DESIGN FOR MANUFACTURING AND ASSEMBLY


 


Introduction


            The use of best practice in modern product design is today an essential requirement in ever competitive markets yet it is a requirement which puts great pressure on small and medium sized companies. Due to a simple lack of resources, many may struggle to stay abreast of the latest technologies and processes.


            Latest technologies that are considered as tools which can do that and more importantly not cut out just 10 per cent, but as much as 40 per cent. In this way, companies are making quite huge benefits. One such tool is called Design for Manufacturing and Assembly (DFMA).


            DFMA allows you to critically evaluate the number of functional parts and measure the cost of handling individual parts during an assembly process. It opens up a lot of questions about how well a product is being designed for manufacturing.


Benefits of DFMA


            DFMA provides real benefits throughout product development organization:


Manufacturing


Design


Cost Management


C-Level Executives


“You want me to manufacture this design? You’re kidding, right?” If you find yourself asking this question more often than you’d like, DFMA can help. You and your design engineers can quickly analyze and manipulate different design approaches. The resulting lean design will contain fewer parts and be easier to manufacture.


You can improve the manufacturability of your design in the DFMA software through product simplification. You can explore alternatives in processes and materials, and immediately see the cost impact of your decisions. You can provide factual data to manufacturing and your managers, so you can all make valid business decisions about your product design.


You have a target cost in mind for a new or existing product. What are the main contributors to the cost of the product? DFMA tools can answer that question for you. They can also help you work more effectively with your design and manufacturing engineers, and outside suppliers.


“What will it cost to produce this? How can we reduce the cost without sacrificing quality?” Our tools make it possible for you to obtain answers to these questions that are based on real-life, accurate data. Data that can be used to support productive, objective discussions, improve products while reducing costs, and hold suppliers to reliable “should cost” estimates.


 


 


 


 


 


Table 1: Benefits of DFMA. Source http://www.dfma.com/


 


Steps Undertaken in this Study


 


            I will discuss to you the steps taken in my case study.


 


            Step 1. Why I choose these three products (FM radio, electric torch, tape measure)?


            These products are for future student use. Besides, it is easy to assembly and disassembly. In addition, it does not have to provide a lot of products to students, so it is cheap.


            Step 2. Design for assembly (using DFA software). The technique involves two important steps for each part in the assembly:


1.    A decision as to whether the part can be considered a candidate for elimination or combination with other parts in the assembly.


2.    An estimation of the time taken to grasp, manipulate and insert the part       after this step, we can get all results, like how much cost saving, part no     saving, assembly time saving and get design efficiency)


            Step 3. Use engineering drawings (Catier drawing software).


 


 


FM Radio


            An FM Radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio.



Figure 1: “finished look”


 


            What we’ll need


Part designator


Part description


C1a,C1b


10 pf, 50 v, ceramic disc capacitor


C2


22 pf, 50 v, ceramic disc capacitor


C3


RF tuning capacitor 


C4


330 pf, 50 v, ceramic disc capacitor


C5,C8


0.001 uf, 50 v, ceramic disc capacitor


C6


0.22 uf, 50 v, film capacitor


C7


0.0047 uf, 50 v, ceramic disc capacitor


C9


22 uf, 16 v, electrolytic capacitor


D1


TL431AIZ voltage control Zener (shunt regulator)


EPH1


High impedance earphone


L2


22 uh RF choke


Q1


2N4416A JFET transistor


R1


470K, 1/4 w, resistor


R2, R3


1K, 1/4 w, resistor


R4


10K, 1/4 w, resistor


R5


1M, 1/4 w, resistor


R6


100 ohm, 1/4 w, resistor


S1


Small SPST switch


screws for C3


screws for mounting C3 (2 needed)


nylon screw


#4 nylon screw used for tuning C3


battery connector


mini battery snap


Table 2: Parts needed for the radio


            Layout. Component layout is very important as this is a superregenerative design. The tuning capacitor, C3, has three leads.  Only the outer two leads are used; the middle lead of C3 is not connected.  Arrange L1 fairly close to C3, but keep it away from where your hand will be.  If your hand is too close to L1 while you tune the radio, it will make tuning very difficult.

