II - Customer service
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At each stage in the life of your tailor welded blank solution, a dedicated Tailored
Blanks partner is available to provide you with a technical solution suited to your
needs.
Stage in the life of the product
ArcelorMittal contact
Preliminary design
BIW experts
Identification of application
Preliminary blank concept
Co-engineering
development
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A multi-competence team consisting of Tailored Blanks development engineers,
ArcelorMittal Auto resident engineers, ArcelorMittal design engineers and
ArcelorMittal stamping engineers analyses the solutions of existing vehicles and
studies optimizations with the following objectives:
ı Weight saving.
ı In-service and crash improved performances.
ı Cost saving.
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wkhfxvwrphu
Resident engineer
Noble Intl. development engineer
Blank optimization
feasibility study
Industrialization
Noble Intl. plant project manager
Detailed specification
of part
Series production
45
Client Technical Support (CTS)
"$
t
%!
(laser welding, …)
% % Safety (crash management,
energy absorption, exceptional loads resistance)
% y (stifffness)
%
% fe
In-service performance
Technical performance
Quality follow-up
ArcelorMittal has a development and technical support department which is
dedicated to automotive customers. An engineering team, using tailor welded blanks
experience of ArcelorMittal, can work on automotive projects and especially tailor
welded parts from design to series production.
Tailored Blanks requires from each customer detailed needs and priorities to optimize
the tailor welded blank solution (see Fig.46).
% #$
#
!
Weight
% % %
Total cost of the function
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Beyond stamping feasibility study of the part, ArcelorMittal teams can design parts
on the basis of speciÝcations and data provided by the customer, such as load
analysis and main dimensioning criteria:
ı DeÞection - stiffness.
ı Plastic strains - resistance.
ı Intrusion - crash.
ı Steel grade and thickness optimization of the different areas of the blanks and
comparison between the behavior of the tailor welded blank solution and the
reference are examples of studies that can be performed (see Fig. 47 and Fig.
48).
II - Customer service
44
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pdghe|ufhorulwwdo
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47
The results can be a comparison between reference and tailor welded blanks version
in terms of deformation, stress, intrusion depth or fatigue resistance for instance.
Of course, for such a study, CAD data of the part or the sub assembly must be
provided by the customer. Studies can be made using generic or customer speciÝc
load cases and dimensioning criteria.
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ArcelorMittal experts can study applications and then prepare a design study by risk
removal and characterisation in a Ýrst step (see feasibility study sub-chapter).
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Specialised software used by ArcelorMittal allows to take into account at an early
stage the characteristics of each application and the manufacturing constraints.
Generally, several different solutions are proposed to the customer together with
in-service behavior analysis (crash, stiffness, etc), stamping, weight and cost
estimations of the different solutions proposed.
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SpeciÝc tools for numerical analysis developed by ArcelorMittal allow the customer
to achieve an accurate analysis taking into account the desired safety margin in the
Ýnal design of the part. Exclusive ArcelorMittal tools are based on:
ı SpeciÝc forming limit curves for the welding areas of tailored welded blanks.
ı SpeciÝc methodologies to analyse forming operations by
Finite Element Model (FEM).
ı SpeciÝc numerical tool to predict and compensate springback
after stamping named Outifo
(examples of results are shown in Fig. 49).
Stamping feasibility studies rely on the Forming Limit Curves (FLC) of the welded
area model developed by ArcelorMittal:
ı The FLC of the weaker material is not sufÝcient to predict the behavior of the
tailor welded blank during stamping.
ı The recognized ArcelorMittal FLC model of the welded area has been presented in
numerous congresses:
- 40th Mechanical Working and Steel Processing.
- ISS congress.
- International Deep Drawing Group Congress.
ı FLCs are further explained in chapter III.
II - Customer service
46
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xdoskdvhÎÒÓðxowlskdvhÊÓÓÓ
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49
ÌÝÊÝ dvhuzhoglqjihdvlelolw|dqdo|vlv
Experts from ArcelorMittal R&D can study tailor welded blanks and parts in order to
provide data preparing the design study in an optimum design. These Ýrst studies are
characterizations and risk removals.
Input data
Results
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With the CAD data of the Ýnished part and data of the stamping tools, the Tailored
Blanks team can supply:
ı Development of the minimum blank shape for stamping.
ı Validation that welds are located in non-critical zones.
ı Complete stamping simulation to validate blank shape and keep costly prototyping
to a minimum.
ı Quick feasibility analysis and risk removal study.
ı Detailed analysis.
ı Zones of thinning and thickening.
ı Strain Ýelds.
ı Minimum blank dimensions and optimized tailor welded blanks.
