Various Aspects of the Machine - Term Paper Example

MACHINE TOOL CHARACTERISTISTICS AND OPERATION Abstract This paper looks at machine tools and characteristics. The degree freedom has been discussed for centre lathe, vertical mill and surface grinder and also how control is achieved in the three machine types. With regard to workholding the chuck features prominently for the lathe machining while for firing and milling machine the vice is the holding device used. Forming and generating operations have been identified as well as tools used being identified. The appropriate machine for use in production of plumb bob body and screw was identified as the lathe machine with the process of production being described as per the tasks involved. The operation plan for production has also been given. Introduction In this paper there is focus on various aspects of machine tools. A machine tool is used for shaping and machining objects mostly metallic, by grinding, cutting, boring shearing or any other forms of deformation. While working on a material it is important to restrain the piece from movement. In order for the workpiece to be restrain there is need to understand the six degree of freedom. There are various tools that are used on different machines and choosing the right tool and using it correctly is important. Task 1 a) With the aid of suitable images, identify and explain the axis conventions on the following machine tools: i) Centre Lathe From the figure it can be seen that the for the centre lathe we have a Z-axis that is horizontal. There is also the X-axis which is parallel to work holding surface. For the centre lathe there is no movement in the Y-axis. ii) Vertical Mill The Z-axis is the axis of rotation of the spindle. The Y-axis movement is effected from the table while the X –axis movement is effected by saddle and is horizontal and perpendicular to X-axis movement. The grinding machine has a column that is guided on a dovetail slide, and this is where the wheelhead is carried at the top end and it also contains the motor and belt drive to the wheel spindle. Both the column and wheelhead are raised and lowered through a screw through screw and nut from a handwheel on the front of the machine. iii) Surface Grinder For the surface grinder we have the Z-axis represent the up and down movement of the wheelhead that is effected through the column. The spindle is in horizontal direction and the and the grinding wheel is attached to it but it does it is not in line with the Z-axis . Just as in the case of the vertical mill the Y-axis movement is effected from the table while the X –axis movement is effected by saddle and is horizontal and perpendicular to X-axis movement. b) For each axis identified in the above task, provide a written explanationon how the drives are controlled, making reference to the use of manual and automated feed actions. The up and down in vertical movement in the vertical milling machine and in the grinding machine represent is the Z-axis movement and is effected through a hand wheel. In the case of the centre lathe we have the work piece being rotated with the speed of rotation being regulated through the gear levers. The power is provided by a motor through the gears. Also in the centre lathe we the Z-axis movement which is parallel to the axis of rotation of workpiece being affected through a hand wheel. The movement of the tool across the work piece is the X-axis movement that is also effected through a hand wheel. Task 2a The chucks and collets are two workholding devices that are common to lathe machine and are attached to the spindle. They locate and hold the workpiece as it rotates on the lathe. The chucks that are used commonly on lathe machines have either three or four jaws which clamp the workpiece when tightened. The chuck when mounted on the machine spindle will enable accommodation of different range of work pieces. The jaws of the chuck are supposed to be strong enough so that they are able to resist the rotational forces as well as the forces of deflection as the cutting tool gets in contact with workpiece. On the other fit into the spindle of a machine tool and are usually available in sets with each collet designed for holding a specific size. Use of collet makes it possible to automatically machine a series of parts from bar stock. Holding device for milling machine The vice can pass as the standard holding device for a milling machine tool and it is able to hold workpieces having simple dimensions. It has one jaw which is free to move while the other is fixed. It has a level that is used in turning of a screw enabling the tightening of the movable jaw to inch closer to fixed jaw. The standard workholding device for the mill is the vise, which can hold workpieces with simple dimensions. The vise has one fixed jaw and one moveable jaw. A lever is used to turn a screw that tightens the moveable jaw against the fixed jaw, as shown in Figure 2. b) By now you would have had some experience in setting up certain machine tools and performing the required manufacturing activity (whether it being at the college or in company). Identify one practical work piece that you have produced that has been processed by secondary machine tools (e.g. centre lathe, mill, etc) and report on the different work holding techniques that can be used. A both side threaded straight bolt has been produced in the machine shop. The iron bar rod is cut to appropriate size length power driven hack saw with the peach being held securely in place by vise. The cut to size piece is then transferred to a lathe machine where it is secured by a chunk to the spindle. A single point tool with rectangular shank is then clumped to a toolpost as can