Preliminary planning of part manufacturing process

Abstract

The solution of manufacturing process planning is a complicated and combined problem therefore
it is necessary to divide the tasks into hierarchical levels. The first level of this hierarchy is called
preliminary process planning, which is the conceptual level of the planning process.
The most important tasks of preliminary process planning are (1) the preparation of process
planning of blank manufacturing, the part manufacturing and the assembly; (2) correction of the design
documents in the view point of manufacturability and assemblebility; (3) selection of manufacturing
system; (4) analysis of the manufacturing tasks and estimation of manufacturing cost and time data.
The aim of this article is to define these tasks, the connections and a possible process of
preliminary manufacturing process planning.

Full text

PERIODICA POLYTECHNICA SER. MECH. ENG. VOL. 43, NO. 2, PP. 97–106 (1999)
PRELIMINARY PLANNING OF PART MANUFACTURING
PROCESS
Balázs MIKÓ, Imre SZEGH and Lajos KUTROVÁCZ
Technical University of Budapest, Department of Manufacturing Engineering
H-1111 Budapest, Egry J. u. 1. E ép. II., Hungary
e-mail: surname@manuf.bme.hu
Received: March 31, 1999
Abstract
The solution of manufacturing process planning is a complicated and combined problem therefore
it is necessary to divide the tasks into hierarchical levels. The first level of this hierarchy is called
preliminary process planning, which is the conceptual level of the planning process.
The most important tasks of preliminary process planning are (1) the preparation of process
planningof blankmanufacturing, thepart manufacturingandthe assembly; (2)correction ofthedesign
documents in the view point of manufacturability and assemblebility; (3) selection of manufacturing
system; (4) analysis of the manufacturing tasks and estimation of manufacturing cost and time data.
The aim of this article is to define these tasks, the connections and a possible process of
preliminary manufacturing process planning.
Keywords: manufacturing process planning, preliminary process planning, CAPP,manufacturability
analysis, blank type selection, cost and time estimation.
1. Introduction
The production process of a new product consists of two main steps. The first is the
design process, when the construction of the product is developed by satisfaction
of the functional expectations, the material restrictions and other guidelines. The
second step is the manufacturing process planning, when the processes, which are
necessary for the manufacturing, are determined.
The manufacturing process planning is acomplicated and combined problem
therefore it is necessary to divide the tasks into hierarchical levels (HORVÁTH [3],
TÓTH [9], ELMARAGHY [1]). In this manner the process plan is defined succes-
sively, step by step, up to down. The ‘up to down’ term means that the planning
process progresses from the complex tasks to the simpler and the process plan
becomes more detailed and concrete.
In technical literature there is no unified standpoint about the number and the
tasks of these planning levels. The five level model of HORVÁTH divides the whole
process planning as follows: (1) preliminary process planning, (2) planning the se-
quence of operations, (3) operations planning, (4) operation elements planning and
(5) post processing (Fig. 1). The preliminary process planning is a less-researched
field and our article tries to summarise the tasks and connections of this planning
level and define a possible process of preliminary process planning.

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Fig. 1. Levels of manufacturing process planning
2. The Tasks of Preliminary Process Planning
The preliminary process planning is the highest level of manufacturing process
planning, the strategy of the manufacturing (SZEGH [8]). In this stage we have
to make many decisions which have essential role in the point of view of tasks of
lower levels, so these decisions determine the quality of the final plan.
The preliminary process planning is different from other levels in many as-
pects. The most important difference is that some tasks regard the assembled
product as a basic unit instead of part. In other words the preliminary planning
examines in the same time every part of the product and their influences whereas
the object of other levels is only one part.
The tasks of the preliminary process planning are as follows:
– Collecting the technological data for the process planning of the blank man-
ufacturing, the part manufacturing and the assembly; rationalising of manu-
facturing process; preparing of manufacturability and assemblebility correct
part, assembly and blank design documentation.
– Determining the strategy of process planning which means the selection of
manufacturing systems and actual manufacturing variant.
– Analysing the manufacturing tasks, estimation of manufacturing cost and
time data.
The validity of the mentioned tasks is the function of actual manufacturing
task. The planning task is different if the manufacturing task is part or product
manufacturing, or it is a new or a returning order.
In the case of returning order the task of preliminary planning is, depending
on the load capacity of manufacturing systems and the batch quantity, the selection

