c. kalavrytinos - reverse engineering of a car headlamp

2012

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MSc Mechanical Engineering

Digital Design & Analysis PG

Christos Kalavrytinos

Reverse Engineering of a CAR Headlamp


ABSTRACT

The aim of this project was to reduce the weight and cost of the MGF's headlamp

assembly using reverse engineering as the means. Data from a 3D scanner were

used as a basis for the CAD model to be produced using generative surface design

techniques.

The designer considered the implementation of Design for Manufacture and

Assembly (DFMA), Finite Element Analysis (FEA) and Failure Modes and Effects

Analysis (FMEA) methods.

New materials were considered and chosen for the new design. More specifically, the

glass for the lens was replaced by polycarbonate (PC), although PMMA was also

considered. The reflector assembly was simplified and the parts were reduced from

four to one using the segmented reflector design. The lens is now bonded with a

special adhesive to the casing instead of using 5 clips and a seal.

The overall weight reduction achieved was 63.2% mainly due to the polycarbonate

lens which contributed to a 40.4% reduction on its own. The remaining reduction was

due to the segmented reflector design.

The casing design was also simplified to reduce weight and cost of manufacture.

The FEA analysis performed showed that the part can withstand a 3G plus 30%

safety factor vertical acceleration that simulates the vehicle travelling over a speed

bump. The stress and deformation were low thus allowing for certainty that the part

components will not fail even if vibrations and fatigue is considered.

Christos Kalavrytinos Page


CONTENTS

ABSTRACT............................................................................................................................... I

CONTENTS.............................................................................................................................. II

1.0 INTRODUCTION................................................................................................................1

1.1 OBJECTIVES.....................................................................................................................1

2.0 RELEVANT THEORY.........................................................................................................1

2.1 REVERSE ENGINEERING....................................................................................................1

2.2 RAPID PROTOTYPING.........................................................................................................2

2.3 PRODUCT DESIGN SPECIFICATION.....................................................................................3

2.4 PDS FOR HEADLAMP:.......................................................................................................3

2.5 DESIGN FOR MANUFACTURE AND ASSEMBLY......................................................................4

3.0 MATERIAL SELECTION...................................................................................................6

4.0 COMPUTER AIDED DESIGN.............................................................................................8

4.1 CASING AND LENS ASSEMBLY..........................................................................................10

4.2 REFLECTOR DESIGN........................................................................................................11

5.0 FINITE ELEMENT ANALYSIS.........................................................................................12

6.0 FAILURE MODE AND EFFECTS ANALYSIS..................................................................15

7.0 RESULTS AND CONCLUSION.......................................................................................16

8.0 RECOMMENDATIONS.....................................................................................................16

REFERENCES....................................................................................................................... 18

Christos Kalavrytinos Page


1.0 Introduction

This project concerns the process of reverse engineering a headlamp assembly of a

1995 MGF car. The headlamp assembly was scanned using a Konica Minolta 3D

scanner and the scan data, otherwise known as point cloud, were processed and

imported in CATIA V5. The main surfaces of the lens were duplicated along with the

more important mounting points of the casing.

1.1 Objectives

In order to successfully complete this reverse engineering process, the following

objectives have been set:

3D scanning of the assembly

Research of reverse engineering, rapid prototyping, headlight design,

regulations

Production of the new Product Design Specifications (PDS)

Application of Failure Mode and Effects Analysis (FMEA)

Consideration of Design For manufacture and Assembly (DFMA)

Produce Computer Aided Design (CAD) solids

Perform Finite Element Analysis (FEA)

Discuss results and recommendations

2.0 Relevant theory

2.1 Reverse engineering

Reverse engineering is a process of measuring, analysing, and testing to reconstruct

the mirror image of an object or retrieve a past event. It is a technology if reinvention,

a road map leading to reconstruction and reproduction. It is also the art of applied

science for preservation of the design intent of the original part.

Reverse engineering can be applied to recreate the high value commercial parts for

business profits. To accomplish this task, the engineer needs an understanding of

the functionality of the original part and the skills to replicate its characteristic details.

(Wang, 2011)

In the case of the headlamp, the engineer is interested in reducing the weight and

cost of the components by redesigning some of the parts and, possibly, materials.

Christos Kalavrytinos Page 1


Since producing a CAD design from the beginning is difficult, 3D scan data and

reverse engineering of the mounting points and important surfaces will be used as a

basis for building the CAD model.

