Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 192 (2017) 113 – 118
TRANSCOM 2017: International scientific conference on sustainable, modern and safe transport
Utilization of strategies to generate and optimize machining sequences in CAD/CAM Tomáš Dodoka*, Nadežda Čuboňováa, Miroslav Císara, Ivan Kurica, Ivan Zajačkoa a
University of Žilina, Faculty of Mechanical Engineering, Department of Automation and Production Systems, Univerzitná 1, 010 26 Žilina, Slovak Republic
Abstract At present some CAD/CAM systems allow to create strategies or macros to accelerate the process of creation NC programs. The article deals with the development of experimental strategies in the CAD/CAM system. These strategies allow to remove repetitive tasks and allow to accelerate the process of creation the NC programs for machine tools. Feature analysis contained basic types of features and additional attributes of features. This feature analysis is based on possibilities of CAD/CAM system. ©2017 2017The TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license © Published by Elsevier Ltd. This (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of TRANSCOM 2017: International scientific conference on responsibility of the scientific committee of TRANSCOM 2017: International scientific conference on sustainable, Peer-review sustainable,under modern and safe transport. modern and safe transport Keywords: Edgecam Strategy Manager ; Strategies ; NC program; Optimisation
1. Introduction The technology of manufacturing is an area, which is constantly growing. At present not only requirements of accuracy and quality of components increase, but also the rate of products manufacturing. It is not only shortening the times in production but also in the creation of NC programs for new component. CAD/CAM systems allow companies to quickly adapt to customer requirements and respond flexibly to changing production of parts. Main advantages of CAD/CAM systems include speed of creation of NC program for parts with complex shapes as well as the simulation of a whole machining process. However, programmer is forced to perform repetitive tasks in the creation of NC programs for new parts, such as a face milling or pocket milling. For that reason, some CAD/CAM
* Corresponding author. Tel.: +421 41 513 2833. E-mail address:
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1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of TRANSCOM 2017: International scientific conference on sustainable, modern and safe transport
doi:10.1016/j.proeng.2017.06.020
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systems offer ways to eliminate repetitive tasks. One such possibility is for example developing of NC strategies. Main advantage of NC strategies is to automate and streamline the entire process of creation of NC programs. The CAD/CAM system that allows creation of the NC strategies is for example CAD/CAM system Edgecam 2016. 2. Feature-based machining and recognition of geometric features in CAD/CAM systems Feature-Based Machining (i.e. FBM) allows the programmer to automate creation of NC programs. We can say that FBM evaluates the components features and automatically creates an effective machining process. This task is usually done in seconds, and the machining process is generated during several minutes. Recognition of geometric features is done after creation of a model in CAD system. Recognition can be made in CAD/CAM systems or in another system used for recognition of features. For feature recognition are necessary two types of data, i.e. geometrical and topological. The recognition of features is done by searching and comparing information stored in the database and the model itself. [1,2] Recognition includes three major tasks: x definition of the features - rules stored in database, x sorting and extracting features from solid model, x storage for further use. Methods for extraction of geometric features from CAD model of a part can be divided into two groups: x Internal, x External. Internal method allows reading data directly from a CAD file of the system in which the model was created and saved. External method allows reading data from files that have been exported to neutral formats - ASCII file. CAD/CAM system Edgecam 2016 uses the first of these methods, i.e. features are recognized directly from the output of CAD file system. Features recognized in Edgecam 2016 can be divided into four basic groups - 2D and 3D features, surfaces and holes. 3. Edgecam 2016 Strategy Manager Edgecam allows creation of an NC programs for CNC turning and milling machines, CNC machining centers and also for wire cutting machines. Main advantage of Edgecam is a support of modern CAD formats like .prt, .itp, .sldprt, .catpart and another. Edgecam Strategy Manager is one of the modules of CAD/CAM system Edgecam 2016. It can be used like a library of knowledge and experience of technologist. Strategy is a set of rules that can automatically generate instruction for machining of the specific features. It also carries information on the different types of geometry and parameters that will apply on machining process that is selected inside of strategy [3,4]. Input data for strategies can be divided into three basic groups: x Geometric data - contain information about the features, dimensions or other information as surface quality and tolerance, x Technological data - contain information about cutting data or chosen strategy of roughing, x Additional data – orders for the tool change. Example of a NC experimental strategy created by Strategy Manager of CAD/CAM system Edgecam 2016 is showed in Fig. 1. The NC strategies are created by using an algorithm and that has form of a flowchart. Each part of the strategy (such as information about geometry and the technological operations) are copied from existing machining processes and they are edited so that they may be used for machining of other similar geometric features.
