US006550302B1

(12) United States Patent (10) Patent N0.2 US 6,550,302 B1 Gh0sh (45) Date 0f Patent: Apr. 22, 2003

(54) SHEET METAL STAMPING DIE DESIGN 4,137,105 A 1/1979 Ness ................... .. 148/115 R FOR WARM FORMING 4,145,903 A 3/1979 Leach et al. ................. .. 72/60

4,227,396 A 10/1980 CroWe . . . . . . . . . .. 72/69

(75) Inventor: Amit K_ Ghosh, Ann Arbor, MI (Us) 4,584,860 A 4/1986 Leonard 72/61 4,888,973 A 12/1989 Comley .... .. 72/342

Assigneez The Regents of the University of A Folmer . . . . . . . . . . . . . . . . . . . . . .. Michigan Ann Arbor MI (Us) 5,515,705 A 5/1996 Weldon et a1. ............. .. 72/19.1

’ ’ 5,729,462 A 3/1998 Newkirk et al. ..... .. 364/468.25

( * ) Notice: Subject to any disclaimer, the term of this FOREIGN PATENT DOCUMENTS

patent is extended or adjusted under 35 FR 2692504 * 12/1993 72/3428 USC‘ 15 4(1)) by 24 days‘ JP 62-270225 * 11/1987 ~~~~~~~~~~ "I: 72/3427

JP 5-212485 * 8/1993 .............. .. 72/342.7

(21) Appl. No.: 09/625,426 JP 6-55230 * 3/1994 ............ .. 72/34292 . JP 6-79353 * 3/1994 72/342.8

(22) P116911 Jul- 25, 2000 SU 1409379 * 7/1988 .............. .. 72/3427

Related US. Application Data * cited by examiner 60 P " l l' t' N. 60145784 ?l d J l. 27

( ) lgggslona app lea Ion 0 / ’ ’ e on u ’ Primary Examiner—Ed Tolan

(51) I t C] 7 B211) 37/16 (74) Attorney, Agent, or Firm—Barbara M. Burns n . . .............................................. ..

(52) US. Cl. ............... .. 72/342.8; 72/3427; 72/347 (57) ABSTRACT

of Search ........................... .. In metal Stamping dies, advantage of improved 726428’ 34292’ 347’ 350’ 364 material ?oW by selectively Warming the die, ?at sections of

56 R f Ct d the die can contribute to the How of material throughout the ( ) e erences l e workpiece. Local surface heating can be accomplished by

US, PATENT DOCUMENTS placing a heating block in the die. Distribution of heating at the ?at loWer train central regions outside of the bend region

2,455,702 A 12/1948 Rechton et a1‘ """"""" " 153/21 alloWs a softer ?oW at a loWer stress to enable material ?oW 2,760,543 A 8/1956 Wood . . . . . . . . . . . . . . .. 153/21 - - - - .

2,944,500 A 7/1960 Raynes ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ “ 113/43 into the thinner, higher strain areas at the bend/s. The heating

2,966,195 A 12/1960 Roberts et a1_ 153/21 block is inserted into the die and is poWered by a poWer 3,025,905 A * 3/1962 Haerr ......... .. 72/34292 Supply

3,528,276 A 9/1970 Schmidt et al. 72/342 3,926,029 A 12/1975 Abson et a1. ............... .. 72/342 12 Claims, 18 Drawing Sheets

16’

U.S. Patent Apr. 22, 2003 Sheet 1 0f 18 US 6,550,302 B1

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14

16’

U.S. Patent Apr. 22, 2003 Sheet 2 0f 18 US 6,550,302 B1

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U.S. Patent Apr. 22, 2003 Sheet 3 0f 18 US 6,550,302 B1

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U.S. Patent Apr. 22, 2003 Sheet 4 0f 18 US 6,550,302 B1

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U.S. Patent Apr. 22, 2003 Sheet 5 0f 18 US 6,550,302 B1

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U.S. Patent Apr. 22, 2003 Sheet 7 0f 18 US 6,550,302 B1

9%

(ww) uldacl 119d

2U wmhm 2

U.S. Patent Apr. 22, 2003 Sheet 8 0f 18 US 6,550,302 B1

e mm m mm n s wmmw .. =0. m d A ppm

A|... A1

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Ldngitudinal Original Distance from Part Center, mm

“Fl 15%

U.S. Patent Apr. 22, 2003 Sheet 9 0f 18 US 6,550,302 B1

CFC! 2%

Die Temperatur?

350 0C

300 °C

250 LC

200 DC lllllll

I l L 1 A l I

1 | 1 l l 2

25

EE .5500 tma

400 350 250 300

Punch TemperatureZ’C 200 150

Die Temperature

‘' 350 DC

‘ 300 0C

I 250 DC

200 0C Al 5182+Mn

25

- - 5 41 EE .EQQD tom

20"

O 41

400 350 250 300

Punch TemperatureZ’C 200 150

‘F1 2C

Die Temperature

350 QC

300 “C

250 0C 200 0C

Al6lll-T4

25

20"

EE .5250 tum

400 350 300 200 250

Punch Temperature 150

U.S. Patent Apr. 22, 2003 Sheet 10 0f 18 US 6,550,302 B1

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g 15 _. O u

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n- 10 _.