ı Tailor welded blanks deÝnition after tailor welded blanks optimization.
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Tailored Blanks performs Ýne tuning in a systematic way in order to:
ı Optimize thickness and grades to decrease weight.
ı Develop nesting solutions to reduce steel consumption.
ı Optimize blank shape to a maximum of parts in a weld cycle.
Deliverables: blank shape, gross and net weight, tailor welded blanks price, steel
grades and thickness.
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ı Compare performance of tailor welded blanks with different steel grades.
ı Obtain a Ýrst feasibility assessment of a part.
ı Provide data for analysis of numerical stamping simulations of a tailor welded
blanks part.
Such data are usually completed by the Forming Limit Curve of the Laser welded
area.
The objective is an experimental evaluation of the formability of the laser welded
seam; the acceptable value depends on the part severity. Such analysis is composed
of different steps:
ı Blanking quality analysis.
ı Hardness measurement in the weld area.
ı Weld geometry.
ı 180¡ Bending test.
ı Erichsen test.
ı Tensile test.
ı U-forming test.
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The objective is to judge if the cutting edge quality of the sub-blanks is acceptable
for laser welding and deÝne the blanking procedure and cutting parameters to obtain
sufÝcient cutting quality (see Fig. 50).
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Cross sectional view
Parameter measurement
ZD
ZL
ZA
P
Definition
ZD (%)
Rounded height
ZL (%)
Sheared height
ZA (%)
Breaking height
P (mm)
Breaking depth
II - Customer service
48
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The objective is to determine the hardness proÝle across the seam in order to
estimate the formability (see Fig. 51 and Fig. 52).
In the laser welding process the heat is very localized. As a consequence, the heat
affected zone is thin and the quenching speed very high. The presence of steel
grades with carbon and alloying elements gives martensitic microstructure with a
very high hardness. However, the dilution of the molten area, by another metal for
instance, results in a less quenched metallic structure with reduced hardness and
better formability during assembly (orange curve).
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In order to analyse the bending behavior, the laser seam is bent at 180¡ at the
maximum and it is determined whether and at which angle it cracks. Obviously a
real part is not subjected to a 180¡ bending. The test can thus be considered as
conservative.
51
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Hardness (Hv)
500
400
300
200
100
Distance from weld seam
0
-3
-2
-1
0
1
3
2
Homogenous welding
Effect of the dillution of the carbon content
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The objective is to measure the geometry of the seam to compare it with the
customer speciÝcations and verify if there is a risk of stress concentration. It may
result in an optimization of the process parameters.
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The tailor welded blanks are blocked and deformed according to an equibiaxial strain
path. A comparison between the height obtained with the base metal and the tailor
welded blanks is made. Such a test gives an idea of the formability of the weld
compared to the base metal.
Generally a requirement of Erichsen ratio (see Fig. 54) higher than 70% is
recommended. It may be discussed according to customer speciÝcations and part
difÝculty.
It is important to point out that this requirement alone has its limits when we
consider the formability of welds in ductile UHSS. The weld may well present a
sufÝcient elongation for a given application, even though the 70% Erichsen criteria
is not met due to the excellent elongation of the base metal. In such a case another
test has to be preferred and a deeper study of the formability requirements of the
part is recommended.
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Height of the stamped specimen
27 +/- 0.05
BM
LW
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Cross sectional view
Parameter measurement
Í
20 +/- 0.05
LE
33 +/- 0.1
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LE
% Erichsen =
LS
ZF
LT = 0,25 LE + 2xLM + L S
Height of the stamped weld
Height of the stamped base metal
x 100
II - Customer service
50
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Tensile tests on laser seams are performed in the longitudinal and transverse
directions. Such measurements of the Ultimate Tensile Strength (UTS) and
Elongation (E%) give an idea of the formability properties in the respective
deformation directions (see Fig. 55).
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UTS
E%
Longitudinal
Transverse
Longitudinal
Transverse
Steel
grade A and B
Weld
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The objective is to analyse the stamping behavior of a U-shape (representative of
the local shape of B-pillars or rails).
For this test, the U-shape is made by stamping. The sides of the blank are blocked
under blank holders. The punch goes up until cracks appear on Þange along the weld
seam. The U-shape is stamped and it is analysed at which depth cracks appear.
Stamping parameters can be adjusted to be as representative as possible of an
industrial part.
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53
Nesting is the process of maximising the number of blanks that can be cut from
a steel coil. It is basically a geometrical exercise but some other aspects must be
respected to optimize the nesting:
ı Rolling direction imposed by the formability requirements of the part or
its in-service behavior.