Figure 2: C1a,C1b 10 pf, 50 v, ceramic disc capacitor (please refer to Table2)


Winding L1. L1 sets the frequency of the radio, acts as the antenna, and is the primary adjustment.  Despite being able to do many important jobs, it is easy to construct.  Get any cylindrical object that is just under 1/2 inch (13 mm) in diameter.  Preferably a thick pencil, but a magic marker or large drill bit work just fine.  #20 bare solid wire works the best, but any wire that holds its shape will do.  Wind 6 turns tightly, side-by-side, on the cylinder, then slip the wire off.  Spread the windings apart from each other so the whole coil is just under an inch (2.5 cm) long.  Find the midpoint and solder a small wire for C2 there.  Mount the ends of the wire on your circuit board keeping some clearance between the coil and the circuit board.

Figure 3: L2 22 uh RF choke (please refer to Table2)


            A Tuning Knob for C3. C3 does not come with a knob.  A knob is important to keep your hand away from the capacitor and coil when you tune in stations.  The solution is to use a #4 nylon screw.  Twist the nylon screw into the threads of the C3 tuning handle. The #4 screw is the wrong thread pitch and will jam (bind) in the threads. Tighten the screw just enough so it stays put as you tune the capacitor.  The resulting arrangement works quite well.              Adjustment. If the radio is wired correctly, when turned on, you may either hear a radio station, a rushing noise, a squeal, or nothing.  If you got a radio station, you are in good shape.  Use another FM radio to see where you are on the FM band.  You can change the tuning range of C3 by squeezing L1 or change C1.  If you hear a rushing noise, you will probably be able to tune in a station.  Try the tuning control and see what you get.  If you hear a squeal or hear nothing, then the circuit is oscillating too little or too much.  Try spreading or compressing L1. Double check your connections.  If you don’t make any progress, then you need to change R4.  Replace R4 with a 20K or larger potentiometer (up to 50K).  A trimmer potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the circuit is working, you can remove the potentiometer, measure its value, and replace it with a fixed resistor.  Some people might want to build the set from the start with a trimmer potentiometer in place.

Figure 4: R4 10K, 1/4 w, resistor (please refer to Table2)


                        Substituting other components. Many of the parts are fairly common and might already be in your junk box.  Only certain component values are critical.  The RF choke should be in the range of 20 to 30 uh, although values from15 to 40 uh might work.  The tuning capacitor value is not critical, but if you use values below 50 pf you should reduce or remove C1. The circuit is designed for the high impedance type earphone.  Normal earphones can be used, but the battery drain is much greater and the circuit must be changed.  To use normal earphones, change R3 to 180 ohms.  Q1 can be replace with any high-frequency N-channel JFET transistor, but only the 2N4416, 2N4416A, and J310 have been tested.  A MPF102 probably will work. C2 is not too critical; any value from 18 to 27 pf will work. C7 is fairly critical.  You can use a .005 or .0047 uf, but don’t change it much more than that.             Improved design for more audio gain. The same printed circuit board can be used with some modifications. The circuit board is important to make sure the tuning end of the radio works properly, so the audio amplifier changes can be squeezed onto the circuit board without fear of wrecking radio operation.  Look closely at the new schematic for the new components and some changed component values (below).

Figure 5: Schematic diagram for the Original One Transistor FM Radio



Figure 6: One Transistor FM Radio with improved audio gain


            Additional Notes. Connect the two sections of the variable capacitor (C3) in series to linearize the tuning somewhat.  That is, use the connections on either end of C3 and don’t use the middle lead. L2, the RF choke should not be near a ground. The same is true for L1. Capacitance to ground will disturb the feedback. The gain is just enough to drive an earphone. If you live too far away from radio stations, you might have trouble hearing one.  There is no option here for an external antenna (that would require and extra transistor). You can drive a speaker if you add an external audio amplifier. If you want a little more audio gain, or you cannot locate a TL431CLP chip, you can use some other audio amplifier in the circuit where pins 1 and 2 of D1 normally connect.


