Abstract : The structure and implementation method of direct digital control (DNC) WEDM system for die manufacturing system are studied to improve the automation level of the system, overall production efficiency and response speed, and provide a certain extent for the composition of the wire cutting DNC system. The theoretical basis.
Keywords: mold manufacturing system wire cutting DNC
1 Introduction
The mold manufacturing level is one of the important signs reflecting the overall manufacturing level of a country. With the development of the national economy, the requirements for molds are also increasing. One of them is that under the conditions of the big market, the mold manufacturing should adapt to the fast characteristics, and the manufacturer's response speed to orders may determine its success or failure in the market. In order to improve the response speed, it is not enough to increase the number of equipment and single production efficiency, and the automation level and management level of the mold manufacturing system should be improved as a whole.
In the mold manufacturing system, WEDM has played an important role. Mould parts, especially the key parts of the mold (mold forming part) are largely completed by wire cutting, and its workload is large. Therefore, it is very meaningful to construct a direct digital control (DNC) WEDM system that is compatible with the mold manufacturing system and has high automation level and certain management coordination ability.
2 The overall structure of the WEDM DNC system
The CNC system of WEDM has become perfect. However, there are still a large number of wire cutting machines that are equipped with a set of control systems. The degree of automatic programming is low, especially the early control systems, which are controlled by a single board machine, and are often manually or computer-programmed and then manually or perforated. The more advanced wire cutting machine is equipped with a microcomputer, which uses the powerful graphics and data processing functions of the computer for drawing, programming, and even control. Even so, it is mostly used alone. This is a slow response and inefficiency for manufacturing systems that produce a large number of molds (multi-category, low-volume), which is incompatible with an efficient mold manufacturing system.
In a larger-scale mold manufacturing plant (workshop), the number of parts requiring wire-cutting processing is large, and several or even dozens of wire-cutting machines of various specifications are often deployed. Therefore, the concept of group control system gradually emerged, but it is simply to connect the automatic programming system with the wire cutting machine, only saving the programming and input workload.
In order to improve the reaction capability and production efficiency, a plurality of wire cutting machines should constitute a complete DNC system. The DNC system itself should have a high level of automation and a certain degree of computer-aided management, while maintaining the flexibility of the stand-alone and system reconfigurability, and integrated with the CAD of the mold manufacturing system, namely the mold CAD software The resulting design information is quickly and securely connected to DNC for CAD/CAM integration.
Figure 1 shows the overall structure of a wire-cut EDM system. The system host computer and the numerical control system computer perform their own functions and interconnections, which not only guarantees the real-time performance of the control system, but also guarantees the independence and reconfigurability of the wire cutting machine. It embodies the characteristics of the open architecture and makes the system have good performance. The scalability, maintainability, portability and other characteristics, each layer through the data interface to achieve the communication between them. The system includes graphics processing functions. On the one hand, it receives CAD information such as virtual enterprise, enterprise alliance, CAD center, etc., and processes the data through an exchange format (such as IGES), and then generates a control program through an automatic programming system; on the other hand, it can The mold parts are designed and converted into control instructions. The programming system can also be programmed directly. The management system plans the DNC work for a number of days so that the various wire cutters in the system can be loaded in a balanced manner and remind the management personnel and the operator of the work.
An overall structure of a wire electric discharge machine system of FIG DNC
3- wire cutting automatic programming system
To achieve system integration of CAD/CAM, we must first solve the graphics input problem. The Auto CAD graphics system has powerful graphics input and editing capabilities and is the most active CAD system on the PC. Wire cutting automatic programming system based on Auto CAD environment has a good application prospect. The module structure of automatic programming system is shown as in Fig. 2.
Fig. 2 The module structure of automatic programming system
Software includes system functions (editing of 3B, 4B, ISO code files, setting of system parameters, etc.), reverse code conversion of code instructions (used to check the accuracy of code instructions), conversion of code instructions, parameterization of individual parts Design, NC communication, etc. The system can accept the design results of the die design software such as UGII and convert it directly into numerical control instructions according to the graphic zoom gap.
