iPOD Case Design for simplified battery replacement

7/29/2019 iPOD Case Design for simplified battery replacement

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IPod Redesign for

Customer RepairIRepair Solutions Inc

Presented to: Dr. Munro

Prepared by: Jeremy Rutledge

4/1/2010


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Abstract

Thousands of Apple IPods are discarded by consumers yearly due to the undesired battery life of their

unit; disregarding the cost to the environment. Often the unit contains several working parts that can be

used by other consumers to upgrade or repair their current models. Apples current marketing strategy

is to overcharge consumers ($ 59 USD) to replace the battery which discourages many consumers from

this repair. Instead they replace their unit with a new one that is on the market. This report examines a

redesign of the 5th generation IPod for consumer repair with a detailed focus on the construction of the

face plates that hold the internal parts together. This design focuses on an approach that is beneficial to

the user without compromising its visual appeal that has become synonymous with users around the

world.

The report includes step-by-step instructions for the current model to demonstrate the necessary

techniques needed for the battery replacement. This redesign focuses on eliminating hard to access

fasteners, adhesives and ensuring that the tools required for the repair would readily available at home.This report does not investigate the economic impact of the required changes and focuses solely on a

redesign from a sustainable viewpoint.


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Table Of Contents

Abstract ......................................................................................................................................................... 2Table Of Contents ......................................................................................................................................... 3Table of Figures ............................................................................................................................................. 4Background ................................................................................................................................................... 5

Scope ......................................................................................................................................................... 5Current Repair Options ............................................................................................................................. 5

Disassembly Procedure: ................................................................................................................................ 6Contents of the Repair kit ......................................................................................................................... 6Disassembly Steps ..................................................................................................................................... 7

Engineering Requirements .......................................................................................................................... 10Design for Repair Factors and Considerations ............................................................................................ 12

Product structure .................................................................................................................................... 12Fasteners ................................................................................................................................................. 13Characteristics of components for disassembly. .................................................................................... 14Conditions for Repair .............................................................................................................................. 14Assembly ................................................................................................................................................. 15Material ................................................................................................................................................... 15Parts consolidation ................................................................................................................................. 16

Design Options ............................................................................................................................................ 16Fasteners ................................................................................................................................................. 16Types of Fasteners .................................................................................................................................. 17Battery and Internal Frame Fasteners .................................................................................................... 22Material ................................................................................................................................................... 22

Proposed testing ......................................................................................................................................... 23Final Design ................................................................................................................................................. 23

Critique of this design ............................................................................................................................. 24Bibliography ................................................................................................................................................ 25


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Table of Figures

Figure 1: Repair kit for IPod 5th generation (Ebay) 6Figure 2: Left. Starting Position for disassembly Right. Appearance of fasteners 7Figure 3: Broken Fastener seat and internal frame screw 8Figure 4: Battery Location 9Figure 5: Location of Battery ribbon cable 9Figure 6: I. Fastener to connect halves II. heat vent and guide IIi. Spot welds that mount fasteners 13Figure 7: Location of internal screw fasteners 13Figure 8: Residual glue after battery removal 14Figure 9: Mating guide and slot 15Figure 10: Left: Clamped end design Right: Hinged design 17Figure 11: Tensile Strain permitted in a brittle material (Malloy, 336) 18Figure 12: Snap Fit Configurations 19Figure 13: Left: Annual Snap fit (Malloy 336) Middle: Slotted annular snap (Malloy, 336) Right: TaperedAnnular snap (PDL, 123) 20Figure 14: Ball and Socket Snap (Malloy, 336) 20Figure 15: 90 degree ejection (Special Techniques)(Malloy, 353) 20Figure 16: Simple angled deflection (Malloy 353) 20Figure 17: Tapered Cantilever Snap Hook Design 21Figure 18: Correction Factor Data 21Figure 19: (a) Over Design View (b) Hinge Locking Mechanism (similar to washer) (c) Close up of Fastener

to hold the front and back panel with the internal frame between 24Figure 20: Battery Locking Mechanism (Malloy 353) 24


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Background

Over the last decade, the digital media market has been dominated by the revolutionary technological

design of the Apple IPod. Despite various technological advances through its generations, one problem

has yet to be addressed by their designers: customer battery replacement. Contrary to their design,

manufacturers such as Sandisk, in particular their Sansa model, allow for easy access to the devices

battery via a removable back plate.

