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ISE 311 Machining II lab in conjunction with Section 22.3 and 22.4 in the text book “Fundamentals of Modern Manufacturing” Third Edition Mikell P. Groover 5/8/2008. Outline. Introduction to milling Cutting conditions in milling Milling machines, milling cutters, and tool holding

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Outline

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  1. ISE 311Machining II labin conjunction withSection 22.3 and 22.4 in the text book“Fundamentals of Modern Manufacturing”Third EditionMikell P. Groover5/8/2008

  2. Outline • Introduction to milling • Cutting conditions in milling • Milling machines, milling cutters, and tool holding • 3-2-1 approach • Edge finding • CNC machining • CAD/ CAM • Lab objectives • Lab Procedure • Summary

  3. Introduction to milling Milling is a machining operation in which a workpart is fed past a rotating cylindrical tool usually with multiple cutting edges. The cutting tool in milling is called a milling cutter and cutting edges are called teeth. The geometric form created by milling is a plane surface. Other geometries can be created either by means of the cutter path or cutter shape.

  4. Introduction to milling The machine tool that traditionally performs this operation is a milling machine (Mill). Milling is an interrupted cutting operation; the teeth enter and exit the work during each revolution. This subjects the teeth to a cycle of impact force and thermal shock on every revolution. The tool material and cutter geometry must be designed to withstand these conditions.

  5. Introduction to milling There are two basic types of milling operations: • Peripheral milling: the axis of the cutter is parallel to the surface being machined, and the machining is performed by cutting edges on the outside periphery of the cutter. - Face milling: the axis of the cutter is perpendicular to the surface being milled, and machining is performed by cutting edges on both the end and outside periphery of the cutter.

  6. Introduction to milling Peripheral milling Face milling

  7. Introduction to milling In peripheral milling, the rotation direction of the cutter distinguishes two forms of milling: • Up (conventional) milling: the direction of motion of the cutter teeth is opposite the feed direction when the teeth cut into the work. • Down (climb) milling: the direction of motion of the cutter teeth is the same as the feed direction when the teeth cut into the work.

  8. Introduction to milling Conventional milling Climb milling

  9. Cutting conditions in milling The cutting speed (v) is determined at the outside diameter of the milling cutter and is related to the diameter of the cutter (D) and the spindle rotational speed (N) in number of Revolution Per Minute (RPM) as follows: v = π*D*N To find the spindle RPM, first look for v in tables and then calculate N using the above formula

  10. Cutting conditions in milling • The feed f in milling is usually given as a feed per cutter tooth; called chip load. • Look for the chip load in tables. • To calculate the feed rate fr (in/min): fr = f * nt * N Where: f: chip load (in/ tooth) nt: number of teeth on the cutter N: spindle speed (rev/ min)

  11. Cutting conditions in milling • The material removal rate (RMR) in milling is determined using the cross sectional area of the cut and the feed rate. RMR = w * d * fr Where: RMR: Material Removal Rate (in3/min) w: width of cut (in) d: depth of cut (in) fr: feed rate (in/min)

  12. Cutting conditions in milling Neglecting the approach and travel distances of the cutter, the time required to mill a work piece of length L can be calculated as follow: Tm = L / fr where: Tm : time to mill (min) L: workpiece length (in) fr: feed rate (in/min)

  13. Milling Machines Milling machines can be classified as horizontal and vertical: • Horizontal milling machines: • Horizontal spindle • Suitable for peripheral milling • Vertical milling machines: • Vertical spindle • Suitable for face milling

  14. Milling Machines Horizontal milling machine Vertical milling machine

  15. Milling Machines Instead of the name “vertical knee-and-column mill”, you will hear the name “BridgePort” a lot in the Machine shop

  16. Milling machines In milling machines: • The knee can move in the z-direction. • The saddle is placed over the knee and can move in the y-direction . • The table is placed over the saddle and can move in the x-direction.

  17. Milling machines • To move the knee, saddle, or table, you have to rotate corresponding traverse cranks. • A micrometer is associated with each of the three cranks. Using these micrometers, you can measure the distance travelled. (some mills have digital readouts to display the x, y, and z coordinates). • The simplest and most common way to clamp the work during milling is to use a vise. (you will use a vise to clamp the work in the lab).

  18. Milling machines The Vise you will be using in the lab

  19. Milling Cutters The milling cutter you will use in the lab is a: HSS, ½”, 4-flute, non-center cutting end mill Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White There are no cutting edges at the center Diameter A flute Material: High Speed Steel

  20. Tool holding • There are many ways to mount the cutter in the machine spindle. The most common ways are: 1- Collets 2- Chucks • In the lab, you will use a 3-jaw chuck

  21. 3-2-1 approach In order to define the location of the work in the three dimensional space, the 3-2-1 approach is usually used: • To define the location in the z-direction, place the work on a plane with known z-coordinate. [a plane is defined by 3 points]. • While the work is on the plane, slide it until it touches a line with known y-coordinate (for example). [a line is defined by 2 points]. • While the work is touching both the plane and the line, slide it in the x-direction until it touches a pin (1point) with known x-coordinate.

