Research on Wire Discharge DNC System for Mold Manufacturing System
Abstract : The structure and implementation method of direct digital control (DNC) wire EDM system for mold manufacturing system are studied to improve the automation level, overall production efficiency and response speed of the system, and provide a certain structure for the wire-cut DNC ​​system. The theoretical basis.
Keywords: mold manufacturing system wire cutting DNC
1 Introduction
Mold manufacturing levels are one of the important indicators that reflect the overall manufacturing level of a country. With the development of the national economy, the requirements for molds are getting higher and higher. 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 the order may determine its success or failure in the market. To improve the response speed, it is not enough to improve the number of equipment and single production efficiency. The automation level and management level of the mold manufacturing system should be improved as a whole.
Wire EDM plays an important role in mold manufacturing systems. A large part of the mold parts, especially the mold key parts (mold forming parts), is completed by wire cutting, and the workload is large. Therefore, it is meaningful to construct a direct digital control (DNC) wire EDM system that matches the mold manufacturing system and has a high level of automation and certain management coordination.
2 The overall structure of the wire-cutting DNC system
The numerical control system of the wire electric discharge machine has been perfected. However, there are still a large number of wire cutting machines that are equipped with a control system. The degree of automatic programming is low, especially in the early control systems. It is controlled by a single board machine, and manual or computerized programming is used to input manually or perforated tape. The more advanced wire cutting machine is equipped with a microcomputer, which uses the larger graphics and data processing functions of the microcomputer for drawing, programming and even control. Even so, most of them are used alone. This is slow and inefficient for manufacturing systems that produce large quantities of molds (multi-variety, small batches), and is incompatible with mold manufacturing systems that require high efficiency.
In a slightly larger mold manufacturing plant (workshop), the number of parts that require wire cutting is large, and often several or even dozens of wire cutters of various specifications are arranged. Therefore, the concept of the group control system gradually appeared, but it simply connected the automatic programming system to the wire cutting machine, but saved the workload of programming and input.
In order to improve the reaction capacity and production efficiency, multiple wire cutting machines should be constructed to form a complete DNC system. The DNC system itself should have a high level of automation and a certain level of computer-aided management, while maintaining the flexibility of the single machine and the reconfigurability of the system, and integrated with the CAD of the mold manufacturing system, that is, the mold CAD software The generated design information is quickly and safely connected to DNC to realize CAD/CAM integration.
Figure 1 shows the overall structure of a wire electric discharge machine DNC 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 ensures the independence and reconfigurability of the wire cutting machine. It embodies the characteristics of the open architecture, so that the system has good system. The scalability, maintainability, portability, etc., through the data interface to achieve communication between the layers. The system includes graphics processing functions. On the one hand, it receives CAD information transmitted by virtual enterprises, enterprise alliances, CAD centers, etc., and after processing by data exchange format (such as IGES), generates control programs through an automatic programming system; on the other hand, it can Design the mold parts and convert them into control commands. The programming system can also be programmed directly. The management system plans DNC work for several days to balance the various line cutters in the system and to alert managers and operators.
Figure 1 The overall structure of the wire-cutting machine DNC system
3-wire cutting automatic programming system
To achieve CAD/CAM integration of the system, we must first solve the problem of inputting graphics. The Auto CAD graphics system has powerful graphics input and editing capabilities and is the most active CAD system on the PC. The wire cutting automatic programming system based on Auto CAD environment has a good application prospect. The module structure of the automatic programming system is shown in Figure 2.
Figure 2 Module structure of the automatic programming system
The software includes system functions (3B, 4B, ISO code file editing and printing, system parameter setting, etc.), code instruction graphic inverse conversion (to check the accuracy of code instructions), code instruction conversion, parameterization of each special part Design, NC communication, etc. The system can accept the design result of the mold design software such as UGII, and directly convert it into CNC command according to the zoomed gap of the graph.
Parametric modeling parametric design for specialized parts such as parabolas, involute parts, cams, gears, and more.
Figure 3 shows the drop-down menu for the module on the system interface.
Figure 3 System interface and parameterized design drop-down menu
In order to realize CAD/CAM integration of wire cutting, it is also necessary to convert CAD graphics into commands that NC machine tools can accept. The algorithm steps are as follows:
(1) Use AutoCAD's offset command to generate a tool curve.
(2) Reorder the CAD graphic elements in processing order. The algorithm is:
STEP1: Select the machining first point and machining direction, find the first element of the machining in the graphics database, and set its end point to the current point. The found graphic elements set the sorted flag.
STEP2: Search for the graphic element related to the current point. If the graphic element is not sorted, the element is the current element, and the other end point of the current element is the current point, and the element is set with the sorted flag.
STEP3: Repeat STEP2 until the graphic is closed or all elements are sorted.
(3) Generate NC commands for all the graphical elements that have been sorted
Wire cutters retain a separate controller structure for improved real-time and reliability. The computer is connected to the line cutter controller communication port through the RS232 serial port, and can control the machine tool by real-time input line cutting program, or control the paper tape input through the machine's telegraph head. At the same time, the controller can transfer the machine status information to the computer, such as wire breakage, short circuit, start and end of machining, etc., to realize the management and control of the computer for multiple wire cutting machines. The serial communication between the computer and the wire cutting machine is realized, and the principle block diagram is shown in FIG. 4 .
Figure 4 Serial bidirectional data transmission schematic
4 Management System
The management system has the following functions:
(1) Generate a cutting process parameter library and provide opinions on parameters such as cutting current, cutting speed and pulse frequency.
(2) Calculate the number of cutting machining hours for each part, and calculate the machining time of the part according to the machining thickness, path length and process parameters of the part.
(3) Generate a scheduling plan.
Schedule the time according to the batch, taking into account the balance and maximum load of the equipment of various specifications. The assignment plan is by day. When assigning, consider: 1 to ensure the completion of the operation plan from the quantity and variety; 2 batches of products are concentrated as much as possible; 3 due to production technology preparation, etc., some parts can be processed after a certain day; Product requirements are completed within the first few days.
The problem is very complicated if you calculate it at the same time every day in the plan. Calculated daily from the first day to the last day according to the above conditions.
Assume that there are m types of wire cutters in the workshop, and i (i = 1, 2, ..., m) is used to process n kinds of products, which are denoted by j (j = 1, 2, ..., n). The planned quantities of these products are indicated by dj.
Aij is used to indicate the number of hours of the i-th machine tool required for the processing unit j product, and bik is the production capacity of the i-th equipment in the k-th day (time). Xjk indicates the number of products planned to be produced on day k.
According to the previous assumptions, such as the 5th and 8th products to the second half of the production, the No. 4 product is required to be completed the next day. Then the second day's linear programming model is:
Satisfy:
The significance is that the total production capacity of the machine tools of various specifications on the first day is the denominator. The total number of machine tool hours required for the production of various products is numerator, and the average equipment utilization factor Z of the first day is calculated, and Z is Objective function.
Then, the linear programming models of subsequent days are sequentially made and solved, and the necessary adjustments are made according to the specific conditions.
(4) Monitoring the processing situation, tracking the processing conditions of each wire cutting machine, and realizing the records, statistics and calculations of fault alarm, workpiece preparation prompt, processing end reminder and processing quantity.
5 control system
The DNC system uses a master-slave computer structure. The wire cutting machine can work independently under the control of the computer. Therefore, the control system should have the control functions of the common numerical control electric discharge wire cutting machine, which will not be discussed in detail here. In addition, the control system should be able to communicate bi-directionally with the host to provide information for monitoring and management.
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