Flashlight


 


            A flashlight or torch is a hand-held portable electric spotlight. It is known as a flashlight mainly in the United States and Canada and as a torch in most Commonwealth countries.


            The Manufacturing Process






Figure 7: Steps in constructing a home made flashlight


                        Plastic housing. The plastic components used in flashlight construction are typically injection molded using polystyrene and other durable polymers. In this process, plastic pellets are mixed with plasticizing agents and colorants. This mixture is liquefied by heating and then injected into appropriately shaped molds via an injection plunger. The mold is then subjected to high pressure to assure that the molds are completely filled, and to hold the molds together against force of injected liquid plastics. The end closures are also molded, where usually both internal and external threads are molded. Pressures as high as 2,500 tons may be used for high-speed or multiple-cavity production molders.


                        After the injection process, the molten plastic is cooled by forcing water through channels in the mold. The plastic hardens as it cools and the pressure is released. At this point, the two halves of the mold are separated and the plastic part can be removed for finishing. The plastic polymers used in this process are thermoplastic, meaning they can be repeatedly melted so the scrap pieces can be reworked to make additional parts. Therefore, there is very little wasted plastic in this process. Subsequent operations may be required to polish, cut, and finish the plastic parts.


                        Light source. Incandescent bulbs are the most common light source used in flashlights. These consist of a metal filament sealed in a glass bulb. When the filament is exposed to an electric current the resistance of the wire causes it to heat up and emit light in the visible wavelengths. The filament is welded to two wires that pass though holes in a cylindrical glass bead that forms the base of the bulb. This structure is placed in a fixture and a cylindrical glass envelope that is closed at one end is placed over the filament. The open end of the glass envelope rests against the glass bead.


                        The structure is placed inside a vacuum chamber and heat is applied to seal the glass envelope to the glass bead. The heat causes the glass to soften, and may cause the filament to be displaced to one side. Therefore, care must be taken to ensure the filament is properly aligned or the bulb will not project a beam of light in the right direction.


                        Other possible light sources include fluorescent bulbs, which are often used in camping lanterns. These bulbs emit light due to the excitation of gas molecules inside the bulb. LEDs, or light emitting diodes, are used in some specialty lights; these emit light when exposed to extremely low levels of electric current. The bulb is often fitted in front of a polished aluminum reflector that helps to focus the light during operation.


                        Switch and controls. The electronic circuitry of a flashlight varies depending on its design. Simple lights rely on an off/on switch to make the connection between the wires connecting the battery terminals to the wires extending from the base of the bulb. This type of switch is most commonly a slide type that moves up or down to make the proper connection. The switch assembly is more complicated in the more sophisticated lights. One United States patent describes a flexible metal strip that is depressed to create a contact between the wires.


                        Assembly. Depending on the design and the manufacturers capability, units may be assembled on an automated conveyor line or by hand. Some models, particularly those using small watch batteries, have the battery inserted during assembly. Otherwise, the unit may be assembled without the batteries that are inserted later by the consumer. This operation involves screwing the lamp assembly onto the threads on the casing.


                        Packaging. Assembled units may be placed in some form of outer packaging, such as a clear plastic blister pack or clam shell. The plastic shell may then be attached to a cardboard display card or packed in a box prior to shipping.


            Quality Control. Completed flashlights undergo a series of quality control tests to ensure they function properly. First, the bulb must be checked to ensure it is properly aligned with the reflector; if it is misaligned performance may suffer. Second, the switch assembly is evaluated to determine if it makes proper contact with the electrical leads. Third, the seal on the battery compartment must be checked to determine if moisture will not inadvertently enter the battery compartment. This seal must allow venting of gasses that may be formed during battery operation.


            The bulb itself must meet separate quality standards. Generally, Division 2-approved flashlights are temperature-rated as TI to T6, where Tl is a temperatures less than, or equal to, 842°F (450°C) and T6 is less than, or equal to, 185°F (85°C). Testing labs used by flashlight manufacturers include Factory Mutual Research Corporation, Underwriters Laboratories, and Demko.


