[Abstract] This paper introduces design and implementation of a precision mold intelligent manufacturing unit. First introduce the overall structure and composition of precision mold intelligent manufacturing unit, elaborate on the overall control principle of system, deeply analyze communication structure and communication methods between industrial robots, processing equipment, PLC controllers, and MES computers. Then it introduces in detail basic control flow of main program of industrial robot, loading and unloading program of material warehouse, loading and unloading program of machine tool. Finally, basic process flow of intelligent manufacturing production system is summarized. Through a small batch processing example of a plastic bottle mold core, it is proved that intelligent manufacturing unit can effectively improve mold production efficiency and reduce single-piece cost.

Mold is an important process equipment in modern industrial production, and mold technology is core technology of manufacturing industry. With development of mold products in direction of larger, more precise, more complex, more economical and rapid, technical content of mold products continues to increase, mold manufacturing cycle is continuously shortened, mold production is developing in direction of precision, efficiency and digitization, traditional labor-intensive molding process has been difficult to satisfy. Digital manufacturing and intelligent manufacturing technology have become a hot spot in research of precision injection mold manufacturing technology. Core is core part of mold, its curved surface structure is complex, processing technology is difficult, and cycle is long. In order to improve efficiency of core processing, an intelligent manufacturing unit for precision mold parts is designed, which includes CNC machining centers, EDM processing equipment, industrial robots, automatic fixtures, RFID technology, MES systems, etc. System realizes automatic clamping of mold parts through 3R fixtures, uses RFID chips to realize rapid identification of mold parts, uses industrial robots to realize automatic loading and unloading of mold parts. Paper expounds control structure and communication network structure of intelligent manufacturing unit in detail, analyzes control flow of industrial robots. Finally, through an example of batch processing of core of plastic bottle mold, basic process flow of intelligent manufacturing unit is summarized.

Hardware of intelligent mold manufacturing unit is composed of processing equipment, industrial robot system, RFID system, material warehouse, loading station, etc. There are a total of 6 processing equipment, of which 2 CNC machining centers are used for milling of mold workpieces (cores), 1 machining center is dedicated to electrode processing, and 3 EDM processing equipment is used for electrical discharge machining of mold workpieces. Intelligent manufacturing unit is equipped with two mold workpiece storage and one electrode storage. Each mold workpiece storage room is divided into 4 layers up and down, each layer can store 4 workpieces; electrode storage room is a rotating storage room, which is divided into 6 layers up and down, each layer can store 30 electrodes. Industrial robots are responsible for automatic loading and unloading of machine tools, as well as automatic loading and unloading of materials at loading station and material warehouse, transporting mold workpieces and electrodes between processing equipment, material warehouse and loading station. In order to extend operating range of robot, it is necessary to configure guide rail to achieve coverage of all operating equipment. The overall layout structure of intelligent manufacturing unit is shown in Figure 1.
Mold workpiece and electrode can be quickly positioned and clamped through 3R fixture. Repeat positioning accuracy of 3R fixture is 0.002mm. Each mold workpiece and electrode is equipped with a tray, and tray is embedded with an RFID chip. A unique identification code is assigned to each mold workpiece/electrode through RFID system, which exists in the entire order cycle of workpiece, is used to identify and track processing status of workpiece, manage processing data of workpiece, such as offset of processing coordinate system, processing program, electrode code, discharge program, etc.
Figure 1 The overall layout of mold intelligent manufacturing system

 

Control of the entire mold intelligent manufacturing unit is divided into three levels: MES layer, control layer and equipment layer. Top MES layer is responsible for production scheduling management, process task scheduling, field equipment management and monitoring, inventory material management at workshop site, including MES software and process database system. Middle control layer is responsible for control of various devices and real-time data collection, mainly including robot controllers and PLC controllers. Bottom equipment layer is responsible for completing specific processing tasks, such as electrical discharge machining, milling processing, and logistics handling, etc. It mainly includes 6 processing equipment, industrial robot bodies, and material warehouses. Figure 2 shows the overall network communication and control structure of intelligent manufacturing unit.
In this system, MES computer is main control calculation, robot controller and PLC are main controllers. MES computer is connected with robot controller and processing equipment through industrial Ethernet, communication between MES computer, robot controller and processing equipment adopts TCP/IP communication protocol. MES software directly reads operating status of processing equipment through open interface of numerical control system, modifies G54 coordinate offset, and downloads processing program to memory of processing equipment. MES software communicates with robot motion control program through SOCKET, MES software realizes interaction and control of robot motion by modifying value of robot R[1]~R[5] register.

