An overview on different manufacturing processes of connecting rod.

1. Design and Construction
of a
Connecting Rod
BY
FAISAL BIN FARUK
DEPARTMENT OF MECHANICAL ENGINEERING
KHULNA UNIVERSITY OF ENGINEERING & TECHNOLOGY
KHULNA-9203, BANGLADESH

2. Outlines
 Objectives
 Introduction
 Manufacturing Process
 Comparison
 Design & Construction
 CAD & Real Models
 References

3. Objectives
 Study of Connecting Rod
 To understand the function of the connecting rod
 CAD Design of Connecting Rod
 To construct a Connecting Rod using different
operations

4. Introduction
 What is a Connecting Rod ?
connecting rod or conrod connects the piston to the
crank or crankshaft in a reciprocating piston engine.
 What does it do ?
transmits the thrust of the piston to the crank shaft, and as
the result the reciprocating motion of the piston is
translated into rotational motion of the crank shaft

5. Introduction (Continued)
 It consists of –
1. A pin – end (Small End)
2. A shank section (Middle), and
3. An crank end (Big End)
 How does it functions ?
Connecting rods are subjected
to forces generated by mass and
fuel combustion. These two
forces results in axial load and
bending stresses.

6. Introduction (Continued)
 Capability
A connecting rod must be capable of transmitting axial
tension (Pull), axial compression (Push), and bending stress
caused by the thrust of the piston and by centrifugal force.

7. Manufacturing Process
 Casting:
 Cast in sand
 Small little seam on both sides of the
parting edge.
 Used in Speed Motor. For example 3.8L
Buick engine.
 Cap in pin-end is fastened with bolts only.
 Maximum rpm 6500. [1]
Fig : Cast Connecting rod

8. Manufacturing Process (Contd.)
 Forging :
 Thick seam on both sides (Left material) of
the parting edge left from the forging dies
in forging process.
 Used in speed motors like small-block
Chevrolet engine.
 I-beam cross section.
 Bolt-Nut assembly.
 Used in engines of rpm range about 5500-
6800 or further. [1]
Fig : Forged Connecting rod

9. Manufacturing Process (Contd.)
 Forged Billet rods:
 Machined from a solid piece of steel.
 No parting edge, 100 % machined.
 H-beam cross section.
 Bolts are screwed to hold the cap on.
 Strongest con-rods. 1200 hp engine [1]

10. Manufacturing Process (Contd.)
 Sintered connecting rods:
 Powdered metal pressed together and
then put into an oven where it is
sintered that means granuals are
melted together and forms the rod.
 Parting edge where cap and the rod
meet is fractured.
 Each cap and each rod is unique with
itself.
 Used in engine of rpm 7000 rpm. [1]

11. Comparison
 Oldest Technology :
Cast Con-rods. Used in old engines.
 Newest Technology :
Sintered Con-rods. Quick acceleration, longer use time. Used
in modern engines.
 Strongest Con-rod :
H-Beam forged connecting rods. Heavy duty engines.

12. Design & Construction
Fig : Analysis of Buckling Load
For a connecting rod
equally strong in Buckling
about the both axes,
WB (X axis) = WB (Y axis)
𝜎 𝑐 𝐴
1+ 𝛼
1
𝑘 𝑥𝑥
2
=
𝜎 𝑐 𝐴
1+
1
2𝑘𝑦𝑦
2
Or, Kxx
2 = 4 kyy
2
Or, Ixx = 4 Iyy (As, I = Ak2)
 In actual practice Ixx is kept slightly lower than 4Iyy
 3 <
𝐼 𝑥𝑥
𝐼 𝑦𝑦
< 3.5
 WB =
𝜎 𝑐
𝐴
1+ 𝛼
𝐿
𝑘 𝑥𝑥
2
...for calculation WB = Max. gas force × Factor of safety (5~6)

13. Design & Construction(contd.)
Example 32.3: Design a connecting rod for an I.C. engine running at 1800 r.p.m. and
developing a maximum pressure of 3.15 N/mm2 . The diameter of the piston is 100 mm ; mass of
the reciprocating parts per cylinder 2.25 kg; length of connecting rod 380 mm; stroke of piston
190 mm and compression ratio 6 : 1. Take a factor of safety of 6 for the design. Take length to
diameter ratio for big end bearing as 1.3 and small end bearing as 2 and the corresponding
bearing pressures as 10 N/mm2 and 15 N/mm2 . The density of material of the rod may be
taken as 8000 kg/m3 and the allowable stress in the bolts as 60 N/mm2 and in cap as 80 N/mm2
. The rod is to be of I-section for which you can choose your own proportions. [2]
Fig : Cross Section
 Solution :
B = 4t
H = 5t
A = 2 (4 t × t) + (3t × t) = 11t2 (Figure a)
𝐼 𝑥𝑥 =
1
12
4𝑡 5𝑡 3 − 3𝑡 3𝑡 3 =
𝟒𝟏𝟗
𝟏𝟐
𝒕 𝟒

