Research of solidity and reliability of mass customised products in a competitive manufacturing system/ Masiskai pritaikytu individualiam vartotojui gaminiu stiprumo ir patikimumo tyrimas konkurencineje gamybos sistemoje.
Cikotiene, D. ; Ramonas, Z. ; Bargelis, A. 等
1. Introduction
1.1. Product customization in modern manufacturing system
The manufacturing of 21st century is globalized and integrated in
development of products, processes and production delivery. The
compliance of various technologies and activities are oneness of
different manufacturing organizations, which are fighting for survival
in globalized markets and competitive manufacturing environment. The
competitive manufacturing organization must enhance the variety of
product types, production flexibility and quality, and decrease the
manufacturing cost and production volume also finding other ways to
understand the customer wishes. The customizing products and services
are among the most critical means to deliver true customer value and
achieve superior competitive advantage. The challenge is not to
customize products and services in itself--but to do it in a profitable
way [1]. The more effective tool of mass customization is a product
configuration system of achieving and implementing this in practice and
offering a reduction of the lead time for products and quotations. It
also achieves faster and more qualified responses to customer inquires,
fewer transfers of responsibility and fewer specification errors, a
reduction of the resources spent for the specification of customised
products, and the possibility of optimising the products according to
the customer requirements.
The involvement of customers in this procedure as soon as possible
in the early development stage can help to activate the products
customization process. Leaving the product open to customization will
allow customers to change the design content of the item for their own
purchase. Customer customization of a producer's products does not
impact the design content of the originally posted item. It simply
allows for the customer to create a personalized variation of the
initial product design for different users. Products customization is
based on their modular design and development of configuration systems.
The art of design the customized items is the capability to create a
large number of product alternatives applying developed modules of basic
seller's products and not limited number of standard components.
This procedure involves analysis of product range, object-oriented
modelling of product conception structure and design of itself product,
implementation and maintenance. The solidity and reliability of
customised products have more problems in manufacturing and quality
control procedures comparing with products of unique design structure
because they are becoming more complicated in both cases point of view
applying technology and management. The process and tooling though
become more complicated in the latter case but customized products
market shearing is bigger and steadier.
1.2. Requirements of products solidity and reliability
The main purpose of manufacturing improvement is to satisfy the
customers' requirements developing new innovative products and
processes through satisfying the requirements of quality and safety
standards. The survive of competitive organization is manufacturing of
required product with low cost, which can be reduced, when the product
is qualitative and is provided to customer without need of rework or
condemn it to market.
The products safety evaluation in Lithuania is performed according
to regulations of Product safety law. There is indicated that if the
product is produced for the market, it must be safe. Every
product's group has specific methods for their solidity and
reliability evaluation at the testing laboratory according to the
requirements of appropriate European standard. European standards for
transport means testing including bicycles are used as Lithuanian
standards and they are provided with status of national standards [2-4].
The manufacturer can chose more testing methods and means for safety
warranty, which are noted at the directive 2001/95/EB of European Union
for common product safety.
The objective of this paper is development of a methodology for
mass customized products solidity and reliability testing, when products
have been produced with minimal cost and high quality. The appropriate
manufacturing network for competitive customized products has been
created and case study of bicycles solidity and reliability testing
methodology and results has been illustrated.
2. Development of a manufacturing network for competitive
customized products
The strategical and structural creation of competitive hybrid
manufacturing systems (HMS) network as a small / large size approach for
development and production of innovative mass customized products is
created (Fig. 1). It uses high skilled humans (engineers and operators),
CNC machine tools, software and hardware and appropriate interfaces. New
HMS structure based on improved collaborative tasks between humans,
robotics and machines versus flexible machine stations (FMS) has better
future perspective looking for indices of competitiveness and
productivity. HMS is able to develop, produce and delivery products and
components with competitive price and quality, because it has a high
flexibility index and processes capability. Created HMS network is able
to apply make or buy strategic approach and seek an excellence of
operational performance in manufacturing because network partners have
high specialization level, experience, skill and effective interfaces.
