The Importance of Metal Stamping
What is Metal stamping?
The metal stamping process began during the industrial revolution as a cold forming means for producing frames and handlebars for bicycles. From its beginnings in Germany, it has grown into an essential part of modern industry for the production of parts and components for a wide variety of industries. The early auto industry transferred its parts production from forging to metal stamping because of the lower cost of the stamping process.
Metal stamping is a relatively simple process where rolled or sheet metal, referred to as a blank, is placed in a press that has a die in the desired shape of the part. With force and compression, the die is pressed into the metal. After a predetermined amount of time, a partially completed part is removed. Though this may seem very easy to understand, in reality, there are several different steps that need to be taken that include trimming, finishing, and other procedures designed to produce the finished part.
Though metal stamping started 100 years ago, over the years, it has been updated, improved, and made a part of the technological age. This can be seen with the introduction of computer numerical control (CNC) into the stamping process where designs are created and tested on a computer then fed into a CNC metal stamping machine.
There are several benefits to metal stamp. It is a cold shaping process that does not require heating to shape the metal, which makes it less expensive. Complex and intricate designs that are impossible to produce using any other process can easily be fabricated. The precision and accuracy of metal stamping has made it the number one method for part manufacturing.
Metal Stamping Basics
Metal stamping takes a flat piece of metal and transforms it into a specific and desired shape. It is a complex process that involves several complicated and intricate procedures. From the auto and aerospace industries to the medical and electronics industries, metal stamping is an integral part of producing affordable and well-crafted parts and components. Metal stamping involves the use of a wide array of processes and techniques such as punching, blanking, embossing, coining, bending, and flanging.
Metal punching is a fabricating process that removes a scrap slug from the workpiece when the punch enters the punching die. Punched material is normally in sheets but rolled metals can be used as well. The process leaves a hole in the die that exactly matches the dimensions of the design. Holes of varying shapes and sizes are accurately produced using this process.
Sheet metal blanking is a shearing and cutting process where a sheet metal piece is removed from a larger sheet of metal. The removed piece is referred to as the “blank” and has the desired shape of the final part. It is mainly a part of a 2D forming process.
Embossing produces a raised or recessed design by forcing a blank against a die in the shape of the desired pattern. When the metal is pushed into the embossing machine, a tool or stylus creates a raised effect on the opposite side of the blank. By placing the blank on a sheet of rubber or foam, the embossed image has a smooth surface finish.
Coining is required when the edges of a stamped part need to be flattened. The process creates a smoother edge, produces finer details, and adds strength to the workpiece. Coining helps avoid any forms of secondary finishing such as deburring or grinding. A great deal of pressure is required for coining to produce the necessary plastic deformation.
Bending refers to a method of deforming metal into L, U, or V-shaped profiles. A press brake bends the metal using a punch and die. The different forms of press braking are mechanical, pneumatic, hydraulic, and CNC. The bending process results in a deformation that stresses above the yield point but below the tensile strength and occurs around a single axis.
Flanging is shaping a metal piece to produce a flare or flange using a die, press, or specialized flanging machine. The process creates a 90 degree bend in the metal. When the breakline of the bend is larger than the trim line, it is called a stretch flange while the condition where the break line is less than the trim line is a shrink flange.
Metal stamping machines can cast, punch, deform, and bend metals using computer programming or computer numerically controlled (CNC) machines for precision and accurate parts. The modern process of stamping can quickly create exact metal shapes with meticulous accuracy and measurements. These highly technical tools provide custom solutions for 300 different kinds of raw materials. The low cost of stamping has made it a major factor in the production of the items we depend on to make life easier.
Different stamping methods
Metal stamping refers to several types of forming processes each of which performs a special type of operation. The type of stamping method depends on several factors from the design of the part to the number of required stamping operations. The choice of procedure is normally defined and specified by the engineer or designer.
Progressive die stamping
Normally, stamping refers to a single operation where a portion of a part is formed in one machine before being moved on to another machine or set of machines. The process requires multiple dies on several pieces of equipment. Finishing and shaping are separate operations performed after the part has been through the various machines. Progressive stamping removes the need for multiple machines performing several functions and handling of the workpiece in a single set of operations. A strip of rolled metal unrolls into a single die press with a number of stations that perform individual functions. Each station adds to what has been done previously resulting in a completed, finished part.
