Authors – Krishnappa Umesh3, V.Omkar Gulavani 1, E.Loganathan 2,

Co-Authors – Nirajkumar Sahay, 4.

1 Lead Design Engineer, Hxxxxx Infoserve Ltd., Bangalore.email: v.omkargulavani@hxxxxx.com2 Team Leader, Hxxxxx Infoserve Ltd., Bangalore.email: e.loganathan@hxxxxx.com3 Global Delivery Head & Head-Auto, Hxxxxx Infoserve Ltd., Bangalore.email: krishnappaumesh@hxxxxx.com4 Project Manager, Hxxxxx Infoserve Ltd., Bangalore.email: nirajkumarsahay@hxxxxx.com

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Concept development of Powertrain components of an ongoing Vehicle Development Program by using Optimization, Design for Manufacturability

and CAE validation Tools – The DFSS (Design for Six Sigma) way.

For Contact: K.UmeshDelivery Head-ATV

Hxxxxx Infoserver Ltd.,# 10 , 3 rd main, Ashwini Layout , EjipuraKoramangala, Bangalore – 560047, India.Email : krishnappaumesh @hxxxxx.com

ABSTRACT

The traditional approach for designing an automotive component or an automobile is to design for performance, design for aesthetics & ergonomics and to design for adequate durability and reliability, so that the performance requirements can be met continuously over the life time of the vehicle.

During the initial design phases, the approach has been to build the factor of safety more than required in certain component or component areas because of the positive and negative interaction effects of casual variables. Thus it can be said that the design is not wholly “optimum”.

This lack of ‘optimum design’ has always given rise to opportunity for further optimization and is popularly known as the value analysis (VA)/value Engineering (VE) approach. The approach has its advantages and many companies have dedicated resources for VA/VE. However on the flip side, it is ‘reactive approach’ and thus can be avoided. In the parlance of six sigma philosophy, it is known as ‘DMAIC (Design, measure, analyze, improve and control) approach’. DMAIC approach solves a problem which has been created.

A more proactive approach known as the DFSS (Design for Six Sigma), which prevents a problem from generating and by using this philosophy it is possible to build ‘value’ and achieve ‘optimization’ in the design phase itself.

The modern day software tools offer great opportunity to use this philosophy in terms of optimization software, DFM software and validation software of CAE for an optimum concept design. Automobile field is currently one of most challenging fields with tougher competition between international automotive players in offering light weight, fuel efficient & low emission vehicles of better reliability and durability. In order to stay alive in this competition, it becomes important for Auto players to launch new vehicles in comparatively shorter span of time with less number of prototypes. So new CAE tools and value engineering methods have to be used in the very early stage of development to achieve these goals.

The Topology Optimization is an appropriate method that changes the density and stiffness distributions in an iterative process to achieve a homogeneous stress distribution which defines the concept design of the component in Virtual Vehicle Development Process. The Classical Optimization process considers either minimization of weight or maximization of frequency approach. This paper addresses three aspects of opti-mization, the Strength aspect and Frequency aspect along with the significant weight reduction during the design. The paper also discusses about the application of the DFM (Design for Manufacturability) concepts to transfer the design proposal in a real manufacturable component. The industrial application of this opti-mization method using Optistruct is demonstrated in this paper for real time vehicle development pro-gramme of a top vehicle manufacturer in the world. The paper ends with a review of future trends in struc-tural optimization applications and their implications.

Keywords: Optimization, DFSS, DFM, Optistruct, Topology

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Concept development of Powertrain components of an ongoing Vehicle Development Program by using Optimization, Design for manufacturability and CAE validation

Tools – The DFSS (Design for Six Sigma) way

1.0 Introduction of the Project:

1.1 What is Vehicle Development Program (VDP)

A ‘ Vehicle Development Program – VDP” is like any new ‘Product Creation Process’ which starts with an idea being generated as a result of customer Feedback and Market Research to find out the future requirements of the Customers; goes through various phases of Planning ,Execution and Delivery and finally again ends with Customer feedback.

Hence it is a Customer to Customer Process Management Program.

A typical ‘VDP’ is shown below with various phases and milestones.

