Feature-Based Machining using Macro

Abstract

This paper presents an on-going research work on the implementation of feature-based machining via macro programming. Repetitive machining features such as holes, slots, pockets etc can readily be encapsulated in macros. Each macro consists of methods on how to machine the shape as defined by the feature. The macro programming technique comprises of a main program and subprograms. The main program allows user to select several subprograms that contain features and define their important parameters. With macros, complex machining routines can be implemented easily and no post processor is required. A case study on machining of a part that comprised of planar face, hole and pocket features using the macro programming technique was carried out. It is envisaged that the macro programming technique can be extended to other feature-based machining fields such as the newly developed STEP-NC domain.

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Abstract—This paper presents an on-going research work on the
implementation of feature-based machining via macro programming.
Repetitive machining features such as holes, slots, pockets etc can
readily be encapsulated in macros. Each macro consists of methods
on how to machine the shape as defined by the feature. The macro
programming technique comprises of a main program and
subprograms. The main program allows user to select several
subprograms that contain features and define their important
parameters. With macros, complex machining routines can be
implemented easily and no post processor is required. A case study
on machining of a part that comprised of planar face, hole and pocket
features using the macro programming technique was carried out. It
is envisaged that the macro programming technique can be extended
to other feature-based machining fields such as the newly developed
STEP-NC domain.
Keywords—Feature-based machining, CNC, Macro, STEP-NC.
I. INTRODUCTION
machining feature can be defined as a closed volume in
space such that upon completion of machining operation,
there shall be no material left in the feature. And at the same
time, there shall be no material removed outside the feature
[1]. Since a feature defines shape, faces and location of the
part, it can be easily revised and updated. In a nutshell,
features are not only describing shapes but also describe how
to produce those shapes using CNC machine [2].
Machining features have now been standardized [3] and an
object oriented methodology is used to define them. Because
of this, it is common to find that majority of current
commercial CAM systems are feature-based. A typical CAM
system converts design feature to machining features by
feature recognition [2] and extraction approaches. Ouyang &
Shen [2] proposed a three modules algorithm, namely design
feature, feature conversion and machining feature. The system
depends on finding of the inner link between independent,
composite and convex features. Thus for a given part with
design features, a CAM system will first identify the
machining features and automatically generate the standard
NC part program based on ISO 6983. Due to nature of the
current standard, the CAM generated part program can be very
long and occupy large memory space [4]. This paper deals
with an alternative method of implementing feature-based
machining using macro programming.
M. Razak is with Universiti Kuala Lumpur Malaysian Spanish Institute,
Kulim, 09000 Kedah, Malaysia (e-mail: alhapis@msi.unikl.edu.my).
A. Jusoh and A. Zakaria is with Universiti Kuala Lumpur Institute of
Product Design and Manufacturing, 119 Jalan 7/91, Tmn Shamelin Perkasa,
56100 Kuala Lumpur, Malaysia (e-mail: abrahim@iprom.unikl.edu.my,
dzakaria@iprom.unikl.edu.my).
II. FEATURE-BASED MACHINING
Most of recent papers on feature-based machining primarily
focus on new standards ISO 14649 (data model for
computerized numerical control) and ISO 10303-238
(application interpreted model for numerical controllers). Both
are collectively known as STEP-NC [3]. In view of the fact
that the two standards were developed by different committees
[3], there are major differences in their implementation. While
the former supports only one kind of data exchange from
CAM to CNC, the later can communicate all the information
required to manufacture a product across the supply chain
from design to manufacture. However ISO 14649 has an edge
over ISO 10303-238 in terms of program size and ease of
programming. An effort is being carried out to integrate both
standards into one [3].
Machining feature as defined in ISO 14649 ARM
(application reference model) is shown in Fig.1. Because of its
object oriented structure, C++ programming language is
normally used in its proposed STEP-NC part program
implementation. One of the serious drawbacks found in the
proposed technique is the lack of feedback ability from user to
designer. Also its complex entity cross-referencing makes the
part program not human readable. Radical approach of STEP-
NC requires a totally new kind of CNC controller. Hence
current implementation on existing machine uses ‘plug and
play’ method where the final STEP-NC codes have to be
converted to the conventional NC codes. This paper proposes
an alternative method to implement feature-based machining
using macro technique, and by extension of its adaptation to
implement STEP-NC machining, without the need of
machine-specific post-processor.
Fig. 1 STEP-NC ARM
III. MACRO
Custom macro or user macro approach adopted in this paper
is specifically referred to Fanuc or Fanuc compliant CNC
M. Razak, A. Jusoh, A. Zakaria
Feature-Based Machining using Macro
A
World Academy of Science, Engineering and Technology
International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering Vol:6, No:8, 2012
1107International Scholarly and Scientific Research & Innovation 6(8) 2012 scholar.waset.org/1999.7/12780
International Science Index, Mathematical and Computational Sciences Vol:6, No:8, 2012 waset.org/Publication/12780

