Chap4 CNC Machining

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Text of Chap4 CNC Machining

  • Section IV

    Computer Numerical Controlled Machining and Computer Aided Manufacturing

    Revised 8/2/05

  • AML Laboratory Manual

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  • CNC MACHINING & CAD

    Table of Contents 1.0 Introduction to CNC CAD/CAM Lab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Instructional Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

    1.2 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

    2.0 Computer Numerical Control Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Defining Numerical Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Advantages of NC and CNC Machining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3 Coordinate Systems and Machine Motions . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.0 Machining Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1 Machining Operations and Machining Practice . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2 Determining Cutting Conditions and Performance . . . . . . . . . . . . . . . . . . . . . . 18 4.0 Manual Part Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.1 Introduction to G Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 4.2 Programming Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.0 Computer Assisted Part Programming/Computer Aided Manufacturing Software . . . 27 5.1 Mastercam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 5.2 Post Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.0 CNC Milling Machine Setup and Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 6.1 Haas VF1 CNC Milling Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 7.0 Abrasive Waterjet Machining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 7.1 Introduction to Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 7.1 Comparison to Other Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 7.3 Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 7.4 Machine Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 7.5 Creating a DXF File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 7.6 FlowPATH Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 7.7 FlowCUT Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Appendices A. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 B. Reference Tables for Standard Drill, Tap, and Screw Sizes . . . . . . . . . . . . . . . . . 48 C. Haas VF1 Control Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 D. G-Code References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

    List of Figures

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  • AML Laboratory Manual

    4.1 A simplified schematic of an NC system. . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2 Computer numerical control (CNC) system schematic. . . . . . . . . . . . . . . . . . . . . . 9 4.3 DNC System Configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.4 Right hand coordinates for vertical milling machines. . . . . . . . . . . . . . . . . . . . . . 12 4.5 CNC lathe coordinate system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.6 Absolute versus incremental positioning. . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.7 Comparison of control system paths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.8 Two-dimensional NC contouring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.9 Three-dimensional NC contouring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.10 Peripheral milling; up milling and down milling shown considerably exaggerated to illustrate the principle of operation . . . . . . . . . . 18 4.11 Pocket Milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.12 Milling Tool Parameter Illustrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.13 Tool Length Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.14 Water Jet Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4.15 Abrasive Water Jet Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4.16 Jet Lag in thick part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.17 Corner Blowout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.18 Curve Taper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 4.19 Yo-Yo Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.20 Grid Part Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.21 Nested Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.21 Lead In / Lead Out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

    List of Tables 4.1 Recommended Surface Speed and Chip Load for Slotting Operations on Different Materials (HSS End Mills with Small Diameters (d

  • CNC MACHINING & CAD

    1.0 Introduction to CNC CAD/CAM Lab The AML CNC CAD/CAM lab provides an introduction to machine tools under computerized numerical control and the use of modern CAD/CAM software packages. Numerical Control (NC) or Computerized Numerical Control (CNC) -we will often use the terms interchangeably, - is the operation of machine tools (and other processes) by a series of coded instructions. Note that numerical control is not a kind of machine tool, but a technique for controlling a wide variety of machines. NC has been applied to assembly machines, inspection equipment, drafting machines, typesetting machines, welding tools, woodworking machines, punch presses and nibblers, wire wrap and insertion machines, as well as the more common metal-cutting machine tools. Since we can program the machine, we can make a variety of parts which are not possible when using specialized or fixed automation. CAD/CAM tools are used to model geometry and create tool paths associated to the geometry.

    In this course the focus will be on machining using a CNC vertical milling machine. You will learn two different ways to create a part on a CNC machine. The first, which we will use with the CNC vertical mill, is the use of Computer Aided Manufacturing software to interface Computer Aided Design (CAD) technology with CNC machine tools. You will use this technology to transform CAD representations of a part into a tangible product. This is one primary application of Computer Aided Manufacturing (CAM) software. The second method is called manual part programming where the user writes the code by hand and directly enters this code into the CNC machine via a keypad on the machine itself. 1.1 Instructional Objectives In the five lab sessions you will: Learn safety procedures. Learn standard machining procedures used for the selection of tools machining operation of

    the milling machine. Learn and or review typical CNC machine tool systems and the differences between point-

    to-point, straight cut, and contouring machine tool control systems. Learn how to write and debug a manual part program. Learn how to use Mastercams machining software to design and machine an injection

    mold insert. 1.2 Requirements For Safe Operation of a CNC Milling Machine PERSONAL SAFETY: A) SAFETY GLASSES MUST BE WORN AT ALL TIMES WHEN IN THE AREA OF THE MILLING MACHINE! Sharp fragments of metal may fly off at high velocity. Protect your eyes at all times. Failure to comply may result in revocation of shop privileges. B) AN ATTENDANT MUST BE AT THE CONTROL PANEL AND A TA OR AML SUPERVISOR MUST BE IN THE IMMEDIATE AREA AT ALL TIMES DURING CNC OPERATION. Furthermore, each student is responsible to know how to emergency stop the

    IV-5

  • AML Laboratory Manual

    milling machine before starting the machine. Software glitches can cause the cutting head to veer off unexpectedly resulting in severe damage to the machine. C) WARNING!! Loose clothing, long hair, personal stereo wires, jewelry, and gloves may become entangled in rotating equipment leading to serious injury or death! Make certai