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POLITECNICO DI MILANO

Scuola di Ingegneria Industriale e dell’Informazione

Corso di Laurea Magistrale in Ingegneria Biomedica

ASSESSMENT OF ASSEMBLY AUTOMATION FOR

PLASTIC MEDICAL DISPOSABLES: FROM STATE

OF THE ART TO FUTURE TRENDS

Supervisor: Prof. Ing. Maria Laura Costantino

Tutor: Dr. Ing. Massimo Cappello

Dr. Alessio Stefani

Master thesis of:

Ashkan Shiravand 893533

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Before everything I would like to thank my supervisor Prof. Maria Laura Costantino for the opportunity she gave me to work under her supervision.

Very special thanks to Dr. Alessio Stefani and Dr. Ing. Massimo Cappello who supported me with their knowledge and experience during the development of this work.

I would like to show my appreciation to SisTer S.p.A that gave me this opportunity to develop this thesis with a close relationship with industry.

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I

INDEX OF CONTENTS

Index of figures ... IV Index of tables ... V ABSTRACT ... VI SOMMARIO ... IX INTRODUCTION ... 1 Automation ... 1 1.1.1 History ... 2

1.1.2 Economic aspects of automation ... 4

Advantages and disadvantages of automation ... 5

Industrial production automation ... 7

1.3.1 Types of Automation systems ... 7

1.3.1.1 Fixed Automation ... 8 1.3.1.2 Programmable Automation ... 8 1.3.1.3 Flexible Automation ... 8 1.3.2 Handling systems ... 8 1.3.3 Packaging systems ... 9 1.3.4 Assembly systems ... 10

1.3.5 Inspection and test systems ... 10

Assembly ... 11

Assembly technologies for plastics ... 11

2.1.1 Welding Processes ... 12

2.1.1.1 Friction welding ... 12

2.1.1.1.1 Spin welding... 12

2.1.1.1.2 Vibration welding... 14

2.1.1.1.3 Ultrasonic welding ... 16

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II

2.1.1.2 External heat source welding ... 21

2.1.1.2.1 Hot plate welding ... 21

2.1.1.2.2 Infrared welding ... 23

2.1.1.2.3 Laser welding ... 25

2.1.1.2.4 Radio frequency welding ... 27

2.1.1.2.5 Heat sealing (Hot bar/Impulse welding) ... 29

2.1.1.3 Implant heating welding ... 30

2.1.1.3.1 Induction welding... 30

2.1.1.3.2 Resistive implant welding ... 31

2.1.1.3.3 Microwave welding ... 32

2.1.2 Solvent welding ... 33

2.1.3 Adhesive bonding ... 36

2.1.4 Mechanical Joining ... 43

2.1.4.1 Molded-in Threads ... 43

2.1.4.2 Press fit/Snap fit ... 44

2.1.4.3 Staking ... 45

Assessment of automated assembly ... 47

Assembly automation importance ... 49

Types of manufacturing process ... 50

Assembly platforms and cycle time ... 52

Quality check techniques ... 54

Comparison of assembly technologies... 55

Conclusion ... 61

Appendix A – Automation Companies ... 64

Appendix B – Questionnaire ... 72

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IV

Index of figures

Figure 1. Control loop ... 1

Figure 2. Production line components ... 7

Figure 3. Conveyors ... 9

Figure 4. Plastic joining techniques ... 11

Figure 5.Spin welded cosmetic and medical devices ... 14

Figure 6. Ultrasonic welded medical devices ... 19

Figure 7. Medical filters ... 23

Figure 8. Laser welded medical devices ... 26

Figure 9. Impulse welding schematic ... 29

Figure 10. Induction welded medical devices ... 31

Figure 11. Solvent dispenser for joining medical equipment, tubes and joints ... 34

Figure 12. a. PVC tube to rigid port solvent welded in IV set b. Stopcock with tube solvent welded ... 36

Figure 13. Costumizable dispensing cell ... 38

Figure 14. UV spot curing system ... 39

Figure 15 Adhesive bonded medical plastics ... 42

Figure 16. LED-curable adhesive for assembling medical plastic ... 43

Figure 17. Automatic screwdriver ... 44

Figure 18. Medical disposables threaded parts ... 44

Figure 19. Medical connectors' snap fit designs ... 45

Figure 20. Heat staking ... 46

Figure 21. Distribution of medical manufacturing system suppliers ... 47

Figure 22. Company evaluation criteria based on internal FMC experience ... 48

Figure 23. Importance of assembly automation on different factors for medical disposable industry .... 49

Figure 24. Medical device industry spending trend on assembly automation ... 50

Figure 25. Distribution of automation level for medical device manufacturing systems ... 51

Figure 26. Distribution of assembly platforms for plastic medical disposables ... 52

Figure 27. Distribution of assembly rates for plastic medical disposable projects ... 53

Figure 28. Distribution of quality check techniques for plastic medical disposable projects ... 55

Figure 29.Application distribution of plastic joining techniques for medical disposables ... 58

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V

Index of tables

Table 1. History of automation ... 3

Table 2. Material weldability for spin welding ... 13

Table 3. Material weldability for vibration welding ... 15

Table 4. Material weldability for Ultrasonic welding ... 17

Table 5. Ultrasonic welding application in various industries ... 18

Table 6. Weld strength efficiency for friction stir welding ... 21

Table 7. Material weldability for hot plate welding ... 22

Table 8. Material weldability reports for infrared welding ... 24

Table 9. Material weldability for laser welding ... 27

Table 10. Material weldability for radio frequency welding ... 28

Table 11. Industrial application of induction welding ... 31

Table 12. Solvent compatibility for similar plastics ... 35

Table 13. Solvent compatibility for joining different plastics ... 35

Table 14. Surface treatment prior to adhesion ... 37

Table 15. Adhesives used for plastics ... 41

Table 16. Advantages of plastic joining techniques ... 56

Table 17. Disadvantages of plastic joining techniques ... 57

Table 18. Automation suppliers ... 71

Table 19. Manufacturing system types ... 72

Table 20. Assembly automation importance ... 72

Table 21. Plastic joining techniques vs application frequency ... 73

Table 22. Plastic joining techniques versus assembly rate... 73

Table 23. Application frequency of different assembly rates ... 74

Table 24. Application frequency of different assembly platforms ... 74

Table 25. Application frequency of different quality check systems ... 74

Table 26. Advantages of joining techniques ... 75

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VI

ABSTRACT

A manufacturing system is a part of the production line consists of different equipment as well as labors that their integration results in processing and assembly operations on the part to produce the final product. These systems can operate manually, semi- or fully-automated.

Nowadays, while technology is progressing at an extremely high-speed, automation in various industries concerns about factory automation (FA) for automatic mass production of a single product to increase the rate and quality of production.

Final products are usually composed of different individual components made of various materials integrated within the manufacturing process. Lightweight and high-efficiency features of plastics have attained attention to replace metallic parts of manufacturing products. Integration of material handling, assembly technologies, and many other processes assemble these components. After the components are placed accurately in close contact, they may be connected by many different assembly technologies.

