Chapter 4: Test Case ELECTROLUX®

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Chapter 4: Test Case ELECTROLUX®

4.1 Introduction

As it is described in the second chapter, to show EAS’s paradigm it is necessary to choose a suitable test case. In this thesis will be considered two different classes of products in order to be more generic as possible. Both of them belong to Electrolux’s set of products. In particular five variants of washing machine porthole handles and three variants of electric valves groups were analysed. This test case selected is characterized by small but significant difficulties, which could add valid and useful information about the development and application of flexibility and modularity concepts.

In fact the classes of products, apparently simple if it is considered the number and the shape of the

elements involved, differ each other not only for characteristics due to the different typologies, but also for changes in the product assembly process.

Showing that the cell “evolving” can be used for both of those classes of products is a step towards more flexible and modular assembly systems or, in other words, towards EAS.

This chapter is so structured. In the first part the products are presented, so once all the products belonging to this two classes of products are shown, the reasons why one per class was decided to be more suitable than the others are highlighted. Then, these chosen parts are described showing also their present assembly process.

Next, the problems found in these products concerning their automatic assembly are pointed out utilizing the DFA2 method. In this context, solutions are also given to improve these weak aspects. Finally, the assembly cycles for the two products selected are illustrated underlining those assumptions that we made in order to make the study of the test case easier. But, at the same time, this approach will not imply a less validity of the results found.

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4.2 Products studied

4.2.1 Washing machine porthole handles

In this section all washing machine porthole handles studied will be described, listing their components. Then, for the one that we selected its current assembly sequence (it is nowadays manually assembled) is presented.

2D drawings belonging to this product can be found in appendix.

Below an exploded view of the washing machine is showed, remarking those components that are interesting for the scope of this thesis (all variants of the handles are made by them, some models own more parts as it is described below).

LATCH LATCH LATCH LATCH SPRING SPRINGSPRING

SPRING PINPIN PINPIN

LATCH LATCHLATCH LATCH RETURN RETURNRETURN RETURN SPRING SPRINGSPRING SPRING HANDLE HANDLE HANDLE HANDLE

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4.2.1.1 Components

In this section some components are described giving their most important characteristic; anyway, as done for the product, also components’ 2D drawings are available in appendix.

Before starting with these descriptions, it is important to highlight the fact that most of these parts, even though belonging to different variants of the product, are the same ones (as it can be seen in the tree of variants table below):

PIN LATCH RETURN SPRING Type 1 RETURN SPRING Type 2 LATCH SPRING Type 1 LATCH SPRING Type 2 DELTA (Test case C) X X X DELTA RIM (Test case B) X X X X ALPHA SENSA (Test case D) X X X X SIGMA (Test case A) X X X ENV06 (Test case E) X X X

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• Pin

A brief description of the Pin is given in the table below:

Sizes (max) Accuracy [mm] Material Other

L 61/40 mm

Ø 0.4 mm L +0.5/-0.5 Iron 44 Hot-drawn h9

• Latch

A brief description of the Latch is given in the table below:

Sizes (max) Accuracy [mm] Material Other

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• Return Handle Spring

a) Type 1:

Sizes (max) Accuracy [mm] Material Forces Other

W≈ 24 mm Wire Ø 0.8 mm W + 0.5 AISI 302 In max working position, load F=12.85±10% N Holes Ø 11.2+ 0.5 mm Weight 1 g b) Type 2

Wire Ø 2 mm W ≈33 mm W+ 0.5 - In max Working position, load F=108±10% N Holes Ø 15+ 0.4 mm

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• Latch Spring

a) Type 1

b) Type 2

Wire Ø 1.4 mm W ≈16 mm W+ 0.5 - In max Working position, load F=108±10% N Holes Ø 5.5- 0.4 mm

Wire Ø 1.4 mm W ≈21 mm W+ 0.5 Wire dacromet black In max Working position, load F=108±10% N Holes Ø 5.5- 0.4 mm

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• Handles

a) Sigma

L ≈ 85 mm W≈ 105 mm H ≈18 mm L ±0.1 H ±0.1 Plastic ABS Load resistance in hole axis F=246 N

