Blanking and Fineblanking

Transcription

1 Blanking and Fineblanking Simulation Techniques in Manufacturing Technology Lecture 5 Laboratory for Machine Tools and Production Engineering Chair of Manufacturing Technology Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke

2 Outline 1 Introduction 2 Requirements on blanking parts 3 Shearing 4 Fineblanking 5 Calculation of blanking parts Seite 2

3 Introduction Sheet Metal Forming Processes Manufacturing Processes according to DIN 8580ff Casting Forming Cutting Joining Coating Changing of Material Properties Compressive Forming Tenso- Compressive Forming Tensile Forming Bend Forming Shear Forming Severing Open Die Forging Closed Die Forging Cold Extrusion Rod Extrusion Rolling Upsetting Hobbing Thread Rolling Deep Drawing Ironing Spinning Hydroforming Wire Drawing Pipe Drawing Collar Forming Stretch Forming Extending Expanding Embossing With linear Tool Movement With rotating Tool Movement Translate Twist Intersperse Shearing Fine Blanking Cutting with a single Blade Cutting with two approaching Blades Splitting Tearing Seite 3

4 Introduction What is blanking? Definition: Mechanical separation of workpieces by a shearing process without formation of chips if necessary, including additional forming-operations. Seite 4

5 Outline 1 Introduction 2 Requirements on blanking parts 3 Shearing 4 Fineblanking 5 Calculation of blanking parts Seite 5

6 Requirements on blanking parts Required quality of blanking parts surface evenness angular deviation draw-in achievable roughness cutting burr smooth sheared zone rupture zone Seite 6

7 Outline 1 Introduction 2 Requirements on blanking parts 3 Shearing 4 Fineblanking 5 Calculation of blanking parts Seite 7

8 Shearing - Introduction Shearing Introduction application IT-classification costs output fine (IT 7) high low sheared surface Shearing rough (IT 11) low high Seite 8

9 Shearing - Characterisation of the process Open and closed cut in shearing open cut closed cut tool flank open flank Seite 9

10 Shearing - Characterisation of the process Differentiation of blanking and piercing blanking piercing waste waste Seite 10

11 Shearing - Characterisation of the process Tool design of shearing u die clearence app. 0,05 x sheet thickness with: u = ½ (a a 1 ) a dimension of cutting die U punch blank holder a 1 punch dimension sheet metal α relief angle of cutting die blanking die Seite 11

12 Shearing - Characterisation of the process Process sequences of shearing charging of the punch 1 2 elastic & plastic deformation shearing & cracking 3 4 break through Seite 12

13 Shearing Achievable accuracy Errors on sheared workpieces draw-in draw-in height h E h E shearing zone rupture zone h G burr height h G t R crack depth t R Seite 13

14 Shearing Achievable accuracy Influence of die clearance on the sheared surfaces formation of distortion wedge small clearance no formation of distortion wedge big clearance By a small die clearance, distortion wedges are generated by squeezing of the material between two cracks Seite 14

15 Shearing Achievable accuracy Quality of sheared surface depending on specific die clearance specific die clearance: die clearance u S / sheet thickness s Seite 15

16 Shearing Achievable accuracy Influence of specific die clearance on crack depth blanking Crack depth t R sheet thickness s Part diameter da = 30 mm specific die clearance u s / % Seite 16

17 Shearing Achievable accuracy Relation between burr height and number of cuts ductile sheet brittle sheet burr height Seite 17

18 Shearing - Forces in shearing Reduction of cutting force by modification of tools plane cut sloped cut F max h = 0 (plane cut) 0,9 F max h = 1/3 s (sloped cut) force F work s(h=0) = work s(h=2s) = s h 0,6 F max h = s (sloped cut) h = 2s (sloped cut) 0,3 F max Contact between punch and sheet 0 s 2s 3s total punch stroke Due to workpiece-bending, sloped cut is only suited for piercing. Seite 18

19 Shearing - Forces in shearing Reduction of cutting force by modification of tools plane cut sloped cut grooved punch conical punch conical die grooved die punch offset Seite 19

20 Shearing - Forces in shearing Dependence of quality on shearing strength of carbon steel carbon concentration tensile strength breaking elongation sheet thickness die clearance part diameter aspect ratio Die / punch radius Cutting resistance k S is defined as the cutting force (F s ) referring to the cutting surface k S = F Smax / A S (with A s = l s *s) Seite 20

21 Shearing Wear Wear on the punch fatigue wear and wear on front face especially appear for lower sheet thickness (s < 2 mm) fatigue wear on front face wear on front face wear on shaft area is caused by friction between punch and sheet in direction of punch movement appears during cutting of thicker sheets (s 2 mm) wear on shaft area Seite 21

