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Deep drawing brass, similar to brass stamping, is a complex process that requires considerable die design and preparation– it’s effective in forming brass products that have considerable depth. The process involves stretching blanks around a plug and then transferring them into a die to be cut into the desired shape. Because of the radial drawing of the brass, deep drawing is a compression-tension technique.
Numerous industries rely heavily on deep-drawn brass for their product applications. Some of these industries include weapon manufacturing, musical instrument production, and electrical and plumbing applications.
While the actual deep drawing process is relatively simple, it takes considerable preparation to minimize wall thinning, uneven thickness, fracturing, and cracking. Here are a few things to keep in mind when preparing to deep draw brass:
Brass thickness
Blank shape and size
Shape of the final product
Speed of the press
Work hardening exponent
Draw radii
Draw ratio
Plastic strain ratio
Surface finish of the die
Die temperature
Shape and size of the draw bead
Lubricant
Binder deflection
Binder pressure
The thickness of the brass blanks is dependent upon desired size and strength of the final product. Thicker brass blanks are inherently stiffer than thinner brass blanks—this allows thicker blanks to hold together better during the deep draw process. The larger the final product, the thicker the brass blank should be. This is because thicker brass retains a higher volume and is therefore capable of stretching further without fracturing.
Excessive friction can disturb deep draw process. If friction during the process is too great, uneven forming or fracturing is likely to occur. To avoid this, select the proper type and amount of lubricant to allow the brass blanks to slide through the deep draw tools.
When calculating the proper amount of lubrication for an application, it is important to consider the die surface finish and die temperature. Different die surface finishes retain different friction levels, and die temperatures directly affect the final viscosity of the lubricant.
The draw ratio is one of the most important factors to consider when deep drawing brass. Draw ratio is the difference in size between the draw post and the blank size. To obtain the best results and allow proper flow resistance, the draw ratio needs to fall within a specific range. If flow resistance is too low, the brass becomes too thin. Too much resistance and the brass is likely to fracture.
The most important factor to remember when calculating draw ratio is the necessary brass blank diameter. To calculate this number, first calculate the total surface area of the final product and then convert this figure into a flat blank diameter. Depending on the thickness of the brass blank, the percentage of reduction from blank to draw will fall between 27 and 49 percent.
Setting the proper binder pressure ensures sufficient brass metal flow. If binder pressure is not taken into consideration, brass wrinkles may occur during compression. To alleviate pressure, standoffs can help by maintaining proper spacing between the draw ring surface and the binder. For optimal results, set the standoffs to 110 percent of the brass thickness.
The shape of the final product plays a role in the deep draw process. Square draws, for example, reduce flow restriction along the straight walls in comparison to the corners. If corners are an important factor, increasing the profile radius to allow for deeper drawing in a single operation may help.
Brass is the chosen deep drawing metal for many applications. Some of the benefits of deep drawing brass include:
Aesthetic appeal: Brass delivers a unique muted yellow tone.
High malleability: It’s easier to deep draw brass than copper or zinc.
Low melting point: Depending on the composition, brass melts between 900 and 940 degrees Celsius.
Corrosion resistant: Brass is resistant to tarnishing.
Germicidal: The copper in brass creates a self-disinfectant that kills bacteria.
The unique composition and characteristics of brass does create a few disadvantages. Before choosing to deep draw brass, consider these possible characteristics:
Stress cracking: Brass is more susceptible to stress corrosion cracking (also called season cracking) than other metals.
Hardness: The medium tensile strength of brass makes it unsuitable for certain applications, although aluminum can be added to brass to increase strength.
Toxicity: When brass is melted, the resulting fumes are poisonous.