Internal pin holes Ø 4+0.1 mm External pin holes

Ø 8 mm

b) Delta RIM

L≈ 71.8 mm W≈ 95 mm H ≈22.1 mm L ±0.1 H ±0.1 Plastic ABS Load resistance in hole axis F=246 N

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c) Delta

L ≈71.8 mm W≈ 95 mm H ≈22.1 mm L ±0.1 H ±0.1 Plastic ABS Load resistance in hole axis F=246 N

Ø 10 mm

d) Alpha Sensa

L ≈ 140 mm W≈ 40 mm H ≈ 43 mm L ±0.1 H ±0.1 Plastic ABS Load resistance in hole axis F=246 N

Ø 8 mm

e) ENV06

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4.2.1.2. Chosen Washing machine porthole handle: “DELTA” Model

The variant that was chosen was the “DELTA” model, whose picture is shown in figure 91:

Fig. 91

The main reason that drove us towards this decision was the fact that this product is composed just by four components, listed below:

Plastic Handle Latch

Latch Spring (Type 1)

Since for our goals what is important is basically to show that two different products can be assembled in the same cell following the EAS principles, this does not depend on the complexity of the products taken into account. Therefore, if we consider products composed by less components, this will mean less operation to accomplish and so easier assembly cycles.

Even “SIGMA” and “ENV06” model are actually made by these parts. Anyway, the final decisions was taken for the variant said because, on the whole, its assembly seemed to present less problems.

Regarding the “SIGMA” model the most critical aspect concerns the small hole (indicated in the figure below) where the latch spring end has to be inserted.

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Fig. 92

Instead, the model “ENV06” has the problem of the insertion of the couple latch-spring into the hole of the handle. In fact the movement that must be accomplished (see figure 93) is not so easy and anyhow, for sure, more complex compared with the one in the “DELTA” model (where the hole is bigger and the insertion direction linear)

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Figure 95 shows the product and its parts:

Fig 95: “Delta” model handle

Its assembly process currently in use, composed just by complete manual operations, is made by batches, through components supplied in containing trays, and considers a minimum batch size of 48 sub assemblies, with a maximum of some thousands, in a multiple of 48, in batch. The cycle time is 19 seconds.

The complete assembly sequence of the Delta RIM model handle, as it is accomplished till now, is illustrated below in its three steps:

First step:

Fig. 96: manual alignment

Disassembled model components Disassembled model componentsDisassembled model components Disassembled model components:

• Plastic handle• Plastic handle• Plastic handle • Plastic handle

• Latch • Latch• Latch • Latch

• PinPinPinPin

• Latch spring • Latch spring • Latch spring

• Latch spring

(Type 1)

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Second step:

Fig. 97: second step

Fig. 98: Alignment between elements

After their coupling, the latch and

the spring are inserted into the

handle, as shown in the picture

The alignment between all

the elements holes has to be

very accurate

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Third step:

Fig. 99: pin insertion

Fig. 100: Delta model handle assembled

Pin insertion (Ø 4 mm) through the

handle holes (Ø 4-0.06 mm) the

spring holes and the latch hole

(Ø 4+0,05 mm).

(Note: the handle has to resist to a

load > of 246 N).

The porthole handle Delta

completely assembled

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4.2.2 Electric valves groups

As done before, in this section the second set of products (electric valves groups) will be described, listing their components and describing the current assembly sequence of the product chosen (again, it is nowadays manually assembled). 2D drawings belonging to these products can be found in appendix.

Fig. 101: one of the products studied

What have to be assembled is the electric valve, which links the hydraulic system of the washing machine, with the tubes that lead water towards detergent basin. Assembly operations consist of the insertion of these tubes into the electric valve, where solenoids are already assembled, and their joining by locking rings.

Tubes used here are characterized by different diameters, because they have to let a different water flow depending on the type of washing programme. Likewise, locking rings are different; not just only cause tube diameter but also for the type of ring.

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4.2.2.1 Components

The table below explains which components compose each product. Note that the terminology used in this table is detailed later when these components are described.

