dfm lab repot

DFM Lab ReportApril 21, 2015 Team 26: Ryan Hamilton Contributors: Keya Gemechu Chris Barnes Scott Gilmour Chris Chu Brent Oursler 1 Contents Executive Summary ........................................................................................................................ 3 Introduction ..................................................................................................................................... 4 Importance of Design For Manufacture ...................................................................................... 4 The Motor ................................................................................................................................... 4 Copper Wiring and Coil Winding ........................................................................................... 5 Design for Manufacturing ......................................................................................................... 11 Material ................................................................................................................................. 11 Armature lamination and Stator lamination.......................................................................... 11 Copper coil winding:............................................................................................................. 11 Wire diameter range .............................................................................................................. 12 Circular hole of the armature lamination: ............................................................................. 12 Cost ........................................................................................................................................... 12 Motor Fan.............................................................................................................................. 13 Costs.......................................................................................................................................... 20 Table of Compatible Materials ................................................................................................. 21 Drafts: ................................................................................................................................... 24 Wall Thickness: .................................................................................................................... 25 Radii and Corners: ................................................................................................................ 26 Ribs: ...................................................................................................................................... 26 Ejector Pins: .......................................................................................................................... 27 Parting Line:.......................................................................................................................... 27 Tolerances: ............................................................................................................................ 27 Conclusion .................................................................................................................................... 28 References ..................................................................................................................................... 29 2 Executive Summary Through our research into the material and manufacturing considerations for the design of the DW272 motor subsystem wiring and fan, we will identify the factors that influenced the design process of these parts. We investigated the material properties and how they were influenced by the manufacturing process, as well as what design features were influenced by the manufacturing process. Based on our investigation, we will identify if design manufacturing guidelines were followed and how it has impacted the overall manufacturing performance. Our team will then be prepared to begin a proposal for an improvement to one of these components. 3 Introduction Importance of Design for Manufacture Design for Manufacturing (DFM) is a key part of the design process of any product. DFM is designing something so it is simple and cheap to produce. If a component design is too complicated, it could require a more expensive process to make. Designing a tool that only uses simple techniques to produce reduces the cost of the product. Choosing the right material for components is equally important. Different materials can be easier to machine and work with, while others can only be cut using expensive machines. Tolerances are also addressed when designing for manufacturing. Manufacturers must be given specific instructions on how to make your component. Pieces that fit together or must move past each other have to be within a certain tolerance limit in order for the whole product to work correctly. In the design for manufacturing, these tolerances must be addressed because different processes produce different errors in the final product. As a designer, one must decide which process will fulfill the product’s requirements. The Motor In the DW272, the motor is what converts the electrical energy from the wall into mechanical rotational energy to drive a screw into drywall. Utilizing the magnetic