Page 42 - MetalForming June 2014

Tooling by Design
By Peter Ulintz
Processing Aluminum Stampings
Aluminum alloys can successfully be formed into com- plex shapes—automotive body panels for example— using existing pressroom production equipment. Pro- duction examples include inner and outer door panels, hoods, deck lids, lift gates, cross members, and structural and reinforcement components. Aluminum properties differ greatly than those for steel, which means that aluminum deforms differently during stamping. This requires a die- and process-design strategy that accounts for these differences.
The first step: Understand the alloy and temper designa- tions for the specific stamping being processed. Aluminum alloys are designated by a four-digit code that describes their primary alloying elements (Table 1).
The 5xxx series alloys find use in consumer electronic cases (strength, appearance and anodizing) and automotive struc- tural components. Since this series of alloys is not heattreat- able, any beneficial strengthening from cold working may be lost if the final part is subjected to a paint-bake cycle.
The 6xxx series alloys provide relatively good formability and will strengthen during the paint-bake cycle, making them useful for automotive body panels and closures.
The 7xxx series alloys are high-strength heattreatable grades that are not easily joined by commercial welding processes, so they are routinely joined by riveting.
Temper Designations
Metalformers select from four basic temper designations when specifying aluminum sheetmetal:
• As-fabricated (F)
• Strain hardened by cold work (H)
• Fully soft (O)
• Heattreated (T).
The temper designation follows the alloy designation
number with a dash and a letter, 5052-O for example.
H and T tempers often are accompanied by additional numer- ic designations that further describe the tempering method. H—Strain hardened (cold worked) with or without ther-
mal treatment
H1x—Strain hardened without thermal treatment H2x—Strain hardened and partially annealed H3x—Strain hardened and stabilized by low tempera-
ture heating
The second digit indicates the degree of hardness: 2 = 1⁄4
hard;4=1⁄2hard;6=3⁄4hard;8=fullhard;and9=extrahard.
Al Alloy Designation
Principal Alloying Element(s)
Heat Treatable
1xxx
None
No
2xxx
Copper (Cu)
Yes
3xxx
Manganese (Mn)
No
4xxx
Silicon (Si)
No
5xxx
Magnesium (Mg)
No
6xxx
Mg + Si
Yes
7xxx
Zinc (Zn)
Yes
8xxx
Other
Yes
Table 1—From ASM Specialty Handbook: Aluminum and Aluminum Alloys
The 1xxx series alloys essentially are commercially pure aluminum—very soft and formable—and are not used where strength is a prime consideration. They typically find use in electrical and chemical industries.
The 2xxx series alloys exhibit high strength, toughness and, in some cases, weldability. They do not resist atmospheric corrosion as well as other aluminum alloys do, so they typ- ically are painted or clad for added protection.
The 3xxx series alloys are the most widely used—stronger than 1100 but still readily formable. Typical applications include radiators, heat exchangers and beverage-can bodies.
The 4xxx series alloys exhibit a relatively low melting point and find use as welding wire.
Peter Ulintz has worked in the metal stamping and tool and die industries since 1978. He has been employed with the Anchor Manufacturing Group in Cleveland, OH, since 1989. His background includes tool and die making, tool engineering, process engi- neering, engineering management and product devel- opment. Peter speaks regularly at PMA seminars and conferences. He is also vice president of the North American Deep Drawing Research Group.
Peter Ulintz
pete.ulintz@toolingbydesign.com, www.toolingbydesign.com
Table 2—Minimum mechanical properties for 0.060-in.-thick sheet (Ref. ASTM B209)
*ASM Specialty Handbook: Aluminum and Aluminum Alloys
Alloy, Temper
Yield Strength, KSI
Tensile Strength, KSI
Total Elongation, %
Minimum Bend Radius* (90-deg. bend)
Cutting Clearance per side*, %t
3003-O
5
14
25
0
5%
3003-H14
17
20
5
0
6%
3003- H16
21
24
4
1t
7%
5052-O
9.5
25
19
0
6.5%
5052-H32
23
31
7
1t
7%
6061-O
12 max
22 max
16
0
5.5%
6061-T4
16
30
16
1t
6%
6061-T-6
35
42
10
1.5t
7%
40 MetalForming/June 2014
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