Mastering Deep Drawing Press: A Comprehensive Tutorial
Deep drawing is a cornerstone metalforming process, transforming flat sheet metal blanks into complex, hollow shapes like cups, cans, casings, and automotive components. Mastering it requires understanding the intricate interplay between the deep drawing press, the tooling, and the material. This tutorial breaks down the key elements you need to control to achieve high-quality, production-ready parts.
Mastering Deep Drawing Press: A Comprehensive Tutorial
1. Understanding the Fundamentals and the Press
At its core, deep drawing involves a punch forcing a blank into a die cavity, forming the metal through a combination of radial drawing and circumferential compression. The press provides the force and motion. There are two primary types:
● Mechanical Presses: Known for high speed and efficiency, ideal for high-volume production of parts with shallow to medium draws. Their constant stroke length is less adaptable to variations in material or blank size.
● Hydraulic Presses: Provide full tonnage throughout the entire stroke, offering superior control over punch speed and pressure. This makes them essential for deep draws, complex shapes, and working with high-strength materials where precise, constant force is critical.
2. The Critical Role of Tooling and Design
The tooling—the punch, die, and blank holder—is where the process is defined.
● Punch and Die Clearance: This is the single-sided gap between the punch and die. It must be precisely calibrated to be slightly larger than the metal thickness to allow material flow without wrinkling or tearing. Too tight a clearance shears the metal; too loose causes wrinkling.
● Die and Punch Radius: Sharp corners create stress concentration points that lead to tearing. Generous radii on both the die entry and the punch nose are essential to allow the metal to flow smoothly into the die cavity.
● Blank Holder Pressure (BHP): The blank holder (or binder) applies a controlled force to hold the periphery of the blank. Its primary function is to prevent wrinkles without restricting the flow of metal into the die. Mastering BHP is a balancing act:
○ Too much pressure: restricts flow, leading to thinning and tearing in the cup wall.
○ Too little pressure: allows compressive stresses to cause wrinkling in the flange or the wall.
3. Material Selection and Preparation
Not all metals deep draw equally. Drawability is a key property, often measured by the n-value (strain hardening exponent) and r-value (plastic strain ratio).
● High r-value materials resist thinning, making them ideal for deep drawing. Common choices include low-carbon steels, stainless steels, aluminum alloys, and copper.
● Surface Finish & Lubrication: A high-quality surface finish on both the blank and the tooling is vital. Proper lubrication is non-negotiable; it reduces friction between the blank and the tooling (die face and blank holder), minimizing wear, controlling heat, and facilitating smooth metal flow. The type of lubricant must be matched to the material and the severity of the draw.
4. Mastering the Process: Key Variables
● Drawing Ratio: This is a fundamental calculation: the ratio of the blank diameter to the punch diameter. It defines the severity of the draw. A higher ratio means a more severe draw. The maximum successful ratio for a first draw is typically around 2.0. Beyond this, parts require multiple draws with intermediate anneals.
● Speed (Press Ram Speed): The speed at which the punch enters the die affects formability. For complex or deep draws, a slower, controlled speed (typical of hydraulic presses) allows the material to flow and work-harden at a manageable rate, reducing the risk of tearing.
● Multi-Stage Operations: Many parts cannot be formed in a single operation. They require a series of progressively deeper draws, often with annealing operations in between to recrystallize the work-hardened grain structure and restore the metal's ductility.
5. Troubleshooting Common Defects
Mastery is shown in diagnosing and correcting issues:
● Tearing: Caused by excessive tensile stress. Check for too much Blank Holder Pressure, insufficient lubrication, too small punch/die radii, or a material with low formability.
● Wrinkling: Caused by compressive buckling. The primary remedy is to increase Blank Holder Pressure. Also, check for excessive clearance or a blank that is too large.
● Earing: Wavy edges on the top of a drawn cup caused by the anisotropic nature of the sheet metal. It is minimized by using material with a high normal anisotropy and can be trimmed as a final step.
Conclusion: Mastery is a Symphony
Mastering the deep drawing press is not about controlling one variable, but about orchestrating them all in harmony. It requires a holistic view of the press capabilities, meticulous tooling design and maintenance, careful material selection, and a disciplined, analytical approach to process setup and troubleshooting. By focusing on these fundamental principles, you can transform sheet metal into robust, complex, and precise components efficiently and reliably.
GOODSJACK HYDRAULIC MACHINERY CO., LTD
DELISHI MACHINERY TECHNOLOGY CO., LTD
Hydraulic Press Machine, Hydraulic Forging Press Manufacturer
Web: www.hydraulic-press-machine.com
www.goodsjack.com
Tel: +86-769-88057683 83223615
Fax: +86-769-83231691
Dongguan Factory
General Factory : No3, Jinfu Road, Jinma Industrial Park, Liaobu Town, Dongguan, Guangdong, China
Hubei Factory
Address: Sanhua Industrial Park, Binjiang New Area, Huangshi, Hubei, China
Eva Lee Sales Manager
Email: sales@goodsjack.com
WhatsApp/Wechat:+ 86 13509801050
Alice Xu Sales Manager
Skype: alice.goodsjack
Email: sales1@goodsjack.com
WhatsApp/Wechat: +86 13642957273
1. Understanding the Fundamentals and the Press
At its core, deep drawing involves a punch forcing a blank into a die cavity, forming the metal through a combination of radial drawing and circumferential compression. The press provides the force and motion. There are two primary types:
● Mechanical Presses: Known for high speed and efficiency, ideal for high-volume production of parts with shallow to medium draws. Their constant stroke length is less adaptable to variations in material or blank size.
