Sheet Metalworking Processes - PowerPoint - PowerPoint

							         Sheet Metalworking Processes




            •Cutting
            •Bending
            •Stretch Forming
            •Deep Drawing
            •Stretch Drawing (Stamping)

Sp ’06                W. Li
                Sheet Metalworking Materials
•   Steels
     – Low carbon steels (<0.15% C)
           • Rimmed steels,
           • Killed steels, DQSK (drawing quality special killed steel)
           • Interstitial-free steels (without Lüder’s lines effect)
     – High-strength steels
           • Cold rolled steels
           • Partially annealed
           • Annealed
           • High-strength, low-alloy steel (HSLA)
     – Coated steels
           • Tin plate
           • Galvanized steel (Zn, Zn-Al coating), galvannealed steel (Fe-Zn)
     – Stainless steel
           • Austenitic steels, high ductility
•   Aluminum (5000 series for automotive, 6000 for aerospace applications)
                   Material Type




  Aluminum                            Stainless Steel




                      Mild Steel


                                   HSLA & Ultra HS Steel
Galvanized Steel                    Lower E Materials
                          Automotive Steels
Types         Yield        Tensile     El. (%)    Examples
              (MPa)        (MPa)

Mild Steels   <210         <400        30 – 40%   DKSQ



Medium        180 – 280    270 – 390   30 – 36%   Bake Hardenable Steels
Strength
Steels
High          210 – 350    270 – 420   20 – 25%   HSLA
Strength
(HSS)
Advanced      280 – 500    490 – 980   20 – 30%   Dual phase, Martensitic,
High                                              TRIP (transformation
Strength                                          induced plasticity)
(AHSS)
        Composition and Strengthening Mechanism
Steel     HSS Grade   Alloying      Major           Minor       Strength
Type      Family      Additions     Constituents    Phases      Mechanisms


C-Mn      CHSS        Mn, P, Si      + Fe3C        N/A         SS+GR



HSLA      CHSS        Ti, Nb, P,     + Fe3C        TiN, TiC,   SS+GR+
                      Mn, Si, B                     NbC         Precipitation
                                                                hard.
Dual      AHSS        Mn, Si, Nb,  +               N/A         SS+GR+
Phase                 V           martensite                    Transformation
                                                                strengthening
TRIP      AHSS        Mn, Si, Al,    + bainite +   N/A         SS+GR+
                      Cr, Mo, Ni    austenite                   Transformation
                                                                strengthening
               Relevant Material Properties
• Discontinuous Yielding and Lüder’s Lines
• YS, TS, el., K, n, and r
   – r value is used to express the anisotropy of materials
             w
          r
             t
        • Planar anisotropy
                  r0  r90  2r45
           r 
                         4
        • Normal anisotropy
                  r0  r90  2r45
           rm 
                         4
               Relevant Material Properties
• Strain hardening exponent n indicates the ductility of the material,
  because u = n.

• Tensile strength can be calculated as
                    n
              n
       TS  K         where e is the base of the natural logarithm, e = 2.7183.
              e
Shearing




• Shearing force         n
                      n
Ps  C1 (TS )hl  C1K   hl
                      e
where C1 = 0.7 on average

• Shearing energy
 Es  C2 Ps h
  where C2 = 0.5 for soft material,
             0.35 for hard material.
Many Types of Operations
Bending

      Neutral line depends on Rb/h ratio:
      Rb/h >2 neutral line at 1/2 h,
      Rb/h <=2, neutral line at 1/3 h.

      Bending limit:
      • Orange peel
      • Localized necking
      • Fracture
      • Crushing
Springback


       • Elastic recovery of part after
         bending is complete
   h   • Factor that make it worse:
          – Thinner sheet



                  R   R  
                                           3
        Ri
            1  3 i 0.2   4 i 0.2 
        Rf        h E  h E 
                Compensating for Springback


• Overbend the part
• Use a smaller radius
  die
• Elevate temperature
• Stretch Bending
• Repeat Bending
• Forge Bend
• Use a thicker sheet to
  start with
                      Stretch Forming




a.   Single die required, low production rate
b.   Male and female dies needed, high production rate
c.   embossing
Deep Drawing

        • Blank is allowed to draw into
          the die, and thickness is
          normally unchanged.
        • Limiting Drawing Ratio (LDR)
              LDR=d0 max / Dp
        • Constraint of blank-holder
          gives improved process control
          and quality
Stamping of Auto Body Parts




              (Auto/Steel Partnership Publication, 1998)
             Stamping Press


Main Shaft        Main Bushing




                                            Strain Gage
                             Thermistor
                             Thermocouple
        Linkage




                    Slide

                            Blank
                            Binder Ring



  Accelerometer
Stamping Failure Diagnosis using Grid Marks
Experimental Strain Analysis
Experimental Strain Analysis
Forming Limit Diagram (FLD)
                        Hydroforming




      (a)
Before Pressure       (b)
   Die Open       Die Closing
                                      (c)
                                1stPressure
                                   Stage
                                Die Closing
                                                    (d)
                                              2nd
                                                Pressure
                                                Stage
                                              Die Closed
         Automotive Structural Part


Stamped Dodge Dakota    Hydroformed Dodge Dakota
  Radiator Enclosure       Radiator Enclosure
    Part Consolidation and Weight Reduction

Stamped Radiator Closure   Hydroformed Radiator Closure




     17 components           8 components ( -9 )
     36.4 Ibs/16.5 kg        25.4 lbs/11.5 kg (-11 Ibs, -30%)
 Forming of Tailor Welded Blanks




            0.66mm
                                           0.70mm




6ton-6ton                  9.6ton-2.4ton
TWB Applications