This article covers all the information you need to know about Metal Stamping.
Read further to learn more about topics such as:
- What is metal stamping?
- Types of metal stamping operations
- Capabilities of metal stampers
- Parts and types of metal stamping dies
- Metals in metal stamping
- Advantages and disadvantages of metal stamping
- And much more…
Chapter 1: What is Metal Stamping?
Metal stamping is a coldworking process that transforms sheets of metal into specific, preset shapes. It uses specialized tooling which involves the stroke of the punch that brings conformational change to the metal sheet. By the application of an ample force to the workpiece by the punch, a metal stamper can either cut or form the metal sheet.
A metal stamper is a versatile machine that is capable of a broad range of cutting and forming operations. It can combine multiple cutting and forming steps in one tooling and may be performed on the workpiece within a single stroke. Multiple parts can be processed simultaneously in the same stroke. Metal stampers are easily automated and controlled, which benefits the metal fabricators by increasing their production rate, reducing labor costs, and augments the parts’ quality, repeatability, and precision. Combined with accurate tooling, they can produce parts with complex designs quickly and efficiently.
Metal stampers can create a variety of useful products from a simple washer, springs, hinges, and brackets, to parts with sophisticated designs such as those found in structural components, engines, industrial machinery, and automotive components. Stamped metal products are beneficial to many industries and end customers.
Chapter 2: Types of Metal Stamping Operations
The types of metal stamping operations employed in a metal fabrication plant are as follows:
Progressive Die Stamping.
In progressive die stamping, a sheet of metal is unrolled, fed into the press, and passes through different stations in the tooling which perform one or more metalworking processes (e.g., cut, bend, and punch). The sheet stays in the conveyor system of the stamper and the part stays connected in its base strip throughout the process. The workpiece stops at each station and is transformed by the die as the press moves down. As the press moves up, the sheet moves horizontally in the bed. The part is gradually formed as the workpiece progresses through the stations. In the last station, the finished part is ejected from the sheet.
The advantages of a progressive die stamping operation are quick production of parts with complex geometries and tight tolerances, high repeatability, and reduced labor costs. It combines multiple metalworking steps in single tooling. However, it is not suitable for parts requiring deep drawing.
Transfer Die Stamping
In transfer die stamping, the workpiece is first separated from the metal sheet and transferred from one stamping station to the other. The separated materials can be transferred to different presses, which enables the fabricator to produce varieties of parts in parallel.
Transfer die stamping is used in forming large parts. Since the part is not connected to its base metal sheet, the punch can go as deep as it can without affecting other operations, hence it is suitable for parts requiring deep drawing. It is also used in processes with intermediate steps in which the separation of the part early in the process would be more efficient.
In fourslide stamping or multi-slide stamping, the rams are aligned horizontally and slide toward the workpiece. It is a unique type of stamping process, different from the traditional stamping process which requires the downward stroke of a press. Each slide has one tool that can simultaneously bend, twist, cut or form in a horizontal stroke. A multi-slide stamping machine can have more than four moving slides.
Fourslide stamping is ideal for creating complex and multiple bends, for bends greater than 900, and for forming cylindrical parts. It has the unique ability to form twists. It can produce parts quickly, has inexpensive tooling, and lower initial cost. It also produces less scrap and reduces material cost because the raw metal piece can be bought to a width closer to the finished part.
In compound stamping, the die can perform multiple operations such as cutting, bending, and punching in one downward stroke. The sheet is continuously fed in the stamper and the finished part is then ejected out from the metal strip. A stroke can create multiple cuts and holes in the workpiece without the use of multiple dies and performing multiple strokes, which reduces production time and augments cost savings.
Compound stamping has good repeatability. However, it is somewhat limited to forming flat metal pieces with simpler geometries, such as washers.
Chapter 3: Capabilities of Metal Stampers
Metal stamping is a collection of several metalworking processes such as blanking, bending, and drawing. A metal stamper is a versatile machine that is capable of many metalworking tasks which transform sheet metal into a useful one. The capabilities of metal stampers are grouped into cutting and forming.
Cutting is the application of a sufficient shearing force to separate material into portions. The shearing force must exceed the material’s ultimate yield strength for the material to fail and separate at the cut location.
Blanking is a metal fabrication step in which the workpiece is cut from its base metal sheet. The downward stroke of the punch shears the outline of the workpiece. The cut-out is called a blank. It is usually the first step in a metal fabrication process. It makes the workpiece more manageable to handle for the succeeding operations. The excess material is scrapped and may be recycled.
A special type of blanking is fine blanking, in which the base metal sheet is supported by high-pressure pads. One of the pads is equipped with an impingement ring (V-ring) which pierces the perimeter of the piece before contacting the die and prevents the metal from flowing away while pushing it towards the punch. It uses a counterdie to provide a reciprocating pressure at the bottom of the workpiece and maintain its flatness. The tight clamping and balanced pressure prevent plastic deformation from occurring which results in smoother and fully sheared edges. After punching, the tool is opened and an ejector pin at the bottom half pushes the finished part.