2.2 Rapid prototyping

Rapid prototyping is the automatic process of constructing parts or components of a

product (sometimes in scale) within a reasonably fast time span, usually by the

additive manufacturing technology. This technology analyses a CAD part and

transforms its shape into a toolpath so that the part can be manufactured by adding

different types of liquid materials which are then cured/ fused.

This technology can be described as "3D printing" as it produces a part without the

requirement of special tools and is, therefore, very flexible and fast.

It is primarily used in various stages of the design process for:

Visualisation

Testing (e.g. packaging constrains)

Increase effective communication

Decrease of development time

Decrease costly mistakes

Minimise sustaining engineering changes

Extent product lifetime by adding necessary features and eliminating

redundant features early in the design

Rapid Prototyping decreases development time by allowing corrections to a product

to be made early in the process. By giving engineering, manufacturing, marketing,

and purchasing a look at the product early in the design process, mistakes can be

corrected and changes can be made while they are still inexpensive. The trends in

manufacturing industries continue to emphasize the following:

Increasing number of variants of products

Increasing product complexity

Decreasing product lifetime before obsolescence

Decreasing delivery time

(www.efunda.com)

In the case study of the headlamp, a rapid prototype can help with testing the

tolerances and packaging limitations on the actual car. Then the parts can be



redesigned to eliminate any flaws. This iterative process is the key to obtaining a

quality product within the Product Design Specifications.

2.3 Product Design Specification

Stuart Pugh was one of the first engineers that analysed the design process and split

it into the most important categories. These are the areas that the design team must

consider before they produce the Product Design Specification documents. These

categories can be seen in Fig. 1.

Figure 1, Pugh's wheel (Pugh, 1991)

2.4 PDS for Headlamp:

1.0 Introduction The goal is a quality product that is environmentally friendly

throughout its lifecycle and is lighter and cheaper than the original headlamp made

by Valeo. Only the most important characteristics that will be altered are mentioned

in this PDS.

2.0 Operational Requirements



2.1 In Use

2.1.1 The headlamp must weigh approximately 10% less than the original part

(2160.7g).

2.1.2 The headlamp must withstand high temperatures, especially the parts near the

light bulb.

2.1.3 The casing mounting points must be the same with the original part.

2.1.4 The lens must be the same shape as the original part.

2.1.5 The lens material must have good optical quality and resist oxidation from UV

rays.

2.1.6 The reflector must be adjustable in angle.

2.2 Safety

2.2.1 The lens must behave in a safe way during impact, to protect pedestrians.

2.2.2 The sensitive parts should be sealed properly in the casing.

2.2.3 Ventilation holes must be designed to allow for heat dissipation.

2.2.4 Operational and safety instructions must be provided to the user through the

user manual.

2.3 Maintenance

2.3.1 The product must be of high quality and carry a 3 year manufacturer’s warranty.

2.3.2 The change of light bulbs must be easy with proper access points.

3.3.3 It must be made known to the customer that if an attempt to fix the product by

disassembling it will void the warranty.

2.5 Design for Manufacture and Assembly

Design for Manufacture and Assembly (DFMA) is the process of designing a product

while considering the raw material, the tools and processes used for manufacture as

well as the resources needed for assembly of the product. It has a big effect by

decreasing development time and cost.

“It a system comprised of various principles that, when used properly, will improve

the ability for a design to be easily manufactured and assembled. It is most beneficial

to consider these principles during the design phase of new product development.

This system can be divided into three major sections. The first is the raw material…

Second is the machines and processes used to work the raw material…Third is the

assembly of the product. It is during the assembly of the finished product that

provides the greatest opportunity to apply DFMA principles.”



(johnyater.hubpages.com/hub/DFMA)

The aim of this report is not to perform a full DFMA analysis. However, the most

important considerations that would be implemented in the DFMA analysis must be

stated.

It is known that the main components of the headlamp assembly will be

manufactured using injection molding since polymers will be used throughout the

parts. The general design guidelines for this specific process are analysed bellow.

Figure 2, Draft angles and ribs (Youssefi, K.)

Figure 3, Rib thickness and sharp corners (Youssefi, K.)



Figure 4, Transitions and bosses (Youssefi, K.)

3.0 Material selection

Choosing the correct material for each component of the headlamp assembly is a

very important stage of the design process. Sticking with the same material chosen

by the original manufacturer, Valeo, can reduce development time, but in this case

changing the materials is the only way to produce a lighter and cheaper product.

