Comput. & Indus. Engng Vol. 6, No. 2, pp. 159-168, 1982 0360-83521821020159-10503.0010 Printed in Great Britain. Pergamon Press Ltd.

A N A U T O M A T E D C O D I N G A N D P R O C E S S P L A N N I N G S Y S T E M U S I N G A D E C PDP-10

CHARLES EMERSON Westinghouse Electric Corporation, Pittsburgh, PA 15238, U.S.A.

and

INYONG HAM Department of Industrial Engineering, The Pennsylvania State University, University Park, PA 16802,

U.S.A.

(Received in revised [orm February 1981)

Abstraet--A semi-generative system has been developed to perform automated process planning using DEC PDP-10 computer. The proposed Automated Coding and Process Selection (ACAPS) package makes use of Group Technology concepts to interactively assign a code number to a part, generate a machining sequence, form part families, and specify operation details for a manufacturing route sheet. Primary consideration is given to rotational components,' though others can be accommodated. ACAPS is designed to lead the planner step-by-step toward a complete process plan, with a minimum of confusion. The program could be adapted to any computer system having FORTRAN capabilities.

1. INTRODUCTION One very crucial task essential in the manufacturing environment, largely performed by manual means today, is the process planning function. For a given part to be fabricated, a document is required specifying the sequence of operations, complete with all process variables, parameters and operator instructions. This document, frequently referred to as a Manu[acturing Route Sheet, or an Operation Sheet, is the task of the process planner.

A process palnner is expected to specify an optimal production method, based on available technology, highest efficiency, lowest cost, acceptable quality, and required standardization[l]. Hopefully, a good process plan will result, exhibiting several characteristics [2]:

"(1) By following the plan, the product will be produced in the desired quantity and at the expected quality level.

(2) There will be a minimum number of set-ups, and a minimum expenditure of resources. (3) Transportation and in-process inventory will be minimal. (4) Documentation will be easy to read and understand. (5) Operating parameters will be realistic. (6) The plan will be used by the shop. (7) Similar parts will utilize common tooling insofar as is feasible". It is clear that overall shop productivity is greatly affected by the quality of the process

planning function. The plans produced affect many other areas in the manufacturing organiza- tion, and if poorly done, the performance of the entire manufacturing concern will suffer.

The "goodness" of plans produced by a planner is heavily dependent on his own personal knowledge and experience, and is not easily learned. Traditionally, the task has been performed by men, many of whom have had much experience on the shop floor, possibly as machinists themselves.

Many problems surface here. In recent years, industry has seen a decline in the number of available process planners. Many are reaching retirement age, with fewer qualified people to replace them. In addition, with today's rapidly changing technology, it is difficult for planners to keep abreast of new process technology developments. Also, there is the problem of dupli- cation. How is the relatively inexperienced planner to know that planning may previously have been done for a similar, or even identical part?

Finally, considering the myriad process alternatives and parameters involved, how can it be guaranteed that the plan developed is the best plan, minimizing cost and/or production time?

159

160 C. EMERSON and 1. HAM

These and other related issues suggest the application of a computer to perform some, if not all, of the planner's task.

2. C O M P U T E R S AND P R O C E S S P L A N N I N G

The concept of Computer-Aided Process Planning (CAPP) has been evolving and growing in acceptance over the last decade. Many useful schemes have been developed to improve the process planning function. All schemes conceived to date may be placed along a continuum, based on the amount of user interaction required. The simplest type of CAPP system, termed a "variant" system, lies at one end of the continuum, and requires a great amount of user input and decision-making. At the opposite extreme of the continuum lie those CAPP schemes which are termed "generative", where the computer using decision logic and optimization formulas produces an optimal process plan, given the paws design data from an engineering drawing. Ideally, even this latter data will have come from a graphical representation of the part resident within the computer's data base.

It must be said at this point that the purely generative CAPP system has yet to be developed. This is due to a technological lack in several areas at present. First, the generative system requires as input a complete description of the part to be planned, which should be available from a Computer-Aided Design (CAD) representation of the part. However, to date, the translation of CAD graphical code into information useful to the CAPP function has not been effectively implemented for the general case. Other areas of lack which hamper effort toward a generative system are in the realm of software to perform process selection and sequencing, cutting conditions optimization, selection of tooling and materials, a comprehensive manufacturing technology data base, etc.

Until such time as a generative system emerges, much effort has gone into "semi- generative" CAPP systems. These serve to reduce user interaction through such features as standard operation sequences Ill, decision tables[3] and mathematical formulas[4]. These schemes are not completely generative, but they can be extremely useful in terms of time and cost savings in the manufacturing environment.

