an intelligent manufacturing system for automatic ...€¦ · functions like costing, process...

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com May 2015, Volume 3 Special Issue, ISSN 2349-4476

114 Arunkumar P1, Anand.S.Deshpande2, A.C.S.Kumar3

An Intelligent Manufacturing System for Automatic Extraction

of Product Data from CAD Models having Prismatic Features

Arunkumar P1, Anand.S.Deshpande

2, A.C.S.Kumar

3

1 Associate Professor, Mechanical Engineering, KLS Gogte Institute of Technology, Karnataka,

2 Principal, KLS Gogte Institute of Technology, Karnataka, India,

3 Professor, Mechanical Engineering, JNTU College of Engineering, AP, India,

Abstract

The current manufacturing scenario emphasizes the integration of CAD/CAM with CAPP or other

Computer Aided systems. Feature based technology (FBT) enables this integration. An important

enabler of FBT is the data transferred. This data has to be consistent, should contain geometric and

technological information about the product and should be stored in a format that enables complete

information transfer between different Computer Aided systems. Though STEP format is suited for

this task, the commercially available versions have Application Protocols that do not support

complete transfer of the required technological information which is necessary for industrial

functions like costing, process planning, part programming etc.

Considering these aspects an attempt has been made to develop an intelligent manufacturing

system for components containing various machining features, based on complex object- oriented

coding concepts to capture/transfer data from/to manufacturing & other industrial functions. This

requires technological data validated by product experts to be added into the existing STEP file

which contains only geometric data; thereby resulting in a new file called "STEP+" containing both

geometric as well as technological data, i.e. product data. All the captured/ generated geometric and

technological data is displayed to the user depending on their function and requirement. The output is

in the form of time-cost details for each machining operation, cost estimate for the product, process

plan and part programs for machining.

Keywords: prismatic feature recognition, STEP+, technological data, process planning.

1. INTRODUCTION

For successful CAD/CAM integration, considerable research has been carried out in the area

of Feature Based Technology. This effort has led to the development of two main approaches namely

design-by-features and feature recognition. In the design-by-features approach, part models are

defined directly by adding, subtracting and manipulating features created as instances of predefined

feature types. This approach allows non-geometric information to be stored into the feature model

but limits the designer to the use of pre-defined features, which thus limits the complexity of the

product design that can be represented and making the resulting feature-based model context-

dependent. Feature recognition involves computationally recognizing features from conventional

geometric models or from neutral data format such as IGES or STEP. This approach avoids the

limitation of design-by-features by attempting to identify features from already designed component

description but requires a complex analysis of the geometric model.

2. LITERATURE REVIEW

The basis for good manufacturing systems is the proper recognition of the features in the

component. Various feature recognition methodologies have been proposed in the recent years.

Attempts have been made to recognize features from 2-D representations of the components [1–3].

Convex hull algorithms are used to recognize features from 2.5-D components [4]. 2.5-D features are




obtained by extruding a 2-D feature along the third direction. Many such 2.5-D features individually

present on different faces as well as intersecting among them result in practical 3-D parts.

Feature recognition endeavors to automatically recognize and extract appropriate features

from a geometrical model. To achieve this, geometric-reasoning techniques are used to interrogate

the data structure of the geometric modeler. The geometric modeler in consideration should usually

be a solid modeler; otherwise the amount of data available in the geometric model may not be

sufficient for the geometric-reasoning process. Substantial research efforts have been expended and

some notable results have been published [5, 6].

Later many feature extraction systems were developed. One of them takes STEP file as input

to define the geometry and topology of a part. In addition, the system generates STEP file, as output

with form feature information is AP224 format for form feature process planning. The STEP file can

be exchanged between various companies and can serve as input to further downstream activities

such as process planning, scheduling and material requirement planning (MRP) [7].

The focus then shifted to Feature-interactions because they have tremendous consequences

on a feature model and its applications, subsequently leading to violation of feature validity, if not

handled properly. Handling feature interactions in feature-based design system is still an unsolved

research issue. Research on feature-interactions in the area of feature-based design approach has had

limited discussion in the literature [8] but has been described widely in feature recognition research

[9]. The research involves analyzing the interaction relationship, decomposing the interacted features

into single features and defining their relationship [10]. Thus, this area of research has become

prominent in feature-based modeling.

Furthermore, the communication between CAD/CAM, CAPP and other CA systems is

necessary to provide transmission of two types of information [11]:

Constructive – (geometric) data, describing design of part.

