LABORATORY MANUAL
MANUFACTURING PROCESSES – 1
(NECESSARy REAdING MATERIAl FOR lAb ANd
PROjECT TURNS FOR All lAb USERS)
TA - 202 lAb
Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY KANPUR
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LABORATORY MANUAL
MANUFACTURING PROCESSES – 1
(NECESSARy REAdING MATERIAl FOR lAb ANd
PROjECT TURNS FOR All lAb USERS)
TA - 202 lAb
Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY KANPUR
GENERAL INSTRUCTION
1. Every student should obtain a set of instruction sheets entitled manufacturing processes Laboratory.
2. For reasons of safety, every student must come to the laboratory in shoes (covering the whole
feet). It is unsafe for the students to come to the laboratory wearing garments with parts that that hang
about loosely and as such the lab users are requested to avoid wearing garments with loose hanging
parts. Students should preferably use half-sleeve shirts wherever possible. The Students should also
ensure that floor around the machine is clear and dry (not oily) to avoid slipping. Please report
immediately to the lab staff on seeing any coolant / oil spillage.
3. An apron will be issued on a returnable basis (returnable after each lab turn) to each student. Students
not wearing an apron will not be permitted to the work in the laboratory.
4. Instruments and tools will be issued from the tool room. Every student must produce his identity card
for the purpose. Tools, etc. must be returned to the tool room on the same day after work hours.
5. The student should take the permission and guidance of the Lab Staff / Tutors before
operating any machine. Unauthorized usage of any machine without prior guidance may lead to fatal
accidents and injury.
6. The student will not lean on the machine or take any kind of support of the machine at any point of
time. If found leaning on a machine without proper reasons serious action would be taken
7. Power to the machines will be put off 10 minutes before the end of laboratory session to allow the
students to return the tools. Please finish up at exactly 4:50pm.
8. Students are required to clear off the chips from the machine and lubricate the guides etc. at the
end of each laboratory session.
9. Laboratory reports should be submitted on A4 size sheets. The students must fill these reports and
hand it over to their group TA after the laboratory session. These have associated some grades.
10. Reports will not be returned to the students. Students may see the graded reports while in the
laboratory.
MACHINING PROCESSES
Machining is one of the processes of manufacturing in which the specified shape to the work piece is imparted by removing surplus material. Conventionally this surplus material from the work-piece is removed in the form of chips by a mutual interaction between the an appropriate tool and the workpiece. The mechanical generation of these chips can be carried out by a single point or multi point tool or by abrasive operationsas classified below:
Machining Process Classification
I
Single point tool operations Multi-point tool operations Abrasive operat:ons
I I I
1. Turning 1. Milling 1. Grinding
2. Boring 2. Drilling 2. Lapping
3. Shaping 3. Tapping 3. Honing
4. Planing 4. Reaming 4. Super-finishing
5. Hobbing
6. Broaching
7. Sawing
The process of chip formation in metal cutting is affected by relative motion between the tool and the work-piece achieved with the aid of a device called machine tool. This relative motion can be obtained by a combination of rotary and translatory movements of either the tool or the workpiece or both. The kind of surface that is produced by the operation depends on the shape of the tool and the path it traverses through the materials. When the workpiece is rotated about an axis and the tool is traversed in a definite path relative to the axis, a surface of revolution is generated. When the tool path is parallel to the axis, the surface generated is a cylinder as in straight turning [Figure 1] or boring operations [Figure 2]. Similarly, planes may be generated by a series of straight cuts without rotating the workpiece as in shaping and planing operations [Figure 3]. In shaping the tool reciprocates and the work piece is moved crosswise at the end of each stroke. Planning is done by reciprocating the workpiece and crosswise movement is provided to the tool.
A surface may be machined by the tools having a number of cutting edges that can cut successively through the workpiece materials. In plane milling, the cutter revolves and moves over the work piece as shown Figure 4. The axis of the cutter is parallel to the surface generated. Similarly in drilling, the drill may turn and be fed into the workpiece and the workpiece may revolve while the drill is fed into it [Figure 5]
The machine tools, in general, provide two kinds of relative motions. The primary motion is responsible for the cutting action and absorbs most of the power required to perform the machining action. The secondary motion is that of feed and may proceed in steps or continuously and absorbs only a fraction of the total power required for machining. When the secondary motion is added to the primary motion, machine surfaces of desired geometric characteristics are produced. .