Plastic medical disposables are made of

sub-components which must be joined by assembly technologies during the production processes. Therefore, medical disposable manufacturers including SisTer S.p.A that produces dialysis disposables have been always looking for state of the art of automated assembly technologies and reputable suppliers to apply the latest techniques for their production purposes.

The selection of the most efficient technology concerning industrial demand is a challenging process that must be evaluated by an expert in assembly technologies applied for different plastic materials. Plastic components can be joined by four main techniques as welding, solvent bonding, adhesive bonding, and mechanical joining.

In Chapter 2 each assembly technology has been elaborated by focusing on the following concepts: process function, advantages and disadvantages, common materials joined by such techniques, integration into an assembly line, latest conversions and their capability to join medical plastics especially for medical disposable industry. This chapter gives practical insights to a medical disposable manufacturer to make their very first step decision about the potential assembly

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Abstract

VII technologies that they can apply for their

specific joining application.

Welding can provide a permanent joint stronger than initial components material by application of heat and/or pressure. Versatile welding processes include friction welding, external heat source welding, and implant heating welding. Friction welding techniques exploit the heat generated by reciprocated rubbing of two components to melt the part surfaces and to form a hermetic seal. This process is usually facilitated by vertical force while two components are held together. The main drawback of friction welding is particulate formation during reciprocated rubbing. Spin welding, vibration welding, ultrasonic welding, and friction stir welding are the typical friction welding techniques.

Welding of two components by use of an external heat source to generate heat at the joint surface while two components are held together by clamping pressure subdivides into several methods based on their energy source as hot plate welding, infrared welding, laser welding, radio frequency welding, and hot bar welding. Implant heating welding relies on the capability of an external component known as an implant to weld joining parts.

The implant is sensitive to energy exposure by which heats and melt plastic components at the joint for subsequent welding. The implant may be heated either electrically as in resistive implant welding or electromagnetically as in induction and microwave welding.

Solvent and adhesive bonding both use additional material at the joint that promotes adhesion. Solvents change the joining surface property for better fusion, while adhesive remains at the joint and bonds the parts itself. Adhesive bonding is more complicated since it needs surface treatment and cure system; nevertheless, both techniques are considered simple and cheap. Mechanical joining of plastics is conducted either by additional components such as screws, bolts, and rivets or by design considerations such as press fits.

The selection of a reliable supplier for the future automated manufacturing system demands of SisTer and understanding the market trend in automated assembly systems for the medical disposable industry were the reasons to screen through 391 automation companies to choose the potential suppliers for automated assembly.

In the following step, a questionnaire was designed to understand the importance of

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VIII assembly automation, types of

manufacturing systems, types of assembly platforms, assembly quality check systems, and trending assembly technologies integrated into medical disposable manufacturing systems. The responses of automation suppliers are discussed in Chapter 3.

The majority of the responses confirms that medical disposable manufacturers tend to apply fully-automated production systems to reduce the costs and increase the productivity and precision of their products. This fact is usually accompanied by using synchronous assembly platforms to meet the relatively high-speed assembly rate of medical disposables with higher distribution in the range of 20-120 parts per minute (ppm).

According to the literatures and automation suppliers’ responses, it can be concluded that ultrasonic welding, laser welding, mechanical joining, and adhesive bonding are the most capable and thereby widely used assembly technologies for joining plastic medical disposables. The application of other assembly technologies based on their specific features and advantages should not be underestimated.

To sum up, the selection of the right technology for joining plastic medical

disposables requires several years of experience to evaluate different technologies available based on their advantages and disadvantages for a specific application by recommended investigation and tests to meet medical device regulations and requirements. Capital cost, cycle time, consistency, material weldability, part geometry, size, complexity, strength, joint cleanliness, and finally a reputable supplier are the parameters that lead to the proper selection of a specific process.

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Sommario

IX

SOMMARIO

Un sistema di assemblaggio è una tipica parte della linea di produzione che consiste in attrezzature che effettuano lavori diversi, la cui integrazione si traduce in operazioni di assemblaggio e lavorazione con l’obiettivo di realizzare un prodotto finito. Questi sistemi possono funzionare in modalità manuale, semi automatica e completamente automatica. Al giorno d'oggi, mentre la tecnologia sta progredendo ad altissima velocità, l’automazione nei vari settori consiste nel “Factory Automation” (FA), ovvero nella produzione di massa in modo automatico di un unico prodotto per aumentare il tasso e la qualità della produzione.

I prodotti finiti sono generalmente composti da diversi componenti singoli realizzati con vari materiali e integrati nel processo di produzione. Le plastiche hanno catturato l’attenzione per la loro leggerezza ed alta efficienza a tal punto da sostituire alcune parti metalliche dei prodotti di fabbricazione. L’integrazione della movimentazione dei materiali, delle tecnologie di assemblaggio e di molti altri processi consente l’assemblaggio di questi componenti. Dopo che i componenti sono stati posti accuratamente in stretto contatto, possono essere poi uniti da diverse tecnologie di assemblaggio.

I dispositivi medici in materiale plastico sono costituiti da sottocomponenti che, durante i processi di produzione, devono essere assemblati per mezzo di varie tecnologie di assemblaggio. Pertanto, i produttori nel settore biomedicale, tra cui SisTer S.p.A che produce dispositivi medici per la dialisi, sono sempre alla ricerca dello stato dell'arte di tecnologie di assemblaggio automatiche nonché di fornitori affidabili per l’applicazione di quest’ultime al fine di raggiungere i loro scopi.

La scelta della tecnologia più efficiente in applicazioni industriali è un processo impegnativo che deve essere valutato da un esperto di tecnologie di assemblaggio specifiche per i diversi materiali plastici. I componenti in plastica possono essere assemblati per mezzo di quattro tecnologie principali: saldatura, incollaggio con solvente, incollaggio con adesivo e giunzione meccanica.

Nel Capitolo 2 ogni tecnologia di assemblaggio è stata esaminata concentrandosi sui seguenti concetti: funzione del processo, vantaggi e svantaggi, principali materiali uniti da tali tecniche, integrazione in una linea di montaggio, ultime conversioni e la loro capacità di unire le plastiche medicali, soprattutto per l'industria dei dispositivi medici. Questo capitolo fornisce al

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X produttore di dispositivi medici

informazioni pratiche e necessarie, specie nella prima fase decisionale, per la scelta delle potenziali tecnologie di assemblaggio che possono essere applicate ad una specifica unione di parti. Con la saldatura si può ottenere un giunto permanente più resistente dei componenti iniziali e si ottiene mediante l'applicazione di calore e/o pressione. I processi di saldatura versatili includono la saldatura ad attrito, la saldatura a caldo e la saldatura ad impianto riscaldante.

Le tecniche di saldatura ad attrito sfruttano il calore generato dallo sfregamento reciproco di due componenti per fondere le superfici del pezzo e formare una tenuta ermetica. Questo processo è solitamente facilitato dalla forza verticale, mentre due componenti sono tenuti insieme. Lo svantaggio principale della saldatura ad attrito è la formazione di particolato durante lo sfregamento reciproco. Saldatura rotante, saldatura a vibrazione, saldatura a ultrasuoni e saldatura a frizione sono le tipiche tecniche di saldatura ad attrito.

