os-06 introduction of optimization tools maruti

8/12/2019 OS-06 Introduction of Optimization Tools Maruti

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Simulate to Innovate 1

Introduction of Optimization Tools in BIW Design

Himanshu ShekharDeputy Manager,

Maruti Suzuki India Ltd,Palam Gurgaon Road,

Gurgaon.

Vimal KumarDeputy Manager,

Maruti Suzuki India Ltd ,Palam Gurgaon Road,

Gurgaon.

Rajdeep KhuranaSectional Manager,

Maruti Suzuki India Ltd, Palam Gurgaon Road,

Gurgaon.

ABBREVIATIONS

OptiStruct-FEA CAE Analysis RunOptiStruct Optimization RunSBA Seat Belt AnchorageBIW Body in WhiteMDB Movable Deformable Barrier

Abstract

While the Indian automotive market is expanding at a very quick pace, intense competition has been instrumental for the OEMs to bringbetter and cheaper products from its predecessors as well as competition.

The major challenge faced by OEMs today is to provide lighter car body structure with better fuel efficiency without compromising onthe Ride and Handling performance.

BIW optimization is a mathematical approach that optimizes material layout within a given design space, for a given set of loads and

boundary conditions such that the resulting layout meets the prescribed set of performance targets. This enhances the designperformance while reducing the overall cost and weight factors.

This paper presents the application of a BIW Optimization tool OptiStruct in order to optimize the existing Design of a Low WeightCompact Car Body Structure and details of optimized design resulting in significant weight as well as cost reduction. One of the keychallenges has been to maintain the body stiffness and torsional rigidity while reducing the weight.

Introduction

Structural optimization is a modern computational design approach that has found widespread use,

particularly in the early design phase of products. Several commercial finite element programs, such as

OptiStruct, now provide user-friendly interfaces to these powerful algorithms so that optimization may now

be incorporated into early design stages.

An optimization problem may be formulated as:

Objective : Minimize Mass of the Structure

Constraint : Structure compliance

Optimization is a comprehensive solution aimed at guiding and simplifying the design of structures.

Optimization is the best strategy in the hand of design engineers to choose the right selection of material,


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shape, orientations. Unless an optimized design is followed, the results often will be an overdesigned part

with redundant material that adds cost and weight.

Additionally the cost of an automotive component stems not just from the material itself but also from R&D,

manufacturing and assembly of the components, which particularly for smaller productions may consume a

larger portion of the final cost. CAE-based design helps easily identify opportunities for part consolidation,

which is one of the tactical advantages of optimization with respect to traditional systems.

Objective

The objective of the study is to apply optimization tool to determine the best layout of the material that

composes the structure of the car. Once a design space is defined using modeling software, a mesh body isconstructed for finite element analysis and optimization. Existing structures such as the roll bars, suspensioncomponents and the engine are added to the model which is subjected to the loads that are to beconsidered as part of the design.

This study focuses on computing the best material distribution under multiple and combined load conditions.A unique feature of this work is to effectively find ways to optimize the existing structure and thus achieveweight reduction. Altair OptiStruct is used at the concept level of the design process to arrive at a designproposal that is then further modified for performance and manufacturability. Thus reduces the designdevelopment time and overall cost while improving design performance.

In some cases, proposals from an optimization may be optimal in design but it may be expensive. Thesechallenges can be resolved through the use of manufacturing constraints in the optimization problemformulation. Using manufacturing constraints, the optimization tool will yield engineering designs that wouldsatisfy practical manufacturing requirements also.

Different Optimization Techniques

Different optimization techniques that are adopted for optimization can be classified into three maincategories as follows:

1. Load Path Optimization (Topology)

Topology can be defined as a tool for optimal Load path identification i.e. material distribution should be onlyon places where it is required and hence elimination of surplus material. A bulk mass automobile structurecan be converted into an optimized structure by placing the components in right places.

2. Bead Placement Optimization (Topography)

Topography can be defined as optimization of bead patterns reinforcement to satisfy the input conditionslike rigidity, panel deformation or natural frequency response of the part. For example natural frequency ofthe given part can be increased by changing the bead pattern of the part.

3. Gauge (Thickness) Optimization

Thickness plays a very important role in optimizing the BIW weight. Region specific thickness requirementscan be achieved by this tool as it gives output of thickness variations in given thickness fringe. For a givensheet this tool can define the thickness variation as shown in the Fig 1 below. This output helps designer todefine the cut line for different thickness sheet boundaries.


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Fig 1: Gauge (Thickness) Optimization Example

Methodology

The methodology for carrying out optimization can be divided into following broad stages:

Preprocessing Stage

a) Meshing

For model making first step is to convert the 3D CAD data into exact mesh model and mesh quality isensured during this activity.

b) Assigning material & property to components

Material properties like Poissons ratio, density, Young modulus and thickness property are assigned toeach and every component of the model so as to represent the actual vehicle conditions.

c) Making Connections

A host of connectors available in the software are used to simulate Weld spots / Bolts / CO2welds / Boltconnections to replicate actual vehicle conditions.

d) Assigning constraints / boundary conditions

Loads are defined in terms of their numerical value, direction and assigned to the areas as per the

regulation requirements. The constraint boundary conditions are provided on case basis.


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Processing Stage

a) Running CAE solver "OptiStruct - FEA" (Target Setting)

After the model is prepared with material properties and applicable load & constraint functions, analysis iscarried out for model response for stress and displacement values. These values are taken as reference foroptimization. Thus, the OptiStruct-FEA CAE solver is used to identify performance targets.

b) Solid Model Preparation (Topology)

The whole model is converted into solid blocks with tetrahedral meshing for solid elements . Solid blocks areused for Load path identification i.e. Topology optimization

c) Assigning objectives

Optimization of mass, compliance, rigidity can be targeted as objective problem while maintaining the sameloading conditions and constraint parameters of original model .

d) Running optimization solver "OptiStruct"

Optimization solver "OptiStruct" is run to achieve the desired objectives with the given load & constraintconditions while maintaining target performance.

