DESIGN AND OPTIMIZATION OF SCISSOR JACK

DESIGN AND OPTIMIZATION OF SCISSOR JACK1Chetan S.Dhamak, 2D.S.Bajaj, 3V.S.AherDepartment of Mechanical Engineering, Amrutvahini College of Engineering,Sangamner. [MS], Savitribai Phule Pune UniversityEmail: 1dhamakchetan@gmail.com, 2dipakbajaj@yahoo.com, 3vsa arya@rediffmail.com Abstract— Every engineering productinvolve cost effective manufacturing and itsversatility in application maintaining itsaesthetics as well as assign service life withoutfailure keeping those parameters in mind wefocused our intention on designing andanalyzing the scissor jack model for actualloads for varying models of automobileL.M.V. sectors. Automobile sectors are verykeen at their productivity and customersatisfaction. We also keen at designing andoptimization of scissor jack at the same timemaintaining its strength and service life.After studying failure modes we made amathematical model analytically and byusing software’s thereby made a new versatilescissor jack that can be used for varyingmodels of L.M.V automobile sector. Alsomodeling made by CATIA and mathematicalmodel made by Visual Basic software can betested by ANSYS software.IndexTerms-MathematicalModel,Optimization and Scissor.I. INTRODUCTIONCar jack is a device used to lift up the cars whilechanging the tires during an emergency. Carjacks are available at the market has somedisadvantages such as requiring more energy tooperate, are not suitable for women and cannotbe used on the uneven surface. The purpose ofthis project is to modify the design of theexisting car jack in terms of its functionality andalso human factors considerations.The day to day usage of cars is keeping onincreasing as the world moves on to a hecticstage. One big problem everyone faces is a flattyre on a voyage to any destination. If the tyregets punctured the driver has to undergo a lot ofpressure and rigorous mechanical work to lift thecar using a screw jack. Then the changing of atyre is a job that can be done systematically andrelatively easy.Fig.Scissor JackToday, many people are familiar with the jackthat is included with their vehicle. Some vehiclesbear screw jacks and others carry a hydraulicjack. Automotive jacks are of three typesmainly:1. Screw Jacks2. Trolley Jacks3. Bottle JacksEach has its own advantages and disadvantages.Screw jack is lesser in cost, as compared totrolley jacks and bottle jacks. While trolley jackand bottle jack can provide a greater lift withlesser application of force. [5]With the increasing levels of technology,the efforts being put to produce any kind of workhas been continuously decreasing. The effortsrequired in achieving the desired output can beeffectively and economically be decreased bythe implementation of better OLUME-2,ISSUE-1,201629

INTERNATIONAL JOURNAL OF ADVANCES IN PRODUCTION AND MECHANICAL ENGINEERING (IJAPME)Scissor or Toggle JackA toggle or Scissor jack is a device which liftsheavy equipment. The most common form is acar jack, floor jack or garage jack which liftsvehicles so that maintenance can be performed.Car jacks usually use toggle advantage to allow ahuman to lift a vehicle by manual force alone.More powerful jacks use hydraulic power toprovide more lift over greater distances.There is a one screw in the toggle jack which isrotating.There are two nuts which are fixed.There are four links connected to both nuts andeight pins to fix all links.There are two rings at both ends of the screw.There is a one platform which is connected to theupper two links for put load.Working of Toggle Jack The jack can be raised and lowered with ametal bar that is inserted into the jack. The operator turns the bar with his hands in aclockwise direction for makes it go up. When the screw lifts the load on the platformwhich placed above will also raise. The bar is turned until the jack is raised to thelevel needed. To lower the jack the bar is turned in theopposite direction.II. METHODOLOGYStartFailure Analysis and NeedLiterature SurveyIII. FAILURE ANALYSIS OF SCISSORJACKTo study the reliability and performance ofscissor jack, it is tested under various conditionsfor failure analysis. In this case we will get toknow the effectiveness & performance of scissorjack on field, when customer implements it forreplacing the tire. The failure analysis isconducted under following cases.Case I: Justification for failure analysis :This analysis is required to be conducted dueto its critical application under emergency, alsoit is essential due to following reasons:A. Impact of the problem Impact on customer:1. Affecting safety of customer.2. Dissatisfaction of customer Impact on Departmental goal:1. Quality indicators effected.2. Increase in warranty cost.Case II: Diagnosing the problem:In this case, the actual area where the jack isfailed is detected. Practical tests are conductedfor this analysis by physically replacing the jackand results are calibrated for getting the solutionby operating the jack for replacement of tire ofBolero. Following results are concluded byperforming this case:Failure I: Arm teeth wear:The scissor jack is failed due to wear of teethon both links at lower end. Due to this the jackgets toppled as shown in figure below. Due to theuse of jack over and over again, the teeth startsgetting wear and after certain time the jack getstoppled from actual position as shown below:Problem DefinitionFormulation of DesignSample Case Study 4-6210,VOLUME-2,ISSUE-1,201630