Consider a situation where both the cutting motions as well as the feed motion (provided at the end of each stroke) are rectilinear and perpendicular to each other simultaneously. Here the machined surface produced is a plane. The line generated by the primary motion (cutting motion) is called the generatrix, while the line representing the secondary motion (feed motion) is called the directrix (Fig. 6a).
Depending upon the shapes of the generatrix and the directrix and their relative orientations. various geometries can be produced on the workpiece. Consider another case when the generatrix is a circle and the dirctrix is a line perpendicular to the plane of the generatrix. It is clear that in this situation the surface produced will be a cylinder (Fig. 6b). A tapered surface can be produced by merely changing the angle that the directrix makes with the plane of the generatrix. When the directrix is in the plane of the circular generatrix (Fig. 6c), lines are generated which results in a plain surface when a number of generatrices and directrices are placed side by side in the direction perpendicular to the plane of the generatrix. In actual practice, the cutting is performed by cutting edge and not a point. Thus.a series of generatrix/directrix combination are involved and the relative motion produces a surface rather than a line.
Basically there are two methods of producing new surfaces, the tracing method and the generation method. In the tracing method the surface is obtained by direct tracing of the generatrices and when the surface produced is the envelope of the generatrix the process is known as generation. Figs. 6(a) & 6{b), the plane and the cylindrical surfaces are obtained by direct tracing, while in Fig. 6(c) the final surface geometry is the envelope of the generatrices.
Fig. 1 Straight turning Fig. 2 Straight boring Fig. 3 Shaping and planning
Fig. 4 Plain milling Fig. 5 Drilling
Fig.6 Concept of generatrix and directrix. (a) Rectilinear generatrix and directrix. (b) Directrix perpendicular to the plane of generatrix. (c) Directrix in the plane of generatrix.
PART (B)
OBJECTIVE: To make the part shown in the sketch from a mild steel rod on a Lathe.
Facing Turning Tapper turning Grooving R H Tread Centre drill
Ф 20 Ф14 Ф12 M
(All dimensions are in MM)
EQUIPMENT: List all tools and instruments used.
OUTLINE OF PROCEDURE
Hold the bar in a three jaw chuck and face the end with a right hand facing tool. Make central hole
with a center drill. Repeat these' operations for the other end of the bar. Hold the live centre in three
jaw chuck and hold the job in a dog carrier between centers. Turn the bar to the required diameter
with rough cuts. Face the steps and finishes the diameters to the required sizes. Machine the taper
with the help of the cross-slide swiveling arrangement. Machine the roots and the groove as per given dimension with form tools. Cut the threads.
OBSERVATIONS
(a) Measure all dimensions (up to second decimal place) on the specimen turned by your
group. Make a neat sketch and indicate all measured dimensions.
(b) Discuss briefly how tapered portion was turned.
(c) Show the calculation of the required gear ratio for thread cutting.
(d) Sketch the main drive unit of 'the- lathe and show how the speed steps are obtained.
MILLING: INTRODUCTION AND PRACTICE
PART (A)
OBJECTIVE: To study the characteristic features of Milling machine.
OUTLINE OF PROCEDURE
i) Run the machine at low speed and observe the motions, which control the shapes of the surfaces
produced. Note particularly the features, which control the geometrical form of the surface.
ji) Learn the names of the major units and the components of each machine. Record these details (Table
A). (Please ensure that the main isolator switch is off and check that the machine cannot be
inadvertently started. Do not remove guards). Use the manufacture's handbook for details that cannot
be inspected.
jii) Record the obtainable speed and feed values (Table B).
iv) Note down the special features of the speed and feed control on each machine.
v) Pay attention to the following:
a. Size specification of various machine tools.
b. Machine tool structures and guide ways I slide ways.
c. Drive mechanism for primary (cutting) motion.
d. Drive mechanism for secondary (feed) motion.
OBSERVATION: Record the following in a tabular form:
Machine Tool Specifications (Table A)
Machine
Type &
Make
Size Speed given to Feed given to
Type of
Surface
Tool Work Tool Work^ Produced
Milling m/c
Speed and Feed Data (Table B)
No. Milling M/c.
