Productivity is a key factor for companies manufacturing parts and
sets to the automotive industry. Automation plays an
important role in this matter, allowing development of entire
manufacturing cells without the direct need of workers. Even in
countries where the labour cost is relatively low, it becomes necessary
to improve the level of automation applied to manufacture
cells and reduce the dependence of the human labour unpredictability,
also increasing the quality and reducing the costs. This
case study was developed based on an industrial request in order to
improve a semi-automatic cell devoted to seat suspension
mat manufacturing. The original cell allows several automatic operations
but it needs two workers for two specific operations not
considered in the initial design. Thus, new concepts of wire feeding and
manipulation were developed in order to allow a better
material flow throughout the cell. The new cell was designed and built
with success, allowing obtain a fully-automated system,
which leads to a better productivity and reliability of the
manufacturing process.
Keywords: Fully-Automated Cells; Labour Reduction; Automation Without Robots; Seat Suspension-Mat; Automotive Industry;
Mechanical Engineering
Introduction
The competitiveness that is inherent in the automotive industry
has and always had a dynamic behaviour. However, there has been,
over the last century, the adoption of different strategies, from craft
production to mass production of Henry Ford, through the brand
policy and the variety of Sloan products, the lean production (lean
manufacturing) and more recently to build-to-order initiatives.
These changes are not only common to the major producers of
vehicles, but were also observed in luxury car producers, seen
as artisan producers [1]. The car mass production was a strategy
adopted in the automotive industry and started with Henry Ford,
founder of “Fordism”, a working model that boiled down to mass
produce cars at low cost [2,3]. Today’s consumer wants to influence
and participate in the product design, which led to a new paradigm
of production strategy. Therefore, at its early stages, the automotive
industry had in the market unique models that had a small variety
of features, such as the Ford T and Volkswagen Beetle, but in
nowadays manufacturing, organizations must be flexible and be
able to comprise a long product variety to remain competitive [4].
Indeed, companies must be able to adapt to the market constant
changes [5,6].
The value chain related to the automotive industry presents
a high degree of complexity [7,8]. A typical supply chain includes
car manufacturer (OEM’s–Original Equipment Manufacturers),
final components or subassemblies suppliers (Tier 1, 2 and 3),
distributors, retailers and customers. The OEM’s are constantly
looking for suppliers to whom they can delegate responsibilities in
areas such development, sourcing and planning, and this constant
search induces pressures in the suppliers to lower prices and make
deliveries within the stipulated deadlines, without compromising
the products quality assurance. Indeed, quality and delivery time are
indicators that highly affect the evaluation of the preferred product
supplier [7,9]. In the specific case of the car seat, the evolution
from mass to a personalized production, according to customer
needs can also be applied. Following the evolution of automobile
production, the seat was traditionally produced as an integral part
of the automobile, where the available possible configurations were
limited or null. With the increasing requirements of customers, this
behaviour has changed along the times. With these new realities, the
seat became an important element, with different configurations
and new component options. The driver can now benefit from a
seat with more comfort, extra features or have the possibility of
seat heating. Once again, companies must follow the trend of the
product variety.
This variety of products can affect the delivery time, which
plays an important role in competitiveness. The delivery time
can be compromised if a product is standardized or customized,
with a shorter time delivery for the first case and longer for the
second. Companies thus have the option to choose to reduce the
delivery time, engaging in standard products, but companies with
customized products must be able to meet the delivery time by
means of increased flexibility for customized products [10]. An
example to optimize the delivery time was presented in the paint
line of the Toyota Motor Manufacturing’s Georgetown plant, where
an electronic signal is sent to seat supplier within the information
of the customized seat of the car that is present in the assembly line.
The seat supplier should manufacture and deliver the seat exactly
where it is installed at the Toyota assembly line [11].
A number of industries have been found to be clearly capitalintensive
and a number of others clearly labour-intensive [12].