Progressive stamping simplifies the production of complex and intricate parts decreasing production time while increasing efficiency. Movements must be precisely aligned since the part is still connected to the metal roll. The first station separates the fabricated part from the rest of the metal. Progressive die stamping is ideal for long runs since the dies last longer and do not sustain any damage as a result of the process. As with several stamping processes, progressive stamping is repeatable. Each station performs a different cut, bend, or punch to gradually achieve the desired end shape and design. Progressive die casting is faster and has limited waste scrap.
Transfer Die Stamping
Transfer die stamping uses a mechanical transport system to move the part from station to station. It is used for tube applications, frames, shells, and structural components. A die can be a simple single die or part of several dies lined up in a row. To perform transfer die stamping, the part is removed from the metal strip as it transfers between stamping stations. Transfer die stamping was developed to produce large parts and workpieces with the additional benefit of lower tooling costs.
Four Slide Stamping
Four slide, multislide, or four way stamping shapes the workpiece horizontally sliding it between four different tools. As the workpiece feeds, it is bent by each tool using a smooth set of processes. Each slide is driven by a shaft controlled by the rotations of a cam. The shafts are connected by a bevel gear with one electrical motor to power the shafts. The workpiece may be shaped with all tools working at once or in succession. The key to four slide stamping is the shafts, which allows the work piece to be shaped on all four sides.
Fine blanking is a special type of stamping that produces flatness and a sheared edge that is impossible with traditional stamping. Any secondary machining of parts is not required since profiles, web sections, and holes are completed in one process. To achieve the perfection of fine blanking, the blank is compressed between the upper and lower punches allowing the process to hold a very tight tolerance. The process is known for its high accuracy and smooth edges. It is done with hydraulic or mechanical presses or a combination of the two.
The three individual movements of the press are used to complete blanking - clamping, blanking, and ejection. Fine blanking presses operate at higher pressures requiring tools capable of withstanding those conditions. The total process is completed in a single cold stamping step.
Stamping Press Categories
The normal categories for stamping presses are mechanical, hydraulic, and mechanical servo. Feeding is done automatically either in sheets, coils, or perfectly sized blanks. The type of feeder depends on the thickness of the sheets. The reel type is used for thinner sheets while thicker metal sheets are fed individually. With roll metal feeders, as the metal unrolls, it is straightened to remove any residual effects.
Mechanical milling is a method for preparing and reshaping metals without the use of heat or chemicals. Its function is to remove metal from a workpiece by using a cutter where the metal has a flat, rough, or irregular surface, and the workpiece is fed into the cutter. Mechanical milling requires a high powered motor to rotate the cutter to break down the structure of the workpiece. The size of the cutter and speed vary depending on the type of machine. Most mechanical milling equipment weighs several tons and is designed for heavy duty operation. They have been a major part of manufacturing and product production since the industrial revolution.
Hydraulic milling machines use the force of hydraulic power to compress the workpiece onto the die. This form of milling is widely used because of its accuracy and cost effectiveness. Pressure applied to the die is more uniform than produced by mechanical milling machines. In many cases, the hydraulic milling machine’s process is referred to as stamping since the workpiece is stamped into the mold or die. The workpiece is fed into the machine and aligned with the die where pressure is applied. The amount of pressure and speed can be adjusted to fit the type of metal. As with all milling equipment, hydraulic machines come in several sizes to fit the type of manufacturing.
Until recently, the only way to increase tonnage on a press was to build a bigger press with a larger motor or flywheel, an expensive process. Press designing engineers decided to build a better press by removing the motor, flywheel, and clutch and replacing them with a servo motor focused on needed energy.
Servo presses offer more flexibility for setting the stroke and slide position, which opens several possibilities. By replacing a flywheel with a servo motor, torque can be delivered by the use of a controlled and programmable system to set the speed making it possible to match velocity, dwell, and stroke depending on the application.
Using high capacity motors, mechanical servo presses can create complicated stampings at a faster rate than hydraulic presses and are powered by a link-assisted drive system or a direct drive one. Of the three types of presses listed, the mechanical servo press is the newest and most expensive. Regardless of the drawback of cost, several manufacturers have installed mechanical servo presses and have found them to be more efficient and cost effective.
What are Stamping Dies?
Stamping dies are precision tools specially designed to cut and form metal sheets into a specific shape or profile. Dies are made from hardened steel called tool steel, a variety of high-hardness and abrasion resistant steel. Included in a die can be cutting and forming sections made from other metals that are hard and wear resistant. Dies for metal stamping can be either single-station or multiple-station.
Dies used for single station operations can be compound or combination . Both perform multiple operations in a single function. The main difference between them is their design and the type of stamping they do where a compound die mainly cuts and a combination die does both cutting and non-cutting processes.
