Precision Metal Stamping: Guide to Materials & Modifications
Precision metal stamping is among the most common metalworking techniques utilized by various industries to turn sheet metal into custom parts.
Progressive metal stamping uses tooling called a progressive die, which contains multiple stamping stations to perform simultaneous operations on a sheet metal strip. A feeding system unrolls the strip from its coil and pushes it through each of the die’s different workstations until the final part is made.
Because this process uses various materials and techniques, it’s essential to understand the options available and factors to consider before getting started.
Precision Metal Stamping Challenges
According to a Research and Markets report, the global metal stamping market will grow to $250 billion in 2027. With increased demand and evolving tools and materials for precision metal stamping, the industry must adapt to overcome challenges. Today’s metal rolling techniques are more advanced than traditional hand processes, but manufacturers still face some common problems during production.
One of these common problems is metal cracking, which can occur along the edges during hot and cold rolling. This is sometimes due to uneven heating or rolling, but there are also metallurgical factors to consider.
Austenitic stainless steel has a high cold hardening index (0.34% for SS). Austenitic stainless steel is a meta-stable type, which will transform deformation, thus inducing a martensitic phase. The martensite phase is brittle and easy to crack. During plasticity deformation, with the increase of extension, the martensitic content will then increase, and the residual stress will also be increased. The greater the relationship between residual stress and martensite content there is, the greater the residual stress, and the easier cracking can occur during processing.
Like most challenges that occur during precision metal stamping, the best way to navigate cracking is to determine and address the root cause. Partnering with a precision reroll mill with metallurgical expertise can be a tremendous help for stampers in performing root cause analysis and resolving issues such as these.
Types of Steel Used for Precision Metal Stamping
Manufacturers can use a variety of metals in precision metal stampings. However, some processes and types of metals perform better in the precision metal stamping process or are a better fit for a particular use case.
Hot rolled steel is roll-pressed at high temperatures and cooled quickly, which leaves a rough surface. For purposes that require closer dimensional tolerances and accuracy, sheet metal is processed further at room temperature through cold finishing techniques.
During the cold rolling process, when the metal is put under mechanical stress, it causes a permanent change to the crystalline structure of the metal. This causes an increase in its strength and often improves corrosion resistance. A cold-rolled stainless steel coil can be precision manufactured, allowing the metal to be produced to extremely tight tolerances. Precision stamping itself uses stamping dies to form metal. This typically occurs at room temperature, making it a cold process.
Compared to hot rolled steel, cold-rolled steel has the following characteristics, making it ideal for the growing needs of precision metal stampers:
- Smooth finished surfaces
- Precise edges and flatness
- Dimensional Uniformity (width, thickness)
- Greater strength and hardness
- Uniform and predictable material properties
When choosing a metal to use, consider the benefits and limitations of each and the requirements for your part.
For example, aluminum is lighter than stainless steel, softer, and a good conductor of electricity. But stainless steel can handle much higher temperatures and more corrosive environments.
Titanium, on the other hand, is also light but much stronger and more durable than aluminum. This makes titanium particularly suited for aerospace, military, and defense applications where a high strength to weight ratio is needed. Titanium is also corrosion-resistant and safe to use in medical implants within the human body.
It’s all about matching the alloy and its properties with the needs of the application being manufactured.
Alloys used in Precision Metal Stamping:
- 300 Series Stainless
- 400 Series Stainless
Key Factors to Consider When Choosing a Material for Precision Metal Stamping
Some of the key factors to consider when choosing a material for precision metal stamping are the metal’s ductility & formability, tensile strength, machinability, and work hardening rate.
Ductility & Formability
Forming occurs somewhere between the yield strength and tensile strength of the material. If yield isn’t exceeded, forming doesn’t occur but exceeding the tensile strength results in a material fracture. In higher-strength materials, the window between yield and tensile is very small.
The grain size of a material is commonly used to indicate its formability, and consistent grain size is highly desirable for forming operations. Grain size can be controlled by a rerolling mill within a very close range by monitoring the temperature of the annealing furnace and the speed at which the strip passes through the line.
Tensile strength measures the amount of force a material can withstand without breaking. Some metals are stronger than others, and the strength varies depending on the component materials in a metal alloy. You should consider the tensile strength of the metal you choose to ensure that it can withstand the amount of force applied during use.
Machinability measures how easily the material can be cut or shaped. Because properties that improve a material’s performance often reduce its machinability, you should consider the machinability of the metal you choose after satisfying other requirements for your part. A machinable material can be cut quickly with a good finish, which reduces costs. However, it’s more important to choose a material that meets the requirements of your part rather than choosing a machinable material.
Work Hardening Rate
As metal is worked or stamped, the temper changes, and the metal either becomes harder and more brittle. The rate that this occurs is work hardening. Depending on how much work is done to the metal and how much it needs to be deformed in a particular operation, the material may require annealing to reset its properties to prevent cracking, breaks, and other material imperfections.
Forming Operations in Precision Metal Stamping
In precision metal stampings, manufacturers use metal forming operations to make parts from metal and metal alloys. It is highly versatile and can be used to create complex, detailed components with an exceptional degree of accuracy and repeatability. What's more, deep-drawn parts are exceptionally strong due to the extreme amount of compression exerted on the metal during the forming process. The fundamental structure of deep-drawn metals is often highly compressed into a very hard crystalline structure.
A design guideline can help you decide the optimal materials and processes.
These are some of the most common forming operations used in precision metal stamping:
Options That Fit Your Needs
Engineer-to-engineer collaboration between stampers and precision re-rollers is highly beneficial, especially during new product and process development.
Ulbrich’s metallurgical experts and wide alloy selection allow us to match precision metal stampers with the ideal material for their applications and equipment.
Contact us to learn how our solutions could help you reduce scrap and die wear.