Designing an Efficient and Functioning Hand Drill - Essay Example

?Design College Introduction A power hand drill is an electric device, which uses drill bits to enlarge existing holes in a material or create holes in them. These materials rang from wood, plastic to even metal. The hand drill can also grind, buff, and brush wires when with other accessories. Hand drills are available in many types, shapes, and sizes that can accommodate accessories with shaft diameters of different lengths and drills bits of different sizes. Hand drills have a number of uses from the house, shop, and workshop and even at factories depending on their sizes. The grouping or classification of hand drills depends mainly by the maximum size of drill bit shaft that the drill chuck can hold. A power drill comprises mainly of two sub-systems, which are mechanical and electrical. The two sub-systems play specific, different, and important roles in the working of the electrical hand drill. The first subsystem, which is the mechanical, has components, which transfer, translate, and apply forces in the hand drill. The electrical subsystem mainly deals with power. It has components that supply and control power flow in the hand drill. In this paper, we look on how to design an efficient and functioning hand drill. We will have a list of each mechanical component, the materials of the parts and the mechanical properties of this material. After designing the hand drill, we try to look on how to improve it to work more efficiently. Specifications of the hand drill 1. The input power is 800w 2. Its speed is 0-800rpm 3. Has a chuck capacity of 10mm 4. Drill capacity (a) Steel: 13mm (b) Wood: 25mm Mechanical components of the hand drill. Frame Shigley, (2008 Pg. 23) This is the outer part of the hand drill and it covers the inner mechanical and electrical components. One can also refer it to the housing. This component comprises of hard plastic. The mechanical property behind the idea of using the plastic is that it is a poor conductor of heat and electricity. Since the hand drill produces heat as it is in use, the frame does not get to harm or burn the user since its conductivity to heat is very low. Plastic also makes it safe for the user to use, as the risk of electric shock is minimal. This part is to be high smooth hence polishing is very important as it should be comfortable for the user to hand while using it. Plastic also makes the machine to be less heavy and the user can comfortably carry it without straining and in case of any accidents, the user is less likely to be less hurt by the frame as it is of plastic in nature. Two gears assembly Shigley, (2008 Pg. 23) There is transmission between the chuck and the motor. This transmission consists of pears of gears. We use gears from alloy steel elements for example stainless steel. Gears require materials of have a high resistance to corrosion. Steel gears offer high strength and has a wide range of heat treatment properties. Steel gears are also very durable and they provide the highest strength. Austenitic stainless steel is non-magnetic and has good corrosion resistance. These are the mechanical properties of this material. They can also be martensitic stainless steel that is easy to harden with heat, has magnetic properties, and have reasonable resistance to corrosion. This stainless steel (martensitic) is more appropriate to use as there is a high power ratings and it will therefore make the machine more effective Chuck Shigley, (2008 Pg. 23) It comprises the outer and front section of the hand drill. It has jaws, which holds the drill bits in position. We use a chuck that has three-jaw attachment that applies radial gripping to certain number of drill bits and accessory shafts. Chucks from stainless steel are the most appropriate. They provide high resistance to corrosion, as they are mainly hard. This mechanical property makes it more suitable as it is always in contact with the drill bits, which are always in constant motion and act on materials of different hardness. Stainless steel also lasts longer and it is therefore durable, it does, wear, and tears within a short period. Stainless steel is also more efficient during transmission due to its mechanical properties and this contributes greatly on this design, as the design is to be an efficient and durable devise after its manufacture. Front-end bearing Shigley, (2008 Pg. 23) These are bearings inside the hand drill and are just behind the chuck. When the hand drill is working, they are always revolving. They therefore encounter a lot of friction as they come in physical contact with each other or with the peripheral parts of the hand drill. The resistance that this bearings encounter as they revolve known as friction. These friction leads to wear and tear of these bearings. In this design, the material to use in making the bearing is hard chromium steel. This material is very resistant to corrosion and can withstand friction. This mechanical property will enable the bearings to last for a long period and work more efficiently. Intermediate bearings Shigley, (2008 Pg. 23) These bearings are between the speed cam and the two-gear assembly. . When the hand drill is working, they are always revolving. They therefore encounter a lot of friction as they come in physical contact with each other or with the peripheral parts of the hand drill. The resistance that this bearings encounter as they revolve known as friction. These friction leads to wear and tear of these bearings. In this design, the material to use in making the bearing is hard chromium steel. This material is very resistant to corrosion and can withstand friction. This mechanical property will enable the bearings to last for a long period and work more efficiently. Rear end bearings Shigley, (2008 Pg. 23) They are inside the hand drill between thrust bearing and the motor shaft. . When the hand drill is working, they are always revolving. They therefore