INTERNATIONAL JOURNAL OF ADVANCES IN PRODUCTION AND MECHANICAL ENGINEERING (IJAPME)Fig. Teeth Wear of Lower ArmFailure II: Screw Failure:This failure is caused after using the jack forcertain amount of time. Due to excessive use andhigh impact on screw, it starts getting wear. Dueto this the jack gets toppled from its actualposition as shown below:Fig. Failure of Jack HeadFig. Failure of Screw and Arm TeethFig. Toppled Scissor Jack due to Arm teethFailureFailure III: Jack head failure:After certain duration and use of jack the headof jack starts bending due to the fatigue loadacting continuously again & again over the headas shown in figure below. This defect occurs dueto improper design of shape and geometry ofexisting head design.IV. SAMPLE DESIGN CALCULATIONType of Vehicle Mahindra BoleroWeight of Vehicle 1615 kgAssuming 65-35 DistributionWeight on Front Axle 1050 kgWeight on Each Wheel of Front Axle 525 kgFor Safe Design we take maximum capacity ofjack 700kgSince while jack is used other three wheels are incontact with ground so assumption of 700 kg issafe.Ground Clearance of Vehicle 280 mmAccording tyre dimension, we take lift of jack as100 mmMaximum Height of Jack 355.4 mmMinimum height of jack 254 mmAssumption:Material for Link, Screw, Pin, Bracket isselected as Medium Carbon Steel (30C8)Since links are in tension-compression andbending mode, higher yield strength as well asless elongation is primary requirement.Medium Carbon Steel has good yield strength(Syt) as well as due to medium carbon content(0.30%) has good hardness and toughness.For Nut, Phosphor Bronze (Bearing Pressure 10 Mpa) is Selected. Since in case of wear withscrew, nut will fail and costly screw will besaved from OLUME-2,ISSUE-1,201631

INTERNATIONAL JOURNAL OF ADVANCES IN PRODUCTION AND MECHANICAL ENGINEERING (IJAPME)Phosphor Bronze is softer than Medium CarbonSteel (30C8)Length of link 200 mmWhen the jack is in bottom position, the link willbe inclined at an angle 39.42oMaximum Capacity of Jack is 700 kg,So that Load (W) 700 9.81 6867 N 7000 N(Approx.)Load (W) 7000 NBy Calculating Pull in the Screw, Total Forcedue to upper and lower link, Core Diameter,Outer Diameter, Mean Diameter, Helix Angle,Friction Angle, Effort Required to Rotate theScrew, Torque Required, Torsional Shear Stress,Maximum Principle Stress and Maximum ShearStress etc.following results are obtained.Fig. Jack Is In Top Most PositionL1 216 mmAnd Similarly, When Jack is in lowest positionL2 339 mmA. Design of Screw:-Material Selected for Screw Medium CarbonSteel (30C8)Syt 400 MPaF.O.S. 4Permissible Tensile Stress ( t) 100 MPaPermissible Shear Stress (Ssy) 0.5(Syt) 50 MPa Our Calculated Value, 30.84 50 MPa is Safe. t is Safe. t 42.34 100 MPa max is Safe. max 58.57 100 MPa max 37.40 50 MPa max is Safe.B. Design of NutFig. Geometry of ScrewMaximum load on screw will occurs when thejack is at bottom most position. The load in thescrew will be tensile. Fig.Geometry of NutThere are two nuts in the assembly of Scissor orToggle Jack.Nut is a stationary part havinginternal thread inside which is used to rotate thescrew by meshing with external thread of theScrew.Nut is also used to hold the lifting arm orlinks at there both end.By calculating Number of threads inside the nut,Height of nut etc. following results is obtained.No. of Internal Thread 6Height of Nut 36 mmFig. Diagram of Top Corner LinkC. Design of -2,ISSUE-1,201632

