Milling Methods PDF

turning tool. 1.2. MILLING METHODS cutting with a multi-teeth rotating tool called cutter. During Milling is aprocess of metal operation again after some interval of cut, comes...

turning tool. 1.2. MILLING METHODS cutting with a multi-teeth rotating tool called cutter. During Milling is aprocess of metal operation again after some interval of cut, comes in cutting rotation each tooth after taking a cool down before the next cutting is done allows the tooth to time. Therefore, this interval edge of the cutter is minimised. The in cutting on the cutting and thus, the heat generated perform these operations. following two methods are commonly used to () Up milling or Conventional milling. (ii) Down milling or Climb milling. 1.2.1. Up milling cutter rotates in a direction opposite In this method of milling as shown in Fig. 1.2, the forgings because method is commonly used for machining castings and to the work is fed. This method enables the cutter to dig in and start the cut below the hard upper surface. Further this increases gradually from A to B as shown in up milling, as the cut proceeds, the chip thickness and maximum at the end of the cut. in figure. It is minimum i.e. zero at the start of the cut -Cutter B A Work Table Fig. 1.2. Up or Conventional milling.  Milling | 33 1.2.2. Down milling In this method of milling as shown in Fig. 1.3, the cutter rotates in the same direction to the work is fed. This method is specially useful for finishing operations_like slot cutting and milling grooves etc. Further in up milling, as the cut proceeds, the chip thickness decreases gradually from B to A as shown in figure. It is maximum in the beginning and minimum i.e. zero at the end. Cutter A Work Table Fig. 1.3. Down or Climb milling. The length of the chip in down milling is less than in up milling. Which means that the cutter is engaged for less time per volume of material cut-out and this tends to increase tool life. in down milling than in up milling. In up milling, there is a tendency of the workpiece to lift off when cutter exits the material, whereas in down milling, cutter force tends to hold the workpiece in position. This is because the direction of the cutting force is tangential to the periphery of the cutter teeth engaged in action. N.B. : Though down milling gives a better finish yet ensure before employing that there is no backlash in the feeding mechanism of the table and the work is held rigidly.  10 Eagle's Workshop 1.5. MILLING OPERATIONS Technology - Different components are machined on a milling machine by performing different operations. Some of the operations are explained below. types of 1.5.1. Face milling The face milling operation is shown in Fig. 1.18. This milling cutter rotated about an axis perpendicular to the work_operation performed by a face is in a plain milling machine, where the cutter is surface. The operation is carried mounted on a surface. The depth of cut is adjusted by rotating the cross feed stub arbor to produce a flat screw of the table. Cutter Work Fig. 1.18. Face milling. 1.52. Angular milling The angular milling other than at right anglesoperation is the operation to to the axis of the millingproduce angular surface on a workpiece an The cutter used is either single or machine spindle or the revolving cuter. or two mutually inclined double angle cutter, depending upon whether a single surface in two different ways. surfaces are machined simultaneously. The angular milling can be done () Using angular milling cutter, the shape of the milling cutter is according to the profile. The simple example of angular milling (as shown if Fig. 1.19) is the desired of V-block. production Cutter Flg. 1.19. Angular mling.  11 Milling (ii) Using face milling cutter, work is held at particular angle using angle plate (Angle plate is work holding device and is used to hold the workpiece at desired angle) as shown in Fig. 1.20. Face milling cutter Workpiece held at angle Fig. 1.20. 1.5.3. Form milling operation is used to machine surface The form milling is shown in Fig. 1.21. This milling cutter. The cutting teeth of this cuter of iregular shape. The cutter used is a form milling have the profile of the surface_to be_produced. ConvexX cutter Work Fig. 1.21. Form milling. 1.5.4. Straddle milling The straddle milling operation is shown in Fig. 1.22. It is the operation of production of flat vertical surfaces_on both sides of a workpiece by using two side milling cutters spaced Cutters Work Fig. 1.22. Straddle milling.  12 apart on an arbor with collars to give Eagle's Workshop Technology iu the required distance milling is commonly used to produce square between the faces. The stradd or hexagonal surfaces. The production of hexagonal surfaces using straddle milling is shown in Fig. 1.23. Cutters Work Fig. 1.23. The various shapes can be 1.24. produced by using straddle milling, which are as shown in Fig. Fig. 1.24. 1.5.5. Gang miling The gang milling operation is shown in operation which involves the use of a Fig. 1.25. It is the name given to a combination of more than twO cutters, milling common arbor, for milling a number of flat mounted on_a horizontal and vertical surfaces simultaneously. This combination may have side milling cutters or plain and of a workpiece both. The gang milling operation saves much of side Work. machining time and is widely usedmilling cutters in repetitive -Cutters Work Fig. 1.25. Gang milllng.  13 Milling 1.5.6. Plain Milling This operation is also called as slab milling. This operation involves production of aflat depth of Surface. In this, the cutting action is parallel to the axis of the cutter rotation. The feed is adjusted by moving the vertical feed screw of _the table. 1.5.7. Side Milling yertical surface on the sides As the name suggests, this operation is used to machine flat vertical feed screw of the of the workpiece. In this operation as well, like in plain milling, table is used to adjust depth of cut. S 1.5.8. End Milling an angle and to produce To produce a flat surface which may be yertical, horizontal or at end milling tools are made from slots, grooves or keywayS end milling is performed. Best yields more durability than the carbide steel. This is an expensive high quality material which cheaper high speed steel (HSS) or cobalt HSS. 1.5.9. Profile Milling concave shapes in two or three This operation covers multi-axis milling of convex_ and the size and dimensions. The planning process for profile milling is directly proportional to complexity of the design. This is divided into- three parts : concepts with radius. 1. Roughing/Semi-roughing: Tool used is round inserts and 2. Semi-finishing : Tool used is ball nose indexable. concept with radius. 