O L . 3, Issu E 2, May - O 2013 ISSN : 2249-5762 (Online) ISSN : 2249 .

ISSN : 2249-5762 (Online) ISSN : 2249-5770 (Print)IJRMET Vol. 3, Issue 2, May - Oct 2013Design and Tolerance Stack up Analysisof Car Side Door Latch11,3,4Chethan H, 2Naveen Udupa, 3Ramakrishna Hegde, 4Girish kumar.RDept. of Mechanical Engineering, R.V.College of Engineering, Bangalore, Karnataka India2IFB Automotive Private Ltd. Bangalore, Karnataka IndiaAbstractSide door latch protects the vehicle occupants from being ejectedthrough the doors which have known to be opened during motionor accidents. The intent of this work was to redesign an existingpassenger car side door latch to improve the manufacturabilityusing Design for Manufacture (DFM) guidelines and tear downanalysis. Tolerance stack up analysis is used to find the clearanceor interference between two features on a part and their assemblyvariation. The check sheet clearly indicated that there was nointerference fit present between any features of assembled partswhich naturally simplifies the assembly process. The assemblyvariation for inside release of the latch was found to be 1.5mmcompared to that of outside release of the latch which wasdetermined to be 1mm. The analysis opens opportunities forreducing the assembly time significantly as the fastening processis eliminated.tolerance is known from the design requirements, whereas theavailable assembly tolerance must be distributed or allocatedamong the components in some rational way.KeywordsSide Door Latch (SDL), DFM & A, Tear Down Analysis, ToleranceStack Up AnalysisI. IntroductionA car door latch refers to the mechanical device used to align thedoor in a closed position relative to the vehicle body framework.The major role of a latch is to perform lock/unlock and latch/unlatch functions. A latch unit consists of several components.The number of components varies according to the complexityand the mechanical/electromechanical features specified by thecustomer [1].Generally the side door latches of a car contain the followingcomponents:1. Striker 2.Catch 3.Pawl 4.Detent lever 5.Inside release lever6.Outside operating lever 7.Intermittent lever 8.Inside lockingleverMaintaining government safety standards and satisfying thedifferent Original Equipment Manufacturer (OEM) designspecifications in a cost-effective, timely manner is a major challengefor a automobile latch manufacturer. Latch manufacturers haveto meet the standards set by governments. At the same time eachmanufacture has its own testing requirements.Tolerance analysis is used to estimate the effects of manufacturingvariation on the finished products. Either design tolerances ormanufacturing process data may be used to define the any variation.Conventional methods used for tolerance stack up analysis areworst-case statistical analysis [2].Manual construction of tolerance check sheet is a commonly usedtool for tolerance analysis. Tolerance check list is used in theindustry by draftsmen and designers to calculate the maximumor minimum distances (clearance or interference) between twofeatures on a part or assembly.The tolerance analysis is different from tolerance allocation.In tolerance analysis the component tolerances are known andthe resulting assembly variation is calculated by summing thecomponent tolerances. In tolerance allocation, the assembly192Fig. 1(a): Tolerance AnalysisFig. 1(b): Tolerance AllocationII. Concept DevelopmentThe concept development consists of the following steps,1. Tear down analysis2. Component analysis3. CAD models of the SDL4. DFM & A of SDLInternational Journal of Research in Mechanical Engineering & Technologyw w w. i j r m e t. c o m

IJRMET Vol. 3, Issue 2, May - Oct 2013ISSN : 2249-5762 (Online) ISSN : 2249-5770 (Print)A. Tear Down and Component AnalysisTear-down analysis and component analysis are the pre-stages ofthe concept development which helps to understand the importanceof the functional parts, interaction between the parts, functionalfeatures, etc.,Feature comparison analysis of existing SDL with new SDL hasbeen carried out for the design verification process.B. Cad Models of the SDLThe SDL was modelled using CATIA V5 R20 software. Themodels were created from the customer requirements and theexisting side door and back door latch drawings. It provided thecomplete data of the SDL and other profiles. All other dimensionswere measured by Vernier calliper.C. DFM & A of SDLThe design for manufacturability and assembly guidelines weredirectly and indirectly applied to redesign the SDL. The followingobjectives were established for the redesign of SDL,1. Fastening process was eliminated.2. Stopper feature on the top plate was eliminated.3. Double side riveting process was designed.4. Functional improvement was achieved.Fig. 2: Comparison Analysis of Existing SDL with New SDLIII. Concept SelectionThe SDL has been selected based on the five important parametersthat are listed below,1. Functionality 2.Manufacturability 3.Assembly 4.Package5.CostA. FunctionalityThe functionality was captured from the existing SDL and it hasbeen implemented in the new SDL. All the concepts have beenworked on without any functional loss.B. ManufacturabilityThe requirements for load conditions vary from one carmanufacturer to another. So the new SDL has been designed witha special attention given on the load improvement.Fig. 3: Comparison Analysis for Existing SDL With New SDLC. AssemblyThe assembly process was improved by eliminating the housingpart and fastening process.D. PackageThe package size is maintained the same as the existing SDL, andsome of the non-functional profiles has been modified. Hence, thenew SDL has been packaged in the existing door module.E. CostThe cost of the new SDL will be reduced, as the fastening assemblyprocess is eliminated. Bending feature in the top plate has beeneliminated along with three screws and a housing part.IV. Design VerificationIn general terms, Verification is a quality control process that isused to evaluate the product that complies with the specificationsand conditions imposed at the start of a development phase.Design verification is a process to examine design outputs andto use objective evidence to confirm that output meets inputrequirements. Verification activities are conducted at all the stagesand levels of product design. The verification can be determinedby inspection, demonstration, test and analysis [3].w w w. i j r m e t. c o mFig. 4: Existing SDLInternational Journal of Research in Mechanical Engineering & Technology193