5 1 1 L 1 a 1 1 L 1 g 1 1 1 1 E 1 1 J_ 1 %

1 50 200 250 300 350 400

Temperature, °C

(Pig; 3

U.S. Patent Apr. 22, 2003 Sheet 12 0f 18 US 6,550,302 B1

Minor Type 1 axis ,

A

/

Formed Part

U.S. Patent Apr. 22, 2003 Sheet 13 0f 18 US 6,550,302 B1

IH

B.

Allo 5754

350 °C

a :1 safe

.25 SF:

12 10

Minor Strain, %

6

U.S. Patent Apr. 22, 2003 Sheet 14 0f 18 US 6,550,302 B1

Minor Strain, e2 %

Temperature

10 15

5 1

6 ..

r l

U I a ma

+P m.

@m 1T 505 Mm 5

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200

Al 61 ll-T4

Forming

250 0C

Minor Strain, 92%

‘Pl

200

150 -

5o -

Minor Strain, e2%

U.S. Patent Apr. 22, 2003 Sheet 15 0f 18 US 6,550,302 B1

‘Pl 854

Die Temperature

30

5

2 2 1 Q0 Fm E eozmmeom Die Temperature

0 O O O O O 5 O 5 O 5 O

3 3 2 2 1 1 Mai _._.E G 59:25 22>

350 300

Punch Temperature,°C 200 350 300 2 0O 2 5 0

Punch Temperature,°C _250

Al 5182+Ml 30

Die Temperature 35 I.

an .E E eozemeom

AI 5182+Ml

Die Temperature

2 2

E 59.26 22>

O

350 2 5 O 3 00

Punch Temperature,°C 200 350 300 2 O O 2 5 0

Punch Temperature,°C

U.S. Patent Apr. 22, 2003 Sheet 16 0f 18 US 6,550,302 B1

@954 @9113 400 F 30

- Al 5754 Al 5754

350': Die-Punch q o a 0 E - 25 Temperatures J50 0300 C

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Blank Holding Pressure, MPa Hank Homing pressure, MP3

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Blank Holding Pressure, MPa Biank Holding Pressure, MPa

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U.S. Patent Apr. 22, 2003 Sheet 17 0f 18 US 6,550,302 B1

‘PC! 1068

Die at35O°C

—°— As- formed

+ Baked

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350 300 250 200 350 300 250 200

Punch Temperature,°C Punch Tem perature,°C

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m 0 .

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U.S. Patent Apr. 22, 2003 Sheet 18 0f 18 US 6,550,302 B1

Table 1 Chemical Compositions (wt. %) of Sheet Alloys

Si Mg Cu Mn Fe Al

5754 0.2 3.1 0.04 0.25 — balance

5182+Mn 0.07 4,05 0.03 [.26 0.22 balance

6111 0.5-0.9 0.6 — - —— balance

Table 2 Room Temperature Tensile Properties Obtained for Different Tempers Alloy and Temper Yield Strength. MPa Elongation. %

(0.2% Off-set] (25.4mm Gauze Length) Al 5754: Hot-rolled (ayreceivedl I01 29

Cold-rolled (before um‘nrt‘orming) 254 7 After 200 “C forming 255 8 After 350 “C forming I05 27

Al SISZTIPQMn: Hot-rolled (as-received) 217 25 Cold-rolled (before “arm-forming) 35l 6 After 200 ‘C forming 350 9 After 350 ’C forming 150 26

KFGI l l: H0t—rolled (LlS‘l‘CCClVCdl 160 l6 T4 (before “arm-forming) 169 23 After 200 4C forming l74 l9 After 350 “C forming 148 37

US 6,550,302 B1 1

SHEET METAL STAMPING DIE DESIGN FOR WARM FORMING

REFERENCE TO RELATED APPLICATION

This application is based on provisional patent application No. 60/145,784, ?led Jul. 27, 1999.

This invention Was made in part With government support aWarded by the Department of Energy Contract LMES 86-X-SU544C. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

The ?eld of the invention pertains to sheet metal stamping and in particular to an apparatus and method to facilitate forming of metal. Material stretches more at a deformation or corner and becomes thinner thereat.

Aluminum is a brittle material, that is, alumninum is less ductile than other materials. In the past, a die Was entirely heated or the sheet of material Was entirely heated to facilitate ?oW during the stamping/molding process. An individual punch could also be heated.

