Numerical Control PDF

16-08-2024 Numerical Control Dr. Gangadharudu Talla Assistant Profess...

16-08-2024 Numerical Control Dr. Gangadharudu Talla Assistant Professor National Institute of Technology Warangal 1 Introduction Numerical control: Programmable automation in which various functions of machine tools are controlled by Numbers, Letters, and Symbols Why NC machines? Flexible automation Numerical Control Part program methodology of manufacture and movements Most NC today is computer numerical control (CNC) 2 2 1  16-08-2024 Automatic functions in NC machine Tool Starting and stopping of machine tool spindle Controlling the spindle speed Positioning the tool tip at desired locations Guiding the tool along desired paths Numerical Control Controlling the feed rate of the tool tip Changing of tools in the spindle 3 3 Operation of NC machine tool Input to the system part geometry cutting process parameters cutting tools Numerical Control Part program -> MCU -> Machine tool 4 4 2  16-08-2024 Elements of NC machine tool operation (open loop system) Numerical Control 5 5 Closed loop system in CNC machine tool Numerical Control 6 6 3  16-08-2024 Axis motion in CNC machine tool Numerical Control 7 7 CNC machine tool operation Hardwired numerical control Softwired numerical control Numerical Control 8 8 4  16-08-2024 CNC control systems NC Modes 9 9 NC elements Machine control unit Part program Program coding systems Part program input NC Elements Tooling 10 10 5  16-08-2024 Machine control unit (MCU) Heart of NC and CNC system Functions of MCU: Reads the coded instructions. Decodes the coded instructions. Implements interpolations NC Elements Feeds the axis motion commands to the amplifier circuits Receives the feedback signals of position and speed for each drive axis. Implements auxiliary control functions 11 11 Machine control unit NC Elements 12 12 6  16-08-2024 Machine control unit Housed in a separate cabinet-like body or mounted on the machine. Appearance looks like a computer with a small display panel (~9”) NC Elements buttons along with a keyboard MCU controls the motion of the cutting tool spindle speeds, feed rate, tool changes, cutting fluid application 13 13 Part program Contains number of NC blocks ISO format Example for word address format N30 G00 X120.0 Y45.0 Z-85.0 NC Elements N40 G90 N50 G03 X200.0 Y200.0 I-100.0 J0 F200 N60 G01 X120.0 Y110.0 Can also be written using higher level languages: APT, UNIAPT, COMPACT II CAD/CAM systems: Unigraphics, Pro Engineer, Euclid, and SDRC I-DEAS CAM systems: MasterCAM, smartCAM, Duct etc. 14 14 7  16-08-2024 Program coding systems Decimal 365 = 3 X 102 + 6 X 101 + 5 X 100 Binary 365 = 101101101 NC Elements Binary coded decimal (BCD) Decimal 0 1 2 3 4 5 6 7 8 9 Binary 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 365 = 0011 0110 0101 Easy conversation to decimal digits and fast calculations 15 15 Part program input Paper tape (now obsolete) 1” wide paper tape with 8 tracks of holes BCD coding specifics numerals 0 to 9 on the first four tracks Tracks 5 to 8 represent other characters NC Elements A row of feeding holes is present between the third and fourth tracks EIA (Electronic Industry Association) code specifies an odd number of holes ISO code (ASCII) codes prescribes even number of holes Some holes may not be detected, or some holes may be spuriously added EIA ASCII 16 16 8  16-08-2024 Part program input Manual Data Input (MDI) Keyboard to directly enter the program into MCU Possible to store and edit number of programs Program can be transferred to MCU through USB or LAN Direct Numerical Control (DNC) NC Elements Personal computer (PC) is connected to the MCU through a serial port (RS 232C) 17 17 NC Tooling Accounts for 20 to 30% of NC machine cost Different adopter for each cutting tool ISO configuration NC Elements Power-operated drawbar pulls the tooling at the retention knob eliminates clearance between spindle and tooling shank Spindle tooling holding an End Mill 18 18 9  16-08-2024 Drawbar working mechanism NC Elements 19 19 NC Tooling Preset tool has adjustable locating faces enables the dimensions between the tool-cutting edges and location faces to be preset to a close tolerance using a presetting device needs to be removed from the machine during batch production NC Elements If tools are stored on a drum, tool file will be automatically updated Preset tooling used in CNC turning machines 20 20 10  16-08-2024 Applications Complex contours Small lot production High accuracy and repeatability Many set-ups and/or NC Machine Tools Frequent design changes and expensive set-ups Significant inspection cost 21 21 Advantages of NC Less nonproductive time Greater accuracy and repeatability Low scrap rates Less inspection requirements NC Machine Tools Complex part geometries Easy engineering changes Simple fixtures Short lead times Reduced parts inventory and less floor space Low skill operator 22 22 11  16-08-2024 Other applications of NC Rapid prototyping and additive manufacturing Water jet cutting and abrasive water jet cutting Component placement machines in electronics assembly Coordinate measuring machines NC Machine Tools Wood routers and granite cutters Tape laying machines for polymer composites Filament winding machines for polymer composites 23 23 Limitations of NC High investment cost High maintenance effort/cost Need for skilled programmers Requirements of conditioned environment NC Machine Tools 24 24 12  16-08-2024 Additional advantages of CNC Storage of more than one part program Part program editing at the machine tool Fixed cycles and programming subroutines Adaptive control NC Machine Tools Positioning features for setup - to help operator align work part on machine tool table Acceleration and deceleration computations Communications interface Tool offset data and tool life management Diagnostics 25 25 Early form of CNC milling machine (Bridgeport Machines Inc., U.S.A.) Practical NC Machines Addition of NC to Tool-room milling machine Combination of drilling and milling machines 26 26 13  16-08-2024 Present day production horizontal axis CNC machining centre (Makino Milling Machines Co. Ltd., Japan) Practical NC Machines High accuracy Reduces other finishing operations 27 27 High production horizontal axis CNC machining centre (Makino Milling Machines Co. Ltd., Tokyo, Japan) Automatic Tool Practical NC Machines Changer (ATC) Automatic Pallet Changer (APC) 28 28 14  16-08-2024 CNC copy milling machine (Makino Milling Machines Co. Ltd., Japan) Practical NC Machines CNC control to copy milling machine Transformation flexibility 29 29 CNC Turning centre with slant bed (George Fischer, Switzerland) Practical NC Machines Slant bed Complex axi-symmetric shapes 30 30 15  16-08-2024 CNC Chucker (Turning) (ACE Designers) Practical NC Machines Chucking components Quick cycle time, high rapid rates and easy chip disposal 31 31 CNC Turning centre with a gantry loader for workpiece handling (George Fischer, Switzerland) Practical NC Machines 32 32 16  16-08-2024 EDM Wire cut machine (Mitsubishi Electric Corp., Tokyo) Practical NC Machines 33 33 CNC Turret punching press (Amada, Japan) Low volume production Quick die and punch change Practical NC Machines 34 34 17  16-08-2024 CNC Coordinate Measuring Machine (Mitutoyo Asia Pacific Pte. Ltd., Singapore) Dimension measurement and automatic inspection Practical NC Machines 35 35 Other CNC machine tools Grinding machines Gear-generating machines Press brakes Practical NC Machines Flame cutting machines Laser cutting machines Pipe-bending and forming machines Folding and shearing machines Filament winding machines Assembly machines 36 36 18  16-08-2024 Bibliography P.N. Rao, "CAD/CAM Principles and Applications”, 3rd Edition, Tata McGraw Hill, New Delhi, 2010 37 37 19