Wzmii u08 Loesung Brs English

Chair of Machine Tools

Prof. Dr.-Ing. Christian Brecher

Exercise 8 Machine Tools II

Topic: Manual programming of NC machines

Assistant

responsible:

Dipl.-Ing. Sebastian Bauer

[email protected]

WZL, 53B R424

Tel.: 0241 / 80-28478

- Solution -

Manual programming of NC machines, WZM II

1

2 Exercise

2.1 Programming exercise

In order to manufacture a part (Fehler! Verweisquelle konnte nicht gefunden

werden.) on an NC lathe, a NC programme must be written. The lathe, tools, self-

centring chuck and clamping position are given.

15 25 15 15 10

Ø 4

0

Ø 5

0

Ø 1

00

60

60

190

Futter Spannbacken

M

R

W

Fig. 1: Technical drawing of the part

Two tools stored in position 1 and position 2 of a tool-changer shall be used for the

operation. Compensation value memories 6 and 7 are chosen for any tool length

compensations. Tool 1 is to be used for roughing and tool 2 for finishing. The tools

have no cutting-edge radius and are placed pre-adjusted in the tool carrier.

chuck yaw


2

Owing to the work material/tool material combination and the installed machine

power, a constant cutting speed of 100 m/min is to be used. In order to ensure good

chip formation, the decisive parameters for the chip cross-section have been chosen

as follows:

Depth-of-cut: a = 10 mm

Feed (roughing): s1 = 0.5 mm/rev.

Feed (finishing): s2 = 0.1 mm/rev.

The pre-processed blank has the following dimensions:

Diameter: D = 100 mm

Length: L = 80 mm

The finishing allowance is to be 1 mm.

The feed rate can be programmed only in mm/min. With absolute dimension pro-

gramming, the x-axis must be programmed in diameter values; with incremental di-

mensions, simple traverse displacements are entered in the x-axis.

Create the NC programme and fill out the coding sheets (see chapter 2.4).


3

2.2 Solution

Step 1

The allowance is removed in a series of longitudinal cuts (Fig. 1). Points 1—18 mark

the end points of the NC blocks with the tool movements.

15 25 15 15 10

20

5

starting point of theroughing operation(tool 1)

starting point of the finishing operation(tool 2)

12

3 4

56

7 8

910

1112

13

1415

1617

18

2 safety distance

z

x

Fig. 1: Cut division

Allowing for the maximum depth-of-cut of 10 mm and the finishing allowance of 1

mm, three cuts are needed for roughing and one cut for finishing.

The coordinate values for the first cut (1-2) are calculated as an example. Xs, and Zs

are the coordinates of the corresponding end-of-block point.


4

zs

40

r

b

h

26

50

xs

According to the drawing: mmr 24=

hmmxs

−= 50

bmmzs

−= 40

It may be stated that: 222bhr +=

22hrb −=

For the first step, taking mmah 10== , the result is:

mmmmb 817.21102422

=−=

mmmmmmx 4010502,1

=−=

mmbmmz 183.18402

=−=

For the second step, taking mmah 202 == :

mmmmb 266.13202422

=−=

mmx 306,5

=

mmz 734.266

=


5

Point x[mm] z[mm]

1 40 82

2 40 18.183

3 42 20

4 42 82

5 30 82

6 30 26.734

7 32 28

8 32 82

. 21 (finishing allowance) 82

. . .

Step 2

The technology values for the speed and feed rate are determined.

According to the task:

v = 100 m/min = const.

s1 = 0,5 mm/rev. (roughing)

s2 = 0,1 mm/rev. (finishing)

The following relationship obtains between the cutting speed, the turned part diame-

ter and the speed:

ndv π=

Using d

vn

π=

it follows, that for Step 1: min

139880

min100

1=

⋅=

mm

m

nπ

and for the feed rate: nsu =

min

13985.01

⋅= mmu


6

For the remaining steps, it follows that:

Cut Feed d [mm] n [min-1

] u [mm/min]

1 - 2 s1 80 398 199

5 - 6 s1 60 530 265

9 - 10 s1 42 758 379

10 - 11 s1 52 612 306

12 - 13 s1 100 318 159

14 - 15 s2 40 796 80

15 - 16 s2 50 637 64

17 - 18 s2 100 318 32

� S � F

Step 3

A zero shift is used to move the machine zero point M to the part zero point W. This

simplifies definition of the movement instructions, since the dimension data from the

part drawing can largely be transferred to the NC programme.

Generally speaking, there are two different methods of zero shifting.

The first uses instructions G53 to G59 and shifts the zero point starting from a refer-

ence point known to the control. A reference point in this sense could, for example,

be the machine zero point M or a previously defined part reference point W.

Example: G54 X0 Z60

Instruction G54, refers the part coordinate system to the machine zero point. The

machine coordinate system is shifted by a value of 0 mm in the x-axis and by a value

of 60 mm in the z-axis.


7

The second method of zero shifting is to set the actual value memory using instruc-

tion G92. The values for the current position are set in the memory and can therefore

be used to specify the part zero point indirectly.

If, for example, the carriage reference point F is at the reference point and if the dis-

tance of the reference point R from the part zero point W in the different axes (XWR,

ZWR) is known (60 mm in the X- and 130 mm in the Z-axis, Y=0), these values can

be set in the actual value memory and establish the position of the reference point in

relation to the part zero point.