At the centre of a network is products' assembling company, which
collaborates with products developers, suppliers of products'
original parts, standard parts and assembling process materials,
research centres and universities and customers of developed and
produced products.
A developer of products being in created network applies concurrent
engineering approach [5] and seeks better communication and partially
overlapped activity with customers, product's parts and material
suppliers, and research centres and universities. The interfaces for
this aim are created and used. They help to use product's modular
design and design for manufacturability and easier assembling (DFMA)
methods. Every design feature (DF) of a product must be examined at the
early product and process development stage on a focus of customer,
designer and manufacturer because they have different point of view.
Designer creates product properties and characteristics applying various
DF and seeking different variety, dimensions, size, volume and
qualitative-quantitative parameters while manufacturer looks for
competitive process. There are, therefore, some conflicts and
trade-offs, which must be solved during early design stage of product
and process employing integrated collaborative work approach among
various HMS network partners. Going to mass customization of a product
is very urgent correct modular product design principle, which is
essential in collaborative design because it helps:
* to clarify customer requirements,
* to select and find technical solutions,
* to generate and evaluate concepts
* to improve an every module.
The systematic approach instead well known trials and errors method
has been used for innovative products and processes development in
generated HMS network. The knowledge base (KB) structure for acquiring
best practice, facts and rules for conclusion formulation is created.
The relation between man and unmanned work was classified and criteria
proposed. New products developers collaborating with University
Technological Experiments Centre originated rules and proposals when
robotics or assembling machines are better to use versus a manual work.
These rules and guidelines were created in virtual environment operating
with technological models and appropriate mathematical formalization [6]
when several assembling processes, their alternatives and machines have
been examined and data systematized. For optimal utilization of a
material aim function was developed that has been used for optimising
the consumption of various materials
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (1)
where k is the coefficient of material consumption; M is the mass
of work piece, kg; p is the number of work pieces; N is the mass of raw
materials used for production of M, kg.
Materials consumption rate is closely related with product
properties and characteristics; when the aim is getting an easier mass
product with sufficient solidity and reliability, it is necessary to use
better materials or vice-versa. These problems are to be solved at the
early new product development stage with customers' discussions
also taking into account product manufacturing cost.
Make or buy strategy requires an effective supplier selection
process for created HMS network. As a supplier selection function the
qualitative-quantitative factors has been used and a trade-off between
tangible and intangible factors as essential techniques in selecting the
best supplier were exploited [7]. Applying these criteria, the available
suppliers of parts and materials have been ranked and their data base
(DB) was created. Wide collaboration with customers in different
countries and organizations, moreover, their involvement in base product
customization process at the early product development stage helped to
increase products types' variety and new ideas finding.
The solidity and reliability of mass customized products are very
urgent for transport means, as driving safety is the most important
requirement. The case study of this paper examines Lithuanian bicycles
manufacturer X as typical representative of HMS, which collaborating
with University Technological Experiments Centre and other partners
created competitive and innovative company.
[FIGURE 1 OMITTED]
3. Research results
3.1. Research methodology
The research presented in this paper pertains to the manufacturing
science which is the applied research aiming at the contribution to both
theoreticians and practitioners. The latter usually do not care of the
research approaches used, as long the results help them solve practical
problems. The methodology used in this paper is an exploration how well
fit the theoretical model of manufacturing system in practice and
creation of the methods and tooling for testing solidity and reliability
of products.
The performed research is closely linked with the activity of a
large Lithuanian enterprise X that produces bicycles. Peculiarity of
this enterprise is that bicycles are assembled, painted, tested and
validated in Lithuania, but most of the materials, parts and components
are purchased from suppliers located in various companies and countries
mostly outside of Lithuania. It produces now close to 3000 various types
of bicycles including bicycles for children, urban and tourist, mountain
bicycles and even special bicycles for sport race. The yearly output of
bicycles at the enterprise is more than 40.000 units. Most bicycle types
are made in small batch volumes according to the customers' orders.
