desig2n and analysi4s

8/12/2019 Desig2n and Analysi4s

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DESIGN AND ANALYSISOF

Contents1 Introduction ........................................................................................... Error! Bookmark not defined.

1.1 Problem Statement ........................................................................ Error! Bookmark not defined.

1.2 Objective .........................................................................................................................................

1.3 schedule .3

2 Research & Decision Making ................................................................................................................. 4

2.1 Product Comparison ..................................................................................................................... 9

2.2 Preliminary Designs ....................................................................................................................... 5

2.3 Decision making ............................................................................................................................ 8

2.4 Final design8

3 Sketches ................................................................................................................................................ 9

3.1 Jack .............................................................................................................................................. 10

3.2 Supports ...................................................................................................................................... 11

4 PRO-e models ...................................................................................................................................... 13

4.1 Parts ............................................................................................................................................ 13

4.2 Assembly ..................................................................................................................................... 17

5 Work done .......................................................................................................................................... 18

5.1 Load criteria and assumptions .................................................................................................... 18

5.2 Material selection ....................................................................................................................... 19

5.3 Stresses acting on various components.20

5.4 Self locking criteria...20


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6 Possible failures and errors ................................................................................................................. 21

7 Work to be done ................................................................................................................................ 22

1.1Roadmap:Here we outline the timeline for the completion of various aspects for

the project. The schedule is set so that the project is completed in

phases. Phase I is market research, Phase II consists of the designprocess, Phase III entails PRO-e modeling of the design and simulation

in ANSYS software, and the final aspect of the project is the

presentation and the work that went into it.

2 Scissor jack:2.1Specifications

The term "scissor jack" describes a wide variety of tools that allfollow the same principle: using crossed beams to lift something.

They do this by acting on the object they are lifting in a diagonal

manner; the lift on the right side lifts the object from its left side

and vice versa. This allows the user to store the jack when it isnot in use (with the diagonal beams flat) and to expand it when it

is needed.


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The major specification of scissor lifts is that they are allsymmetrical. In order to work, the distance from the loaded

point to the cross point must be the same as the distance from

the cross point to the ground. This ensures that weight is

distributed equally throughout the scissor lift beams.

Since scissor lifts have such a wide variety of use, they also havea wide variety of power sources. Scissor lifts for lifting cars can be

powered electrically, hydraulically and of course mechanically.

On the other end of the spectrum, industrial scissor lifts that

people stand on are often powered by diesel, although electrical

options do exist.

Scissor lifts basically fall into two categories: single scissor liftsand multiple scissor lifts. A single scissor lift has just two

crossbeams and one "x." This means it can only go so high

because the length of the crossbeams restricts the height of the

lift, and making them too long would make it unstable.

On the other hand, multiple lifts have beams crossing each other, and

then attaching to more beams that go the opposite direction. This

allows the scissor lift to rise higher.


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2.2AssemblyA scissor jack has four main pieces of metal and two base ends. The

four metal pieces are all connected at the corners with a bolt that

allows the corners to swivel. A screw thread runs across this assembly

and through the corners. As the screw thread is turned, the jack arms

travel across it and collapse or come together, forming a straight line

when closed. Then, moving back the other way, they raise and come

together. When opened, the four metal arms contract together, coming

together at the middle, raising the jack. When closed, the arms spread

back apart and the jack closes or flattens out again.

2.3WorkingA scissor jack uses a simple theory of gears to get its power. As the

screw section is turned, two ends of the jack move closer together.

Because the gears of the screw are pushing up the arms, the amount of

force being applied is multiplied. It takes a very small amount of force

to turn the crank handle, yet that action causes the brace arms to slide

across and together.

As this happens the arms extend upward. The car's gravitational weight

is not enough to prevent the jack from opening or to stop the screw

from turning, since it is not applying force directly to it. If you were to

put pressure directly on the crank, or lean your weight against the

crank, the person would not be able to turn it, even though your weight

is asmall percentage of cars.

2.4Components Frame
http://www.ehow.com/travel/http://www.ehow.com/travel/


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Power screw Rivets Coupling nut Crank

Frame:The entire frame of the scissor jack consists of links(top and bottom),

base frame, support frame. The frame is manufactured by sheet metal

processes and forming by low-medium carbon steel.

Power screw:Power screws are used to convert rotary motion in to translational

motion. It is also called translational screw. They find use in machines

such as universal tensile testing machines,

machine tools, automotive jacks, vises; aircraft flap extenders, trench

braces, linear actuators, adjustable floor posts, micrometers, and C-

clamps. A screw thread is formed by cutting a continuous helical

groove around the cylinder. These grooves are cut either left hand or

right hand.

