The Influence of Assembly Workplace Layout on Ergonomics

VÁCLAV ŠTEFAN, KAMENSZKÁ ADRIANA

Institute of Production Technologies

Slovak University of Technology, Faculty of Materials Science and Technology

Jána Bottu 2781/25, 917 24 Trnava

SLOVAKIA

Abstract: - Assembly is an important element in the production process. It largely influences the quality of the

product and especially the time required to produce the final product. Studies in the field of assembly show that

as technology advances, it is necessary to use new improvements at each stage of production, which includes

the assembly stage. The aim of every enterprise should be to make the best and most economical use of all the

resources at its disposal, on the one hand, and to increase productivity, on the other. Nowadays, ergonomics

must be taken into account when solving problems or rationalizing assembly, since most assembly operations

are carried out manually. In the theoretical part of the document, the assembly process is described together

with the factors that influence it, focusing on manual assembly and its impact on ergonomics. The practical part

describes an experiment carried out with the aim to increase the ergonomics of workers and to make the

assembly process more efficient at an assembly workplace in a selected industrial enterprise through pre-

arrangement of the workplace.

Key-Words: Assembly Process, Manual Assembly, Ergonomics, Workplace Design, Layout, Experiment

Received: June 21, 2021. Revised: March 15, 2022. Accepted: April 14, 2022. Published: May 7, 2022.

1 Introduction

The assembly process consists of assembly

operations of joining components into units

(assembly nodes, groups) and final products [6][3].

It is realized in a specific technically and

economically expedient sequence. From the point of

view of organization, assembly can also include

preparatory, auxiliary, and service activities. These

not only support the assembly process, but also

rationalize it. Assembly processes are carried out

according to predetermined rules and take place in

specific technical, technological, organizational and

economic conditions [7].

If the assembly process needs to ensure

successful goal-directed behaviour, its goal-directed

design is already essential. If the assembly process

already exists, it needs to be innovated or

rationalized. For this reason, a thorough knowledge

of the various factors that influence the assembly

process and its design is important. It is also

necessary to take into account the interactions and

interrelationships between the different factors. The

assembly process is strongly influenced by factors

that can be summarized in 5 groups [9]:

1) Properties of the object of

assembly/assembled product –

dimensionality, weight, complexity, etc.

2) Production conditions – in particular the

level of preparation of design and

technological documentation, the total

number of pieces, the length of the period,

the seriality

3) Workforce – number of workers, demands

on their expertise, physical and mental

workload

4) Work resources – types, number, level of

automation

5) Process organization and management –

applied organizational form of assembly,

division of labour, etc.

In addition to the factors mentioned above,

automation also has a significant impact on the

assembly process. According to the degree of

automation, the assembly process can be divided

into [1]:

- Manual Assembly

- Mechanised Assembly

- Automated Assembly

The basic structural unit of assembly processes is

the assembly operation, which is carried out at the

assembly site. The organisation of assembly

processes has a strong influence on the realisation of

assembly. The main task of the organisation is to

ensure the appropriate temporal, spatial and material

progression of the assembly process [14].

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The big trend today is to increase assembly

efficiency through automation, but many companies

still have a number of assembly tasks that require

human input. This means that even in today's

"automated age" there is still manual assembly [10].

2 Ergonomics in Manual Assembly

2.1 Manual Assembly

Manual assembly is the traditional, in some cases

(from a technical and economic point of view)

necessary way of joining components, assemblies

and units. In manual assembly, a worker assembles

previously manufactured components and/or sub-

assemblies into a complete product or product unit.

This type of assembly uses mainly the energy of the

worker's hands. Manual assembly has the following

characteristics [3]:

- the use of simple fixtures,

- use of universal assembly tools,

- alignment of the parts to be joined,

- economical handling and transport of

handled parts,

- ergonomically optimal workplace of the

worker.

The work activity that is carried out in such

workplaces is characterized by monotony and work

at a forced work pace. Simply put, the worker is not

free to choose the work pace and his/her activity is

subordinated to the rhythm of the work process

and/or the rhythm of other workers in the process

[11].

The trend in designing or innovating assembly

workplaces is precisely the ergonomic aspect, which

addresses the interaction of the worker and his

working environment to increase work productivity,

efficiency and, last but not least, work safety [13].

2.2 Ergonomics

Ergonomics is a field focused on human factors

and describes the scientific consideration of working

conditions, particularly with respect to the physical

and mental characteristics of human operators,

abilities, limitations, and needs [8].