La saldatura di due componenti è ottenuta mediante una fonte di calore esterna che genera calore sulla superficie del giunto, mentre i due componenti sono tenuti insieme. Questa saldatura si suddivide in

diversi tipi a seconda del tipo di fonte di energia esterna utilizzata e per cui si possono avere: saldatura a lama calda, saldatura a infrarossi, saldatura laser, saldatura a radiofrequenza, saldatura ad impulsi o a barra calda.

La saldatura ad impianto riscaldante si basa sulla capacità di un componente esterno, noto come impianto, di saldare le parti di giunzione. L'impianto è sensibile all'esposizione energetica per cui si riscalda e fonde i componenti in plastica del giunto creando la saldatura. L'impianto dunque può essere riscaldato elettricamente nel caso della saldatura resistiva o elettromagneticamente come nel caso della saldatura a induzione e quella a microonde.

Solvente e adesivo sono utilizzati come additivi in corrispondenza del giunto al fine di promuovere l’incollaggio dei componenti. I solventi modificano la proprietà della superficie di giunzione per una migliore fusione, mentre l'adesivo rimane nel giunto e unisce le parti stesse. L'incollaggio con adesivo è più complicato in quanto necessita di un trattamento superficiale e di un sistema apposito che permetta di finalizzare l’incollaggio (luce, plasma, calore etc.); tuttavia, entrambe le tecniche sono considerate semplici ed economiche. La giunzione delle plastiche può avvenire

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Sommario

XI anche meccanicamente ed è effettuata sia

utilizzando componenti additivi come viti, bulloni e rivetti, sia facendo delle considerazioni progettuali come innesti a pressione.

Al fine di individuare i fornitori potenziali per le future richieste dei sistemi di produzione automatizzati di SisTer è stata effettuata una selezione tra 391 aziende di automazione basandosi su due punti fondamentali: affidabilità del fornitore e tendenza di mercato riguardo i sistemi di assemblaggio automatizzato per l’industria dei dispositivi medici.

Nella fase successiva, è stato elaborato un questionario per comprendere l'importanza dell'automazione nei processi di assemblaggio, i tipi di sistemi di fabbricazione, i tipi di piattaforme di montaggio, i sistemi di controllo della qualità nell'assemblaggio e le tecnologie di tendenza integrate nei sistemi di produzione dei dispositivi medici. Le risposte dei fornitori sono discusse nel Capitolo 3.

La maggior parte delle risposte confermano che i produttori dei dispositivi medici tendono ad applicare sistemi di produzione completamente automatizzati per ridurre i costi, aumentare la produttività e la precisione dei loro prodotti. Questo fatto è di solito associato

all’utilizzo di piattaforme di assemblaggio sincrone che soddisfano il tasso di velocità elevata richiesto nell’assemblaggio dei dispositivi medici, con una maggiore distribuzione nel range 20-120 parti per minuto (ppm).

Inoltre, secondo la letteratura e le risposte dei fornitori, si può concludere che la saldatura ad ultrasuoni, la saldatura laser, la giunzione meccanica, e l’incollaggio con adesivo sono le tecnologie di assemblaggio più efficaci e quindi ampiamente utilizzate per l'unione delle plastiche medicali. Tuttavia, non va sottovalutata l'applicazione di altre tecnologie di assemblaggio basate sulle loro caratteristiche e vantaggi specifici. Riassumendo, la scelta della giusta tecnologia per assemblare i materiali plastici medicali richiede diversi anni di esperienza per valutare le diverse tecnologie disponibili in base ai loro vantaggi e svantaggi per una specifica applicazione, ma anche molto tempo per effettuare le indagini e i test per soddisfare le normative e i requisiti dei dispositivi medici. Infine, i parametri che portano alla corretta selezione di un processo specifico sono i costi del capitale, i tempi ciclo, la costanza, la saldabilità dei materiali, la geometria delle parti, le dimensioni, la complessità, la resistenza, la pulizia del giunto e un fornitore affidabile.

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1

INTRODUCTION

Automation

Automation is a combination of two Greek words “Auto” and “Matos” which means self-moving and describe any system and mechanism with the ability of self-movement having more effective performance in terms of precision, accuracy, rate, and strength.

According to Encyclopedia Britannica automation refers to the application of integrated machines to manual or impossible tasks, while mechanization often refers to the simple replacement of human labor by machines.

Automation refers to any automatic operation and activity with minimal incorporation of the human being as a way for humans to extend the capability of their tools and machines. Two meanings are defined for the automation terminology: 1. Automatic regulation by feedback, and 2. Integration of several machines [1]. The second meaning deals with the automatic production of any type of goods in a manufacturing system.

The inclusion of logical programming commands to control and guide the integrated machines and equipment is the primary concept of automation which reduces manual activities and responses. Subsequently, it eliminates human sensory and mental requirements [2].

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Chapter 1 Introduction

2 Automation has been achieved by the cooperation of different systems including mechanical, hydraulic, pneumatic, electrical, electronic devices, and computers. In a control loop, the comparator compares the feedback signal coming from the sensor with a desired input value and based on the error obtained in this step, controller makes an action on the system to achieve a desired variable. Figure 1 illustrates the schematic of a simple control loop. Nowadays, while technology is progressing at an extremely high-speed, automation in various industries concerns about factory automation (FA) for automatic mass production of a single product to increase the rate and quality of production.

1.1.1 History

Human being has been always trying to simplify and facilitate the daily life activities. Therefore, tools started to be included in human life for the past million years ago. Many years later people tried to incorporate simple machines capable to transmit a force to conduct mechanical operation. Later, these machines were used in manufacturing systems which led to efficiency improvement.

After the industrial revolution, the introduction of the interchangeability principle accompanied by machine developments enhanced mass production. Several automated tools were produced in this period such as mechanical clocks, boilers, mills, windmills, etc. This movement is called automatization and led to the manufacturing of the first fully automated spinning mill called water frame in 1771 followed by the invention of flour mills in 1785 [3].

By the advancement of electronics and control engineering in the 20th century another revolution based on factory electrifications and electrical control of tools happened, however, the demand for basic control of devices was still under the responsibilities of skilled workers. For instance, workers followed the production charts and corrected the manufacturing processes by manual interventions such as valve switching until the controllers were introduced.

