Scissor jack Final project 82381-07 PDF

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2017MEKELLE UNIVERSITYSchool of Mechanical and Industrial Engineering Department of Mechanical EngineeringHaben Desta Section – 04 ID Number – EITM/UR 82381/ Year – 4 th Design Project – 1[DESIGN OF SINGLE MECHANICAL SCISSOR JACK]A Single mechanical Scissor jack is used to lift the heavy loads in wh...

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2017

MEKELLE UNIVERSITY School of Mechanical and Industrial Engineering Department of Mechanical Engineering

Haben Desta Section – 04 ID Number – EITM/UR 82381/07 Year – 4th

Design Project – 1

[DESIGN OF SINGLE MECHANICAL SCISSOR JACK] A Single mechanical Scissor jack is used to lift the heavy loads in which rotary motion is converted in to linear motion. In this project , a unique design of single mechanical scissor jack is compile to lift low as well as heavy load with different conditions.

Design of Single mechanical scissor jack

Mekelle University Ethiopian Institute of Technology School of Mechanical and Industrial Engineering

Machine Design Project -I-(MEng4066) Design Project A

Name : Haben Desta Gebremical

ID.No.: EITM/UR82381/07

It is required to design a Scissor Jack, which is used to lift an automobile during tyre replacement. The jack should be designed to be operated manually, and manufactured from locally available materials with the use of simple manufacturing methods. Additional specification Type: Mechanical Scissor Jack Maximum lift load: 14KN Minimum lift height: 150mm Maximum lift height: 250mm Design the jack based on the operation conditions specified above

Task 1. 2. 3. 4. 5.

Design the jack: gears, screw, nut, cap, base, handle and housing, etc Design all necessary fasteners and other components in the jack. Prepare a report outlining all your design calculation, considerations and selections. Prepare detailed part drawings for all components in the jack. Prepare an assembly drawing with necessary views that includes details of all the joints in the jack. Submission deadline: Monday December 11, 2017

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Design of Single mechanical scissor jack

Acknowledgement First of all thank

God

for his endless love and support.

then , I want to address my deepest gratitude to my advisors

Instructor Meron

and Instructor Equby leaek for helping me and giving important suggestions and their time on my design. And finally , I want to say thanks to all my friends who help me by materials and other resources.

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Abstract A screw jack serves to give mechanical advantage by changing rotational force to linear force thus allowing one to lift a load and support it at a given height. On road emergency, i.e. tire gets punctured, is a common problem observed in automobile and also it is big headache to driver. Scissor jacks are one of the best option to overcome this headache. Scissor jack is used to lift the heavy loads in which rotary motion is converted into linear motion.

In this Project,

a unique design of scissor jack is compile to lift low as well as heavy load with different conditions. The main purpose and significance of this paper is to design, optimize and standardize the current toggle jack to make the task easier and reliable. Solid work is used to develop and analyzed the scissor jack. Mathematical model of design procedure is also made which will supposed to help in standardization of scissor jack design. The design calculation includes design of Power Screw, Link design, Design of Nut, Rivet Design etc. All products from engineering should be versatile with application by maintaining its aesthetics and ergonomics. This project mainly focused on designing and standardization of scissor jack model of automobile and trying for weight reduction of scissor jack with good strength. Also some changes are done in design procedure so that it will be useful for different models in automobile industry. Car jacks that are available in the market has some disadvantages such as required more energy to operate, are not suitable for woman and cannot be used on the uneven surface. So that, this design is modified for the existing car jacks in terms of its functionality and human factor consideration.

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Contents Pages

Part one ………………………………………………………………………… introduction …………………………………………….07 1.1 Mechanical jack …………………………………………………….08 1.2 Scissor jack ……………………………………………………………08 1.3 Applications ………………………………………………………….09 1.4 Advanteges …………………………………………………………..09 1.5 working principles …………………………………………………10 1.6 Problem statement ………………………………………………10

Part Two ………………………………………… Objective ….……………………………..……………………..12 2.1 Main objective ………………………………………………………13 2.2 Specific objective …………………………………………………13 2.3 Methodolegy ………………………………………………………...14

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Part Three ………………………………………. Specifications…………………………………………….15 3.1 Specifications ………………………………………………...16 3.2 Components ………………………………………………….17 3.3 Assembley …………………………………………………….21 3.4 Litrature review …………………………………………...24 3.4.1 Product comparison ……………………….26

Part Four ……………………………………. Geometry Analysis ..………………………………..28 4.1 Give specification …………………………………………29

Part five ……………………………………... How to assemble the components ? ……..59 5.1 How to assemble the components ? ……………...60 5.2 Maintenance ………………………………………………….60

Part six ……………………………………….. cost analysis ……………………………………….63 6.1 Cost analysis …………………………………………………….64 6.2 Material cost ……………………………………………………64 6.3 Labor cost ………………………………………………………..64

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Part seven …………………………………… Conclusion and Recommendation …………… 65 7.1 Conclusion ……………………………………………………….66 7.2 Recommendation …………………………………………….67

Reference …………………………………………………….68

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Part one INTRODUCTION

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Introduction 1.1 Mechanical jack A jack is mechanical device used to lift heavy loads or apply great forces. Jacks employ a screw thread or hydraulic cylinder to apply very high linear forces. A mechanical jack is a device which lifts heavy equipment. The most common form is a car jack, floor jack or garage jack which lifts vehicles so that maintenance can be performed. Car jacks usually use mechanical advantage to allow a human to lift a vehicle by manual force alone. More powerful jacks use hydraulic power to provide more lift over greater distances. Mechanical jacks are usually rated for a maximum lifting capacity.

