Design and analysis of scissor jack final report 8 sem (1)
1. DESIGN AND Analysis OF SCISSOR JACK
Presented by:-
Rahmatullah 16MEB203
Muzeer Ahmad 16MEB366
Mohd Tayyab 16MEB314
Under the supervision of
Dr. Najeeb ur Rahman
2. Introduction
-what is scissor jack
-what is the purpose
Types of jack
Nomenclature
Components
Study of selected parts of Scissor Jack
-Power Screw
-Trunion
-top & bottom arm
-top & bottom plate
Calculation of Scissor Jack
Static Analysis of Scissor Jack
Outline
3. A mechanical device which is used to lift heavy vehicles, partially or fully in the air for
breakdown and maintenance. Components of scissor jack are
• One power screw
• Two fixed nuts
• Four links which is connected to nuts
• Eight pins used to fixed that four links
• Two rings provided at screw end and
• load platform supported by upper two links.
Introduction
What is scissor jack ?
What is the purpose ?
• Used to lift up the cars while changing the tires during an emergency.
• To raised and lowered Heavy equipment
• By using it maintenance can be performed
6. Components
a. Frame(top and bottom arm top and
bottom plate)
b. Power screw
c. Rivets
d. Trunion
a. Frame:
• The entire frame of the scissor jack consists of links (top and bottom),
• Top frame
• Base frame
• The frame is manufactured by sheet metal processes and forming by medium
carbon steel.
7. b.Power screws:(Component)
A power screw is a mechanical device used for
converting rotary motion into linear motion
and transmitting power
Applications:
The main applications of power screws are as follows:
1.To raise the load, e.g. screw-jack, scissor jack.
2.To obtain accurate motion in machining operations, e.g.
lead-screw of lathe,
3.To clamp a work piece, e.g. bench vice
4.To load a specimen, e.g. universal testing machine.
8. Types of screw threads used in power screws are
1. Square threads:
Power transmission in either direction
Maximum efficiency and minimum efforts.
Employed in screw jacks and clamps
2. Acme threads:
Modification of square thread
Efficiency is lower than square threads
Easily manufactured
3. Buttress Thread:
Used when large forces act along the screw axis in one direction
only.
High efficiency .
Ease of cutting like acme threads.
Strongest thread of all
Forms of Threads:
9. • A rivet is a permanent mechanical fastener.
• Before being installed a rivet consists of a smooth cylindrical shaft with
a head on one end.
• On installation the rivet is placed in a punched or pre-drilled hole, and
the tail is upset, or bucked (i.e. deformed)
• It is more reliable.
c. Rivet:(Component)
d. Trunion:
• same as nut is a threaded fastener for joining two threads.
10. Scissor jacks advantages:
a. The jack is light and compact.
b. Making it easy to lift any size vehicle.
c.The jack’s lightweight design makes it user friendly for people of all strengths and
physical abilities.
d. A scissor jack will not suddenly “leak” and drop down like some hydraulic jacks.
e.The precision of these jacks allows for extremely precise lifting capabilities.
Stress Calculations:
On screw, there are mainly 6 types of failures.They are as follows:-
I) For screw body
Tensile failure
Buckling failure
Twisting failure
II) For screw thread
Crushing failure
Bending failure
Shear failure
11. Scissor Jack design for some specific range of weight up to 2000 kg of cars
as some of them mention below
s.no company Name of car Varient/model Gross weight(kg)
1 Audi Audi R8 1895
2 Ford ford Freestyle freestyle 1210
3 Maruti Suzuki swift AMT ZDI Plus
(Diesel) 1405
4 Maruti Vitara Breza ZDi Plus AMT
Dual Tone (Diesel)
1680
5 Toyota Glanza V CVT (Petrol) 1360
6 Tata Tiago Z plus 1200
7 Renault Duster E KVN(Diesel) 1349
13. Design Calculations:
1)power screw:
Material Selected -Medium carbon steel
Length of each arm = L1 =L2 =L3 =L4=170mm
Length of the power screw = (w1+w2+w3) = 380mm
w1= w3 = 160 mm, w2 = 60 mm
Maximum lift of the jack = (h1+h2) = 310 mm
q is the angle made by link with horizontal when jack is at its lowest position
cos (q) = 160/170 = 19.74˚.Let the weight of car =2 ton,then weight acting on rear
axle= 40%2ton=800kg,therefore weight on front axle=60%2ton=1200kg, weight on
each wheel of front axle=600 kg.