1.2 Involvement of TVS-Hxxxxx in Vehicle Development Program:

As described in the abstract and as can be seen from the above VDP, it is obvious that the ‘Concept

Phase’ is a very critical phase and it is possible to build “Value” pro-actively by following proper Quality System and Software tools.

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Fig 1- The flowchart comparing the approaches of DFSS Vs. DMAIC

DFSS

DMAIC

It can be seen form the shaded area in the VDP that the scope of work for Hxxxxx is:

- Component Concept Generation

- Component Concept Optimization for given road loads and other loads

- Analysis and Verification of the Concept using CAE

- Verification of concept for DFM.

- Re-optimization of concept if possible

- And prototype batch1

- Working for components for around 10 VDP across Europe, NA and Asia-Pacific.

1.3 What is the Approach Followed for Project (DFSS Way)

For any breakthrough project, it is important that a proper Process Discipline is followed and being a

Process Oriented Organization, “Six Sigma” concepts are used.

Six Sigma Methodology prescribed two approaches which are mainly:-

a. DMAIC approach: - Reactive approach once the problem has occurred. b. DFSS approach : - Pro-active approach to prevent a problem and optimum results.

In a new Product creation Process like ‘VDP’ it is better to use DFSS to build value initially itself. It helps to reduce costs, improve productivity and cut down cycle times drastically. The flowchart of the DFSS is shown in Comparision to DMAIC below with steps of DFSS. The complete project explanation will be done using the following steps of DFSS:

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2.0 Define Phase (Project Background, Project Definition):

2.1 Background of the Project: The client of TVS-Hxxxxx is “Technology Specialist” in the Noise and Vibration Control Area in the Powertrain & Chassis (PT&C) domain of the automotive. They are involved in around 10 different Vehicle Development Programs across North America, Europe and Asia –Pacific at this point of time. Due to cost and speed considerations, they have been outsourcing the Concept Development, Verification and Prototype batch1 work to the reputed Engineering Solution Providers.

After a thorough supplier evaluation process, they have selected TVS-Hxxxxx Infoserve Ltd. as their long term partner for concept development of PT&C components.

2.2 Definition of the Project: Shown below is the typical chassis for a High end car.

Fig 2- Location of Engine mounting brackets on chassis

The application requirement of an Engine mountings are as follows:-

- To support the engine.

- To mount the engine on chassis.

- To damp the induced engine vibrations.

For meeting the above application requirements, it is important that the following concept generation / design criteria and ‘Critical Success factors’ (i.e. Big ‘Y’s’) are met.

a. Critical frequency: To avoid resonance, it is important that the critical frequency should not lie within ± 10 % of excitation frequency induced due to engine, road loads and other loads.

b. Weight is another Critical Success Factor as it influences the fuel efficiency, tyre wear out. c. Strength: Mounting brackets have to withstand minimum 15 years of service life. During this period those should not undergo permanent deformation which will affect functioning of mating part or buckle or crack.

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Fig 1 Comparison of DFSS and DMAIC

3. Identify Phase (Identification of CTQ’s, Resources, and Process Flow Chart):

3.1 Identification of Critical Success Factors (Big ‘Y’s’) and correlation to CTQ’s – Critical To Quality (i.e. Big ‘Y” flowdown to ‘X’)

Sl.No Critical Success Factors (Big 'Y' ) CTQ's ( Big ' X' )

a Resonance, Noise and Vibrations First mode eigen frequency should be>600 Hz

b Weight Reduction target = 50 %

c Strength Factor of Safety (FOS) >= 1.5

d Ease for manufacturing Use of Design for Manufacturing (DFM) concepts

3.2 Identification of Resources:

3.2.1 Identification of Team:

Cross functional team is formed for carrying out this project. This cross functional team consists of two Finite element analysis engineers, 2 designers and Project manager who has vast amount of industrial experience in foundry.

3.2.2 Identification of Softwares:

Software Application

Hypermesh FE Modeling & Pre-processing

Optistruct Topology Optimization & Linear Analysis

ANSYS Modal Analysis & Service load non-linear Analysis

3.2.3 Identification for Customer Communication:

- Single point email contact of Project Manager with client

- Weekly teleconference of the TVS-Hxxxxx team with the Client.

