The Basics of Metal Stamping
Metal stamping is a manufacturing process used to convert flat metal sheets into specific shapes.
It is a complex process that can include a number of metal forming techniques — blanking, punching, bending and piercing, to name a few. There are thousands of companies across the U.S. that offer metal stamping services to deliver components for industries in automotive, aerospace, medical, and other markets.
As global markets evolve, there is an escalated need for quickly-produced large quantities of complex parts. Metal stamping is a fast and cost-effective solution for this large-quantity manufacturing need. Manufacturers who need metal parts stamped for a project generally look for three important qualities:
- High quality/durability
- Low cost
- Fast turnaround time
The following guide illustrates best practices and formulas commonly employed in the metal stamping design process and includes tips to incorporate cost cutting considerations into parts.
Types of Metal Stamping
There are three major types of metal stamping techniques: progressive, fourslide and deep draw.
Progressive Die Stamping
Progressive die stamping features a number of stations, each with a unique function.
First, strip metal is feds through a progressive stamping press. The strip unrolls steadily from a coil and into the die press, where each station in the tool then performs a different cut, punch, or bend.
The actions of each successive station add onto the work of the previous stations, resulting in a completed part.
For very simple parts, progressive die metal stamping may not be the best option. But progressive stamping is ideal for fabricating parts that require more than a bend or two, which previously could be costly and inefficient.
A manufacturer might have to repeatedly change the tool on a single press or occupy a number of presses, each performing one action required for a completed part. Even using multiple presses, secondary machining services were often required to truly complete a part. For that reason, progressive die stamping is the ideal solution for metal parts with complex geometry to meet:
- Faster turnaround
- Lower labor cost
- Shorter run length
- Higher repeatability
Fourslide, or multi-slide, uses a horizontal stamping press with tools controlled by a series of cams. Unlike progressive, which stamps the metal in a vertical motion, multi-sliding leverages a combination of laterally moving slides.
As its name implies, a fourslide has four slides — meaning that up to four different tools, one per slide, can be used to achieve multiple bends simultaneously. Each slide of a fourslide is driven by a shaft, which is controlled by the rotations of a cam. As material feeds into a fourslide, it is bent in quick succession by each shaft that is equipped with a tool.
Fourslide metal stamping can offer several advantages over traditional press stamping that make it an ideal choice for many applications. Some of these advantages include:
- Versatility for more complex parts
- More flexibility for design changes
Deep Draw Stamping
Deep drawing involves pulling a sheet metal blank into the die via a punch, forming it into a shape. The method is referred to as “deep drawing” when the depth of the drawn part exceeds its diameter. A series of punches can further increase the length of the part with minimal changes to its wall thickness to deliver cylindrical shapes.
This type of forming is ideal for creating components that need several series of diameters and is a cost-effective alternative to turning processes, which typically require using up more raw materials.
Common applications and products made from deep drawing include:
- Automotive components
- Aircraft parts
- Electronic relays
- Utensils and cookware
Manufacturing Tools for Stamping
There are several steps in producing metal stamping. The first step is designing and manufacturing the actual tool used to create the product.
Let’s take a look at how this initial tool is created:
Stock Strip Layout & Design: A designer uses is used to design the strip and determine dimensions, tolerances, feed direction, scrap minimization and more.
Tool Steel and Die Set Machining: CNC ensures a higher level of precision and repeatability for even the most complex dies. Equipment like 5-axis CNC mills and wire EDM machines can cut through hardened tool steels with extremely tight tolerances.
Secondary Processing: Heat treating is applied to metal parts to enhance their strength and make them more durable for their application. Grinding is used to finish parts requiring high surface quality and dimension accuracy.
Wire EDM: Wire electrical discharge machining shapes metal materials with an electrically-charged strand of brass wire. Wire EDM can cut the most intricate shapes, including small angles and contours.
Die Assembly: After the tool components are manufactured, the die is assembled to match the design. High precision is necessary to ensure the tool can stamp the parts to exact measurements.
Metal Stamping Design Processes
Metal stamping is a complex process that can include a number of metal forming processes —blanking, punching, bending, and piercing and more.
Blanking: This process is about cutting the rough outline or shape of the product. This stage is about minimizing and avoiding burrs, which can drive up the cost of your part and extend lead time. The step is where you determine hole diameter, geometry/taper, the spacing between edge-to-hole and insert the first piercing.
Bending: When you are designing the bends into your stamped metal part, it is important to allow for enough material — make sure to design your part and its blank so that there is enough material to perform the bend.
Some important factors to remember:
- If a bend is made too close to the hole, it can become deformed.
- Notches and tabs, as well as slots, should be designed with widths that are at least 1.5x the thickness of the material. If made any smaller, they can be difficult to create due to the force exerted on punches, causing them to break.
- Every corner in your blank design should have a radius that is at least half of the material thickness.
- To minimize instances and severity of burrs, avoid sharp corners and complex cutouts when possible. When such factors cannot be avoided, be sure to note burr direction in your design so they can be taken into account during stamping
Coining: This action is when the edges of a stamped metal part are struck to flatten or break the burr; this can create a much smoother edge in the coined area of the part geometry; this can also add additional strength to localized areas of the part and this can be utilized to avoid secondary process like deburring and grinding.
Some important factors to remember:
- Plasticity and grain direction – Plasticity is the measure of permanent deformation a material undergoes when subjected to force. Metals with more plasticity are easier to form. Grain direction is important in high strength materials, such as tempered metals and stainless steel. If a bend goes along the grain of a high strength, it can be prone to cracking.
- Bend height – The overall height of a bend has minimum requirements to be formed effectively and should be at minimum, 2.5x the thickness of the material + the radius of the bend
- Bend relief – Add small notches located immediately adjacent to the portion of the part to be bent — they should be a minimum of twice as wide as the material is thick, and as long as the bend radius plus material thickness.
Bend Distortion/Bulge: The bulging caused by bend distortion can be as large as ½ the material thickness. As material thickness increases and bend radius decreases the distortion/bulge becomes more severe.
Carrying Web and “Mismatch” Cut: This is when a very slight cut-in or bump-out on the part is required and is typically about .005” deep. This feature is not necessary when utilizing compound or transfer type tooling but is required when utilizing progressive die tooling.
What ESI Clients Are Saying
We could not be happier about being a customer of ESI for the past 10 years. They are extremely professional, provide excellent quality, and best of all, make working with them fun.
Northwest Fastener Sales
I would recommend ESI for future stamped parts (sheet metal parts) in the future. The Gemini shields don’t seem particularly easy to make, and, as you know, we had a difficult time finding a suitable vendor. The quality of work has been great and the dimensional accuracy outstanding. I find them very easy to work with and very accomodating for development. The pricing is fair and it’s nice to work with a local outfit.
Senior Mechanical Engineer
Casmed Medical Systems, Inc.