Scope

The scope of this paper is to present a feasible re-design of the 5th generation IPod video to allow for

better customer repair of the battery. Accomplishing this task will require a detailed dissection of the

current mechanisms for fastening the case and redesigning it for customer use. This project is based on

the concept of sustainability and not from a business perspective. In other words, this project is not

designed to maximize the profit of Apple as a proprietor but to promote the reduction, reuse andrecyclability of the product throughout its entire life cycle.

Current Repair Options

The design of the Apple IPod, specifically the 5th generation video model examined, was not designed for

the intent to be worked on by the customer. The reasons for this are underlined in the presumption that

Apple believed that the battery would function longer than the life cycle of the other component

systems. Based on customer testimonials, the average lifespan of a 5 th generation battery is over four

years; a point at which most people would choose to upgrade their models. However for the consumer

who wishes to replace their battery, the following options currently exist.

a) Return to Apple for replacement: This process entails returning the unit to Apple to allow atechnician to repair the unit. This requires additional cost for shipment, energy

considerations for the shipment (ie. the gas emissions of the delivery method) and

additional time that the user must wait for their unit to be returned. Apple offers this

replacement service for $59 USD + shipping as quoted from:

http://www.apple.com/support/ipod/service/prices/#us .

At this point it is best to state that the cost of a replacement battery from Hong Kong via

Ebay was approximately $4 USD with shipping. Factoring in the replacement time of a

trained technician of approx 10mins (estimate determined later in paper), $59 USD seems

highly overpriced. It should be noted that similar wait times for shipping of 2-3 weeks was

needed for the arrival of the replacement battery as well. Shorter shipping times can be

achieved by quicker shipment methods which are inherently more expensive.
http://www.apple.com/support/ipod/service/prices/#ushttp://www.apple.com/support/ipod/service/prices/#ushttp://www.apple.com/support/ipod/service/prices/#us


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b) Take your IPod to a 3rd party location: Several outlets have been opened by entrepreneursto exploit the large markup that Apple charges to their consumers. They promise on the

spot replacement in the time that it will take for you to grab a coffee from the nearest

location down the block. Such services are usually offered for $20-30 USD but a disclaimer

for damages is needed to alleviate any liability to the technician if the IPod becomes

damaged. IPod on the other hand offers 100% customer satisfaction and the consumer

holds some rights against property damage.

c) Do It Yourself: This was the option explored for the purpose of this report. Several websites,including Ebay, offer replacement kits for this particular model of IPod. They ranged

anywhere from $4-30 USD online. The contents of the kit will be detailed later.

d) Recycle the whole unit to a location that recycles electronics such as FutureShop, etc. Otheroptions include selling the unit for repair parts on Ebay as fellow DIY consumers are looking

for other components that may work in your model, such as the HD (replacements are very

expensive).

Disassembly Procedure:

Contents of the Repair kit

After the purchase on Ebay and two weeks wait time for arrival, the following packaged kit arrived as

shown in the figure below.

Figure 1: Repair kit for IPod 5th generation (Ebay)

The package consisted of the following:

1 x replacement battery 1 x instruction sheet 2 x green plastic specialty tools for opening the case


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Disassembly Steps

These are given by the accompanying documentation that was present in the kit upon purchase. It

should be noted that the instruction leaflet was black and white with pictures that were slightly larger

than an inch squared which provided insufficient detail.

CAUTION: It should be noted that online tutorials are available on Youtube, and various other locations,

on the proper procedure to ensure that no pieces are damaged. Screenshots from these videos will be

added when deemed necessary to exemplify points that were not clear in the instruction pamphlet.

Video location:http://www.youtube.com/watch?v=9csNyvh2mw0

Estimated time for repair by practiced technician: Under ten minutes.

Step 1

Flatly place IPod when replacing battery. Using the included IPod screwdriver (specialty tool) or other

available tools to pry open the side of the case, starting around the area that lines up with FFWD button

that is approximately 1.5 from the topside as shown. Gently twist the screwdriver and pry up the

bottom corner closest to the screwdriver.