Heating of certain metals to modest temperatures above room temperature can increase their strain to failure, and simultaneously increase their strain rate sensitivity. These characteristics produce favorable conditions for forming sheet metals, but strain localiZation at elevated temperatures can be intense due to a loss in their Work hardening capacity thus minimiZing strain uniformity in the part. Maintaining of spatial variation in temperature on mated die surfaces can alloW How of softened material from certain sections of the part to other regions to enhance the overall formability of sheets. It is hoWever not clear as hoW to provide appropriate control of differential temperature in different regions of the die or hoW to construct these dies to avoid excessive heat loss, support of internally imbedded heating elements With out heat equilibrium betWeen different regions and provide the most desirable extent of metal ?oW.

Recently there has been a remarkable increase in the use of aluminum alloys in automotive industry, e. g. the shipment of aluminum to automotive market increased from 1.6 billion pounds in 1987 to 4.04 billion pounds in 1997. This increase is attributed not only to issues of energy-saving, but also to those of safety, resource conservation and environ ment friendliness. HoWever, structural and body parts that rely on the formability of sheet metals, aluminum alloys are ranked far behind loW carbon steels in automotive applications, despite their higher strength-to-Weight ratio and excellent corrosion resistance. The limited use of alu minum alloys in the automotive industry is partly due to their poor formability at room temperature and thus, if Warm forming at a rapid forming rate can be implemented in production, many of the goals related to lightWeighting, energy and environmental friendliness can be realiZed.

Warm forming by deep draWing both rectangular and circular cups from annealed and hardened aluminum sheet alloys has been investigated in the past. Studies shoWed signi?cant improvement in the draWability (in terms of cup height) at a relatively moderate temperature of about 150 degrees C. even for the precipitation hardened alloys (like 2024-T4 and 7075-T6). The draWability of these hardened alloys are better than the annealed alloys at room temperature, suggesting the possibility of draWing high strength aluminum alloys for structural parts at moderate elevated temperatures rather than draWing them in the annealed state and heat-treating after forming.

10

15

20

25

30

35

40

45

55

60

65

2 Forming speed (strain rate) effect in addition to tempera

ture effect Was observed With cup height increased With increasing forming temperature and/or decreasing punch speed for an Al—2Mg alloy. Punch stretching alloy 5182-O, required similar temperature and forming speed. Strains near the neck of the stretched part Were more uniformly distrib uted at higher temperatures and sloWer punch speeds, imply ing increased strain rate sensitivity. By punch stretching the same alloy at a typical automotive strain rate of 1 sec-1, forming temperature had to exceed about 250 degrees C. to make improvements over the room temperature value, or, the punch speed had to be sloW enough (about 10% of a typical automotive strain rate) to exhibit improved Warm forming performance over that of AKDQ steel at room temperature. Moreover, plant trials of Warm forming Were conducted, forming alloy 5182-O at 120 degrees C. in General Motors proved successful in producing inner door panels and a V-6 oil pan at commercial press speeds, by heating both the die and the blank and using a mica lubricant and a MoSi2/graphite release agent. Cooperative investiga tions betWeen Alcan and Chrysler tested various alloys, precipitation hardenable bumper alloys 7046-T6 and 7029 T6 to the strain hardenable alloys 5182-H14 and 5083-H14, Were tested at elevated temperatures using heated blanks but unheated dies. It Was found that some precipitation hardened alloys could also be Warm formed successfully to produce components at 250 degrees C. at a cycling rate (~5 parts/ min.). The optimum forming temperatures Were found to be 200 degrees C. and 250 degrees C. for the precipitation hardened and the strain hardened alloys, respectively. These early trials act as an important database for today’s advanced manufacturing and/or further exploration of Warm forming potential of existing and neW aluminum alloys.

The need for Fuel Savings and Structural Weight Reduc tion in vehicles is driving the replacement of Steel by Aluminum. But formability of Al alloys is half that of steels. This poses a major economic barrier to its application Goal: Formability of Al alloys must be improved under rapid manufacturing conditions (strain rate ~1—10 s—1). Technical Issues: Most Aluminum Alloys have the loWest formability at or near room temperature. At temperatures beloW room temperature, Strain Hardening Rate of AlAlloys is improved someWhat, but not enough. At Modestly Elevated Tempera tures (200—350° C.), the Strain Rate Sensitivity and Forming Limit of Al alloys are improved signi?cantly. L(derOs Band and Surface Defects are eliminated by Warm Forming. Critical QuestionszWarm formability drops With increasing Forming Rate. Can sufficient formability be achieved at high strain rate? Which alloys and micro structure Will maximiZe Warm formability and yet not degrade room temperature strength?

In uniaxial tension, total elongation generally increases With increasing temperature but decreases With increasing strain rate. Strain rate sensitivity increases With increasing temperature. Strain hardening index decreases With increas ing temperature, indicating a softening effect. HoWever, the Warm forming as described above has been directed to Warming of the blank and/or the entire die and not selective Warming of certain segments of a die.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide selective heating to a die facilitate Warm forming.

It is also an object of this invention to provide such selective heating to enable material ?oW into a end region from a ?at region of a die.