Example: G92 X60 Z130

(Note: There is no need for zero shifting if the position of the tool at the beginning of

the machining operation is known and if all dimensions are programmed incremen-

tally.)1

Step 4

The NC programme is drafted and is encoded with the aid of the programming key

(see chap. 2.3).

1 It should be noted here that the use of these instructions often varies on different control systems. It

is, for example, possible that, when instruction G54 is invoked, the magnitude of the shift need not be

specified explicitly in the NC programme, but has already been communicated to the control before the

beginning of the operation. Instruction G54 will then only retrieve the saved values.


8

2.3 Programming key

Code Function and meaning

% Start of programme

: 1 to 9999 Main block N Block number /: Maskable main block

/N Maskable block

G 00 Rapid traverse 01 Linear interpolation 02 Clockwise circular interpolation 03 Counter-clockwise circular interpolation 33 Thread cutting

G � 04 Dwell time defined in ms at address X

G 17 Plane selection X-Y 15 Plane selection X-Z 19 Plane selection Y-Z

G 39 Corner correction for cutter radius path compensation

G 40 Cancel tool compensation 41 Tool path compensation left, tool left of part 42 Tool path compensation right, tool right of part

G 53 No zero shifting

G 54 Zero shifting 1 55 Zero shifting 2

G 70 Input system inches 71 Input system metrical

G 80 Cancel work cycle 81 to 89 Work cycles

G 90 Absolute dimension inputs 91 Incremental dimension inputs

G � 92 Set actual value memory

G 94 Feed in mm/min at address F 95 Feed in mm/U at address F

D 1 to 99 Tool compensation number

X 0 to ± 99999,999 Displacement information in mm 1 to 99999,999 Dwell time in ms

Y 0 to ± 99999.999 Displacement information in mm

Z 0 to ± 99999,999 Displacement information in mm

4th

axis 0 to ± 99999,999 Displacement information in mm or degrees Possible addresses A, B, C, U, V, W

R 0 to n Parameters (e.g. for sub-routines)

I 0 to ± 99999,999 Interpolation parameters for X-axis for circular interpolation or 1 to 2000,000 Thread lead in mm

J 0 to ± 99999,999 Interpolation parameters for Y-axis for circular interpolation or 1 to 2000.000 Thread lead in mm

K 0 to ± 99999,999 Interpolation parameters for Z-axis for circular interpolation or 1 to 2000,000 Thread lead in mm

F 0 to Fmax Feed in mm/min or mm/U

S 0 to Smax Spindle speed in min-1

T 1 to 9999 Tool number

H 1 to 999 Auxiliary function

L 01 to 99 Number of sub-routine to be invoked

M � 00 Programmed stop, unconditional 01 Programmed stop, conditional 02 End of programme without rewind, in final block of programme 30 End of programme with rewind to start of programme, in last block of pro-

gramme

M 03 Spindle rotation clockwise 04 Spindle rotation counter-clockwise 05 Spindle stop

M 00 to 99 Extra functions, some freely programmable

( Start of comment ) End of comment

LF End of block

� only valid for one NC-block (current line of program), all others are modal


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2.4 Coding sheet

Comment Spindle Feed N G X Z I K F S T M

x[mm] z[mm] n[min-1

] u[mm/U]

1 Beginning of program %

2 Zero shift 60 130 N10 G92 X60 Z130

3 Spindle on, Tool 1 398 N20 G04 X2000 S398 T0106 M04

4 Abs. dimensioning N30 G90

5 Infeed R->1 ∅ 80 82 Eil N40 G00 X80 Z82

6 1st cut 1->2 ∅ 80 18,183 199 N50 G01 Z18,183 F199

7 Retract 2->3 ∅ 84 20 Eil N60 G00 X84 Z20

8 Move back 3->4 ∅ 84 82 530 Eil N70 Z82 S530

9 Infeed 4->5 ∅ 60 82 Eil N80 X60

10 2nd cut 5->6 ∅ 60 26,733 265 N90 G01 Z26,733 F265

11 Retract 6->7 ∅ 64 28 Eil N100 G00 X64 Z28

12 Move back 7->8 ∅ 64 82 758 Eil N110 Z82 S758

13 Infeed 8->9 ∅ 42 82 Eil N120 X42

14 Inc. dimensioning N130 G91

15 3rd cut 9->10 0 -12 379 N140 G01 Z-12 F379

16 Dwell time 612 N150 G04 X1000 S612

17 4th cut 10->11 5 -15 306 N160 G01 X5 Z-15 F306

18 5th cut 11->12 0 -15 N170 Z-15

1 Dwell time 318 N180 G04 X1000 S318

2 6th cut 12->13 24 -24 159 N190 G02 X24 Z-24 I24 F159


4 Return to R R ∅ 120 130 796 N210 G00 X120 Z130 S796

5 Tool change N220 T0207

6 Infeed R->14 ∅ 40 82 N230 X40 Z82

7 Inc. dimensioning N240 G91

8 7th cut 14->15 0 -12 80 N250 G01 Z-12 F80

9 Dwell time 637 N260 G04 X1000 S637

10 8th cut 15->16 5 -15 64 N270 G01 X5 Z-15 F64

11 9th cut 16->17 0 -15 N280 Z-15

12 Dwell time 318 N290 G04 X1000 S318

13 10th cut 17->18 25 -25 32 N300 G02 X25 Z-25 I25 F32


15 Return to R, Sp. off ∅ 120 130 N320 G00 X120 Z130 M05

16 End of program N330 M30

Movement

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