dfma report

DFMA ReportThe Design for Manufacturing and Assembly Features of a Deskjet Printer

Kerrie Noble, 4th Year PDE, 200948192

11/5/2012

I declare that this submission is entirely my own original work.This is the final version of my submission.I declare that, except where fully referenced direct quotations have been included, no aspect of this submission has been copied from any other source.I declare that all other works cited in this submission have been appropriately referenced.I understand that any act of Academic Dishonesty such as plagiarism or collusion may result in the non-award of my degree.

Signed …………………….…………………... Date 05/11/2012

ContentsIntroduction to Design for Manufacture and Assembly........................................................................3

My Chosen Product...............................................................................................................................3

Design for Automation and Assembly...................................................................................................5

Design for Plastics................................................................................................................................17

Design for Fastening and Other Joining Methods................................................................................32

Design Considerations for Boring....................................................................................................32

Design Considerations for Drilling...................................................................................................35

Design Considerations for Soldering................................................................................................36

Design for Mechanical Fastening.....................................................................................................37

Design for Sheet Metal and Presswork................................................................................................42

Conclusion...........................................................................................................................................47

References...........................................................................................................................................48

Introduction to Design for Manufacture and AssemblyIn many instances the failure of a component or product can be traced back to the design of parts and assembly procedures being used. Design for Manufacture and Assembly, more commonly abbreviated to DFMA, is the process by which designs, assembly sequences and procedures are analysed and altered in order to increase the effectiveness of automated assembly. (unknown author, dora.eeap) The term ‘increasing effectiveness’, is defined as minimising the cost of production and/or time to market for a product, while maintaining an appropriate level of quality. (Cook, C., and Youssefi, K,) This can be expanded further, to the point where DFMA can also be defined as the process of proactively designing products to optimize all the manufacturing functions: fabrication, assembly, test, procurement, shipping, delivery, service, and repair while also assuring the best cost, quality, reliability, regulatory compliance, safety, time-to-market, and customer satisfaction. (Hamidi, M., and Farahmand, K, 2008)

To achieve the objectives of DFMA, which were outlined above, there are some key guidelines to follow during the design stage of any mass produced product;

Minimize part count Make parts multi-functional Reduce the number of screws and screw types Facilitate parts handling Use standard parts and hardware Encourage modular assembly Use stack assemblies/Don’t fight gravity Design parts with self-locating features Minimize number of surfaces Assemble in the open Simplify and optimize the manufacturing process Eliminate interfaces Design for part inter-changeability Design tolerances to meet process capability

These key guidelines lead to the ability to identify many features within a typical mass produced product. (unknown author, smaplab) To show how DFMA is applied in an industrial setting I have chosen to look at a mass produced product where many DFMA features can be highlighted.

My Chosen ProductThe product which I have chosen to analyse for this study on DFMA is the HP Deskjet F4200 All-In-One series printer. The Desk-top printer was first developed in 2007 and has since been produced in China for the Hewlett-Packard Development Company. This is a mass produced product within the printer and copier business sector, and is sold world-wide.

Ink-jet printers are a multi-billion dollar industry worldwide, and since the introduction of the deskjet product series in the 80’s, the market and competition within it has grown significantly. In the 90’s HP faced the following conflictions when designing the latest desk-jet products;

Upholding the HP reputation for quality and service Meeting the increasing demand for printing products and increasing the company’s market

share Achieving the targets for profit and revenue growth And also sustaining the ‘HP Way’ of management

HP set a target of producing 300,000 printers per month from the production line in Vancouver with the aid of an automated manufacturing system. The operations report produced in 2008, as a joint venture with the Hewlett-Packard company and the Massachusetts Institute of Technology, outlined the new system design for the production of the Deskjet product and highlighted the success the company were having with this at that particular time within the company’s history. (Burman, M., Gershwin, S. B., and Suyematsu, C, 1998)

This report highlighted that Design for Manufacture and Assembly was a large consideration for this company, as far back as 1998. Through the use of system design the company appeared to have re-assessed the design for production needs within the product, and had a large success with this. As a result I was interested in finding out if DFMA was still considered in depth by the company through the analysing of the design of one of their more recent Deskjet printer models. With DFMA there are nine main design areas which should be considered;

Design for machining Design for casting Design for forging Design for sheet metal and presswork Design for welding Design for fastening and other joining methods Design for plastics Design for assembly and automation Fault tree analysis

The four areas which have been highlighted above, design for sheet metal and presswork, design for fastening and other joining methods, design for plastics, and design for assembly and automation,

are the four DFMA design areas which I will explore throughout the report as I felt these were key areas for design consideration which mainly affected the design outcome of a Deskjet printer.

Design for Automation and AssemblyThe main aim of Design for Assembly is to simplify the product so that the cost of manufacture is reduced. This includes both part design and the design of the whole product with an analytical approach in order to identify any assembly problems early within the design process. (Chan, V., and Salustri, F. A., 2005)

There are a few recommended guidelines for this small area of Design for Manufacture and Assembly;

Use pyramid assembly, avoid the need to reposition the partially completed assembly in the fixture

Design parts that have end-to-end symmetry and rotational symmetry around the axis of insertion

Design parts that, in those instances in which the part cannot be made symmetric, are obviously asymmetric

Provide features that will avoid jamming of parts Avoid features that will allow tangling of parts Avoid parts that are sticky or slippery Reduce the number of different parts to a minimum Consider a reduction in the number of separate parts Introduce guides and chamfers to help with the placement of parts Show consideration within the design of difficulty of assembly in directions other than above Create a large base on which the assembly can be built. Features that make it suitable for

quick and accurate location on the work carrier

These are the main Design for Automation and Assembly guidelines as given in a report by Wisconsin University concerning Design for Assembly guidelines. These are the features which I will analyse within the HP Deskjet printer.

Use pyramid assembly, avoid the need to reposition the partially completed assembly in the fixture – Figure 1 shows a plan view of the hinge system which is use to attach the scanner/copier top cover. The areas highlighted within the picture clearly illustrate the ‘open-nature’ of the hinges on the outer surface of the product. This means that there are no sides or top to the hinge allowing the connection from the cover to slot into the correct place from directly above, the main direction of insertion when using a pyramidal assembly. Within the red triangular section which I have highlighted within the picture, the screw type used for assembling this product can be clearly identified. As this screw appears on the top surface of the printer,

Figure 1

this also helps to suggest a pyramidal assembly as the top of the screw appears to be in the same plane as the other features identified in the product. If the screw top had appeared to have been on a different plane to the hinge system which had been previously identified, then I would not have suggested the use of pyramidal assembly within this product. This would be because of the need for separate assembly actions to occur in many different directions during the entire assembly process. However, as this picture illustrates, separate components have been located into their correct position and then secured in place in a stacked assembly style, the main characteristic of pyramidal assembly. This is further evidenced in figure 2 below.

The colour coordinated spots in figure 3 highlight the many different component levels within the printer base, with green being the highest placed component and red denoting the lowest placed component. This helps to show the obvious structure with which the printer was assembled. The structure in the centre of the picture illustrates the black plastic casing, which is used for housing the ink cartridges, which is located on slide rails which are attached to sheet metal component. The only way the assembly for these particular components can be successful is to insert the components in the correct order in a sequential fashion, where the next component is stacked on top of the other. I believe this shows a good example of pyramidal assembly as it clearly illustrates the stacking of the components and the order of component insertion has also had to be considered in detail.

Figure 2 Figure 3

Figure 5

This figure shows a closer view of how the components within the printer are stacked. This illustrates the pyramidal assembly which was highlighted in figure 3.

Figure 5 shows how the stacking of components continues to lower levels than those which were highlighted in the previous figure. The arrow head in this figure is highlighting the roller bar which exists below the ink-head assembly which was discussed in the previous figure. This further highlights the extent of pyramidal assembly which is in use within this product.

Design parts that have end-to-end symmetry and rotational symmetry around the axis of insertion – The Deskjet printer has many components which need to be inserted during any assembly procedure. This therefore means that the inclusion of components with features that allow for quick and easy assembly location are necessary. One such feature which allows for quick and easy assembly location is the use of components with characteristic symmetry in many directions, to avoid confusion over the orientation of the component prior to locating the component within the assembly.