Speed Feed
SHAPING: INTRODUCTION AND PRACTICE
PART (A)
OBJECTIVE: To study the characteristic features of Shaper.
OUTLINE OF PROCEDURE
i) Run the machine at low speed and observe the motions. Which control the shapes of the surfaces produced? Note particularly the features, which control the geometrical form of the surface.
ii) Learn the names of the major units and the components of each machine. Record these details (Table A). (Please ensure that the main isolator switch is off and check that the machine cannot be inadvertently started. Do not remove guards). Use the manufacture's handbook for details that cannot be inspected.
iii} Record the obtainable speed and feed values (Table B).
iv) Note down the special features of the speed and feed control on each machine.
v) Pay attention to the following: a. Size specification of various machine tools. b. Machine tool structures and guide ways I slide ways. c. Drive mechanism for primary (cutting) motion. d. Drive mechanism for secondary (feed) motion.
OBSERVATION Record the following in a tabular form:
Machine Tool Specifications (Table A)
Machine
Type & Make Size
Speed given to .Feed given to Type of Surface Tool Work Tool Work Produced
Shaper M/c.
Speed and Feed Data (Table 2)
No. Shaper M/c.
Speed Feed
PART (B)
OBJECTIVE:
To machine a V-block as shown in the sketch out of the work piece provided.
EQUIPMENT
List all tools and instruments used.
OUTLINE OF PROCEDURE
Hold the work piece in a vice and machine the bottom surface shown in the sketch. Invert the casting
in the vice and machine the top surface till the desired height is obtained. Machine the inclined. Faces
using right and left hand tools. Finally machine the groove.
OBSERVATIONS:
(a) Measure all dimensions (up to second decimal place) on he specimen machined by your group. Make a neat sketch and indicate all measured dimensions.
(b) Calculate the machining time for the bottom surface of the specimen.
(c) Explain -the quick return mechanism.
(d) Explain the use of clapper box on the machine.
PART (B)
OBJECTIVE: To drill, file, as shown in the sketch, ream and tap holes on the mild steel plate.
S s – Saw Cut
R – Reamed hole, 9.8 mm drill
& 10 mm reamer
T - Tapped hole, 8.5 mm drill
& M10 tapped
25 R T F - Filed edge
F
10
(All dimensions are in MM)
EQUIPMENT : List all tools and instruments used.
OUTLINE OF PROCEDURE
File two sides of the mild steel work piece ensuring with a trisquare that the angle are 90°. Mark the object as per dimension with the help of height gauge & supporting “V” block. Punch at the center of
the required hole and saw cut length. Drill and ream the holes as required, Tap the hole using a set
of three taps, and saw cut.
OBSERVATIONS
(a) Measure all dimensions (up to second decimal place) on the specimen made by your
group. Make a neat sketch and indicate all measured dimensions.
(b) Explain how power is transmitted from drill spindle to drill shank.
(c) Sketch a reamer and show its main features.
(d) Explain why a set of three taps was used.
Overview of Numerical Control
A new technique for controlling the machine / production tools, the Numerical Control (NC) was developed in mid 50's. Prior to this, all the machine / production tools were manually operated and controlled. Quality of the products produced by manually operated machines is totally dependent on the skills and mind status of the human operator. Numerical control machines are more accurate than manually operated machines, can produce components more uniformly, faster and in the long-run tooling costs are smaller but the initial investment is higher. Numerical Control (NC) has been defined by the Electronic industries Association (EIA) as 'a system in which actions are con- trolled by direct insertion of numerical data at some point'. This system automatically interprets symbolic instructions (numerical data) to control machine tools and other manufacturing systems. Symbolic instructions or the numerical data required to produce a part is called a 'part program'. Traditionally, in NC machining, part drawing of the component to be machined is studied by the NC programmer who translates the information on the drawing to the necessary programme which issues operational instructions to the machine tools. The programme represents the instantaneous path or action that the machine tool must follow to do machining on the part as described in the engineering drawing. In the initial stages of NC development the programmed instructions were stored on punched tapes and were interpreted by electromechanical tape readers connected to the machine tool. The main problem with tapes was that it was very difficult to change the instructions on these tapes once the punching was completed. Even to make very minor instructional change in the operating programme, a completely new tape had to be punched in addition to interrupting the machining. operation. Another draw-back of using the tapes was many runs for many components. So, essentially number of components required Would determine the tape life. With rapid developments in the computational technology and overall data processing capabilities, the problems associated with punched paper/plastic tape have been solved. Rapid development in numeric control (NC) technology lead to direct numerical control (DNC) and computer numerical control (CNC) and distributed numerical control (DNC).