Research shows that the majority of car manufacturers have switched from glass

headlamp lenses to polymer ones, mostly Polycarbonate (PC). This is an effort to

reduce the weight of the lens, reduce the chances of cracking caused by small rocks/

gravel, and increase the safety of pedestrians during a crash.

The polycarbonate lenses are thinner and more flexible when compared to the glass

lenses, illustrated in Fig. 5, which are thicker, heavier and more brittle.

Figure 5, MGF headlamp lens



The CES Edupack material selection software can be used to set limits and analyse

possible material choices for a certain application. In this analysis, the software is set

up to look for polymers with good and excellent optical properties that can withstand

temperatures of up to 100 degrees C so that their prices can be compared. The trend

of the automotive industry at the moment is the use of Polycarbonate for the lenses

of the headlamps and Polymethylmethacrylate (PMMA) for indicators and rear lights.

This is mainly due to the better refractive index of PC (1.54-1.58) compared to PMMA

(1.49-1.5) as shown in Fig. 6.

Moreover, the impact strength of PC (9-10 kJ/m^2) is a lot higher than PMMA's (2.6-

2.9 kJ/m^2) which is a governing factor as far as safety is concerned.

Figure 6, CES Edupack material selection for lens

The casing is made of Polypropylene that withstands high temperatures (100-115

degrees C) is fairly cheap and easy to produce injection molded components from it.

The reflector material is probably a BMC composite with Polyester and other

additives such as glass fibres. All the material information can be found in the

Appendix.

Table 1, Bill of materials

Part No. Part Name Material

1 Casing Polypropylene (PP)

2 Lens Polycarbonate (PC)

3 Reflector BMC composite

4 Cover Caps Polypropylene (PP)



4.0 Computer Aided Design

Computer Aided Design (CAD) is the process of designing parts and components

using a computer programme. The headlamp components are designed using CATIA

V5 R20 which produces the 3D solid models as well as an assembly with full

drawings.

The basis of the design is the point cloud (Fig. 7) that was obtained using data from

the 3D scanner (Fig. 8)

Figure 7, Point cloud in CATIA

Figure 8, 3D Scanner and headlamp



Using the 3D scan data as a basis, the surfaces of the components can be

duplicated. This can be done by splitting the part using a plane, and following a

curve and extruding it through a guide curve. This procedure can be seen in Fig. 9.

The basic mounting points are also designed first for the casing as they are the only

constrain for the headlamp to fit in its place properly.

Figure 10 illustrates how the surfaces are modelled to be approximately the same as

the point cloud.

Figure 11 shows the surfaces generated for the front of the lens and other surfaces

used to cut and blend the ellipses to obtain a smooth outcome.

Figure 9, Cut part by plane

Figure 10, Lens and casing



Figure 11, Surfaces

The casing, lens, reflector and back cover caps were modelled. The exact shape of

the casing was not duplicated as it was simplified in order to reduce weight,

complexity of mold and therefore cost.

4.1 Casing and lens assembly

The casing and lens assembly in the original part was done through the use of metal

clips and a rubber seal. In order to reduce weight, cost and the risk of humidity in the

headlamp, the lens is going to be bonded on the casing using a special adhesive that

when heated a lot, can be removed and the lens can be separated from the casing. A

disassembly method is shown in Fig. 12.

Figure 12, Lens-casing disassembly



4.2 Reflector design

In the original design included a 2 part reflector joined with a smaller lens and a seal.

The whole assembly of 4 parts weighed 520 grams. A new trend for reflector design

uses the reflector as a lens too focus light therefore the lens and seal is not needed.

This technology is called segmented reflector design. An example can be seen in

Fig. 13, and Fig. 14 shows the reflector designed in CATIA.

Figure 13, Segmented reflector example

Figure 14, Segmented reflector in CATIA



5.0 Finite Element Analysis

Finite Element Analysis (FEA) is the analysis method of dividing a part into small

elements and nodes, so that local stresses and strains can be calculated. It is a

useful tool during the design process, as it can point out weak areas of a part that

need to be redesigned to withstands the specification loads before a prototype is

manufactured.

The general procedure of the analysis is to define the material properties, create a

mesh for the part (i.e. divide it into small elements), apply constrains and degrees of

freedom, apply loads and calculate the results (i.e. stress, strain, deformation).

