2.1 Features and structure of WEDM
Wire Cut EDM (
Wire Cut EDM
) is a kind of EDM in special processing.
A process that directly utilizes electrical or thermal energy for processing. The basic principle of processing is to use the rail fixed on the guide wire frame
Continuously moving electrode wire (molybdenum wire
/
copper wire) on the track is used as the electrode, and there is an appropriate gap between the electrode and the material to be processed.
Under the premise, apply enough pulse voltage to make spark discharge between the electrode wire and the workpiece, etch away the processed material.
material, and at the same time control the movement of the machine tool worktable to form a relative movement with the movement of the electrode wire, so as to achieve the erosion of the surface,
The purpose of cutting and forming is to process products that meet user requirements. The principle of wire electric discharge machining process is shown in the figure
2-1
shown. The processing structure of the wire cutting machine tool is as follows
[25]
:
The processing method of wire cutting machine tool has the following characteristics:
1
) There is no need to make electrodes with specific shapes, and the use of electrode wires with smaller diameters is not only low loss, but also beneficial to
The pulse width and average current are reduced, and the setting range of process parameters is small, thereby improving the precision of EDM,
Reduce costs while shortening the processing cycle;
2
) The wire cutting machine tool is mainly for processing plane graphics, and generally complex cavities can be processed, except for the inner
For parts with a minimum arc limit at the corner, due to the error between the machining gap and the electrode wire, the corner arc must be
must exist;
3
) The amount of erosion of the workpiece during the processing is small, and for the trial production of precious material parts, the processing materials are saved,
Make the trial production of parts have more operating space;
4
) The working fluid of wire electric discharge cutting adopts water-based fluid or deionized water, etc., which has no pollution to the environment and is harmful to the human body.
No harm, can be used repeatedly after filtration;
5
) Most of the WEDM machine tools have four-axis linkage function, which can realize up and down special-shaped, variable taper and torsion
Surface processing. Using the combination of movement and rotation, it can process more complex surfaces such as spiral surfaces and hyperbolic surfaces.
complex spatial surfaces.
Wire EDM can be divided into high-speed reciprocating wire EDM according to the wire speed
wire
"
), medium wire electric discharge machine and low speed one-way wire electric discharge machine (commonly known as
"
slow wire
"
) three
kind. The high-speed reciprocating wire electric discharge machine tool is a model independently developed by my country. Its structure is simple and cost-effective
High, fast processing speed, but the electrode wire shakes a lot, and it is easy to break the wire during processing, which is caused by the reciprocating use of the electrode wire
loss, which reduces the quality of product processing. Medium-feeding wire is a compound wire-feeding technology, which can
In the high-speed wire-feeding machine,
8-12mm/s
high-speed wire-feeding is used for rough machining, and
1-3mm/s
low-speed wire-feeding is used for rough machining.
Perform fine machining and use multiple cutting technology to achieve the purpose of improving the surface quality and cutting accuracy of the workpiece.
Low-speed unidirectional wire EDM machine tool generally
performs unidirectional cutting movement at a cutting speed lower than
0.2m/s .
Equipped with automatic wire threading and constant tension device, the electrode wire tension control is constant without shaking, the processing process is stable and high precision
Processing, using non-resistive anti-electrolysis power supply.
The high-speed reciprocating wire EDM machine tool consists of the following four parts
[28]
:
Machine bed body: The bed body includes the machine bed, the wire feeding system composed of the wire feeding cylinder and the wire guide arm, and the
XY
direction feeding system.
Move the workbench. The bed is the foundation of the machine tool, which plays the role of fixing and supporting. A good bed is the wire cutting machine tool
The key to stable operation. The wire walking system is divided into a wire roller and a wire guide frame, and the motor drives the motor on the wire roller and the wire guide frame.
The reciprocating motion of the pole wire is a part of the motion control of the wire cutting machine tool.
The XY
table is the movement of the wire cutting machine tool
The soul of control, its movement is mainly driven by two stepper motors, and the motor is driven according to the NC code to complete the contact with the electrode
The relative movement of the wire can cut out the required shape and size of the workpiece.
Working fluid system: working coolant for wire cutting, generally has good cooling, lubricating and cleaning functions,
It also has special properties such as anti-broken wire and de-separation. The working fluid can help the product to obtain the ideal processing finish, and at the same time
Improve the processing efficiency and prolong the life of the machine tool. Generally speaking, the ordinary working fluid can be reused many times after being filtered.
High-frequency pulse power supply: In the processing engineering, the high-frequency pulse power supply has a high output between the electrode wire and the workpiece
Frequency pulse voltage, the positive pole of the power supply is connected to the workpiece or the conductive block of the machine tool, and the negative pole is connected to the electrode wire. can pass through
The pulse generation module generates pulses, and changes the spark discharge voltage by adjusting the pulse width and pulse amplitude of the pulse signal.