Components Model A Model B Model C

2 ways connection - electric valve

X

3 ways connection - electric valve

X

Tube – type 1

X

Tube – type 2

X

Tube – type 3

X

Tube – type 4

X

Tube – type 5

X

Tube – type 6

X

Tube – type 7

X

Clamp Rings (type 1)

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Clamp Rings (type 2)

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Snap Rings (type 1)

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Snap Rings (type 2)

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Tab. 4

When in the cells appears (n), it means that model is composed by n parts of the component considered.

Next, some details of components are given to understand how product studied are structured and so why the test case was applied on that version.

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4.2.2.1.1 Electric valves

Two types of electric valves was considered in this thesis’ context

▪ 2 ways connection- electric valve (see figure 102)

Fig. 102

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4.2.2.1.2 Tubes

In this section some details of the tubes used are given, but more can be found in appendix.

Fig. 104: tubes’ characteristics

Here there are some common constructive characteristics belonging to all kinds of tubes considered:

MATERIAL MAX TEMPERATURE PRESSURE

EPDM 70 RUBBER

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In the next table tubes’ dimensions are shown:

Table. 5: tubes dimensions

Model Diameter (D) [mm] Thickness (S) [mm] Length (L) [mm] Type

10 ± 0.3 3± 0.15 160± 1 1 2 ways connection (clamp rings) 12± 0.3 3± 0.15 160± 1 2 10± 0.3 3± 0.15 255± 1.5 3 2 ways connection (snap rings) 12± 0.3 3± 0.15 255± 1.5 4 10± 0.3 3± 0.15 5 3 ways connection (curve tubes) 12± 0.3 3± 0.15 From 64.9 ±1 to 124 ±2.5 6 3 ways connection (central tube) 10± 0.3 3± 0.15 variable 7

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4.2. 2.1.3 Locking Rings

Two types of locking rings are used to fasten tubes to the plastic parts: spring type and clamp type. Below a description of these components is given.

▪ Snap Ring (see figure 105)

Fig. 105

They are used to fasten the tube in correspondence of the connection, once that this has been inserted in the nozzle.

T o be correctly fastened, when they are tightened, their width, in the closing point, must not be higher than 3 mm.

The material used is ALUZINK 500 A.

Different diameters can be utilized, as shown in the table 6 (see also figure 106).

Type Thickness (S) [mm] Diameter (D) [mm] H max [mm]

1 0.8 17.5 21.5

2 0.8 18.5 23.5

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Fig. 106: Snap rings’ drawing

▪ Clamp Ring (see figure 107)

Fig. 107

Unlike the type described above this type of locking rings are assembled on both ends of the tubes.

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In the following table their dimensions are given depending on the diameter that must be fastened.

Type Thickness (d) [mm] Diameter max [mm] Diameter min [mm] h [mm]

1 1.8 16.26 15.49 8

2 1.9 18.70 17.70 9

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4.2.2.2 Chosen Electric-valve Group

The version chosen was the 2 ways connection - electric valve fastened by clamp rings (“B” model). Its picture is shown below.

Fig. 109

The reason rely upon the fact the model this is the product with the easiest way to assemble. In fact, first of all it is composed just by two tubes (and not tree). Furthermore these tubes are linear and not curve: they are easier to feed and, likely, to handle.

Referring with the other version, which has the 2 way connection electric valve as well, the difference is made by the locking rings: the clamp ones requires a much lower opening force and the result is not different. Therefore, the product indicated was selected for our test case.

At the moment, as said in the introduction, this product is manually assembled using pneumatic tools to make easier the operations. Moreover, the electric valves are positioned onto a particular fixture (shown in fig. 110) to let a stable and safe insertion of the water tubes.

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As far as the assembly processes currently in use are concerned, they are made by batches.

Figure 111 shows the product and its parts:

Fig. 111

As first step of the process (step zero), the electric-valve (where the solenoids have been already assembled) has to be positioned onto the fixture as explained before.