Introduction of electrification in manufacturing companies opened a new period for mass production in industries and the terminology of automation was introduced by Ford company in 1936 [1] followed by their first fully automated production system. Finally, after the advancement of different manufacturing technologies, including CAD/CAM, industrial

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3

4 million Advent of tools 1900 Hydraulic/Electric copy machines in Italy

532 BC Lathe 1913 Car assembly by Ford in USA

285-222 BC

Pneumatic machines such as water clock 1920 Introduction of robot Terminology by Capek in Czechoslovakia

10-70 BC Theater automata and aeolipile 1923 Copy shaper by Keller in USA

6 BC Mass production 1924 Transfer machine by Morris motor in UK 6-2 BC Machine tools 1924-26 Carbide tool by Krupp in Germany 1 BC Heron automatics in Greece 1930 Numerical control initiation in USA AD 8 Wind powered automata 1936 Automation Terminology by Harder in

USA

1306 Pin production machine in Germany 1920-40 Transfer machines and mass productions 1495 Leonardo robot 1940 Introduction of first electronic computing

machine 1613 Introduction of mass production principle in

Italy

1945 Numerically controlled milling machine by Kearney and Trecker in USA

1713 Gun drilling machine in Switzerland 1947 First mechanical automation by Ford in USA

1725 Punch card machine 1950 Fully automated press machine by Ford 1736-61 New clocks 1950 Fully automated piston production in

Russia

1737 The first true robot as flute player 1950-60 Process automation in USA

1760 Industrial revolution in UK 1952 Three axis NC milling machine by MIT in USA

1765 Introduction of interchangeability in France 1954 Industrial robot introduction by Devol in USA

1766 Precision mechanics initiation 1958 Automatic programming system in USA 1775 Boring machine by Wilkinson in UK 1958 Machining center by Kearney & Trecker 1778 Conveyor-driven flour mill in USA 1958 Automatic drawing machine by Garber in

USA

1796 First modern factory (Watt) in UK 1960 Adaptive controlled milling machine by Bendix

1797 Screw lathe by Maudsley in UK 1960 Industrial robots 1800 Loom by Jacquard in France 1961 Resistor machining line 1811-12 Appearance of Luddite movement in UK 1962 Coordinate robot 1818 Mechanical copy machine by Blanchard in

UK

1962 2D CAD

1820 Planer in UK 1965 Low cost automation

1835 Automatics by Whitworth in UK 1965 Large scale integrated circuits 1843 Turret machine in France 1967 CAD/CAM software by Lockheed 1855 Universal milling machine by Braun in USA 1968 Programmable logic controllers 1860 Introduction of assembly line principle in

USA

1970 Introduction of integrated manufacturing systems: welding line by robots by General motors

1863 Automatic piano player 1977 Small group assembly without conveyor by Volvo

1864 Cylindrical grinding machine in US 1980 Manufacturing automation protocol (MAP) by General Motors

1873 Automatic screw machine by Spencer in USA

1980s Advent of artificial intelligence

1880-90 Hobbing machine in USA 1991 Intelligent manufacturing system (IMS) project by Japan and USA

1895 Multiple spindle lathe in USA 1990-2000s

Integrated manufacturing systems 1898 High speed steel tool by White-Taylor in

USA

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Chapter 1 Introduction

4 robots, process automation, integrated circuits, and many other technologies, integrated manufacturing systems were introduced by General Motors in the USA as a welding line integrated by robots in 1970. Based on this concept Volvo Company in Sweden introduced small group assembly without conveyor in 1977. Table 1-1 collected most of the important events that gradually contributed to introduce intelligent computer-integrated manufacturing systems (I-CIMS) that have led to enhance mass production efficiency.

1.1.2 Economic aspects of automation

Many evidences prove that industrial automation increases the production rate. Moreover, automation reduces the expenses related to workers and subsequently their supervisors. Despite all positive effects on costs, the transformation of some variable costs to fixed costs happens as the increased capital intensity depends on higher investment. Consequently, the variation of profit concerning production volume and greater automation risk is induced. However, companies prefer to increase automation to obtain a higher production rate. Regarding macroeconomy, it has been demonstrated that automation decline the short-term inflation induced by salary increases because it increases the productivity to cover higher fixed costs.

Overall, automation has showed beneficial effects on workers salary and unemployment trend over a mid-term period if automation technologies do not prevent the market trend toward equilibrium [6] as recently the World bank's World Development Report (WDR) 2019 demonstrated the evidence that the new industries and jobs in the technology sector outweigh the economic effects of workers being displaced by automation [7].

Profit of a company is obtained based on the difference between price and cost of products. Hence production of high-quality products in larger volumes with less production cost and time employing industrial automation, profit may increase. The economy of scale can be accomplished by automation since as production increases, the cost of individual product drops.

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5

Advantages and disadvantages of automation

One of today’s controversial issues in the field of automation is the estimation of advantages and disadvantages of automation applications in manufacturing systems. Herein the most important pros and cons of manufacturing automation are listed [2].

Advantages:

• Difficult and labor-intensive activities like moving heavy or even very tiny objects that are beyond the human abilities have been conducted by automated systems • Labor activities in a dangerous environment such as those with extremely high

temperature or toxicity and radiation are easily conducted by automated systems • Products that are required to be made with the very quick or slow speed that is beyond

human capability are produced easier

• Production speed increases while total cost per product drops due to less labor cost per product

• Accuracy and precision of the automation system thanks to the incorporation of quality control systems is higher which results in high quality and uniform products with less defect

• Automation systems never become tired or bored and they do not call in sick • Enabling the production of multiple shifts and weekends [8]

• According to the statistics in countries like Germany and Japan in the 20th century, the presence of manufacturing automation has a positive effect on gross national income which results in the economy growth and people quality of life

• More free time for workers to do other tasks

• Increases the number of higher-level jobs in the automation production, maintenance, and running of the automated processes

• The flexibility of manufacturing processes to switch from one product to the other one without the need to build a new production line

Disadvantages:

• There are still many processes such as assembly of products with inconsistent component sizes that are not possible to be automated

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Chapter 1 Introduction

6 • Automation is usually effective for repeated, consistent and large volume products

otherwise expenses of automation would be more than manual processes

• Initial costs to run an automated manufacturing system is quite high since it requires advanced machinery, hardware, and components

• Increase of stress and reduction of relaxing tasks

• The maintenance department is demanded for any services and maintenance of the automation system in case of breakdowns or stops

• Production loss in case of failures and breakdowns of the system

• Accurate estimation of automating cost in a company is quite difficult which may impact on wrong profitability calculation and lead to no economic advantage of process automation

• Engineering and product design challenges to have the capability of production by present automated systems

• Social effects which lead to change the nature of the work from manual to automated that makes many workers jobless or displacement

The issue of unemployment has been always under debate as a group of researchers estimated how computerization can affect future jobs [9] and they realized that 47% of US employment is at risk. However, many researches demonstrated that these findings have been lacking evidences [10]. An analysis conducted between 1990 and 2007 on US labors revealed the negative impact of robots on employment as in their estimation one robot per thousands of workers decreases employment by 0.2 percentage [11]. Despite the unemployment of unskilled workers, the demand for skilled workers and new industries such as robotics, computer, and design has been increasing and overall, we can state that the only thing has been affected is the nature of job [7].

Overall, a comparison of advantages and disadvantages of automation reveals that automation benefits outweigh its defects and nowadays many companies tend to change the nature of the work and improve their production efficiency even if the benefits may appear some years after the company has invested in process automation.

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7

Industrial production automation

The manufacturing system is a part of the production system consists of different equipment as well as labors that their integration results in processing or assembly operation on raw material to produce a finished product. These systems can operate manually or semi- and fully-automated [12].

Although industrial automation and information technology are two separated concepts, wide involvement of information technologies in the areas of control and signal processing, communication and networking, real-time computation, databases, simulation, design, analysis, and optimization can be seen. The usage of IT is dramatically increasing by the expansion of automated systems.

Automation of process and assembly systems, test and inspection system and material handling are the main objectives of industrial automation. General-purpose controllers for industrial processes include programmable logic controllers, stand-alone I/O modules, and computers. Mechanized equipment and logical programming commands replace the human feedback reflexes in industrial automation. Figure 2 illustrates the main components of the manufacturing system schematically.