Flow size, excellent power supply system, can control processing feed according to different materials and different processing requirements, automatic
Master Regulator Output Voltage.
Control system: The control system is the core of the wire cutting machine tool motion completion, from engineering drawing drawing to reading processing
The program code and the final product cutting process all supervise and control the movement of the machine tool. excellent line
Cutting CNC expert system can monitor trajectory control (worktable movement) and quality control (electrical control) in real time during processing.
Source system), detect the average voltage of the discharge gap during processing, and respond through the feedback of the frequency converter, so that
Automatically adjust the processing feed rate
[29]
.
2.2 Design of WEDM software system
This topic takes the high-speed reciprocating wire EDM CNC machine tool as the operating object platform, and designs an electric circuit for it.
Spark wire cutting motion control system. The realization of the functions of the WEDM numerical control system needs to be combined from the software level and the hardware level.
Comprehensive consideration of the two levels of the software level, respectively analyzing the functions required to be completed by the software and hardware, and collaborative development to achieve
The purpose of the final automatic control
[30]
. The function realization design of the system software level is as follows:
Software-level functions
:
software functions mainly realize
CAD/CAM
functions.
Realized by
CAD function module
The function is to generate engineering drawings, provide graphics drawing functions (such as rectangles, arcs, curves, etc.) and graphics editing
Functions (such as cutting, mirroring, chamfering, etc.), this module also provides auxiliary functions (key point capture, text
file management, etc.).
The CAM
module is divided into four parts: parameter configuration, trajectory acquisition, code generation, and processing simulation
[25]
,
After
the processing graphics generated by the
CAD module are sorted, track offset, and processed by processing simulation, they are transferred to
Replace it with displacement increment and store it in the code, and carry out computer simulation to verify the accuracy of processing according to the generated code.
To realize the control of the wire cutting machine tool, the requirement at the software level is that it must be able to allow users to quickly and accurately
Draw engineering drawings that can be used for processing, help users set relevant parameters, and simulate processing through the system
function, the system automatically performs operations such as trajectory offset, and stores the primitive information and position coordinate information for downloading
One-step software motion control calls
[32]
. The schematic diagram of software function realization is shown in Figure
2-2
.
The laboratory has completed the development of three versions of the wire cutting software control system, which are the development of
the PC
side
Development,
Windows CE
development,
Android
development and application research. Among the three versions,
the PC
side
The software is the source,
the PC
version of
CAWEP
software is complete and powerful, and the next two versions are based on
the PC
version
After the development, the software on
Windows CE
and
Android
have realized
the functions of wire cutting
CAD
and
CAM .
It can meet the basic requirements of wire cutting machine tool software level.
Android
version and
Windows CE
version development, implementation
After the basic functions are realized, it is still being optimized and perfected.
The software running on
the Windows CE
side and
the Android side is
shown in Figure 2-3 .
Show.
Due to its open source and rich hardware options, the Android
platform has unique advantages in the development of CNC systems.
Advantages, the industrial control development of
the Android
system is well in line with the purpose of Made in China
2025
, and it is also the future industrial
According to the trend of control development,
the Android
system has a huge development space in the field of industrial control applications
[25]
. this topic
Aiming at the needs of embedded CNC system and actual industrial control, the group is written in
Java
and
C/C++
mixed programming
The Android
version of
CAWEP
software, in order to solve
the stability and real-time problems of the
Android industrial control system, provides
However, only a few machine tool manufacturers are currently researching
embedded CNC systems based on
Android .
There are not many motion control devices on the market that can support
the Android
system
[34]
.
There are also many unresolved problems for industrial-grade motherboards running
Android systems, such as underlying drivers and interfaces
Calling, etc., although its real-time performance and stability have been greatly improved, but the main field of the current Android system is the real-time
Timeliness, real-time, and power consumption requirements are not too high, but
on systems that have certain requirements for
GUI .
Work on the current market
Considering the requirements of the control system,
the Windows CE operating system is used in industrial control embedded devices, and still has strong competition.
competitiveness.
Windows CE
is
an embedded operating system developed by Microsoft based on
Windows PC system.
Both system customization and software development have strong guarantees provided by Microsoft, and
C/C++
is used as a development language,
It is the best language for mechanical and electronic control for low-level applications, and it still has great advantages in the field of industrial control.
Windows
The main features of the CE
system are structured, modular, multi-threaded, and preemptive multi-tasking operations. These features can
It ensures the stability and real-time performance when it is applied in industry, and can be directly developed for the underlying application.
Windows
The CE
system design concept is customizable, combined and configured, and the design concept of
the Windows CE
system is the same as that of the embedded
Consistent with each other, developers can develop custom minimum functional systems according to actual needs
[35]
.
Windows CE
software application development programming is close to
windows
, the development cycle is short, and the system stability coefficient is high.