As things stand the shareholders of the company X decided
systematically analyze the nonquality and manufacturing cost problems
inside and outside of the company, and initiated close collaboration
with academia. The Technological Experiments Centre at the Siauliai
University was established for well-rounded experiments of bicycles and
their parts and components. All tests of quality control are performed
according to the requirements of standards [2-4]. Tests are accomplished
on more responsible parts of bicycles from every supply lot of products
according to the quality management requirements [8]. These tests showed
which parts, sections, assembling units and so on are improper and where
risk of breaking can appear. An appropriate stands for testing solidity
and reliability of mass customized bicycles and their parts have been
developed and implemented.
3.2. Testing results
Part of tests, accomplished at the Technological Experiments Centre
during the period 2008-04-01--201101-01 is presented in Table. The data
of only weakest parts of bicycle, where the risk of breaking is the
highest according to test results are presented in this Table. Parts of
bicycles, which didn't break during the tests detected that these
parts are substantial, reliable and quality is quite enough. Table shows
most vulnerable spots of bicycles.
Total quality of the assembled bicycle depends on reliability and
quality of all parts of bicycle [9]. As shown in the Table, the weakest
parts of tested bicycles are brakes, carriers and front fork. The
different suppliers of HMS network deliver original and standard parts
for bicycle assembling company X. It permanently does quality control
and analysis of reliability the every supplier in accordance of standard
deviation average of errors and defects [10]. The suppliers are ranked
on this index and worst of them are rejected from HMS network.
Brakes of a bicycle are one of the most important parts to ensure
safety of bicyclist, so this testing is very important to ensure, that
brakes of bicycle will work properly.
The visual and functional evaluation of brakes is performed. This
is performed for assembled bicycle (Fig. 2). Handle of the handbrake is
loaded with 300 N for min 15 seconds. This load is concentrated 25 mm
from the end of break handle. The test is repeated for 10 times.
[FIGURE 2 OMITTED]
The footbrake test is also performed for assembled bicycle. When
the footbrake is used, the angle between drive and brakes near the pedal
can not exceed 60[degrees], when the tree of pedal is load with torque
of 14 N.
Parts of drive and bicycle systems can not disengage or break
during the testing. A pedal in horizontal position is loaded with
vertical force of 1500 N every other second. Such testing is performed
10 times.
The special attention for the quality of braking has been paid
designing brakes. Generally, for brakes design lever transmissions with
the optimized transmission ratio and number of parts have been used.
Ratio of the transmission must be high and the number of parts must be
low. Analysis of different lever constructions exhibited that the most
effective is "V-Brake" design--ratio of the transmission for
this design is the highest in comparison with other lever design
alternatives. The most effective design is pointed in Fig. 3.
[FIGURE 3 OMITTED]
Ratio of the transmission for this design is high: K = b/a =
3.0-3.5. Also the number S of parts in this design is not high, s = 15.
It was stated, that such design is simple, but works effectively.
Another reason of brakes nonquality is material, used for the brake
slipper. Influence of the brake slipper for the quality of braking is
very high. Frictional force [F.sub.fr] (N), between the brake slipper
and wheel rim
[F.sub.fr] = [F.sub.s] [mu] (2)
where [F.sub.S] is force of lever transmission, N; [mu] is
coefficient of friction.
[F.sub.s] depend on the force from brake handle F and on the
transmission ratio K. Investigation of the contact between hard surface
(wheel rim) and elastic surface (brake slippers) was performed. Elastic
surface is pressed to the hard surface with force [F.sub.s]. Resilience
upstarts in the area of contact between elastic surface and hard
surface. The value of this resilience depends on average strain a (MPa),
which can be determined
[sigma] = [F.sub.s]/A (3)
where A is total area of the contact, [m.sup.2].
When brake slippers are slipping on wheel rim at the fixed speed,
frictional force will be composed of two components
[F.sub.fr] = [F.sub.adg] + [F.sub.hyst] (4)
where [F.sub.adg] is adhesive component and [F.sub.hyst] is
hysteresis component.