encounter a lot of friction as they come in physical contact with each other or with the peripheral parts of the hand drill. The resistance that this bearings encounter as they revolve known as friction. These friction leads to wear and tear of these bearings. In this design, the material to use in making the bearing is hard chromium steel. This material is very resistant to corrosion and can withstand friction. This mechanical property will enable the bearings to last for a long period and work more efficiently. Thrust bearing Shigley, (2008 Pg. 23) These bearings are also inside the hand drill just after the rear end bearings. . When the hand drill is working, they are always revolving. They therefore encounter a lot of friction as they come in physical contact with each other or with the peripheral parts of the hand drill. The resistance that this bearings encounter as they revolve known as friction. These friction leads to wear and tear of these bearings. In this design, the material to use in making the bearing is hard chromium steel. This material is very resistant to corrosion and can withstand friction. This mechanical property will enable the bearings to last for a long period and work more efficiently. Motor shaft It is metallic in nature and mainly of stainless still. It has a cylindrical shape and makes part of the motor rotor. The mechanical property of component is that it is magnetic and the motor rotor generates magnetic currents within the hand drill. Main shaft Shigley, (2008 Pg. 23) The main shaft runs from the outer to the inner part of the hand drill. It connects the chuck to the inner component such as; intermediate bearings, front-end bearings and the two speed gear assembly. Power transmission mechanism of the hand drill After switching on the hand drill, which is already in connection to a power supply, there is transmission between the chuck and the motor. The electrical system consists of the motor, a switch, a cord, and the internal wiring. The motor converts electrical current into rotary motion. The basis of the motor is that opposite magnetic poles attract each other. The motor sets a stationery magnetic field and another magnetic field can rotate with it simultaneously. Due to high torque ratings, there is use of a series wound universal motors. These motors provide the required starting torque. This torque finally leads to the rotating of the drill. The load determines the rotational speed for the motor. In other words, the greater the torque required then the slower the rotational speed of the drill. The motor speed varies with the voltage. Applicability of codes and standards for the mechanical components Several codes and standards apply to the mechanical components of this device. The motors shall comply with ASHRAE/IES 90.1, NEMA MG-1, and IEEE 112 for their application, characteristics, and testing . Motors less than 250 watts are in use. Motor selection shall incorporate a minimum 10%safety factor between nominal motor horsepower. The design for temperature rise or fall is in accordance with NEMA limits for insulation class, motor enclosure type and service factor. There energy efficiency is in accordance to NEMA requirements. Influence of torsion and bending to the design Torsion is twisting of an object due to application of torque and is therefore in the expression Newton Metre (Nm). When the hand drill is at work, there is vibration and therefore there are tensional vibration effects. During grinding, torsion properties of both the work piece and the wheel system affect the chatter. The grinding force varies with the oscillation of the work piece speed and the diameter of the drill bit. Torsional vibration also affect power transmission system using rotating shafts or couplings and it can lead to failure of the hand drill if it is not controlled. Torsional vibration is also a concern in the shafts of the hand drill. If torsion is in regulation in the shafts it can cause failure in the shafts are other accessories that are running in the hand drill. This high damaging vibration is often under control by locating torsional dampers. These mechanical properties therefore makes the design of the hand drill to be in such a way that the will be minimum torsion as much as possible. Bending also influence the design of the hand drill, bending refers to the change of shape of parts of the hand drill. Bending is mainly due to change in temperature or application of a force to the material such that the material cannot resist or overcome the applied force. Bending affects the design in such a way that the materials to use in making the mechanical components to be of high resistance for example stainless steel. The engineering principles to support these are the principle of force and the principle of stress, which explain on idea behind torsion, bending, and how they come about. Load diagram of the hand drill. The load diagram of the hand drill is very important when arranging the mechanical and electrical component of the hand drill. By using the load diagram in putting the components to their correct places accurately, the final output will be an efficient device. Working of gear assembly in power hand drill Gears of the power hand drill are in connection to one another and they work simultaneously in a systematic manner. They connection is in a series if teeth that interlock them and keep them in contact as they rotate. The gears rotate in either clockwise or anticlockwise direction. Gears are mounting on shafts and they are in a group depending on the tooth form, arrangement of the shaft, quality, and pitch. Shaft arrangement determines the relative directions of output and input motion. Considering the rotation between two pairs of gears, the smaller gear is the driving gear or the input gear. The next gear is the output gear and its movement is dependent on the input gear. Since the system of gears is in static equilibrium, the larger gear pushes back on the input