Comments: After close inspection, a small open slot can be observed at the location indicated.

As per instructions, the tool was inserted and twisted with little difficulty.

Step 2

With the screwdriver wedged inside the case, carefully work your way together with another

screwdriver up to the top of the IPOD, unclipping the case clips as you go.

Figure 2: Left. Starting Position for disassembly Right. Appearance of fasteners

Comments: This is the trickiest part of the disassembly and is not clearly defined in these

instructions for the following reasons.
http://www.youtube.com/watch?v=9csNyvh2mw0http://www.youtube.com/watch?v=9csNyvh2mw0http://www.youtube.com/watch?v=9csNyvh2mw0http://www.youtube.com/watch?v=9csNyvh2mw0


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1. The intent of keeping the first screwdriver in place is to apply a lateral force onto themiddle clip. Theoretically this should cause a slight deformation of the other clips

located near the corners due to bending. Mirroring this effect is that when pressure is

placed on the corner clips, a force is transmitted to the initial holding screwdriver which

several times caused the holding screwdriver to become dislodged.

2. The installation required two hands and the unfastening of the other clips were difficultas their locations were not indicated in the instructions or on the unit itself. Combined

with other factors to be discussed later, it is sufficient to state that this IPod will never

be closed properly again.

Step 3

Pay attention to the structure of each fastener when opening the case and make sure to completely pop

up each button.

Comments: This step is imperative for the consumer to follow as if the clips are not recognized

and opened properly, tab seats can be broken (indicated by the circles in the figure). One of the

small internal screws for holding the internal frame to the front panel is also shown in this

figure.

Figure 3: Broken Fastener seat and internal frame screw

Step 4

After opening the case, take up the upper case and hard drive with one hand, and then use the other

hand to pry the battery from the glue spot. The location of the battery and its attached ribbon are

shown below in the figure below.

Removal of the battery required a lot of force to pry it free from the case (in actuality, the

plastic tool used snapped from the prying moment applied). This prying moment also caused the

unit to move along the flat surface so an edge of a table or surface is needed to prevent the unit

from moving.


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Figure 4: Battery Location

Step 5

Fully open the case and pay attention to the structure of each button as shown and also to the

orientation of the battery and cable.

Comments: When placing the halves side by side as the instruction indicated in the photo, thebattery cable actually was dislodged. This was not an issue as this actually is the next step for

the assembly. Also if the front panel is upside down during this point of disassembly, the hard

drive and all internal components will fall out of place and are very difficult to realign for

assembly.

Step 6

Using the screwdriver or your hand, disconnect the power cord connector from the socket which is

shown in the accompanying figure.

Comments: The unlocking mechanism to remove the cable was not explained. It is noted that

the lock can be overcome with little force, but it may also cause damage to the ribbon that

could be avoided.

Figure 5: Location of Battery ribbon cable

Step 7

Then the cable connector can be pulled out safely after disconnecting the power cord connector.


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Comment: This step is completely unnecessary and is omitted from the online video tutorial for

repair.

Step 8

Apply the new battery to the original orientation and glue spots, move the power cable to the original

spot and insert the cable connector into the socket.

Comments: This step was intuitive as it is a retracing the steps used for disassembly.

Step 9

Lock the cable connector by pressing down the lock mechanism with the screwdriver.

Comment: Similar to step 8, this is a reverse of the disassembly.

Step 10

Turn the IPod on when the battery is completely installed and then snap the case back if the IPod can

work normally. Your new batter will need a minimum of three hour of charging before first use.

Comments: This step contrasts and exemplifies that the unit was designed for assembly only and

not disassembly as the halves easily rejoin (if all fasteners are intact).

Engineering Requirements

There are multiple engineering challenges in designing this case and are dictated by several factors such

as cost, manufacturability, and aesthetic. The following requirements of the design are outlined.

1. Lightweight design. This design criterion is primarily driven by the ergonomics of the userwho do not wish to carry heavy objects on their personal beings. This is the driving reason

why these units are being parts consolidated to include cell phone, internet and other

functions to reduce the need for other devices. This parts consolidation is beyond the scope

of the report but is a point of interest, especially as newer IPods are now capable of takingphotos, downloading from the internet and more. Modifications to the new design should

not add significant weight to the existing product.