fields created by electricity running through coils of copper wire on the rotating armature and the stationary walls surrounding it, the motor spins faster than 4000 revolutions per minute. Attached to the armature is a fan that moves air through the screw gun to cool the brushes and the rest of motor. The shaft in the middle of the armature outputs the rotational energy through the front of the motor housing and into the gear casing. The fan attached to the armature is a very important piece of the screw gun. It is what keeps the whole screw gun from overheating. Overheating would cause the screw gun to fail; the plastics would melt, the brushes would be less efficient, the screw gun would underperform, and the metal would get dangerously hot, which could harm the operator. While the armature spins, the fan also spins, pushing air out the slits in the side of the motor housing. This creates a vacuum that pulls air in from more holes in the housing, which gets pushed out again by the fan, 4 creating a continuous flow of relatively cool air across the hot motor. The screw gun must have inlet and outlet holes in the housing for the fan to work. Only having one or the other would not let air flow through and cool the motor. The motor also has to be spinning for the fan to work, this means that the screw gun is not getting cooled after it has been turned off, but it is still hot. In the Thermal Lab, we saw that after the screw gun was turned off the inside temperature of the screw gun initially increased before cooling down. The copper coils on the armature are what allow the motor to spin. The alternating current coming in from the wall is fed directly to the copper coils on the motor housing and through carbon brushes to the copper coils on the rotating armature. The coils on the armature are wrapped around in all directions, but each direction is connected to its own section of a segmented contact. These two sets of copper coils create magnetic fields when a current is run through them. Thanks to the brushes and segmented contacts, the two magnetic fields are always offset, creating a net force that spins the armature. Without the brushes and contacts giving the right loops the current at the right time, the magnetic fields produced by the coils would not spin the motor as efficiently, if at all. These coils must conduct electricity well and must be malleable and ductile enough to be made into wire coils. Additionally, because of the long length of wire used, it must be relatively cheap. Copper Wiring and Coil Winding This component uses copper for the wires. Although silver is the only material more conductive than copper, silver is $20 per ounce vs. copper’s $2.79 per pound (Vincent Metals), making copper the most cost effective way to conduct electricity in this application. Typically, you still see some silver within copper wires. Using 0.01% of silver in copper wires increases the strength of the wire for withstanding more stress in applications (Basic Materials). Copper is also resistant to corrosion and easy to install into almost every application because of its ductility. In order to get copper into its wire form, scrap metal containing copper is sent to a factory. This part of the process is excellent for recycling old electric products for its copper. All of the scrap metal together is heated at a very high temperature (1085 degrees Celsius) and pressure, melting the copper and disintegrating many other materials. The temperature is 5 increased until the copper starts to boil (2562 degrees Celsius). Then, the molten copper and impurities flow into molds of slabs inside the factory. The slabs are cooled inside water and sent to electrolysis labs to shed off their impurities. This process cleans conductive metals by breaking off less conductive metals at the molecular level. Once the copper is pure, it is melted and cooled again to be cold drawn to the necessary diameters for wires (Gizmodo). Although cold drawing gets the wires to their proper dimensions, it makes the copper very brittle and inflexible due to all the stress and strain of the process. To make wire flexible again, it is annealed. That process involves putting the wire into an electric furnace, letting the metal recrystallize into its original structure, making it soft again for application (eHow). Because pure copper is hard to find in nature, an alternate method involves taking copper ores (compounds that include copper bonded within) mined from the ground and sending it to the factory. The most common copper ores are known as sulfur ores, but copper can be found bonded with many other elements such as: carbon, silver, gold, etc. Typically in the United States, copper only makes up 1.2 to 1.6% of the weight of these copper ores. Once it’s sent to the factory, it’s crushed into small pieces with the sulfur and mixed with water. That mixture is sent to a large cylinder with steel rods inside. The cylinder rotates on its horizontal axis, grinding up the small pieces into finely ground ore. They end up being little balls that are around three millimeters in diameter. The mixture is then sent to tanks with air injected through the bottom. As the air bubbles rise to the top, copper particles cling on. The top layer of the mixture will be mostly sulfides with 25% to 35% of sulfides containing copper. That top layer