The component in Figure 6, shows a bad example of part symmetry within this product. The dashed line depicts the axis of insertion for this particular component. Therefore there are many features within the component design which prevent this component from being symmetrical, in a rotational sense, around the axis of insertion. There are many features highlighted in this figure which all contribute to making this component non-symmetrical. The first of these features are the recesses on the top

edge of the component, these are large in comparison to the size of the component and

are all individually sized. These recesses are also not replicated on the bottom edge of the component. The inclusion of roller bearings on one side of this component also creates a non-symmetrical part around the axis of insertion. The bottom edge of this component includes ridges which have been incorporated into the design in order to increase the strength due to the thin wall thickness of the part. The top edge of the component has a much larger wall thickness and therefore does not need these ridges to provide support or increase strength, these features therefore also add to the non-symmetrical nature of the component. This is a particularly bad example of end-to-end and rotational symmetry within part design, however, there are also good examples of part symmetry within this product.

Figure 6

Figure 7

The axle and rotating bearings, in figure 7, are part of a larger sub-assembly within the product. The axis of rotation is again shown by the dashed line which has been imposed on the picture. In this instance it is clear to see that the bearings and axle are all cylindrical shapes with no added features, this means that the component has rotational symmetry around the axis of insertion. This clearly demonstrates this specific guideline for designing for automation and assembly. In addition this component also has end-to-end symmetry, the blue dashed line denotes the axis of symmetry around the centre of the component. This figure therefore clearly demonstrates the advantages of component design with end-to-end and rotational symmetry. The benefits of this type of component design when considering assembly procedures is now clear, it is easy to assume that, with this type of component, assembly will be much more efficient due to reduction of time needed to correctly orient the component during the assembly process. With this type of component design the orientation is removed as a factor of concern as the component will operate regardless of its orientation.

Design parts that, in those instances in which the part cannot be made symmetric, are obviously asymmetric – Upon further analysis of the Deskjet printer it became evident that the majority of components within the product were designed with this guideline as a key limiting factor. Some

examples from the product are shown below;

In the example shown in Figure 8, the main outline of this component is symmetrical about the centre-line axis, shown here in red. There are however, some small but significant features incorporated within the design which make this component deliberately asymmetric to assist with assembly operations. Some of the asymmetric features include the use of rounded corners within insets which have been cut into the surface of the design, these features are highlighted in blue. A second

asymmetric feature incorporated in this design is the use of an additional feature added onto the face of the top surface of the component, this feature is used as a catch feature in order to keep a hinged component in place when the printer is not in use. This feature is highlighted in the figure in green. These features help to make the component asymmetric in nature to ensure the component can only be inserted in the correct orientation during assembly. Similar features have also been identified in a second component within the product, shown in figure 9.

Figure 8

Figure 9

In this figure it is easier to identify an asymmetric feature and to visualise how this has helped place the component during assembly. The sheet metal component highlighted in the picture has a side panel on only one edge of the component. Due to the positioning of other components relative to this piece of sheet metal, and the inclusion of the side panel, it therefore means that this particular component can only be fitted in one orientation during assembly, this is only possible through the use of this simple asymmetric feature.

Provide features that will avoid jamming of parts – For quick and efficient assembly, it is important that any part does not jam while in storage before being moved onto the production line. This is also an important consideration at an early stage of the design process for any component of the Deskjet printer.

The figures included above show a number of features, incorporated within various components of

the Deskjet printer, which avoid the jamming of parts before and during the assembly procedure. In Figure 10 the use of ribs has been highlighted. As with most products, it is obvious that features such as ribs are primarily there to add strength and support to large, flat polymer surfaces, however these features secondary role is to prevent components from jamming while contained in storage before being moved to the assembly line. The inclusion of these features prevents identical component parts being stacked and consequently becoming jammed while being stored in respective batches. There are many other examples of many types of features aimed at avoiding the jamming of parts during storage.

In figure 11 you can see two very different features which I believe also help prevent jamming in one of the various components within the Deskjet printer. The component shown here is the cover used

Figure 10 Figure 11

Figure 12

for the scanning component of the printer. The two key features here are the use and shape of the hinges and also the differing level heights which have been designed into the component. The different height levels prevent the internal stacking of these components, for example, plastic cups may be able to stack internally due to the conal shape of the product. With the component shown here, this cannot happen due to the lack of indented surface features and the differing surface heights. Also by placing the hinges on the outer edge of the product, with a relatively large height, prevents two of these components in storage becoming jammed.

The features in figure 12 work in a similar way to that of the ribs in figure 10. These three-dimensional features directly prevent the stacking of components within a storage situation. Finally, figure 13 shows an item of trim used for aesthetic appeal within the Deskjet printer. The design features outlined in this picture are the outer edges which have suitably rounded corners and the top-surface indentation. From experience, components tend to become jammed when flat surfaces and sharp corners are used within the design of the product. This component deliberately differentiates the top and bottom surfaces by including the surface indent, as highlighted, to prevent stacking. The rounded corners also help to lessen the probability of components becoming jammed or damaged during storage.

The figures above are again highlighting more features which I believe could lead to the jamming of parts, however, with these features I believe the jamming is more likely to occur during the assembly process rather than during storage before being used for assembly.

Figure 15

Figure 16

Figure 14shows the mounted circuit board within the assembly. In this figure the wires coming from the circuit board have been highlighted. This component design has a good element in that the wires all leave the circuit board in the same direction so that they can be contained in one corner of the assembly. I do believe that this design could also be improved. I believe it could be possible to include a track within the design of the printer base where the wires can be fed through during assembly, this would prevent the wires becoming tangled with other components which are added to the assembly after the circuit board has been secured. This would however, need to be considered as the time taken to feed wires through an enclosed track within the base would adversely affect the total time taken to assemble the product.

Figure 15 and 16 show the electronic tape connecting the print-head to the circuit board, this is effectively the intelligence within the product. In figure 15 features which have been specifically designed for this type of product to ensure the tape is secured in place and also to prevent jamming when the printer is in use and the prevention of tangling with other components during assembly. I think this is successful design as the operation of the product is not limited in any way but consideration has also clearly been given to the manufacturing process. Figure 16 however shows how closely the tape is secured to other components concerned with the movement of the print-head and the high potential tangling of these components due to compact and difficult circumstances surrounding assembly. The electronic tape is secured in place, however the toothed belt which drives the movement of the print-head has to be inserted manually alongside the tape. The space between these two components is minimal and therefore the risk of tangling and the difficulty of assembly must be high.

Avoid parts that are sticky or slippery – Before disassembling the printer to discover the design of the components being used within this particular model I assumed that this specific design guideline may be hard to achieve within this product due to the need for moving parts which are primarily of metallic structure. This was proved when the components were analysed in more detail.

In figure 17 the arrow head is highlighting the use of a metallic axle, believed to be steel, which is used to mount and secure the ink cartridge head within the assembly. The ink cartridge head is the principle moving component within the printer and it moves in a horizontal motion along this axle. Therefore, this component within the printer will have to endure the highest level of force and friction during constant use of a sustained period of time. Due to these requirements it is imperative that the

axle is lubricated to overcome the friction caused by the motion of the print-head. This lubrication causes the surface of the axle to become very slippery and therefore makes the assembly of this component difficult. This is an unavoidable use of a sticky and slippery surface because to the

Figure 17

operational requirements of the product, however, I believe the axle placed in a sub-assembly before being placed and fixed within the main body of the printer. This is due to the nature of the other components surrounding the axle, the fixtures being used and also the experience I had when trying to disassemble the component to analyse the design. If this component has been placed in the main assembly as part of a smaller sub-assembly then I believe this shows thought within the design process of how a difficult component can be inserted into the main assembly with more ease.