2. Size. Miniaturization is vital as this will help reduce the weight, as well as the space allocatedon the users personal being. Thus all modifications should be able to fit into the current size

restrictions that are imposed by the motherboard circuit and all other components.


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3. Structural. Most users have at one point in the life cycle of the product dropped it from adistance (assumed to be 1m for practical tests for most fastener designs). Thus the case, as

well as the clips must be able to handle significant impact loading.

4. Aesthetic. The case has to be visually appealing for consumers to buy it. This dictates thematerial choices and the design of the product. Market research was likely the driving force

for the choice of the aluminum back cover and modifications to the cover should be kept

minimal. Even at this early stage, it is known that access points or markings will be placed on

the unit which will modify its visual appeal.

5. Scratch resistance and durability. The products case ideally would be able to withstandwear and tear from regular transport where scratches can occur. The buttons and other

interactive components must be also able to handle the repeated usage of the user. The

modifications however do not need to handle repeated use as it is assumed that the user

will only open the case a few times in its lifespan.

6. Climates. The material selection should not have a coefficient of expansion such that ithinders its internal restraining capability. If the case expands as a varying rate to that of the

internals it holds, the hard drive could shift internally and damage the non-solid state drive.

Thus it should be designed to handle regular climates in N. America. Water absorption is

also important as the mechanical properties of some polymers can be drastically changed in

high humidity.

7. Automation. The case should be designed to be manufactured by automated means due tohigh volumes of sales. Additionally, the case should be designed to be integrated with other

internal components to allow for automated assembly.

8. Thermal consideration. In the small confined space of the unit, it is assumed that theelectrical components, as well as the LCD screen will radiate some heat that should be

dissipated to the surroundings. Small vents are located on the inside of the back cover which

also serve the purpose as a guide for assembly. Therefore these vents need to be present

within the modified design as well.

9. Fastener should not protrude from the surface of the casing. This will minimize the risk for itto be caught on clothing while in the users pocket.

10.Hardwired connections to the circuitboard such as solder will not be used as mostconsumers do not own the required tools. The current clip and ribbon system will be utilized

as well. Due to unknown design constraints of the main circuitboard, all features such as the

position of the headphone jack, LCD, and main wheel button will not be moved.


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11. Other factors should include that the unit is resistant to accidental openings in pockets; aswell as able to handle drop from its user.

Design for Repair Factors and Considerations

The proposed solution should include the following:

1. Components that are readily accessible to the user2. Components that can be readily replaced by the user

The main contributing factor to the ability of the customer to repair this unit is not the battery

installation but the access to the battery points itself. Therefore this products effectiveness will be

analyzed from this perspective.

Product structure

Creation of a modular design

This criterion was satisfied in the current design as the main components can be replaced when

unfastened from the unit. This drives the DIY movement and the sale of non-working components on

Ebay and other sites as once the case is fully exposed, the replacement of the hard drive, battery and

screen are almost intuitive. New replacement parts, similar to the battery in this case, are available for

the hard drive, LCD screen from 3rd party distributors that can be easily found online through Google.

Minimization of Parts

This design concept should be applied to the new design as it will reduce the amount of parts that may

fail and need to be replaced during the units lifespan; necessitating that only a few modules would

need to be offered for replacement. Proper reductions should also make it easier for dismantling the

unit, allow for easier recycling, and reduce the units overall size.

Minimize Product variants

Through research online, it is evident that Apple utilized sufficient forethought to reuse the case and

screen of this model on their Apple Classic design which was released a year later. This model is stillbeing produced today (the 5th generation dismantled was released in 2005/2006). Therefore

replacement/upgrade parts can be offered as a cost effective solution to the user, as opposed to

providing them with an entirely new product. An example would be to offer a larger hard drive for older

models as this is the main reason users purchase a new unit (most other features are unchanged

between this unit and the classic, just new marketing and branding). Screen replacements should also be

offered as it is a standard size and style for several models.


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Fasteners

Minimization of Fasteners

Fasteners that connect the outer silver case to the front casings

These fasteners are essential to holding the internal parts to the component together. The focus will not

to eliminate them but to redesign them to meet design criteria.

