In the deep drawing process, a part is formed by placing the chosen material into a shaped die cavity where a blanking or forming punch forces the material into the shape of the die. The resulting product has thin walls impossible to achieve with other processes, such as spinning, stretching, injection molding.
Because deep drawing can form thin-walled parts, it is commonly used in making beer cans, cartridge cases for small-caliber ammunition, oil cans, and many other products. It also offers increased rigidity and does not require extra thickness. In short, it can form thin wall components that are inherently strong.
Deep drawing appeared in the Indus Valley Civilization around 1400 BC, making it one of the oldest metalworking methods in current use. It was used primarily to manufacture flat, circular discs from copper. The technique spread and was widely employed by the first millennium AD. It was used extensively in weapons production and consisted of shaping iron into tools and weapons by hammering it directly against the hardened edge of a shaped punch. In recent decades, deep drawing has been extended to include sheet forming processes, such as pressing tubular shapes against a die.
Deep drawing using stainless steel offers several advantages over other materials. It is corrosion resistant, can be formed into intricate shapes, and withstands high temperatures without losing its shape or strength. However, stainless steel sports several disadvantages that need to be considered when designing parts for deep drawing. Chief among these, is it is difficult to form and tends to warp or crack under pressure. Several solutions have been developed to overcome these issues so that quality parts can be produced to meet the requirements of a given application.
Reduce Wall Thickness
Reducing wall thickness simplest way to overcome the problems associated with deep drawing stainless steel, making the part easier to form and less prone to cracking or warping. However, reducing wall thickness may also reduce the strength and rigidity of the part, so don’t take this too far. A good rule of thumb is to keep the wall thickness at around 1/8 inch (3 mm).
Parts with thick walls are difficult to form using deep drawing. Deep-drawn components usually have wall thicknesses of around 0.007 of an inch (0.18 mm) or more. Few parts require wall thicknesses greater than this.
This solution is straightforward and has the added advantage of being low cost.
Be mindful that component strength and durability may suffer if wall thickness is reduced. This option is not recommended for parts requiring high stability.
Alterthe Part’s Design
In many cases, stainless steel deep drawing problems can be overcome by modifying the part. For example, you may decrease its overall size and/or complexity. This might include streamlining internal details, reducing bolt bosses, other projections, downsizing ribs, and flanges.
The smaller and more streamlined the part’s design, the easier it is to form and the less likely it is to warp or crack under pressure. This also means less material must be removed from the workpiece prior to deep drawing, which reduces cost and waste.
This solution is relatively simple and low cost, and you can use it without making significant changes to the part design, which is helpful.
The disadvantage is that it may not be suitable for all applications, particularly those where high strength and durability are required.
Lubrication
Lubricants keep the metal from sticking to the die wall, allowing the component to exit smoothly from the die. This minimizes surface flaws on the part. While many deep-drawn components can benefit from lubrication, it is of particular concern for small parts with thin walls. Use organic lubricants such as oil, grease, wax (including PTFE-based compounds), and inorganic lubricants including graphite, molybdenum disulfide, and boron nitride.
You can use almost any lubricant as long as it is compatible with stainless steel and does not cause any adverse effects, such as corrosion.
The advantage of lubrication is that it is cheap, easy to implement, and requires no design changes.
The disadvantages are that some lubricants may harm the quality of the part produced, so use care in selecting the right one for the application at hand. Cycle time is increased because of time spent lubricating and cleaning the die after each component is struck.
Choose a Softer Grade of Stainless Steel
Using a softer grade of stainless steel can overcome some problems associated with deep drawing. Softer stainless steel is easier to form and less likely to warp or crack under pressure. However, a softer grade of stainless steel will be less durable and less resistant to corrosion than a harder one.
The most common grades of stainless steel used for deep drawing are 304 and 316. The former is more complex and resistant to corrosion than the latter, but it is also more challenging to form.
Advantages of using a softer grade of stainless steel are that it is cheaper and easier to form, which means reduced cycle time.
The disadvantage is that the component will be less durable and less resistant to corrosion than one made from a harder grade.
Anneal the Part
The annealing heat treatment process softens the metal and makes it easier to deform. Annealing can overcome problems associated with deep drawing stainless steel parts, but it must be carried out correctly to be effective. If done incorrectly, annealing can make the situation worse.
The best way to anneal a stainless steel part is by heating it up to around 1000 degrees F (538 degrees C) and then cooling it down slowly in a furnace or other controlled atmosphere. This will cause the metal to recrystallize and become softer.
The advantages of annealing stainless steel include making the metal easier to form and reducing warping or cracking under pressure.
The disadvantages are that it is a relatively costly process and that some parts cannot be successfully annealed because of their design or geometry.
Use a Forging Process
Forging is another process you can use to overcome problems associated with deep drawing stainless steel parts. It involves compressing the metal into the die at high pressure, which causes it to deform plastically and become stronger.
Although forging can produce parts in any shape, but it is most commonly used for round or square shapes and requires specialized equipment.
The benefits of forging stainless steel parts include making the metal more robust and easier to form, which reduces warping or cracking under pressure.
The disadvantages are that it is a more expensive process than deep drawing and requires specialized equipment.
Use a Vacuum Die
Vacuum dies can overcome some problems associated with deep drawing stainless steel parts. It is a specially designed die that has been evacuated of air, which creates a vacuum inside the die cavity. This causes the metal to deform plastically and become stronger.
Vacuum dies are most commonly used for small parts with thin walls. Typical applications include medical devices, electrical components, and semiconductor parts.
Using a vacuum die offers several benefits over other methods, such as hydroforming and stamping. The metal is not in contact with any liquid, so there is no risk of corrosion. There is also no need for a lubricant, which reduces cycle time and waste.
The disadvantage of the vacuum die is that it can only be used for small, thin walled parts.
The Take-Away
People can use several methods to overcome the problems associated with deep drawing stainless steel parts. The most common methods include using a softer grade of stainless steel, annealing, forging, and using a vacuum die.
Each method has advantages and disadvantages, meaning the best way to overcome the problems associated with deep drawing stainless steel parts depends on the specific application involved. By understanding the different options available, engineers and designers can make informed decisions and produce parts most effectively. The above information should help you understand your options.
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