1.3.1 Types of Automation systems

Industrial manufacturing processes can be divided into different categories based on the volume of production and the possibility of modification scope for production of variable products as following [13] :

Finished product Input Material

Process & Assembly Quality control

Handling system

Packaging system

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Chapter 1 Introduction

8

1.3.1.1 Fixed Automation

Fixed automation is dedicated to high volume production of a certain product by using the fixed and repeated sequences of processing operations. The complexity of such a system due to custom-engineered equipment leads to a high initial investment.

1.3.1.2 Programmable Automation

Programmable automation refers to sequences of processes operation and designs within equipment that can be reprogrammed however it needs a significant effort to change the program as it is used for the processes in which the change of the process and product is small.

1.3.1.3 Flexible Automation

Regarding flexible automation, operators control the operations of manufacturing systems using commands and codes. A set of equipment is controlled by a central computer that can process multiple products. These systems are widely used for low to medium production volumes in which products and demands may vary frequently and thereby it requires modification of design and operation.

1.3.2 Handling systems

Handling systems are used to move, protect, store and control the position of materials and products within the manufacturing systems. Material handling systems involve much manual and automated equipment including conveyors, pallets, feeders, and indexers which facilitate the movement and positioning of parts between the activities of production systems. In general, parts handling controls the motion of components within a system. Transport of parts from one point to another point between different production processes is usually done by different types of conveyors shown in Figure 3 that is driven by electrical or mechanical actuators.

Indexers transfer a part to a new location quickly with high precision to avoid cumulative errors. This type of movement can be also done by walking beams and pick and place mechanisms. Indexers are usually known by their rotational motion known as dial tables that lead to a circular movement of a part within a certain degree [14]; however, linear indexers are also used for transferring the parts with precise movement through systems.

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9 The other important part of the handling system to achieve manufacturing line automation is parts feeder which supplies different manufacturing processes by components. Feeders usually have arranging parts known as outfeed sections that promote precise locating of parts for pickup.

1.3.3 Packaging systems

To deliver the final product produced in a manufacturing process, packaging plays an important role as a final process stage. Packaging contains containment and labeling of the final product by integration handling and control system. Packaging machinery uses a wide range of technologies ranging from simple control and mechanical components to high-speed servo and robotic systems. Arrangement of boxes and packages on a pallet is conducted by palletizers that are usually robotic [2].

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Chapter 1 Introduction

10

1.3.4 Assembly systems

Final products are usually composed of different individual components made of various materials integrated within the manufacturing process. Material handling, assembly technologies, and many other processes corporation assemble these components.

Assembly machines may be manual, semi-automated or fully-automated. Handling systems approach the components into proximity with each other and assemble them together. Components are usually located on a dial table or moving fixtures employing mechanized tools with high accuracy. After the components are placed accurately in close contact, they may be connected by many different technologies including fasteners, adhesives or welding methods.

1.3.5 Inspection and test systems

Inspection and test systems control the quality of the product during and at the end of the manufacturing processes to avoid the products with defects enter the market. During an inspection the function of individual components and the final assembled product is tested. Gauging and measurement are used to check the dimension of parts by using vision systems and optical sensors. Some types of products such as seals and filters are needed to be tested for leaks and airflows; ion source leak testing recognizes the size of very small holes in materials. Many other parameters may be tested during manufacturing processes. For instance, ultrasonic or laser testers check the cracks and flaws through a solid product and eddy current testers check the threads on the inside of holes.

For instance, adhesive joining is tested by UV sensors that recognize dyes mixed into the adhesives. Linear variable differential transformer (LVDTs) as an electromechanical sensor checks the dimension.

Defects are usually removed from the manufacturing line or marked to be removed in the later steps. Components can be tracked either through shift registers in the software or by bar codes and RFID tag.

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11

Assembly

Assembly technologies for plastics

Nowadays, the ideal features of plastics including lightweight and high efficiency have attained attention to replace metallic parts of manufacturing products. Most of the plastic systems are difficult to be molded in one step and it needs to be separated into the subsystem for easier manufacturing. Therefore, produced components should be assembled by different techniques in industrial manufacturing.

The selection of the most efficient technology concerning industrial demand is a challenging process that must be evaluated by an expert in assembly technologies applied for different plastics. Figure 4 depicts the joining techniques used to join plastics.

Joining Techniques Welding Solvent Welding Adhesive bonding Mechanical Friction welding

External heat source

Implant heating

Spin welding

Vibration welding

Ultrasonic welding

Friction stir welding

Induction welding Resistive implant Microwave welding Heat sealing RF welding Laser welding Infrared welding Hot plate welding

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Chapter 2 Assembly Technologies

12 As it is clear from the figure, plastic components can be joined together by four main techniques as welding, solvent bonding, adhesive bonding, and mechanical fastening.

2.1.1 Welding Processes

Welding can provide a permanent joint stronger than initial components materials by application of heat and/or pressure. Most of the welding methods are performed manually and they are dangerous due to the usage of high energy. Moreover, defects are difficult to be recognized and result in low strength [17]. To promote adhesion of the surfaces, a filler material may be used in the contact area.

Thermoplastics can be welded only if they are chemically compatible to have molecular bonds after materials melt together. Similar thermoplastics (e.g. PC-PC) have more possibility to be welded compared to dissimilar ones. Different properties and factors including melt temperature, plasticizers, hygroscopicity, fillers, crystal structure, lubricants, resin grades, release agents and many other parameters will affect the weldability of dissimilar materials. For example, dissimilar thermoplastics with melt temperature difference within 6ºC can be welded by ultrasonic welding technique.

2.1.1.1 Friction welding

Friction welding techniques exploit the heat generated by reciprocated rubbing of two components to melt the part surfaces and to form a hermetic seal. This process is usually facilitated by vertical force while two components are held together under pressure. The main drawback of friction welding is particulate formation during reciprocated rubbing.

2.1.1.1.1 Spin welding

Spin welding or rotary friction welding is a simple and fast welding method with cycle time about 5-15 s and spin speed of 200-14000 rpm that join round parts of small to large dimension hermetically by rubbing them together rotationally with applied axial pressure up to the melting point of the components.

Spin welding machines can be easily integrated into automated assembly lines. Loading and unloading of the parts onto and out of the nests are performed automatically and spinning motion is provided by a pneumatic motor with a control valve (in inertial spin welder) or

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13 servo motor. Air cylinder together with pressure transducers regulate the axial force and weld displacement is measured by the encoder. The process can be time-controlled (oriented spin welding) or energy controlled (Inertia spin welding).

Most of the thermoplastics can be spin welded. Table 2 demonstrates the possibility of various thermoplastics that are spin welded [15]. Weld strength obtained by SW may be different in different materials as PA and PS attained a weak weld strength while ABS had the highest weld strength [16]. Moreover, the effect of pressure and spinning time may lead to different weld strength [17]. Materials that can be welded by SW are generally the same as those suitable for vibration welding [18]. Fillers and additives hamper the weld strength and moisture will affect the weld strength, although this effect is less than other techniques like ultrasonic welding.