3. Finishing/Super-finishing : Tool used is ball nose end mill and 1.5.10. Gear Cutting the This operation can be performed by milling, hobbing and even forging. In milling, the teeth is rotated form relieved cutter, which has shape exactly identical to the space between head and then indexing and the gear is cut on a gear blank by holding it on universal dividing it. 1.5.11. Helical Milling periphery of a cylindrical or This operation is performed on helical grooves around the required helix angle, or conical workpieçe. It can be done either by swivelling the table to the This is used to produce helical swilling the cutter. Another way can be by giving constant feed. gear, helical cutters, reamer etc, 1.6. WORK HOLDING DEVICES properly and securely held on he It is essential that the work during milling should be following are the usual devices milling machine table for effective machining operations. The to hold work on the table.  1.8. DETAILS OF COLUMN AND KNEE TYPE MILLING MACHINE Column and knee type milling machine is the commonly used low production milling machine on the vertical in which the table is mounted on the knee casting, which in turn is mounted can be slides of the column. The knee is vertically adjustable on the column so that the table milling moved up and down to acccommodate work of various heights. Further, this type of machines are classified according to the various methods of supplying power to the table, different and (b) movements of the table and different axis of rotation of the main spindle. Fig. 1.35 (a) These are shows the schematic and block diagram of a column and knee type milling machine. further sub-divided in the following types. Motor Cutter Over arm Over arm Arbor Column Spindle or Table arbor P555 -Saddle Workpiece Column -Knee Table Knee Saddle -Elevating Screw Screw Base jack Base (a) Schematic diagram of milling machine. (b) Block diagram of milling machine. Fig. 1.35.  Eagle's Workshop 28 generally used for cutting threads of coarse pitch on long screwed parts Technology |-| as in leadscrews and worms etc. The other consists of a number of such rows spaced at a distance equal to pitch from one another as shown in Fig. 1.46 (b). It is used for comparatively shorter lengths. 1.8.5. Principal parts of a plain milling machine 1he plain milling machine is shown in Fig. 1.47. Its principal parts are described below 1. Base and column : The base of the machine is a grey iron casting machined on top and bottom surface and serves as a foundation for all other parts. The base is made hollow o serve as a reservoir for the cutting fluid. Column is the main supporting frame mounted vertically and houses all the driving mechanisms for the spindle and table feed. The top of the column is finished to hold an over arm which extends outwards towards the front of the machine. Over arm Collars Noke Spindle nose Cutter Brace Arbor Work Ways Table Column Saddle Knee Knee elevating Screw Fig. 1.47. Plain milling machine. 2. Knee : The knee is a rigid grey iron casting which slides up and down on the vertical wavs of the column. It houses the feed mechanism of the table and different controls to operate it. 3. Saddle : It is a casting mounted on the top of the knee. The top of the saddle is finished to form a way to support the table. 4. Table : It is a rectangular casting which is supported on the top of the saddle. The table is fed longitudinally either with a hand wheel or power drive parallel to the face of the column. The table is clamped in position during cutting operations to provide rigidity. 5. Over arm : The top of the column holds an over arm that extends towards the front of the machine. To support the arbor properly, the over arm is moved in or out of the colunn to the required length. 6. Spindle : The spindle of the machine is located in the upper part of the column. t receives power from the motor through belts, gears or clutches andtransmits it to the arbor. Tne accuracy in metal machining by the cutter depends on the strength and rigidity of the spindle.  1.13. THREAD MILLING The thread milling operation of production of threads, external and internal by using a single or multiple thread milling cutter is shown in Fig. 1.56. This operation requires three driving motions in the machine i.e. one for the cutter, second for the Work and the third for the longitudinal movement of the cutter. For the single thread milling cutter, the cutter head is swivelled to the exact helix angle of the thread. The cutter is rotated on the spindle, while the Milling | 39 work is revolved slowily about its axis. The thread is completed in one cut by setting the cuter to the full depth of the thread and feeding it along the entire length of the workpiece. For the multiple thread milling cutter, the cutter axis and the work spindle are set parallel to_each other after adjusting the depth of cut equal to the full depth of the thread. The thread is completed by feeding the revolving cutter longitudinally through a distance equal to the pitch length of the thread while the work is rotated through one complete revolution. Thread milling cutter -Work Work Thread milling cutter (a) External thread milling operation. (b) Internal thread milling operation. Fig. 1.56. Thread milling operation. 4 Dloe far millina  Fill in the blanks 1. Milling is a machining process in which the removal of metal takes place due to the cuting action of a revolving cutter when the work is fed against it. 2. The size of a milling machine is signified by the dimensions i.e. and of the working surface of the table. 3. In milling machine the on the cutting teeth is not so heavy as in the case of turning tool. 46 Eagle's Workshop Technology - II| 4. Basically indexing head is designed to divide a into the desired number. 5. In up milling method the cutter rotates in a direction to the work is fed, while in down milling method the cutter rotates in the direction to the work is fed. 6. The names concave or convex of the cutter do not indicate the shape of the to be produced but the shape of the teeth. 7. The straddle milling operation is commonly used to produce or surfaces. 8. The gang milling operation saves much of machining time and is widely used in work. 9. The indexing or dividing head helps to change the position of the component in relation to the 10. In thread milling operation, the thread is completed by feeding the revolving cutter through a distance equal to the pitch length of the thread, while the work is rotated thronoh complete revolution.  ANSWERS Fill in the blanks : 1. multi point 2. length, breadth 3. stresS 4. workpiece 5. opposite, same 6. surface, cuter 7. square, hexagonal 8. repetitive 9. angular, cutter 10. longitudinally, one.