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عدد المساهمات : 18928 التقييم : 35294 تاريخ التسجيل : 01/07/2009 الدولة : مصر العمل : مدير منتدى هندسة الإنتاج والتصميم الميكانيكى
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أخوانى فى الله أحضرت لكم أسئلة محلولة فى مادة التشغيل Production B (Machining) Dr. Mh-El 3asy
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Ch 1 Q1: What are the reasons for using the machining process? - Casting improves severe problems from the point of view of material properties and accuracy, whereas forming becomes impractical when the job is either very large; which requires very large forming force and consequently very large machines; or the material is not suitable for the forming operation. A part from these, the geometric complexity of the final job may be such that these methods are of no use. Q2: What is the meaning of machining? - The method used is such that the desired shape, size, and finish are obtained through the removal of excess material from the original work piece of a suitable size and shape in the form of small chips. Q3: Define the cutting tool? - The body which removes the excess material through a direct mechanical contact. Q4: Define the machine tool? - The machine which provides the necessary relative motions between the work piece and the tool. Q5: Define the cutting (or primary) motion? - The relative motion between the tool and the work piece responsible for the cutting actionProduction B (Machining) 2 Q6: Define the feed (secondary) motion? - The responsible for gradually feeding the uncut portion. Q7: What is the turning? - This is a very basic operation and produced a cylindrical surface. The machine tool used for this type of an operation is known as a lathe. The figure 1 shows: FIGURE 1: TURNING OPERATION Q8: What is shipping? - The cutting tool is given a reciprocating motion, and after every cutting stroke, the work is fed. The figure 2 shows: FIGURE 2: SHAPING OPERATION FIGURE 2Production B (Machining) 3 Q9: What is planning? - For a long job, it becomes inconvenient to provide long cutting strokes with the mechanism used in a shaping machine. In such a case, the work is provided with the cutting motion, whereas the feed is given to the tool; this is known as planning .The basic geometry of the machining operation is the same as that of shaping. Q10: What is milling? - The tool, normally known as a milling cutter, possesses a number of cutting edges. It is provided with a rotary motion and the work piece is gradually fed. Small chips are removed by each cutting edge during revolution, and finally a flat surface is produces. The figure 3 shows: FIGURE 3 SCHEME OF MILLING OPERATIONProduction B (Machining) 4 Q11: What is grinding? - In grinding, the cutting tools are the sharp edges of the abrasive grains of the grinding wheel .The figure 4 shows: Figure 4 scheme of grinding operationProduction B (Machining) 5 Q12: What is drilling? - This is used for making a hole in a solid body. The cutting motion is provided to the cutting edged (lips) by rotating the drill, and the feeding is done by giving a rectilinear motion to the drill in the axial direction the final surface obtained is an internal cylindrical surface. The figure 5 shows: Figure 5 DRILLING OPERATION Q13: Draw a sketch showing the cutting tools angels and state the functions of each angle? - Figure 6 shows the basic mechanic operation and important parameters which can be summarized as follows:Production B (Machining) 6 1-the thickness of uncut layer (t1) 2- The thickness of chips produced (t2) 3-the inclination of the chip-tool interface with respect to the cutting velocity i.e., the rake angle (a) 4-the relative velocity of the work piece and tool (v) **To make the cutting possible by reducing the friction between the machined surface and the flank surface of the tool, a clearance angle ( ): is also provided. **Tool angle: is angle between rake surface and flank surface. FIGURE 6 IMPORTANT PARAMETERS IN MACHINING OPERATION Q14: Define the orthogonal cutting? The relevant velocity of the work and the tool is perpendicular to the cutting edge. Figure 7 FIGURE 7 ORTHOGONALProduction B (Machining) 7 Q15: Define the oblique cutting? The relative velocity of the work piece and the tool in not perpendicular to the cutting edge as shown in figure 8 FIGURE 8 OBLIQUE Q16: Explain with the aid of neat sketch the mechanism of chip formation? - The uncut layer deforms into a chip after it goes through a sever plastic deformation in the primary shear zone as shown in figure 9 just after its formation, the chip flows over the rake surface of the tool andProduction B (Machining) 8 the newly-formed chip surface results in some sticking .thus, the chip material at this surface undergoes a further plastic deformation since, despite the sticking, it flows. This zone is referred to as the secondary shear zone. FIGURE 9 SHEAR ZONES Q17: Explain with the aid of neat sketch formation of built –up edge (BUE)? - *continuous chips with BUE: 1- Strong adhesion between the chips and tool face. 2- Low rake angle.Production B (Machining) 9 3- Large uncut thickness. 4- The cutting fluid is not efficient. Figure 10 shows: FIGURE 10 BUILT UP EDGE FORMATIONProduction B (Machining) 10 Q18: What are the conditions for the various types of chips? -1-discontinuous chips: (a) Brittle work piece material (b) Low cutting speed (c) Small rake angle (d) Large uncut thickness 2- Continues chips: (a) Ductile work piece material (b) High cutting speed (c) Large rake angel (d) Small uncut thickness (e) Using suitable cutting fluid 3- Continuous chips with BUE: (a) Strong adhesion between the chips and tool face (b) Low rake angle (c) Large uncut thickness (d) The cutting fluid is not efficientProduction B (Machining) 11 FIGURE 11 FORMATIONS OF DISCONTINUOUS CHIPS Q19: What are the disadvantages of BUE formation? 