- Circulation of Dashboards for hours of billing.

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3.3 Process Flow: The overall Process flow is as follows.

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Define boundary conditions, material properties and load for Optimization FE model

Specify optimized and non-optimized regions

Design proposal identifies feasible design

Design proposal hintsFeasible design

Design proposal not to be converted

Generation of CAD model based on Optimized iges and DFM Concepts

FE calculation of Final CAD model

Is the design satisfies the strength & frequency constraints

Preparation of final Prototype & Physical Testing

Manufacturing of brackets & shipment

Define objective function and constraint (Eigen frequency and compliance) for the topological optimization

Perform Topology Optimization

Creation of iges file

Modification of package space

Yes

Review reference assembly data in CAD format

Preparation of package model based on the assembly data and other functional features

Build FE Model from the package model using HyperMesh maintaining the Quality Parameters.

No

4. Design Phase (Material Selection, Topology Optimization):

The design phase will be explained by using one specific example in the following manner:

- Selection of the material.

- FE Modeling Approach

- Definition of the Optimization problem

- Postprocessing for the Optimization results.

4.1 Selection of the material:

The aluminium alloy (AlSi9Cu3) is selected for the brackets based on following advantages:-

- Better castability, availability.

- High Strength to Weight ratio and low shrinkage

Material properties for AlSi9Cu3 are tabulated below,

Material property ValueYoung’s Modulus 71*103 MPaPoisson’s ratio 0.34Density 2750 kg/m3

Tensile strength 275 MPaYield strength 195 MPa% Elongation 1.5%

4.2 FE Model Approach:

The FE model of the package space for the engine mounting bracket is prepared based on the assembly with other brackets, fasteners. Package space is the maximum available space for the design. Higher order tetra element is used. Weight of the package space is 1.85 kg.

4.3 Definition of optimization problem:

4.3.1 Definition of Design and Non-Design Space: The topology optimization redistributes the material based on the problem definition. So it becomes very important to define the Design and Non-Design Space. The design of the areas for the assembly purpose, mating surfaces, fastening joints can not be altered so those regions become the non-optimized region. In figure the Yellow colour indicates the non-optimized region whereas Blue indicates the region to be optimized. 4.3.2 Loads and Boundary Conditions:

• For optimization the strength as well as eigen frequency considerations are taken into the account.• The unit load of 1KN is applied in +X, +Y, +Z IN Global Co-ordinate system.• Idealization of the components attached to the brackets is represented using lumped mass placed at

its CG location (mass = 0.303 kg) and connections to the bracket are represented by rigid elements. 8

Fig 3- Package Space

4.3.3 Optimization Problem Definition:

The optimization problem is defined as follows,

Global objective function: Minimization of compliance for six unit load cases characterizing acceleration loads, road loads and vehicle turning around corner in both directions.

Constraints: 1) Lower bound for the first mode of the natural frequency > 600 Hz2) Upper bound on the volume fraction>0.3

4.4 Post processing for Optimization results: The results from the optimization analysis of great importance are element densities. The element density of 0 indicates the non-required material whereas 1 indicates the regions to be retained. The design guideline given by the Optistruct is shown in following figure.

5. Optimization Phase (Selection of Concept, DFM Evaluation Matrix):

5.1 DFM Evaluation Matrix:

Various alternatives of housings were evaluated for DFM based on uniform and adequate wall thickness throughout, Complexity of the housing for tooling, ease of material flow, minimum number of side cores, ease of ejection from die, possibility of casting defects, suitability to be held in m/c fixture, accessibility for m/c tool to perform metal removal, process and material cost.

Based on these DFM criteria, overall DFM rating was arrived out for alternative housing configurations.

5.2 Selection of the Optimum Concept:Depending on the DFM aspects and topology guidelines the 4 different concepts are developed. Optimization will help in selection the optimum concept by using DFM evaluation matrix.

Fig 5- Different views of the Final Concept selected based on DFM ratings and optimization

The summary of different concepts, their evaluation criteria and the reason of the rejection is summarized in the following table

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Fig 4- Optimized iges Model from optimization

6. Verification Phase (FE Computation):

The Optimized concept is verified by two ways,

- FE Computation for frequency and strength aspect.