overflows from the tank and is sent to a furnace. Simultaneously, the water + particle mixture in the tank, called gangue or tailings, is pumped to a settling pond to dry. That same top layer later goes to a furnace where it’s mixed with a silica material. Fuel oil and oxygen-enriched is forced into the furnace chamber, bonding the oxygen and sulfur together. Once those two elements bond to make sulfur dioxide, it leaves the furnace as a gas, leaving a higher percentage of copper within the furnace (up to 60%). This process is repeated multiple times with different silica materials to remove the last of the sulfur (except a small amount) and other materials such as iron. As a result, there will be at least 99% copper left in the furnace. Next, the copper goes into an electrolysis stage in a tank. Within the tank the copper acts as an anode and the surrounding fluid, copper sulfate, acts as a cathode. As the cathode runs as a current around the anode, the 6 copper clings onto the copper sulfate and the last of the impurities sink to the bottom of the tank, allowing the copper to take 99.99% percent of its total weight. Finally, the copper is cold drawn to make wires, similar to the first method. To assemble the copper coil winding onto the armature, the basic fundamental parts that are needed include armature lamination (rings), armature shaft, commutator, stator, and bearing. As shown in Figure 1. Laminations are the steel portions of the stator and the rotor consisting of thin lamination sheets stacked together. Laminations sheets are stacked together either by welding (stator laminations), or stacked “loose” together (armature lamination). (Polaris Laser Laminations, LLC) Multiple lamination rings with slots and teeth will be stacked together to make up the part of the armature where the copper coil will be wound together. This lamination is made of multiple stacks of flat rings that all have similar shapes and are pressed together. As shown in Figure 1 the armature shaft piece is then inserted in the center hole of this lamination, once the stack has been pushed together so it can stick. Although the armature shaft is shaped circular, it is important to recognize the center hole of the lamination ring is not circular. As shown in Figure 8, the center hole of the lamination ring has hexagon so that it helps to Figure 1 prevent slipping of the armature shaft piece during operation. Lamination sheets are used instead of solid piece of steel in order to reduce eddy current losses. In addition it should be noted that the lamination rings are made of steel combined with silicon in order to increase electrical resistance. The stator is the housing for the armature. This is where the armature with the copper coil wrapped around it goes inside. As shown in Figure 2, the stator also has copper windings around it that creates an opposing magnetic field against the magnetic field coming from the armature when current flows thru it. Some motors use permanent magnets in order to make up the stator; however the DEWALT272 does not use permanent magnets. The stator, similar to the armature lamination is made of multiple stacks. However, unlike the lamination, the stator has the stacks welded Figure 2 7 together as shown in Figure 8. Some stators multiple lined slots, each of which holds a copper coil. The more powerful the motor, the bigger the stator and the larger the slots. The first step is to line the slots with insulation as shown in Figure 11. This insulation will keep the voltage confined to the coils. The coils are made from several copper wires wound together by programmable machines. Bigger motor, more wires per coil. The coils are then tied together, this prevents the wires from unraveling while being inserted into the stator slots. Insulate the copper coil on the outside with fiber glass sheets. Lock the coil inside the slots. Submerge the stator and the coil in a polystyrene varnish and vacuum it to prevent the stator to being a moist resistance Both stator and armature laminations are created by using electrical steel laminations. In many electrical systems where electromagnetic fields are important, silicon steel is used. Combining silicon to steel increases electrical resistance, while at the same time, improving the ability of magnetic fields to penetrate it, and also reduces the steel’s hysteresis loss (Polaris Laser Laminations, LLC). The copper coil is wrapped around the armature lamination and the stator lamination. Once the lamination has been assembled with the armature shaft of the motor, there will be an asymmetric winding process that wraps the coil onto the armature as shown in Figure 3. There are multiple ways of copper winding process. An example of copper coil winding machine is the Dual flyer Armature Winding Machine from Nide Mechanical, Figure 4. This machine similar to most other winding machines has a system where the number of winding are kept tracked. On Figure 4, on the top right side is shown a screen where the number of windings and RPMs tracked. This dual flyer winding machine takes the armature lamination assembly with the armature shaft in a horizontal position and inserts it to the space where copper wire is ready to be wrapped around the lamination Figure 3. Note, copper is wrapped around only two slots of the armature laminations at a time. Then it is rotated for the next set of two slots. 