Technological – data describing way of manufacturing/ machining of part

The combination of the above two types of information constitutes Product Data. The purpose of

STEP is to build a common standard that ensures the product data can be communicated

electronically across different platforms, e.g. CAD, CAM and CAPP. The STEP standard differs

from IGES by incorporating a formal object-oriented model for data exchange [12].

STEP enables all individuals contributing to the design, manufacturing, marketing and supply

of a product and its components to contribute to, to access, and to share information. STEP aims at

eliminating the concept of “islands of automation”. STEP also attempts to unite manufacturing

efforts among corporate partners, distant subsidiaries and suppliers across diverse computer

environments. STEP addresses the issues of diversified engineering applications and covers security

aspects, which become relevant now that several companies would be sharing the same product

information [13].

The STEP neutral file is a text file that contains geometrical data of a component including

boundary representation data such as shells, faces, vertices; surface geometric data such as planes,

cylinders, cones, curve geometric such as lines, circles, ellipses, b-spline curves [14].

The current commercial STEP versions found in commonly available CAD modelers have

AP‟s (AP203) that do not completely support storage/ transfer of technological information. Hence,

taking all these aspects into consideration the present research work has been carried out.

In the research work, STEP (AP 203) containing geometric information about the product has

been used. The Intelligent Feature Recognition System takes this as input, processes it, generates the

Technological information required for the product manufacturing/ machining like time-cost

calculations, process plan part program and other details by taking inputs from Product expert

module, User & validated Knowledge base, finally adds this technological information back to the




STEP file thereby generating a new file called "STEP+" which contains both Geometric and

Technological data of the product.

3. THE FEATURE RECOGNITION LOGIC

A product model can have any number and types of features. In order to prove the concept,

general types and combinations of features have been considered in the present work. The STEP files

of all these components with features were analyzed and the logic developed for different feature

types, some of which are shown in Fig 1.

Fig -1: Different prismatic features on components

The feature analysis has been carried out by grouping the extracted features into the following types:

Pocket: Square/Rectangular, either blind or through

Slot: Square/Rectangular, Dovetail, T-slot either blind or through.

The axis system and origin taken for the logic is shown in the Fig 2.

Fig -2: Axis system and origin of prismatic component

The system deals with a unique, novel and exhaustive method to identify and extract required data

from the above mentioned features. The logic and the algorithms used in the system development

have been briefly explained in the following sections.

3.1 Prismatic Feature Recognition

The "Prismatic Feature Identification Logic" has been proposed to analyze the prismatic

features. The concept and the coded logic have been briefly explained in this section.

Searching for the string representing an EDGE CURVE in the STEP file of the CAD model.




Analysis of the string, character-by-character to find the hash codes corresponding to Vertex

points thereby leading to the Cartesian points.

Identification of the edges forming part of the feature. This is done by eliminating the edges

which have minimum and maximum coordinate values in X, Y and Z directions.

Identification of the line type viz. horizontal, vertical or inclined.

Inferring the relationship between the lines e.g. parallel or perpendicular, equal or unrelated.

Recognition of the prismatic feature is carried out by the Edge theory.

The Maximum values of X, Y and Z indicate the length, width and height of the plate.

If length of slot = Length of Plate, it is a through slot, else blind.

The feature recognition logic for t-slot in addition to identifying other prismatic features has been

shown in the flowchart form in Fig 3.

Fig -3: Flowchart showing Feature Recognition Logic for Prismatic features




4. A FEATURE BASED INTELLIGENT MANUFACTURING SYSTEM

The system comprises of three well

integrated modules:

i. Intelligent feature recognition

System

ii. Product Expert module

iii. Operation Scheduling module

The workflow of the system is shown in

Fig 4. The CAD model for the required

part is created & the STEP file (AP 203)

is extracted. This file is then analyzed by

the intelligent feature recognition system

which identifies & extracts the

machining features in the model. The

output is a graphic representation of the

feature along with geometric data like

dimensions of the model, volume, weight

etc. To give this type of information,

technological data is also needed.

This data is authenticated & fed

into the system by the Product Expert

module which has access to all data

related to Overhead costs, Tool Database

& Parameters, Machine Database,

Customer Database, Cutting Speed and

Feed data based on machine capabilities.

This data is collected from user input as

well as a reliable & validated Knowledge

base of technological data. Thus the file

that has geometric as well as

technological data is now termed “STEP

+” file in the present work. The output/

reports generated cater to all functions of

industry. Cost estimates, workshop

capacity including DB of machines &

tools, process planning, part programs

have been the outputs of this system.

Fig -4: System Workflow

5. THE INTELLIGENT MANUFACTURING SYSTEM

Many components containing features like prismatic, rotational, free form, interaction of

prismatic-rotational etc., have been taken for the research work. However, in this paper the

component having prismatic pocket feature has been considered (Fig 5). With respect to this, the

flow of the intelligent manufacturing system to generate the required output has been explained with

the help of screenshots.