1-Changes the geometry of cutting 2-Produced bad surface finish 3-Decreaser tool life (crater wear as explained later) 4-Leads of the distraction of the hard cutting tool Q20: Explain the single point tool geometry? -*Single point tools have shanks of rectangular cross-section which is the part from which the tool is clamped as shown in FIGURE 12,the cutting edges are formed on *the front end (called the point ) of the tool . There are *three main surfaces (unusually planes) in the tool head *They are *the face (the area adjacent to the Machined surface) and *end flank (the area adjacent to the machining surface).Production B (Machining) 12 *The cutting edges are classified as the side- and end-cutting edges. The side-cutting edge is formed by the intersection of the face and side flank. The chips are removed by this cutting edge. The end-cutting edge is formed by the intersection of the face and end flank. The nose of a single-point tool is the conjunction of the side-and end-cutting edges. FIGURE12 ELEMENTS OF A SINGLE POINT TOOLProduction B (Machining) 13 Q20: How to measure the tool life? - Tool time is the time elapsed between two successive grinding of the cutting tool. The tool life may be measured in the following ways: 1- Actual cutting time to failure 2- Volume of metal removed to failure 3- Number of components to failure 4- Cutting speed for a given time to failure. Q21: list the factors affecting the tool life? 1- Material of the tool. 2- Material of the work piece. 3- The tool geometry.Production B (Machining) 14 4- The cooling facilities. 5- The cutting conditions. Q22: What is the failure of cutting modes? - 1- plastic deformation of tool due to high temperature and large stress. Figure 13 a 2- Mechanical breakage of the tool due to high force and insufficient strength and toughness of the tool material. Figure 13 b 3- Blunting of the cutting edge of the tool through a process of gradual wear .figure 13c FIGURE 13 Q23: How to prevent plastic deformation and the mechanical failure? - By 1- a proper selection of the cutting tool material. 2- Tool geometry.Production B (Machining) 15 3- Cutting conditions. 4- The cooling facilities. Q24: What are the two types of tool wear? - The crater wear: which takes place on the rake surface where the chip flows over the tool. The flank wear: which takes place on the flank surface where the rubbing between the work piece and the tool occurs. FIGURE 14: CRATER AND FLANK WEARProduction B (Machining) 16 Q25What are the reasons for the tool removal? - 1 - Fracture or shipping of the cutting edge. 2-finish of the work piece is too rough. 3- Tolerances in dimensions are exceeded. 4- Cutting forces are excessive. 5- The tool has reached a practical limit of wear. Q26: What are the properties of an ideal tool material? -1-Hot hardness: the cutting tool should maintain its hardness at elevated temperature. 2-Hardness and toughness: the tool must be harder than the work piece material. It should be tough enough to withstand shocks. 3- Wear resistance: the tool should provide a large resistance to the wearing action so that excessive wear does not occur. 4- Thermal resistance: the thermal conductivity and specific heat of the cutting tool should be high.Production B (Machining) 17 Q27: List the materials commonly used for making the cutting tool? - 1- high carbon steel. 2- Medium alloy steel. 3- High speed steel (HSS). 4-cast alloys. 5-Cemented carbides. 6- Ceramics. 7- Diamonds. Q28: What is High Carbon Steels? - contain from 0.7 to 1.4 carbons. A disadvantage of carbon steel tool is their comparatively low heat- and wear-resistance. Therefore they may only used in the manufacture of tools operating at low cutting speeds. Q29: What is High Speed Steels (HSS)? - (HSS) are widely used in metal cutting. They have a relatively high percent of alloying elements which provide for the high heat- and wearresistance of these steels. Therefore, tools made of HSS can be operating at cutting speeds 5 or 6 times higher than for carbon steelProduction B (Machining) 18 tools. HSS is used for manufacturing ordinary and tools, milling cutters, etc. Q30: What is the cutting fluids purpose? -1- To remove heat generated during cutting. 2-To lubricate and reduce friction. 3-To wash away the chips and cleaning the machining zone. Q31: What is the direct effect of using an efficient cutting fluid? -1- Reducing the energy consumption. 2- Increase the tool life. The cutting fluid is preventing the formation of BUE, so that crater wear disappears. Decreasing the flank wear. 3- Improve the surface finish.
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عدد المساهمات : 394 التقييم : 588 تاريخ التسجيل : 07/10/2012 العمر : 31 الدولة : مصر العمل : طالب بكلية الهندسة الجامعة : المنوفية
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عدد المساهمات : 18928 التقييم : 35294 تاريخ التسجيل : 01/07/2009 الدولة : مصر العمل : مدير منتدى هندسة الإنتاج والتصميم الميكانيكى
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عدد المساهمات : 394 التقييم : 588 تاريخ التسجيل : 07/10/2012 العمر : 31 الدولة : مصر العمل : طالب بكلية الهندسة الجامعة : المنوفية
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عدد المساهمات : 18928 التقييم : 35294 تاريخ التسجيل : 01/07/2009 الدولة : مصر العمل : مدير منتدى هندسة الإنتاج والتصميم الميكانيكى
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