8 Once the armature lamination slots have been insulated as shown in Figure 9 with slot liner from insulating film, commonly polyester or nomex, the copper coil winding process begins. There is a separate winding process for the stator lamination. The most common method of placing wire within the stator is by winding a Figure 5 concentric coil and injecting it into the insulated core of the stator (Keith). Most of the electric motor industry uses “shed” type coil winders. As shown in Figure 3, first the winder system separately wraps specific amount of round copper coil wires. Then the winder system wraps the wire around a tapered coliform step then pushes the wrapped copper coil down the taper into the slots of the stator using an injection machine as seen in Figure 3 and Figure 10(Keith). There are different types of machines that are used for winding process of copper coil in the process of assembling the motor. There is a specific machine that is used for winding process of the armature and another type of machine that is used for stator windings, an example of stator winding machine is shown in Figure 5 Figure 4, and Figure 5, respectively. For armature windings, machines have different features such as dual flyer winding machines as shown in Figure 4 and single flyer winding machines. There are specifications that are taken into account during the operation of these machines. Technical parameters that have to be specified when using the winding machines include, wire diameter range, maximum winding speed, maximum coil segments, suitable stack height, suitable motor poles, air pressure, rolling capacity, distance between spindles (segments), power requirements, dimension and weight of the motor Figure 5 (UMANG Electricals). An example of technical parameters for coil winding machines is shown 9 in Figure 6 for armature winding machine and Figure 7 stator winding machine. The productivity of the winding machine can be analyzed by studying its performance given a certain parameters. For example, given a 12 slot armature, with 0.38 mm wire diameter, how many armatures could the machine wind within 10 minutes? Analyzing the performance of the machines given these constraints, it is possible to determine the productivity. Finally, it is important the machines have the capability to take inputs from the user. The machines shown in Figure 4 and Figure 5 have a computer interface where the user could edit, modify and save specification data for multiple types of motor models. Figure 8 Figure 8 Figure 8 10 Design for Manufacturing DFM guidelines are essential in making the production process of parts as efficient as possible. The copper coil winding follow a set of DFM guidelines that ensure an economical. The DFM guidelines achieve production efficiency by minimizing total parts, standardizing the across multiple models and products, allowing wide tolerance, and standardizing design features. We have identified several cases where DFM guidelines were used to increase production processes: Material: Standard steel metal combined with 3% silicon alloy is used in manufacturing of the motor. This is a standard material that is used universally. This also reduces additional cost from having to make parts with specific material properties. Armature lamination and Stator lamination: In the production of the armature lamination, the lamination ring pieces are only pressed together without any additional molding process. In addition, during the production of the stator lamination, we have identified that the lamination rings of the stator are only welded on one side of the stator. Thus keeping design parts at ease of fabrication. Therefore, the die cutter is able to perform multiple functions of cutting, measuring, and stamping of the armature lamination all in one place. Copper coil winding: We have noticed that the copper coil windings both on the armature and the stator are not dipped into any chemical solution to bind them together. When studying the pieces, we were able to pull a single strand of copper coil from the winding. Other motors we have studied use an insulation method where the stator and the armature is dipped into chemical solution that binds the coils together. For example, one of the fan blower stator we looked at in class had a green material that helped bind the copper coil together, this may have been useful, when it is operating in dusty environment. However, we were able to recognize in the production 11 of the DW272, DeWalt does not use this method, and it will save time and additional cost during manufacturing process. Wire diameter range: There is a manufacturing requirement of range of copper coil diameter range that the armature lamination and the stator lamination (similar) will need for it to work with the winding machine during production. Since DeWalt uses similar types of copper coil winding system, it is possible to make the production process efficient by standardizing a common wire diameter range across multiple products and varying models. Circular hole of the armature lamination: as shown in Figure 8 the center of the armature lamination is not fully circular. By avoiding small tolerance, in this case perfect circular hole, it is possible to make the production cost lower. It is also important the to note the fact that the