3. Result Interpretation

a) Result interpretation.

The OptiStruct output is post-processed. Based on OptiStruct output, the 3D CAD data is then modified.

b) Verification of the new data.

The modified 3D CAD data thus obtained is subjected again for performance validation, maintainingidentified loads & constraints. This is an iterative process. The various optimization techniques i.e. Topology

/ Topography / Size optimization follow the above methodology in general. The differences are there insetting up of constraints, objectives, data type (Solid/Shell) on case basis.

Case Studies Using Optistruct

OptiStruct tool is applied on current production Model to find scope for achieving further optimizedstructure. Study was carried out in two major BIW areas with different OptiStruct tools. These areas are:

a) C Pillar

b) B Pillar

Total BIW model is converted into finite element mesh and analysis is carried out.


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Case Study 1: C Pillar Optimization

(By Topology)

C Pillar is the rear most BIW Area of a car as shown in Fig 2. It is subjected to severe Suspension and bodytwist loads. In addition to this, Seat Belt Anchorage (SBA) Loads comes to this area while deceleration.

Fig 2: Structure of Model

For C Pillar optimizations following loads are taken into consideration

1. BIW Twist Load.2. RR Seat Belt Anchorage as per ECE R 14.3. RR Vertical Durability Test for RR Suspension.

With the above mentioned load cases RADIOSS CAE reference values are obtained. These values are

taken as performance parameter benchmark for optimization iterations.

Since Topology is a material layout Optimization technique, solid 3D CAD data is used for the same. Fig 3shows the structure of C pillar for which Solid 3D Data is made.


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Fig 3: Structure of C Pillar

Preparation Of Solid Model With Boundary Conditions

Fig 4 shows that the entire C Pillar area is converted to solid block and attached with BIW by the help ofrigid connectors to make the whole body act as one system.

Fig 4: Material block of C Pillar


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After application of loads, OptiStruct generates the material density distribution. That means with zerodensity elements no load is absorbed or transmitted so those element regions can be eliminated as these

are surplus material region. Also, a high density region highlights essential material requirement for the setloads and constraints.

A typical material layout obtained is as follows.

Fig 5: Topological material layout of C Pillar

The following inferences can be drawn as per Fig 5:

1. Structure indicates that Suspension load carrying member should be merged gradually in Back DoorArea.

2. QTR Upper Area & RR Door Ring has very high element density.

Based on this inference after several iterations consisting of topology as well as Gauze optimization,Derived data structure (as compare to Current data Structure as per Fig6) is explained in Fig 7.


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Fig 6: Current C Pillar Structure

Fig 7: Proposed C Pillar


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This area is subjected to following major loads.

1. BIW Twist load.2. Front Seat Belt Anchorage as per ECE R 14.3. Side MDB crash as per AIS 099.

Solid block is created in B Pillar Area. Load conditions as identified are applied and topology optimizationon solid body is carried out.

Fig 9: B Pillar Topology Results

The following inferences can be drawn from the topology result as shown in Fig 9:

1. The material layout suggested by software shows box kind of structure, connecting from Roof Rail areato Side Sill structure.

2. More material tends towards inner & outer side of structure.3. More material density is shown in upper area compared to lower area.4. There is possibility of material reduction in lower B Pillar region.

Results from topology optimization can be interpreted as Requirement of shell structure in B Pillar area.Thus shell structure was created & Gauge Optimization tool was used to further optimize the shell structure.


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Simulate to Innovate

Fig

Fig 10 illustrates that local thicknHence proposal is generated with 1

Similarly Panel, RR Pillar Inner opti

Fi

0: Reinf Hinge pillar thickness optimization

ess requirements in Reinf. Hinge Pillar varies.4 mm in upper region & 1.2mm in lower region.

imization is done with 1mm & 0.8 mm thickness

11: Panel, Ctr Pillar Inner thickness Optimization

11

from 1.2mm to 1.6mm.

s shown in Fig 11 .


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Case Study Conclusion:

With the proposed Design total weight saving of 1380 gm per vehicle (RH & LH) was achieved in B PillarArea.

Conclusion

The optimization tool OptiStruct is quite helpful in optimizing the design space. The case studiesconverged to a total weight saving of 2.33 Kg per vehicle.

With the above reference it is quite evident that OptiStruct tool is very much relevant for early stageDesigner conceptualization application. It is helpful in placing the components tactfully while doing designconsiderations, also reduces the dependence on the designer judgment. These case studies include therelevancy of Topology for Optimal Load Path, which means that extra material can be avoided without

compromising the performance of the vehicle.

Topography can be used for bead pattern generation without adding any extra component or weight. Thisalso optimizes the parts compliance performance.

Gauze (Size) optimization is instrumental in deciding final sheet thickness.

ACKNOWLEDGMENT

The authors would like to sincerely thank the team of their seniors Mr. DN Dave, Mr. Alok Jaitley and Mr.Parveen Kr Sharma for their continuous support and encouragement throughout the development of thisproject.

Also authors would like to extend their thanks to CAE Team for understanding the load case input and M/sAltair for their support in CAE Model Making without which the analysis was not possible.

REFERENCES

1. Seat Belt Anchorage as per Seat Belt Anchorage regulation (ECE R 14)

2. Side MDB crash as per AIS 099Approval of Vehicles With Regards To the Protection of the Occupants In The Event Of a Lateral Collision

3. http://www.altairhyperworks.com/tutorials

4. http://altairenlighten.com/knowledge-center/

os-06 introduction of optimization tools maruti

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