Material A B S A B S/ P C A SA Ce llu lo si cs H IP S LCP PA PA I P B T PC PC/ P B T P C/ P ET PE PEE K P EI PEO PES PET PMM A P M P P O M PP PPO PPS PS PSO PSU PV C P V D F SA N SB C TE O TP E U H M W P E ABS ABS/PC ASA Cellulosics HIPS LCP PA PAI PBT PC PC/PBT PC/PET PE PEEK PEI PEO PES PET PMMA PMP POM PP PPO PPS PS PSO PSU PVC PVDF SAN SBC TEO TPE UHMWPE

Compatible reported by literatures Compatible reports by Forward technology Compatible reported by Dukane

Occasionally compatible reported by Dukane (based on composition)

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Chapter 2 Assembly Technologies

14 Spin welding results in a hermetic seal and therefore it is used for joining of liquid containers, pipes, valves, and many similar applications. Spin welding application in the cosmetic industry has been reported by Mecasonic due to the high-quality welds to obtain good appearance for joining cosmetics tubes and circular objects as illustrated in Figure 5a. Regarding medical applications, surgical trocar as shown in Figure 5b due to the circular geometry can be welded by this technique as [19].

2.1.1.1.2 Vibration welding

Melting point or glass transition temperature of welding components in vibration welding are obtained by friction at the joint induced through their reciprocal linear or circular motion. Then molten material flows within the joint and after solidification occurs under the pressure to bond the components. Circular vibration welding is not widely used however, complex-shaped components are possible to be welded by this mode.

Most of the thermoplastics with large dimensions and irregular shapes can be hermetically sealed by vibration welding in a relatively short time (1-10s) without the introduction of welder material and sensitivity to moisture, however, particulates may be generated due to the friction that can be decreased by heating the joint surfaces. The process needs expensive equipment which is quite noisy. Generally, vibration welding works better for a planar joint. Vibration welding technique can be easily automated. Every system is equipped with a PC controlled process and data management. Electromagnets drive the vibrator tool (welding head) which is supported by spring to bear vertical pressure applied for the assembly of two components held in the aluminum or polyurethane nests. Loading is accomplished by highly

a b

Figure 5.Spin welded cosmetic and medical devices . a. Cosmetic objects (Source:

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15 accurate positioners then components are brought into contact by hydraulic, electrical or pneumatic energy. Vibration frequency (100-240 Hz) is controlled by a microprocessor that regulates the vibration amplitude. High frequency is suitable for no flash applications and results in strong welds in some materials such as polyetherimide [20] while low frequency welding is used for long and thin parts welding. Welding is controlled based on either time or displacement of molten material.

Apart from fluoropolymers such as polytetrafluoroethylene (PTFE) most of the thermoplastics with or without particulates and glass fillers can be easily welded by vibration welding. However, a large amount of fillers or water content may decrease weld strength [21] [22]. Dissimilar thermoplastics provided that their melting temperature difference is

Material A B S A SA CA CA B CA P H IP S LCP PA PB T PC PC/ A B S P C/ P B T P C/ P ET PE PEE K P EI PEO PES PET PMM A P M P P O M PP PP /E P D M P P E/ P A PPO PPS PS PSO PSU PV C P V D F SB C SA N TE O U H M W P E ABS ASA CA CAB CAP HIPS LCP PA PBT PC PC/ABS PC/PBT PC/PET PE PEEK PEI PEO PES PET PMMA PMP POM PP PP/EPDM PPE/PA PPO PPS PS PSO PSU PVC PVDF SBC SAN TEO UHMWPE

Compatible reported by Forward technology Successful welded reports

Compatible reported by KLN Ultraschall Compatible reported by Dukane

Occasionally compatible reported by Dukane (based on composition)

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Chapter 2 Assembly Technologies

16 less than 38°C may be welded by vibration welding [23]. Many similar and dissimilar materials are welded by vibration welding as collected in Table 3 [24] [23] [25] [26]. Thanks to many positive features of vibration welding this technique has been used in many industries such as automotive, appliance, aircraft, computer and toy industries and demonstrated advantages compared to other welding techniques like hot plate welding and adhesive bonding for some case studies [20]. Vibration welding is typically used in the automotive industry and not widely used in medical applications [27]. Infrared preheating of the parts may be used to avoid particulate formation during vibration without significant cycle time increase [28] and this technique is considered as clean vibration used to produce patient monitors, infusion pumps and reservoirs [19]. Examples of medical applications are reservoirs, valves and pressure vessels [23]. DSM has reported other examples in the medical industry including IV units, filters, and bedpans.

2.1.1.1.3 Ultrasonic welding

Ultrasonic welding is known as one of the fastest welding techniques (0.1-1s) that welds thermoplastics using high frequency ultrasonic energies (20-40 kHz) for making small vibrations (1-25 μm) that transmits energy to the joint interface and increases the temperature up to the components melting point. Part of the transmitted energy is dissipated through the intermolecular friction dependent on geometry and material absorption property. Near-field welding is a type of ultrasonic welding with ultrasonic source and joint distance less than 6.4mm used for low stiffness materials and results in low energy dissipation. Conversely, far-field welding distance is greater than 6.4 mm used for high stiffness materials (low ultrasonic absorption) [23].

Microprocessor controls ultrasonic welding machine in different modes depending on the machine design. The control variable in open-loop control mode is the time while in the closed-loop mode power, energy level or horn displacement is the control variable. Parts are held under pressure of actuator onto a nest known as an anvil. Electricity is converted to vibrations by piezoelectric transducers and then transmits to the horns (sonotrode) by boosters that amplify or reduce the vibration and finally to the components. Ultrasonic welders can be easily integrated into the production line to operate automatically while welding parameters (weld time, force, cooling time, frequency and power level) are displayed and controlled by monitor and microprocessor, respectively. Servo-driven welders

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17 are capable to control weld thickness and melting speed precisely to produce higher quality weld compared to pneumatically controlled welders.

Ultrasonic welding is a fast and simple process that can be easily automated for mass production purposes. Compared to other methods, ultrasonic welding is faster and there is no need to remove heat or fume due to sticking of molten materials into the nest or horn. However, large components (25 × 30 cm) cannot be joined by this technique and joint designs must be specific for welding by ultrasound [29]. For instance, thin and curved geometries are difficult to be joined. The molecular structure of both components joined should be similar (chemically compatible) with the maximum melting point difference of 22°C as an example PP and PE cannot be ultrasonically welded since they are not chemically compatible. Material A B S A B S/ P C CA ( Ce llu lo se a ce ta te ) ECT FE H IP S LCP PA PBT PC PC/ P B T P C/ P ET PE PEE K P EI PEO PES PET PMM A ( A cr yl ic ) P O M ( A ce ta l) PP PPO PPS PS (p o ly sty re n e) P SU ( p o ly su lf o n e) P TF E P V C P V D F SA N SB C ABS ABS/PC CA (Cellulose acetate) ECTFE HIPS LCP PA PBT PC PC/PBT PC/PET PE PEEK PEI PEO PES PET PMMA (Acrylic) POM (Acetal) PP PPO PPS PS (polystyrene) PSU (polysulfone) PTFE PVC PVDF SAN SBC

Compatible reported by TWI Ltd and Dukane Partly Compatible reported by TWI Ltd Compatible reports by Branson

Occasionally Compatible reported by Dukane Successful welded reports

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Chapter 2 Assembly Technologies

18 Mold release agents, lubricants, flame retardants and glass content of higher than 30% inhibit the welding process [30]. Table 4 illustrates the compatibility of different materials for ultrasonic welding reported by various literatures and companies [29] [23].