This is another example of the use of a slippery/sticky component within the printer. As with the previous component, the axle, this component is a necessity due to the operational requirements of the product. The difference between this component and the axle is the way in which this product has been placed into the main assembly of the printer. The axle which has been discussed above has been placed within a sub-assembly before being included in the main assembly procedure. In this figure, it is clear to see that the component is not part of a sub-assembly and has simply been placed into the required position within the component. From this picture it is clear to see the amount of liquid included within the texture of this component. I believe this could have caused the speed of the production and assembly of this product to slow however, overcoming this through design may be difficult. I believe the only possible solution to this problem would be to look into the use of different materials which satisfy the criteria of use during the product’s life-span.

Reduce the number of different parts to a minimum – As the Deskjet printer is a complex product, the number of different components involved will be higher than most other mass produced products.

Figure 19 shows some of the screws used to assemble the product. It is clear to see from the picture that all of the screws are the same diameter and length. They are also the same type of screw, all were removed from the product using the same, standard sized Allen-key. This is a prime example of designing to minimize the number of different parts used within the assembly of a product.

Figure 18

Figure 19Figure 20

Figure 20 illustrates the all the components which are part of the HP Deskjet printer assembly. As part of this assembly I counted approximately 53 different components within this product. Although this is a complex product involving the use of many mechanisms and fixtures, it is also a small and compact product so I believe this is a large number of different components for such a small product. I believe this number of components adds to the overall weight of the product. When comparing the physical specifications of this product with another similar model from a rival company, it is easy to see how design and the number of different components within the assembly may matter.

Physical Specification for HP Deskjet F4200 All-in-One Series

Height – 161.5mm

Width – 437.5mm

Depth – 290.4mm

Weight – 4.9kg

Physical Specifications for Epson Stylus SX130 Printer, Scanner, Copier (argos, 2012)

Height – 150mm

Width – 436mm

Depth – 365mm

Weight – 3.9kg

It is clear to see from this comparison that the two products are very similar in size but the Epson printer is 1kg lighter than the HP Deskjet being analysed in this report. I believe one of the main factors in this must be the number of different components being used within the design. I believe that the number of different parts being used in a product proportionally affects the weight of the product. However, to prove this I would also need to analyse the Epson Stylus SX130.

Consider a reduction in the number of separate parts – It became clear during the disassembly of this product that sub-assemblies had been used throughout the assembly procedure for this product.

Figure 21

When first looking at the product the overall impression it creates is one of complexity, large number of parts and time consuming assembly procedures. This is what is shown in figure 21. However, upon further analysis it became clear that the complex appearance of the product soon became split into more manageable sub-assemblies. These are shown in figure 22 and 23. These are two of the main sub-assemblies within the main base assembly of the product. When these sub-

assemblies were removed from the product there were few components left within the main base of the printer. Those components which were left were small, light components which were directly fixed to the plastic base of the product.

Introduce chamfers and guides to help with the placement of parts – Chamfers and guides are essential for ease of assembly, which helps to reduce the time taken to produce the product. There were many examples within this product of the use of chamfers and guides.

In figure 24, the use of guides can be clearly seen. The guides here are situated on the side of the main polymer base for printer to aid the placement of the many sub-assemblies which are inserted during the main assembly procedure. Upon inspection of the sub-assemblies when I was dis-assembling the product it was evident that these guides were extremely important in the placing of the sub-assemblies. The guides pin-pointed the exact position of each sub-assembly, I also noticed that it was impossible to place any sub-assembly into the wrong position due to the design of these guides and also due to the shape and size of the components which were being used throughout the product.

Figure 22 Figure 23

In figure 25, the simplicity of the design of the guides used for assembly is shown. The design is a simple t-intersection with the wall of the polymer base. Although simplistic this design is an easy and effective way of placing components within a product and I feel it is used widely and successfully within this product. Relatively large forces can be present due to the movement of components within a printer but these guides successfully secure the components in place with no problems occurring during the use of

the product.

Show consideration within the design of difficulty of assembly in directions other than above – The figure used above also demonstrated this key design guideline, it is easy to see from the ‘t’ design of the guide that components can be inserted by sliding them into place from directly above the product. There were many other design cases throughout the product which also considered this design for assembly feature.

Figure 26 highlights one of the bosses used for securing components. This boss is positioned in a vertical direction from the horizontal plane. This indicates that during assembly all components must be inserted from above to coincide with this design feature, as this indicates that screws are inserted in a downward direction from directly above the base of the product. This was evidenced within every component and sub-assembly within the product and I think HP have fulfilled this design guideline with great success. There was however on instance where the screw had been inserted in a vertically upward direction from the bottom surface on the under-side of the base. This is shown in figure 28 where the base of the product has been turned upside down. It is then clear to see that a specific component has been inserted in the opposite direction from every other component within the product. This would suggest bad design and I think the company need to review the design of the base of the printer and decide if a separately attached component on this surface is necessary.

Figure 24 Figure 25

Figure 26

Figure 27 Figure 28

In figure 27 there is another clear example of design consideration for assembly from above. The highlighted hinge component is part of the front paper tray which can be raised and lowered during the operation of the printer. This hinge feature has three sides, one side has been removed to allow tolerancing so the tray can be closed without interference and collisions with the other component part. This means that the only possible direction of insertion during the assembly procedure is from directly above, a simple design solution which aids the assembly process.

Create a large base on which the assembly can be built – This is the final design guideline for design for automation and assembly. This particular design guideline, I feel, is showcased well within this product.

Figure 29 shows the bottom surface of the polymer base used for the Deskjet printer. When the base size was compared to other similar products (see page 11/12) it was established that this size of base was average for this type of product, in terms of assembly it is a good size to avoid trying to insert components into tightly pact, small spaces. This picture also highlights some other features which are important for automation during assembly. The features highlighted are locating features used to secure the product to the production line so the product does not have to be moved, or does not slip during the assembly procedure. These features will therefore allow for self-location which is ideal for use within an automated assembly line. (homepages, Wisconsin)

How do these design guidelines relate to the overall guidelines on DFMA?

I believe the design guidelines discussed in this section help to achieve these main points set-out by the Design for Manufacture and Assembly guidelines;

- Minimise part count – reducing part count also reduces the overall cost of the product. It stands to reason that if the design is simpler and easier to assembly then the production time decreases and the product becomes cheaper to produce as it is spending less time on the production line before being sold.

- Facilitate parts handling- Use standard parts and hardware

The two points above both help achieve increased reliability within the product. If parts are designed with handling in mind, either manual or automated, then the assembly procedure becomes more consistent and therefore more reliable. Also if standard parts are used the process becomes simplified and less opportunities for errors arise.

- Encourage modular assembly- Use stack assemblies/Don’t fight gravity

Figure 29

- Design parts with self-locating features- Assemble in the open

By achieving these DFMA points the product will also become less expensive to produce, however it will also increase the quality of the product. If the product is composed of smaller sub-assemblies then they can be assembled with more attention to detail, if all components were inserted into one main assembly, the process would become rushed and lead to errors lowering the quality of the output. It also encourages the designer to constantly try to review the design and make it lighter and more compact, resulting in a higher quality output for the user.

Design for PlasticsDue to the large quantities in which this product is produced I believe this product was produced using injection moulding. This was evident when analysing the polymer components used throughout the design of the product as some ejection marks were evident on the surface of particular components. This therefore means that certain design guidelines for injection moulding and plastics must be considered within the product and its components from an early stage in the design process. According to a resource from San Jose State University the main design for plastics guidelines are; (Youssefi, K., unknown year)

Provide adequate draft angle for easier part removal from the mould (2˚ minimum) Minimize section thickness; cooling time is proportional to the square of the thickness.

Reduce cost by reducing cooling time. 0.065’’≤t≤0.5’’ Keep rib thickness 60% of the part thickness in order to prevent voids and sinks Avoid sharp corners, they produce high stress and obstruct material flow Provide smooth transitions, avoid changes in thickness when possible Keep section thickness uniform around bosses Use standard general tolerances; do not tolerance Minimum thickness recommended; 0.25in or 0.65mm, up to 0.125mm for large parts Round interior and exterior corners to 0.1 – 0.015 in radius (min.) to prevent an edge from

chipping Be careful of interactions with other materials which may cause degradation of the plastic Use transfers instead of embossing so that parts are interchangeable between product

ranges Re-entrants or undercuts should avoided Large flat surfaces should be avoided as they tend to warp

Many of these are evidenced within the design of the printer and are discussed below.