Figure 6: I. Fastener to connect halves II. heat vent and guide IIi. Spot welds that mount fasteners

Fasteners that connect the inner frame to the front panel

These fasteners are 3 screws positioned on each side of the front panel that are used to connect it to

the internal frame as shown. To reduce parts, the new design will investigate a snap mechanism that is

capable of holding the inner frame, front panel and rear panel together in a sandwich structure.

Figure 7: Location of internal screw fasteners

Visible and accessible joints


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The snap fits are hidden underneath the case with no obvious marking as to their locations. Thus one

needs to locate them by feel with the appropriate tool which to the inexperienced is difficult and can

result in damaged parts as previously mentioned. Therefore the fastener mechanism utilized in the new

design will be visible on the outside exterior of the case.

Joints that are easy to assemble and disassemble

These joints are not easy to take apart as they are designed with a sharp radius that is difficult in its

orientation to dislodge from the seat located on the front frame. The large amount of force applied a

high amount of torque on the tool which can cause it to snap. It is important to note that this was an

intentional feature implemented by the designer to ensure that the unit remains closed during everyday

use.

Note: The plastic tools are used to ensure that no damage is done to the aluminum back casing. A

screwdriver can be used which would be stronger but also may scratch the rear casing.

Fasteners rather than adhesives.

The new design will not use glue to hold the battery in place. A clip system will be introduced in the new

design. The amount of adhesive used is shown below by the residue after the battery was removed.

Figure 8: Residual glue after battery removal

Characteristics of components for disassembly.

Robust, minimize fragile parts

It is fairly common for beginners to break the bottoms of the plastic seats that lock the fasteners in the

current model; as was done in my attempt at this DIY project. This is a catastrophic problem as these

clips are molded into the front case. Therefore the new fastener system should be constructed to avoid

failure or implement redundancy if one set of fasteners are broken.

Conditions for Repair


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Elimination of specialized tools

One should not need to have specialized tools to conduct this project. There is no reason that a common

household tool cannot be used to conduct this project (ie. screwdriver, pentip, etc).

Disassembly technique that is easy to understand from a set of instructions

It is difficult to fully grasp the technique of this project without trying it because this method is not used

on other equipment familiar to users. A preferred technique would be familiar to most users as it is

intuitive or commonplace with other consumer goods. For instance, one should not have to think for

several minutes or be told where the access point to the case is located as present in the current design.

Assembly

Uni-directional assembly and disassembly and the use of the heating vents as guides to align the rear

cover with the internal frame will remain unchanged in this design.

Figure 9: Mating guide and slot

Material

Minimization of different materials

The inclusion of different case materials within this design makes the process of recycling more difficult

and also requires different manufacturing processes. The aluminum case is stretched formed, with the

fastener rail attached on the inner sides with several spot welds as previously shown; a permanent joint

which should be avoided from the sustainable perspective.

The aluminum fastener rail is partially pierced and bent into its configuration and could be included into

the rear cover using injection molding. This process is a near net shape process, as is sheet metal

processes, and thus no additional material waste is incurred.

Recyclable Materials


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All of the case materials are presumably recyclable within the current design. However it should be

noted that the front and back casings, as well as the elastomer hard drive mounts can not be recycled

together in the same process. Integrated snaps for the battery would promote recycling as removing the

glue would require a special process. The internal circuits would also require their own recycle process

due to the need to recapture some of the precious metals located in the LCD screen such as gallium and

indium. Energy to create the aluminum from raw materials is much larger than the energy that is used

for its recycling. Therefore it is in the best interest of the manufacturer of this product to recapture as

much as possible through recycling. A program should be introduced by Apple, similar to the Kodak

camera, to recapture the units for recycling.

Renewable materials

Alternative materials are being offered that are 100% bio-degradable and do not pose any risk to the

earth. The new design will investigate whether any new materials since the production of this unit has

been invented can be used to fulfill the design criteria.

Parts consolidation

Plastic cable entrance piece on the metal case

This piece is presumably used to promote easier sliding of the connecting cable to the unit. It may be

used also for electrical insulating so that two metal contacts are not touching that can promote ill

desired effects. Regardless of its intent, it can be easily integrated into the rear plate if it was

manufactured from similar material to that of the back cover. This will result also in the removal of two

screws that are used to hold the plastic insert to the cover. Similarly the headphone insert can be

molded in the rear plate to remove an internal screw and piece.