PRELIMINARY PLANNING OF PART MANUFACTURING PROCESS
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of the optimal manufacturing variant and estimation of manufacturing cost and time
data. In the case of new order the process of preliminary planning is more compli-
cated. The necessary steps are the following:
– Preparation of manufacturability and assemblebility correct design documen-
tation.
– Selection of blank types and design of blank parts.
– Analysis of manufacturing tasks.
– Assigning the manufacturing system.
– Selection of the optimal manufacturing variant.
– Estimation of manufacturing cost and time data.
The connection between the preliminary planning and other areas is deter-
mined by these planning tasks. Briefly the data flow between the preliminary plan-
ning and the management, the design engineering unit and the production planning
unit is bi-directional, but the connection to fields of process planning is just data
supply (Fig. 2).
Fig. 2. The connection between the preliminary planning and other areas
The preliminary planning is a complicated process therefore its internal and
external data flow is complicated, too. Follow the data flow for understanding it.
3. The Process of Preliminary Planning
The aim of manufacturing process planning is to generate the manufacturing doc-
umentation for fulfilling of planned production projects by production unit consid-
ering the financial aims of the company management. Therefore one of the basic
item of information of preliminary planning is the long terminate production plan.

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The actual design documentation, which consists of assembly drawings, detailed
drawings, BOM lists and other descriptions, is provided by the design engineering
unit.
3.1. Design Analysis
The first step of preliminary planning is the design analysis (Fig. 3).
Fig. 3. Design analysis
Theaimofdesignanalysis isrationalisingof manufacturingprocess, lowering
costs by analysing the product from the viewpoint of manufacturing. The design
analysis indicates a feedback to the design engineering unit and it assures the correct
andcomplete design documentation. Thedesign analysis consists of twomaintasks:
the analysis of assemblebility and the analysis of manufacturability.
The purpose of analysis of assemblebility is to study the existence of topo-
logical conditions of assembly. This is a complicated problem, which is hard to
automate and it needs the detailed understanding of the functional connection of
the product. The assemblebility analysis contains the measurement chain analysis,
which is an exact mathematical problem. During the calculation of tolerances each
part is controlled and/or determined considering the number of series, the process
of assembly and the condition of manufacturing equipment. The result of assem-
bleblility analysis indicates design modification demands to design engineering
unit. The second step is the manufacturability analysis of the parts, which may
indicate design modification demands, too. The analysis of manufacturability can
be executed in two levels. The global level concentrates on the theoretical manu-
facturability of each feature, in fact it is an aspect of the design process which is

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the problem of design of manufacturing (e.g. design for casting). The other level
is called local level and it studies the possibility of manufacturing considering the
available manufacturing equipment. The necessary data of this analysis is the man-
ufacturing capacity (list of manufacturing methods, accuracy, size of workspace,
etc.) of manufacturing environment (machine tools, tools, jigs and fixtures, etc.).
The analysis can be made on two approaches (GUPTA et al. [2]).
In the case of rule-base approach (Fig. 4a) the analysis is executed directly on
geometrical data by rules. The rules are domain and environment specific, because
the general solution of the problem is impossible or it needs so large a set of rules,
which can be unmanageable and unutilizable.
Fig. 4.a) Rule-base approach of manufacturability analysis; b) Plan-base approach of
manufacturability analysis
When we apply the plan-base approach, the base of the analysis is a skeletal
process plan (Fig. 4b). On the strength of geometrical data of the part the manu-
facturing demands are detected, and manufacturing sub-processes can be assigned.
Considering the characteristic of the potential manufacturing systems, the analysis
is executed. The analysis is suitable if the required manufacturing demands can be
satisfied on the potential manufacturing system. If it is not possible the reasons of
failure must be disclosed.
There are many methods for measure of manufacturability (GUPTA et al. [2]).
The most basic and the simplest method is the binary method which simply
reports whether a part can be manufactured or not.
During the qualitative measure qualitative grades are assigned to manufac-
turability, like ‘poor’, ‘average’, ‘good’, ‘excellent’. The weakness of this method
is that it is hard to interpret these categories, especially the assemblebility and the