The majority of screws are tightened by clockwise rotation, which is

termed a right-hand thread. Screws with left-hand threads are used in

exceptional cases. For example, anticlockwise forces are applied to the

screw (which would work to undo a right-hand thread), a left-hand-

threaded screw would be an appropriate choice.

Power screws are typically made from carbon steel, alloy steel, or

stainless steel and they are usually used with bronze, plastic, or steel

mating nuts. Bronze and plastic nuts are popular for higher duty


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applications and they provide low coefficients of friction for minimizing

drive torques.

There are important terms and figures that need to be understood

before designing power screws:

1. Pitch: is the distance from a point on one thread to the

corresponding thread on the

next adjacent thread, measured parallel to the axial plane.

2. Lead: is the distance the screw would advance relative to the nut in

one rotation. For

single thread screw, lead is equal to pitch.

3. Helix Angle: is related to the lead and the mean radius by the

equation below;

Basics of power screws

Power screws provide a compact means for transmitting motion and

power. They are ideal for replacing hydraulic and pneumatic drive

systems as they require no compressors, pumps, piping, filters, tanks,


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valves or any other support items required by these systems. Also,

screws don't leak so there are no problems with seals which are so

common to hydraulic and pneumatic systems. And, screw systems are

quiet running - no noisy compressors, pumps or exhaust valves. Screw

systems are simple, reliable and easy to utilize.

Power screw motions

There are four distinct motion converting actions that can be produced

by power screws and nuts. The two most common involve torque

conversion to thrust. In Figure 1, the screw is rotated (torqued) and the

nut moves linearly producing thrust or the nut is rotated (torqued) and

the screw moves linearly. The two less common motions involve thrust

conversion to torque. In Figure 2, the nut undergoes a linear force

(thrust) and the screw rotates or the screw undergoes a linear force

(thrust) and the nut rotates. These two motions are commonly referred

to as "back driving", "overhauling", or, improperly, "reversing".

Fig1. Fig2.

Types of power screws

There are 3 types of screw threads used in power screws:

1.Square threads: Is used for power transmission in either direction Results in maximum efficiency and minimum


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It is employed in screw jacks and clamps2.Acme threads: It is a modification of square thread Efficiency is lower than square threads

The slope increases the area for shear It is easily manufactured3.Buttress Thread: It is used when large forces act along the screw axis in one

direction only.

It has higher efficiency like square threads and ease of cutting likeacme threads.

It is the strongest thread of all It has limited use of power transmission

Rivets:A rivetis a permanent mechanicalfastener.Before being installed a

rivet consists of a smoothcylindrical shaft with a head on one end. Theend opposite the head is called the buck-tail. On installation the rivet is

placed in a punched or pre-drilled hole, and the tail is upset, or bucked

(i.e. deformed), so that it expands to about 1.5 times the original shaft

diameter, holding the rivet in place. To distinguish between the two

ends of the rivet, the original head is called the factory head and the

deformed end is called the shop head or buck-tail.

Coupling nut:A coupling nut is athreadedfastener for joining two male threads, most

commonlythreaded rod.The outside of the fastener is usually a hex so a

wrench can hold it. Variations include reducing coupling nuts, for
http://c/wiki/Fastenerhttp://c/wiki/Cylinder_(geometry)http://c/wiki/Screw_threadhttp://c/wiki/Threaded_rodhttp://c/wiki/Threaded_rodhttp://c/wiki/Screw_threadhttp://c/wiki/Screw_threadhttp://c/wiki/Cylinder_(geometry)http://c/wiki/Fastener


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joining two different size threads; sight hole coupling nuts, which have a

sight hole for observing the amount ofengagement;and coupling nuts

with left-handed threads.

Crank:is an arm keyed at right angles to the end of a shaft, by

which motion is imparted to the power screw .It mainly suffers

from torsional stresses so medium carbon steel is used as it

combines merits of malleability and sufficient torsional strength.

PHASE-I(market research):

3 Research & Decision Making:3.1 Product ComparisonBelow are analyses two other car jacks that are similar to the jack I wish

to design. They represent the two primary models of scissor jacks

available; those powered by electricity and those that require manual

input
http://c/wiki/Engagement_(thread)http://c/wiki/Engagement_(thread)

desig2n and analysi4s

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