The camshaft and crankshaft are key components that convert reciprocating to rotational motion in automobile engines. The camshaft uses lobes to push the valves open and closed according to the rotation of the crankshaft. Crankshafts are typically made of forged steel or cast iron and experience high static and dynamic stresses that require high rigidity. Surface hardening through carburizing or nitriding increases the hardness of these components. New microalloyed steels and treatments like plasma ion nitriding further enhance strength.

1. Material and technology
for Automotive engine:
brief overview
o The camshaft
o The crankshaft
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

2. The camshaft
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

3. The camshaft - 1
The valve operating mechanism
transforms rotation of the
crankshaft into reciprocating
motion in the valves.
The valves protrude into
the combustion chamber and
are pushed back by the reactive
force of the valve spring.
Ωcamshaft= Ωcrankshaft/2
- Ωcamshaft high: contact pressure is reduced by the inertia of the valve lifter (oil is
providing hydrodynamic lubrication);
- Ωcamshaft low: contact pressure is highest and lubrication most challenging.
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

4. The camshaft - 2
Machining, dimension
accuracy, clearance, rou
Wear of sliding portion
ghness Friction condition 1. Rugged surface due to wear
1. Lubrication
2. Contact 2. Adhesive wear
Lubricating oil 3. Foreign object 3. Fatigue wear
condition 4. Corrosive wear
Flaking (scagliatura)
Pitting (corrosione per vaiolatura)
• It is very important to choose an appropriate combination of materials.
• The torque from the crankshaft drives the camshaft: it must have high torsional rigidity.
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

5. The camshaft - 3
Chill hardening cannot be used where the gap between the cam lobes is narrow because
of the difficulty in using the chiller, so forged camshafts are used.
Tough martensite is more resistant to pitting than the chill microstructure.
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

6. The camshaft - 4
• Finishing – boring and grinding
• ASSEMBLING
• E.g.: Hydroforming
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

7. The crankshaft
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

8. The crankshaft - 1
The crankshaft converts reciprocative motion to rotational motion.
Two types:
• the monolithic type
• the assembled type
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

9. The crankshaft - 2
Note:
Included lead or MnS
Carbon steel particles significantly
function as a chip
breaker and a solid
Alloyed steel lubricant and increase
machinability.
Micro Alloyed steel
Typical materials • less expensive
• nodular cast iron: for high-
volume, low-load production. • lower rigidity: abnormal vibrations (resonance)
• increases in rigidity of more than 10%
• reduces noise levels and harshness
• forged steel: for fuel-efficient • makes possible a careful design
engines requiring a high power-to-
displacement ratio. • more expensive
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

10. The crankshaft - 3
• Static: combustion pressure, inertial
forces of the piston and con-
rod, bearing load and drive torque.
STRESS on
Crankshaft • Dynamic: The vibration causes
dynamic stress. If it occurs at the
resonating frequency, the deformation Fatigue fracture of a carbon steel
will be very high and will instantly S50C crankshaft
rupture the crankshaft.
HIGH STATIC AND DYNAMIC RIGIDITY:
- increasing the crankpin diameter (increasing weight)
- using forged steel
- Surface-hardening methods
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

11. Fatigue behaviour: principles and survey
Principi (macro)
σa Wöhler [1860]
Ampiezza
tensione
applicata
Vita finita * Legge di Basquin:
σa = σf’ (2Nf)b
*
Tipici
Curva tipica
acciai
per acciai
σL
Leghe di
alluminio
Vita infinita
104 105 106 107
Cicli alla rottura, Nf
Dipende da:
•Tipo di materiale • Concentrazione di • Contenuto di inclusioni e
tensioni impurezze
• Trattamento termico • Tensione media e
superficiale tipo di sollecitazione
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

12. The crankshaft - 4
HOT FORGING PROCESS (for a four-stroke crankshaft)
• The coarse structure is broke down and is
replaced, as recrystallisation proceeds, by one
which is of relatively fine grain
• Impuritires are redistribuited in a fibrous form
• Introduction of compressive residual stresses
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

13. The crankshaft - 5
SURFACE HARDENING
(carburizing, nitring, carbonitring and nitrocarburizing):
• CARBURIZING
O: origins
S: a few beachmarks
B: arrest lines
R: ratchet marks
Pitting observed at a crankpin surface
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

14. The crankshaft - 6
SURFACE HARDENING
(carburizing, nitring, carbonitring and nitrocarburizing):
• CARBURIZING
Compressive residual stress
generated by carburizing
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

15. The crankshaft - 7
Modern carburizing technology: Acetylene Vacuum Carburizing- AvaC
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

16. The crankshaft - 7
Avac - Adsorbimento (T>Taustenitizzazione)
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

17. The crankshaft - 7
Avac - Decomposizione in radicali
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

18. The crankshaft - 7
Avac - Inizio cementazione (T>Taustenitizzazione)
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

19. The crankshaft - 7
Avac - Inizio cementazione (T>Taustenitizzazione)
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

20. The crankshaft - 7
Avac - Inizio cementazione (T>Taustenitizzazione)
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

21. The crankshaft - 7
Diffusione nell‘acciaio (T>Taustenitizzazione)
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

22. The crankshaft - 7
Saturazione
Steel
Fe
Acetilene Siti di adsorbimento
Cr
C H2
Mn
Materials and technology for automotive engine
A. Manicone Catania, 06/07/2012, A.Manicone

23. The crankshaft - 7
SURFACE HARDENING
(carburizing, nitring, carbonitring and nitrocarburizing):
• NITRING: NH3
decomposes at the steel surface to catalytically generate elemental nitrogen, which
diffuses into the material. The nitrogen expands the iron lattice and also forms hard
compounds (the nitrides Fe4N and Fe3N) with iron atoms.
Nitridable steel reaches the necessary hardness by forming stable nitrides (Al, Cr, V…)
• NITROCARBURIZING, CARBONITRURING
• higher hardness surface,
• but lower toughness
• INDUCTION HARDENING
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

24. The crankshaft - 8
RECENT TRENDS: Micro alloyed steel, via plasma ion nitring
Precipitation hardening is the main method for increasing strength at the
cooling stage after hot forging.
Micro-alloyed steel contains a small amount of V, which dissolves in the
matrix during hot forging above 1,200 °C. During air cooling, the dissolved V
combines with carbon and nitrogen to precipitate as vanadium carbide and
nitride at around 900 °C.
the vanadium
carbide and nitride will
be more finely
dispersed.
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

25. The crankshaft - 9
Manufacturing process
• Trade-off:
machinability-fatigue
resistance
• Surface roughness
For low and medium loaded bearings: Ra = 15
microinch max. Rz = 60 microinch max.
For highly loaded bearings: Ra = 10 microinch
max. Rz = 30 microinch max.
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

26. The crankshaft - 10
Conclusions: Methods to strengthen crankshafts
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone

27. Material and technology
for Automotive engine:
brief overview
Thanks for
attention
Materials and technology for automotive engine
Catania, 06/07/2012, A.Manicone