be seen in the below where we have a four-way turret-type tool post. The tool is set to centre height using packing strips and then adjusted to appropriate position. With everything in position the lathe machine is started to set the workpiece rotating and then the tool is moved as to make the desired cut on the workpiece. A number of feed motion is made along the workpiece up to a point when the workpiece has been reduced to desired diemeter. The workpiece is then removed so that the other side that initially was being held by the chunk is cut to desired diameter too. With the desires diameter achieved the workpiece is maintained in the chuck but now we have single tool appropriate for cutting the desired thread being clumped on the tool post. With appropriate movement of thread cutting tool we have threads of desired length cut before the workpiece is reversed to make another thread on the other side. Task 3 a) With respect to work holding techniques provide a written description that detail about the six degrees of freedom of a rigid body. Support your written detail with relevant images. A body in space will be free to move in any direction as can be seen from figure. The body will the freedom of moving along any of the two axes, translating to six degree of freedom. Suppose the body is a workpiece that need to be worked on, then it will be necessary to be restricted to a desired position by restraining its degree of movement. Figure is an illustration of principle of location where it can be observed that at the base of the first plane surface there exist three point of restraints for the component that is located along the Z-Z axis , X-X axis and Y-Y . In the second plane we have two point of restraint that serve to restrain the component along the Y-Y and Z-Z axis. In the third plane there is provision of one point of restraint for the component along X-X axis. Here we have all the six degree of freedom being fully taken care of through the incorporation of effective clamping. Task 4 a)assesses the suitability of the workshop’s machinery and select appropriate manufacturing equipment that can be used for producing the given articles and their specific feature (N.B: more than one machine may be needed for its production). For both the plumb bob body and plumb bob knut the appropriate tool is the lathe machine. Body The 20mm×82mm material fixed in the chuck with about 20mm protruding. A facing tool is clumped on the tool post. The toolpost set to appropriate centre height using packing strips and is expected to remain at this point for subsequent operations. The facing is effected by moving the tool along the face of the workpiece. After the facing the next process is drilling 6.8mm×19mm hole from the faced section. This is effected by attaching a drilling bit at the tailstock and the sliding it towards the rotating workpiece. The surface of the workpiece is to be turned at turn19.5mm×50mm. This means that the workpiece has to be readjusted with atleast 60mm length protruding. A turning tool is attached to the tool post with the previous centre height still in place. The turn is effected by moving the tool along the rotating workpiece up to a point when the required diameter is achieved. Knurling is achieved by attaching the knurling tool to the toolpost and positioning it at the right position on the workpiece. With the tool touching the workpiece with enough pressure the workpiece is put in motion at relatively lower speed and the tool is set to move along the workpiece up to the point when the length of knurling desired is achieved. Turning is done on the workpience for turn16mm×10mm by attaching and position of the cutting tool and then moving it along work piece. The piece near the drilled hole is chamfered by a champfering tool, to have Chamfer1mm×45. The piece is then removed from the chunk and turned 180 o. After turning the exposed side is faced to reduce the length to 80mm. After the turnaround, cutting tool is used to turn16 mm×30mm from the faced side. A Chamfer4mm×45 is then turned after which we have turning process used to taper40 b) Operational plan Safety measures need to be put into consideration when working on the lathe machine. Safety glasses are to be worn when using the lathe machine. The clothe worn are not supposed to be loose, as well as hanging hair and jewellery are to be avoided. It is important to familiarize yourself with the equipment and know exactly the processes that need to be undertaken. The chuck key is supposed to be removed after use and one is not to take their hand off the chuck key when it is in the chuck. It recommended turning the chuck so as to check for freedom of movement and clearance for tool rest. The shop supervisor needs to be consulted with regards to the correct speeds, long feeds and cross feed speeds. It is important to make sure the machine is set in the right speed before starting. If gears are to be changed once when working on a piece it is important to stop the machine first before effecting the changes. When cutting is taking place there will be ejection of long cut pieces. Grabbing or pulling these pieces is discouraged as they are likely to be sharp and hot. It is important to use cooling liquid when fast cutting speeds are involved as the liquid serve the purpose of cooling and lubrication. b) Details the operational plan for producing the articles to specification. Your plan must include health & safety awareness, the identification of machines tools and cutting tools to be used for manufacture, including any other equipment relevant to the manufacture of the products (e.g. measuring and inspection equipment, gauges, etc). Task 5 a) With respect to the engineering drawings (attached