Provide adequate draft angle for easier part removal from the mould (2 ̊ minimum) – This product is composed of many injection moulded polymer parts, there was therefore many examples of the inclusion of draft angles within the design of each component. The figures below highlight some of these.

Figure 30 shows one of the polymer components used for housing roller bearings which moves the paper through the printing operation. This is one of the more complex polymer components used within

the design of this product, however it is still viable to see a draft angle within this component design. The solid red lines within this picture highlight the angular nature of each of the outer edges of the component, the dotted red lines have been added to represent the angle of these edges to the normal vertical line. From these red lines it is therefore easy to see the angular nature of the edges used within this component design, it is also clear to see that the draft angle is more than the 2˚ minimum required to help the removal of the component from the mould during the manufacturing process.

Figure 31 also highlights the use of draft angles within the design of the main base design for the printer. This is a side view of the component and again the solid red lines highlight the slope of the outer edges. This is another good design example of the use of draft angles within this product. Again it is easy to see that the draft angles used here are greater than the minimum required.

The final example of the use of draft angles within the design of one of the components used within this product has been taken from the front panel component of the printer. This component is the main component which can be seen when the printer is in use, this component also houses the paper tray and allows access to the print-head to enable the changing of the ink cartridges. This is an example of the use of draft angles within a component with a very specific and high surface finish specification. This proves that regardless to the required tolerancing and finishing of the component, there is still a need for draft angles. The draft angle on this component is more complex than those looked at previously, this is due to the angular nature of the front surface. This is highlighted through the use of the arrow head in figure 32. This effectively adds another angular dimension to the design.

Figure 30

Figure 31

Figure 32

Minimise section thickness; cooling time is proportional to the square of the thickness. Reduce cost by reducing the cooling time. 0.065’’ ≤ t ≤ 0.5’’ – The minimisation of wall thickness within this type of product must be a key consideration during the design stage. This is a key area which can add to the weight of the product, and also determine if the product can ultimately withstand the forces which occur during general use. Therefore minimising the wall thickness whilst maintaining performance of the product is an important element to consider.

This picture shows a complex component used within the assembly of the Deskjet printer. From the initial appearance of this product it looks as though the wall thickness of this component is consistently varying across the component. Upon further inspection of this component the thought about wall thickness within the design becomes clearer. When looking at this product in more detail it becomes apparent that snap fits have been used to join two separate polymer components to create a sub-assembly for use in

the printer. These are highlighted by the red circles in the picture. When these two separate

components were looked at, it became evident that the wall thickness throughout each of these components was uniform. I believe the two components were joined together in order to add

strength to this component within the printer assembly and also to enable this particular component to withstand a greater force as this component is hinged and therefore can be opened and closed by the user of the product and has the potential to be mis-used. This is a case where, what first appears to be bad design within the product results in the identification of a clever design technique used by the HP company in order to improve the design of their product.

The pictures above show the complex polymer component which was discussed above in more detail. These pictures show the two separate components with more clarity, whilst also illustrating

Figure 33

Figure 34 Figure 35

how the wall thickness of these components remains constant throughout the component design, despite initial appearances.

Figure 36 shows the size of the wall thickness used throughout design of every component within the product. The wall thickness is represented by the red lines within this picture. This shows good, consistent design. Every component will consistently have the same cooling time due to the use of the same wall thickness all over, it also provides a better appearance when finished. The wall thickness used within this product is 3mm. This is within the 0.065 – 0.5 inch limit and also gives a corresponding cooling time of 9 minutes. This

proved to be a suitable wall thickness for this product as there were no signs of voids or sinking, as a result of the cooling of the material, when the components were inspected.

Keep rib thickness 60% of the part thickness in order to prevent voids and sinks – Ribs are used widely within this product to provide added strength and support to key areas, such as large flat surfaces and these are shown in the pictures below.

This figure shows some of the main ribs used to support the structure of the main polymer base used within this assembly. The picture shows the wall thickness measurement of the rib to be 1mm. The previous measurement of the wall thickness of the main component was 3mm. The rib thickness has therefore been limited to 30% of the part thickness in order to prevent the forming of voids and sinks within the design.

Figure 38 shows an example of bad rib design within the same product. The ribs highlighted here were measured to be 3mm, the same thickness as the component part. This does not follow the design guideline which states that the rib thickness should be limited to 60% of the part thickness. With this rule in mind the maximum size of the rib thickness should have been 2mm. Although this is an example of bad design, is does not seem to have resulted in the appearance of any voids or sinking on the

Figure 36

Figure 37

Figure 38

Figure 39

component surfaces. Although voids and sinking has not occurred I believe that this bad design feature should be addressed as it may have caused flaws within other batches of the production of this component.

Avoid sharp corners, they produce high stresses and obstruct material flow – Every polymer component used within this product appeared to avoid the use of sharp corners. As a result there were many examples of good design procedure throughout the product.

This design guideline states that the radius of the corner should be equal to 3/8 of the part thickness and must be more than 0.06 inches in measurement. The example included in figure 39, shows the use of very large rounded corners within the main base of the product. It is clear to see that this example obeys the guideline set out and in the case of this product also adds to the aesthetic appeal of the finished product. As an approximation the radius used within this example design is around

10mm, this was the largest example of design to avoid the use of sharp corners within the product.

Figure 40 shows how this design guideline for plastics can also be applied to the ribs which are included within the design of the printer. This example shows how HP have incorporated a radius on the corners which join every rib in this component, this is highlighted by the red arrow heads in the picture. Due to the size of these radii it

was

impossible to accurately measure the dimensions used for this guideline within this specific component and therefore I am unable to say if these radii adhere to the dimensional rule, radius = 3/8 part thickness and greater than 0.06 inches.

Figure 41 illustrates the use of radii on the corner of a structurally supportive rib. This is highlighted by the red circle within the picture. Due to the positioning of this radii it was difficult to accurately measure the size

of the radii used, however when proportionally comparing the size of this radii to that of the part thickness an estimated radii would be around 1.5mm or greater. This radii therefore also follows the guidelines for the design for plastics in regards to avoiding sharp corners.

Figure 40

Figure 41

Provide smooth transitions, avoid changes in thickness when possible – When it is not possible to use constant wall thickness throughout the design of a component then it is advised that a gradual transition between the different thicknesses is achieved. A few examples were found in this product.

The sequence of photographs above shows hoe the wall thickness within a singular component is mainly constant throughout, however, in some instances within this component there is a fluctuation in the part thickness, these have been highlighted in red.

The hinge design within this component shows a successful design which provides a smooth transition between the two part thicknesses involved. The use of curved design within this feature allows the change in thickness to be introduced into the part

gradually, avoiding the tendency for a sharp change in part thickness to cause the feature to become brittle and snap. There is one point of weakness within this feature where the curve takes a sharp change in direction which may cause problems with the robustness and durability of this design. This weak point has been identified with the red arrow head in the photographs.

In contrast with the hinge design on this component, there is an illustration of bad design when concerning transitions between differing part thicknesses. This is shown with the large, sloping, step

Figure 42 Figure 43

Figure 44 Figure 45

Figure 46

change which has been highlighted in figure 45. When comparing these two highlighted features there is a clear distinction between how the part thickness changes over the gradient of the feature design within the component. In the hinge the change is gradual and in the sloping feature the change is sudden and drastic. This area of design for plastics is one which I feel needs to be further developed by the company.

Keep section thicknesses uniform around bosses – There are many bosses which are used within the component design of this product. Due to the forces experienced during normal operating conditions within the product, the most secure way of ensuring the forces do not disturb the placing of the components through vibration is to secure each component and sub-assembly with screws.

This ensures a large number of bosses must be included in the design of this product.

