Application of Machine Tools - Report Example

Application of Machine Tools Introduction Machine Tool Application involves the process of cutting away/ eroding a metal casting or block with the intension of creating a section, with the aid of sharp-edged tools. This process usually takes into considerations a wide range of skills as it requires the use of different types of tools and specialized machines, i.e. electric discharging machines, shearing machines, and drilling machines, for metal cutting purposes. However, machine tools are faced with a number of challenges that make them dangerous and, hence, necessitating the need to address safety and efficiency in machine operations. Some of the challenges include faster acceleration/ deceleration rates; high speed and position accuracy; complex input/output interfaces; large speed ranges, high speed operations; low maintenance, durability; constant high torque productions; and continuous operations (Weck 1980). Axis conventions of the centre lathe and milling machine Generating shapes using tool movements, forming shapes using tool shapes and a combination of the two procedures (generation and formation of shapes) are basic ways of turning on the centre lathe. Looking at each case, below are observed: Shape generation outcome is determined by the movement of the tool and never by the shape of the tool. Forming: in the production of a shape through forming, shapes of tools used determine the resulting shape of the tool. Forming and generation: such a combination can be used in shape production in a single operation. This technique helps in avoiding alterations and making unique shapes very easy. In CNC machines, the Cartesian coordinate system for programming coordinates is also used. The axes, however, have variations as illustrated below: i. The convention that the axis aligned with the spindle are to be designed “Z” are followed by the turning centers. ii. Axis at the right angle to the spindle has the designation “X”. iii. Taking note of each axis’ direction, positive X points towards the back of the machine while positive Z points to the right of the spindle; this is because the typical CNC turning center is usually constructed with the tool mounted to the opposite of the operator. Drives associated with the center lathe and vertical milling machine Centre lathe is a tool ground to a point for accuracy in positioning any work piece on an axis. It is primarily meant to ensure production of concentric work by allowing the work piece to be transferred between machines. A lathe center is used in supporting longer work pieces where cutting forces may have the deflection effects on the work, excessively reducing the finishing and accuracy required of the work piece. Lathe center is further classified into dead center, soft center, revolving center, pipe center, cup center, drive center, and spring center; all with different functionalities in the machine operations. A milling machine is devised to remove metal through the use of a revolving cutting tool called a milling-cutter. It can be used to slot, bore, divide circular milling, and drill. The horizontal and vertical classifications are just to indicate the axis of the milling machine spindle. Below is a picture of a vertical milling machine. In situations of comparing the two (center lathe and vertical milling machine), it is true that in programming lathe machine CNC controls are by far less standardized as compared to that of milling. Therefore, the lack of standardization influences the magnitude of time that a programmer has to take learning the specific codes for each machine tool (International library of technology 1914). Restraining six degrees of freedom of a rigid using a machine vice and a 4-jack lathe chuck The degree of freedom of a system is the number of independent variables that are required to completely identify the configuration of the mechanical system. It can also be defined as the number of independent inputs needed to drive all the rigid objects within the mechanical systems. Restrain are mechanisms that are applied as safeguard measures for both full and part revolution mechanical power press. The twelve degrees of freedom (as show by the arrows of clockwise and anti-clockwise directions) all relate to a common and central axis of the work piece, as noticed of the six degrees of freedom and six radial degrees of freedom. Straight-line movements in all the six directions along these three principal axes X, Y and Z are allowed by the axial degrees of freedom (Ni, Huang & Wu 1992). i. A machine vice This is a device used to hold a work piece during the operation of a milling machine or a drill press machines. A machine vice is capable of being adjustable in different ways, by allowing any work piece to be manipulated into any position or angle as may be required. It is majorly important when certain angle is to be repeated on several pieces. This machine’s precision movement allows for the creation of pin-point operations through manipulation of the vice’s controls. For the milling operations, it is used to move the work piece into the cutting tool and complete the machining operations as the cutting tool remains stationary (Fan, Chen, & Huang 1998). ii. A four jaw lathe chuck A 4-jaw lathe chucks have the advantages of high precision in centering work. It can handle square or rectangular bars perfectly as compared to 3-jaw. This four jaw lathe chuck can also turn work off-centre, with its relatively more grips on the round stocks. Despite all these, it has a limitation of lack of self-centering conveniences as that of the 3-jaw chuck. Methods for securely locating cutting tools in a center lathe and vertical milling machine For the purposes of enhanced performance, work holders have to be accurately and consistently positioned. Any work piece relative to the cutting tool should be properly referenced (work piece positions relative to the work holders) and the whole process is repeated. There exist three forms of location, i.e. concentric, plane and radial. The characteristics of each are that plane locators locate a work piece from whatever surface; concentric locators majorly locate a work piece from central axis; and radial locators do restrict movements of any work piece around a concentric locator. In addition, it is important to note that locating can be done from both external and internal surfaces. i. A centre lathe In ordinary straight turning, the cutting tool moves along a parallel line to the axis of the work for a finishing of equal diameter dimensions on a piece of work. However, a piece of work is tapered if its diameter dimension changes uniformly from one point to the next. Most lathes have two tools feed mechanisms which cause cutting tool to move when engaged. These are: A larger screw: this causes the lathe cutter to advance in greater lengths (quickly), and is mostly used to cut screws at feed rates ranging from 0.05” to 0.5” per revolution. A smaller screw: it moves the cutter to shorter lengths (slowly). It is largely applicable when performing rough cuts or finishing operations, of 0.001” to 0.010” feeds per revolution. ii. A vertical milling machine The process of milling on a vertical mill is in most instances accomplished by end mills. Cutters used by this machine are designed to cut with both ends. Through raising and lowering the entire milling head with the “Z” axis feed screw, the drilling process is successfully accomplished. Center drills are used prior to drilling to set the required degree of accuracy. Boring, a method of making accurate holes through rotating a tool with a single cutting edge (boring head), is meant to open up drilled holes to the desired dimensions/ diameter. Cutting actions of milling cutters vary depending on the direction of feed. In one direction, the tool tends to climb onto the work while in the other cases the tool will tend to move away from the cut. References Fan, K.C., Chen, M.J., & Huang, W.M. (1998). A six-degree-of-freedom measurement system for the motion accuracy of linear stages. Int J Mach Tools Manufacture, 38: 155–64. International library of technology. (1914). Drilling; Lathe work; Boring-mill work; Working chilled iron; Bench, vise, and floor work; Erecting, 138, International Textbook, p. 21. Ni, J., Huang, P.S., & Wu, S.M. (1992). A multi-degree-of-freedom measuring system for CMM geometric errors. J Engng Ind, Trans ASME, 114: 362–9 Weck, M.M. (1980). Geometric and kinematic errors. Technology of Machine Tools, 5: 9–12. Read More