The main goal of ergonomics is to preserve

human health, i.e., his physical, mental, and social

satisfaction, to create optimal conditions for the

performance of his work and to ensure his well-

being at work. In addition to these factors, the use of

ergonomic principles also has a positive impact on

economic indicators. These are directly influenced

by a reduction in the cost of sick leave, accident

rates, an increase in a person's performance capacity

and, consequently, an increase in labour

productivity [4]. According to the authors

Gilbertová & Matoušek, a person's executive

capacity is affected by [2]:

a) sensory capacity – includes primarily the

function of sight and hearing

b) mental capacity – its basis is the intellectual

level of a human

c) human adaptation to working conditions – it

is influenced by several factors, such as the

type and content of work activity, the risk

associated with work, the work and rest

regime and the social climate at the

workplace

As we mentioned in the previous section, there

are still many assembly activities that must be

performed by a human. Figure 1 shows the elements

of the working system that affect the level of

manual assembly from an ergonomic point of view

[12].

Fig. 1 Elements of a Working System [12]

When designing or upgrading assembly

processes and workplaces with regard to manual

assembly, the following areas must be addressed

from a human perspective [11]:

- organisation of working movements -

elimination of complex and strenuous

movements

- physical and psychological stress at work

- work and rest regime

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- dimensional and spatial arrangement of the

workplace - elimination of redundant

walking of the worker, shortening of

travelled paths

It is the area of dimensional and spatial

arrangement of the workplace that can largely affect

the ergonomics of the assembly worker in the form

of excessive walking during the assembly process.

3 Description of the Current State of

the Assembly Workplace

3.1 Assembly Workplace Layout

The subject of the experiment is the assembly

workplace of piston valves, which are part of the

construction of hydraulic dampers. The assembly

workplace concentrates on manual assembly and

can therefore be classified as one of the more

dimensionally compact workplaces. The workplace

consists of 5 sections:

1. Section for part pre-assembly

2. Section for part crimping

3. Lubrication section of the component

4. Final part testing and packing section

5. Expedition

The overall layout of the assembly workplace

along with the workplace elements are shown in

Figure 2, which represents the layout of the

workplace.

Fig. 2 Layout of the Assembly Workplace

The pre-assembly section consists of two

workbenches. On the first table, connected to the

rack, manual pre-assembly of the part is carried out

according to the BOM. The second assembly table

houses the equipment for assembling the gasket.

The pressing section is equipped with one

hydraulic press, on which 3 pressing operations of

the part are performed in sequence. The assembly

section includes two auxiliary trolleys on which the

parts are placed before and after the pressing

operation.

Next is the lubrication section, which houses the

equipment by means of which the lubrication of the

part of the component is carried out. This part of the

component is very important and necessary for the

complete assembly of the valve and its functionality.

The last section where the assembly operation is

carried out is the section of testing and packaging of

components. The first part of the section is the

equipment that is needed to test and check the

functionality of every single assembled component.

The second part of the section is the workbench on

which the functional parts are packed into boxes of a

certain number of pieces.

3.2 Description of the Component Assembly

Process

The assembly process begins with the first

operation, namely the pre-assembly of the

component on the first assembly table. The worker

removes the prescribed number of components from

the boxes according to the BOM and inserts them

successively on the individual pins of the assembly

pallet. The assembly pallet is a plastic tool of certain

dimensions from which 10 pins protrude. These pins

are used to 'thread' the components one by one

according to the type of component. Assembly is

always carried out on one pallet only, with a

capacity of 10 components. After the first operation,

the worker moves with the pallet to a second table,

where a seal is applied to each stacked part. The

seals are assembled with the aid of the machine.

In the next part of the assembly, a worker with a

pallet of pre-assembled parts passes to the pressing

section. The pressing operation is carried out on one

piece of equipment and is divided into:

- Pressing operation I. – Crimping

- Pressing operation II. – Hard characteristic

- Pressing operation III. – Fine characteristic

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Each pressing operation is different, depending

on the jigs used and also the pressing pressure

settings. Therefore, it is necessary that the entire

pallet, i.e. 10 pieces, goes through each pressing

operation. The worker then changes the jigs, adjusts

the equipment and proceeds with Pressing operation

II. However, Pressing operation II. and Pressing

operation III. do not follow directly after each other.

After the Pressing operation II. is performed, the

worker with the pallet moves to the next assembly

section, namely the Lubrication Section. This

assembly operation involves the application of

lubricant to a critical component of the part. The

lubricant is applied to the component by a special

automatic device.

After this operation, the worker returns to the

Pressing Section to complete the last pressing

operation of the part.

The whole assembly process is completed by

final testing and packaging. The individual

components are tested on special test equipment.

The equipment tests the oil flow through the valve.

This operation is important from a quality point of

view. Every single assembled component is tested

on the equipment to meet all quality principles. The

parts are then packed by a certain number of pieces

into boxes that are moved for shipment - palletized.

3.3 Definition of the Issue of Current State

Based on the information from the enterprise and

the observation made during operation, the

following details of the assembly site were

summarized:

- the assembly workplace is set up for two-

shift operation, with each shift lasting 7.5

hours = 450 minutes of networking time,

- the production of one shift is set to 140

pieces of manufactured parts,

- each component goes through a total of 5

sections and 7 assembly operations,

- the parts go through the process on pallets =

pallet capacity is 10 parts,

- the worker goes through the entire assembly

process a total of 14 times to meet the shift

production quota.