INTERNATIONAL JOURNAL OF ADVANCES IN PRODUCTION AND MECHANICAL ENGINEERING (IJAPME)Pins or Rivets are the most important parts inthe assembly of Scissor jack or Toggle Jackwhich is used to make the Scissor Jack inassembled form throughout its operation andworking. There are total six pins are used in theassembly of screw jack, out of that two pins areused to assemble load carrier member with upperlifting arm or links, Two pins are used toassemble base and lower lifting arm of the of thescissor jack and another two pins are used toassemble Nut and both lifting arms or links.These pins are in Double Shear,So that,We Select Diameter of Pin 8 mmLength of Pin 40 mmDiameter of Pin Head (dph) 1.5 dp 1.5 8 12 mmThickness of Pin Head (tph) 2 mmSplit Pins are used to keep the pins in position.D. Design of LinkFig. Geometry of LinkLinks or Lifting Arms are the main component inthe assembly of Scissor or Toggle Jack. We cansay that links are the heart of Scissor Jack. Thereare set of four links in whole assembly out ofwhich two links are at upper portion and anothertwo links are at lower portion. The tooth profileon the one end of the links is used as a force andmotion transmitting element like gear tooth. Thewhole operation of Scissor Jack i.e. movement ofScissor or Toggle Jack is basically depends onmeshing of these tooth profile. If tooth gets weardue to misalignment of the jack at the time ofoperation then is affect on movement of theassembly of Scissor Jack.Load on each link F/2 sec F/2 sec 39.2 2.7670 KNLet b1 width of link and t1 thickness of linkAssuming, b1 3t1Area of cross-section of link,A 3 ݐ 1²For buckling of links in the vertical plane, theends are considered hinged. Therefore by usingRankine - Gordon formula.By calculating various values like Moment ofInertia, Least Radius of Gyration, Both criticalloads etc. following results are obtained. With F.O.S. 5For design load, ܲܿ ݎ F.O.S (F/2) 3ܲܿ ݎ 13.832 KNNow, For Critical LoadPcr 17.28 KNHere Critical Load (17.28 KN) Design Load(13.832 KN) Design of Link is Safe.V. CONCLUSIONThe result shows that alloy steel for screw andphosphorus bronze for nut is the best suitablecombination for pair. The value shows that ifthere is a combination of MS – MS, it inducesless magnitude of bearing stress in nut.Based on the input parameter & result obtainfrom the design, As the helix angle increases theefficiency increases up to certain limit afterwhich it decreases, the critical load decreases,the no of threads decreases, turning momentreduces, outer diameter decreases, core diameterdecreases, the pitch does not change it remainsconstant up to certain value & then it reduces.REFERENCES[1] Prof. Nitinchandra R. Patel et.al. (2013),“Design Of Toggle Jack �� International Journal ofInnovative Research in Science, Engineeringand Technology Vol. 2, Issue 5, (2013).[2] TianHongyu and Zhang Ziyi (2011),“Design and Simulation Based on Pro/E for aHydraulic LiftPlatform in Scissors Type”,International Workshop on Automobile,Power and Energy Engineering, LUME-2,ISSUE-1,201633