Figure 46 shows an example of the boss design within this product. This design shows good uniformity regarding wall thickness around the boss and also around the ribs which have been used to support and strengthen the material around the boss. There are many other examples of this boss design being used throughout many components which make-up this printer assembly. This is illustrated in figures 47, 48 and 49.

These pictures all help to illustrate the point that regardless of where the boss is placed in relation to the components’ surfaces, faces and edges, the section thickness remains constant. From my point

Figure 47 Figure 48

Figure 49

of view this helps maintain consistency in terms of the force loading which the material will experience from the mechanical fastenings used and also maintains a constant look across the product. It also ensures that the same size of fastenings can be used, reducing the number of different mechanical fastenings within the product to the minimum possible.

In contrast to the majority of the bosses used for fastening within the product I discovered the boss within this component which has been highlighted in red. It is very clear that the wall thickness surrounding this boss is non-uniform. This boss almost gives the impression that during the manufacturing of the mould used for the injection moulding process, a hole was drilled which was not concentric with another circular component. The arrow head in figure 50 is showing that one side of this boss clearly has a much greater thickness when compared to the other side. This is the worst example which I found to demonstrate the non-uniform thickness surrounding a boss. This means that HP have provided a good design outcome ensuring that most bosses have good uniform thickness, however, there is room for improvement. In a competitive market place there is a need to pursue perfection and therefore the aim is to have all bosses designed with uniform thickness. Cases of bad design, like that shown in figure 50 add additional cost to the cost to produce the product.

Use standard general tolerances; do not tolerance – Tolerances allow for some movement between two joined components. The presence of these tolerances can prevent extra strain being placed on the material around the join and resulting in the cracking or snapping of the material, but it also makes the assembly process easier. The table below shows a list of standard general tolerances. (Youssefi, K., unknown year)

Dimension Tolerance Dimension Tolerance0 ≤ d ≤ 25 ± 0.5 mm 0 ≤ d ≤ 1.0 ± 0.02 inch

25 ≤ d ≤ 125 ± 0.8 mm 1 ≤ d ≤ 5.0 ± 0.03 inch

125 ≤ d ≤ 300 ± 1.0 mm 5 ≤ d ≤ 12.0 ± 0.04 inch

300 ± 1.5 mm 12.0 ± 0.05 inch

Using this table there were a couple of identified features within the product where these general tolerances may be used.

Figure 52 shows the placing of some plastic components within the base of the printer. There are some tolerances being used to help place these components.

Figure 50

Figure 51

The arrow heads are highlighting the small gaps which are evident between the placed component and the guide which is a feature on the base component. The dimension of the smaller components which have been placed into the base component fall into the 0 – 25mm category outlined in the general tolerance table. This means a tolerance of ±0.5mm should be used. The approximate size of the tolerance gap highlighted in this picture is between 0.5mm and 0.75mm. This was a very rough measurement which was taken so assumptions have been made that the tolerance being used here is the general tolerance of 0.5mm. This picture therefore illustrates the use of general tolerancing being utilized within the design for plastic components within this product.

Figure 53 shows a component of the assembly which uses one of the boss features within the product as its securing mechanism. From this picture you can see that the hole in the component is off-set from the top of the boss. This ultimately means when a screw is inserted during the assembly process, the screw will not fit and the component will be unable to be secured. This error may be due to tolerancing issues within the design. To overcome this design flaw, the hole should have a greater tolerance, resulting a slightly larger diameter hole to ensure the top of the boss is not obscured in any way.

Minimum thickness recommended; 0.025in or 0.65mm, up to 0.125mm for large parts – The thickness of a component will directly reflect the strength and robustness which that part contains, as a result there must be a minimum thickness which is acceptable within any product. The following photographs show the wall thickness in use in the Deskjet printer.

This picture shows the measurement of the wall thickness of the largest component within the printer assembly, the plastic base component. This picture shows that the wall thickness here is approximately between 3 – 4mm. This is much greater than the minimum recommended thickness and proportionally looks correct for the size of the component part. When analysing the component there were no cracks within the material surface or around any of the main corners or other key features suggesting the

presence of good strength within the component, this is primarily because of good design and the

use of correct component thickness.

Round interior and exterior corners to 0.01 – 0.015 in radius (minimum), to prevent and edge from chipping – This particular design guideline is displayed well within this product.

Figure 55 shows some of the structural ribs within the product. This picture illustrates the

Figure 54

presence of rounded corners on all surfaces of the ribs. These are key features in providing additional structural support and strength and may be prone to chipping and damage from other components during the assembly process so it is important to round the corners of these features to try and prevent this from happening. This is a good example of this in action as a small radii has been placed on every edge, corner and intersection within this component.

Figure 56 shows a component which has high user interaction, however after years of use during the product’s life-span the component still looks relatively new. I believe this is due to the attention during the design stage to rounding corners in order to ensure the chipping of edges were minimalized. As the picture shows there are many internal corners which all have small radii placed on them. I am assuming these are all within the limits of the design guideline as it is too difficult to get a measurement for their actual dimensional size.

This figure shows an example of corner radii on an external corner. The radii used in this situation appears to be the same as the radii applied to internal corners within this product. As with the internal corners, the radii prevents the chipping of edges but it also provides the product with a professional surface finish which will appeal to the user. It also prevents the user from injury due to the use of sharp external corners. This is good design as one design feature has the ability to address many important issues which arise during

the research and testing stages of the design process.

Be careful of interactions with other materials which may cause degradation of the plastic – Interactions with other materials used within the product could cause some degradation the polymer material used in the product. In the case of this printer the other material which needs to

Figure 56

Figure 57

Figure 58 Figure 59

be considered carefully during design is the type of ink used during printing and consideration of potential reactions needs to occur during the material selection process.

The photographs above show the extent and type of interaction which occurs between the chosen polymer material, ABS Plastic, and the printing ink which is used within this product. The interaction between the two materials is contained to one area of the main base of the product. The photographs show that the extent of the reaction extends to discolouring of the ABS and aluminium components in this small, specific area of the product. If the wrong plastic material had been chosen for use within this product then the reaction between these materials may have led to bubbling and melting of the plastic material. This is not occurring within this product therefore this is a successful design.

Use of transfers instead of embossing symbols onto the polymer components so that parts are transferrable between product ranges – I believe that some plastic components within this product have used transferrable stickers instead of embossed symbols so that the information appearing on some components may easily be changed, perhaps so that a particular component may be used

within another product range produced by the company, much in the way the automotive industry produces many ranges of different cars but has standardised components which are used within many of the different product ranges.

This figure shows an example of this being used within the product. The tranfer used at the

Figure 60 Figure 61

Figure 62

Figure 64

bottom of the component is clear due to its use of colour within the text, this is not achieveable when ebossed text has been used. This also appears on what I would class as a standrad component within a printer, the hinged door which allows access to the print-head for the changing of ink cartridge etc. My thoughts were that this tranfers could be removed, a different transfer could be placed on the component and then this component could be easily placed into the assembly of a different range of printers produced by HP. There are other examples of components where this is not the case and the information has been emboassed on the plastic component.

The photographs above show the use of embossed information on plastic components within the printer. I do not necessarily think this is bad design as the components on which this information appears on are also standard components which can be interchangeable with other product ranges produced by HP. The main difference between these components and the component discussed previously is the type of information included on the surface of the component. The name on the previous component which used a transfer was a particular name associated with this product range. The information contained on the components shown above is material, safety and information regarding the directions of use. I feel embossing this information is a good design

Figure 64

Figure 65 Figure 66

Figure 67

decision as this type of information is common to every product range therefore incurring no costly remanufacture of components to change the embossed information for specific product ranges.

Re-entrants or undercuts should be avoided – Upon inspection of the plastic components within this product there were no re-entrants or undercuts evidenced within the design of any of the components. This is a very good, economic design decision from HP as re-entrants and undercuts can be a costly additional expense during manufacturing if these features are required.

Large flat surfaces should be avoided as they tend to warp – Large flat surfaces tend to warp due to no strengthening elements supporting the surface during the cooling process. The images below identify the size of flat surfaces used within the component design of the printer.