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manufacturability have to be measured together.
The abstract quantitative method assigns numerical ratings along some ab-
stract scale. As qualitative measuring scheme, it can be difficult to interpret such
measures or to compare and combine them.
The manufacturability can be characterised by cost and time data, which
provide an easy interpretation and comparison.
At the end of design analysis the correct design documentatio of the product
and its parts are provided.
3.2. Preparation of Sub-processes of Planning
The manufacturing process planning consists of three planning fields (Fig. 5): the
planning of blank manufacturing, part manufacturing and the assembly. The aim
of these stages are to define the manufacturing process of blanks and parts, and the
process of assembly.
The first task is to define the interfaces between these sub-processes, which
means definition of intermediate states of parts.
Fig. 5. Sub-processes of planning
The source of parts has to be decided to define the interface between assembly
and part manufacturing. We have to decide which parts have to be manufactured
in our workshop or in an other factory and which parts can be considered as com-
mercial parts. The solution of this problem requires close cooperation between
process planning unit, logistic unit and management, whether it is solved as an
optimization problem or by simple management decision. The manufacturing task
is indispensable information to the planning of part manufacturing.
The interface between part manufacturing and blank manufacturing is the
blank (Fig. 6). We have to define two properties of it: the type of blank (like cast,
forged, rolled etc.) and the allowances for machining. The type of blank depends

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on many conditions. The most important are: material, geometry, size and mass
of the part, the batch quantity, deadlines and set of potential blank manufacturing
technologies. We have to strive to realise the minimal summarised cost of blank and
part manufacturing. The exact definition of the geometry of the blank is a design
task. That is why we have to cooperate with design engineering unit.
Fig. 6. Blank type selection
On the base of the manufacturing equipment the manufacturing task analysis
produces the skeletal process plans for each manufacturing process (Fig. 8). These
plans can be used as concept or strategy during the other levels of process planning.
Skeletal process plans have important role in solving of other planning tasks,
too, like in manufacturability analysis (see above). Fig. 7 shows additional possi-
bilities.
The optimal manufacturing system can be selected on the base of the results
of this session.
3.3. Time and Cost Estimation
The role of time and cost estimation is to supply some indispensable information
to the production planning and scheduling unit and the company management.
The aim of the estimation is to determine the deadlines of purchases and to check
the capacity of manufacturing system. This task can be solved by two methods
(PAPSTEL –SAKS [7]).
Taking the case-base approach previous cases are stored in the data-base and
the most similar one is retrieved by an appropriate classification system. More
accurate result is generated if the case-base consists of data of features of the parts
instead of data of parts.

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Fig. 7. Utilisation of skeletal process plan
During plan-base approach skeletal process plan has to be generated and the
cost and time data can be derived from the evaluation of this process plan.
The limited accuracy of these methods satisfies the requirements of prelimi-
nary process planning.
The abovementioned subprocesses of the preliminary process planning are
not succeeded in this sequence. Certain subprocesses can be executed in parallel
or the execution of one of them can interrupt the execution of an other one. For
example we have to identify the blank type just of those parts which are selected
for manufacturing.
4. Implementation
On the base of overview of tasks and relations of preliminary process planning it
can be proved that the preliminary process planning is a complicated and complex
planning level which requires many different solving methods and its output in-
fluences decisively the success of subsequent planning levels, the efficiency of the
process plan and the strategic decisions of the management.
During our research we developed many methods and procedures for the
automation of tasks of preliminary process planning. As we see above several tasks
canbesolvedonthebaseof the skeletal processplan so our research interestfocused
on the generation of it.
Thedevelopedprocess planningsystem applies case-basedreasoning method,
namely the suitable process plan can be generated on the base of process plan of

PRELIMINARY PLANNING OFPART MANUFACTURING PROCESS
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Fig. 8. Skeletal process planning and time and cost estimation
a stored appropriate part. The description of parts is realised by a free structure
question graph, which is easy to adapt to an application environment (MIKÓ –
KUTROVÁC –SZEGH [4]). The estimation of similarity is helped by an artificial
neural network (MIKÓ –SZEGH –KUTROVÁC [5]). The structural adaptation of
process plan can be managed by a user-friendly plan editor or a rule-based ex-
pert system depending on the content of case-base (particular process plan/group
technology), while parameter estimation is done by a genetic algorithm based op-
timisation method (MIKÓ –SZEGH –KUTROVÁC [6]).
Another important task of preliminary process planning is the blank type
selection and identification of allowances for machining. For this task we have
developed a rule-based expert system which determines the blank manufacturing
technology and the allowances on the base of general data (material, mass, batch
quantity, etc.) and geometry of the part and then selects the best variant on the point
of view of total cost.

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Acknowledgements
This domain has been researched for more than ten years by our team in the Technical
Universityof Budapest, DepartmentofManufacturingEngineering. Thecurrentresearch is
supported by the Research Fund of the HungarianAcademy of Sciences (OTKA T024117).
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