In fact the problems which were faced by NC lead to the development of a concept known as direct numerical control (dNC) which eliminated the use of tape as a medium of carrying the programmed instructions. In dNC many machine tools are connected to a host computer through a data transmission link as shown in Fig. 15.13. Here, the NC programmes required to operate the machines are stored in the host computer and are fed to the machine tool through data transmission lines. Even though dNC eliminates the use of tape, it l suffers whenever the host computer goes down and reintitializing is a big problem. This shortcoming of dNC has led to the development of a computer numerical control (CNC) which allows the NC machines at remote locations to be connected and controlledby a host computer. The development: of programmable logic controllers (PLC) and micro-computers has lead to the development of computer numerical control (CNC). In CNC technology, each machine tool has a PLC or a micro-computer which allows the programme to be dowlaoded and stored at each and every machine. In addition,. programmes can be developed off-line and down-loaded to the micro- processor/PLC present at the individual machine tools. This system as developed rectified the problems associated with the down-time of host computer as in dNC but allowed a new problem called data management to come into limelight. For exampIe, the same program that might get loaded on many different microcomputers could control the machine tools randomly primarily owing to the non communication between the individual terminals. This problem was solved by the development of distributed numerical control (DNC). Distributed numerical control (Fig. 15.14) was developed by combining the positive point of both direct numerical control (dNC) and computer numerical control (CNC). Hence, in distributed numerical control (DNC) both host and local computers were present at individual machine tools. Here host computers were used as main storage devices and programs were down-loaded to the mini- computers present at various machines where they were stored or transmitted to the NC machines depending on localized control. Mini-computer controllers also served as back-up memory devices whenever the host computer was down and thus saved down time. Therefore, in this system the NC machines do not have to be down when the host computer is down or switched off and there is some degree of local control using individual PCs.. An effective data transmission network from the host computer to the micro-computer controls the NC machines and is key to the success of distributed numerical control systems. In rest of this text material, NC is used as a synonym for CNC
Various components present in NC machine tool are:
. Machine tool . Machine Control Unit (MCU) . Communication interface and accessories The machine tool may be any type of machine tool used in the manufacturing industry. Machine control unit (MCV) is the control unit that reads and interprets the numerical data/part programme from the tap or any other media and passes on this information in the form of electrical signals to various activators / drive mechanisms of the machine to operate the machine tool in the desired way. Numerical control Machines are classified based on the type of motion control. the presence of feed-back loops, the power drives the positioning system used and the number of axes of motion which can be controlled. Two types of motion controls are used on NC machines. They are point-to-point or continuous-path controlled. As the name implies, the point-to-point (PTP) controlled machines move in a series of steps from one point to the other point. A machine with PTP control can perform very limited number of machining opera ions. In almost all the cases where PTP control is used,
Numerical-Control Programming
10.1 NC PART PROGRAMMING
10.1.1 Coordinate Systems
In an NC system, each axis of motion is equipped with a separate driving source that replaces the hand wheel of the conventional machine. The driving source can be a DC motor, a stepping motor, or a hydraulic actuator. The source selected is determined mainly based on the precision requirements of the machine, as described in Chapter 9. The relative movement between tools and workpieces is achieved by the motion of the machine tool slides. The three main axes of motion are referred to as the X, Y. and Z axes. The Z axis is perpendicular to both the X and Y axes in order to create a right-hand coordinate system, as shown in Figure 10.1.A positive Motion in the Z direction moves the cutting tool away from the workpiece. This is detailed as follows:
Z AXIS
- On a workpiece -rotating machine, such as a lathe, the Z axis is parallel In the spindle, and the positive Motion moves the tool away from the workpiece (figure 10.2).
- On a tool-rotating machine, such as a milling or boring machine, the Z axis is parallel to the tool axis, and the positive motion moves the tool away from the workpiece (Figures 10.3 and 10.4).