The surface highlighted in figure 68 is a relatively large flat surface with little support from ribs which are placed on the inside face of the component. From inspecting this component there is no clear evidence to suggest that any warping of this surface has taken place, however, I still feel that placing a few more substantial support ribs could reduce the probability of this occurring during multiple cycles of the production process for this component, this will avoid the need for any remanufacture to occur.

This figure shows suitable use of ribs in order to strengthen and support the bottom surface of the plastic base component used within this product. This figure shows good design where support is given in multiple directions due to the strategic placing of horizontal, vertical and some diagonal ribs. The primary role of these ribs is to prevent the bottom of the base from warping. This is the largest flat surface used within the product and having a true flat surface is key to producing a product which sits well on an office desk, which is the intended purpose for this product.



- Minimize part count - Make parts multi-functional- Eliminate interfaces- Design for part inter-changeability

Figure 68

Figure 69

The above points all help to reduce the part count also reduces the overall cost of the product. It stands to reason that if the design is simpler and easier to assembly then the production time decreases and the product becomes cheaper to produce as it is spending less time on the production line before being sold.

- Design tolerances to meet process capability- Design parts with self-locating features- Minimize number of surfaces

The points above help achieve increased reliability within the product. If parts are designed with self-locating features in mind, then the assembly procedure becomes more consistent and therefore more reliable. Also if standard parts are used the process becomes simplified and less opportunity for errors arises.

By achieving these DFMA points the quality of the product will also increase. If the product is composed of smaller sub-assemblies then they can be assembled with more attention to detail, if all components were inserted into one main assembly, the process would become rushed and lead to errors lowering the quality of the output. It also encourages the designer to constantly try to review the design and make it lighter and more compact, resulting in a higher quality output for the user.

Design for Fastening and Other Joining MethodsDesign considerations for mechanical fastening and other joining methods are widely discussed in the publication entitled Manufacturing Engineering and Technology, Kalpakjian, S., and Schmid, S. R., 2009. Some the design guidelines suggested in this publication which were evidenced within the printer assembly were;

Whenever possible, through holes rather than blind holes should be specified Interrupted internal surfaces – such as internal splines or radial holes that go through the

thickness of the part – should be avoided Designs should allow holes to be placed on flat surfaces Hole bottoms should match, if possible, standard drill-point angles; flat bottoms or odd

shapes should be avoided Joints should be placed so that there is easy access for a soldering iron nozzle There should be good fit-up of soldered joints Consideration of the type of loading being placed on the material should be considered in

the type of mechanical fastening used Compatibility of the fastening material with that of the component should be considered It is generally less costly to use fewer, but larger, fasteners than to use a large number of

smaller ones The fit between parts to be joined should be as loose as possible to reduce costs and to

facilitate the assembly process Fasteners of standard size should be used whenever possible Holes should not be too close to edges or corners, to avoid the possibility of tearing the

material when it is subjected to external forces

Many of these were clear to see in every component used within the design of the Deskjet printer.

Design Considerations for BoringWhenever possible, through holes rather than blind holes should be specified – Screws are the main fixture used within the assembly. This involves having the correct hole through which the screw can be placed. (Kalpakjian, S., and Schmid, S. R., 2009, pg 642)

Figure 70 and 71 show the use of a blind hole within a boss feature situated on the under-side of one of the trim pieces used within the design of this product. It is clear to see that this shows the use of a blind hole, which directly ignores the design guideline given. Although this appears to oppose the guideline, this particular hole needs to be a blind hole. The nature of this component requires an uninterrupted surface finish on the outer surface of the product. This is used as a trim piece for providing the final presentation look of the finished product, this is what the customer will see when they are considering buying and using the product, if the aesthetic of the product had been spoilt with the use of a through hole, this would make the finish of the product look unprofessional and unattractive to the customer. This therefore shows good design and self-judgement on when the correct time to obey or oppose a specific guideline is needed.

Figure 72 highlights the use of a through hole within the design of this product. This component is an internal polymer component which does not have any effect on the outer appearance of the product. Due to the nature of the placement and use of this component it is therefore negligible if the top of end of the screw fixture can be seen from any particular surface of the component. Again I think this shows good judgement on the part of the design as to the requirements of the component and the expenditure on the design feature within the manufacturing

process.

Figure 70 Figure 71

Figure 72

Figures 73, 74 and 75 show various other instances of the use of blind and through holes throughout the design of the printer. Again I think each of these examples has shown that the designer has had to seriously consider the aesthetics of the finished product, the use requirements of the component and also the placement of the component within the assembly. Sometimes this results in the designer deciding to ignore the design guideline when appropriate.

Interrupted internal surfaces – such as internal splines or radial holes that go through the thickness of the part – should be avoided – Interrupted internal surfaces can cause difficulty in the placing of components during assembly and effect the overall positioning of components and therefore needs

to be considered within the design stage.

Figure 76 shows a heavily interrupted internal surface. This ribs shown in this picture are necessary in providing extra strength for the product however, it affects the positioning of other components. The presence of this kind of internal surface interference ultimately means that the positioning of other components must come about

as a result of this design. If this

Figure 73 Figure 74

Figure 75

Figure 76

interrupted surface was not here, then it may ultimately mean that HP could produce a more compact, lightweight printer.

The figures above show attempts within the design to avoid the use of radial holes which protrude

through the thickness of the component. The bosses shown in these photographs are the design solution to avoiding the use of a radial, through-thickness hole.

Design Considerations for DrillingDesigns should allow holes to be placed on flat surfaces – It is important that holes, or in the case of the printer bosses, are placed on flat surfaces as this prevents the introduction of load force at the base of the boss feature resulting in a shearing of the feature. It also prevents a bad join between components with bad fit-up and badly fitting screws being less likely to occur. (Kalpakjian, S., and Schmid, S. R., 2009, pg. 651)

This picture of the mounted circuit board from the printer illustrates how this design for fastening guideline applies to the design of the circuit board as well as the individual plastic and metal components which also make-up the printer assembly. As highlighted in this picture, the holes required for the secure fixturing of the component are all placed on a flat surface and are placed so as not to cause concern about interference with any of the electronic components included on the circuit board.

Figure 80 illustrates bad design concerning the placement of a boss on the internal surface of the polymer base. It is clear to see from the photograph that this boss is situated on the edge of a very large radius. This can cause a great force loading to occur around the bottom of the base where the boss feature joins the surface of the polymer base. This may increase the probability of shearing occurring around this point.

Figure 77 Figure 78

Figure 79 Figure 80

Hole bottoms should match, if possible, standard drill-point angles; flat bottoms or odd shapes should be avoided – The inclusion of standardised drill-point angles will eliminate the need for customising the bottom of the screw which will ultimately be inserted into the pre-drilled hole. The drill-point angles are manufactured to correspond with the screw-tip angles available within standard specification screws.

Figure 81 and 82 illustrate the use of flat-bottomed bosses which consequently mean the use of flat-bottom screws. These screws upon closer analysis have clearly been through a manual operation to file away the pointed tip of the screw thread, this was apparent due to the markings and finish quality which could be seen on the screw tip. The screw has only had to undergo extra operations due to the hole design within this boss, if the tip of the screw and the angle which this involves had not been removed then the screw would have been too long to fit correctly in the boss and would have caused damage to the exterior of the polymer material. This shows bad design and the consequences which bad design may have on the finish of the product and also the production time taken to assemble the product.

Design Considerations for SolderingJoints should be placed so that there is easy access for a soldering iron nozzle – This directly relates to the soldering of components to a circuit board. This design consideration is shown on various components on the mounted circuit board within the printer. (Kalpakjian, S., and Schmid, S. R., 2009, pg. 931)

Figure 81 Figure 82

Figure 83 Figure 84

Figures 83 and 84 show the placing of many electronic components on the circuit board. The spacing between these components is large allowing for the size of the soldering iron nozzle which is needed to complete the soldering process. These photographs also highlight the presence of two very distinctive types of soldering, one highlighted in red and the other in blue. The soldering techniques highlighted in blue is an automated soldering technique and so allows for the positioning of components to be more densely compact compared to those which are soldered using a manual process. This shows design consideration for how the soldering process will be undertaken and how the use of automated techniques can help improve the outcome.