In the last thirty years, many companies located in industrialized
countries have been centralized their efforts by upgrading the
technological level of their production lines to keep in competition
with countries where the production costs are lower, due to low
labour costs (non-industrialized countries). This resulted in
companies in industrialized countries to migrate from the labour
to the capital-intensive model [13]. In some way, a company can be
rated in accordance with the amount of capital or labour. If, in one
hand, a company with a capital-intensive model has high levels of
automation in detriment of hand labour, on the other hand, a labour
intensive model usually uses a high amount of hand labour [14].
The automotive industry is not an exception of this classification
model and neither of this behaviour. Although the automotive
sector involves a high number of hand labour operations [15], and
at the same time high automation rates, some companies in less
developed countries, is fairly automated and use an intensive hand
labour to decrease production costs, although in the industrialized
world the manufacturing companies use highly automated and
robotized systems. Thus, in general, the automotive sector adopts a
capital-intensive model, due to the constant seek for an automated
production process. Furthermore, manual assembly lines usually
congregate in a complex number of relationships often difficult to
study and understand [16,17].
As described before, the customer is an important player
in the value chain, and wants his requirements fulfilled. As a
consequence, the companies must be in constant changes due to
market variations, and to adopt new processes and production
technologies using mainly automation [18,19]. Independently
of the technologies involved in this process, must of the times
companies use automation and robotics systems to increase their
competitiveness and productivity, ensuring as well as high levels of
quality and repeatability [20]. Automation and robotics, apart from
playing an important role in ergonomic problems [21], also help
companies to increase productivity and flexibility, despite of some
conflicts between these features. Indeed, production and assembly
line with high levels of productivity tend to be dedicated and not
a flexible system. The automotive industry is endowed with very
similar products that can be assembled in the same production line
with minor adjustments they adapt their lines. With automation a
company is able to reduce the setup time, increase the productivity,
improve assembly accuracy, and reduce the human operations [22].
Case Study
Scope
Figure 1: Suspension mat-main components.
Among various elements that comprise the car configuration, the
seat is seen as a key element in the safety and comfort of the driver
and remaining passengers. The seat is the element that connects
the occupants to the vehicle and plays a key role in security in the
event of an accident or sudden manoeuvres, keeping the driver
attached to the vehicle frame [23]. This case study was performed
on a production line that manufactures a specific component for
car seats. The company where the line is installed is dedicated to
the production of automobile systems and components. The line is
responsible for the manufacturing and assembly of one of several
products of the same family, the “Suspension Mat”. Suspension mat
is composed by several components obtained by spring steel wire,
which vary their geometry and size (Figure 1). Suspension mat
support foams either the seat or backrest and is a component that
gives the desirable flexibility to the car seat, being as well an
element
that helps the vibrations absorption from the vehicle structure to
the occupants. These features work together aiming to increase
the comfort. A brief introduction to the main operations present in
the product original process is made in Table 1. Therefore, in order to
understand the configuration of the original suspension mat
production line, a process layout is presented in Figure 2. A brief
overview of process layout is made
Table 1: Main operations of suspension line production line.
Figure 2: Initial process layout of the suspension mat
production line.
a) Seven workstations - two of them require human labour
to accomplish the final operations (winding and staples
workstations), the others five workstations are fully automated.
b) Handling operations - manual handling between several
workstations (vertical wires and winding workstation; spine
and winding workstation; hook and staples workstation),
automatic handling between the winding, castle and hook
workstations
Regarding the initial scenario, the suspension mat production
line has an inefficient configuration. If, on one hand, the spine
and vertical workstation are located in a less favourable area, on
the other hand, the cycle time highly varies due to the manual
operations (assembly and handling). Apart from this, the layout
line configuration is inappropriate to the flow of the suspension
mat assembly as well. Although the line has automatic operations,
it requires, besides manual handling and assembly between some
workstations to complete components, feeding operations of raw
materials. Due to these facts, the suspension mat assembly cycle
time has an irregular behaviour that affect the process flow. The
continuous intervention of manual operations consolidates the
assumption: the line is semi-automatic and must be upgraded to
a fully automatic line. Indeed, at the original stage, the line has a
certain degree of automation that requires a compromise between
manual and automatic operations.
