Each year, more semi-gpnerative CAPP system for a mold ... The CAPP system is based on part .... sequence, machines, tools and parameters together with time.
.
An Integrated Computer-Aided Process Planning System for Injection Mold Manufacturing Urnit Bilge
Mehmetgik Kalay
Osman Turkay
Dept. of Industrial Engineering
Bekoteknik San.A.8.
Dept. of Mechanical Engineering
BogaziGi University
CAD/CAM Department
BogaziGi University
Bekk 80815, Istanbul
B.Cekmece 34901, Istanbul
Bebek 80815, Istanbul
Turkey
Turkey
Turkey
- This
Abstract
paper describes the development of
planning (PI') task is performed manually. Each year, more
a
mold
than 7500 individualprocess plans are created that amounts to
designs
and
the 15-18 % of the engineering expenditure. The burden on
plastic
the process planners has increased even further because the
componentis. The CAPP system is based on part
plastic injection shop whose capacity exceeds the company's
coding anld decision trees and
aims to provide
internal demand recently started taking orders from a number
the CAD, CAM, production
of external customers from different sectors such as
a
semi-gpnerative
productioin
department
manufacti,ires
integration planning facility.
injection
between
i
.
nd
CAPP
system that molds
for
of
shop floor control systems in the
automotive industry. Although the machinery at the mold manufacturing shop offers a large: degree of processing flexibility,in practice none of this flexibility can be utilized since process plans are
1. INTRODUCTION
sequentialized far in advance of processing considering only the development of a computer-aidedprocess
the static technological constraints. Without knowledge of
system for a mold production department
the actual status of the shop floor, fixing the resource allocations before the scheduling/control stage decreases the chances of efficient production sequencing and scheduling. Furthermore if a process plan is changed in the shop floor by
is a large manufacturer finished goods per
an operator, this is rarely recorded as feedback information in the PP department.
an internal annual The main objectives in computerizing the PP activities of
each consisting
the departmentcan be stated as:
components are manufactured only once and over 80% are manufactured in lots of one unit. Few of the production lots include moie than two units. While the CAD models and
- reducing the PP effort for non-similar components, - reducing repetitive clerical work and resulting errors,
are generated using a
- increasing the quality and consistency of process plans,
CAD/CAM software, process
0-7803-3685/-2/96$5.00 0 1996 IEEE
- standardizing the process plans for similar components,
123
- designing a PP procedure which provides integration with
and reliable CAPP system is required within a reasonable length of time, and the system has to encompass both
shop floor in terms of resource allocation [ 1,2],
- providing feedback from shop floor to employ "design for
generative and GT features since approximately 80% of the components in a given mold are similar to the components of
manufacturing" concepts [31.
other molds, while the remaining are unique. 11. THE PROPOSED CAPP SYSTEM A high skilled CAD/CAM software is already in use for
The two basic approaches of CAPP systems are the
designing solid models and generating CNC codes. The
variant and generative methods. The variant approach is based
activities remaining to be automated are process selection,
on Group Technology (GT) principles and involves retrieving a process plan from a library of existing family process
recommendations for alternative machines, tooling and various parameters, and cost and time estimations. As an
plans and editing it to accommodate for the specific
initial step of the study a structured systems analysis [8] is
requirements of a new product. Generative systems, on the
carried out for
other hand, develop new process plans from scratch, without
modeling functional and information
requirements for the proposed CAPP system. The resulting
human interference or reference to any existing plans. Given
information requirements model and the design of CAPP
the CAD data of the part and a comprehensive description of
system based on this model is summarized in the next two
the manufacturing conditions, the system emulates the
sections.
decision logic used by a human process planner to design an optimum process plan. Some popular CAPP systems and
A . Overview of the Proposed Model for the Mold
the state-of-the-artCAPP research are reviewed in [4] and [51.
Production Department
From a CIM point of view, the generative approach is the
The mold production department which is a typical
desired direction since it facilitates the integration of CAD
engineer-to-order[91 type of manufacturingsystem facing
expensive,
problems such as extensive engineering, long cumulative lead
difficult and time-consuming to design and implement, and
times, low level of production learning and increased
organizations.
implementation of concurrent engineering (CE) concepts and
and CAM. However, these systems are
thorough integration of design, planning and manufacturing
A practically oriented interim approach found in most of
the industrial applications can be named as semi-generative PP systems [ 6 ] . These serve to reduce user interaction
through such features as standard operation sequences, decision treedtables, and mathematical formulas. They are
activities. A key factor in achieving this is designing the PP system as a bridge between product design and manufacturing which requires reengineering of several activities within the department. The data flow diagram (DFD) for the department
given in Fig. 1 displays the functional and information
not completely generative, but the required process plan modification is minor compared to the variant approach, and they can be highly time and cost effective [7]. In our study, a semi-generative approach is employed because an operating
requirements for the proposed system. A brief explanation for the diagram which will not be decomposed any further here is given below.