ı Tool constraints such as feasibility of the press geometry, evacuation of the
blanks and the scrap, and the cutting quality of the edges to be welded.
ı Coil width feasibility and economics.
ı Tailor welded blanks production process (number of parts per weld cycle, edge
preparation, linear/non-linear welding).
The blanks can be divided into two families depending on their shape (see Fig. 57):
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These blanks can be cut on a shear line and require no part speciÝc investments.
This process is well suited for low and medium volume vehicles.
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Blanking is made with tools on press line. The tools are dedicated to a speciÝc
part. For this reason, this process is efÝcient for high volume series where the
investment is low per vehicle.
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dqgeodqnvkdshfrpsoh{lw|
Complex shaped blanks
Simple shaped blanks
High volume car
> 400,000 vehicles/year
Tool blanking
Tool blanking
for increased productivity
Low volume car
< 50,000 vehicles/year
High tool cost per part,
try to review the design of
the tailor welded blanks
Shear blanking
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ghwhuplqhgehiruhwkheodqnlqjwrrovduhrughuhg
Some cases are worth being dealt with in more detail:
ı rzyroxphyhklfohvzlwkfrpsoh{vkdshgeodqnvÝ
The part cost is signiÝcanly increased if a tool investment is required.
Therefore it is often better to review the design of the tailor welded blank and
replace the complex shaped blanks by simple shaped blanks. As a consequence of
this there will be a gross weight increase of the tailor welded blank and some more
engineering scrap will be generated during stamping. But as long as the cost of the
increased gross weight is lower than the tool cost per part, this approach is still
advantageous.
II - Customer service
52
If the volume is only about 10,000 vehicles per year, laser cutting may be an
efÝcient alternative. This gives us the possibility to reduce engineering scrap and to
avoid tool investments:
ı ljkyroxphyhklfohvzlwkvlpsohvkdshgeodqnvÝ
Even though it is possible to blank on a shearing line, it may be advantageous to use
tools as two or even more parts can be cut in one stroke. Tools mean investments
and scrap between the blanks in the cutting process but the costs generated by
these aspects are compensated by a signiÝcantly increased productivity.
Blanking tools have the beneÝt of a stable and repeatable process with minimised
geometrical tolerances. The cut edges will be of good quality.
This is important in particular for the edge that has to be welded, for which special
attention has to be taken.
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+ No investment needed
- More scrap
- Less productivity
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+ Investment per part is low thanks to the high volume
+ Minimised scrap
+ High productivity as many blanks can be cut in one stroke
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Material utilization rates are affected by product design, blank nesting and drawing
die developments. For parts requiring a drawing die operation, material utilization
rates as high as 80% and as low as 30% are common. This can be estimated by the
product development in the early process and design stages. Parts that are more
rectangular in outline normally have higher utilization rates. In general, rectangular
or trapezoidal shaped parts lend themselves to signiÝcantly improved nesting
efÝciencies.
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Parts which are rectangular or trapezoidal blank shapes (such as Þoor panels) will
have a higher yield than parts that require irregular shaped blanks. For example,
some elements of the body side inner have such irregular shapes that the blanks
cannot be nested efÝciently. Very low yield rates such as 30% for monolithic
parts have been seen in the industry for these parts. This means that 70% of the
purchased sheet steel ends up as engineering scrap.
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55
1.0 mm
2.0 mm
1.5 mm
2.0 mm
This can be optimised by using a tailor welded blank. Splitting the blank into pieces
gives a very effective nesting. Later on, using the tailored blanks technology, the
welding will produce the desired irregular shaped blank (see Fig. 59). Cost savings
and yield rate will be improved considerably.
ÍÝÌÝ hvljqjxlgholqhviruqhvwlqj
The design of the blanks is always strongly related to the welding process. Big or
small sizes of the blanks need different space on the welding line. Sometimes a small
reduction of the size of the blank can result in a big gain on total welding costs as
the production plant can weld one more blank in the welding cycle. In that case the
productivity increases and the costs for welded parts are less expensive. Therefore,
a close cooperation between the development engineer and the customer is
recommended.
Furthermore it is also recommended to locate the weld in low stress areas in order to
avoid stamping problems. In general the weld does not move too far perpendicularly
to the stamping direction, especially in the case of a big thickness difference
between the two blanks. This important fact should also be considered when the
design and the nesting are deÝned.
II - Customer service
54
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57
Forming limit
True values
Major strain
Safety strain
0.317
0.330
0.344
0.357
0.371
0.384
0.397
0.411
0.424
0.438
0.451
0.465
0.478
Tailored Blanks has developed a whole range of services offering speciÝc solutions
for these products. This support is based on the utilization of tools speciÝcally
developed to analyze and optimize the forming behavior of welded blanks. These
actions are aimed at ensuring reliable production at lowest cost and at achieving zero
defects from the outset of part series production.
