1. Study of Operational Concepts of Conventional and CNC Machines - Lathe & Milling Pratik Basu Final year B.E student Lingaya’s Inst. Of Mgmt. & Tech.
7. Lathe Machine The 2 principal conventional machines on which we are focusing are the lathe and milling machines. Lathes are designed for precisely machining relatively hard materials. With their inherent versatility, they are used in a wide range of applications, and can machine a broad range of materials. These lathe machine removes material from a rotating work piece via the linear movements of various cutting tools, such as tool bits and drill bits.
10. Milling machine A milling machine is a machine tool used for the shaping of metal and other solid materials. Its basic form is that of a rotating cutter, which rotates about the spindle axis (similar to a drill), and a table to which the workpiece is affixed. In contrast to the lathe machine, in the milling machine the workpiece moves longitudinally against the rotating cutter. Milling machines may be operated manually or by CNC.
11. Types of milling cutters In vertical mills , milling cutters with solid shafts are usually used. End mills are designed for cutting slots, keyways and pockets. Two fluted end mills can be used to plunge into work like a drill. Ball end mills can produce a fillet.
13. Computer and Numerically Controlled Machines Numerically Controlled (NC) NC is the operation of M/c tool by a series of coded instructions consisting of numbers, letters of the alphabets and symbols, which the MCU (Machine Control Unit) can understand. Computer numerically controlled (CNC) When numerical control is performed under computer supervision, it is called computer numerical control (CNC). Computers are the control units of CNC machines. A programmer enters some information in the program, but the computer calculates all necessary data to get the job done. For both NC and CNC systems, working principles are the same. Only the way in which the execution is controlled is different. Normally, new systems are faster, more powerful, and more versatile.
21. 5. Tool changers Several different cutting tools are used to produce a part. The tools must be replaced quickly for the next machining operation. For this reason, the majority of NC/CNC machine tools are equipped with automatic tool changers. They allow tool changing without the intervention of the operator. An automatic tool changer grips the tool in the spindle, pulls it out, and replaces it with another tool. Tool changers are equipped for either random or sequential selection. In random tool selection there is no specific pattern of tool selection. In sequential tool selection , the tools must be loaded in the exact order in which they are called for in the program. 3. AC servo motors (controlled by varying the voltage frequency to control speed, more power than a DC servo, used to drive a lead screw and gear mechanism ) 4. Fluid servo motors (variable speed motors, produce more power, in the case of pneumatic motors, than electric servomotors)
28. Co-ordinate codes These indicate the co-ordinates for the tool movement. Four to five axis machines can have the following axes. Feed rate (F-code) This specifies the feed rate for the operation. The units may be mm per minute or mm per revolution (indicated by the G-code used), with the decimal point implied at a fixed position from the right. Spindle speed (s-code) This specifies the spindle speed to be used for the operation. Tool Number This indicates to the controller which tool is to be used for the operation. In case of tool adaptors with multiple tool slots, the machine just switches to the next tool without removing the earlier one form the adaptor. J B Y K C Z I A X Circular Interpolation about Cartesian axes Angular positions for the Cartesian axes Cartesian Co-ordinates
29. Miscellaneous Code (M-code) These codes program various auxiliary functions on the machine tool. The miscellaneous function may be acted upon at the start or the end of the motion described by a block of instruction. With word address format, information need not be repeated in successive blocks if it is to remain the same for subsequent blocks. ISO MISCELLANEOUS FUNCTIONS ( M-Codes ) CODE FUNCTION M00 Program stop, spindle and coolant off M01 Optional programmable stop M02 End of program-often interchangeable with M30 M04 Spindle on CCW M05 Spindle stop M06 Tool change M07 Coolant supply No. 1 on M08 Coolant supply No. 2 on M09 Coolant off M10 Clamp M11 Unclamp M13 Spindle on, CW + Coolant on
30. M14 Spindle on, CCW + Coolant on M 20 – 29 Unassigned M30 Program stops at end of tape+ tape rewind M31 Interlock by-pass M40-M45 Gear Changes; otherwise unassigned M90 Reserved for user M99 (Subroutine call) Reserved for user G - Codes (Fanuc Machine Control) G CODE FUNCTION G00 Positioning (Rapid traverse) G01 Linear Interpolation (Cutting feed) G02 Circular interpolation /Helical cutting CW G03 Circular interpolation/Helical cutting CCW G04 Dwell Time G17 XY plane selection G18 ZX plane selection G19 YZ plane selection G20- 21 Input in inch and mm respectively.
31. G28 Return to reference point G40 Cutter compensation cancel G41 Cutter compensation left G42 Cutter compensation right G43 Tool length compensation + direction G44 Tool length compensation – direction G53 Machine coordinates system selection G54 - 59 Work co-ordinate system 1 -6 selection G80 Canned cycle cancel G81 Drilling cycle, spot boring G82 Drilling cycle, counter boring G83 Peck drilling cycle G84 Tapping cycle G85 Rough Boring cycle G86 Finish Boring cycle G90 Absolute command G91 Incremental command G92 Programming of absolute zero point G94/98 Feed per minute G95/99 Feed per rotation G96 Constant surface speed control
32. G97 Constant surface speed controls cancel G98 Return to initial point in canned cycle G99 Return to R point in canned cycle Sample Code G00 X 5.0 Y 5.0 ; Here we rapid tool movement to co-ordinates (5,5). “Air cutting” is minimized by G00 and tool need move along a straight line only. G41(Radius compensation on the left side of the profile) G42(Radius compensation on the right side of the profile)
36. CONCLUSION The importance of lathes and milling machines even if they are conventional cannot be undermined. These machines have played a real important role in bringing about industrial revolution and have laid the foundations. But the bringing about of the new technology in the present era is very important. The conventional machines are required in small quantities whereas the CNC machines must be increased to improve the quantity and quality of production.