14. Design & Construction(contd.)
𝐼 𝑦𝑦 = 2 ×
1
12
× 𝑡 4𝑡 3 +
1
12
× 3𝑡 × 𝑡3 =
𝟏𝟑𝟏
𝟏𝟐
𝒕 𝟒
As,
𝐼𝑥𝑥
𝐼𝑦𝑦
=
419
12
×
12
131
= 3.2, so the proprtion chosen is satisfactory.
Now, force on connecting rod = maximum gas pressure on piston
𝐹 𝐶 = 𝐹𝐿 =
𝜋𝐷2
4
× 𝑝 =
𝜋 100 2
4
× 3.15 = 24740 𝑁
Buckling Load, 𝑊 𝐵 = 𝐹𝐶 × 𝐹. 𝑆. = 24740 × 6 = 148440 𝑁
𝐾 𝑥𝑥 =
𝐼 𝑥𝑥
𝐴
=
419 𝑡4
12
×
1
11 𝑡2
= 1.78𝑡
Length of crank, 𝑟 =
𝑆𝑡𝑟𝑜𝑘𝑒 𝑜𝑓 𝑃𝑖𝑠𝑡𝑜𝑛
2
=
190
2
= 95 𝑚𝑚
Fig : Cross Section

15. Design & Construction(contd.)
Length of the connecting rod, 𝑙 = 380 𝑚𝑚 so, for both ends hinged, 𝐿 = 𝑙 = 380 𝑚𝑚
Rankine’s formula , 𝑊 𝐵 =
𝜎 𝐶
𝐴
1+ 𝛼
𝐿
𝑘 𝑥𝑥
2
148440 =
320 × 11𝑡2
1 +
1
7500
380
1.78𝑡
2
Or, 𝑡4 − 42.2𝑡2 − 257.3 = 0
Taking positive value , 𝑡2 = 47.6 𝑂𝑟, 𝑡 = 6.9 ≅ 𝟕𝒎𝒎
So, thickness of flange is 7mm
Now 𝑤𝑖𝑑𝑡ℎ 𝑩 = 𝟒𝒕 = 𝟐𝟖𝒎𝒎 𝑎𝑛𝑑 𝑑𝑒𝑝𝑡ℎ, 𝑯 = 𝟓𝒕 = 𝟑𝟓 𝒎𝒎
Width stays constant but depth varies .....
at crank end 𝟏. 𝟏𝑯 𝒕𝒐 𝟏. 𝟐𝟓𝑯 & at pin end 𝟎. 𝟕𝟓𝑯 𝒕𝒐 𝟎. 𝟗𝑯

16. Design & Construction(contd.)
Fig : Right side view and Front View
Fig : Cross section
B = 7 mm
H = 11 mm
A = 2(2x7) + (7x4) mm2 = 56 mm2 (Middle)
𝑙 = 95mm
dC = 25mm, dP = 8.5 mm
tC = 6mm, tP = 4.75mm

17. Design & Construction(contd.)
Material Aluminium 2014-O Alloy
Property Value Units
Elastic Modulas 72.4-73.1 GPa
Fatigue Strenth 89.6 MPa
Density 2.8 g/cc
Tensile Strength 186 MPa
Brinnel Hardness 45
Machinability 30%
Melting Point 507-638 Degree Celsius
Ingredient Percentage by
Weight
Al 90.4-95
Cu 3.9-5
Fe 0.7
Si 0.5-1.2
Mn 0.4-1.2
Cr Max 0.1
Mg 0.2-0.8
[3
]

18. CAD Model
Theoretical

19. Real Model
Experimental

20. Referrences
 [1] Chen, N., L. Han, W. Zhang and X. Hao, 2006. "Enhancing
Mechanical Properties and Avoiding Cracks by Simulation of
Quenching Connecting Rod". Material Letters, 61: 3021-3024.
 [2] Khurmi R.S., Gupta J.K., “A Textbook of Machine Design”,14th
edition 2005, Eurasia Publishing House.
 [3] Boyer H.E. and Gall T.L., "Metals Handbook", Eds., American
Society for Metals, Materials Park, OH, 1985

21. Thank You