3 THE ACAPS SYSTEM

A semi-generative CAPP scheme, Automated Coding and Process Selection (ACAPS), has been developed which integrates many of the recent advances in the realm of automated planning. It is an exploratory package which operates in a time-sharing environment with the user supplying input interactively from a terminal. ACAPS is solidly based on the principles of Group Technology (GT), the philosophy which "identifies and exploits the underlying sameness of parts"[5] for the purposes of improving productivity. Parts are assigned a GT code number, based on such characteristics as geometry, size, material and processing requirements. This number serves to identify a Part Family to which each part belongs. Family membership then dictates many of the subsequent planning steps.

Software ACAPS has a modular structure, as seen in the flow diagram of Fig. 1. It is written entirely

in ANSI FORTRAN IV, with the exception of the terminal I/O routines and file control statements peculiar to the TOPS-10 operating system.

Hardware ACAPS has been developed and implemented using a DEC PDP-10 mainframe computer.

The program requires 50 K words of core, hard disk storage, a line printer and a terminal (preferably a CRT).

ACAPS executive The process planning task is performed in several separate stages. At the outset of the

program, as well as at the completion of each stage, the user is returned to the Executive to select the next planning step. Each of these steps will now be described briefly.

(a) ACAPS coding. Process planning done by ACAPS is based on part geometry, overall dimensions and material sepcification. These items can be conveniently represented using a

An automated coding and process planning system using a DEC PDP-10 161

Group Technology code number (a 21-digit code developed to contain the information neces- sary to the process planning task). Therefore, the first phase in the development of an ACAPS process plan is to interactively assign a code number to the part, which represents the part's design and manufacturing characteristics.

Interactive coding of parts is quite easy using the ACAPS system. User responses to queries are either "Y" (Yes), "N" (No) or a number, such as a dimension, in either English or metric units. The user is advised of the current column position after each digit is completed, and is given the final code number at the conclusion of the 21 digits. If errors are made, a backtracking capability is available throughout. After coding a part, the options are then presented to code more parts or quit, and to save or delete the part code just generated. The code may be immediately placed into its proper part family, or simply retained for later batch processing.

(b) Part .family grouping. Families of parts are formed in the ACAPS system based on similarity of processing requirements. Examination of the GT code serves as the basis for selecting appropriate pieces of manufacturing equipment. For instance, a shaft three inches long and one-half inch in diameter will require a turning operation, but certainly not on the same lathe as a 3 ft shaft, eight inches in diameter.

The following algorithm is used by the computer to allocate processing operations (see Fig. 2):

• Select part feature requiring process. • Examine part feature complexity. • Check process capacity. • Repeat the above for each part feature. • Allocate part to appropriate part family.

Acs CODING

CODED

I ACAPS EXECUTIVE

PART FAMILY

FORMATION

2 I

, t PRIMARY PROCESS SELECTION

4 _ _

PROCESS I I OP 'TION ] SELECTION AND ~__.__~ SHEET | PLANNING}

I eR°cESS I I DATA I Q 2 )

T I - -

Fig. 1. ACAPS flow diagram.

I FEATURE MASK H COMP~ITY

MASK CAPACITY MASK

(i) (ii) (iii) (iv) (v)

Fig. 2. Part family grouping scheme.

162 C. EMEI~SOg and I. HAM

A data base of typical machine tools is used to match against part dimensions, ensuring that process capacities are not exceeded.

Each iteration through the above procedure produces at most one machine assignment in the operation sequence. Examination of the code proceeds resulting in a workable sequence of machining oeprations.

Exercising of the ACAPS Part Family Grouping module results in the formation of part families; each having a unique operation sequence associated with them. This is illustrated in Figs. 3 and 4.

The ACAPS Part Family Grouping Module may be employed in two ways. It may be invoked to batch process a number of coded parts, placing them into their respective families, and creating new families if no match is found. And second, the module may be used to insert a single part (the one just coded) into its proper part family. It returns the part family number to the user, and the corresponding operation sequence to the planning modules to be executed later.

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An automated coding and process planning system using a DEC PDP-10 163

(c) Primary process selection. This module performs a cost analysis of basic processes involved in producing the general configuration of the part to be fabricated. For metallic parts these processes include casting, forging and pressing processes, extrusions, powdered metals, weldments, roll forming and rough machining from stock. Analysis for plastic parts is also available, considering such processes as compression molding, injection molding, thermoform- ing, blow molding, casting, extrusion, transfer molding and machining.