Then, again, this model is assembled repeating twice (because there are two tubes that have to be fastened) the assembly sequence illustrated below:

Electric Electric Electric Electric ---- valve valve valve valve ( 2 ways conn ( 2 ways conn( 2 ways conn

( 2 ways connection) ection) ection) ection)

Clamp Rings ( type 1 [2] )Clamp Rings ( type 1 [2] )Clamp Rings ( type 1 [2] )Clamp Rings ( type 1 [2] )

• Tube ( type 3 ) • Tube ( type 3 )• Tube ( type 3 ) • Tube ( type 3 ) Disassembled model Disassembled model Disassembled model Disassembled model components: components: components: components:

Clamp Rings ( type 2 [2] )Clamp Rings ( type 2 [2] )Clamp Rings ( type 2 [2] ) Clamp Rings ( type 2 [2] )

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First step:

Fig. 112: tube lubrication

Fig. 113: sponge used for lubrication

To make easier the insertion of the

tube into the electric-valve, one of

the ends is lubricated

To lubricate tubes a sponge

impregnated by oily liquid is used

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Second step:

Fig. 114: tubes inserted

Third step:

Fig. 115: tube fastening

Tubes are manually inserted in the

nozzles respecting

position and diameter

Clamp rings corresponding to the

diameter of the tube are fastened at

both ends of the same tube making

use of a special pneumatic tool

(different from the one used in the

process described above).

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Fig. 116: Pneumatic tool

In the figure below the Electric-valve Group completely assembled is shown.

Fig. 117: picture of the 2 Electric-valve Group

Currently the process described above is performed in 0.6 min.

4.3 DFA2

The products shown in the former paragraph are not suitable for an automatic assembly. In

The special tool is used to open

the rings to thread them along the

tube and then to release them

once they are positioned

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design errors emerge, consequently it is possible to correct them following the rules and the suggestions of the method.

DFA2 consist of two parts, product level and part level. It is suggested that the method is first used to analyse (or design) a product at product level, thereafter each part at part level. Each section in the method correspond to an evaluation criterion and its design rules. The evaluation results are noted on data sheets. Each section of the model has an evaluation criterion.

Before beginning with the application of the method, it is opportune to choose the most adapted products for our purpose. A first analysis shows that among the handles, the best one is the “C” model; in this model, it is easier to fit the latch-spring group into the plastic handle: during the joining, in fact, it is not necessary to change the direction, the trajectory is simply a straight. Moreover, in this handle there is not a return handle spring: the lower is the number of parts (especially springs), the easier is the automatic assembly. As far as the “electric valve group”, we will put the focus on the “2” model; the “Clamp Ring” used to fit the plastic tube in the valve group, are more suitable for an automatic manipulator than the other kind of rings.

After these necessary premises it is possible to begin the DFA2 analysis.

4.3.1 Handle Analysis

In the following figure the handle analysed is shown.

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1 3 5 u ct l ev el e su m m ar iz es t h e sc o re o b ta in ed b y t h e h an d le : Handle “C” 9 Reduce numbers of 1 Unique parts 1 Base object 9 Design base object 3 Assembly directions 1 Parallel operation 9 Chain of tolerance PRODUCT LEVEL 33 SUM

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Section 2: Part level

The following scheme summarize the score got by each part in the evaluation model.

P in Sp rin g L at ch P la sti c h an d le L is t o f a ll p ar ts

1 1 1 1 _{Numbers of identical parts} 9 1 1 9 _{Need to assemble part?} 9 9 9 9 _{Level of defects} 9 9 9 9 _Orientation 9 9 9 9 _{Fragile parts} 9 1 9 9 _Hooking 1 3 3 3 _{Centre of gravity} 9 1 1 1 _Shape 3 3 3 3 _Weight 3 9 9 3 _Length 3 1 3 9 _Gripping 1 1 1 9 _{Assembly motions} 3 1 1 9 _Reachability 1 1 1 9 _Insertion 1 1 1 9 _Tolerances

9 1 1 9 _{Holding assembled parts} 9 9 9 9 _{Fastening method} 1 1 1 9 _Joining T O T A L S U M : ₃ ₃ ₃ ₉ Check/Adjust 3 7 0 9 3 65 75 13₇ SUM P A R T L E V E L

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Total Sum

370 Assembly index B =

B =

57%

Maximum point* number of parts

162 * 4

=

Referring to handle taking here into consideration, it should be noted the main difficult is due to try performing tasks that, at the moment, are exclusively made by hands, because they require coordination and simultaneity and a three-dimensional working space, at least.