gear with force to that of the input gear to the output gear. The output gear rotates at a slower rate the input gear, the torque applied about the output shaft is greater than the torque applied about the input shaft. This series of rotations between the gears finally enable the drill bits to rotate when it is grinding’’’’ Load effects in the main shaft and motor shaft The load is the work piece that the hand drill is working on. The load can be of different shapes, size, and even hardness. The hardness of the load will depend on the material of the load. This hardness is the one, which mainly affects the shafts. Different types of loads have different effects on the main shaft and the motor shaft. The effect of wood on the main shaft and the motor shaft is not as high as that of steel. This is mainly because steel is harder compared to wood hence it causes much heating effect inside the hand drill and therefore the main shaft and the motor shaft are more damaged. To reduce damaging of these shafts then very hard loads should be avoided and encourage drilling of softer loads such as wood and concrete. Design factors when selecting bearings The design factors we use in the selection of bearings are their size and the material in use. Their sizes should be the same so that they can work properly as they rotate. If they are of different sizes then they will not be more efficient. The other factor is the material used in making them. They should be hard and have a smooth surface to resist corrosion. When the hand drill is working, they are always revolving. They therefore encounter a lot of friction as they come in physical contact with each other or with the peripheral parts of the hand drill. Bearing selection also requires considering their strength. They should have high fatigue strength, this means that they will be durable and there last much longer. Bearings should also have low friction to reduce wear and tear. Thermal conductivity is also an important factor to note. Bearings of high thermal conductivity are better since they will help to remove heat from thy surface. They generated heat is easily and quickly lost. Bearings with the ability to absorb and discard small particles of wood, plastic and metal to keep them from damaging the shaft are better. The resistance these bearings encounter as they revolve known as friction. These friction leads to wear and tear of these bearings. In this design, the material to use in making the bearing is hard chromium steel. This material is very resistant to corrosion and can withstand friction. The shape of this bearing should also in consideration when selecting them. Rounded bearings are more appropriate as the will rotate more easily and reduce friction as they into contact with each other and with other parts of the hand drill. Changing in design parameter affects the whole design process. Design parameters are the specifications, which we will be using as we are designing the power hand drill. These parameters are the ones, which guide us on the sizes and specifications of mechanical sub-system parts and electrical sub-system. It is not a waste of time to have these parameters because they actually help in the designing and when beginning to work on the project. A change in these parameters will affect the design of the hand drill. This means that the hand drill has to be in a design to fit or match the actual specifications given. If we change the shaft, we have to consider the fact that the diameter of the shaft is based on the power it transmits, speed and loading regime. The parameters to change include the transmitted power, shaft speed, torsion moment, and the preliminary minimum diameter of the shaft. The calculations below shows how the changes the efficiency and the rate of metal removal and power calculation. CALCULATING POWER DEMAND Pc=(Q/39600.n0*Kc Effective rake angle value can be Add the value of the actual cutter. Pc = Power HP Q = Metal removal rate in3/min _ = Efficiency Kc = Cutting force per inch2 (Lbf/inch2) Calculate metal removal rate, Q Calculate power demand for a drill mill used In a drilling operation: 216.19, O 1.57 inch. Material group = 3 Feed per tooth fz = .0055 inch/tooth Cutting speed VC = 509 ft/min Calculate RPM and feed speed K-value for drilling = 1 VF = 1 · .0055 · 1233 = 6.8 inch/min Calculating Metal Removal Rate, Q Multiply the feed speed VF with the cross-section area of the cut AT in the feed direction. Example: For a drill Calculate Power, Pc Efficiency _ = 80% Power Pc = Calculate cutting force per inch2 kc See page 297 material group 3 Kc1.1-value = 218,000 Lbf/inch2 Rake angle for cutter = –5° page 228 Mc-exponent = 0.25 Rake angle for insert = 0° page 259 Cutting edge angle _ ? 90° Effective rake angle _o = –5° Average chip thickness HD = .0055 · sin 90° = .0055 inch Cutting force per inch2 kc = Pc = · kc Q 396,000 · _ Q = = 13.16 in3/min 6.8 · _ · (1.57)2 4 AT = _ · D2 4 · 218,000 = 375,898 Lbs/inch2 1–0.01 · (–5) (.0055) .25 · 375,898 = 15.61 H D Kc = Cutting force/inch2 N/mm2 HD = Nominal chip thickness inch Mc = Exponent kc1.1 = Cutting force for .040 inch chip thickness Power Calculation – Drilling/Plunging Calculating the Power Demand HD = Nominal chip thickness inch Fz = Feed per tooth inch/tooth _ = Cutting edge angle for drilling/plunging n = = 1233 RPM 509 · 12 _ · 1.57 Q = if · AT Calculating Cutting Force kc = · kc1.1 1–.01 · _o Bibliography SHIGLEY, J. E., & MISCHKE, C. R. (1989). Mechanical engineering design. New York, McGraw-Hill. SHIGLEY, J. E. (1977). Mechanical engineering design. New York, McGraw-Hill. BUDYNAS, R. G., NISBETT, J. K., & SHIGLEY, J. E. (2008). Shigley's mechanical engineering design. Boston, McGraw-Hill. DENNIS, L. J., & PARKER, M. A. (1990). Mechanical engineering design. Thomas. SHIGLEY, J. E., & MISCHKE, C. R. (1989). Mechanical engineering design. New York [etc.], McGraw-Hill. REDFORD, G. D. (1973). Mechanical engineering design. [London], Macmillan Read More