In fine blanking, the clearance is minimized to less than 0.0005 inches to achieve a fully-sheared edge when combined with high pressures. The clearance is much smaller compared to traditional punching. Hence, it is prone to accelerated tool wear because of the occasional contact between the die and the punch. Deburring is necessary since the impingement ring consumes a small area that is attached to the finished part after punching.
Fine blanking is ideal for parts that require flatness, geometric accuracy, and must have smooth edges. It can also pierce small holes in the part. However, it is more expensive compared to traditional blanking.
Punching, or sometimes referred to as piercing, works in a similar fashion to blanking. It is the process of boring small shapes (e.g., holes) in the workpiece by application of a shearing force. A portion of the blank is cut from the blank and is discarded after ejection. Punching may be combined with the blanking step in a single downward stroke of the punch.
Trimming is the step in which the width is reduced to its desired profile by cutting out the outer perimeter of the workpiece. The excess material is often discarded or may be recycled.
Lancing is the step in which a portion of the workpiece is partially cut without separating it from its base sheet.
Forming is the re-shaping of a section in a material by applying a combination of compressive and tensile stresses to induce deformation.
Bending is a metalworking process of forming an angle or a curvature in the workpiece by inducing a plastic deformation to form the bend. It is done by forcing the forming die in the workpiece which is fixed in an opposing bottom die. The downward stroke of the punch gives the bend profile to be enforced in the workpiece. Some of the bending methods that can be performed in a stamping process include the following:
In bottom pressing or bottoming, the punch presses the workpiece and touches the bottom surface of a V or U-shaped die. The die determines the final angle of the bend. This method produces precise bends and has less tendency of a springback in the workpiece as more bending force is applied.
In air bending or partial bending, the punch presses the workpiece partially so that it will not touch the bottom surface of the die. A sharper bend can be achieved by applying more bending force. This method is less accurate than bottom pressing and coining.
Coining is a bending process that compresses the workpiece between the punch and the die. The compressive force is 30 times greater than the other bending process. The punch and the die complement each other and its internal dimensions give the exact angle or curvature to the workpiece. This method produces a more accurate bending and eliminates the tendency of a springback.
In flanging or wipe bending, the workpiece is held between the bottom die and the upper pressure pad, and the protruding material is pushed down by a forming punch. The springback is compensated by modifying the die and punch angle. This method is suitable for making perpendicular bends.
Drawing is a metalworking process of forming the blank into a hollow or concave shape with a seamless edge and parts with several diameters. It is performed by clamping the blank into a die by a blank holder and forced through it using a drawing punch. As the draw punch strokes downward towards the cavity, the workpiece experiences a complex sequence of stresses and deformation to form the finished part.
When the blank is drawn longer than its diameter, it is considered a deep drawing. Otherwise, it is referred to as shallow drawing.
Coining is a metalworking process of modifying the roughness of the surface of the workpiece by applying compressive stress resulting in plastic deformation. This operation results in a reduced surface grain size and a harder surface in the workpiece while maintaining its toughness and ductility.
This operation is different from coining in bending. It is used in manufacturing coins, buttons, and badges.
Embossing and Debossing.
Embossing is the process of creating a raised surface on the workpiece, while debossing creates a bump or depressed area in the workpiece. These processes are accomplished by pressing the workpiece against a male and female die. These processes are used to label or decorate a workpiece by adding unique and specific details such as texts, logos, and images.
Chapter 4: Parts and Types of Metal Stamping Dies
Dies are the sets of tooling used to cut or shape the material to create specific customized parts. Dies may be classified as a cutting die or forming die, but they have almost the same components:
- The die block is the female portion of the die. It is located at the bottom part of the die assembly wherein the punch is inserted. It is sometimes shaped like the final part and it also contains the holes and protrusions which are necessary for forming the material. It is also made from strong, rigid material like the punch.
- The die holder supports the die block that is clamped by a bolster plate.
- The punch is the male portion of the die that moves towards and applies sufficient force to the workpiece to either cut or form it. It is usually made of hardened steel or tungsten carbide. For cutting, the punch must be constructed from a material harder than the stock material.
- The punch plate is where the punching component is attached. It is further connected to a system that drives its movement. It is usually powered by hydraulic or mechanical means.
- The pressure pads hold the workpiece during cutting or forming.
- The stripper plate ejects the formed or trimmed parts from the punch after each stroke.
- The guide pins align the two halves of the die.
- The pressure plates are installed to distribute the pressure exerted by the punch.
Die assemblies are classified as follows:
Simple dies are dies that can perform only one task per stroke. It is commonly utilized for fabrication processes with few steps and for processing workpieces of low volumes. It may be less efficient but these specialized dies can perform a cutting or bending operation more precisely.