6.1 FE Computation:

6.1.1 FE modeling Approach and Boundary Conditions:

For FE modeling and Pre-processing Hypermesh is used.

Boundary conditions:1. In absence of mating component, threaded connection nodes are completely constrained in all three degrees of freedom to simulate bolting condition.2. Housing bottom surfaces is constrained in three degrees of freedom

6.1.2 Results FE Analysis:

ANSYS and Optistruct programs are used for FE calculations. 6.1.2.1 Results of the Modal Analysis:

Quality Parame-ter

Required Actual

Element size<4mm(Global element size)

100 % elements are <4mm

min. angle >20 >20.04max. angle <120 <119.9Collapse >0.2 >0.21

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Fig 6- Boundary condition plot

It can be seen that the first eigen frequency is 648 Hz which is well above the target 600 Hz. Thus the optimized model satisfies the eigenfrequency constraint.

6.1.2.2 Results of the Strength Analysis:

Unit loads and results:

In order to study the sensibility of the housing referring to the load directions each calculation starts with the calculation of the unit loads. A unit load of 1 KN is applied at the load point (Centre of the housing ring).The maximum principle stress at the surface of the part is analyzed for each loadcase.The ultimate load Fmax is calculated for each load direction calculated as the ratio of ultimate strength divided by maximum principal stress.The ultimate load is compared with the maximum measured and / or calculated forces, especially under misuse conditions. The calculated force has to be 1.5 times higher than the measured / calculated values for each load direction.

Service loads / results

For the evaluation of the durability the maximum measured / calculated forces from the load history (no misuse) have to be taken into account. The maximum von Mises stress at the surface of the part is analyzed for each loadcase. The maximum stress should not exceed the stress of the yield point of the material. These load cases represent a conservative estimation of the potential for durability of the part. The final configuration of housing is evaluated for six unit load conditions (+ FX, +FY and +FZ) and also for service load condition and it is found to be safe.

Consolidate table indicating achieved CTQ’s versus actual CTQ’s as shown below,

7.0 Monitor Phase (EPA):

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Fig 8- Load case and Max. Principal Stress Plot (σ1) for LC1 ( Fx = 1KN )

Fig 7- First Mode shape

The two factors for monitoring the whole process is,

- Evaluation Performance Assessment which is the feedback given by the Customer.

7.1 Engagement Performance Assessment (EPA):

As the ultimate goal of the project is to develop the component which satisfies the customer, fulfilling all the requirements; the feedback from the customer is an important parameter of monitoring the process. The feedback is captured in the Engagement Performance Assessment (EPA) which is done by the Customer in the following format.

Engagement Performance Assessment Form

8.0 Conclusion:

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Design and manufacturing experience together with understanding of the optimized shape has resulted in the design which meets the manufacturing constraints whilst maintaining the strength and frequency requirements. The tangible benefits are measured in terms of Quality Net Income (QNI). QNI is calculated as follows,

The cost estimation for development of one bracket is a follows.

Weight reduction/component = Initial weight-optimized weight =1850-891 = 959 g.

The intangible benefits are better fuel efficiency, reduction in vibration levels and smooth drive. Pro-active value engineering in unison with topology optimization techniques is a new trend which will lead to future product development much faster and reliable.

With advances in hardware and software, in near future, multi-disciplinary design optimization will become a reality and this will result in optimum design for structural, acoustic performance and flow performance simultaneously.

9.0 References:

Guidelines provided by the Top 10 Automobile Manufacturer in the world.

Hypermesh 7.0 – Section “Optistruct” documentation & ANSYS – Theory Documentation.

ParameterIndustrial rates for ALSi9Cu3

Costs saving / Annum(2000 parts/month)

Project cost billed by TVS-Hxxxxx

Net Quality Income

Material Cost Saving

100 Rs/kg 0.959*100*24000 = 23,01,600

3,00,000 20,00,000

High Integrity Die Casting Processes by Edward J. Vinarcik.

Sigmax manuals.

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