 

Figure 2 System control and communication structure
Robot controller is responsible for controlling movement of robot and end effector. PLC is responsible for controlling logic control and signal acquisition of the entire production line. Robot controller and PLC communicate through CC-LINK bus. PLC chooses Mitsubishi Q series, main base board Q38B, CPU Q03UDECPU, configures a remote communication module QJ61BT11N, input and output modules QX40/QY40P. PLC is master station, processing equipment is remote IO station, rotating electrode library is remote equipment station, remote communication module is responsible for communicating with remote equipment station and remote IO station. Remote end is equipped with 1 CC-LINK input module AJ65SBTB1-16D1, which is used to collect signals from processing equipment such as air pressure and equipment status; it configures 3 CC-LINK output modules AJ65SBTB1-8T, used to control fixture switch of processing equipment, machine tool air blowing, equipment pressurization and other actions; in addition, a separate Mitsubishi FX5U-64M PLC is used to control rotating electrode library. For loading station and material warehouse, I/O communication is directly carried out through input and output module QX40/QY40P.

Industrial robots are key equipment to realize automatic mold production. In this system, main function of industrial robot is to receive tasks from MES software, to complete material transfer between processing equipment, material warehouses, and loading stations, to transfer data with PLC controller. Therefore, its tasks are mainly divided into functions such as loading and unloading of materials in warehouse, loading and unloading of machine tools, scanning, and zero return.
Robot controller receives tasks from MES software through Socket Message. Mitsubishi robot controller allows use of registers R[1]~R[5] to communicate with upper computer. Definition of communication protocol between the two is shown in Table 1.
SOCKET communication R variable definition

Detailed process of robot master control program is as follows:
(1) Step 1. Program initialization, initialize register value.
(2) Step 2. Check R[5] register value. If R[5] register value is not equal to local R[20] value, it means that a new task is issued, otherwise no new task is issued, and system continues to wait to receive new tasks.
(3) Step 3. Accept new task, assign R[5] register value to local register R[20], and assign value of R[1]~R[4] register to local register R[11]~R[14] respectively. Mark robot status as busy, and no more new tasks will be accepted at this time.
(4) Step 4. Judging value of R[11], robot enters a different subroutine.
(5) Step 5. If value of R[11] is 1, 2, 3, 4, enter subroutines of workpiece scanning, material storage reclaiming, machine loading and unloading, material storage discharging respectively, and perform corresponding operations. After execution is completed, main program jumps to step 1 and continues to wait for task of host computer.
(6) Step 6. If value of R[11] is 99, it means task is over, and program terminates after robot motion returns to zero position. Main program flow of robot is shown in Figure 3.

 

Figure 3 Robot main program flow

Intelligent mold manufacturing unit is equipped with two Beijing Jingdiao JDMR600 5-axis machining centers and one 3-axis engraving machine JDCT600T, three Mitsubishi EA8A CNC EDM machines, and one FANUC R-2000iC/210F 6-axis articulated robot. As shown in Figure 4.
Take small batch (200 pieces) processing of a beverage bottle mold core as an example, automatic production process is:
(1) System preparation. Turn on system, check whether CNC and EDM machine tools are working normally, check whether oil level and air pressure are normal. After finishing preparation of processing equipment, set equipment to automatic state after equipment returns to zero.
(2) Workpiece clamping. Install workpiece material on 3R fixture through a special fixture, as shown in Figure 5.
(3) Workpiece is centered. Use CMM to complete centering of workpiece, record coordinate offset from origin of workpiece to origin of 3R fixture.
(4) Create MES order. Create an order in MES software, set coordinate offset, upload CNC program, and write code to RFID chip on 3R fixture tray.
(5) Automatic processing. Put workpiece into loading station, MES starts to automatically execute order task; after system detects signal of loading station, robot automatically picks up material at loading station and places it in storage.
(6) MES software automatically arranges orders according to current material warehouse information and CNC status to complete processing of workpiece.
(7) Reclaiming at loading station: After processing is completed, robot puts completed workpiece into loading station. Operator manually takes out workpiece.
Using automatic production mode, this unit can work continuously for 24 hours, production cycle of a single bottle mold product is shortened to 5 hours, and a single device can process 4.8 products per day, which can effectively improve efficiency and reduce labor costs.

 

Figure 4 An example of an intelligent manufacturing cell

 

Figure 5 Examples of processing plastic bottle cores

In order to improve processing efficiency of core parts, an intelligent manufacturing unit for mold parts is designed to realize automatic milling and electrical discharge machining of core parts and other parts. Through a small batch processing case of a plastic bottle mold core, manufacturing process flow of intelligent manufacturing unit is analyzed, it is confirmed that intelligent manufacturing unit can significantly improve processing efficiency of parts and save labor costs.