controller. For many years, it has been ignored by both
industry and academia [4]. In general, it is similar to
subroutine except it has additional control features [5]. These
features allow macros to be programmed in similar manner as
other high level language programming such as VB or C.
More importantly, the user may include elements of
intelligence in decision making by using IF, THEN or WHILE
functions.
In the current standard of ISO 6983 (also known as ‘G-
code’), NC code is produced according to the path of cutter
location data (CL) with respect to the machine axes [3]. In
macro, similar to the high level programming language, users
have the ability to control the variables [5]. This method is
powerful and useful in improving the programming efficiency
[4]. Unlike the normal NC program, macro structure offers
solutions for much more sophisticated part machining [6].
There are two programs involved in this type of programming
technique. They are the main macro program and macro
subprogram. Macro can be called not only by the main
program, but also by any other subprogram or macro as well
[6]. The normal subprogram always uses fixed data, which
values cannot be changed. On the other hand, Macro uses
variable data that can be changed very quickly [6]. Therefore,
this technique is appropriate to be employed in feature-based
machining [7].
IV. CONCEPT OF IMPLEMENTATION
Fig. 2 Concept of IMS
In this research, a new machining system called Intelligent
Machining System (IMS) is being developed. The concept of
implementation for IMS is shown in Fig.2, which comprises of
two modules. The first module contains machining function
routines such as determination of machining conditions,
selection of machining cycles and machining strategies written
in macros resided in the machine memory. The second module
is a part program generator where user defined workpiece
geometry and features are input via GUI (graphical user
interface). Final part program generated will consist of process
plan and machining steps. In the operation, this part program
will interact with the contents of the machine memory via
macro call commands.
The machining parameters can be retrieved and stored by
means of global variables of the macro. This advantage
enables user to view the machining history.
Fig. 3 Example of how macros are implemented
In the macro approach, macro program number can
represent a function. In the example as shown in Fig.3, there
are two strategies for pocketing. They are spiral and zigzag.
These two strategies are represented by a macro program
number. Similarly, speed and feedrate calculations can be
represented by a macro program number.
Fig. 4 Example of workpiece
An example from ISO 14649-11 [8] as shown in Fig.4,
comprised of three features namely planar face, hole, and
pocket has been selected as a case study. To produce the part,
IMS will call macros for cutting operation according to
workplan steps. In this case, it starts with planar face and
continues with hole, and finally the pocket.
The flowchart of macro execution of machining feature is
shown in Fig.5. The system will first determine the type of
feature to be machined. Then, it will call macros for executing
the operation. If there is more than one workingstep to
produce the feature, specific macros are called according to
the sequence. After the feature is completed, the system will
check for the next feature.
machining_operation
strategy
technologyO0141
_
Speed&
feedrate
O0146
_
Spiral
pocket
O0148
_
Zigzag
pocket
List of Macros
Planar
Pocket
Hole
Technology
Strategy
Part Program
(workpiece)
(workplan)
(workingstep)
GUI
World Academy of Science, Engineering and Technology
International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering Vol:6, No:8, 2012
1108International Scholarly and Scientific Research & Innovation 6(8) 2012 scholar.waset.org/1999.7/12780
International Science Index, Mathematical and Computational Sciences Vol:6, No:8, 2012 waset.org/Publication/12780