0.8
0.7
0.6
FLC FB450
0.5
0.4
Safety margin
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ghvljqskdvhâlqrughuwrpd{lpl}hjdlqv
0.3
0.2
5 years +
2-5 years
< 18 months
Current vehicle
0.1
Weld spot
Minor strain
Step 1
Advanced
engineering
Step 2
Vehicle concept
and design
Step 3
Tool development
and prototyping
0
-0.4
Step 4
Production
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
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Simulation without LWB FLC for material A1 and B1
Fracture on real part
> Innovative solutions
> Development planning
> Introduction of new
steel products and
technologies
> Stamping
> Monitoring of working
groups for the
industrialization
of new solutions
> Forming and joinin g
assistance:
- Stamping
- Simulation
- Tools design
- Tools optimization
- etc.
Major strain
> Quality management
0.5
> Production assistance
0.4
> Cost reduction
0.3
A1
B1
0.2
> Parts and process
design support
Part feasibility seams OK
0.1
0.0
Thanks to its cooperation with tool manufacturers, welded blank production sites
and stampers, ArcelorMittal is in a position to take part in the industrialization of
these parts.
This work, which supplements the work carried out in the design phase, will reduce
tool adjustment times and tool manufacturing costs, as well as optimize the tool
integration cost and time at the series production site.
Possible actions during this phase are for instance:
ı Delivery of prototype drawings.
ı Transfer of ArcelorMittal welded blank know-how to tool manufacturers Ï
simulations and tool design.
ı Supply of data needed to perform stamping simulations - FLCs of the various
materials and weld areas, tensile curves, etc. (further explained in chapter III).
ı Support for stamping sequence design (Fig. 61 and Fig. 62).
ı Performance of forming simulations (if required).
ı Support for interpretation of stamping simulations.
ı Stamping analysis by strain measurement with a type-approved device
(Fig. 61 and Fig. 62).
ı Acceptance and validation of tooling.
ı As required, optimization of the blank shape and/or weld position in case
difÝculties arise with tool adjustment.
0.1
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
Minor strain
LWB FLC allows to predict rupture by stamping simulation
Simulation with LWB FLC for material A1 and B1
Major strain
0.30
0.25
0.20
A1
B1
0.15
0.10
0.05
0.00
0.05
-0.10 -0.05 -0.00 0.05 0.10 0.15 0.20 0.25
Minor strain
Rupture prediction
II - Customer service
56
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Strain levels must be veriÝed at the end of tool adjustment, as they are crucial to
ensure optimum tool productivity. This requires the use of a speciÝc tool (welded
blank FLC) and detailed analysis of the behavior of the materials in the weld area.
Analysis is required to ensure the quality of mass-produced parts.
This assistance, as well as cost reduction proposals, continuous quality improvements
and any product modiÝcations, is provided throughout series production.
The project manager based at the plant to which the part has been assigned takes
over from the Tailored Blanks development engineer, who works with the customer
plant in order to Ýne tune the technical speciÝcations and packaging of the welded
blanks.
The human and technical resources (order of speciÝc cutting tools, welding tools,
etc.) needed to ensure the proper start-up of series production are deÝned in
conjunction with the Client Technical Support and the quality and logistics managers
of the Tailored Blanks plant.
Delivery of initial compliant samples validates the launch of series production.
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59
ÐÝÊÝ khvhuylfhriihu
Together with industrial partners active in the automotive industry, ArcelorMittal
has developed a model for estimating the total cost of production of a part in order
to support the choice between different technical solutions as early as in the design
stage. The cost structure will of course vary from one customer to another but as
the model aims at comparing different solutions rather than determining nominal
costs, the differences between the modelÔs and the customerÔs real cost structure
will be eliminated to a large extent.
The model, which allows an evaluation of the whole production process, is validated
in discussions with customers and on the basis of numerous examples, made for both
tailor welded blanks and other types of solutions.
Tailored Blanks has drawn up a catalogue of generic parts based upon several years
of experience of working with all the major OEMs and subcontractors in Europe.
These parts have been designed to give the same technical performance as the
monolithic post-assembled alternative.
Once the design is validated, the production process of the tailor welded blanks is
optimized according to the number of parts to be produced. Finally the costs are
estimated and compared to those of a conventional monolithic post-assembled
solution.
Tailored Blanks also performs cost assessments on real customer projects in order
to determine whether an application is economically viable as a tailor welded blank or
not. Data needed from the customer: CAD Ýle of part and potential reinforcements
to be integrated with the tailor welded blank.