Different frequencies in ultrasonic welding are applied for different applications. Typical medical application frequencies are 20 and 40kHz. 20kHz ultrasonic welding is a powerful technique for welding of medium-sized parts while it is expensive and noisy. On the other hand, 40kHz ultrasonic welding does not make significant noise and it only welds small parts since power amplitude is less [31].

Ultrasonic welding is an interesting welding technique for biomedical applications as it does not introduce contamination through the joint, the operation time is very fast for mass production and capital cost is reasonable. The method has been first used for plastics during the 60s and became widely used in the medical industry very soon [31]. Continuous ultrasonic bonding assembles material layers such as fabrics and films by passing between the horn and a rotary anvil. Continuous ultrasonic bonding application in the medical industry includes diapers, gowns, hair, and shoe covers, hook and loop straps and garments [23] [32]. Plunge welding is another ultrasonic technique through which the horn connects to the components periodically. Medical examples welded by this technique are connectors and blood filters as they need to be bonded tightly without leakage. Reservoirs, ostomy bags, masks, and catheters are the other medical examples assembled by ultrasonic welding [31] [32]. Assembly of different membranes on medical plastic components can be operated by ultrasonic welders as Telsonic company assembled membrane on ventilation opening. Although dissimilar materials are difficult to be joined by this method, Herrmann company joined polystyrene (PS) to polyethylene terephthalate (PET) for a dental applicator. Challenging welding of delicate polystyrene microfluidic test chip and same PS film was accomplished by ultrasonic welding made by Hermann company through a heretic bond and

Table 5. Ultrasonic welding application in various industries

Thermoplastic couple Industry Sector Product

PS-PS Appliances Coffee pot

ABS-ABS Electronic Electrical switch

ABS-PC Electronic Reflector

ABS-PMMA Electrical Electrical lens

PS-PS Electrical Rotor

Nylon66 Automotive Fuel filter

PC-PC Medical Medical bottle

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19 optical transparency with mark-free joint [34]. Industrial examples especially medical ones are given in table 5 and the following figures.

. a b f e d c

Figure 6. Ultrasonic welded medical devices a. Blood filter (source: www.twi-global.com) b. Fluid containers and

filters (Source:www.hermannultrasonics.com) c&d. Source: www.st-rong.com e. Microfluidic chip (Source:

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Chapter 2 Assembly Technologies

20

2.1.1.1.4 Friction stir welding

Friction stir welding (FSW) is a mode of friction welding which bonds two components in contact on a support plate by spinning a tool along the joint line while axial pressure is applied, melting the components and welding them by mixing the molten plastics. Downward pressure is applied by hydraulic pressure and components are kept in contact by horizontal force.

Conventional friction stir welding is a successful joining method for metals like aluminum alloys, titanium, copper, and steel whilst due to viscoelastic and thermal properties of plastic, it is not widely used for polymers. The process contains hole removal that is filled afterward by flowing the molten plastic. This may result in stress concentration and reduction of hermeticity [33]. Modified FSW called Vi-blade welding is the technique used for plastics and exploits linear vibration machine with titanium blade along the joint line mounted on PTFE shoulder working at a determined frequency and amplitude [34]. The FSW has shown many advantages and it can be easily automated [35] although it has not commercially used for thermoplastic welding. Proper tool modification is the main concern of researchers to achieve good results for FSW [23].

Many thermoplastics can be welded by FSW including PVC, PVDF, PPS, and PEEK [36] [37]. Potential friction stir welding of polypropylene was investigated compared to other welding methods [38]. The results demonstrated a 95% joint efficiency with high repeatability. Heat assisted FSW results for welding of HDPE sheets also showed acceptable weld strength [39]. PP sheet of 9mm welded by vi-blade welding technique and attained an acceptable result in terms of weld strength and speed compared to other welding techniques including hot gas and extrusion welding [40]. Machine tools and parameters modification of FSW have been studied for welding of different polymers like ABS [41] [42] [43], PA6 [44], PE [45] [46], UHMWPE [47] and PP composites [48] [49] in order to develop and obtain the best process parameters for an efficient weld strength. Weld strength efficiency of different materials has been illustrated in table 6 [50]. Moreover, friction stir spot welding of dissimilar polymers like PMMA to ABS has been successfully reported [51].

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21

2.1.1.2 External heat source welding

Welding of two components by use of an external heat source to generate heat at the joint surface while two components are held together by clamping pressure subdivides into several methods based on their energy source as follows. Pressure applied to hold the parts together is very important and should not be underestimated. Moreover, it should not exceed a certain amount in order not to decrease the weld strength.

2.1.1.2.1 Hot plate welding

Heated tool welding or hot plate welding joins the plastic components using a heated metallic plate called hot tool along with simultaneous pressure application on joined components. The welds obtained by this simple method are strong and hermetic and can be applied automatically. However, hot plate welding has a long cycle time (10-20s for small components) and high temperature is required.

Hot plate welding can be used for almost any thermoplastic provided that two joining materials are chemically compatible, although it is more preferred for softer thermoplastics such as PP and PE. One of the examples of joining plastics with this method can be found in the automotive industry where acrylonitrile-butadiene-styrene (ABS) tail light housing is connected to polymethylmethacrylate (PMMA) or polycarbonate (PC) colored lens. The

Material A B S P A 6 PC MD P E H D P E U H M W P E P P /CF P P /G F PP ABS PA6 PC MDPE HDPE UHMWPE PP/CF PP/GF PP

Weld strength efficiency > 80% Weld strength efficiency > 60% Weld strength efficiency > 50% Weld strength efficiency >30% Weld strength efficiency <30%

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Chapter 2 Assembly Technologies

22 other typical application is to weld pipes. For two dissimilar materials with different melting temperature two hot plates concerning plastics melting temperature must be used. Table 7 illustrates the materials that are compatible with hot plate welding [23] [52]

Hot plate welding machine may be manual, semi-automated or fully-automated. An automated system consists of conveyors and indexers which load the components into the device fixtures that hold the parts. The actuation system is activated by pneumatic or hydraulic energy to activate mechanical fixtures to control the pressure and align the parts. The plate is electrically heated in an even form and its temperature is regulated by thermocouples. In high-temperature welding, smoke extractors may be used to remove the vapors of materials that remain on the plate surface. The actuator brings the parts in contact with the hot tool while all the welding parameters are controlled and programmed by microprocessors. Welding parameters (temperature of the plates, heating time, welding

Material A B S A SA PA PBT PC PC/A B S P C/ P B T P C/ P et PE PEI PET PM M A P M P P O M PP PPO PPS PS PSO SAN TPE PV C P V D F ABS ASA PA PBT PC PC/ABS PC/PBT PC/PET PE PEI PET PMMA PMP POM PP PPO PPS PS PSO SAN TPE PVC PVDF Compatible

Successful welded reports

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23 pressure and welding time) are displayed and set via the machine-operator interface. If one parameter is not in a certain programmed range the machine will stop or produces an alert for the operator. The tool is coated by special anti-stick materials like PTFE that prevents plastics to stick the platen. The latest advancement is using servo control which removes the plastics from heated platen much more rapidly.