Provide a good fit-up of soldered joints – Providing a good fit-up of the surfaces to be joined is necessary in order to create a strong, stable soldered joint which cannot degrade and become detached through excessive movement within the joint.

The photographs above help to illustrate what is meant by the good fit-up of a soldered joint. The photographs show how each electronic components sits tightly on the surface of the circuit board, this tight interaction with the circuit board is the good ‘fit-up’ talked about in this design guideline. This tight fit provides a much stronger soldered joint. If there was a space between the surface of the circuit board and the component movement would be apparent within the joint leading to the eventual failure due to stresses within that joint.

Design for Mechanical FasteningConsideration of the type of loading being placed on the material should be considered in the type of mechanical fastening used – The loading which is placed on a plastic component through any

mechanical fastening can be large and can provide one of the main causes of failure. (Kalpakjian, S., and Schmid, S. R., 2009, pg. 942)

The possible effects of mechanical fastening loading has been considered well within this design, you can see the wall thickness used in the boass design and also the number of ribs which help support and strengthen the design. This will

help disperse the loading of the

Figure 85 Figure 86

Figure 87

mechanical fastneing throughout the design of the boss feature.

The type of screw used within this design has also been well considered with regards to loading from a mechanical fastening. When designing a product the temptation is to use a countersink screw so that the screw face finishes flush with the surface of the component to provide a neat finish, however, this should generally be avoided when fastening plastic components. The use of a countersink screw requires additional drilling operations, these operations reduce the part thickness around the hole. The large forces exerted trhough the fixture then cause the plastic to crack around the weakened hole design, leading to a failure of the part. In this design the screw which has been used has a flat top, this will avoid the failure of the material around the hole designed for the screw and will distibute the load from the fastening more evenly. This is a good example of design for fastening within this product.

Compatibility of the fastnener material with that of the component material – The design of a component needs to consider any degradation which may occur due to the incompatability of the component material and that of the fastner which is joining two components. In the case of the HP Deskjet rpinter the component material is ABS plastic and the fastenrr material is an aluminium screw. The example of the degradation caused by this fastener within one area of this product is shown below.

When dis-assembling the printer to analyse the components it was clear in one case within the base component of the assembly that the fastener had caused some damage to the component material. Damage such as this was not apparent in any other component, or in any other area in the base component, however this illustrates the importance of ensuring the compatability of the two materials before using them for the product assembly. I wouldn’t suggest that this shows a great deal of bad design due to material selection, I think other design factors were also to blame for the damge seen in this picture.

It is generally less costly to use fewer, but larger, fasteners than to use a large number of smaller ones – The main fastener used throughout this assembly is a small torsion screw. The photograph below illustrates the number of fastneings used within the whole assembly.

Figure 89

Figure 90 shows the number of fasteners used within the assembly. There are at least 24 fasteners shown in this photograph. This is a large number when considering a large number of the sub-assemblies did not use screws, except for securing them to the base component within the main assembly. There was also two different sizes of screw used, both were small in size. The two different sizes of screw are highlighted in the photograph. I believe the number of fasteners used within the assembly of this product could have been reduced with a review of the design

and the size of the screws used.

In other instances throughout the assembly of this product there were many examples of how snap fits have also been used as a method of fastening within the product. An example of the type of snap fits is shown in figure 91. I believe the design of this product could be improved if the design was to include more snap fits to reduce the number of required mechanical fasteners. This will result in a reduction in the net weight of the product and also make assembly times quicker.

The fit between parts to be joined should be as loose as possible to reduce costs and to facilitate the assembly process – This design guideline is aimed at reducing the time taken to assemble the product. I found due to the nature of the use of the product that joints were tight with little or no room for movement between the two components.

Figure 92 shows an assembly which includes bearings used for the paper feeding mechanism within the printer. The areas highlighted within this picture shows the tight tolerances which exist in the assembly between two component parts. During the analysis of this component I tried to test the ‘play’ within the assembly to see how loose or tight the assembly was. Components within this assembly did not move in any direction, or in any rotation or orientation in comparison to the surrounding components. This could be

classed as bad design according to this design guideline however, without the tight tolerances

Figure 90

Figure 91

Figure 92

which are evident in this sub-assembly the working of the product would not be of the performance required by the customer.

Fasteners of standard size should be used whenever possible – The diametric size of the fasteners used within this product were a standard M3 size, however the length of screw used were not standard. When analysed the end of the screw thread appeared to have manually cut to size due to the markings and rough appearance of the edges on the screw thread. This is shown in figures 93 and 94 below.

Figure 93 shows the two lengths of screw used and the flat bottom of the screw thread can also be seen in this photograph. The end of the screw thread which appears to have been cut to size is shown in more detail in figure 94.

Holes should not be too close to edges or corners, to avoid the possibility of tearing the material when it is subjected to external forces – The part thickness surrounding holes and bosses have been examined previously in this report, however the position of the hole relative to the edges and corners of the product have not yet been examined.

Figure 95 shows the positioning of holes along the outer edge of a sheet metal component which houses axles and bearings which was placed directly in the centre of the assembly. It is easy to see that the position of each of these holes has been considered carefully. The smallest distance of any of these holes to the nearest edge is around 4-5mm. This is especially important within this component due to the low strength of the material and the part thickness of the sheet metal which has been used.

Figure 93 Figure 94

Figure 95

Figure 96 again looks at the placement of holes within a component relative to edges and corners. The design shown here has positive and negative points to it, the hole does not appear to be too close to outer edge of the featured surface, it does however appear to be very close to the inner edge where the height of the surface suddenly takes a step change to become higher than the surface on which the hole is placed. This does not present a problem with regards to forces exerted on the hole and the possible cracking of the material, it may however prove to be awkward when trying to insert a fastening or component into this hole.



- Minimize part count- Make parts multi-functional- Reduce the number of screws and screw types

The above points all help to reduce the part count also reduces the overall cost of the product. It stands to reason that if the design is simpler and easier to assembly then the production time decreases and the product becomes cheaper to produce as it is spending less time on the production line before being sold.

- Use standard parts and hardware- Encourage modular assembly

The two points above both help achieve increased reliability within the product. If parts are designed with modular assembly in mind, then the assembly procedure becomes more consistent and therefore more reliable. Also if standard parts are used the process becomes simplified and less opportunity for errors arises.


Figure 96

Design for Sheet Metal and PressworkDesign for sheet metal and presswork is also discussed within the Manufacturing Engineering and Technology (2009) publication. Some of the main design guidelines outlined for sheet metal and presswork in this publication are; (Kalpakjian, S., and Schmid, S. R., 2009, pg. 428)

The design of the sheet metal part should reduce scrap to a minimum To avoid material fracture, wrinkling, or the inability to form a bend, a relief notch should be

incorporated into the component design of a part for bending A crescent or ear should be used for hole design occurring near a bend Scoring or embossing should be used to obtain a sharp inner radius in bending Design for ease of blanking Shear and form operations should have a minimum height (h) of 2 ½ the blank thickness

Many of these design features, good and bad, are shown in the following figures.

The design of the sheet metal part should reduce scrap to a minimum – The reduction of scrap during the production process of any sheet metal part directly relates to savings in the cost of production for that component.

Figures 97 and 98 show the main sources of scrap material from the design of this component. Figure 97 shows the blanking operations which are

required within this component design. Figure 98 however shows that not all of the area which appears to have been blanked in figure 97 is reduced to scrap. Some of the blanked material is used to form a surface on which some gears can be placed as shown in the picture. This shows some clever design and provides insight into how the waste from blanking operations can be reduced.

In contrast to the design shown above, figure 99 shows part of the design of this component which creates waste material during the production procedure. The ends of the sheet metal component are shown within this photograph. It is clear to see the non-symmetrical nature of the ends of this component. This means that

Figure 97 Figure 98

when produced on a large sheet of aluminium in a batch product when many of these components are cut from the same sheet, then there is going to be waste material generated from cutting material from the perimeter of each of these components. Having symmetrical ends may reduce the amount of scrap material being removed during the production process.

