PROFESSOR METAL'S METAL FORMING AND FABRICATION LESSONS

Deep Drawing is the process of forming a metal part from sheet stock, or a metal blank. In this lesson, Professor Metal explains how deep drawing, multiple deep draws and hydroforming produce metal cups, cans, pans, domes and shaped metal products.

Deep Drawing is the process of forming a part from metal sheet stock, commonly referred to as a blank, around a punch as it is drawn through a die. The edges of the metal blank are restrained by a “BLANK HOLDER” or a sleeve in the case of a redraw. Since the state of the art does not allow us to go as deep as we might need to go in one draw operation we can institute a redraw, whereby we reduce the diameter and increase the height of a previously drawn shell. There are many shapes that can be made through deep drawing such as cups, pans, cylinders, domes & hemispheres, as well as irregular shaped products. The terms Hydroform and Deep Draw are many times used interchangeably, with Hydroform now being the industry “buzz word” for metal forming. Both process offer their own unique advantages to metal forming.

Professor Metal explains how hydroforming utilizes a punch, a ring, a pressurized forming chamber, and a flexible rubber diaphragm to transform a ductile metal blank into a shaped metal part.

Hydroforming is a manufacturing process where fluid pressure is applied to a ductile metallic blank to form a desired component shape. This process requires hydroforming tools, consisting of a punch made in the shape of the desired part, a ring contoured to fit around the punch and a pressurized forming chamber sealed by a flexible rubber diaphragm.

The typical process cycle starts by placing the metal blank onto a ring that is located over the lower tool (punch). The chamber is then closed over the blank and fluid pressure is applied to the top side of the sheet metal blank. At the same time the punch is pushed up into the blank. The pressure is sufficient to cause the blank to form and take the shape of the punch.

The terms Hydroform and Deep Draw are many times used interchangeably, with Hydroform now being the industry “buzz word” for metal forming. Both processes offer their own unique advantages to metal forming.

How deep can you draw metal to form a deep drawn can, shell, or cylinder? Professor Metal provides guidelines for deep draw depth, noting the limits for single draws and the importance of material selection.

ROUND SHELLS: Approximately 40% of the blank diameter can be drawn into one operation with one set of tools, i.e. 10″ diameter blank can be drawn to 6″ diameter in one operation. This will result in a height of 2 ¾”.

SQUARE SHELLS: They can be drawn from a round blank using the same percentages as for round shells resulting in approximately the same heights.

RECTANGULAR SHELLS: A rectangular shell may be drawn to an approximate height of 86% of its width.

NOTE: The percentages above are approximate and will vary, depending on: type of metal, alloy radii’, blank thickness, quality of material etc.

Aware that the chosen deep draw radius can impact tool costs and per unit price, Professor Metal outlines a good rule of thumb for deep draw radius, when deep drawing metal into round, rectangular, or square shells.

How important is the radius?
The sharpness of radii can affect both tool cost and unit price

A Good Rule of Thumb

Round Shell: Bottom radius and draw die radius (radius under flange if there is to be one) should be four to seven times metal thickness.

Rectangular and Square Shells: Bottom radius and radius under flange, again, should be four to seven times metal thickness.

Corner radii should be eight to ten times metal thickness. If sharper radii are needed, additional tooling and operations will be required.

What metals can be deep drawn? Professor Metal explores metal alloy selection for deep drawing, addressing tooling costs, finish, and deep draw percentages.

What Type of Metal?
Do you have a choice or does design call for a particular alloy?

Aluminum is a good material. It is light yet strong, It is easily worked (drawn); readily accepts a host of finishes; can be washed and shipped in an as-fabricated condition without rusting and has a pleasing appearance. Tooling for aluminum is less expensive than steel.

STEEL:

Mild low carbon steel in the annealed condition that is of good deep draw quality can be drawn quite easily (tensile in “O” temper 45000 PSI). There are an infinite variety of other steel alloys that can be drawn in their “O” temper then heat treated for strength:

THINGS TO CONSIDER:

Tooling is expensive – you need extra hard steel to draw properly
Rust is a problem during transit as well as in a final use if it is not finished properly or protected.
Other common metals that can be successfully drawn are: copper, brass and stainless steel?

1100-0 Alum. Weighs .0979 lb/cu. in.
Brass = 3.1 x wgt 1100 Alum
Copper = 3.3 x wgt 1100 Alum
Steel = 2.89 x wgt. 1100 Alum
The same approximate draw percentages used for steel and aluminum can be used for these metals.

Once a drawn metal part is tooled properly, it can be made quickly and reliably. Professor Metal shows how quickly tooling costs are amortized over a quantity of manufactured pieces, and notes the beauty of tool-controlled parts.

If you want one or two units, we’ll give them to you free! Just pay me for setup.