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Materials
Engaged material
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The ArcelorMittal Customer Technical Support engineer (CTS) at the customer plant
works closely with the quality manager at the Tailored Blanks plant to ensure quality
monitoring. They are supported by ArcelorMittalÔs stamping and welding specialists.
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The CTS proposes studies aimed at reducing cost, weight and part forming
operations. These studies are carried out by a multi-disciplinary team and, if
appropriate, with the support of R&D and ArcelorMittal Auto product processing
experts.
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The logistics manager at the Tailored Blanks plant and the ArcelorMittal Auto sales
team ensure day-to-day service which is measured by service ratings and safety
inventories.
Scraps
> Including tails of
coils
Rejects
Scrap and rejects
recycling
Matic addition
Cutting
Stamping
Machines
> Depreciation
> Maintenance
> Consumables
(including energy)
> Surface area used
Assembly
Logistics
Machines
> Depreciation
> Maintenance
> Consumables
(including energy)
> Surface area used
Machines
> Depreciation
> Maintenance
> Consumables
(including energy)
> Surface area used
Tools
> Depreciation
> Maintenance
Tools
> Depreciation
> Maintenance
Tools
> Depreciation
> Maintenance
Labour
> Operators
> Supervisors
> Absenteeism rate
Labour
> Operators
> Supervisors
> Absenteeism rate
Labour
> Operators
> Supervisors
> Absenteeism rate
Process
> Capacity utilization
> Speed
> Added value loss due to rejects
Volume
Process
> Capacity utilization
> Speed
> Added value loss due to rejects
Cost of capital Taxes
Taken into account in ArcelorMittal Auto cost approach
Process
> Capacity utilization
> Speed
> Added value loss due to rejects
Specific development cost
(engineering studies, prototyping,
fine tuning time of tools)
Inventory costs
> Surface area
> Inventory value
> Consignment
inventory
Handling
> Labour
> Packaging
> Pallets
(delivery and
intermediate
inventories)
Flow management
cost
> References
management
> Invoicing
> Quality control
II - Customer service
58
Steps: Compare the designs (monolithic vs tailor welded blanks) technically to
validate that the performance is equal, optimize the tailor welded blanks solution
from a production point of view and determine the sales price. Finally the costs are
compared for the respective processes by the customer:
For the post assembled monolithic case (composed of 2 different parts):
ıCoils cost + coils storage + 2 x blanking + 2 x stamping + 1 x assembly.
For the tailor welded blanks case:
ıTailor welded blanks cost + 1 x stamping.
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This cost assessment model focuses on a comparison of the secondary processing
costs of the various material solutions. It takes into account the full range of
cost structure elements of a Ýnished part or sub-assembly to be mounted on an
assembly line at the premises of a car manufacturer or sub-contractor.
These elements are divided into:
ıFixed costs: capacity equipment, speciÝc tools, maintenance, buildings, etc.
ı Variable costs: labour, materials, consumables, etc.
The approach taken by this model is based on a comprehensive and chronological
description of the manufacturing sequence used to form and join the various
elements making up the part or sub-assembly from the tailor welded blanks supplied
(or from coils in the case of a monolithic part).
Each stage of the manufacturing sequence or forming (cutting, stamping, roll
forming, etc.) and joining (welding, bonding, crimping, etc.) processes is thus covered
by a detailed description of operating costs integrating all cost elements mentioned
above, which constitutes the input data for the assessment model.
The accuracy of the input data determines the relevance of the Ýnal assessment
result and thus the cost of the solution.
Assessment model input data:
4 data input categories can be distinguished:
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ı Dimensions of the used blank or of the coil, in the case of the monolithic solution.
ı Rate of material engaged, resulting from nesting optimization.
ı Ex-works cost of the product and cost of recycling generated scrap.
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ı Capital investment costs (machines and tools).
ı Depreciation of capital investments.
ı Cost of consumables, including cost of energy.
ı Cost of labour.
ı Production speed of lines at their productivity level.
ı Reject rate.
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ı Cost of storage.
ı Cost of packaging.
61
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ı Return on capital employed.
ı Business-related taxes, etc.
All this data is entered into the model at each stage of the manufacturing process,
generating an assessment of the cost of the Ýnished part for a given volume of parts
to be produced over a given period of time.
This approximation of the overall cost makes it possible to quantify the economic
advantages of the proposed Tailor Blank solution by comparison with a reference
monolithic solution. Furthermore, the model provides a detailed description of the
cost structure to support the technical arguments, and it can be used to identify
additional optimization of the proposed solution.
II - Customer service
60