The module is built around the technique developed by Niebel[6, 7] for the selection of primary forming processes, using analytical techniques to evaluate cost through the first operation. Processes are first of all eliminated from consideration based on: (a) the part material, (b) its geometry, (c) its size or weight, and (d) the quantity to be produced. For instance, constraint (a) would eliminate forging from consideration if the part's geometry is complex; and die casting would never be done for a small lot size, by constriant (d). Once the constraints are passed, the remaining processes are output as alternatives in ascending order of relative cost, along with an estimate of average production time for the lot, as seen in Fig. 5.

(d) Process selection and planning. During this phase of ACAPS the actual operation sheet is produced. Process selection and planning are performed in ACAPS on the basis of geometri- cal features. The operation sequence for the current part family serves to assist the planner in selecting the next feature to be processed by simply indicating the point at which a new operation is to begin at a different work center.

The geometric features handled by ACAPS at present are: holes, slots or grooves, plane surfaces and turned surfaces. The menu shown to the user at the completion of each feature is given in Fig. 6. Gears and splines, which require manual planning presently, are included for future development work. Comments may be added to the operation sheet directly from the keyboard as desired.

Once a feature has been selected, the planning task requires that certain surface descriptors be supplied by the user. These are necessary in order for ACAPS to perform process selection, feed and speed calculations, tooling specifications and cutting time estimation. The descriptors required vary according to the surface type specified.

Holes. Holes are described in terms of the number of diameters to be produced, as well as the general shape of the hole, (e.g. simple cylindrical, tapered, threaded, with keyway, etc.). Each diameter is then isolated and the user is asked to supply additional information such as:

--diameter and tolerances --depth of this diameter --surface finish (CLA) --form geometry specifications (e.g. straightness, roundness, etc.) --any fillets or chamfers at top or bottom of this diameter --threads per inch, if threaded, and thread tolerances --indicate if hole wall is interrupted. Once this information is complete for each diameter in the hole, as well as some general

data regarding hardness, coring and spot facing requirements, ACAPS will automatically select and plan the processes to produce the entire hole. Output includes operation descriptions, tooling recommendations and optimal feeds and speeds.

Slots and grooves. Description of slots or grooves involves the following information: --general shape (e.g. dovetail, Y or T-slot, stright, etc.) --cutter path (linear, circular, etc.) --open or blind end(s) --dimensions and tolerances --bottom configuration (flat, angular or radiused) --surface finish (CLA) --form geometry specifications (e.g. parallelism, flatness, etc.) --cutter diameter (optional). ACAPS then utilizes this data to select the optimize milling processes which will produce

this feature.

Plane surfaces. The description of plane surfaces is similar to that for slots and grooves, requiring the user to supply:

164 C. EMERSON and l. H~M

i •

• PRIHARY PROCESS * Q •

• SELECTION NODULE *

PART NAHE: GUIDE PLATE DRAUlNC ~ D - : 22 CURRENT CODE N O . : 3 1 5 6 0 1 1 1 0 0 0 0 0 2 3 0 0 0 0 0 5 HATERIA~: FERROUS

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An automated coding and process planning system using a DEC PDP-10 165

NEXT FEATURE OR OPERATION:

I - HOLE

2 - PLANE SIII~FACE

3 - SLOT OR C, ROOVE

4 - TURNED SURFACE

.5 - G E A R

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I0 - QUIT PLANNING

Fig. 6. Planning menu.

--general shape (e.g. face, slab, form, etc.) --curvature (flat, concave or convex) --dimensions --angle or radius produced --surface finish (CLA) --form geometry specifications --tool description (optional). Turned surfaces. ACAPS will handle external turning operations such as straight and taper

turning, facing, forming and cutoffs. The planner is asked to supply for these cuts: --tool material (HSS or carbide) --cut type (rough, semi-finish or finish) --critical factor: cost or time --length of cut --starting dimension --final dimension (this cut) --tolerances (finish cuts only) --surface finish (finish cuts only) --tool width (cutoff and forming only) --depth of cut (cutoff and forming only). Through a process of exhaustive enumeration of all lbossible combinations of feed, speed

and depth of cut available on the machine being utilized, the best 100 sets are ranked in order of increasing cost or production time, as specified by the user. Many are eliminated from consideration because they do not meet surface finish, depth of cut or horsepower requirements [8].