1.2 Scissor jack  Scissor jacks are simple mechanisms used to drive large loads for short distances. The power screw design of a common scissor jack reduces the amount of force required by the user to drive the mechanism. Most scissor jacks are similar in design, consisting of four main members driven by a power screw.  A scissor jack is operated simply by turning a small crank that is inserted into one end of the scissor jack. This crank is usually "Z" shaped. The end fits into a ring hole mounted on the end of the screw, which is the object of force on the scissor jack. When this crank is turned, the screw turns, and this raises the jack. The screw acts like a gear mechanism. It has teeth (the screw thread), which turn and move the two arms, producing work. Just by turning this screw thread, the scissor jack can lift a vehicle that is several thousand pounds. Power screw in a scissor jack is the foundation of whole mechanism of scissor jack.

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Design of Single mechanical scissor jack Scissor jack is divided in specifically two types. Those are 1) Mechanical scissor jack 2) Hydraulic scissor jack since hydraulic jack are not cheap in cost and easy to manufacture Need additional oil so we select the mechanical type. Generally, they are used to lift a load depending on the design specification to with stand to lift different load.

1.3 APPLICATION For cars (automobile) which have 1tone weight, for lifting purpose.

1.4 ADVANTAGES The advantages of scissor type automobile screw jack are:Construction is very simple. Capital investment and installation cost are relatively low. Easy to operate, easy to maintain and easy to carry. Operation time is in short period.  There is no require fuel, electricity and other power sources to operate this jack. The strength of the jack is more compact than other type of the jacks. The size of the jack is so small and the overall weight of the jack is so light.

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1.5 Working principle  A 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 pressuredirectly on the crank, or lean your weight against the crank, the person would not be able to turn it, even though your weight is as small percentage of cars.

Fig :3 scisser jack at lowest position

fig :4 scisser maximum position

1.6 Problem Statement: Nowadays in this country, most of the cars were equipped with the scissor car jack. We found that the car jack were very difficult to be used especially by women, we want to develop a product based from the problem faced by the users who drive a car regarding to this issue. To overcome this problem, a research has been conducted to find the solution on how to design a car jack for Mekelle University

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Design of Single mechanical scissor jack the car using the simplest and cheapest way while it is energy saving. Although there were many ways to solve this problem, we recommend that the design this car jack system is the practical way when we considered all the factors and consequences especially about the analysis to develop this product. During the research, we have found that most of the car user has difficulties in maintaining their vehicles breakdown especially cars in the scope of changing tires. The normal car jack we have in the market is operated using bare hands and it is time consuming. It also requires much energy from the person to rotate the jack. Hence, this report had been prepared to recommend the design of the car jack that is user friendly and easier to operate as do not required too much money to develop this product.

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Part Two Objective

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2.1 Main objective The project main objective is to redesign of mechanically operated simple scissor jack.

2.2 Specific objective The project make the design reliable and easy to utilize operated using simple mechanical advantage and its analysis .The project also aims at designing and finding stresses, efficiency, expected life of screw, in addition it develops a screw jack such that it is cost effective, having a long life and can be handled and maintained easily Specifically we design the single mechanical scissor jack components such us it’s: upper link lower link base plate power screw fixed nut (screw housing) main nut(protective) driving handle

 

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2.3 Methodology  The design starts with the set of all possible equations bounded by the external constrains and by a process of progressive evaluation and selection narrows down the range of candidates to fined the ‘best’ design for the purpose. There are so many steps are there in the design process.

 Select a proper material that is able to withstand the applied load at different elevation (height from 250mm-150mm). 



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Part Three Specifications

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3.1 Specifications The term "scissor jack" describes a wide variety of tools that all follow 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 is not in use (with the diagonal beams flat) and to expand it when it is needed. 

The major specification of scissor lifts is that they are all symmetrical. 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 have a 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.  The project has limiting specifications such that the maximum and minimum lifting heights are 250mm and 150mm.the maximum lifting load is 14KN.

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3.2. Components Power screw Rivets Coupling nut Crank (Handle)  Links e.c.t 

 Power screw: 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.[3] 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 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. Mekelle University

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Design of Single mechanical scissor jack 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, valves or any other support items required by these systems. [3]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

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Design of Single mechanical scissor jack 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. o These two motions are commonly referred to as "back driving", "overhauling", or, improperly, "reversing".

Rivets: A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end 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. Mekelle University

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 Coupling nut: A coupling nut is a threaded fastener for joining two male threads, most commonly threaded rod. The outside of the fastener is usually a hex so a wrench can hold it. Variations include reducing coupling nuts, for joining two different size threads; sight hole coupling nuts, which have a sight hole for observing the amount of engagement; and coupling nuts with left-handed threads.

Fig 3: Copling nut ( power screw housing)

 Crank 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.

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Fig 4 :crank ( Handle)

3.3 . Assembly  A 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.

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3.4 Literature review A scissor lift contain multiple stag...