22 Shearing wear Influences on wear Tool Machine material hardness surface guidance die clearance stiffness kinematics tool wear Workpiece Type of process alloy stiffness hardness dimension shape open cut closed cut open cut closed cut Source: reiner, Müller Weingarten, Feintool Seite 22

23 Shearing Tool design Multi-stage blanking tool 4 stage Multi-stage blanking tool for shearing of rotor- and stator-sheets stator rotor Seite 23

24 Outline 1 Introduction 2 Requirements on blanking parts 3 Shearing 4 Fineblanking 5 Calculation of blanking parts Seite 24

25 Fineblanking - Introduction Fineblanking - Introduction application IT-classification costs output fine (IT 7) high low sheared surface fineblanking shearing rough (IT 11) low high Seite 25

26 Fineblanking Characterisation of the process Animation of fineblanking clamping plastic deformation cutting Seite 26

27 Fineblanking Characterisation of the process Differences between shearing and fineblanking shearing fineblanking F S punch force F S punch force F R vee ring and blank holder force F G counter punch force 1 cutting die (2 guiding plate) 3 punch 1 cutting die 2 vee ring and blank holder 3 punch 4 counter punch 5% die clearance 0,5% Seite 27

28 Fineblanking Details Geometry of vee rings thin sheets vee ring cutting line sheet thickness s 3 5 mm outward notch toothed inward notch cutting die blank holder with vee ring thick sheets sheet thickness s 5 15 mm vee ring cutting line intention: create compression stresses prevent horizontal movement of the sheet / material flow Seite 28

29 Fineblanking - Details Dependence of workpiece quality on influencing quantities Process parameters affect workpiece quality: example: counter punch force draw-in width draw-in height smooth shearing zone deflexion Workpiece quality can be influenced by process parameters: example: draw-in height die clearance sheet thickness blank holder force counter punch force Seite 29

30 Fineblanking obtainable precision Definition of degree of difficulty in fineblanking degree of difficulty edge angle a S1 easy S2 medium S3 difficult slot a, stick b / mm edge radius r i, r a / mm sheet thickness s / mm sheet thickness s / mm Seite 30

31 Fineblanking comparison of techniques Comparison of sheared surface in shearing and fineblanking shearing fineblanking In fineblanking, the smooth sheared zone can take a share of 100% Seite 31

32 Fineblanking application Application examples fineblanking shearing In fineblanking, the sheared surface can be used as a functional surface Seite 32

33 Fineblanking Field of application Application examples in automotive industry gear shifting gate door lock window lift valve plate synchronising disc gear belt pretensioner brakes ABSpulse generator seat adjustment seat belt components cooling system Seite 33

34 Outline 1 Introduction 2 Requirements on blanking parts 3 Shearing 4 Fineblanking 5 Calculation of blanking parts Seite 34

35 Calculation of blanking process Analytical calculation method Principals and drawbacks FEA of (fine)blanking processes Advantage over analytical calculation by means of examples Seite 35

36 Calculation of blanking process - cutting force F S max = s l S k S maximum cutting force s :sheet thickness l S :length of cutting line k S :cutting resistance k = 0, 8 S R m approximate calculation with tensile strength Seite 36

37 Calculation of blanking process - cutting energy W S = x g 0 F S ( x) dx cutting energy x :cutting distance F S :current cutting force W S = c x g F S max c :correction factor including variables like material properties, effective cutting distance, size of die clearance and friction Seite 37

38 Calculation of fine blanking process - vee ring force F R = 4 l h R approximation value for the vee ring force R R m l R :length of vee ring h R :overall height of vee ring R m :material tensile strength Seite 38

39 Calculation of fine blanking process - counter punch force F G = A q q G Approximation for the counter punch force A q :cutting piece surface q G :specific counter punch force q G = 20 mm N 2 Value of the specific counter punch force for small sized, thin workpieces q G = 70 mm N 2 Value of the specific counter punch force for large, thick workpieces Seite 39

40 Calculation of fine blanking process - cutting force F k S S = C = 1 F S F St FS A F G F l max S max = = k R S m S τ S s = lg s S = C1 0,6 < C1 < 0,9 l g s R m cutting force F St :punch force F G :counter punch force shearing resistance F smax :maximum cutting force A S :shearing surface factor of shearing strength k S :shearing resistance R m :tensile strength calculation according to VDI-standard 3345 l g :total length of cutting lines s :material thickness τ S :shear strength C 1 :factor of shearing strength due to yield stress ratio R m :material tensile stress advised value is C 1 = 0,9 (safety) Seite 40

41 Simulation fine blanking Simulation of fine blanking offers the opportunity to include: flow stress data friction properties thermomechanical coupling More exact input data can be enclosed: instead of F S = C 1 lg s Rm R m = const. This leads to the following results: force over punch travel stress field strain rate field draw-ins prediction of fracture Seite 41