Adhesive component is clear defect of the surface and hysteresis
component is volumetric expression, which depends on elastic features of
elastic surface. The equation (4) is divided by force of lever
transmission [F.sub.S], then it can be written
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (5)
where [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] is
adhesive friction coefficient;
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] is hysteresis
friction coefficient.
Both of these components are the result of energy loss. This energy
raises temperature in the line of two bodies contact. Conditions during
the experiment have a big influence on coefficients [[mu].sub.A] and
[[mu].sub.H]. When the wheel rim is very smooth and the brake slippers
are not very elastics, the hysteresis component is going down. Adhesive
component is reduced by the water, which is passed into friction zone.
For the most effective breaking the brake slippers must be made from
two different materials with different hardness to secure sufficient
frictional coefficient during the braking on dry way and on sloppy way
as well.
When effectiveness of the brakes is tested, the deceleration of
braking is calculated according to the equation
a = [F.sub.Br]/m (6)
where a is value of the braking deceleration, m/[s.sup.2];
[F.sub.Br] is force of the braking, N; m is mass, kg.
For testing of adults bicycles is used 100 kg mass, for childish
bicycles--60 kg.
Tests of the braking in dry and wet conditions are performed. Fig.
4 shows variation of performances of braking during the testing of front
wheel in dry conditions.
[FIGURE 4 OMITTED]
The results of braking force testing of the same wheel in wet
conditions are shown in Fig. 5.
[FIGURE 5 OMITTED]
The value of breaking performances in dry conditions must be more
than 3.4 m/[s.sup.2] for front wheel and more than 2.2 m/[s.sup.2] for
back wheel. In wet conditions this meaning must be respectively 2.2
m/[s.sup.2] and 1.4 m/[s.sup.2].
Testing of carriers is performed loading it with 25 kg in the
middle of carrier. Cycle is repeated 100.000 times. Different breaks
were noticed after testing: one side of support snapped of after 82394
cycles of testing.
Another carrier was broken after 44370 cycles the horizontal part
of front support break down. One more the carrier was broken after 13552
cycles--the upper part of the carrier break down. The main reason of
carrier either any other part failures which has applied welding during
solidity and reliability testing is nonqualities during welding process,
as wrong welding facility, work regimes and human errors seeking less
manufacturing cost and high productivity [11]. The ways avoiding welding
process errors and defects seeking quality, productivity and least
manufacturing cost is proposed in many research papers; one of them is
presented in research works of Lappeenranta University of Technology,
which is a partner of Lithuanian industry and academia in manufacturing
science field [12].
The testing-bench for dynamical testing of front fork is shown in
Fig. 6. The front fork of bicycle is loaded with the force of 600 N, for
100.000 cycles. If there appear any cracks or fork breaks during the
testing, it can not be used for assembling of the bicycle. Similar
testing is performed for all main parts of the bicycles.
[FIGURE 6 OMITTED]
Front fork is tested using the load of 600 N, this is repeated for
100.000 cycles. Different breaks were noticed after the testing: fork
was broken after 65057 cycles of dynamical testing with 600 N load (Fig.
7). Break of the front fork in this part was noticed most often during
the testing of nonquality forks, which do not stand during the testing.
Differs only the number of cycles--a part of forks was broken after a
long time of testing, another does not stand for a long time of loading.
The number of cycles differs from 27647 to 88741 cycles during the
period of testing.
[FIGURE 7 OMITTED]
In the other cases front fork achieves different cracks after the
testing. Cracks are noticed in one or both sides of the fork (sometimes
cracks are noticed when testing is finished, sometimes--after different
number of testing cycles).
When a part of the bicycle is broken during the testing, it is
replaced with another one and it is tested repeatedly. When testing
results are satisfactory, after the testing the part can be used for
assembling of a bicycle.
Dynamical testing for assembled bicycle is performed according to
DIN plus program for different bicycles. Different parts of assembled
bicycles are loaded with appropriate loads and the bicycle starts to run
on the stand with reels. All parts are watched during the testing and
places of cracks are fixed (Fig. 8).