Hot-plate welding is considered a long process and more popular for large devices therefore, it is not widely used in the medical industry [53]. However, due to simple control and consistent results it has been used in the medical industry to weld the medical filters by forward technology company (Figure 7). Other examples include manifolds and pumps, tubes and catheters, chest drainage units, home testing kits, testing trays and filters for anesthesia, blood, IV, and oxygenators [32].

2.1.1.2.2 Infrared welding

Infrared welding or IR welding is an alternative welding technique using electromagnetic radiation which addresses contact issues of heat tools in hot plate welding and welds the parts in shorter cycle time. First IR type is more like hot tool welding that uses IR lamps or electrically heated metal plates to melt the parts held into the nests, while through transmission IR welding (TTIRW) is more like laser welding with short cycle time (3-5s) in which IR radiation transmits through one part and absorbed by the other part for a hermetic weld. Therefore, TTIRW requires transparent and absorbent components or pigmentation and IR absorbers. TTIRW is different from transmission laser welding which produces intense single-wavelength energy focused on a fine point. Conversely, TTIRW heats a focal area with less intense multi-wavelength energy.

Automatic feeder places the components onto the nests which can be moved by pneumatic driven clamping devices after components are heated. Welding parameters may be controlled by microprocessors. Infrared welder sub-components are coolers for cycle time

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Chapter 2 Assembly Technologies

24 reduction, vacuum to hold the part onto the nests, sensors to avoid contact and melting thickness controllers. IR radiators include quartz-halogen (1000-30000 ºC), tungsten filament line heaters, nickel-chromium (850º C) and ceramic coated heating elements (320-530º C). This process can be very cost-effective since there is the possibility to design a platen and change the masks only. Although IR welding cycle time is shorter than hot plate welding, it is still considered as a long process compared to vibration welding and this issue has been solved by Dukan’s rotary infrared welding system by simultaneous welding processes (loading, melting, joining, and unloading) on a rotary indexing machine.

Due to non-contact welding, this process is suitable for high melting temperature plastics as well as soft thermoplastics such as elastomers. Table 8 illustrates acceptable welding materials reported by Forward technology, Dukane and Orbi-tech corporations [15]. Moreover, IR welding is free of contamination with high weld quality. As a result, IR welding is the development of hot plate welding for mass production of highly flexible materials like blood filters, however, TTIRW is not still commercially available [27].

Materials Through-transmission Surface Heating

PC Good Good

PMMA (Acrylic & Lucite) Good Good

PS Good Good

ABS (Cycolac) Transparent grade only Good

PVC Transparent grade only Good

PE Thickness < 5 mm Good

PP Thickness < 5 mm Good

PK Thickness < 5 mm Fair

Elastomers Thickness < 5 mm Fair

PA (Nylon & Zytel) Thickness < 5 mm Good

POM (Acetal & Delrin) Thickness < 5 mm Good

PTFE Thickness < 5 mm Poor

PBT (Valox & Enduran) - Good

PET (Ployester) - Good

PPO (Noryl) - Good

PPS (Ryton) - Good

PSO (Udel) - Good

TPE (Santoprene) - Good

ABS-PC Good -

PS-PMMA Good -

ABS-PMMA Good -

ABS-SAN Good -

PBT-PC Good -

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25

2.1.1.2.3 Laser welding

Laser welding (LW) is highly automated and it is one of the fastest welding methods used to join plastics hermetically in the non-contact mode for mass production since the late 90s. Melting of thermoplastics at a discrete joint location is done by applying laser beam coming from laser source directed to the joint by optical lens, mirrors or fibers with high precision while components are in contact under clamp force. Different lasers are used for welding of thermoplastics including Nd: YAG, CO2, diode, gas (e.g. Ar, Xe, Ne) and fiber lasers. CO2 lasers are better used for film welding or laser cutting since they are absorbed very quickly while other lasers are more suitable for transmission laser welding based on the absorption property of polymers with or without absorbers such as carbon black. Direct laser welding is more used for thin-film joining, although new techniques using lasers with 2-μm wavelength (fiber or Ho: YAG) or transmissive cover for CO2 laser have the possibility to weld thicker sheets. A more widely used laser joining technique for thermoplastic is called transmission laser welding employing Nd: YAG, diode and fiber lasers within range of 0.8-1.1-μm wavelength along with absorbers (Carbon or Clearweld) [23]. For automated assembly, an array of laser beams may be used to increase welding speed for simultaneous welding of similar spots.

Transmission laser welding is an attractive welding method used to weld molded parts, films, and textiles for various industries especially biomedical devices. The reason why it has been widely used in plastic medical devices assembly is the importance of flash free welds and transparent products by using Clearweld absorber. 2-micron lasers are the latest innovation of laser welding that are easily absorbed by clear polymers and so eliminates the need to use absorbers and simplifies the welding process for medical applications although their application due to high costs is still limited. Other unique features of laser welding make them attractive for medical application are high heating precision which results in minimal thermal damage, cleanroom compatibility due to clean non-contact welding process and particulate-free process [54]. Polycarbonate (PC) microfluidic devices and bioMEMS can be laser welded and achieve hermetic seals, high precision and rapid mass production [55]. Laser welding is also used to weld polymer catheter balloon to polymer shaft and tube bonding in medical applications. Polystyrene (PS) fabric to PS film in vascular graft, gowns, masks, and hospital dresses can be welded by lasers [54]. Royal national hospital for rheumatic disease welded two PS sheets together for an inflatable neck brace. A

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Chapter 2 Assembly Technologies

26 polycarbonate infusion pump was welded to a transparent lid by Novolas laser transmission welding for RoweMed company [56]. Many medical disposables such as filters, blood test devices with simple housing and catheters join by laser welding. Figure 8 shows some of the biomedical products welded by lasers.

Many thermoplastics are welded by laser welding with less sensitivity of resin chemistry and melt temperature differences provided that proper laser source and joint design are selected [23]. Semi-crystalline plastics like PE and PA and amorphous plastics like PC, PMMA, and PS can be welded by transmission laser welding up to 10mm and 100mm thickness, respectively, while PEEK could only be welded when the thickness is less than 1 mm as in medical packaging [54]. PEEK weld was investigated by adding a different concentration of carbon absorber to obtain the optimum results [57]. Acceptable weld strength has been achieved for PE and PP as well [58]. HDPE is difficult to be welded by ultrasonic welding while welds very easy with laser [59]. Table 9 collects the weldability of different plastics based on their position as transparent or absorbing welding components reported by LEISTER assembly company.

Figure 8. Laser welded medical devices a. Plastic microfluidic device (Source: Branson Corp) b. Insulin management system (Source: LPKF laser & Electronics) c. Microfluidic device (Source: LPKF laser & Electronics) d. Medical cartridges (Source: LPKF laser & Electronics)

a

c d

Riferimenti

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