Chapter 1: What is the process of metal stamping?
Metal stamping processes are included a wide variety of associated operations. Determine which process is applicable for a particular part is a critical step in the design process.The part design may require one or more process for a complete part.
- Blanking: Blankingis a metal fabricating process, during which a metal work piece is removed from the primary metal strip or sheet when it is punched. The material that is removed is the new metal work piece or blank. Sheet metal blanking on steel, stainless steel, aluminum, copper, brass and alloy is carried out with punching and matrixes.
- Piercing: Piercing is a shearing process where a punch and die are used to create a hole in sheet metal or a plate. The process and machinery are usually the same as that used in blanking, except that the piece being punched out is scrap in the piercing process. An alternative name of piercing is punching.
- Bending: Bending is a process in which the metal is deform in such a way that the length and thickness before bending and after bending remains same. It only changes shape of the work piece.Bending is a process that occurs when a metal is distorted bu deforming the material and changing its shape.
- Forming: Forming is a process that similar to bending and complex parts such as U sections and channel sections of various profiles can be economical produced with multiple bends without altering the material thickness.
- Drawing(Deep & Shallow): Drawing is the process of drawing the blank of sheet metal that is held at the edges, and the middle section of the part is forced by a punch into a die to stretch the metal into a shape defined by the die set.Deep draw refers to the process of pulling a flat “blank” of material over a radiused die edge and into a cavity, producing a closed bottom, round or irregularly shaped cup or cylinder. It should not be confused with stretch -forming. The blank is actually forced into a plastic state as it is dragged over the die radius and down into the die. This process is done under calculated and very controlled conditions involving blank-holding pressures, punch and die radii, punch speed and lubrication.Anatomy of a Deep DrawThe 2 stages of a draw are cupping and drawing. When the punch first contacts the blank, the nose of the punch initially embosses the material into the die. Some stretching occurs at this point and produces what is known as a “shock line”. This is a pronounced area of thinning around the radius at the bottom and just up into the straight wall of the shell. Depending on the shape of the bottom, the material may still be near original thickness across the bottom face (flat bottom) or thinned out by a stretching action (spherical bottom). As the blank is pulled into the die, the material at the circumference gathers and the wall progressively thickens. As the blank is pulled in to near shell diameter, the material thickens to as much as 10% over the original thickness. Clearance must be provided for this thickening to occur so that the material will not get bound up between punch and die. In addition, the punch must be tapered so that the finished shell can be stripped off. Therefore, a drawn shell will taper from bottom to top. It is possible to minimize this through subsequent sizing operations, but not eliminate it entirely.The blank used to produce a shell is cut from rolled strip material with a grain structure elongated across the blank in the direction of rolling. Since this cross-grain does not pull into a drawn shape evenly from all directions, great stresses are induced in the shell wall. Due to these uneven stresses, a drawn shell will not be perfectly round. A flange added to the top of the shell will minimize this, but the smaller the flange, the less strength it has to keep the shell round.
Specifying a Drawn Shell
Since the original blank is so altered by the deep draw process, the wall thickness cannot be specified in terms of mill tolerances. Depending on application, the three ways of specifying the thickness of material in a shell would be to call out the thickness of material to be used, the minimum wall thickness or the maximum wall thickness. Wall thickness can be specified in more detail, but only after development work has been done with the draw process. Since the material is formed around the punch, shells are typically dimensioned to the inside diameter, with taper allowed from bottom to top. Alternatively, the shell can be dimensioned to the outside diameter with the maximum size found at the top, and tapering down to the bottom.
If a straight shell with no flange is required, the shell will be “pinch-trimmed” – that is trimmed flush with the outside diameter. Since the shell has a radius at the top, the remaining trimmed edge will have a partial radius from the inside, abruptly ending in a somewhat sharp outer edge. Also, since the die must have enough clearance to accept the shell, there will be a slight flare at the top of the shell. The bottom of a shell can be pierced out in a similar manner to produce a tubular part, but the same pinch-trim principles apply to the inside diameter. If a straight, cut-off edge is desired, it would require a secondary machining or cut-off operation and should be specified on the part draw in.
