Transcript COLT Design Manual for Cold Forging Dies Case study: spline profiles (1) Case study: Cold forging of spline profiles • Die material: Vanadis 23,

COLT Design Manual for Cold Forging Dies
Case study: spline profiles (1)
Case study: Cold forging of spline profiles
• Die material:
Vanadis 23, 60 HRc
Net-shape forged spline tap
• Prestressing system:
ID 50 mm, OD 140 mm
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (2)
Typical failure mode
• Fatigue cracks in the grounds of the spline geometry
• The cracks start in the fillets in axial direction and propagate on the
top in radial direction.
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (3)
FE model of the tooling system
2D model of the die, here prestressed by STRECON E+
A) conventional container with double ring
0.6% interference
Stripwinding and casing
E=205 GPa, n=0.3, elastic
Carbide winding core
E=540GPa, n=0.23, elastic
B) STRECON® Basic, 0.8% interference
Die, E=225GPa, n=0.3
elastic-plastic
process load:
1000 MPa
C) STRECON® E+, 0.5% interference
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (4)
A) Prestressing by a double stress ring at 0.6% interference
Tangential stress distribution
at max. process load
Tangential stress-strain response
in the fillet (for one load cycle)
1500
570
MPa
1000
380
500
Stress in MPa
190
0
-190
-380
-570
-760
565 MPa
0
-1.5
-500
-0.5
0
0.5
1
Ds=
2850
-1000
-1500
MPa
-2000
-950
-2500
-1140
-3000
-1330
-1
Total strain in %
 risk of early crack initiation due to tensile stresses
at maximum process load and large stress range
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (5)
B) Prestressing by STRECON® Basic at 0.8% interference
Tangential stress distribution
at max. process load
570
Tangential stress-strain response
in the fillet (for one load cycle)
1500
MPa
1000
190
500
0
-190
-380
-570
-760
-950
-1140
-1330
40 MPa
Stress in MPa
380
0
-1.5
-500
-1
-0.5
0
0.5
1
-1000
-1500
Ds=
2840
-2000
MPa
-2500
-3000
Total strain in %
 Enhanced fatigue strength due to the elimination of tensile stresses,
but still the same stress range as the conventional double stress ring
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (6)
Risk of over-prestressing
Condition of the die after prestressing by 0.8% and subsequent
disassembly (e.g. for separate surface treatment).
200
Residual stresses
0.20
180
0.18
160
0.16
140
0.14
120
0.12
100
0.10
80
60
190 MPa
0.08
%
Equivalent plastic
strains
0.2%
0.06
40
0.04
20
0.02
0
0
 If the die is prestressed by a high interference level and taken out from
the prestressing system, cracks may occur in subsequent treatments.
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (7)
C) Prestressing by a STRECON® E+ at 0.5% interference
Tangential stress distribution
at max. process load
570
Tangential stress-strain response
in the fillet (for one load cycle)
1500
MPa
1000
190
500
0
-190
-380
-570
-760
-950
-1140
-1330
-125 MPa
Stress in MPa
380
0
-1.5
-500
-1000
-1500
-2000
-1
-0.5
0
0.5
1
Ds=
2480
MPa
-2500
-3000
Total strain in %
 Optimum fatigue strength due to the elimination
of tensile stresses and the minimization of the stress range
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (8)
Further optimization: change of the diameter ratio
Design C: die OD ø 50 mm
prestressed by STRECON E+
ø 50
Design D: die OD ø 40 mm
prestressed by STRECON E+
ø 40
 The closer the carbide winding core to the inner contour of the die insert,
the more effective the stiffness of the STRECON E+ container.
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (9)
Design D: Prestressing by modified STRECON® E+ container
(ID reduced from 50 to 40 mm) at 0.45% interference
Tangential stress distribution
at max. process load
570
Tangential stress-strain response
in the fillet (for one load cycle)
1500
MPa
1000
190
500
0
-190
-380
-570
-760
-950
-1140
-1330
-210 MPa
Stress in MPa
380
0
-1.5
-500
-1000
-1500
-1
-0.5
0
0.5
1
Ds=
2240
MPa
-2000
-2500
-3000
Total strain in %
 Optimum fatigue strength due to the elimination of tensile stresses
and the minimization of the stress range (from 2850 down to 2240 MPa)
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (10)
Comparison of elastic expansion under process load
Diameter change under process load
contour under
process load
contour under
prestressing
1
0.18
Diameter change in mm
Elastic expansion under
process pressure
0.16
0.14
0.12
0.1
0.08
1
2
1
2
1
2
1
2
0.06
2
A)
B) STRECON C) STRECON D) STRECON
conventional
Basic
E+ (ID 50)
E+ (ID 40)
 Reduced elastic expansion due to stiffness of STRECON E+ container
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.
COLT Design Manual for Cold Forging Dies
Case study: spline profiles (11)
Recommendations for the design
of dies for the cold forging of spline profiles
Recommended die material:
• Powder-metallurgical tool steel
provides an excellent fatigue strength
Recommended prestressing system:
• STRECON® E+
reduces the stresses and cyclic plastic strains in the fillets,
leads to improved fatigue life
The outer diameter of the die insert should be close
to the inner contour (better effectivity of the stiff carbide
winding core).
For variable adjustment of the inner diameter of the die
(to compensate for wear and manufacturing tolerances),
a STRECON® VARI-FIT is recommended, see case study.
Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools
with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.