124
7 I
I
material availability
material requirements
Coordinate Production
request order data
I
I
production status
21
Mold Design
part data
similarity codes
process plans
31
b I
&pare ProcessPlans PP hardcopy
dynamic status additional dynamic data
Control Shop Floor
I
Fig. 1. Data flow diagram for the mold production department
125
Coordinate Production function synchronizes all design, PP
passes information to the NC programmer to be used as a
and shop floor control (SFC) activities and facilitates the
decision aid during the CAM activities. As it can be seen
implementation of CE related concepts to ensure team-work
from Fig.1, the PP function is the core task which has
within the department towards the common goals of reducing
access to all data stores. Standard operation sequences,
lead time and cost, and increasing quality in designing and
machine compatibility, time and cost estimates, and standard
manufacturing molds. Its main activities are setting price and
tools and parameters data stores constitute the static
duedates for customer orders based on conceptualdesigns and
manufacturing database which is updated when required only.
initial cost estimates: carrying out project planning and
The dynamic manufacturing database (i.e. molds, machine
capacity planning based on bill-of-materials (BOM) and
status, and tool status data stores) is updated on a continuous
process plans; releasing material purchasing requests, final
base.
PP release requests and manufacturing orders based on the
SFC funcfion carries out dispatching and executes
project schedule: and monitoring and updating the project plans. These activities are to be carried out largely on regular departmental meetings. Molds datastore is the basic data store
manufacturing orders based on the prioritization schemes (i.e., latest starting times)
provided by production
coordination, and process plans and machine allocations
that covers all relevant data.
provided by PP function. It collects data and monitors shop Mold design function is implemented concurrently with
the design of the plastic part to be produced. Given the solid
floor so that the common dynamic manufacturing database is kept updated with latest information available.
model of the plastic part, the mold designer determines the Analysis of shop floor data function
core and cavity sections of the mold, the coolant system, the
carries out
ejector system and designs solid models of each part and
performance evaluation by filtering and examining data
subassembly using the CAD software. The BOM is created
collated in dynamic manufacturing data stores. As well as
by the software.
monitoring duedate satisfaction,operator performance,quality performance and comparison of actual costs against estimated
P P function embodies the semi-generativeCAPP system
costs, this function should be designed to include several
and the generation of NC codes task. The CAPP system
statistical tools to estimate manufacturing parameters such as
determines the process plans including the operation
time and cost for machines, and to pinpoint problems and
sequence, machines, tools and parameters together with time
potential areas of improvement in design and manufacturing.
and cost estimates for the parts and stores the plans in the
The main idea behind the analysis function is closing the
database. This task can be repeated a number of times to
loop between design and manufacturing in pursuit of
support design, project planning and capacity planning
continuous improvement. The information generated is used
activities. Upon receiving process plan release request from
to support CE efforts in product and process design, to update
the production coordination function just-in-time for
static manufacturing data stores such that they represent the
manufacturing, the CAPP system makes the final resource
best known manufacturing methods, and to provide reports to
allocation decision incorporating the latest actual workload
the management.
information, issues hard copies for the shop floor, and
126
B . Overview of the Semi-generative CAPP System
TABLE I STRlJClWtE OF THE SIMILARITY CODE
The input to the CAPP system is a 14-digit polycode [lo] which descrlbes basic features and surface characteristicsof the part. The basic structure of this similarity code developed in-house is shown in Table 1. The code is extracted automaticalliy from the CAD model except for a few digits
Di it 1 2 3 4 5a
Definition Material Length Width Height General external shape Main shape surface Extemal auxiliary shape Extemal auxiliary shape surface Auxiliary internal shape Auxiliary intemal shape surface Surface relations Main hole Auxiliary hole Auxiliaq hole shape
similarity ci de. There exists six main part families for
6 7a 8a 9a loa 11 12 13 14
similar partli determined through the analysis of previous
a part family formation digits
which should. be interactively specified by the designer.
b
The PP fq ction is carried out in three stages. In the first stage the operation sequence for a given part is specified.The decision lo& is modeled as a decision tree driven by the
i
mold compbnents. For similar components, five critical digits of the code is used to define the part family and the remaining cines to determine the specific processes of the members W Ithin a family. For non-similar items, all of the digits are used to select appropriate operation sequences. sequences can be considered as standard
objectives are evaluated by means of fuzzy membership functions [11,12]. It is essential for PP and shop floor control integration that machine workload balancing is considered at this stage using real-time data and machine allocationsare fixed just before production.
plans. They are tested and proven
In the last stage, tools and related parameters to be used in
based on static factory
machining olperations are recommended with reference to a
and expert knowledge.
standard tools and parameters file after a few additional steps
operation sequence the
in the decision tree. Availability of the suggested tools are
and tool and
checked from dynamic tool status file so that alternative tooling plans can be provided if necessary.
Given thle machine compatibility, time and cost, and
The process plan generated in this fashion may require
dynamic status data for the set of machines available in the
some modifiication by the process planner in some cases..
shop floor, I he machine allocation stage determines the most
Extensive experimentation carried out with the system
preferable machine alternative for the part with respect to a
revealed thal the human intervention that may be required is
set of objeci.tives.The main objectives are maximizing the
minor and limited to only 5% of the generated plans for a
technologiclal preferability defined in terms of a number of
complicated mold. Elimination of this human intervention
attributes, balancing the workload allocated to machines and
through implementation of feature-recognitionconcepts and
minimizing the cost of the operation. The decision making
proper updating of the decision tree is a natural direction for
tool is a mu lti-attribute decision making model where the
future study which leads to a generative system and requires a
contributiorls of each machine alternative to different
significanteffort.
127
111. IMPLEMENTATIONAND CONCLUSIONS
realized. Even more important than the visible efficiency resulting from the CAPP system is its impact within the
A multi-staged approach employing rapid prototyping concepts [13] is being used in development and implementation of the proposed system to verify the concept
company which created an understanding of integration concepts, and an ongoing effort for reengineering towards achieving greater extent of integration.
and the model before the full system is constructed, and to IV. REFERENCES
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