with this assessment), identify whether each feature is either a result of a generated or formed material removal process. Also, provide written describes how these cutting processes will be performed. In G2 we have generated material removal process. First figure shows the cutting tools which are used on a workpiece that is attached and rotated on a lathe machine. The tools are used in parallel turning where the workpiece diameter is reduced. The work is held and rotated by a chuck attached to a spindle. In order to make sure that the workpiece does not bend as a result of the bending moment introduced by the tool, the workpiece is held between centres. In the second figure we have cutting operation where the cutters are to be mounted on a horizontal mill. In the first case we have a slab mill as the cutting tool while the other is a side and face cutter. The two tools are held in the central position of the arbor by collets. The tool is rotated from the spindles and then the workpiece is fed to the cutting tools thus effecting the machining operation. The third figure we have tools mounted on a vertical mills. The first tool is a face mill while a slab mill that is vertically mounted. The workpiece is moved on a straight line so that a flat source is machined. In F1 figure (a) we have forming operation effected on a lathe machine by use of a radius forming tool and a chamfer tool. In these two cases it can be seen that there is a forming operation because radius contour on the workpiece dictated by the radius of the tool and also the angle of the chamfer matched the design angle of the chamfer tool, a clear indication of forming operation. In figure (b) we have operation effected on a milling machine. The tools are held at appropriate positions by a collar and keying. This is a gang milling operation where all the three cutters are in operation at the same time. The workpiece is moved perpendicular to the axis of rotation of the cutters and the end result is shaping of the workpiece that resembles shape of the cutters. In the last figure we have a counter sink bit being mounted on a vertical mill so as to have a countersunk whole in shape and size of the tool. b) Produce written descriptions on the following 2 processes demonstrated in the mechanical workshop: i) Broaching of a keyway for a given articles In this process the machine used is the press. The broach of the required size is selected for the process. Also a bush of appropriate size is also selected, this being one with diameter just slightly smaller than the bore radius of the gear in which a key way is to be broached. The bush and gear are assembled and position just below the press. The broach of appropriate size is then placed in position so that it can appropriately make the key through the gear. After applying the cutting oil in assembly the press is released to force the broach down the assembly with care being taken to make sure that the press force is applied purely down wards without any side forces being experienced. After the broach is made to pass through the gear , the gear is turned so that the side that was facing down now faces upward. The broach is held in position just above the press and the process is repeated again. The subsequent process involves putting shims with increasing width behind the broach so as to increase the depth of cut key in the gear. ii) Bending of a Keep plate for a toolmakers clamp (see workshop example) In this process there is also use of a press. The plate is place on a die with a desired shape. The press is then released so that it shapes the metals as desired. (i & ii) Discussion From the paper we first looked at the axis convention of the different machines. For the lathe machine we found that the Z-axis was horizontally placed and there is no Y-axis movement for this machine. For vertical mill we have seen that it has freedom of movement in the three axes with the Z-axis being vertically placed. In the paper we have also looked at holding of workpiece firmly. The chuck was seen to be an important holding device in lathe machine. The firmness of grip enabling resisting of any rotation forces as well resisting deflection of the chuck are some important aspect that have been linked to the chuck. Avoiding deflection of the workpiece was also addressed by ensuring the protrusion is not excessive. Deflection will depend on the dimension of the workpiece where for cylindrical pieces higher diameter can allow longer protrusion without deflection. The material characteristics also come into play. Highly rigid material can sustain longer protrusion without deflection. Depth of cut and speed of cut also can determine whether there is deflection and effectiveness of cut. We have also seen that for different machines we can have creation of features through generation or through forming. There can also be creation of features by a tool and workpiece movement combination that results to both forming and generation comes into play simultaneously. Conclusion In conclusion we have seen that when using machine tools can be used to successfully manufacture components by addressing various important aspects including holding the workpiece , choosing the right tool and a good operation plan. References Parker, Dana T.(2013). Building Victory: Aircraft Manufacturing in the Los Angeles Area in World War II, pp. 5, 7-8, Cypress, CA. ISBN 978-0-9897906-0-4. Thomson, Ross (2009), Structures of Change in the Mechanical Age: Technological Invention in the United States 1790-1865, Baltimore, MD: The Johns Hopkins University Press, ISBN 978-0-8018-9141-0 Zelinski, Peter (2013)."Hybrid machine combines milling and additive manufacturing", Modern Machine Shop Read More