- On other machines, such as a press, a planing machine, or shearing machine, the Z axis is perpendicular to the tool set, and the positive motion increases the distance between the tool and the workpiece.
X AXIS
- On a lathe, the X axis is the direction of tool movement, and the positive motionmoves the tool away from the workpiece
- On a horizontal milling machine, the X axis is parallel to the table.
- On a vertical milling machine, the positive X axis points to the right when the prorammer is facing the machine.
The Y axis is the axis left in a standard Cartesian coordinate system.
10.1.2 NC Program Storage Media
Modern CNC controllers provide several ways of transferring data. Perhaps the most typical data-communication methods used to transfer part program files is an RS-232C interface (see Chapter 8). An NC part program is stored in a file on a computer or a CNC controller. The file download (or upload) can be initiated by setting up a transfer mode on the CNC controller. On the other side of the communication cable is a computer that sends or receives data byte by byte. The operator must start and end the data-transfer process on both the CNC controller and the computer. Some machines use higher-level protocols to ensure an error-free data transfer. Two of the higher-level protocols used are Kermit and Xmodem. Kermit and Xmodem arc widely accepted in the computer-to-computer telecommunication file-transfer process. These protocols allow the file transfer to be controlled by either the computer or the controller. The computer can send and retrieve data directly.
Some machines also provide local-area network (LAN) instead of serial communication. Ethernet and MAP are two technologies used. Some CNC controllers allow the entire controller function to be initiated from a remote computer through the data-communication network.
10.1.
A BCD (binary-coded decimal) or ASCII (American Standard Code for Information interchange) code is frequently used in NC applications.
. BCD: An eight-track punched tape is one of the more common input media for NC systems. Hence, all data in the f orm of symbols, letters, und numbers must be: represent able by eight binary fields. The BCD code has been devised to satisfy this requirement. In a BCD code, the numerals 0 through 9 are specified using only the first four tracks, quantities 1,2,4, and 8. Note that the four number: 1.2,4. and 8. added together as needed make all numbers from 1 to 15. Letters, symbols and spccial instructions are indicated by using tracks 5 through 8 in combination with the numeral tracks. A complete BCD character set, based on EIA Standard RS244A, is illustrated in Figure 10.6. Each BCD character must have all odd number of holes. By punching a parity bit along with all even bit strings, all characters have an odd number of holes_._ If an even number of holes is detected, it is by definition an error, and a parity check occurs. This simple method provides some: protection from input errors resulting in part damage. . ASCII: ASCII was formulated to standardize punched-tape codes regardless of applications (Pressman and Williams, 1979). Hence, ASCII is used in computer and telecommunications as well as in NC applications. ASCII code was devised to support a large character set that includes uppercase and lowercase letters and additional special symbols not used in NC application Figure 10.6 illustrates the ASCII subset applicable to NC. Many new control systems now accept both BCD and ASCII codes. It is likely that the move toward ASCII standardization will progress as older NC equipment is replaced.
10.1.4 Tape Input Formats
The organization of words within blocks is called the tape format (EIA Standard RS274) (Groover, 1980). Four tape formats are used for NC input (Pressman and Williams, 1979):
- The fixed sequential format requires that each NC block be the same length and contain the same number of characters. This restriction enables the block to be divided into substrings corresponding to each of the NC data types. Because block length is invariant, all values must appear even if some types are not required.
- The block-address format eliminates the need for specifying redundant illformation in subsequent NC blocks through the specification of a change code. The change code follows the block sequence number and indicates which values arc to be changed relative to the preceding blocks. All data must contain a predefined number of digits in this form t.
- The tab sequential format derives its name because words are listed in a fixed sequence and separated by depressing the tab key (TAB) when typing the manuscript on a Flexowriter. Two or more tabs immediately following one another indicate that the data that -would normally occupy the null locations are redundant and have been omitted. An example of tab sequential NC code is
TOO1 TO1 TO7500 TO6250 T10000 T612 T718 T T EOB TO02 T T08725 TO6750 T T T T EOB TO03 T T T TO5000 T520 T620 TO1 T EOB (T represents a tab character.)