● Hydraulic Presses: Provide full tonnage throughout the entire stroke, offering superior control over punch speed and pressure. This makes them essential for deep draws, complex shapes, and working with high-strength materials where precise, constant force is critical.
2. The Critical Role of Tooling and Design
The tooling—the punch, die, and blank holder—is where the process is defined.
● Punch and Die Clearance: This is the single-sided gap between the punch and die. It must be precisely calibrated to be slightly larger than the metal thickness to allow material flow without wrinkling or tearing. Too tight a clearance shears the metal; too loose causes wrinkling.
● Die and Punch Radius: Sharp corners create stress concentration points that lead to tearing. Generous radii on both the die entry and the punch nose are essential to allow the metal to flow smoothly into the die cavity.
● Blank Holder Pressure (BHP): The blank holder (or binder) applies a controlled force to hold the periphery of the blank. Its primary function is to prevent wrinkles without restricting the flow of metal into the die. Mastering BHP is a balancing act:
○ Too much pressure: restricts flow, leading to thinning and tearing in the cup wall.
○ Too little pressure: allows compressive stresses to cause wrinkling in the flange or the wall.
3. Material Selection and Preparation
Not all metals deep draw equally. Drawability is a key property, often measured by the n-value (strain hardening exponent) and r-value (plastic strain ratio).
● High r-value materials resist thinning, making them ideal for deep drawing. Common choices include low-carbon steels, stainless steels, aluminum alloys, and copper.
● Surface Finish & Lubrication: A high-quality surface finish on both the blank and the tooling is vital. Proper lubrication is non-negotiable; it reduces friction between the blank and the tooling (die face and blank holder), minimizing wear, controlling heat, and facilitating smooth metal flow. The type of lubricant must be matched to the material and the severity of the draw.
4. Mastering the Process: Key Variables
● Drawing Ratio: This is a fundamental calculation: the ratio of the blank diameter to the punch diameter. It defines the severity of the draw. A higher ratio means a more severe draw. The maximum successful ratio for a first draw is typically around 2.0. Beyond this, parts require multiple draws with intermediate anneals.
● Speed (Press Ram Speed): The speed at which the punch enters the die affects formability. For complex or deep draws, a slower, controlled speed (typical of hydraulic presses) allows the material to flow and work-harden at a manageable rate, reducing the risk of tearing.
● Multi-Stage Operations: Many parts cannot be formed in a single operation. They require a series of progressively deeper draws, often with annealing operations in between to recrystallize the work-hardened grain structure and restore the metal's ductility.
5. Troubleshooting Common Defects
Mastery is shown in diagnosing and correcting issues:
● Tearing: Caused by excessive tensile stress. Check for too much Blank Holder Pressure, insufficient lubrication, too small punch/die radii, or a material with low formability.
● Wrinkling: Caused by compressive buckling. The primary remedy is to increase Blank Holder Pressure. Also, check for excessive clearance or a blank that is too large.
● Earing: Wavy edges on the top of a drawn cup caused by the anisotropic nature of the sheet metal. It is minimized by using material with a high normal anisotropy and can be trimmed as a final step.
Conclusion: Mastery is a Symphony
Mastering the deep drawing press is not about controlling one variable, but about orchestrating them all in harmony. It requires a holistic view of the press capabilities, meticulous tooling design and maintenance, careful material selection, and a disciplined, analytical approach to process setup and troubleshooting. By focusing on these fundamental principles, you can transform sheet metal into robust, complex, and precise components efficiently and reliably.
GOODSJACK HYDRAULIC MACHINERY CO., LTD
DELISHI MACHINERY TECHNOLOGY CO., LTD
Hydraulic Press Machine, Hydraulic Forging Press Manufacturer
Web: www.hydraulic-press-machine.com
www.goodsjack.com
Tel: +86-769-88057683 83223615
Fax: +86-769-83231691
Dongguan Factory
General Factory : No3, Jinfu Road, Jinma Industrial Park, Liaobu Town, Dongguan, Guangdong, China
Hubei Factory
Address: Sanhua Industrial Park, Binjiang New Area, Huangshi, Hubei, China
Eva Lee Sales Manager
Email: sales@goodsjack.com
WhatsApp/Wechat:+ 86 13509801050
Alice Xu Sales Manager
Skype: alice.goodsjack
Email: sales1@goodsjack.com
WhatsApp/Wechat: +86 13642957273
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