The Design of Basic Mechanical Systems - Essay Example

CONTRIBUTE TO THE DESIGN OF BASIC MECHANICAL SYSTEMS By The success of the manufacturing industry relies majorly on its quality and productivity. Productivity is measured by many factors, among the key factors is manufacturing efficiency used to perform the operation/activities. Productivity may be enhanced by minimizing the total machining time or carrying out multiple operations simultaneously. For mass production involving many tasks and huge quantities, it is extremely necessary to increase the rate of production. This cannot be accomplished by performing the production using general purpose machines. The most appropriate means of improving the productivity without compromising on quality is by the use of special purpose machines. Design, performance and utility of a single spindle drilling machine is evaluated and discussed in this report. 1. Summary. Drilling is among the fundamental machining procedures of making holes that is widely used in manufacturing industries such as automobile industry, semiconductors, aerospace industry, watch manufacturing industry and medical industries. Drilling machines are used for cutting circular holes, including dug in holes, in items using a rotating component known as a bit or drill. During the action of the rotating component of the drill, the item remains stationary. This report presents the procedure entailed in the design of a free standing single spindle drilling machine for a machine shop with spindle turning at 3000 rpm. The spindle shaft is driven by an electric motor through a suitable drive and the motor power is 1.5KW. 2. Introduction. Drilling is essential in many industries for assembly associated with mechanical fasteners. For instance, it is reported that approximately 55000 holes are drilled as an entire single unit fabrication of the Air bus A350 aircraft. Drilling of metals is gradually more required as artifacts become tinier and more vastly functional. The requirement of deeper and tinier holes needed in such industries necessitates that drilling process technologies achieve higher productivity and higher accuracy. Various conventional and non conventional fabrication processes that use drilling exist, but conventional drilling process are ideal for general applications due to their greater economical gains compared to other processes and their high productivity. Single spindle drilling machines are used in mechanical industry in order to maximize the productivity of machining systems when drilling holes in a work piece. The spindle is driven by a motor and fed in to the work piece. The feeding motions are attained either by lowering the drill heads or raising the work table. Drill jigs are used to guide the drills in the work piece during mass production work in order to achieve accurate results. In the present market, the customer requires products of right quantity, right quality, and right cost and at the right time. It is therefore necessary to enhance quality and productivity so as to meet these requirements of final product. A free standing single spindle drilling machine has many industrial application including paper, metal and wood drilling applications. To achieve a high drilling accuracy at the high speed of 3000 rpm at 1.5KW, many issues have to be addressed in the design. The base components must be precision engineered as this is among the primary fundamental foundations for maximum precision and the materials must be chosen from the best class available. The standing single spindle drilling machine designed in this report takes these factors into account. The machine will be attached to a brushless DC permanent magnet motor powered by a 1.5KW PWM drive. 3. List of components. i. Base plate: provides a mounting surface for locators and clamps and moves the spindle up and down. ii. Bolts and nuts: tightening joints. iii. Column and transversal section. iv. Belts protection screen. v. Work holding table. vi. Chuck: enables rotating. vii. Spindle. viii. Electric motor: source of power. ix. Belt drives. x. Pulleys: conveys power from the motor to the drilling machine . xi. Bearing. xii. Power on/off switch: controls the machine. xiii. Feed handle. xiv. Drilling head. 4. Assumptions. i. The machine can be used to drill a single hole at a time. A drill bit monitor is attached to the drilling machine. ii. The drill bit is monitored at all times during the drilling cycle. Immediately the drill bit monitor senses a wrecked drill the cycle is disrupted