The Problem
Companies adopt strategies to raise their production rates while
reducing the costs. One of the ways to perform that is to reduce
labour costs, especially whose who have repetitive tasks. Unlike
the general opinion, cost reduction with employees does not mean
the dismissal of the worker, but somehow a growth possibility for
the worker, assuming new tasks with higher added-value through
adequate formation plans. A lot of advantages are available both for
the company and worker.
In order to increase the production rate a strategy for this
line migration, which can be defined as semi-automatic, to a
fully automated line, was made. At the same time, a zero worker
dependency and a standardization of the cycle time should be
achieved, in order to reduce the cycle time of product assembly. The
implementation of automatic systems where manual intervention
exists to complete some tasks is proposed to perform this
optimization. Manual feeding of components and the packaging
of the final product do not make part of the proposed migration
process. To perform the migration process to a fully automated line,
it was imperative to execute a survey around the main requirements.
As a result of this analysis, several requirements were accounted
for. Despite the identification of many detailed requirements, only
the main ones were listed:
a) Automatic handling of the vertical wires to the winding
station;
b) Automatic handling of the spine to the winding station;
c) Automatic handling of the spine after the previous
workstation (hook workstation);
d) Automatic feeding and handling of the lower wire;
e) Final station / Automatic transfer between all stations.
Solutions
To meet all requirements mentioned before, a strategy was
defined for the optimization to be possible. As said before, the
line is characterized by having two workers that complete the
unfinished tasks of the line and, thus, the design strategy focused
on the respective stations. Therefore, the optimization process was
divided in two different moments: one in the winding workstation,
where the first worker is located and at the staples workstation,
where the second worker operates.
Phase 1-Winding Workstation
At this station, the worker assembles two components:
the vertical wires (vertical workstation) and the central spine
(spine workstation). The handling of the two components is also
performed by the worker.
Before these two phases and leading to support the manual
handling elimination between some workstations, a new layout was
set. The spine and vertical wires workstation, which was located
outside of the suspension mat assembly process flow is now in a
position to improve concepts for handling the components without
manual operations.
a) Vertical Wires Automatic Handling to the Winding Station
A handler was designed between the spine and the winding
workstation, aiming to copy the manual handling movements of
the suspension mat spine performed by the worker. Indeed, all
systems and concepts idealized in the production line to help the
optimization of a fully automated line were applied to replicate
the same operations performed by the worker. To proceed with
the idealized handler concept, it was necessary a study about the
best movement sequence between workstations. Special care has
been taken to avoid collisions. If in one hand the handler must fulfil
the movement sequence, on the other hand it cannot compromise
the workstations operation. To complete the task, the handler was
assembled in the existing transfer which, in this stage, transfers
the product to one more workstation (Figure 3). It is important to
remember that, at the beginning, this transfer only carried out the
handling between three workstations.
Figure 3: Spine handler assembled in transfer - handler was implemented in the main transfer in order to simplify the number
of movements.
b) Spine Automatic Handling to the Winding Station
Similar attention in handling the vertical wires to the winding
workstation was taken. A simple handling system was considered,
which follows a “pick & place” philosophy. This system executes a
movement at the same alignment and only has to transport the wire
from one location to another. A study was carried out to make the
alignment possible and to avoid collisions, aiming to keep the system
as simple as possible. Changes in the vertical wires workstation had
to be made because the position of the vertical wire is not equal
between the two workstations, so this difference could comprise
the “pick & place” philosophy. Changes in the workstation and the
automatic handling system of the vertical wires were successfully
implemented (Figure 4).
Figure 4: Implemented “Pick & place” philosophy - it was possible to develop a compact system to connect two workstations
with this philosophy (vertical wires and winding workstations).