Parametric modeling is parametric in the design of specialized parts such as parabolas, involute parts, cams, and gears.
Figure 3 shows the drop-down menu for this module on the system interface.
Figure 3: System interface and parameterized design drop-down menu
In order to realize CAD/CAM integration of line cutting, CAD drawings must also be converted into instructions that the NC machine can accept. The algorithm steps are as follows:
(1) Use the AutoCAD offset command to generate the tool curve.
(2) Reorder the CAD graphic elements according to the processing sequence. The algorithm is:
STEP1: Select the first machining point and machining direction, find the first element of machining in the graphics database, and set its end point as the current point. The found graphic element sets the sorted flag.
STEP2: Search for a graphic element related to the current point. If the graphic element is not sorted, then the element is the current element, the other endpoint of the current element is the current point, and the element is set to the sorted flag.
STEP3: Repeat STEP2 until the graph is closed or all elements are sorted.
(3) Generate NC instructions for all sorted graphic elements
The wire cutter retains a separate controller structure for improved real-time and reliability. The computer is connected to the wire cutter controller communication port through the RS232 serial port. The wire cutting program can be input in real time to control the machine tool, or can be controlled by the machine's telegraph head to simulate the paper tape input. At the same time, the controller can transmit the status information of the machine to the computer, such as broken wire, short circuit, processing start, end, etc., to realize the computer's management and control of multiple wire cutting machines. Realize the serial communication of computer and wire cutting machine, its functional block diagram is shown as in Fig. 4.
Figure 4 Schematic diagram of serial bidirectional data transmission
4 Management System
The management system has the following functions:
(1) Create a cutting process parameter library, and give opinions on parameters such as cutting current, cutting speed, and pulse frequency.
(2) Calculate the number of cutting man-hours for each part, and calculate the part's processing time based on the part's processing thickness, path length, and process parameters.
(3) Generate a schedule.
Plan the schedule according to the time of the batch, taking into account the equilibrium and maximum load of various specifications of the equipment. Job assignment plan by day. Distribution should be considered: 1 to ensure the completion of the operation plan from the quantity and variety; 2 batches of products to focus on production as much as possible; 3 due to production technology preparation and other reasons, some parts can only be processed after a certain day; 4 some Product requirements are completed within the first few days.
The problem is very complicated if it is calculated at the same time every day within the plan. Based on the above conditions from the first day to the last day calculations.
Assume that there are m types of wire cutting machines in the workshop, denoted by i (i=1, 2,..., M), and n kinds of products are processed, respectively represented by j (j=1, 2,..., N). These product planning quantities are represented by dj.
Use aij to indicate the number of units of the type i machine required for the processing unit j products, and bik indicates the capacity of the type i equipment in the first k days (in units of units). Xjk indicates the number of j products planned to be produced on the kth day.
According to the previous assumptions, such as the fifth and eighth products to the second half of production, the fourth product is required to complete before the second day. Then the second day linear programming model is:
Satisfy:
The significance of this is that the total production capacity of all kinds of machine tools on the first day is the denominator, and the total number of machine tools required for producing various products is the numerator. The average device utilization factor Z on the first day is calculated and Z is used. Objective function.
Then, the linear programming models for subsequent days are successively made and solved, and then the calculation results are adjusted as necessary according to the specific conditions.
(4) Monitor the processing conditions, track the processing conditions of the wire cutting machines, and realize the recording, statistics, and calculation of fault alarms, workpiece preparation prompts, processing end reminders, and machining quantities.
5 control system
The DNC system uses a master-slave computer architecture. The wire cutting machine can work independently under the control of a computer. Therefore, the control system should have the control function of a common CNC wire electric discharge machine, which will not be discussed in detail here. In addition, the control system should be capable of two-way communication with the host to provide information for monitoring and management.
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