shape of the hole is intended to avoid slipping between the surface of the armature shaft and the armature lamination. Cost The coil winding machines range from $10,000 up to $90,000 (Alibaba). It is possible tool manufacturers to have a higher costing winding machines, because they have to have a higher standards. With increased amount of features, and productivity rate, the cost of the winding machines increase. For example, the winding machine shown in Figure 5, has a technical specification shown in Figure 7 and the cost of this particular machine is around $50,000 USD (Alibaba). When considering the cost of manufacturing the copper wire, you have to consider the precision of each stage. For the beginning first method, taking scrap metal won’t be very expensive because they are old goods that people don’t want anymore. However, in the second method, mining is added to the equation. The dynamite needed to extract the material, usage of all the dump trucks, and transport of the material to the factory all need to be considered for an additional cost compared to the first method. Later into both methods, the first uses hot temperatures to melt the copper, but the send method mixes copper ore and water, along with a crushing stage to assist extracting the copper material. To get rid of the impurities, the first method relies on one round of electrolysis, but the other uses multiple rounds of combustion and silica injections. One could consider that the second method is much more precise, but it has 12 more stages, increasing cost to manufacture. On average the price for this final copper wire, as previously stated, is roughly $2.79 per pound (Vincent Metals). Motor Fan The fan is made from either one of two materials. The primary material is Ultramid B3ZG6 BK30564 30% glass filled PA6 while the alternative material is BOILN Pemaron 260G6HI 91BK 30% glass filled PA6/GF30 (Stanley Black & Decker Inc.). These materials were chosen for their strength, weight, cost, and melting temperature. The fan does not support any substantial load, and must merely resist severe deflection from the torque that results from rotational air resistance. The primary material offers a flexural strength of 220 MPa and a flexural modulus of 7.40 GPa, both of which are more than enough to satisfy the strength requirement (Matweb 2015). In the name of ergonomics, an engineer would want the fan to be as light as possible without sacrificing other important characteristics. The Ultramid has a density of 1330 kg/m3, which reduces the moment on the user’s wrist during operation. Because keeping the price of the tool as low as possible offers a distinct competitive advantage, this material is likely one of the cheapest that was available. Upon researching it, we found the Ultramid material to be $0.07 per fan when an order of one million fans are produced (CustomPart.net 2015). Since the inside of the DW272 gets fairly hot, the fan must be able to withstand these temperatures without deforming or becoming very soft. However, the material also must be able to be easily melted and injected into a mold to form its shape. The Ultramid has a melting point of 220oC and a melt flow of 3.325 g/min under a load of 5.00 kg at 275oC (Matweb). This allows the material to be injected into a mold easily and efficiently. Finally, this Ultramid has a linear mold shrinkage of 0.005cm/cm. This property ensures that the fan will not experience a large amount of deformation once it is cast into the mold and cooled. For this part, plastic injection molding was used to create it. This process was used because it is relatively cheap, able to accurately and reliably reproduce parts with complex geometry, and it is able to produce a large volume of parts fairly quickly. Evidence of this manufacturing method can be seen in the ejector pin indentations in figure 3-1 and the ridges along the support ring seen in figure 3-2. Likewise, the fan blade thicknesses are tapered, which indicates drafting was used. The fan consists of 80 individual blades, as well as an imprinted “5” on the front as seen in figure 3-3. 13 Figure 3-1 14 Figure 3-2 15 Figure 3-3 Accomplishing this by another manufacturing process would likely be very expensive and time consuming. The ability to quickly produce the parts is also crucial to manufacturing. This is especially true if the tool is competing for a first-to-market position and all other components can be produced more quickly. Although the fan is important to the overall function of the DW272, DeWalt cannot afford to spend a large amount of money on this one-piece component. When producing parts in large volume, injection molding is usually the cheapest method. The other viable methods for reproducing the fan are spin casting, laser cutting, and standard 3-D printing. Spin casting is a similar process to injection molding, except that it uses the centrifugal force from a rotating mold to force the material into the cavity. However, this method would likely take a longer time for each mold in this application. Laser cutting from a solid block of Ultramid would produce much more waste material than injection molding. Some of this can be recycled and reused for formation into another block of stock material, but there 16 are limitations on the percentage of new and recycled material that can be used. Both recycling material and discarding waste material will add extra cost to the final product. Additionally, the high temperatures required for laser cutting may deform the edges of the fan. Because of its geometry, the fan may not have the ability to be fully reproduced by a laser cutting procedure, and the stock material would likely need to be tooled with a lathe as well to replicate the three dimensional shape. 