Having tested and ranked the best 100 combinations of cutting parameters, ACAPS will advise the user of the best choice found. The planner may then review additional alternatives at his terminal. Information is given regarding feed, speed, depth of cut, number of passes, expected tool life, metal removal rate, horsepower requirements, production rate and cost per piece for each combination viewed as shown in Fig. 7. Final selection for the operation sheet is left to the user.

Select new machine. This indicates to ACAPS that all processing on the current machine is complete, and that another machine is to be selected. ACAPS will respond with the next machine in the file from the part's family operation sequence, and ask for user confirmation. If given, this becomes the next machine on which to plan processes. Otherwise, the user may select an alternate from the keyboard. (If the end of the family operation sequence is reached, manual selection is required from that point.)

(e) Planning example. Parts involving the above-mentioned features can quickly be planned using ACAPS. The sample part of Fig. 8 was planned, resulting in the Operation Sheet of Fig. 9. The part was first coded using the ACAPS Coding module, resulting in the GT code number shown in the header of Fig. 9. Part family grouping resulted in a family operation sequence of 2-41-50, referring to Work Centers in the shop. Further palnning gave the turning, drilling and boring operations illustrated on the Operation Sheet.

166 C. EMERSON and i. HAM

q l N I q l l M COST COH~ITION REST q COMBINATIONS

REMOVAL HORSE TIME COST RANR TOOL RATE IN PO~ER REQUIRED PER

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CUTTING DEPTH NO. RPM TO RANK SPEED FEED OF OF START

INTENDED CUT PASS WITH (FPM) (IPR) (IN) REO. (RPM)

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6 2 8 2 6 . 2 6 2 5 7 . 7 9 2 2 l i . 6 9 5 . 1 7 2 0 . 5 1 7 1 1 . 6 0 1 7 7 3323.8561 7.4222 11.13 5.175 O.517 11.5944 $ 3 9 0 9 . 0 5 6 3 7 . 0 6 9 7 1 0 . 6 0 5 . 1 7 8 0 . 5 1 8 1 1 . 5 8 6 5 9 4597.2873 6.7340 1 0 . 1 0 5 . 1 ~ 2 O.519 11.5778

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4. SUMMARY

The ACAPS system has been developed as an exploratory scheme in the realm of semi-generative process planning. It has succeeded in producing satisfactory process plans for the operations which it considers. ACAPS exhibits several advantages over existing CAPP packages, none of which has all of the capabilities of ACAPS:

(1) Part coding is performed interactively, with no manual handling of code numbers. (2) ACAPS automates the formation of part families, expanding its own data base as more

parts are coded. (3) A sequence of machining operations is generated by ACAPS, based on a part's GT code

number. (4) ACAPS performs an economic analysis of primary forming process alternatives, provi-

ding quantitative data on which to base the "make-or-buy" decision. (5) Secondary machining operations are planned generatively, resulting in optimized cutting

conditions for minimum machining time or cost per piece. (6) ACAPS considers the human factor throughout, thus providing the user with simplicity

of operation and minimal confusion and chance of error. ACAPS is still an exploratory package in the realm of Automated Process Planning, and has

not yet been implemented in a production environment. Further work is being carried on with it, and the package is available to seriously interested parties from:

Dr. Inyong Ham Dept. of Industrial & Mgt. Systems Engineering The Pennsylvania State University 207 Hammond Building University Park, PA 16802, U.S.A.

REFERENCES 1. CAM-I, Inc. CAPP 2.1 User's Manual. No. PS-76-PPP-03, CAM-I, Inc., Arlington, TX, 1976. 2. D. K. Allen, Generative Process Planning Using the DCLASS Information System. Brigham Young University, Provo,

Utah (1979). 3. Cincinnati Milacron, Inc. Generative Process Planning: A Proposal to the Process Planning Project. CAM-I, Inc.,

Arlington, Texas (n.d.). 4. R. A. Wysk, M. M. Barash and C. L. Moodie, The Optimal Planning of Computerized Manufacturing Systems; Unit

Machine Operations; Part 2; APPAS--Automated Process Selection and Planning Program. Purdue University, Lafayette, Indiana (1977).

5. I. Ham, Introduction to group technology. SME Tech. Paper MMR-76-03, Feb. 1976. 6. B. W. Niebel, An analytical technique for the selection of manufacturing operations. J. Industr. Engng 598-603 (1966). 7. B. W. Niebel, Fortran program for selection of primary forming processes. U.S. Army Management Engineering

Training Agency (n.d.). 8. I. Ham, Computer Optimization of Machining Conditions for Shop Production, Engineering Bulletin B-105 (84 pp.).

College of Engineering, The Pennsylvania State University (May 1972).