Fig. 5 Macro execution of machining feature
In macro program, variable numbers represent specific
information declared by user or referred to earlier part
programs. For instance, #1 is representing how many features
involved and #2 refers to what feature to be machined. Every
single function or operation can be written separately using
macros. For example, if the main program calls program
number 0100 for workingstep 1, the system will then find
program number 0100 to be executed.
To generate a new program for different design, the user
needs only to redefine the variables in the macro. As there is
no new program added, the memory used in the controller
remains more or less constant.
V. METHODOLOGY
The example given in the ISO 14649-11 [8] has been used
as the case study (as shown in Fig.4). A process planning for
the part is carried out as a prerequisite before the actual
machining. The origin point is clearly shown in this example.
By applying the developed IMS, an experiment was carried
out on a chemical wood workpiece to confirm the IMS
functionality. High speed steel (HSS) cutting tools were used
in this study. Basically, all dimensions in the example were
utilized for graphical simulation. Fanuc Robodrill Į-T14ȓFse
machine with Fanuc Series 31ȓ-Model-A controller was used
for this purpose. Single machining process for planar, hole,
zigzag rectangular pocket and spiral rectangular pocket were
carried out. Subsequently combination of all features
machining was carried out twice: one was for pocket with
zigzag strategy and the other for spiral.
VI. RESULT
%
O0140(MAIN PROGRAM IMS)
(Blank Definition)
G1902B100.D120.H50.I0.J0.K0.
(user input: start)
#1=3(NO_FEATURE)
#2=1(FEATURE_i/START FEATURE)
#3=1(WORKPIECE MATERIAL)(M)
(Feature 1: PLANAR)
#4=100(WORKPIECE LENGTH, I)(A)
#5=120(WORKPIECE WIDTH, J)(B)
#6=2(PLANAR_HIGH TO CUT, K)(C)
#7=1(PLANAR DEPTH OF CUT)(U)
(Feature 2: HOLE)
#520=20.(HOLE LOCATION, X)(X)
#521=60.(HOLE LOCATION, Y)(Y)
#522=30.(HOLE DEPTH)(Z)
#523=2(DRILLING STRATEGY)(S)
(Feature 3 : POCKET)
#9=2(POCKET STRATEGY)(1=SPIRAL, 2=ZIGZAG)
#527=45.(POCKET LOCATION, X)(X)
#528=30.(POCKET LOCATION, Y)(Y)
#529=50(POCKET LENGTH, I)(I)
#530=80(POCKET WIDTH, J)(J)
#531=30(POCKET DEPTH)(K)
#532=20(ENDMILL DIAMETER)(D)
#533=1(POCKET DEPTH OF CUT)(V)
(user input : end))
Yes
No
Yes
No
Machining
feature
Start
Workin
g
ste
p
3
Workin
g
ste
p
2
Workin
g
ste
p
1
Finish
Feature
1
Any
other
feature?
World Academy of Science, Engineering and Technology
International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering Vol:6, No:8, 2012
1109International Scholarly and Scientific Research & Innovation 6(8) 2012 scholar.waset.org/1999.7/12780
International Science Index, Mathematical and Computational Sciences Vol:6, No:8, 2012 waset.org/Publication/12780