ISSN : 2249-5762 (Online) ISSN : 2249-5770 (Print)IJRMET Vol. 3, Issue 2, May - Oct 2013V. Tolerance Stack Up AnalysisA. Tolerance Check SheetManual construction of tolerance check sheet is a popular techniquefor analyzing tolerance accumulation in parts.Fig. 5: Modified SDLFor SDL assembly, tolerance check sheets were developed forall parts listed below.1. Base plate vs. Catch / Pawl rivet2. Catch vs. Catch rivet3. Pawl vs. Pawl rivet4. Top plate vs. Catch / Pawl rivet5. Top plate vs. Inside release lever rivet6. Inside release lever vs. Inside release lever rivet7. Outside operating lever vs. Outside release lever rivet8. Top plate vs. Outside release lever rivet9. Outside operating lever vs. Outside operating lever rivet10. ALH release lever vs. Outside operating lever rivetThe manual construction of tolerance check list only deals withthe worst-case analysis and it considers variation in only onedirection at a time, i.e. length or diameter. In Table 1 the lengthwas considered for the first direction. The catch and catch rivet isindicated by A and B respectively. The basic dimensions and itstolerances as per drawing are added in the check list. The valuesof all the clearance fits are calculated and the same is tabulated.(Table 1)Table 1: Tolerance Stack Up Check Sheet- Catch vs. Catch Rivet1. CalculationsMinimum condition: Bmin - Amax 5.6 - 5.7 0.1 Clearance194International Journal of Research in Mechanical Engineering & Technologyw w w. i j r m e t. c o m

IJRMET Vol. 3, Issue 2, May - Oct 2013ISSN : 2249-5762 (Online) ISSN : 2249-5770 (Print)Nominal condition: B – A 5.6 – 5.4 0.2 ClearanceMaximum condition: Bmax - Amin 5.75 – 5.3 0.45 ClearanceFor the second direction, diameter was considered. Here the catchand catch rivet diameter is identified by C and D respectively.Minimum condition: Cmin – Dmax 7–6.9 0.1 ClearanceNominal condition: C – D 7 – 6.9 0.1 ClearanceMaximum condition: Cmax – Dmin 7.15 – 6.8 0.25 ClearanceFig. 7: Inner Release Variation for Maximum Condition(iii). Minimum Assembly VariationThe contributing dimensions for minimum variation condition wasidentified and applied to the model to find the variations for innerrelease of the latch. Fig. 8 shows the minimum variation.B. Tolerance AnalysisTolerance analysis is a method of predicting and analysingassembly variation due to tolerance of individual components andassembly operations. Tolerance analysis is carried out when thetolerances of individual parts are known and the designer intendsto find out or allocate the dimensions for assembly.This involves: Gathering data on the individual component variations. Creating an assembly model to identify which dimensionscontribute to the final assembly dimensions. Applying the manufactured component variations to themodel to predict the variations in assembly dimension.1. Assembly Variation for Inner Release of the Side DoorLatch(i). Nominal Assembly VariationThe Free, Operating and Full length for inside release of the latchis shown in fig. 6Fig. 8: Inner Release Variation for Minimum Condition2. Assembly Variation for Outer Release of the Side DoorLatch(i). Nominal VariationThe Free, Operating and Full length for outer release of the latchis showed in fig. 9.Fig. 6: Inner Release Basic Dimensions for NominalConditions(ii). Maximum Assembly VariationThe contributing dimensions for maximum variation conditionwas identified and applied to the model to find the variations forinner release of the latch. Fig. 6 shows the maximum variation.Fig. 9: Outer Release Basic Dimensions for Nominal Conditionsw w w. i j r m e t. c o mInternational Journal of Research in Mechanical Engineering & Technology195