 to 20 seconds.

Limited Materials. This hot-forming process cannot be applied to galvanized or prepainted steel; only boron materials can be hot-stamped. Boron is the element that gives the material the capacity to change from a regular material to a martensite material when it cools.

9. How Do I Compare Costs?

Calculating the weight and cost differences can be a challenge because a direct comparison of a cold-formed part to a hot-formed part would not be accurate, Kotagiri said.

"For example, you cannot take a cold-formed B pillar and compare it to a hot-stamped B pillar and ask, 'What's the cost difference?' because you're getting more out of your part in the hot-forming process," Kotagiri said. "The question is, 'We need this performance; now give us your design with hot stamping and tell us how much you saved in mass.'"

10. What Is the Future of Hot Stamping?

Cosma's Kotagiri anticipates that the rising demands for high strength-to-weight ratios will heighten demand for hot-formed components. "We think it will increase until about 8 to 12 percent of body structures will be martensite material, and then it will plateau at that point."

R&D efforts are under way to shorten quench cycle times and improve part integrity verification and lubrication and trimming methods. Research is also being done to improve control over thermal stress concentration so that strength and stress can be varied throughout the component.

Kotagiri said that one of the most important aspects of successfully applying hot-forming technology is being able to understand how the material is affected as it goes through the heating process in the furnace, and to understand the technology for quenching in the die.

"'How can I make parts consistently over a period of time and know exactly how quickly they cooled, how much they have cooled, and control the part temperature?' We have found the applications and ways to mass-produce components using this process. It is a very controlled, consistent cooling process," Kotagiri said.

The company is the world’s best Cardboard Stamping Machine supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.