            Hazardous environment. Any flashlight that will be used in a hazardous environment or confined space must be properly tested to ascertain that it meets or exceeds all applicable safety standards for those locations. Hazardous Locations are defined by the National Electric Code and include the following classifications. Class I locations are areas where flammable gases may be present in sufficient quantities to produce explosive or flammable mixtures. Class II locations can be described as hazardous because of the presence of combustible dust. Class III locations contain easily ignitable fibers and filings. Hazardous atmospheres are further defined by “groups.” These include atmospheres containing acetylene, hydrogen, or gases or vapors of equivalent hazard, such as ethylether vapors, ethylene, cyclo-propane, gasoline, hexane, naptha, benzene, butane, propane, alcohol, acetone, benzol, lacquer solvent vapors, or natural gas. Metal dust, including aluminum, magnesium, and their commercial alloys, may also create hazardous atmospheres. Environments containing carbon black, coal or coke dust, flour, starch, or grain dusts, are classified by the Code. Flashlights designed for use in these environments are individually tested before leaving the factory.


Design for Manufacturing / Assembly Guidelines


           


            1. Simplify the design and reduce the number of parts because for each part, there is an opportunity for a defective part and an assembly error. The probability of a perfect product goes down exponentially as the number of parts increases. Ask the following: Does the part move relative to all other moving parts? Must the part absolutely be of a different material from the other parts? Must the part be different to allow possible disassembly?


            2. Standardize and use common parts and materials to facilitate design activities, to minimize the amount of inventory in the system, and to standardize handling and assembly operations.


            3. Design for ease of fabrication. Select processes compatible with the materials and production volumes. Select materials compatible with production processes and that minimize processing time while meeting functional requirements. Avoid unnecessary part features because they involve extra processing effort and/or more complex tooling. Apply specific guidelines appropriate for the fabrication process.


            4. Design within process capabilities and avoid unneeded surface finish requirements. Know the production process capabilities of equipment and establish controlled processes. Avoid unnecessarily tight tolerances that are beyond the natural capability of the manufacturing processes. Determine when new production process capabilities are needed early to allow sufficient time to determine optimal process parameters and establish a controlled process. Design in the center of a component’s parameter range to improve reliability and limit the range of variance around the parameter objective.


            5. Mistake-proof product design and assembly (poka-yoke) so that the assembly process is unambiguous. Components should be designed so that they can only be assembled in one way; they cannot be reversed.


            6. Design for parts orientation and handling to minimize non-value-added manual effort and ambiguity in orienting and merging parts.


            7. Minimize flexible parts and interconnections. Avoid flexible and flimsy parts such as belts, gaskets, tubing, cables and wire harnesses. Their flexibility makes material handling and assembly more difficult and these parts are more susceptible to damage. Use plug-in boards and backplanes to minimize wire harnesses.


            8. Design for ease of assembly by utilizing simple patterns of movement and minimizing the axes of assembly. Complex orientation and assembly movements in various directions should be avoided.


           9. Design for efficient joining and fastening. Evaluate other bonding techniques with adhesives. Match fastening techniques to materials, product functional requirements, and disassembly/servicing requirements.


            10. Design modular products to facilitate assembly with building block components and subassemblies. Modules can be manufactured and tested before final assembly. The short final assembly leadtime can result in a wide variety of products being made to a customer’s order in a short period of time without having to stock a significant level of inventory.


            11. Design for automated production. Automated production involves less flexibility than manual production. The product must be designed in a way that can be more handled with automation. There are two automation approaches: flexible robotic assembly and high speed automated assembly.


            12. Design printed circuit boards for assembly. With printed circuit boards (PCB’s), guidelines include: minimizing component variety, standardizing component packaging, using auto-insertable or placeable components, using a common component orientation and component placement to minimize soldering “shadows”, selecting component and trace width that is within the process capability, using appropriate pad and trace configuration and spacing to assure good solder joints and avoid bridging, using standard board and panel sizes, using tooling holes, establishing minimum borders, and avoiding or minimizing adjustments.



Credit:ivythesis.typepad.com


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