For example the correct alignment of the holes could be a serious problem: to permit the pin positioning, the spring has to be controlled, keeping hold the latch too. All parts should be possible to assembly with one hand: manual assembly with one hand resembles automatic assembly.

The pin insertion could also create some difficulties, looking at an automatic assembly process: the related handle holes (three), due to plastic manufacturing process, couldn’t be always considered completely aligned each other and without burrs, and the same pin could present a rough surface, too. Consequently, the required nominal insertion force could be not always the same, even if we consider a high precision pin positioning into the first handle hole (e.g. avoid equipment small vibrations).

The product was first analysed using the product level of DFA2. The product is simple, so the low scores, given to the sections “parallel operation” and “Unique parts” are not very meaningful. On the contrary, the two assembly directions and the design of the base object could be improved in order to simplify all the process; however, this two aspects involve aesthetic and functional issues of the whole product and so we will not modify them.

Each part was also analysed using the part level of DFA2. Since that product is not designed for automatic assembly, there are many sections of this model that got a low score. The spring for example has caught up only 65 points: it was expectable, because of the springs, in general, are not suitable for automatic assembly ; they are usually difficult to feed, to grab and to manipulate. Moreover, during the evaluation, the possibility to integrate the functionalities of the latch and the spring surfaced.

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In the next paragraph, we will attempt to find a solution to some of the issues emerged, with several redesign actions. As already said, the modifications will not regard aesthetic or functional aspects of the handle.

Redesign Actions

As already said, it would be necessary to integrate the functionalities of the Latch and the Spring eliminating the Spring, that is not adapted for automatic assembly.

However, in order to follow as much as possible the real product, we addressed our attention on the Latch and to the Plastic Handle.

In the following figure it is represented the redesign proposal for the Latch.

Figure 119. The modified Latch

The Surface 1 is added in order to favour the gripping actions; this surfaces in fact is parallel to that one on the back. The next figure shows the solution.

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Figure 120. New Gripping surfaces.

On the other hand, since the high number of different handles which uses that kind of Latch, could be economically convenient to produce a dedicated gripper; such a gripper would be useful also for aligning.

The Surface 2 has a double purpose: first of all, it allow to get a snap fit between Latch and Spring, and than it keep the parts joined and in the right position during the insertion in the Plastic Handle. This surface is very useful even for a manual assembly process.

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As far as the Plastic Handle the modification deal with the two insertion zones, for the Spring-Latch sub assembled and for the Pin.

Figure 122. The modified Plastic Handle

As you can see in the previous figure, we added two chamfer for the pin insertion and a central guide surface for the Spring-Latch group. The last surface has three proposals: to make easier insertion, to support the sub-assembled and to align it for pin insertion.

Evaluation of the modified handle.

In order to show the improvements of the object after the redesign actions, we introduce the results of the DFA2 method for the new product.

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Section 1: Product level H an d le “C ” 9 R ed u ce n u m b er s o f 1 U n iq u e p ar ts 1 B as e o b je ct 9 D es ig n b as e o b je ct 3 A ss em b ly d ire ct io n s 1 P ar al le l o p er at io n 9 C h ai n o f to le ra n ce P R O D U C T L E V E L 3 3 SU M

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Section 2: Part level. P in Sp rin g L at ch P la sti c h an d le L is t o f a ll p ar ts

1 1 1 1 _{Numbers of identical parts} 9 1 1 9 _{Need to assemble part?} 9 9 9 9 _{Level of defects} 9 9 9 9 _Orientation 9 9 9 9 _{Fragile parts} 9 1 9 9 _Hooking 1 3 3 3 _{Centre of gravity} 9 1 1 1 _Shape 3 3 3 3 _Weight 3 9 9 3 _Length 3 1 9 9 _Gripping 9 9 9 9 _{Assembly motions} 3 9 9 9 _Reachability 9 9 9 9 _Insertion 1 1 1 9 _Tolerances

