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Sheet Metal Forming

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Shearing force a) straight parallel cutters b) straight inclined cutters c) rotary cutters 2.2 Deformation mechanism of blanking and punching 1. ... – PowerPoint PPT presentation

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Title: Sheet Metal Forming


1
Taiyuan University of Technology
Sheet Metal Forming Processes and Die Design
?????????
College of Materials Science and Engineering
LecturerCAO Xiao-qing(???) May,2009
2
CHAPTER 2 SHEARING AND BLANKING
  • Main contents
  • Shearing
  • Deformation mechanism of blanking and punching
  • Clearance of blanking and punching
  • Punch force, power and methods to decrease the
    force
  • The principle and methods to calculate the cut
    edges of punch and die
  • Materials economy

3
Key points
  • Blanking and punching clearance
  • Punch force, punch power and methods to decrease
    punch force
  • Calculate the cut edges of punch and die

4
New words
  • clearance(??)
  • punch and die edge(?????)
  • lay-out(??)scrap bridge(??)
  • punch force(???)
  • straight parallel cutter(??)
  • straight inclined cutter/bevel-cut edge(??)
  • obtuseness(?)
  • punch penetration(????)

5
2.1 Shearing
  1. Definition
  2. Shearing process
  3. Shearing force

6
1. Definition
  • the cutting of flat material forms
  • done by different types of blades or cutters
  • machines driven by mechanical, hydraulic, or
    pneumatic power

7
2. Shearing process
  • 3 phaseselastic deformation, plastic
    deformation,
  • and fracture

8
3. Shearing force
  • May be calculated according to the edge types
    of the cutters
  • a)      straight parallel cutters,
  • b)      straight inclined cutters,
  • c)       rotary cutters.

9
 a) straight parallel cutters
  • F t A
  • FM 1.3 F (reasons p24)

10
b) straight inclined cutters
11
c) rotary cutters
12
2.2 Deformation mechanism of blanking and
punching
  • 1. Deformation process three phases, deformation
    zone
  • 2. Stress analysis five characteristic points
    in deformation zone
  • 3.    ?Section quality(Features of edges)

13
1. Deformation process
  • Three phases
  • elastic deformation
  • plastic deformation
  • fracture

14
1. Deformation process
  • Deformation zone spindly area between the
    cutting edges of the punch and die.

15
Grammar
  • Note the articles on page30
  • During phase III, in ,turn into, followed
    by.
  • in start atof onof , atonof propagate
    alongfrom

16
2. Stress analysis
Forces applied to sheet a) section analysis b)
force analysis
17
2. Stress analysis
Forces caused by moment Left without press pad
Right with press pad
18
2. Stress analysis
  • five characteristic points in deformation zone

19
3.  Section quality (Features of edges)
  • 3.1 Four parts rollover, burnish zone, fracture,
    burr

20
3.  Section quality (Features of edges)
  • 3.2 Affecting factors
  • materials property (plasticity)
  • ?clearancelarge, proper, small
  • cutting edge conditionwearing and obtuse
  • Lubrication good or bad

21
2.3 Clearance of blanking and punching
  • 1.The definition and significance of clearance
  • 2.The effects of clearance on the process of
    blanking
  • 3.How to determine and choose reasonable value of
    clearance

22
1.The definition and significance of clearance
  • ZDd -dp
  • c(Dd dp ) /2
  • the space between the punch and the die opening

23
2.The effects of clearance on the process of
blanking
  • a)   section quality
  • b)   dimension precision
  • c)   power consumption
  • d) die life

24
2.The effects of clearance on the process of
blanking
  • a)   section quality
  • Z gtgt Zr , burnish zone rollover burr and
    fracture
  • Z Zr
  • Z ltlt Zr, burnish zone rollover fracture
    burr (thin and long)

25
2.The effects of clearance on the process of
blanking
  • b) dimension precision
  • Z gtgt Zr , the slug
    burnish zone contracts
  • Z Zr, the
    contractionthe expansion
  • Z ltlt Zr, the slug
    burnish zone expands

26
2.The effects of clearance on the process of
blanking
  • c) power consumption( punch force)
  • Z gtgt Zr, F excessive
  • Z Zr , F (See Ch-t p11,Fig.2-14)proper
  • Z ltlt Zr, F not sufficient especially the power
  • d) die life
  • Z gtgt Zr, life
  • Z Zr
  • Z ltlt Zr, life

27
3.How to determine and choose reasonable value of
clearance
  • Theoretical way
  • Enable the fractures to start ideally at the
    cutting edge of the punch and also at the die.
  • The fracture will proceed toward each other until
    they meet .
  • Function of the kind, thickness, and temper of
    the material
  • Experimental way
  • Zkt

28
2.4 The calculation of punch and die cutting edge
  • 1.   Principles of calculation
  • benchmarks
  • limit dimension
  • accuracy of dimension
  • 2.   Methods of calculation
  • separately
  • coordinately
  • electric spark machining
  • 3. Examples

29
1.   Principles of calculation
  • deformation law
  • punching?punch dp
  • blanking ?die opening Dd
  • accuracy of dimension
  • proper clearance
  • wearing law Dmin, dmax
  • machining method

30
1.   Principles of calculation
  • 1.1 benchmarks
  • taped edge of parts
  • punching?punch,
  • blanking?die

31
1.   Principles of calculation
  • 1.2 limit dimension
  • die wearing law
  • punch?upper
  • blanking?lower

32
1.   Principles of calculation
  • 1.3 accuracy of die dimension
  • maintenance and cost
  • determined by the accuracy of parts
  • (see Ch-t p11,table 2-1)