Phase 2-Staples Workstation
After the conclusion of the first phase, attention was focused
on the second phase. The worker assembles two components in
this workstation: the subassembly of the suspension mat arriving from
the hook workstation and the lower wire. As in the first phase
the manual operations carried out by the worker were studied to
complete the migration to a fully automated line.
a) Automatic Handling of the Spine after the Previous
Workstation (Hook Workstation)
The communication between the hook and staples
workstations was studied in detail. The existing space between
the two workstations was eliminated, and an optimized layout
was achieved with the removal of this useless area in the line. The
staples workstation was moved closer to the hook workstation, and
the handling is now made by the main transfer.
b) Automatic Feeding and Handling of the Lower Wire
At this point, the necessary conditions for the automatic feeding
and handling of the lower wire were created. The idealized structure
to allocate and feed the lower wire to the line allows the continuity
of the line as long as possible. The feeding control is assumed by a
system that only provides one lower wire when it is requested. To
take the lower wire outside of the feeder area, a table was created
below the feeder, which creates the proposed conditions, receiving
and moving the lower wire with a linear motion, waiting for its
removal. To perform the removal and the transport of the lower
wire between the feeder and the final position at the workstation, a
handler was idealized. Once again, a “pick & place” philosophy was
adopted, which is the simplest and fastest solution to perform this
operation (Figure 5).
Figure 5: Communication system between workstations - once again “Pick & place” philosophy was adopted.
At the same time, and to complete the implementation of the
lower wire feeding, it was necessary to define the best position for
the feeder and handler set. As in the vertical wire workstation, the
feeding of the lower wire is perpendicular to the process flow of
the suspension mat, hereupon the only decision to be made was to
move the feeder and handler to the front or to the back of staples
workstation. Trying to avoid collisions with a pair of automatic
staplers existing in the station, and to keep the system as simple as
possible, the feeder and handler set was placed at the front of the
workstation.
Figure 6: Applied concepts in the final station: a) Suspension mat collecting system at the final workstation; b) Automatic
transfer between workstations.
c) Final Station / Automatic Transfer Between All Stations
At the final of the suspension mat assembly, necessary
conditions to remove the final set were created. After the staples
workstation, a new station was implanted aiming to receive and
collect a number of final suspension mat (Figure 6). In order to avoid
mechanical or pneumatic support and using only gravity to move the
suspension mat, a simple structure was designed. To handle the
complete suspension mat to the final station a handler was used as
the existing ones in the transfer. The transfer is now able to handle
the suspension mat between all workstations. Indeed, the line was
successfully migrated to a fully-automated line with the idealized
solutions.
Conclusion
The idealized concepts described in the case study have been
useful to achieve the proposed goals and helped the complete
migration for a fully-automatic line. The proposed solutions were
based on careful studies on the worker movements, especially in
the handling operations. At the same time, the studies executed
before the improvements of the final solutions avoid situations
like collisions that could compromise the project implementation.
Besides the automation be an area with relative complexity, it was
possible to prove that with simple concepts it is possible to solve
problems that originally seemed complicated. Indeed, was possible
to improve the level of automation and increased the productivity
of the line using low cost and simple solutions. The cost/benefit
ratio of the solutions is quite important for the final decision. With
the replacement of the manual operations by simple and automatic
systems, it was possible to transform an inadequate behaviour on
the flow process registered in the initial production line scenario
in a stable and fluid process, eliminating, among others, possible
stops due to lack of materials.
As every automatic migration process, a strategy must be chosen
and one of the key points that are questioned is the elimination
of the human resources. The elimination of manual stations and
the replacement of manual by automatic operations do not imply
the dismissal of the worker from the company. Actually, this is an
opportunity for both the workers and the company. The worker
assumes new functions with higher value and the company benefits
by keeping the worker away from repetitive tasks and movements
that could be easily replaced by automatic systems. Regarding the
new production system now developed, it is expected an increase
in the production rate of about 18%, a completely cut of the human
labour costs and an increase in the quality level of around 15%. The
payback time was estimated in 21 months, i.e., clearly shorter than
the expected lifetime expected of the product (about 60 months for
this model).
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