Compound dies perform more than one cutting operation in a single press, such as the case of the multiple cuts needed to create a simple washer from steel. They can produce a part every three seconds, which reduces labor costs and shortens lead times. Complex parts are easily cut with one stroke ensuring accuracy for every part. The high accuracy of compound dies reduces waste, another cost savings factor.
Combination dies have cutting and non-cutting tools and can complete reshaping in one action where cutting such as drawing or bending are completed together. One of the benefits of combination dies is their ability to handle large projects efficiently and economically. Die set up is faster, and there is a significant decrease in waste. A single cut can produce holes and flanging.
Multi-station dies use progressive milling to automatically move the workpiece through several stations. Raw metal is fed into the machine where it is cut, bent, coined, or punched depending on the system’s programming and the requirements of the part. Each station can perform one or multiple functions.
Steel rule dies, also referred to as knife dies or cookie cutter dies, were first used to cut softer surfaces such as plastics, wood, cork, felt, fabrics, and paperboard. Though they are not as sturdy as steel dies, they have found use in the cutting and shaping of thin non-ferrous metals such as aluminum, copper, and brass.
Steel rule dies are made of high grade, high density, and hardwood plywood with steel strips added. Slits are cut into the flat plywood. Steel rule, which is similar to a razor blade, is inserted into the slits. Rubber is glued to the flat side of the plywood to help eject it after the cutting process and prevent it from sticking to the metal press. Steel rule dies come in several thicknesses depending on the application.
The steel strip material used for the cutting surface is designed to match the desired shape. The characteristics of the workpiece, such as thickness and hardness, help determine the steel rule thickness to be used in the cutting blade. Steel rule dies can be used to cut exotic materials, thick foam, carpet, and rubber. It is an inexpensive and effective method of cutting thin sheet metals.
What to consider when choosing metals for stamping
Stamping requires a certain amount of knowledge of metals and how to work and shape them. The type of metal for a project depends on the desired outcome. Though metal is normally considered for stamping, other non-metal materials can also be shaped by stamping such as paper, leather, or rubber. Do it yourselfers and hobbyists use hand operated stampers for home projects and shaping non-ferrous metals.
Though there are thousands of metals that can be stamped, there are two general categories - ferrous and nonferrous where ferrous metals have iron and nonferrous do not. Nonferrous metals that are commonly stamped are aluminum, brass, bronze, gold, silver, tin, and copper. One of the factors that determines the formability of a metal is its carbon content, though carbon is only one of many factors.
Alloys, a compound of two or more metals, are commonly used in metal stamping. Each alloyed metal has special characteristics that has to be considered when being used for metal stamping. For example, non-standard alloys, such as beryllium nickel and beryllium copper, are excellent for metalworking, forming, and shaping musical instruments and bullets.
The shaping and forming of precious metals is an ancient process that goes back to the time of the Romans, Greeks, and Egyptians. What was once the work of highly trained and talented craftsmen has been transformed by modern stamping machines. Silver, gold, and platinum can be molded in intricate patterns with the use of dies and cutting tools. The skills of the craftsmen of years ago has been replaced by machines and technology.
Ferrous metals are ideal for forming components due to their durability, high tensile strength, and hardness. Low carbon metals have excellent formability and can be used for hardened machine parts and are very versatile.
As with any industrial process, careful planning and preparation are necessary when using metal stamping. The selection of the correct metal and the quality of the final product depends on the type and quality of the materials for the process.
What happens at finishing
When a workpiece has completed the stamping process, it may require other processes to remove any imperfections, deformities, or excesses as well as the addition of other parts and applications. This is performed during post stamping production operations, which include deburring, tapping, reaming, and counterboring.
Rough sharp ragged edges or ridges can be left after stamping. These deformities are referred to as burrs. The process for removing them is called deburring, which can be performed by hand, electrochemically, or using a thermal method. Deburring may be required for several sections of a workpiece since burrs can occur in seams as well as edges.
Deburring improves the quality, aesthetic value, functionality, and appearance of a workpiece. Also, there is the matter of safety where a small notch or deformity can catch on a piece of equipment or cause personal injury. More difficult burrs may need to be flanged over to produce a smoothed edge and direct the burred edge to the inside fold where it will not cause injuries or be noticed.
The importance of the design
When a design is created using CAD, onscreen results and calculations give the impression that what has been produced is perfect and flawless. What may be ignored are some of the limitations to processing and types of material, which can lead to the production of parts that do not perform as they were designed. Thickness, formatting area, grain direction, and hardness all have an influence on the design of a part and the stamping process.