Design Options

It is evident from the previous discussion that the fastener type, position and materials are the most

significant design choices. This section is dedicated to the available options and their pros and cons.

Fasteners

Fully clamped or free side design

Two designs are examined: a fully clamped design which utilizes a set of fasteners on either side of the

front panel as within the current design or a hinged design which would require on fasteners on one

side with a guided slot located on the other side. This author believes that the latter would be most

beneficial to this design as it is reduces the complexity of the disassembly (and thus the assembly) as the


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font cover could be removed easily and intuitively by the user without the movement of internal pieces.

These are shown respectively below.

Figure 10: Left: Clamped end design Right: Hinged design

Location/Amount

The current design utilizes three locations for fastening the front panel to the back casing on each side;

as well as 3 other locations (one on opposite sides of the USB connection and another located at the top

above the screen). The side panels are located at each corner with one in the center which is intended

to prevent any cantilever loading of the casing if a corner is caught on clothing or another device. The

bottom fasteners are located at the center points on either side of the connector which is used to

provide additional support to ensure that the alignment of the connector relative to the back case is

kept within close tolerance. All fasteners, coupled with tight tolerances allow for a tight seal against

contaminants that could harm the internal components.

It also is of interest that during disassembly, the front case was twisted about the side axis which

illustrates the weak torsional rigidity of front panel when some of the fasteners are not locked in placed.

Therefore the fasteners should limit the vertical deflections needed to unlock fasteners to ensure that

the torsional effects occur within the elastic region of the material.

Types of Fasteners

It is important to re-emphasize that any screws, permanent joints or adhesives are not considered for

final design.

Press Fits

Press fits are the simplest means of connecting injection molded pieces together as they utilize the

materials elastic properties to provide high pressure between mating pieces which induce high

frictional holding forces. They are commonly used in the mating of two cylindrical components such as


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gears and hubs on shifts due to the uniform distribution of stresses around their circumference.

However, relaxation and crazing (especially in glossy thermoplastics) due to the long-term

tensile/compressive stress loading can occur in each mating material. Also rigid glossy polymers have

typical breaking strains of less than 1.0% and as shown in the figure should not be used in press-fit

applications.

Figure 11: Tensile Strain permitted in a brittle material (Malloy, 336)

Snap fits

Snap or interference fits can be designed to be beneficial for assembly and disassembly (repair) if

correctly designed. Snap fits can have a multitude of different geometries but all posses the same

underlying principle;

a protruding feature on one component, such as a hook or beam, is deflected briefly during the product

assembly operation due to an interference, after which the protruding part recovers elastically, and

catches an undercut or indentation on the mating component.

(Malloy, 1994)

The deflection can cause additionally stresses to the system but are usually relieved when the snap fit is

engaged.

Disadvantages:

As demonstrated with the current design, snap fits can fail due to improper handling during the

assembly process. These joints also may need to be designed for fatigue loading which is not a primary

concern for this project as the case is suspected to be only opened a limited amount of times during its

life cycle. A failed snap joint due to its integration into other parts of the design can result in component

failure; contrary to external fasteners which can be easily interchanged without affecting other

components in the design. Therefore for this design, it will be deemed advantageous to overdesign the

number of snap fits needed to act as a redundancy system for foreseen breaks. All joints therefore will

be reinforced with redundancy.

Types


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Snap hooks or beams:

Further categorization can include non-separable and separable which will be the type examined for this

project. Cantilever beams are the most common type of snap fit that are used within practice. The types

usually used for plastic parts are shown inthe figure below. Separable joints exhibit both lead in and

lead out angles that are used to promote the deflection of the piece when a force is applied.

Portion (a) of the figure is a perfect example of a 90 degree return angle which is not good for

disassembly as high forces (most likely to the point of breaking) will actually be needed to open the part

which is not desirable for customer repair. However the application of an access slot as shown in (c) will

provide access for the customer to easily open the slot. The location of the access port can be

positioned vertically at the bottom of the cantilever to increase the bending torque per unit force on the

beam.

