Master of Simulation Techniques. Lecture No.5. Blanking. Blanking. Fine

Transcription

1 Master of Simulation Techniques Lecture No.5 Fine Blanking Prof. Dr.-Ing. F. Klocke Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes

2 Separation processes Phases in shearing

3 Influence of die clearance on the formation of cracks and sheared surfaces Sheared surface in blanking

4 Quality of sheared surface depending on specific die clearance Components of cutting force in blanking

5 Qualitative diagram of cutting force in dependence on the cutting way Reduction of cutting force by modification of tools

6 Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes Forms of wear on cutting punches

7 Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes Open and closed cut in shearing

8 Differentiation of blanking and perforating Sectional image of tool guiding construction

9 Multi-stage blanking tool Example for multi-stage punching

10 Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes Geometry errors on blanked parts

11 Influence of the specific die clearance on the crack depth Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes

12 Comparison blanking - fine blanking Process sequence of fine blanking

13 Animation fine blanking Comparison of sheared surface in blanking and fine blanking

14 Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes Influence of stress state on the ductility

15 Stress states in the cutting zone in fine blanking Fine blanked parts

16 Fine blanked parts Characteristics of quality of a fine blanked workpiece

17 Correlations of process variables in fine blanking Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes

18 Definition of degree of difficulty in fine blanking Fine blanking of a disc

19 Geometry of vee rings Forces in fine blanking

20 Fine blanking of a disc by multi step blanking Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes

21 Fine blanked control disc (one step blanking) Knife of an electric tin opener

22 Fine blanking of a clutchdisc Quality of sheared surface and margin area properties

23 Wöhler-diagram for perforated sheet : Comparison fine blanking / machining Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes

24 Calculation of blanking process Analytical calculation method Principals and drawbacks FEA of (fine)blanking processes Advantage over analytical calculation by means of examples 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 ks = 0, 8R m approximate calculation with tensile strength

25 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 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

26 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 big, thick workpieces. Calculation of fine blanking process - cutting force F k S = F St FS A F G F l max S max S = = S S s C = 1 F k R S m τ S = l g 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)

27 Structure of the lecture Blanking Sheared surface and force Wear Blanking processes and blanking tools Errors on sheared workpieces Fine blanking Comparison to normal blanking Process details and degree of difficulty Tool setup and tool materials Examples of fine blanking parts Calculation of blanking processes analytical calculation method FEA of fine blanking processes 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

28 Simulation fine blanking: Example material flow detail Simulation fine blanking: Example damage

29 Simulation fine blanking: Example strain-rate Simulation fine blanking: Example strain

30 Simulation fine blanking: material flow as a function of friction Simulation fine blanking: Example maximum principle stress in blanking punch and workpiece forces in the tool: blanking die blankholder blanking punch counterpunch

31 Simulation fine blanking: Example stresses in the tool Simulation blanking: Example workpiece fracture - deleting elements detail

32 Simulation fine blanking: Example 3D-simulation - draw-ins Simulation fine blanking: Example 3D-simulation - strain

33 Questions What does the sheared surface look like in blanking? Why is this surface not completely smooth? Please explain the punch force over punch travel for blanking! Why are blanking tools made of hardened and tempered material? Why are sheet metal parts of high quantity made preferably through blanking and not through CNC-wire Electro-erosion? What is the maximum stroke frequency of a blanking machine? Why is there an increased fraction of smooth surface in fine blanking in comparison to normal blanking? What is the reason behind the difficulty classes in fine blanking? Why can a protruding part be not arbitrarily thin? Why can a radius not be arbitrarily small? Can hardened and annealed materials be used as workpiece material in fine blanking? What is the maximum plastic strain in fine blanking?