IF[#1EQ0]GOTO9020
IF[#1GT3]GOTO9021
IF[#2EQ0]GOTO9022
IF[#2GT3]GOTO9023
IF[#3EQ0]GOTO9024
IF[#3GT2]GOTO9025
#130=#1(NO_FEATURE)
#131=#2(FEATURE_i)
#132=#9(POCKET STRATEGY)
#510=[0-#6](Z-OFFSET AFTER PLANAR CUT)
WHILE[#131LE#130]DO1
IF[#131EQ1]GOTO1(PLANAR)
IF[#131EQ2]GOTO2(HOLE)
IF[#131EQ3]GOTO3(POCKET)
(workingstep : PLANAR))
N1G65P0142A#4B#5C#6D#8U#7M#3
GOTO20
(workingstep : HOLE)
N2G65P0144X#520Y#521Z#522S#523M#3A#524B#525C#526
GOTO20
(workingstep: POCKET )
N3(SELECT POCKET STRATEGY)
IF[#132EQ1]GOTO10(SPIRAL)
IF[#132EQ2]GOTO11(ZIGZAG)
(SPIRAL)
N10G65P0146X#527Y#528I#529J#530K#531D#532V#533W#534M#3
GOTO20
(ZIG_ZAG)
N11G65P0148X#527Y#528I#529J#530K#531D#532V#533W#534M#3(POCKET_
ZIGZAG)
N20#131=#131+1
END1
GOTO100
(ERROR MESSAGES)
N9020#3000=120(PLEASE INPUT NO. OF FEATURE)
N9021#3000=121(EXCEED NO. OF FEATURES)
N9022#3000=122(SELECT START FEATURE)
N9023#3000=123(WRONG FEATURE CODE)
N9024#3000=124(SELECT MATERIAL 1 OR 2)
N9025#3000=125(WRONG MATERIAL CODE INPUT)
N100M30
%
Fig. 6 IMS main program
The example of main program of IMS is shown in Fig.6.
From the observation during the machining process and
inspection of finished product, it was verified that IMS has
met its expectations. All the features were produced with
correct dimensions. Fig.7 and 8 shows the graphic animation
on CNC controller and finished part.
Fig. 7 Simulation on CNC controller
Fig. 8 Front view simulation
Memory size on the controller for the whole system is only
16 Kbytes. With this system, the program’s memory size
remain constant regardless the changes of feature size. This is
due to the fact that the feature size changes can be done by
simply redefining the feature variables.
VII. CONCLUSION
The IMS has successfully machined the features using the
macro programming technique, without the need of machine-
World Academy of Science, Engineering and Technology
International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering Vol:6, No:8, 2012
1110International Scholarly and Scientific Research & Innovation 6(8) 2012 scholar.waset.org/1999.7/12780
International Science Index, Mathematical and Computational Sciences Vol:6, No:8, 2012 waset.org/Publication/12780

specific post-processor. In term of part accuracy, there was no
difference between this system and the normal standard or
commercial CAM system. The difference in the accuracy of
the machining results would depend on the machine and tool
conditions. As can be seen in Fig. 6, the macro program is
simple, concise and human readable. A simple interactive GUI
can now be developed to automatically generate the part
program. With the macro technique, user can expect
comparatively much smaller program size compared to the
CAM generated NC, and also with the ease of implementation.
The ability to record changes made during the actual
machining process is distinct advantage of the macro. It is
envisaged that the macro programming technique can be
extended to other feature-based machining fields such as the
newly developed STEP-NC domain. In view of absence of
hitherto new type of controller that can implement the STEP-
NC approach, the work in this research opens an exciting
opportunity to venture into. Contingent to the availability of
the new STEP-compliant controller, this approach is more
practical and a way forward in implementing the STEP-NC
without the need to disrupt the current entrenched G-code
system.
ACKNOWLEDGMENT
The authors acknowledge Universiti Kuala Lumpur for
funding this research with Short Term Research Grant (STRG)
and the technical support from UniKL Institute of Product
Design and Manufacturing.
REFERENCES
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[3] X.W. Xu and S.T. Newman, “Making CNC machine tools more open,
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[9] ISO/FDIS 14649-10: 2002, Data Model for Computer Numerical
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World Academy of Science, Engineering and Technology
International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering Vol:6, No:8, 2012
1111International Scholarly and Scientific Research & Innovation 6(8) 2012 scholar.waset.org/1999.7/12780
International Science Index, Mathematical and Computational Sciences Vol:6, No:8, 2012 waset.org/Publication/12780