  22. Edge Finding • In order to machine a feature in the work in the proper location, the location of the cutter should be defined with respect to certain references, usually the “Datum Planes” of the work. • Assuming that a datum surface is perfectly flat, the cutter can be located with respect to this datum using a tool called the “Offset Edge Finder”. • The “Offset Edge Finder” consists of a shank with a floating tip that is retained by an internal spring. The edge finder tip is accurately machined to a known diameter, usually 0.2 or 0.5 in. Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White

  23. Edge Finding The edge finder you will use in the lab Edge finder tip

  24. Edge Finding The procedure for using an Edge Finder: • Secure the edge finder in a collet or chuck in the machine spindle. • Set the spindle speed to about 600 to 800 rpm and slide the edge finder tip over so that it is off-center. • Start the spindle and lower the quill or raise the knee so that the edge finder tip can contact the edge of the part to be located. Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White

  25. Edge Finding The procedure for using an Edge Finder (continued) • Turn the table or spindle cranks and move the workpiece until it contacts the rotating edge finder tip. Continue to slowly advance the workpiece against the edge finder tip until the tip suddenly moves sideways. Stop movement at this moment. The machine spindle is now positioned a distance equal to the edge finder tip radius from the edge of the work. • Lower the work or raise the quill • If you want to drill a hole 1 in away from the datum plane, then you have to move the work a distance equal to 1 in plus the radius of the edge finder. Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White

  26. CNC machining • Numerical Control (NC) is a form of programmable automation in which the mechanical actions of a piece of equipment are controlled by a program containing coded alphanumeric data. • The data represent relative position between a workhead (the spindle or cutting tool in case of NC machining) and the workpiece. • Both the motion of the tool with respect to the workpiece and sequence of motions can be controlled in NC machining.

  27. CNC machining • NC system consists of three basic components: • Part program: a code (set of commands) which describes the sequence of operations to be done. • Processing equipment: the unit which performs the manufacturing operations according to the part program. • Machine control unit (MCU): stores the program and executes it by converting each command into actions by the processing unit. • If the MCU is a computer, then the NC is called CNC (Computer Numerical Control)

  28. CNC machining • In CNC machining, more than one axis can be controlled simultaneously. These axis are: - x, y, z axes (linear axes) - a, b, c axes (rotational axes around x, y, z axes respectively)

  29. CNC machining • In 2-axis milling machines, the x and y axes can be controlled simultaneously. • In 3-axis milling machines, the x, y, and z axes can be controlled simultaneously. • In 2 ½ milling machines, the z-axis is fixed at a certain value and then the x and y axes are controlled simultaneously.

  30. CNC machining • G-code, M-code and others are used in CNC programming. • The two main advantage of CNC machining are: • Complex geometries can be machined. • The process is automated.

  31. CAD/ CAM • CAD/ CAM stands for Computer-Aided Design/ Computer-Aided Manufacturing. • The CAD software is used to construct the initial workpiece geometry. • The CAM software is used to generate the cutting tool path. The CAD geometry can be saved and retrieved at any time.

  32. CAD/ CAM • The programmer can see a simulation of the tool path before actual production and corrects the program mistakes accordingly. • Portion of the tool path generated can be automated such as milling around the outside periphery of the part, milling a pocket into the surface of the part, surface contouring, and certain point-to-point operations. These routines are usually called “Macros”

  33. Lab Objectives The objectives of this lab are: • To learn the fundamentals of milling operations. • To learn how to select/ calculate cutting conditions for milling operations. • To observe the capabilities of a 3-axis CNC milling machine. • To understand the basics of how CNC machine tools are programmed.

  34. Lab Procedure The following procedure will be followed in the lab: Part1: Manual Milling 1- Peripheral mill one end of the workpiece to form a flat and perpendicular surface. 2- Reposition the work in the vice so that the unfinished end is protruding . 3- Use the edge finder to establish at the front-left corner of the part. (see part print in Appendix A) 4- Peripheral mill the protruding end to achieve the 1.75” dimension.

  35. Lab Procedure Part1: Manual milling (Continued) 5- Face mill the top of the workpiece to achieve the 0.313” dimension. 6- On the mill, center drill the hole locations. 7- If time permits, move the workpiece to the drill press and drill the holes. Note: For all milling operations in this lab, do not exceed 0.025” depth of cut

  36. Lab Procedure Part2: CNC demo 1- Observe the Haas machining center demonstration. 2- Observe the sample parts made on the CNC mill. 3- Observe the CAM demo.

  37. Pictures A picture showing the peripheral milling operation Feed direction

  38. Pictures A picture showing the face milling operation Feed direction

  39. Pictures Pictures showing center drilling on the vertical mill

  40. Pictures The part you will machine using the CNC milling machine Machined part Initial stock

  41. Pictures The CNC milling machine you will use in the lab

  42. Summary-Machining II Lab This lab preparation material introduced: • Basic principles of milling • CNC machining and CAD/ CAM systems • Lab objectives and procedures • Pictures

  43. Appendix A The part you will machine in the lab

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