Following the literature review of the paper and

the stated objective of the experiment, the focus of

the above-mentioned requisites is on the total path

travelled by the worker during the work shift, which

is directly affected by the layout of the assembly

workplace. Figure 3 shows the layout of the

assembly workplace, which illustrates the paths

between each operation that a worker must complete

to accomplish the complete assembly process. The

assembly process paths are marked in sequence,

following the established assembly sequence.

Fig. 3 Layout of the assembly workplace with paths

In terms of ergonomics, the number of steps was

observed and analysed, and the length of the

routes in meters were determined by mathematical

calculation. In the calculation, we considered an

employee step length of 1 step = 0.7 m, which was

obtained by calculating the arithmetic average of the

step lengths of five different employees. The

obtained and recalculated values of the individual

assembly workplace routes in meters and number of

steps per shift in the current state are shown in Table

Tab. 1 Current State of Workplace

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3.4 Conclusion from the Analysis of the

Current Situation

In the current chapter, we have analysed and

described the current state of the piston valve

assembly workplace. Based on the information from

the company and the observation made by us, it can

be concluded that not only time is lost in the

assembly process at the workplace, but especially

the redundant walking of the worker is caused by

the inefficient layout of the workplace.

4 Assembly Workplace Design

In order to ensure that the current state of the

assembly workplace was made more efficient from

an ergonomic point of view, certain changes and

measures had to be introduced. The most significant

change that would go a long way towards achieving

the stated objective in the workplace is the use of a

different type of assembly workplace or a

modification of the layout of the assembly

workplace. This assertion is proven by the

experiment carried out.

4.1 Experimental Setup

The following design is made to eliminate the

number of worker steps and thus make the

workplace ergonomics more efficient. The future

state of the workplace layout is visualized in a

similar way to the current state.

In Figure 4, a layout for the future state of the

piston valve assembly site is developed. The

workplace is re-arranged, with the change in layout

depending on the sequence of the different

operations of the assembly process.

In order to verify the correctness and

functionality of the incorporated changes, the

rationalization tool - the Spaghetti Diagram - has

been re-used in the proposal. Subsequently, an

individual pathway analysis was performed, Table

2. The evaluation criteria were the same as in the

current state, both the number of steps travelled, and

the length travelled in meters.

Fig. 4 Layout for the future state with paths

Tab. 2 Future State of Workplace

4.2 Evaluation of the Experiment

Having analysed the proposal, we have

concluded that the incorporation of the proposed

changes will achieve the expected positive change in

the workplace. If the proposal is applied, there will

be a reduction in the number of steps and also a

47.5% reduction in worker routes. This change can

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translate into a saving of approximately 51

kilometres in an ideal production year. The

comparison of the individual routes in meters but

also the differences in the number of steps of the

current and future state are visualized through the

graphs in Figure 5.

Fig. 5 Comparison of Current and Future State

5 Conclusion

Manual assembly is a work activity that causes

physical and mental strain on the worker. It should

be a priority for every company to reduce this

burden. In order to achieve ergonomic efficiency,

appropriately chosen ergonomic measures can create

conditions in the workplace in which the worker is

able to perform at an increased level and at the same

time contribute to an increase in labour productivity.

One measure is to make the assembly workplace

more efficient.

The aim of the experiment was to increase the

ergonomics of the worker at the workplace and to

make the assembly process more efficient through

the pre-arrangement of a manual assembly

workplace in a selected industrial enterprise.

One of the rationalization tools called Spaghetti

diagram was used to analyse the current situation

and to verify the correctness of the assembly

workplace design. By using the diagram

appropriately, the assembly workplace and the

assembly process itself can be analysed and efficient

and inefficient routes can also be identified.

Using the diagram, the wastage in the current

state at the assembly site was identified.

Consequently, changes to the workplace layout were

proposed and implemented with a view to

improving ergonomics. The final part involved

verifying the functionality of the design in practice.

Thus, based on the results of the verification, it can

be stated that the new layout and routing eliminated

redundant walking of employees by up to 47.5%,

thus ensuring process efficiency and increased

ergonomics at the selected assembly workplace.

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Contribution of individual authors to

the creation of a scientific article

(ghostwriting policy)

The authors Štefan Václav and Adriana Kamenszká

prepared both the theoretical and practical parts of

the article together.

Follow: www.wseas.org/multimedia/contributor-

role-instruction.pdf

Acknowledgements

The contribution is sponsored by the project

VEGA 1/0019/20: Accurate calculations, modelling

and simulation of new surfaces based on physical

causes of machined surfaces and additive

technology surfaces in machinery and robotically

machining conditions.

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