9 9 9 9 _{Holding assembled parts} 9 9 9 9 _{Fastening method} 9 9 9 9 _Joining T O T A L S U M : ₉ ₉ ₉ ₉ _Check/Adjust 4 9 8 1 2 3 1 1 1 1 2 7 1 3 7 SUM P A R T L E V E L

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Total Sum

498 Assembly index B =

B =

77%

Maximum point* number of parts

162 * 4

=

As you can see, from the point of view of the parts, the analysis allows us to perform a substantial improvement of the correspondent index.

4.3.2 Electric Valve Group Analysis

The next picture shows the electric valve.

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1 4 4 S ec ti o n 1 P ro d u ct l ev el . T h e n ex t sc h em e su m m ar iz es t h e sc o re o b ta in ed b y t h e v al v e: E.Valve “2” ₉ Reduce numbers of 1 Unique parts 1 Base object 9 Design base object 9 Assembly directions 9 Parallel operation 9 Chain of tolerance PRODUCT LEVEL 47 SUM

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1 4 5 le v el Clamp Ring 1 Tube 2 Tube 1 Electric valve List of all parts

1 1 1 1 N u m b er s o f id en ti ca l p ar ts 9 9 9 9 N ee d t o a ss em b le p ar t? 9 9 9 9 L ev el o f d ef ec ts 3 3 3 9 O ri en ta ti o n 9 9 9 9 F ra g il e p ar ts 1 9 9 9 H o o k in g 3 1 1 3 C en tr e o f g ra v it y 1 9 9 1 S h ap e 3 3 3 9 W ei g h t 9 3 3 3 L en g th 1 1 1 9 G ri p p in g 9 9 9 9 A ss em b ly m o ti o n s 1 9 9 9 R ea ch ab il it y 1 3 3 9 In se rt io n 1 1 1 9 T o le ra n ce s 9 9 9 9 H o ld in g a ss em b le d p ar ts 3 3 3 9 F as te n in g m et h o d 3 3 3 9 Jo in in g 3 9 9 9 C h ec k /A d ju st 79 103 103 143 S U M PART LEVEL

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Total Sum

507 Assembly index B =

B =

63%

Maximum point* number of parts

162*5

=

The first step of the analysis (the product level), produce a good score for the electric valve group. The low scores in the section “Unique parts” could be improved, for example, using the same kind of tube and ring. The low score in the section of “Base object” suggests to redesign it in order to avoid any additional fixtures.

The second section of DFA2 evidences, some designing lack. First of all, the tube are made by rubber: this material are not suitable to be manipulate with mechanical grippers because of the deformation due to the pressure. Moreover, it is not necessary to share the function of the tube and the ring: it would be better to design a directly screwing, or snap fitting, tube; this solution would allow to reduce the number of parts and the assembly operations.

On the present tube there are not any guide surfaces for the insertion, and it forces to use grease.

Anyway the present value of the indexes, allows to deal with the assembly process definition without any particular redesign intervention.

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4.4 Assembly cycles

In this paragraph, the assembly cycles for the modified handle and for the valve group will be shortly introduced: this kind of cycles, in fact, normally belongs to the product documentation and so they can be considered very important input information to produce the Specific Ontologies. The following schedules are presented only in order to provide a “possible” way to assembly the products. The presented level will be the one of the single joining operations.

• “DELTA Model Handle” Assembly Cycle.

The necessary operations to assemble the Handle:

1. Snap fit of the Latch into the Spring.

2. Insertion of the sub-assembled “Latch-Spring” in the Plastic Handle.

3. Insertion of the Pin in the sub-assembled “Latch-Spring-Plastic Handle”.

• “Valve Group” Assembly Cycle.

The necessary operation to assemble the Valve Group:

1. Insert the first Tube in the Electric Valve.

2. Fix the Tube with the first Clamp Ring.