3D printing involves individually printing each piece from a computer model of that piece. This method of manufacturing can begin producing parts much faster than injection molding because no core or cavity is required to be made before manufacturing can begin. This also means that at low volume production, this method can be much cheaper than injection molding. However, as we can see from the graphs below, when hundreds of thousands to millions of parts are being produced, the price for injection molding per part becomes much lower than 3D printing. Currently, 3D printers are only compatible with specific materials, and they may not be able to support a material that could fulfill the critical requirements of the fan. Figure 3-4 (3ders 2015) 17 Figure 3-5 (3ders) Figure 3-6 (3ders) Figure 3-7 (3ders) 18 Process + Machinery The fan for the DW272 was specifically manufactured using hot runner injection molding. A diagram of a screw-type hot runner injection mold can be seen in Figure 3-8. Figure 3-8 (Balázs 2014) There are several types of injection machines, but they all operate on the same basic principles and steps. The first step for any injection molding procedure is creating a core and a cavity. An example of a simple core and cavity pair can be seen in figure 3-9. Figure 3-9 (Mudrak 2015) This is the most expensive step in this process because it consists of custom-tooled pieces and is usually between $10k and $20k depending on part complexity (Plastic Portal). After this is complete, the injection-molding machine can mindlessly reproduce the remaining molded pieces. 19 The remainder of the process consists of two main phases: an injection phase and a clamping phase. Injection phase: Plastic pellets are first supplied into a hopper and then fall into a heated barrel. As the threaded barrel turns, it forces the material down towards the mold cavity and simultaneously heats it. This barrel is kept between 265 and 290 degC depending on the length of the barrel (Plastic Portal 2015). Clamping Phase: As the melted plastic moves past the barrel, it passes through a nozzle that is kept between 270 and 290 degC. The plastic then enters the molding cavity, which is kept at a surface temperature between 80-95 degC to ensure that the material solidifies almost as soon as contact is made with the mold surface. A constant pressure of 30-125 bar is kept inside the mold to compensate for shrinkage and to reduce trapped air (Plastic Portal). Faster fill rates are recommended to ensure a uniform distribution of material inside the mold. Once the mold is sufficiently cooled, the core and cavity separate and the part is removed via ejector pins (Plastic Portal). Costs Injection molding has a very large initial cost, and a very small cost per component afterwards. This is because a core and cavity must be produced, which is a custom part and will cost a lot of money. Using a cost estimator from CustomParts.net, we were able to estimate the cost for tooling this component to be roughly $25,000. The complex geometry of the fan adds a lot to this price. However, from a larger supplier that has a history with DeWalt, we can assume this cost will likely be lower. Assuming an order of about one million fans, the material cost was estimated at only around $0.07 per fan. Production Labor was estimated at $0.22 per part. These figures combine for a total estimated cost of $0.56 (CustomPartNet 2015). From the cost BOM found on canvas (Stanley Black & Decker), we found that the actual total cost per fan was only $0.14. This difference could result from a larger order of fans, or a more efficient manufacturer. 20 Table of Compatible Materials Injection molding supports a wide variety of materials and applications. Table 3-1 shows a list of the materials offered by Proto Labs for injection molding. A complete list of all available materials is likely much longer. Material ABS, Black (Cycolac MG47-BK4500) ABS, Black (Lustran 433-904000) ABS, Black (Polylac PA-765) ABS, Black (Polylac PA-746) ABS, Cool Gray (Lustran 348-G28633-P) ABS, Light Grey (Platable) (Lustran PG 298-703693) ABS, Natural (Lustran 433-000000) ABS, Natural (Polylac PA-765 (Natural)) ABS, Sno White (Lustran 348-012002) ABS, Black 30% Glass Fiber (RTP 600 605) ABS/PC, Black (Bayblend FR 110-901510) ABS/PC, Black (Cycoloy C2950-701) ABS/PC, Black (Bayblend FR3010-901510) ABS/PC, Black (Bayblend T85 XF-901510) ABS/PC, Natural (Bayblend T65 XF-000000) ABS/PC, Natural (Bayblend T85 XF-000000) ABS/PC, Natural (Cycoloy C6600-111) ABS/PC, Natural (Bayblend FR 110-000000) ABS/PC, Natural (Cycoloy C2950-111) Acetal, Black 10% Glass Bead (RTP 800 800 GB 10) Acetal, Black 20% Glass Bead (RTP 800 800 GB 20) Acetal Copolymer, Black (Celcon M90 CD3068) Acetal Copolymer, Natural (Celcon M90 CF2001) Acetal Homopolymer, Black (Delrin 500P BK602) Acetal Homopolymer, Natural (Delrin 500P NC010) Acrylic (PMMA), Clear (Plexiglas V052-100) ETPU, Natural (Isoplast 202EZ) HDPE, Natural (Unipol DMDA 8007) HDPE, Natural (Marlex 9006 HID) LCP, Black 30% Glass Fiber (Vectra E130ID-2 VD3005 Black A1) LDPE, Natural (Dow LDPE 722) 21 LLDPE, Natural (Dowlex 2517) Nylon 6, Natural 15% Glass Fiber (Zytel 73G15L NC010) Nylon 6/12, Black 33% Glass Fiber (Zytel 77G33L BK031) Nylon 66, Black (RTP 200 200 UV) Nylon 66, Black (Zytel 101L BKB009) Nylon 66, Black (Hylon Select N1000EHL) Nylon 66, Natural (Zytel 103 HSL NC010) Nylon 66, Black 13% Glass Fiber (Zytel 70G13 HS1L BK031) Nylon 66, Black 13% Glass Fiber (Hylon Select N1013HL) Nylon 66, Natural 13% Glass Fiber (Zytel 70G13 HS1L NC010) Nylon 66, Black 14% Glass Fiber (Zytel 8018 HS BKB085) Nylon 66, Natural 14% Glass Fiber (Zytel 80G14AHS NC010) Nylon 66, Black 20% Glass Fiber (RTP 200 203 FR) Nylon 66, Black 33% Glass Fiber (Zytel 70G33 HS1L BK031) Nylon 66, Black 33% Glass Fiber (Vydyne R533H BK02) Nylon 66, Black 33% Glass Fiber (Hylon Select N1033HL) Nylon 66, Natural 33% Glass Fiber (Zytel 70G33 HSIL NC010) Nylon 66, Black 40% Mineral Reinforced (Minlon 10B40 BK061) Nylon 66, Black Impact Modifier, Rubber (Zytel ST-801 BK010) Nylon 66, Natural Impact Modifier, Rubber (Zytel ST-801 NC010) PBT, Black (Valox 357-BK1066) PBT, Black (Crastin S600F20 BK851 (same as S610)) PBT, Natural (Valox 357-1001) PBT, Black 30% Glass Fiber (Valox 420SEO-BK1066-BG) PBT, Natural 30% Glass Fiber (Valox 420 SEO 1001 Nat) PC, Black (Makrolon 2405-901510) PC, Black (Lexan 940-701) PC, Black (Hylex P1025L) PC, Blue Tint (Makrolon RX2530-451118) PC, Clear (Makrolon 2407-550115) PC, Clear (Makrolon 2458-550115) PC, Infrared (Lexan 121 S-80362) PC, Smoke (RTP 300 399X71833 S-94450) PC, Natural 10% Glass Fiber (RTP 300 301) PC, Natural 20% Glass Fiber (Lexan 3412R-131) PC/PBT, Black (Xenoy 6620-BK1066) PET, Black 30% Glass Fiber (Rynite 530-BK503) 22 PET, Black 35% Glass Mica Low Warp (Rynite 935 BK505) PETG, Clear (Eastar 6763) PP, Natural (RTP Anti-static Permastat 100) PP Homopolymer, Black (Maxxam FR PP 301BLK1284-11S) PP Homopolymer, Natural (Profax 6323) PP Homopolymer, Natural (Profax 6523) PP Homopolymer, Natural (Profax PD702) PP Impact Copolymer, Natural (Profax SG-702) PP Random Copolymer, Natural (FHR PP P5M6K-048) PPA, Natural 35% Glass Fiber (Zytel HTN 51G35HSL NC010) PPE/PS, Black (Noryl 731-701) PPS, Black 40% Glass Fiber (Ryton R-4-02) PPS, Natural 40% Glass Fiber (Ryton R-4) PPSU, Black (Radel R-5100 BK937) PPSU, Off-White (Radel R-5100 NT15) PS (GPPS), Clear (Styron 666D) PS (HIPS), Natural (Styron 498) PSU, Natural (Udel P-3703 NT 11) SB, Clear (K-Resin KR01K CPC BDS CL) TPE, Black (Santoprene 111-35) TPE, Black (Santoprene 111-45) TPE, Black (Santoprene 101-64) TPE, Natural (Santoprene 211-45) TPE, Natural (Santoprene 251-70W232 70A Durometer) TPE, Natural (Santoprene 201-64) TPU-Polyester, Natural (Texin 245) TPU-Polyether, Natural (Texin 983-000000) TPV, Black (Santoprene 101-87) TPV, Black (Santoprene 101-55) TPV, Black (Santoprene 101-73) TPV, Natural (Santoprene 201-87) PEEK, Natural (Victrex 450G) PEEK, Natural 30% Glass Fiber (Vestakeep 4000 GF30) PEI, Black (RTP 2100 2100 LF Black) Magnesium, Grey (Magnesium AZ-91) MIM Hardenable Nickel Steel (Catamold FN0205) MIM Nickel Steel (Catamold FN02 MIM Case Hardening Nickel Steel) 23 MIM Stainless Steel (Catamold 17-4 PH K) MIM Stainless Steel (Catamold 316L K) MIM Steel Alloy (Catamold 42CrMo4) Silicone, Clear (Elastosil 3003/50 A/B) Silicone, Clear (Elastosil 3003/30 A/B) Silicone, Clear (Elastosil 3003/70 A/B) Silicone, Optically Clear (Dow Corning MS-1002) Silicone, Water Clear (Dow Corning QP1-250) Table 3-1 (Proto Labs) Design for manufacturing is a method of design guidelines where manufacturability is the measure of performance. DFM guidelines are essential in making the production process of parts as efficient as possible. Plastic injection molding follows a set of DFM guidelines that ensure a versatile, economical, and precise product. Although the tooling is expensive, the cost per part is very low because of clever production processes and the DFM guidelines. There is no, one written in stone DFM guideline for injection molding; yet the fundamental design guidelines can be explained in just a number of design rules. Drafts: Part design should include draft features (angled surfaces) to facilitate removal from the mold. Depending on the particular surface length, draft angles down to half a degree are reasonable. Typical draft angles should be about 1 to 2 degrees for part surfaces not exceeding 5 inches. Dimensional tolerance specification will govern the part cost and manufacturability. If you have a small region of the part that needs higher tolerances, say the location of a critical feature used for alignment, then the cost for tooling the mold cavity will increase. Figure 3-10 24 Wall Thickness: Wall thickness for a thin part such as a soda bottle is quite reasonable and economical. Thick wall sections are possible as well. Uneven wall thickness present challenges to the plastic molder manufacturer. Designing your part with uniform walls and cross section will simplify manufacturing and costing. At wall intersection or "tees" sinking will occur. Thick walls cool slower and greater shrinking will occur. Thin walls cool faster and thus, less shrinking. Observing proper (and uniform) wall thickness helps parts avoid potential issues such as sink marks and