To avoid material fracture, wrinkling, or the inability to form a bend, a relief notch should be incorporated into the component design of a part for bending – To illustrate what is meant by the term ‘relief notch’ I have included the diagram shown in figure 100. (efunda.com)

The cut inset cut highlighted in the figure above shows a relief notch. This simple cut in the material allows a bend to be formed without the material next to the bend ripping and tearing which is unwanted and causes stresses and strains within the material. The photographs below show some bends within the sheet metal component in the printer.

Figure 100

Figure 102

Figure 103

Figure 101

Figures 101, 102 and 103, show instances where relief notches have been used through the sheet metal component. It is clear to see that there are no tears appearing the material due to the bend which has been formed. This is a good example of relief notch design.

A crescent or ear should be used for hole design occurring near a bend – Introducing a hole close to a bend may result in the distortion of the hole during and after the bending operation. The will therefore leave the hole unusable due to the distorted shape which will be apparent in the design.

Figure 104 illustrates how consideration has been given to the positioning of a hole near a bend in the sheet metal component. The hole has been placed with sufficient space from the edge and the bend within the feature of the sheet metal component. This is successful part design where failure through cracking, tearing and snapping due to an ill placed hole has been eliminated from this component.

Scoring or embossing should be used to obtain a sharp inner radius in bending – Much in the way a prototype is made, by scoring a line in card before a subsequent bending action, bends within sheet metal components are also produced in this way. His gives a more controlled output with sharp inner corners on the internal face of the component.

Figure 105 shows the use of both embossing and scoring in the creation of the bend in this sheet metal component. The circle in the picture highlights the embossed section which runs along the bottom face of the component. The arrow head is being used to point-out the scoring which has been used to mark the position of the bend before the bending operation was undertaken. It is just visible as a dark line alone the length of the interior surface of the bend. This shows a good combination of techniques in order to achieve a successful and highly professional outcome.

Design for ease of blanking – There are many blanked features within the design of this component. These will be highlighted in turn however there are some key dimensional and geometric features which need to be defined before analysing the design of the features within the printer component. (engr)

Figure 104

Figure 105

The diagram above was taken from an online resource provided by San Jose State University, this outlines the important dimensional restrictions when producing blanked parts. These features have been identified within the sheet metal component from the printer and are shown in the figure.

Figure 106

Figure 107

The feature outlined in red in this figure corresponds to W in the previous diagram. The constraint for this feature was the minimum width thickness of the cut which was stated as 0.04 inches minimum for materials which are thinner than 0.047 inches, if possible this should be wider. The feature in the component part from the printer meets this criteria with ease. The width of this feature lies between 2-3mm and the thickness of the material is between 1-2mm. The second feature highlighted by the thick green line is the length of the cut within this designed blanked feature. The length of this cut is approximately 5mm. The maximum dimension recommended was 5W. W was previously established as measuring between 2-3mm, this therefore means that the design for blanking within this piece falls well within the limits of the given guidelines, meaning the weakness in the strength of the thin material is kept to a minimum where possible.

Shear and for operations should have a minimum height (h) of 2 ½ the blank thickness – This is the last feature to be considered as part of the design consideration followed when producing the sheet

metal component. From the previous figure, the blank thickness was previously established as being approximately 1mm. The minimum height for the shear in this component should therefore be 2 ½ mm.

Figure 108 shows one of the shear features present in this component. When the height of the shear feature was measured, the dimensional value was found to be approximately 3mm. This

feature then fulfils the dimensional restrictions identified by the design guideline. This will help to prevent the possibility of failure occurring due to inappropriate design within a very thin sheet metal component. This again, is another successful design feature included in the design for the HP Deskjet printer.



- Make parts multi-functional

This point helps to reduce the part count also reduces the overall cost of the product. It stands to reason that if the design is simpler and easier to assembly then the production time decreases and the product becomes cheaper to produce as it is spending less time on the production line before being sold.

- Use standard parts and hardware- Design parts with self-locating features- Minimize number of surfaces

Figure 108

- Simplify and optimize the manufacturing process- Design tolerances to meet process capability

The points above both help achieve increased reliability within the product. If parts are designed with modular self-locating features in mind, then the assembly procedure becomes more consistent and therefore more reliable. Also if standard parts are used the process becomes simplified and less opportunity for errors arises.


ConclusionI believe this report has shown a successful design for a mass produced product from the HP company. There have been many examples of good design features, such as designing the circuit board to allow easy access for the nozzle of the soldering iron. The have also been some examples of bad design within this product, for example the use of screws within this product was not good, too many were used and they were not of a standard size as they appear to have been cut to length to fit the boss design of a component part.

As a result I think my conclusion is that the product showcases some good Design for Manufacture and Assembly features, however there is room for improvement. The design could be made less expensive to produce, more reliable and of better quality if a few of the bad design examples highlighted in this report were re-worked.

ReferencesArgos, 2012, [ONLINE], Available at; http://www.argos.co.uk/static/Product/partNumber/9371424.htm#pdpFullProductInformation accessed November 3rd 2012

Burman, M., Gershwin, S. B., and Suyematsu, C, 1998, Hewlett-Packard Uses Operations Research to Improve the Design of a Printer Production Line, [ONLINE], Available at; http://interfaces.journal.informs.org.proxy.lib.strath.ac.uk/content/28/1/24.full.pdf+html accessed November 3rd 2012

Chan, V., and Salustri, F. A., 2005, Design for Assembly, [ONLINE], Available at; http://deed.ryerson.ca/~fil/t/dfmdfa.html accessed November 3rd 2012

Cook, C and Youssefi, K, unknown year, University of Berkley; DFMA Guidelines, [ONLINE], Available at; https://mail.esdnl.ca/~craig_cook/df2202/dfma/DesignForManufacturingAndAssembly.pdf accessed November 3rd 2012

https://mail.esdnl.ca/~craig_cook/df2202/dfma/DesignForManufacturingAndAssembly.pdf

http://deed.ryerson.ca/~fil/t/dfmdfa.html

http://interfaces.journal.informs.org.proxy.lib.strath.ac.uk/content/28/1/24.full.pdf+html

eFunda, 2012, Sheet Metal; Forming, [ONLINE] Available at; http://www.efunda.com/processes/metal_processing/stamping_forming.cfm accessed November 3rd 2012

Hamidi, M and Farahmand, K, 2008, North Dakota State University; Developing a Design for Manufacturing Handbook, [ONLINE], Available at; http://www.ijme.us/cd_08/PDF/220%20IT%20302.pdf accessed November 3rd 2012

Unknown author, [ONLINE] Available at; http://dora.eeap.cwru.edu/gcc/dissertation/chap_4.pdf accessed November 3rd 2012

Unknown author, unknown year, [ONLINE], Available at; http://smaplab.ri.uah.edu/ipd/2_1.pdf accessed November 3rd 2012

Unknown Author, unknown year, University of Wisconsin; Detailed Design for Assembly Guidelines, [ONLINE], Available at; http://homepages.cae.wisc.edu/~me349/lecture_notes/detailed_dfa.pdf accessed November 3rd 2012

Youssefi, K., unknown year, San Jose State University; Design for Manufacture and Assembly II: Design Guidelines, [ONLINE], Available at; http://www.engr.sjsu.edu/minicurric/images/lecture_powerpoints/DFMA_II_Design_Guidelines.pdf accessed November 3rd 2012

Kalpakjian, S., and Schmid, S. R., 2009, Manufacturing Engineering and Technology, 6 th Edition, pg 642, 651, 931, 942 and 428

http://smaplab.ri.uah.edu/ipd/2_1.pdf

http://dora.eeap.cwru.edu/gcc/dissertation/chap_4.pdf

http://www.ijme.us/cd_08/PDF/220%20IT%20302.pdf

http://www.ijme.us/cd_08/PDF/220%20IT%20302.pdf

dfma report

Documents