Figure 12: Snap Fit Configurations

Option A is similar to the current design as it is for assembly only. Option B is designed for disassembly

but would require a large clamping force on the sides to lift the fastener out of place. Option D has a

protrusion on the top surface which can be snagged on clothes and other items during daily use.Therefore Option C is deemed the most viable, despite the obvious tradeoff that the unit will become

higher risk to contaminants and possess a higher risk of accidental opening. It is assumed however, that

the horizontal and vertical forces needed to open the unit will not accidentally occur simultaneously.

Annular or ring snaps

These are usually applied to cylindrical components as shown in the figure below. Another useful

adaption of this fit is the slotted annular snap which is used for rigid polymers where deflections per

beam are limited. However these options result in a low clamping force, protrusion from surface for

access, and design for assembly only as respectively shown.


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Figure 13: Left: Annual Snap fit (Malloy 336) Middle: Slotted annular snap (Malloy, 336) Right: Tapered Annular snap (PDL, 123)

Ball and socket/Torsional Snaps

Neither of these designs were considered due to the weak holding forces they impose.

Figure 14: Ball and Socket Snap (Malloy, 336)

Molding

Despite the simplifications to the assembly and disassembly processes, snap fits can impose complex

geometries that are hard to manufacturer. Snap fits must have undercuts which defines that the

ejection process must be able of releasing the finished part from the mold. Although not perceived to be

an issue in this design, small thickness to length ratios can cause issues with mold filling. The problem of

ejection is shown below.

Figure 15: 90 degree ejection (Special Techniques)(Malloy, 353)

Therefore the cantilever beams used in the design will be in-plane which does not require any special

mold actions, relative to those experienced in the figure above. In-plane geometry is displayed below.

Figure 16: Simple angled deflection (Malloy 353)


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Design

For this design model, the beam will be examined individually from that of the surrounding parts. It is

assumed that the part can be manufactured, as a result of the investigation into the molding process.

Thus, the remaining two design concerns are as follows:

1. Stresses undergone throughout assembly and disassembly2. The mechanical stresses imposed at the final step

Bending stress

This project will use a simplified model based on the classic beam theory and its associated

simplifications. For accurate results, a finite-element model or physical testing of the product can be

performed to see the influence of fillet radii, adjacent wall deflections, and true geometries. For

application of the beam theory, the designer must select whether the beam is of a constant or tapered

thickness. The cantilever can have both a variable thickness through its thickness and width. Relative to

constant thickness beams, tapered beams exhibit a more uniform stress distribution along the beam and

allow for larger deflections of up to 60%.

A common tapered beam design which tapers over the full length with a reduction of 50% in depth will

be utilized as space for the fastener is limited. Relating the deflection to the bending strain using classic

beam theory can be shown as:

Figure 17: Tapered Cantilever Snap Hook Design

Figure 18: Correction Factor Data

where

y is deflection in m

(1)


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L is the length of the beam

d is the depth of the beam

c is a correction factor

Despite tapered beams having a better ability for deflection, they do suffer a loss in ultimate strength

and disassembly force due to the reduction in its stiffness which may be a significant factor if the unit

undergoes large impact loads.

Appropriate stress concentrations should be applied for the fillet connecting the beam to its base.

Battery and Internal Frame Fasteners

The internal battery will be restrained in a housing designed on the back cover that utilizes two

cantilever snaps for assembly and disassembly. This is shown in the final design drawings at the end of

the report.

The internal frame will be held in place by the lugged hinge that is on the front housing. This lug will

sandwich the internal frame between both the front and rear panels. Annular snap or circular press fits

were not considered to be placed in the location of the screws on the internal frame (to mate with the

corresponding location on the front panel) for one simple reason: the internal frame is too rigid to

undergo the necessary deflections for (dis)assembly. Altering the material to allow for the deflection

was not considered as this would likely add significantly to the size of the frame.

Material

For this project, the material of the back casing will be selected to match that of the front casing. This

alteration has shown to be effective in the new classic models which indicate that the rear cover was for

aesthetic purposes only and not structural. However the internal infrastructure is presumed to have

been engineered to a distinct thickness to resist the bending moments applied by the front case, fatigue

loading, and thermal heat. Sufficient testing under these conditions should be conducted on the front

and rear casing as well but the minute changes are assumed to only affect the fasteners and not the

connected parts.