and the fracture is recorded. The drill bit is reinstated and the drilling cycle is restarted with operator intervention. iii. The size of machine is smaller making it very easy to transport. The general space needed to store the machine is small and its efficiency is high. iv. Large power and cost savings have been achieved and the machine can be operated simply. Operator Involvement The drilling machine operator may be a skilled or unskilled worker. The drilling machine is often operated by anyone in the shop and harm may transpire due to carelessness. Therefore the operator must ensure that the position of the stock is accurate, fit the drilling machine, control and monitor, and uphold housekeeping. Also, the operator must modify feeds and speeds when necessary. 5. Calculations. Designing of shaft: combined bending and torsion The shaft is subjected to a combination of twisting and bending stresses. The stresses considered in shaft design include: Max tensile stress = 60 N/mm2 Max bending stress = 70 N/mm2 Max shear stress = 40 N/mm2 N1D1= N2D2 N2= N1D1/D2 = 1440*40/80 Half the diameter of the driven pulley is selected to lower the rpm to half and raise the torque. = 3000 RPM Torque calculation Power of motor = ½ hp = 1.5KW P = 2 πN T / 60 = 2 *3.14 * 720 * T / 60 T = 373 *60 / 4521.6 = 4.94 N-M = 4940 Nmm Taking into account 25 % overload, Tmax = 6175 N-mm Maximum bending moment Mmax = force from belt tension x distance =1100 N –mm Equivalent Bending moment of shaft; Me = ½ *[M +(M2+T2)1/2] = 1174 N-mm Adding the bending failure of shaft, Me = 3.14 / 32 * D3 d = 12.25 ≈ 15 mm Design of pulley shaft T = twisting moment M = bending moment Max hp of motor transmitted by pulley = 0.5 HP N =460 rpm. (Experimental min rpm needed for drilling) Angle of deflection = 0.250 = 0.00436 rad. Spindle length = 15 cm. Modulus of rigidity; G = 0.84 x 106kg/cm2 T = torque transmitted by shaft T = P x 60/2π N = 597 N.m 6. Health and Safety. Potential Hazards: i. Poor operator judgment is among the common causes of accidents encountered when using drilling machines. In most cases, the operator may try to hold the stock with the hand in the process of drilling. The drill may hold and twist the stock from the operator when it enters the work, leading to an unrestrained rotational piece. Other hazards at the point of operation include hot chip generation and the mostly unguarded rotating drill. ii. The power transmission components are frequently exposed. iii. The operating controls are on-off push-switches that lack emergency stop devices. iv. The drilling machine is frequently filled with scraps and chips that may create a hazardous work area. v. The drilling machine is less dangerous compared to others due to its simple operation. However, the operator needs to be familiar with its operation. Possible Counter Measures: i. Enclosures and barricades may be set up around the drilling machine to separate the operator from the machine. ii. At the point of operation, guarding is a challenge due to the nature of the drilling process. As the drill progressively feeds into the work, it is often changed for the chips to escape and the stock is moved around to eliminate the option of using guards at the drill. Guards used may have to be removed as the drilling continues thus a hold-down fixture should be used instead of the hands. iii. Push button switches should be shrouded and an emergency switch set in place near the machine for disconnecting in case of emergencies. iv. Power transmission elements should be covered fully on such machines with adjustable belt drives. The enclosed area should have an interlocked access door to aid speed alterations. v. Operator training and proper housekeeping must be maintained at all times. (Adam & Humphreys 2008; Khurmi & Gupta 2008; Khurmi & Gupta 2008). 7. Reference List Adam, F., & Humphreys, P. (2008). Encyclopedia of decision making and decision support technologies. Hershey, PA, Information Science Reference. Khurmi, R. S., & Gupta, J. K. (2008). A textbook of machine design (S.I. units): [a textbook for the students of B.E. / B. Tech., U.P.S.C. (Engg. Services) ; Section B of A.M.I.E. (1)]. Ram Nagar, New Delhi, Eurasia Pub. House. Khurmi, R. S., & Gupta, J. K. (2008). Theory of machines: [a textbook for the students of B.E. / B. Tech., U.P.S.C. (Engg. Services) ; Section B of A.M.I.E. (I)]. Ram Nagar, New Delhi, Eurasia Pub. House. 8. Appendix (Attach drawings from other unit). 9. Appendix (Attach pages of catalogue and highlight the selected item). Read More