These are the main processes involved in the design of manufacturing your metal parts in all industries fields: automotive, household appliances, electrical device and many more.
Types of Stamping Operations
Progressive die stamping
Progressive die stamping uses a sequence of stamping stations. A metal coil is fed into a reciprocating stamping press with progressive stamping dies. The die moves with the press, and when the press moves down the die closes to stamp the metal and form the part. When the press moves up, the metal moves horizontally along to the next station. These movements must be precisely aligned as the part is still connected to the metal strip. The final station separates the newly-fabricated part from the rest of the metal. Progressive die stamping is ideal for long runs, because the dies last a long time without becoming damaged, and the process is highly repeatable. Each step in the process performs a different cut, bend, or punching operation on the metal, thus gradually achieving the desired end-product shape and design. It is also a faster process with a limited amount of wasted scrap.
Transfer Die Stamping
Transfer die stamping is similar to progressive die stamping, but the part is separated from the metal trip early on in the process and is transferred from one stamping station to the next by another mechanical transport system, such as a conveyor belt. This process is usually used on larger parts that may need to be transferred to different presses.
Four-slide stamping is also called multi-slide or four-way stamping. This technique is best-suited for crafting complex components that have numerous bends or twists. It uses four sliding tools, instead of one vertical slide, to shape the workpiece through multiple deformations. Two slides, or rams, strike the workpiece horizontally to shape it, and no dies are used. Multi-slide stamping can also have more than four moving slides.
Four-slide stamping is a very versatile type of stamping, as different tools can be attached to each slide. It also has a relatively low cost, and production is fast.
Fine blanking, also known as fine-edge blanking, is valuable for providing high accuracy and smooth edges. Usually done on a hydraulic or mechanical press, or by a combination of the two, fine blanking operations consist of three distinct movements:
- Clamping of the workpiece or work material in place
- Performance of the blanking operation
- Ejection of the finished part
Fine blanking presses operate at higher pressures than those used in conventional stamping operations, hence tools and machinery need to be designed with these higher operating pressures in mind.
The edges that are produced from fine blanking avoid fractures as produced with conventional tooling and surface flatness can exceed that available from other stamping methods. Since it is a cold extrusion technique, fine blanking is a single-step process, reducing the overall costs of fabrication.
Types of Stamping Dies
Dies that are used in metal stamping operations can be characterized as either single-station or multiple-station dies.
Single-station dies include both compound dies and combination dies. 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.
Combination dies are ones which incorporate both cutting and non-cutting operations into a single press stroke. An example might be a die that produces a cut as well as a flange for a given metal blank.
Multi-station dies include both progressive dies and transfer dies, where notching, punching, and cutting operations occur in sequence from the same die-set.
Steel rule dies, also referred to as knife dies, are were initially used with softer materials such leather, paper, or cardboard, but have also found application in cutting and shaping of metals including aluminum, copper, and brass. The steel strip material used for the cutting surface is designed to match the desired shape, and a slot is cut into the die shoe to hold the steel rule material. The characteristics of the material to be cut, such as its thickness and hardness, help establish the steel rule thickness to be used in the cutting blade.
Chapter 2: How to select the best material for your project?
A successful design hinges significantly on the right choice of metal.Select the right material, whether it will be stainless steel, aluminum or cold rolled steel, is to ensuring top-notch quality products.
Depending on specific project needs, there are many parameters we evaluate before proposing the right material, including:
- Material grade
- Material temper
- Material hardness
- Material thickness
- Material tensile strength
- Material weight
- Required tolerance
Materials we’ve stamped:
The materials FORTUNA has stamped included:
- Stainless Steel
- Carbon Steel
- Spring Steel
- Beryllium Copper
- Phosphor Bronze
- Nickel & Nickel Alloys
- Specialty Metals
- And many more….
You can also ask FORTUNA to propose and utilize the most economic, best performing materials for your projects.