With the tool touching the workpiece with enough pressure the workpiece is put in motion at relatively lower speed and the tool is set to move along the workpiece up to the point when the length of knurling desired is achieved. Turning is done on the workpience for turn16mm×10mm by attaching and position of the cutting tool and then moving it along work piece. The piece near the drilled hole is chamfered by a champfering tool, to have Chamfer1mm×45. The piece is then removed from the chunk and turned 180 o.

After turning the exposed side is faced to reduce the length to 80mm. After the turnaround, cutting tool is used to turn16 mm×30mm from the faced side. A Chamfer4mm×45 is then turned after which we have turning process used to taper40 b) Operational plan Safety measures need to be put into consideration when working on the lathe machine. Safety glasses are to be worn when using the lathe machine. The clothe worn are not supposed to be loose, as well as hanging hair and jewellery are to be avoided.

It is important to familiarize yourself with the equipment and know exactly the processes that need to be undertaken. The chuck key is supposed to be removed after use and one is not to take their hand off the chuck key when it is in the chuck. It recommended turning the chuck so as to check for freedom of movement and clearance for tool rest. The shop supervisor needs to be consulted with regards to the correct speeds, long feeds and cross feed speeds. It is important to make sure the machine is set in the right speed before starting.

If gears are to be changed once when working on a piece it is important to stop the machine first before effecting the changes. When cutting is taking place there will be ejection of long cut pieces. Grabbing or pulling these pieces is discouraged as they are likely to be sharp and hot. It is important to use cooling liquid when fast cutting speeds are involved as the liquid serve the purpose of cooling and lubrication. b) Details the operational plan for producing the articles to specification.

Your plan must include health & safety awareness, the identification of machines tools and cutting tools to be used for manufacture, including any other equipment relevant to the manufacture of the products (e.g. measuring and inspection equipment, gauges, etc). Task 5 a) With respect to the engineering drawings (attached with this assessment), identify whether each feature is either a result of a generated or formed material removal process. Also, provide written describes how these cutting processes will be performed.

In G2 we have generated material removal process. First figure shows the cutting tools which are used on a workpiece that is attached and rotated on a lathe machine. The tools are used in parallel turning where the workpiece diameter is reduced. The work is held and rotated by a chuck attached to a spindle. In order to make sure that the workpiece does not bend as a result of the bending moment introduced by the tool, the workpiece is held between centres. In the second figure we have cutting operation where the cutters are to be mounted on a horizontal mill.

In the first case we have a slab mill as the cutting tool while the other is a side and face cutter. The two tools are held in the central position of the arbor by collets. The tool is rotated from the spindles and then the workpiece is fed to the cutting tools thus effecting the machining operation. The third figure we have tools mounted on a vertical mills. The first tool is a face mill while a slab mill that is vertically mounted. The workpiece is moved on a straight line so that a flat source is machined.

In F1 figure (a) we have forming operation effected on a lathe machine by use of a radius forming tool and a chamfer tool. In these two cases it can be seen that there is a forming operation because radius contour on the workpiece dictated by the radius of the tool and also the angle of the chamfer matched the design angle of the chamfer tool, a clear indication of forming operation.

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