There are design flaws that can reduce the quality of the final product. One of those is overly narrow projections, which can distort the workpiece.
Designs are created for a manufacturer’s available equipment, tools, dies, and materials. Custom dies or using special equipment increases manufacturing and fabricating costs as well as the cost of the final product.
Special consideration is necessary regarding sharp edges, corners, and bends in a design to help in the reduction of burrs and other deformities since they will require special finishing and other secondary treatments. Sharp bends or corners may cause cracking due to increased stress on the workpiece. Increased stress can lead to failure of the part.
The dimensions of a product are restricted by the width and length of the workpiece. In the design phase, careful adjustments need to be made for folds on edges, flanges, and material removal that fit the dimensions of the workpiece.
Large stampings require a stamping press with a large bed and higher tonnage. When larger machines are not available or practical, production can be completed by using multiple steps that are later joined together.
Punching is a cutting process used to modify and deform a metal blank where shearing force is applied. It is similar to blanking with the exception of the piece being removed, slug, is scrap. Punched holes are in simple geometric shapes either individually or combined. Holes formed from punching normally require secondary finishing since burrs are left around the edges of the hole. The punch is driven into the workpiece at high speed. CNC punch presses can be hydraulic, pneumatic, or electrical able to deliver over 500 punches per minute. Most punches have a turret that can hold close to 100 different styles of punches.
Bending is applying force to the workpiece causing it to bend at an angle to create a desired shape. The operation is performed along one axis, but a set of operations are possible for complex pieces. Parts can be as small as a bracket or several feet. Bending creates both tension and compression in the workpiece. The outside part will have tension while the inside, as it shortens, experiences compression. In some cases, it may be necessary to overbend to account for any springback.
When milling holes by punching or drilling, the holes should be two times the sheet thickness apart. The distance ensures metal strength, and prevents the holes from being bent or otherwise deformed. When holes are placed at the edge of a workpiece, they should be the thickness of the workpiece away from the edge. The space between holes and bends should allow for the bend radius and be sufficiently far from the bend.
When stamping can be used and when it is not appropriate
Metal stamping is an easy way to reshape and deform metal sheets. It can be used to produce highly complex and intricate designs that are not possible with any other process. A plain flat piece of metal can easily be turned into a practical and usable shape.
There are several benefits to metal stamping, which include lower costs for dies and any secondary factors. Modern era stamping machines are automated and work with little need for any handling of the workpiece. The dies and tools required for stamping are inexpensive and can be used multiple times. Cleaning, plating, and other secondary processes are less expensive since many products are nearly finished after being pressed. Automation processes for stamping machines are uncomplicated and adaptable. Various computer programs offer precision, control, and precise dimensions for the completion of a product providing quicker turnaround times. An added benefit of automation is a significant decrease in labor costs.
One of the drawbacks to metal stamping is the cost. Upfront cost of equipment, tools, and dies are high and require a significant investment. For custom parts or designs, a special steel die has to be created leading to longer pre-production and extended turn around times. Changing dies during production due to design flaws can be difficult and time consuming.
Where metal stamping is used
Metal stamping is one of the fastest growing production processes in the world. It is estimated that in the next ten years the market for stamping will grow to 300 billion dollars worldwide. Though this may seem to be an over exaggeration, it is easy to understand when considering the number of industries that use the stamping process.
The process of metal stamping is used by industry to produce parts and products with high precision, accuracy, and speed. Products produced using stamping methods have lower errors per production cycle than any other process, which eliminates flawed or faulty products.
Several industries rely on stamping to produce products. The automotive industry uses it for structural components such as body frames, electrical systems, and steering systems. The aerospace industry requires parts that need to meet strict manufacturer specifications to ensure safety and maintain certifications. The medical industry has requirements similar to aerospace and depends on metal stamping for its accuracy and reliability.
Computer and electronics manufacturers use metal stamping to create their internal components. Technical parts have special shapes and dimensions requiring precision manufacturing and production methods. The stamping process plays a critical role in the fabrication of these modern conveniences.
The metal stamping industry has played a part in the production of most of the items found in homes, schools, business, and offices. It has become an essential part of 21st Century advancements. It is highly likely industry will continue to depend on it for many years to come.
Stamping is a major part of manufacturing and part production. It is very likely that it will continue to play an important role in the production of future parts for innovations and inventions that are presently on the drawing board or in the imaginations of engineers. For more information on milling and stamping companies consult IQS Directory for a complete listing of local and national fabricators, processors, and producers who can meet your production requirements.