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Decision block contains data about features:
Pocket Rough
Pocket Profiling
Pocket Rough and Profiling blocks contain data that describe technology and toolpaths.
Fig. 1. Edgecam 2016 Strategy Manager and an example of strategy with conditions
3.1. Creation of strategy in Edgecam Strategy Manager The strategy can be created for machining of the specific component or the specific feature. The strategies are essentially algorithms that may include a number of machining processes for a variety of geometric features. Machine cycles and geometric shapes can be combined within a single strategy. The process of the strategy creating consists of the following steps: x Definition of the feature – for which the NC strategy will be used, x Selection of the machining cycle – the machining cycle for the chosen feature, conditions for the selection of the right tool, x Creation of the algorithm - insertion and definition of the decision blocks, insertion of machining processes and ends of strategy, x Adding of properties - for example function for stock update. The resulting strategy can be simple or complex. Simple experimental strategy (Fig. 2 A) contains only one machining process that can be used for machining of only the one type of feature. The complex experimental strategy (Fig. 2 B) may contain several machining processes and several decision blocks. The decision block allows to specify conditions and decides how the strategy works after detection of the feature [5,6,7].
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a
b
Fig. 2. (a) Simple experimental strategy (b) Complex experimental strategy
4. Analyze of features for creation of experimental strategies in Edgecam 2016 Geometric data are necessary to creation of NC strategy for that reason we made analysis of milled features. The feature analysis contains basic types of features and additional attributes of features. Complete analysis is listed in Table 1. For all of these types of features were created the sample parts. These parts were used for creation of the experimental strategies. Table 1. Features analysis for experimental strategies. Attributes Feature Base Shape
Depth
Open/closed
Additional attributes
Regular Surface
N/A
N/A
N/A
N/A
N/A
N/A
Complex Regular Irregular Step
Contured Complex
Tomáš Dodok et al. / Procedia Engineering 192 (2017) 113 – 118 Table 1. (Continued) Features analysis for experimental strategies.
Attributes
Feature Base Shape
Depth
Open/closed
Blind
Open
Additional attributes
Regular Irregular Pocket
N/A Contured Through
Closed
Complex Regular Slot
Irregular
Open N/A
Straight Curved
Closed Contured
Complex
Regular Boss
Irregular
N/A
N/A
Thread
Regular
Blind
N/A
Irregular
Through
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Non-Uniform Hole
Thread External
Chamfer Internal External Fillet Internal
5. Experimental NC strategies based on analysis of selected features The experimental strategies are based on the analysis of selected features in CAD/CAM system Edgecam 2016. The experimental NC strategies were created after the sample parts creating. The experimental NC strategies are designed as simple strategies (Fig. 2 A) and they contain these steps: x conditions for use strategy - defined features for which the strategy will be used, x choice of Tool - the conditions for the selection of the right tool based on characteristics of features, x machine cycles - roughing and finishing cycles. The experimental NC strategies have been applied on five experimental components. The experimental parts contain several different types of features. Figure 3 shows the comparison of time necessary to create machining process with and without use of these strategies. Implementation of custom experimental strategies allows reducing time necessary to prepare machining process in CAD/CAM system Edgecam 2016. By verifying the correctness and functionality of created experimental NC strategies will be developed complex experimental NC strategies in future. These strategies will be designed to be able to clearly demonstrate the benefits of their use or identifying their weaknesses.
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Time required to creation of the machining process with and without the strategies use 35 30 30
Time [min]
25 25
21
20 15
18
17
15 10
10
10
6
4
5 0 without strategies Component 1
Component 2
with strategies Component 3
Component 4
Component 5
Fig. 3. Time necessary to the machining process preparation with and without implementation of the strategies
6. Conclusion The use of NC strategies in CAD/CAM software Edgecam is possible to see two benefits. The first is the possibility of storing knowledge and experience of technologist. The second is reducing the time needed for creating the NC program. The main advantages of creating strategies is speed of creation of NC program and the versatility of use. Strategies can be used for number of components based on similarity of geometric features. Analysis of geometric features and development of strategies highlighted a several problems in CAD/CAM system Edgecam 2016. The most significant problem is recognition of fillet or chamfer. CAD/CAM system Edgecam 2016 recognizes these features as 2D Step. The problem is caused by the absence of rules for recognition these geometric features. Next step in analysis of features will be analysis of complex geometric features such as 3D surfaces and another 3D geometric features. This analysis will be also used for creation of complex strategies and it will point out on possible limitations and weaknesses of strategies. These analyzes of geometric features will be used for creation of strategies in another CAD/CAM systems.
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