- The word-address format places a letter preceding each word and is used to identify the word type and to Address the data to a particular location in thecontroller. The X prefix identifies an X-coordinate word, 30 S prefix identifies spindle speed, and so on. The standard sequence of words in 2t block for a three axis NC machine is.
N word G word X word Y word Z word F word S word T word M word and EOB
A word-address NC code is NOO1 GO1 X07500 Y06250 Z1OOOO F612 5718 EOB NOO2 X08752 Y06750 EOB NOO3 Z05000F520 S620 MO1 EOB
A block of NC part program consists of several words. A part program written in this data format is called a G-code program. A G-code program contains the following words: N. G, X, Y, Z, A, B. C. I, J. K, F, S, T, R. M Through these words, all NC control functions can be programmed. An EIA standard. RS-273, defines a set of standard codes. However, it also allows for the customizing of certain codes. Even with this standard, there is still a wide variation of cod format. A program written for one controller often does not run on another. It is, therefore,
TABLE 10.1 G CODES
G00 Rapid traverse G40 Cutter compensation cancel G01 Linear interpolation G41 Cutter compensation left G02 Circular interpolation CW G42 Cutter compensation right G03 Circular interpolation CCW G70 Inch format G04 Dwell G71 Metric format G08 Acceleration G74 Full-circle programming off G09 Deceleration G75 Full-circle programming on G17 X-Y plane G80 Fixed-cycle cancel G18 Z-X Plane G81-89 Fixed cycles G19 Y-Z Plane G90 Absolute dimension program G91 Incremental dimension
XY. YZ , and XZ planes. The interpolation plane can be selected using G 17, G18 or G 19. When a machine is equipped with thread-cutting capability, (G33-G35), the part program must specify the proper way to cut the thread. Codes G4O-G43 deal with cutter compensation. They simplify the cutter-center offset calculation. More details of cutter compensation are discussed later in Section 10.2.2. Most canned cycles are manufacturer-defined. They include drilling, peck drilling, spot drilling, milling, and profile turning cycles. The machine-tool manufacturer may assign them to one of the nine G codes reserved for machine manufacturers (GS)-G89). A user also can program the machine using either absolute (G90) or incremental (G91) coordinates. In the same program, the coordinate system can be changed. In order to simplify the presentation, most of the examples given in this chapter use absolute coordinate. Many controllers also allow the user to use either inch units (G70) or metric units (G71). Because hardwired NC circular interpolators work only in one quadrant and many CNC systems allow full-circle interpolation, a (G74) code emulates NC circular interpolation for CNC controllers. G75 returns the CNC back to the full-circle circular interpolation mode. X,Y,Z,A,B and C-Codes. These words provide the coordinate positions of the tool. X, Y and Z define the three translational (Cartesian) axes of a machine. A. B. C are used for the three rotational axes about the X,Y, and Z axes. For a three axis there can be only three translational axes. Most applications only require X. Y.and Z codes in part programs. However, for four-, five-,or six-axis machine tools. A, B, and C are also used. The coordinates may be specified in decimal number (decimal programming) or integer number (BLU programming). For a controller with a data format of "3.4", to move the cutter to (1.12,2.275. 1.0). the codes are :
X1.1200 Y2.2750 Z1.OOO
In BLU programming, the programmer also may need to specify leading zero(s), or trailing-zero formats. A leading-zero format means that zeros must be entered in the space proceeding the numeric value. In this format, the controller locates the decimal point by counting the digits from the beginning of a number. In trailing-zero format, it is reversed. The number specified is in the BLU unit. The data format "3.4" implies that a BLU equals 0.0001 in. (fourth decimal place). By using the data from preceding example, the leading-zero program would be
X.0112 Y002275 Z00l
In the trailing-zero format, the program looks like X.11200 Y22750 Z
For circular motion, more information is needed. A circular are is defined by the start and end points, the center, and the direction. Because the start point is always the current tool position, only the end point, the circle center. And the direction needs to be specified. I, J. and K words are used to specify the center. Usually, circular interpolation works only on either X- Y, Y-Z. or X-Z planes. When interpolating a circular are on the X - Y plane, the I word provides the X. coordinate value of the circle center and the J word provides the Y coordinate value. X and Y words specify the end point. Clockwise or counterclockwise motions me specified by the G-code (G02 versus G03). There are many variations in circular interpolation programming. Each NC controller vendor has its own form and formal. Also they can depend on the combination of absolute or incremental, full-circle on or off modes. The following example is based on absolute programming with full circle on for a hypothetical controller.
