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Body In White (BIW) Benchmarking

Automotive industry is pushing limits to shorten their launch to launch cycle time & target very competitive cost of their products. With the increase in the strictness of the safety norms, NCAP ratings & customer needs, the challenge of reducing vehicle development cost and time has become more difficult.

If we look at the bill of material (BOM) for a passenger vehicle, BIW (Body in White) + DIW (Door in White) constitutes close to 40% of the total weight of the vehicle and has a significant role in impacting the overall vehicle cost and time of development. Refer the below mentioned graphs that show the weight distribution of all the subsystems of 4 Compact SUVs.

Sample- Sub-System Wise Weight Distribution For 4 vehicles
Fig. 1 Sub-System wise weight distribution chart for 4 vehicles
Automotive Sub-system nomenclature
Fig. 2 Sub-system nomenclature

In order to support OEM clients in achieving their challenging automotive cost reduction targets, we targeted BIW & DIW benchmarking for mass reduction of car biw for detailed study. We have designed a range of custom services (Fig. 3) with respect to passenger car Body in White (BIW) based specifically on their recent requirements that help in lightweight design of a car. We have divided the set of services in 3 parts in order to explain things in a detailed manner. This particular blog is Part-1(Fig. 3) & will pivot entirely around the CAD engineering specific services we offer. We have focused on generating 3D CAD Data for a biw through automotive 3d scanning and reverse engineering which is extremely useful in crashworthiness analysis of a car biw, and how 2D CAD outputs are useful to automotive design engineers in analysing  section modulus for strength requirements.

List Of BIW Specific Engineering Services Provided By ASI
Fig. 3 List of BIW & DIW specific engineering services

Part-1 CAD Engineering:

When we say CAD engineering, it includes all the categorized outputs or deliverables in digital format (CATIA/NX/Solid Edge/Solid Works) achieved through automotive reverse engineering that can be readily accessible to design engineers during design process.
For instance, while designing passenger seat support bracket on Body in White (BIW), the designer needs to consider the following constraints:CAD Engineering Constraints While Designing A Passanger Seat

Now, each of the constraint has further level of detail which guides the design of the bracket in a particular direction. Ideally designing the bracket meeting all these requirements is very challenging in a limited period of time. If the engineer performs all the studies individually from scratch and tries to balance out on all the above fronts, the overall automotive design time required will be very high.

On the other hand, if appropriate automotive benchmark data in suitable format is readily available, detailed study time can be reduced and decision-making process can be expedited. For e.g. if the benchmark vehicle passes homologation and the seat assembly weight is in range, the thickness map of the benchmark bracket can be used as a reference to start the vehicle design. It will save many iterations for CAE.

Based on a recent study the availability of automotive benchmark data at the right time while designing can reduce the overall time of design engineers by 23.7%.

As the data required by a Body in White (BIW) engineer while working on a new product model, a facelift model or a minor change model can vary from stage to stage, we provide the solution in 2 forms divided in further stages.

1. 3D CAD:

This includes Automotive 3D Scanning and Reverse Engineering. By using top-bottom approach detailed 3D data is generated for the entire Body in White (BIW) in following 2 ways.


Scan Body in White BIW  Generate rough surface  Disassemble Parts Scan All parts Generate rough surface data for all components Assemble all components.

Non-Parametric rough surface data of Body in White (BIW) Assembly, DIW assembly and all components in.iges/.stp/.prt/.Catpart format. Vehicle co-ordinate system will be different for all the parts and assembly CAD files.

Few Uses:
1. Study of position, size and packaging of components with low accuracy.
2. Ergonomics reference study.
3. Dimension based homologation checks.
4. Rough Sectional Study

Sample- Non-Parametric Rough Surface Data of Body in White (BIW) Assembly
Fig 4. Sample Non-Parametric surface data


Assign reference vehicle co-ordinate system (VCS) Scan Body in White (BIW) Generate rough surface Disassemble Parts Hierarchy wise Scan All parts in assembled and non-assembled condition Generate rough surface data for all components Assemble all components Clean-Up CAD and generate CAE suitable CAD  Add weld information with exact quantity, size and location.

Parametric solid 3D CAD data of Body in White (BIW) Assembly, DIW assembly and all components in.iges/.stp/.prt/.Catpart format. Hierarchy wise properly assembled all components in assembly with common VCS.

Few Uses:
1. Everything from Process-1 with higher accuracy.
2. Detailed thickness map of all the components.
3. CAE analysis for crash, vibration and fatigue.
4. Tool development & Proto Building.
5. Features and holes positioning and mapping.
6. Detailed sections can be cut and studied.

Sample- Reverse Engineered 3D CAD Data
Fig. 5 Sample CAD Data

Sample CAE Data For Crash, Vibration and Fatigue
Fig. 6 Sample CAE Data

2. 2D CAD:

For 2D CAD deliveries we need not disassemble Body in White (BIW) unless for a specific requirement and sections are cut from the BIW assembly at all critical locations. After that the cut pieces are scanned/traced and imported in the required CAD software for section modelling. 2D CAD modelling of the section includes all thickness details (paint, anti-rust coating and panels) & exact profile.

For higher accuracy, the sections are cut using reciprocating saw, where speed, feed and depth of the cut is controlled and monitored. Also, during scanning/tracing & CAD making, dimensions are corelated with the physical section piece. In general, the accuracy of the section profile size is within 100 microns & thickness values within 10 microns.

Sample Section 2D-CAD : A-Pillar Of BIW
Fig. 6 Sample Section 2D CAD

Fig. 6 shows just an example of a 1:1 scale 2D CAD section made using NX software, this section is from the A-Pillar region of the Body in White (BIW). Automotive design engineer can use this section to study the A-Pillar obstruction (should be less than 6 degrees), section modulus for strength requirements, weld size and space availability, number of layers for spot weld and many more. Also, as this data will be available in the digital format, so she/he can verify & check shape/dimensions on the design software being used.

Major Challenges

The 2 major challenges that clients face while obtaining automotive benchmark data are getting the right data at the right time and accuracy of the same. At ASI we develop new methods and improve the efficiency of these methods over time in order to deliver accurate automotive benchmark data at the right time. We have standard operation procedures (SOPs) for making 3D CAD, Automotive Scanning, Section profile cutting and CAE activity and these standards have been developed with various Japanese, Indian and European Automobile OEMs. Also, the tools and machines used are calibrated and highly accurate.


In the 2nd part of this blog we will discuss the Body in White (BIW) teardown process and BOM generation.

Pratik Shukla

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