[FIGURE 8 OMITTED]
4. Discussions and conclusions
The research in this paper presents a network of HMS for mass
customized products development, production, assembling, testing and
validation. Particular attention has been made on creation of testing
methodology, testing tooling and techniques for solidity and reliability
of transport means, in particular bicycles. The new innovative product
and process design is the essential task of the manufacturing
organization that defines its productivity and effectiveness.
Cross-discipline and inter-departmental collaboration inside and outside
of a HMS is an effective way finding new innovative solutions and ideas
for products and processes development.
The methodology of HMS net creation and solidity and reliability
testing of products that has been described in this paper accomplishes
the objective of this research. It has several advantages: the
originated testing stands for customized products have been developed
and validated. The created testing methodology is able to estimate the
solidity and reliability of itself product and its parts. Briefly it is
conclude as follows:
1. The created manufacturing network for competitive customized
products is able to develop and produce competitive mass customized
products with less production cost.
2. The created product's solidity and reliability of testing
methodology and facilities help to disclose the regularity of design and
manufacturing errors and defects; the combination of applied materials,
design features of parts and customized product type diminish
manufacturing cost and increase quality.
3. New human-robot interactive cooperation in advanced HMS with
motivated employees and their satisfaction of work can increase quality
and productivity and reduce manufacturing cost.
4. Knowledge-based innovation in HMS processes, products and deep
collaboration is a new alternative going from cost cutting to knowledge
acquisition and value adding.
Acknowledgment
This research was partially supported by contracts with industry
No. 06351, 2008; No. 06164, 2009 and No. 0626, 2010.
Received February 02, 2011
Accepted November 30, 2011
References
[1.] Hvam, L.; Mortensen, N.; Riis, J. 2008. Product Customization,
Springer: London. 283p.
[2.] LST EN 14765:2006+A1:2008. Bicycles for children. Requirements
for safety and methods of testing.
[3.] LST EN 14764:2006. Urban and tourist bicycles. Requirements
for safety and methods of testing.
[4.] LST EN 14766:2006. Mountain bicycles. Requirements for safety
and methods of testing.
[5.] Boothroyd, G.; Dewhurst, P.; Knight, W. 2002. Product Design
for Manufacture and Assembly, Marcel Dekker, Inc.: New York. 698p.
[6.] Ayyub, B.M. 2001. Elicitation of Expert Opinions for
Uncertainty and Risks. CRC Press LLC: New York. 302p.
[7.] Tahiri, F.; Osman, M.R.; Ali, A. and Yusuff, R.M. 2008. A
review of supplier selection methods in manufacturing industries,
Suranaree J. Sci. Technol. 15(3): 201-208.
[8.] Ross, J.E. 1999. Total Quality Management: Text, cases and
readings, St. Lucie Press: New York. 550p.
[9.] Setijono, D.; Dahlgaard, J.J. 2008. The value of quality
improvements, Int. J. of Quality & Reliability Management 25(3):
292-312.
[10.] Chase, K.W.; Parkinson, A.R. 1991. A survey of research in
the application of tolerance analysis to the design of mechanical
assemblies. ADCATS Report No91(1). 42p.
[11.] Ollikainen, M.; Varis, J. 2006. Human errors play a
remarkable role in sheet metal industry, Mechanika 5(61): 51-56.
[12.] Kah, P.; Salminen, A.; Martikainen, J. 2010. The effect of
the relative location of laser beam with arc in different hybrid welding
processes, Mechanika 3(83): 68-74.
D. Cikotiene *, Z. Ramonas *, A. Bargelis **
* Siauliai University, Vilniaus 141, 76353 Siauliai, Lithuania,
E-mail: dalia@tf.su.lt
** Kaunas University of Technology, Kestucio 27, 44312 Kaunas,
Lithuania, E-mail: algirdas.bargelis@ktu.lt
Table
List of tests with bicycle parts and assembled products
Name of test Number of tests Below standards
Dynamical tests of assem- 84 38
bled bicycle
Tests of brakes 70 31
Dynamics tests of pedals 14 2
Dynamics tests of carriers 52 24
Tests of front fork 44 12