F-Code. The F-code specifics the feed speed of the tool motion. It is the relative speed between the cutting tool and the work piece. It is typically specified in in./min (ipm). From a machinability data handbook, feed is given in in./rev (ipr). A conversion has to be done either by hand or on-hoard the controller. Some Controllers offer a G-code that specifies the ipr programming mode. When the ipr programming mode is used, the tool diameter and the number of teeth must he specified by the operator. The F-code must be given before G01, G02 or G03 can be used. Feed speed can be changed frequently in a program, as needed. When an F-code is present in a block, it takes effect immediately. To specify a 6.00- ipm feed speed for the cutting motion in Figure 10.7, one would program.
N0100 G02 X7.000 Y2.000 15.000 .: .O( I ,c,: OIJ
S-Code. The S-code is the cutting-speed code. Cutting speed is the specification of the relative surface speed of the cutting edge with respect to the work piece. It is the result of the tool (or workpiece in turning) rotation. Therefore, it is programmed in rpm. The Machinability Data Handbook (Machinability Data Center, 1980 ) gives these values in surface feet per minute (sfpm), and conversion is required before programming is done. When a controller is equipped with a sfpm programming option, the operator must specify the tool diameter. The S-code is specified before the spindle is turned on The S-code does not turn on the spindle. The spindle is turned on by an M-code. To specify a 1000-rpm spindle speed, the. program block is
N0010 S
I-code. The I-code is used to specify the tool number. It is used only when an automatic tool changer is present. It specifies the stot number on the tool magazine in which the next tool is located. Actual tool change does not occur until a tool-change M-code is specified. R –Code. The R -code is used for cycle parameter. When a drill cycle is specified, one must give a clearance height (R plane) (see- Figure 10.8). The R-code is used to specify this clearance height. In Figure 10.8, the drill cycle consists of five operations:
- Rapid to location (1.2.2).
- Rapid down to the R plane.
- Feed to the x point. the bottom of the hole.
- Operation at the bottom of the hole, for example, dwelling.
- Rapid or feed to either the R plane or the initial height. The cycle may be programmed in one block, such as (cycle programming is vendor-specific)
N0010. G81 X1.000 Y2.000 Z0.000 R 1.
M-Code. The M-code is called the miscellaneous word and is used 10 control miscellaneous functions of the machine. Such functions include turn the spindle on/off, start/stop the machine, turn on/off the coolant, change the tool, and rewind the program (tape) (Table 10.2). M00 and M01 both stops the machine in the middle of a program. M01 is effective only when the optional stop button on the control panel is depressed. The program can be resumed through the control panel. M02 marks the end of the program. M03 turns on the spindle (clockwise). The spindle rpm must be specified in the same line or in a previous line. M04 is Similar to M03, except it turns the spindle on counterclockwise. M05 turns off the spindle. M06 signals the tool-change operation. On a machine equipped with an automatic tool changer, it stops the spindle, retracts the spindle to the tool-change position, and then changes the tool to the one specified in the T -code. M07 and M08 turn on different modes of coolant. MO9 turns off the coolant. M30 marks the end of the tape. It stops the spindle and rewinds the program (tape). On some controllers, more than one M-code is allowed in the same block.
TABLE 10.2 M-CODES M00 Program stop M06 Tool change M01 Optional stop M07 Flood coolant on M02 End of program M08 Mist coolant on M03 Spindle CW M09 Coolant off M04 Spindle CCW M30 End of tape
10.2 MANUAL PART PROGRAMMING
10.2.1 Part Programs In manual part programming, the machining instructions are recorded on a document, called a part-program manuscript (see Figure 10.9) by the part programmer. The manuscript is essentially on ordered list of program blocks. The manuscript is other entered as a computer file or punched on a paper tape. Each symbol on the numeric or special characters, corresponds to a perforation(s)on the tape (or magnetic bit pattern on a disk) and is referred to as a character. Each line: of the manuscript is equivalent to a block on the: punched tap and is followed by an EOB (end-of-block) character. When it is stored in a computer file, a tape-image format is used.