33
2. Methods of calculation
  • 2.1 processed separately
  • Suitable condition simple contour especially
    circle or rectangular
  • Premise dd dp Z max Z min
  • or dd0.6( Z max Z min )
  • dp0.4( Z max Z min )
  • Features
  • advantages----interchangeability, short machine
    time
  • disadvantages----high cost (small tolerance)

34
2. Methods of calculation
blanking punching
35
2. Methods of calculation
  • ?blanking,
    Z min ?D p

  • ?punching, Z min ?d d
  • x-a coefficient to make the dimension of punching
    and blanking part be close to the middle in
    tolerance band. In the range of 0.51

36
2. Methods of calculation
  • 2.2 processed coordinately
  • Suitable condition complex contour or thin sheet
  • Aim ensure the clearance
  • Benefit small clearance, expand the tolerance of
    benchmark, easy made
  • Methodbenchmark ?wearing line ?dimension change
    ?calculate

37
2. Methods of calculation
  • Type of dimension(wearing law)
  • ? increscent? as
    blanking
  • ? decrescent?as
    punching
  • ? invariable
  • d?/4, d ?/8

38
2. Methods of calculation
  • blanking

39
2. Methods of calculation
  • punching

40
2. Methods of calculation
  • 2.3 electric spark machining
  • Both tolerance and dimension are marked on
  • punch.
  • Blanking (1)D d ? - Z min ?D p
  • (2) D p ?De
  • (3) De ? D d
  • Punching (1) D p ?De
  • (2) De ? D d

41
2. Methods of calculation
  • Conversion (only for blanking)
  • (A?B)
  • (B?A)

42
3. Examples
  • Separately Q235,t1.5mm
  • tractor part gasket

43
3. Examples
  • Coordinately H62,t0.5mm

44
Homework
  • Page45.No3 and No 4
  • 2 supplements

1. 20 carbon steel t3mm Z0.460.64
45
Homework
2. 10 carbon steel, t1.5mm, Z0.1320.24
46
2.5 Punch force, power and decreasing methods
  • 1. The calculation of punch force
  • calculation formula
  • affecting factors
  • 2.  Methods to reduce the force
  • stepping punch
  • heated blanking and punching
  • bevel-cut edges
  • 3. Press choosing
  • other forces needed
  • total force and press choosing
  • examples

47
1. The calculation of punch force
  • 1.1 calculation formula
  • k
    1.11.3
  • unequal thickness of the material
  • Inhomogeneous mechanical property of the
    material
  • friction between the punch and the work part
  • poorly sharpened edges.

48
1. The calculation of punch force
  • 1.2 affecting factors
  • work part L? t
  • material t
  • clearance c/Z

49
2.  Methods to reduce the force
  • L? stepping punch(multiple punches)

50
2.  Methods to reduce the force
  • t?heated blanking and punching
  • Lt?bevel-cut edges

51
3. Press choosing
  • 3.1 other forces needed
  • stripping force F x
  • knockout force
  • ejecting force F d -against
  • knocking force Ft -along

52
3. Press choosing

3.2 total force and press choosing
  • According to different die structure
  • elastic stripper, upwards
  • elastic stripper, downwards
  • stationary stripper,downwards

53
elastic stripper, upwards
return-blank die
54
elastic stripper, downwards
drop-blank die
55
stationary stripper,downwards
drop-blank die
56
3. Press choosing
  • 3.2 examples
  • Simple/plain die
  • compound die positive assembly
  • inverted assembly
  • progressive die multi-station(p103)

57
compound die positive assembly
58
compound die inverted assembly
59
2.6 Material economy
  • 1. Layout
  • meaning
  • form
  • 2. Scrap
  • function and determination
  • width of sheet scrap
  • 3. Calculation

60
1.  Layout
  • 1.1 meaning
  • layout relative position of the blanks on the
    work material
  • scrap
  • technical scrap edge of the blank to side of
    strip
  • distance from blank to
    blank
  • structural scrap

61
1.  Layout
  • 1.2 form of layout
  • A) type of scrap
  • (1)mgt0, ngt0 with scrap layout
  • (2)m0,ngt0 less scrap layout
  • (3) m0,n0. no scrap layout

62
1.  Layout

m distance from the edge of the blank to the
side of the strip n the distance from blank to
blank. EL - (N.t n)
63
1.  Layout
  • B) position of blanks
  • (1) straightforward square, rectangular
  • (2)opposite layout L/T-shaped, triangular,
    trapeziform(??),half circular
  • (3) in an angle layout L/T-shaped, cross-shaped,
    ellipse(??)
  • (4)single-pass, multi-line layout (Used for
    smaller, simple-shaped workpiece)

64
1.  Layout
Alternate multi-line layout B D 0.87(D n)(
i 1) 2m where D- -width of blank, i --number
of lines.
  • 62.5?76.5? 81.8The?
  • greatest material economy

65
1.  Layout

Utilize the scrap from one piece as a material
for another piece (scrap from piece Ias the
material for piece 2 scrap from piece 2 as
the material for piece 3).
66
2. Scrap
  • 2.1 function and determination
  • function
  • (1) compensate orientation error
  • (2) keep the rigidity of the strip to ensure the
    quality and stock movement
  • (3) protect dies
  • determination
  • (1)  materials property hard, m, n? soft and
    brittle, m, n?
  • (2)  thickness of the sheet t??m, n?
  • (3)  shape of part complex and large, small
    radii m, n?
  • (4) die structure guiding and stopping mode

67
2. Scrap
  • 2.2 width of sheet scrap
  • The minimum value should ensure the rational
    scrap around work part, and the maximum value
    should ensure the strip move well between guiding
    rails and is of certain distance between the edge
    of strip and guiding rails.
  • B D2m

68
3.Calculation
Homework Calculate the materials efficiency for
the workpiece on Page45.No3 and No 4.
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