Alternatives are becoming more and more available for designers to use. An expanding field of bio-

plastics is emerging from the markets desire for a renewable material. Brazilian chemical groupBraskem plans to introduce this year a bio-polyethylene that is not only renewable but has 5/7 less

carbon emissions than current practices. However, it should be noted that most of these processes rely

on some form of natural agriculture (sugar in the Braskam case) which relies on farm machinery, etc that

run on petroleum derivatives. Thus the reduced emissions is only in regards to its manufacturing process


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and does not take into account the emissions that are required in obtaining the raw material. Further

research provided insufficient evidence as to whether this material could be recycled. Therefore despite

an initial appearance of a more sustainable material a detailed review indicates that for repeated life

cycles (assuming recycling is performed) it may not produce less overall emissions that the current

petroleum options. (http://en.wikipedia.org/wiki/Bioplastic)

Proposed testing

Impact testing such as the Izod and Charpy tests of notched specimens, the tensile impact test, and the

falling dart test could be used to estimate if the snap fits will fail or become loose when dropped from a

height of 1m above the ground. Prototype testing should also be carried out on the final design.

Final Design

The final design will have the following major changes.

1. The rear casing will be made of the similar acrylic material that is on the front cover for thepurpose of parts consolidation and reduction in process such as spot welding. It will be

manufactured through injection molding.

2. Non-destructive disassembly techniques will be utilized by changing the types of fasteners3. Fasteners will be visible and accessible to the user4. The need for specialized tools will be eliminated as the fasteners will be able to be manipulated

by standard tools that all consumers are expected to own.

5. The fasteners require a laternal and vertical force for opening to ensure that the unit is notopened during normal use.

6. The size and placement of external features were not compromised.7. The hinged design will intuitively indicate how the part is to be opened and can be easily shown

in instruction schematics.

8. The screw fasteners for the internal components are removed.9. The adhesive for the battery is removed.

It is essential to note that this final design is purely conceptual with no design calculations performed,

despite being introduced in the previous sections. The final conceptual drawing is illustrated on the

following pages:


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The final design is shown in the figures below:

Figure 19: (a) Case Design (b) Hinge Locking Mechanism (similar to washer) (c) Close up of Fastener to hold the front and back

panel with the internal frame between

Figure 20: Battery Locking Mechanism (Malloy 353)

Critique of this design

The goals of the redesign should be kept clearly in mind as the Apple designers incorporated several

other factors that were omitted in this design which were cost, market research results, among others.

However some notable trade-offs can be discussed.

1.

The additional application of battery fasteners will add to the overall size of the unit. Glue doesnot add considerably weight or size to a design and this is why it was chosen initially. The trade-

off using fasteners is better recyclability and customer repair ability.

2. The implementation of redundancy on the case fasteners will result in longer lasting productsbut imposes extra material and more complex manufacturing.

3. The removal of the end fasteners that were present was performed as sufficient clamping powershould be provided by the lug and extra side fasteners. Due to added fasteners on the side,

some of the heating vents may need to be relocated to the top and bottom panels. The removal

results in a more compact and lighter unit but may cause sealing problems if the top and bottom

panels begin to bend apart from normal use. Test should be done to address these issues to

optimize the placement of the vents and fasteners.

4. The hard drive guides will need to be molded into the rear casing, rather than its location in thefront panel currently. Since injection molding is to be done on this part, the inclusion of this is

deemed not a problem.


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5. The aesthetic appeal of the back plate is altered and significant market research should be doneto find out the implications of this change. This applies to the effect of the slotted design as well.

This research may have been the primary reason for the current fastener design without access

locations.

Bibliography

Malloy, R. A. (1994). Plastic Part Design for Injection Moulding. New York: Hanser.

PDL Group. Handbook of Plastics Joining: A Practical Guide.

Access Location:http://orbis.uottawa.ca/record=b3157131~S0
http://orbis.uottawa.ca/record=b3157131~S0http://orbis.uottawa.ca/record=b3157131~S0http://orbis.uottawa.ca/record=b3157131~S0http://orbis.uottawa.ca/record=b3157131~S0

Documents

iPOD Case Design for simplified battery replacement