Compound dies perform more than one cutting operation per stroke, such as simultaneous blanking and piercing that is usually combined. They are used to produce parts with multiple cuts and complex designs, which perform the task faster. However, they are not suitable for forming operations as these processes require more force. A typical application of compound dies is in the production of flat washers.
Combination dies are sophisticated dies that are capable of performing more than one cutting and forming operations by a single stroke. Simultaneous cutting and forming (e.g., trimming and flanging) done in the workpiece speeds up the production time.
Progressive dies are used to gradually cut or form a workpiece by passing through the series of stations arranged within the die according to the sequence of steps involved in the fabrication of the part. The metal sheet is continuously fed in the metal stamper. It moves horizontally on the stamper’s conveying system when the die is open, then stops at the next station after the other. The distance between each station of the die is equal to each other. The final step is usually the ejection of the stamped part out from its base sheet.
Transfer dies are a series of multiple dies that are arranged on the production floor according to the sequence of steps involved in the fabrication of the part. Its operation begins with the workpiece being separated from its base metal sheet in the first station, and then transferred to the series of dies by a conveying system. Two or more sets of transfer dies may be used to run different products in parallel.
Transfer dies are used in the fabrication of parts that are large and have complex designs which require specialized dies to operate precisely.
Chapter 5: Metals in Metal Stamping Process
The metals commonly processed in a stamping process are the following:
Copper alloys are non-sparking and non-magnetic metals. They possess excellent electrical and thermal conductivity, corrosion resistance, and anti-microbial properties. Copper alloys can be stamped and formed with minimal difficulty because it is less hard, ductile and malleable. They have good compatibility with cold forming processes. Stamped copper alloys are durable and decorative.
Copper alloys that are commonly processed using metal stamping are brass, bronze, beryllium copper, and nickel silver.
Steel is a wide class of alloys that mainly consists of iron and carbon. Their mechanical properties primarily depend on the concentration of their alloying elements. Higher carbon content makes steel harder, more brittle, and less ductile. Meanwhile, higher nickel and chromium content make the steel more corrosion-resistant. Generally, steel alloys have high strength and high toughness and can withstand extreme temperatures, but they are quite challenging to be stamped.
The common steel alloys in metal stamping include stainless steel and carbon steel.
Aluminum is a low-cost, lightweight, and non-ferrous metal. It is also corrosion-resistant, can withstand extreme temperatures, has good thermal and electrical conductivity, and has a high decorative value. Because of its ductility, flexibility, malleability, softness, and high strength-to-weight ratio, it can be stamped smoothly without failing.
Chapter 6: Advantages and Disadvantages of Metal Stamping Process
The advantages of utilizing a metal stamping process are the following:
High Production Rates
Metal stamping can produce parts quickly. It can process multiple parts and can perform more than one cutting and forming operations in a single stroke, which shortens the production time.
High Repeatability and Precision
Metal stampers can produce parts after every stroke that are guaranteed to be dimensionally and visually identical with each other. Metal stampers can produce cuts and shapes with dimensional precision, even though the design is complex, because of its automated controls and accurate tooling. This is important if product consistency is greatly valued.
Low Labor Cost
Since metal stamping nowadays is automated, it only requires a minimal intervention of the operator who controls the machine. All steps in the fabrication process are done by the stamping machine and manual labor involved is seldom.
Low Maintenance Cost
The metal stamping dies are easily maintained during their service life.
The downsides of a metal stamping process are the following:
High Investment CostsStarting up a metal stamping operation might be tedious. A group of designers and fabricators create the prototype die based on the conceptualized design of the part to be produced. Furthermore, several iterations on the tooling and trial production runs are also performed that augments the investment costs and can be time-consuming.
Expensive ToolingThe tooling is made of a hard and durable material to create a smooth and precise shape or cut and its fabrication process can be costly. However, metal stamping dies can produce thousands of parts before coming to wear and needing replacement.
Difficulty in Making Changes to the Part DesignCustomizing specific parts or changing the design of the parts to be produced requires modifications in the dies from the original tooling.
- Metal stamping is a straightforward operation that can perform cutting or forming operations quickly, and process numerous parts simultaneously, in a single stroke of the press. The force applied by the press brings conformational change to the stock metal sheet.
- Metal stamping operations are classified based on the configuration and sequence of the tooling needed to produce the part. These are progressive die stamping, compound stamping, transfer die stamping, and fourslide stamping.
- Cutting and forming are the two subgroups of operations that a metal stamper can perform.
- Ductility and malleability are the minimum characteristics of a metal that can be stamped with relative ease.
- The advantages of a metal stamping process are a high production rate, high repeatability, and precision, low labor and maintenance costs.
- Dies are classified based on the station configurations and the operations they can perform. The types of dies are simple dies, compound dies, combination dies, progressive dies, and transfer dies.
- The downsides of a metal stamping process are expensive tooling, high investment costs, and difficulty in making changes in the part design.