W = (load * g) = (600*10) = 6000 N
The tensionT acting on the power screw is shown in the above Fig
14. Formula Used-
Total tension = 2*T = W/tan (q)
Let dc be the core diameter of the screw. But load on the screw is
Load = (π/4)* dc 2* st
So,
2*T = W/tan (q) = (π/4)* dc2*st
Outer diameter, do=dc + P
Mean diameter, d = do – P
Check for self-locking
tan (a) = Lead/π*d; a=helix angle
Lead L = 2*P; since the screw has a double start square thread.
tan (a) = 2*p/π*d
15. Coefficient of friction; μ = tan (f) = 0.20
Condition for self locking
f > a
Effort required to support the load = 2*T tan (f+a)
Torque required to rotate the screw = effort *d/2
= 16*T/ (π* dc
3)
But tensile stress st = 2*T/ (π/4) * dc
2
st max = st/2 + ((st/2)2+ 2
)
Maximum shear stress max = ((st /2)2+2
)
If the maximum stresses st max and max within the safe limits, the design of double
started square threaded screw is satisfactory.
17. Trunion
Material Selected Cast iron
Let n be the number of threads in contact with the screw assumed that load is Uniformly
Distributed over the cross section area of the nut. Allowable Bearing pressure between
the threads (Pb) = 16N/mm2.
Pb = (2*T)/((π/4)*(do2-dc2)*n)
Nut thickness = n*p
Width of Nut b =1.5*do
Pins in Nut
Design calculations
Let d1 = diameter of pins in the nuts Since Pins are in double shear stress
Load on pins = W/2 = 2*(π/4)*d21*
19. Top Arm
Material selected Medium carbon Steel
Design calculations
σt = σyt/F.S
σc = 1.25*σt
Cross section area (A)
Moment of Inertia Ixx , Iyy
Radius of Gyration Rx, Ry
Rankine’s constant (a) =1/7500
Ends are hinged (Leff = L)
Pcr rankine crippling load in vertical plane
σc= crushing stress
Pcr = (σc*A)/ (1+a*(L/ Ry)2)
Pcr in horizontal plane
Pcr = (σc*A)/(1+a*(L/2*Rx)2)
If Buckling load is more than Design load the dimensions of the link safe.
22. Top Plate
Material used Medium carbon Steel
Design calculations Moment, M = (p*l)/4
Z = (b*h2)/6
σb = M/Z
If The permissible stress for Medium carbon steel is greater than
σb.
The top plate design is safe
31. CONCLUSION
In this project, a scissor jack is modelled in SOLIDWORKS and
a structural analysis of scissor jack with a force of 6000 N is also
performed in SOLIDWORKS software. The Resultant
Displacement, Equivalent Strain and Von-mises stress of the
scissor jack is analyzed. From the results, it is observed that the
Resultant Displacement, Equivalent Strain and the Von-mises
stress of the scissor jack are within the limits. Therefore,
modelled Scissor Jack is safe to use and has long life. In future
scope, different types of jacks can be modelled by taking
different materials and by giving different loading conditions for
structural analysis.
32. References:
Design Data Handbook for mechanical engineers, K. Mahadevan.
Mechanical Engineering Design Joseph Edward, Shigley.
Mechanical Design Engineering Handbook, Peter R. N. Childs.
Materials Selection in Mechanical Design, Michael F. Ashby.
Detailed Mechanical Design: A Practical Guide, James G. Skakoon.
INPRESSCO-GERNAL ARTICLE; E-ISSN2277-4106, AUTOMATED CAR JACK.
Academia.edu/6167889/Modification_of_the_Existing_Design_of_a_Car_Jack.
http://en.wikipedia.org/wiki/Jackscrew
Powerjacks.com/downloads/Design%20Guides/PJLMPT-02/S1-Screw-Jacks PJLMPTDG-
02.pdf
Design and fabrication of motorized automated object lifting jack; IOSRJEN.ISSN (e):2250-
3021.
http://www.ijceronline.com/papers/Vol4_issue07/Version-1/A0470101011.pdf
IOSR Journal of Engineering (IOSRJEN) www.iosrjen.org, ISSN (e): 2250-3021, ISSN (p):
2278-8719, Vol. 04, Issue 07 (July. 2014), ||V1|| PP 15-28.