warping as well as minimizing residual stresses. Recommended thicknesses vary by material: Resin Inches ABS 0.045 - 0.140 Acetal 0.030 - 0.120 Acrylic 0.025 - 0.500 Liquid crystal polymer 0.030 - 0.120 Long-fiber reinforced plastics 0.075 - 1.000 Nylon 0.030 - 0.115 Polycarbonate 0.040 - 0.150 Polyester 0.025 - 0.125 Polyethylene 0.030 - 0.200 Polyphenylene sulfide 0.020 - 0.180 25 Polypropylene 0.025 - 0.150 Polystyrene 0.035 - 0.150 Polyurethane 0.080 - 0.750 Table 3-2: The table shows wall thicknesses that Protomold recommends according to resin. Radii and Corners: The design must maintain uniform wall thickness at corners. External and internal radius should share the same center point. External radii = internal radii + wall thickness. The minimum radii should not be less than 1/4 minimum wall thickness. Design for radii to be 1/2 to 3/4 of the nominal wall thickness. When significant stress is present, a larger radius is recommended as larger radii distribute stress more uniformly. Ribs: Ribs increase the bending stiffness of a part. Without ribs, the thickness has to be increased to increase the bending stiffness, thereby increasing part weight, materials costs, and cycle time costs. Adding ribs increases the moment of inertia, which increases the bending stiffness. Bending stiffness = E (Young's Modulus) x I (Moment of Inertia). Ribs should be 1/2 to 2/3 of the nominal wall thickness and less than 3 times thickness in height in order to keep sinking to a minimum. Taper of 1 deg. is typical. Excess rib height combined with taper will produce thin sections requiring extra fill time at the mold. • Diameter = (Outside Diameter) \ (Inside Diameter) = 2 to 3 • Thickness = 1/2 to 2/3 nominal wall thickness • Gusset Height = 2/3 Height • Height = Fastener minimum requirements • Taper = 1 deg. all around • Diameter Ratio should be minimum ratio of 2,this will reduce risk of failure. • Surface Finish (micro-inches) 64 or higher, depending on material, down to 7-16 is possible 26 Ejector Pins: Ejector pins must be strategically sized and placed in order to minimize the effect on the design and need to be approved by DeWalt engineers prior to tooling. For the fan, these indentations are visible towards the center of both the front and rear of the fan. This location has a minimal effect on airflow and the fan’s structural stability. Parting Line: The parting line or “witness line” refers to the line of raised material on the part resulting from the crease in the core and cavity. This defect is an unavoidable side effect in most circumstances. However, the fan of the DW272 has no notable witness line. It is likely that the fan mold was cleverly designed so that the crease in the mold was placed in between naturally occurring features of the fan such as the blades and support ring. Tolerances: This fan part had tolerances of +/- 0.3 for 0 & 1 place decimal, +/- 0.10 for 2 place decimal, and +/- 1.0 degrees for angles, based on the design schematics. Using calipers, we were able to measure our fan part to see if the guidelines and tolerances were met. Wall thickness was between the recommended guide of .762 mm and 2.921 mm for nylons. Uniform wall thickness at corners was also achieved for each section and draft was applied to the vertical faces of the blades to prevent the mold from being parallel to the motion of the mold opening. Surface finish was too small to measure down to the micro inch. The minimum radii is not less than ¼ the minimum wall thickness. The ejector pin and gate location imprints further show that the components of the DFM guidelines were met. 27 Conclusion Through our research and investigation, we became more familiar with the materials and manufacturing processes of the fan and armature wire of the DW272 motor. In addition, we were able to find evidence that DFM guidelines were used during the manufacturing process to increase ease of fabrication process. We now understand many of the design decisions that went into these components including the die casting method, copper coil production and winding process and the overall armature fan fabrication process. Based on our studies we were able to identify manufacturing decision that influenced the production efficiency. These decisions include the material, manufacturing process, manufacturing guidelines, and features of these components that are directly related to manufacturing. Our research also uncovered other possible manufacturing processes that were available to engineers and why they chose the particular ones that were used. Armed with this knowledge, we now feel confident that we can further investigate the components of the tool and make suggestions for improvement. These improvements could come in the form of cost, weight, overall tool efficiency, or time to manufacture. Deciding on the improvement that may be made will require further research and testing of the tool and that particular part. This will allow us to determine the critical requirements for the part and suggest other methods for meeting those requirements. 28 References "Injection Molding Materials." Guide. Proto Labs, 2015. Web. 22 Apr. 2015. <http://www.protolabs.com/resources/molding-materials>. "Is 3D Printing a Viable and Affordable Alternative to Injection Molding Production?" 3ders. N.p., n.d. 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