In order to carry out the FE analysis for the headlamp, the mounting brackets were

considered areas of interest. Therefore, the geometry of the casing was exported

from CATIA as an .stp file and imported into ANSYS. Figure 12 shows the material

properties that were used as found in CES Edupack (edited from Poluthylene) and

Fig. 13 illustrates the geometry of the component and the generated mesh. The

constrains (i.e. fixed supports) and loads applied can be seen in Fig. 14. An

assumption was made that a vertical acceleration of 3G plus 30% safety factor is

applied on the components to simulate the vehicle travelling over a speed bump or

pothole.

Figure 15, Polypropylene properties



Figure 16, Geometry and mesh

Figure 17 Fixed supports (blue) and acceleration (yellow)

The model is then solved to obtain values for stress and deformation. Figure 15

illustrates the results for maximum stress at 2.3 MPa and the maximum deformation

of 0.05mm can be seen in Fig. 16.

Therefore, the stress of 2.3 MPa is well within the yield stress for the material used at

37.2 MPa and that ensures the components will not fail in a speed bump scenario

and that it can withstand the fatigue from the vibrations of the vehicle.



Figure 18, Maximum stress

Figure 19, Maximum deformation



6.0 Failure Mode and Effects Analysis

Failure Modes and Effects Analysis (FMEA) is the process of analysing the ways in

which a part might fail as well as the effects of that failure. The process looks at the

part functions, failure modes (e.g. corrosion), the effects of the failure (e.g. the lens

becomes hazy) and the consequences of the failure occurring (e.g. MOT failure).

These failures are then weighed in terms of the severity of the failure, the probability

of occurrence and the difficulty of detection. These numbers are then multiplied to

produce a Risk Priority Number (or RPN). Therefore, the design team must focus on

the high RPN scores first in order to eliminate design flaws.

An FMEA analysis for a product such as the headlamp, could be very long and time

consuming and therefore only example of possible considerations for the failure

modes and effects are mentioned.

Example: Headlamp lens

Function: Provides protection of interior headlamp components and is transparent

Potential Failure Mode: Oxidation of polycarbonate due to UV radiation (Fig. 15)

Potential Effect: Reduced optical quality, increased glare, MOT failure

Figure 20, Failure mode- foggy lens



7.0 Results and Conclusion

The main goal of this reverse engineering process is to reduce the weight, complexity

and cost of the headlamp assembly. Nowadays, there is a trend in the automotive

industry for reducing the weight of the car components to increase fuel efficiency and

reduce cost. As far as headlamp design is concerned, the main breakthroughs over

the past years were the change from the use of glass in the lenses to polycarbonate

as well as the use of the segmented reflector design to reduce the number of parts

used and therefore the weight and cost.

However, this trend has led to the need for the whole assembly to be replaced in

most cases.

Just by changing the material of the lens from glass to polycarbonate, the weight of

the assembly was reduced by 40.4% from 2160.7 kg to 1186.4 kg. Moreover, a

further reduction of the reflector assembly from 520 gr to 30 gr was achieved by

implementing the segmented reflector technology thus achieving an overall weight

reduction of 63.2%.

Furthermore, since the complexity and sharp corners of the casing were reduced, the

manufacturing cost, as well as the tooling (e.g. mold complexity) cost could be

decreased.

In addition, the FEA analysis showed that the part performs within the design

specifications and when subjected to a vertical acceleration of 3G plus a 30% safety

factor, the stress is well below the yield point of the material and thus allows for

certain behaviour even under repetitive loads and fatigue.

8.0 Recommendations

In order for this piece of work to be improved, more careful design according to

Design For Manufacture methods must be completed, in order to introduce features

such as ribs and bosses that can help to further reduce the material used and reduce

the weight.

Moreover, a better quality point cloud could have been achieved if the scanned parts

were sprayed to a matte surface as the reflective surfaces interfere with the scan and

produce false points.



The most important factor in the outcome of this report was the personal judgment

since the way each engineer duplicates the surfaces is different ways.

If this project was an actual automotive industry project, there would be a team of

engineers and they would have a chance to produce a rapid prototype to check

tolerances and fits. This feedback would then help to redesign the components

eliminating any flaws and improving the design. This is an iterative process and is

usually performed at least three times before an acceptable outcome is achieved.



References

Pugh, S (1991). Total Design: Integrated Methods for Successful Product

Engineering. Addison-Wesley.

Wang, W (2011). Reverse Engineering: Technology of Reinvention. CRC Press.

Youssefi, K. Design for Manufacturing and Assembly Notes. San Jose State

University


c. kalavrytinos - reverse engineering of a car headlamp

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