Deep Drawing with Stainless Steel
Deep drawn stainless steel enclosures are corrosion resistant, strong, heat resistant and chemical resistant. Because of these characteristics due to the high chromium content, many companies choose stainless steel material for essential components used in aerospace and defense, medical devices and plumbing and HVAC industries. Unlike low carbon steels, stainless steels have less formability because of the combined hardness of its chemical composition. Ductility and malleability limit the deep draw process. In most cases wall thickness corresponds closely to the starting gauge of the raw material (see below).
Deep draw stainless applications include cans, eyelets, tubes, caps and ferrules.
The process for deep drawing stainless steel involves applying force to stretch a flat piece of material over a form in a die. Depending on the depth of draw, some parts must go through a series of operations to achieve the desired measurements. Stainless steel is deep drawn at room temperature, called a cold working process. Cold Drawing may create work hardening, in process or post stamping annealing is recommended to remove deep draw induced work hardening.
Stainless Steel Grades Suited for Deep Draw
Two types of stainless steel can be formed into deep drawn components: 400 series (ferritic group) and 300 series (austenitic group). 300 grade stainless steels are best suited for deep draw forming due to the high nickel content which allows for increased ductility and ultra-corrosion resistant.
Some difficult deep drawing may require a special version of grade 304 having slightly higher nickel content. This grade is commonly referred to as 304 DDQ (deep draw quality)- the downside is that it is more expensive and not as easy to obtain. Besides, most deep drawing can be readily achieved with standard grades such as 304 and 305.
Design Tips for Drawing Stainless Steel Enclosures
Things to consider when designing deep draw components from Stainless Steel. Wall thickness and flat, horizontal surfaces will have relatively the same thickness. Whereas Cold Rolled Steel can be thinned creating different thicknesses between horizontal and vertical surfaces. Coining, pinching, and thinning is not a typical process for Stainless Steel. Non round parts will tend to wrinkle in the corners and create stress cracking which may not be present immediately after forming. Stainless Steel parts as stamped from the machine with a light coat of oil have a long shelf life. If stresses are not induced in the deep draw process, Stainless Steel parts are dimensionally stable over time.
Challenges with Deep Drawing Stainless Steel
Stainless steel offers several unique benefits over other materials; however these characteristics can make it a challenge for deep drawn metal stampings. Below are some points to consider:
- Drawing stainless steel requires a greater level of force than other common drawing materials because it work hardens faster.
- There is a layer of oxidized chromium that gives stainless steel its characteristic corrosion resistance and also creates a higher level of friction between the steel and the die, which also contributes to a need for more force.
- Tooling must be coated and lubricated properly to minimize the cost of wear and tear.
- The speed of deep drawing stainless must be adjusted to account for high friction, high pressure, depth of draw as well as other factors. Failing to calibrate the speed correctly can result in breakage or wrinkles. Typically, the deeper the draw, the slower the speed needs to be.
Prospect Machine Products: Trusted Experts in Deep Drawing Stainless Steel
For over 70 years, PMP has worked with customers over a wide range of industrial sectors to provide cost-effective, high quality deep drawn solutions in a variety of metals including stainless steel. We will get you your part at the right time and at the right cost.