Fig -5: Sample component with prismatic features

In Fig 6, the decoded STEP file of a component containing prismatic pocket feature is shown.

It contains the geometric data w.r.t Cartesian points and their X, Y, Z values.

Fig -6: STP File processing

Fig 7 depicts the details of the object including dimensions of individual features along with

volume, density & weight. The material type & density values are taken from Product expert

database.

The details of the manufacturing processes and their sequence, needed for the feature is

displayed to the user based on the technological information submitted by user in the form of Process

Capabilities (Table 1). The values entered are compared with standard values of machining processes

available in the database and the suitable processes are recommended, when the "View Processes"

button gets activated.

Table -1: Process capabilities of Milling




Fig -7: Object Details

The Time-Cost Calculations based on processes recommended is shown in Fig 8. The

machine and tool are selected from Product expert database by the user. Only the machines and tools

present in the workshop are available for selection based on machining recommendations. The Total

Manufacturing Time as well as Total Cost for the entire order is calculated using standard formulae

embedded in the code. Recommended values of cutting speed are also shown to user within brackets.

From this screen, the Cost estimate, Part Program and Process Plan can be generated.

Fig -8: Time-Cost data




The Cost estimate as shown in Fig 9 takes input from the user, Customer Database and

previous screens to calculate & display the values in the text fields. The field values marked with "*"

are to be entered by user, whereas other values are calculated and displayed. The cost estimate can be

printed or saved as pdf file enabling it to be sent to customers by email.

Fig -9: Cost estimate

The Process Plan as shown in Fig 10 takes data inputs from Time-Cost & Object Details

forms. A standard process plan format has been developed taking into consideration part

requirements, raw material selection, manufacturing operations recommendations, machine tool

selection, tool selection, selection of manufacturing conditions i.e. cutting speed, feed and depth of

cut and manufacturing time based on machining, delay, setup and auxiliary time.

Fig -10: Process plan

The Part programs (G & M codes) for machining the feature has been generated (as shown in

Fig 11) based on FANUC controller as it is used by majority of Indian manufacturers for CNC

machining. The toolpath is calculated and coded using values of depth of cut, coordinates and

interpolations.




Fig -11: Part program

6. SCHEDULING MODULE

The Scheduling of Operations for any part is carried out in the “Scheduling Module”

provided in the Main GUI screen as shown in Fig 12. The machine no, tool no, manufacturing time

of each operation is stored in DB when the time cost calculations are done. The time has to be

selected for scheduling of an operation, depending on the availability of the slot either the operation

will be scheduled or the machine status will be displayed as „busy‟.

Another feature called the "Machine Status chart" has been provided which displays the

status of the machine at any point of time. The machine status (engaged/ free) can be observed in the

status chart as shown in Fig 13. The ticks in the check boxes indicate the engaged slots whereas the

blank check boxes indicate the free slots. This can be taken as a basis for optimal capacity utilization

on the shop floor.

Fig -12: Scheduling the operations in respective machines & specifying the operation start time

Fig -13: Viewing the machine/ work status




7. STEP+ FILE

The geometric data in the STEP (AP203) input file is added with the technological data

generated from the intelligent system, product expert & the user. The result is a new file called

“STEP+” file, which contains both geometric & technological data. A sample STEP+ file is shown in

Fig 14.

The STEP+ file contains the following data:

Entire Geometric data of the part contained in STEP file

Object/ feature dimensions

Process sequence

Time-Cost data of each operation

Machine and Tool data

Machining parameters like Cutting Speed, Feed, DOC etc.

Fig -14: Sample „STEP+‟ File containing geometric & technological data for a component

This can be seen as a platform for future works in the field of Product Lifecycle Management (PLM)

as the entire product data is available in a single master file.

CONCLUSIONS

The work has led to the design and development of an Intelligent Feature based

Manufacturing system with a focus on general and commonly observed product manufacturing

environment and procedures. The part programs generated from the system have been executed on

Fanuc controlled CNC machines and no errors; either in the syntax or logic have been found. The

geometric dimensions on the machined parts were found to match the values given in the CAD

model. The part programs and process plans are found to be compatible with real life manufacturing

environment.

ACKNOWLEDGEMENT

We profoundly thank AICTE, New Delhi for funding the research work by providing the

RPS grant. We also thank the Management, KLS Gogte Institute of Technology for providing the

funds and infrastructure to setup Computer Integrated Manufacturing lab used in conducting the

research work.




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