Windows Embedded Compact 7
began to support multi-core operation. The industrial field requires the system platform to have real-time
Features such as stability, stability, and convenient development environment, relying on
MSMQ
(
Microsoft Message Queuing
)
Under the advanced application service,
the Windows CE
system realizes the comprehensive integration of industrial production functions, for real-time
For some intelligent industrial control industries with high performance requirements,
the Windows CE
system can also handle it with ease.
Comprehensively consider the advantages and disadvantages of the two embedded version software, the difficulty of the actual development process, and the
After considering factors such as the processing requirements of the machine tool and supporting applications in the market, it was finally decided to use
the Windows CE
version software
CAWEP
(
Computer Aided Wire-EDM CNC Programming System
-Computer Aided Wire Cutting
CNC programming system) software as the basis, complete the follow-up development, and realize its motion control function.
WindowsCE
The operating system can be customized according to the basic functional requirements of the wire cutting machine tool to ensure its performance and reduce the
power consumption, startup time, etc.
In the process of application software development, the Windows API
that can be used
reduces the difficulty of development,
And there are a large number of mature motion control hardware products supporting
Windows CE
system on the market.
This paper develops
CAWEP
software, the development tools used are
Visual Studio 2005
components, developed
Commonly used components such as editor, debugger and compiler are included in
Visual Studio 2005
,
Visual Studio 2005
includes
VB
,
VC++
,
C#
and other compilation environments, and the code writing for the realization of specific functions
It is all done under the framework of
MFC
dialog box.
MFC (Microsoft Foundation Classes)
is an object-oriented programming and
Application
The perfect combination of framework
is a
C++
class library of Microsoft Corporation, which is the core of
VC++
and encapsulates many
Many
windows API
functions are a combination of
C++
and
Windows API
; they are completely
encapsulated in
C++
The structure and functions in
the Windows SDK ;
MFC
is mostly used to develop various visual programs including windows, graphics, etc.
sequence.
Creating a new MFC project in
VC++
is equivalent to establishing a general framework for development
The developer has completed the initialization of the generation and management of various windows, toolbars, and menus, and the developer does not need to go to
Solve the more complex but tedious basic problems such as window registration, generation and management using
Windows API
[36] .
The MFC
generator framework is shown in Figure
2-4
.
2.3 Hardware system design of WEDM
After designing the software main control system, combined with the existing hardware equipment, aiming at the actual motion control, complete the machine
The movement of each part of the bed realizes the movement control of the machine tool. This article uses the Foster
DK77
series of experimental machine tools
In order to realize the motion control of WEDM machine tools, it is necessary to understand the basic information of the machine tool,
The composition structure and control principle, and the basic information of the machine tool are shown in Figure
2-5
.
In this paper, the design of hardware function modules is divided into the following major modules:
1
) The main control system of the workbench: consists of
XY
Composed of stepping motors in two directions, the relative movement trajectory between it and the electrode wire is the outline of the product.
The control of the digital workbench is called trajectory control
[37]
;
2
) The wire transport system and the working fluid system: the movement of the wire drum drives the motor
The movement of the pole wire, the guide rail of the wire rack is the movement path of the motor wire, the cooperation of the two determines the movement of the electrode wire, the electrode wire
The tension, vibration, etc. will affect the processing quality;
3
) Working fluid system: in the process of processing, to the electric
The pole wire sprays working fluid, its function is to gather electric energy, protect the electrode wire, etc.;
4
) Power supply system, the load of the power supply system
Responsible for providing high-frequency pulse voltage to the electrode wire to generate spark discharge, voltage, current, and feed speed during processing
Both determine the quality of the workpiece, so the power system is also called quality control
[38]
. Understand the function of each hardware part
It is a function that needs to be realized at the hardware level to find out the corresponding control method.
The control of wire cutting machine can be divided into motion control, electrical control and power control. Machine tool table
XY
square
Directional motion control is the core of machine tool motion control. Its motion is mainly driven by two stepping motors. According to the above
The data information of the bit machine completes the relative movement with the electrode wire, so as to cut out the required shape and size of the workpiece;
The excellent power supply system can control the processing feed and independently adjust the output according to different materials and processing requirements.
output voltage, this topic uses the power supply as the research group's self-made power supply, which can be adjusted by adjusting the pulse width of the pulse signal and
The pulse amplitude changes the magnitude of the spark discharge current; the main task of the electrical control of the machine tool is to control the three-phase electrical
The start and stop of the machine, speed regulation, forward and reverse rotation and switch of the working fluid pump.
At the beginning of the project implementation, there are two sets of schemes for the design of hardware function realization in this experiment. One is dual core
Control the single board,
run the software in the
ARM chip, get the processing data, and
convert the data in the DSP chip
Into a processing instruction, two chips are welded to a
PCB
board, and the two chips
communicate with the
SPI bus.
Completion of the above concept requires good software and hardware capabilities. The software needs to complete the development and integration of the existing
CAWEP
software
Optimization, as well as a large number of programs such as underlying drivers, hardware requires comprehensive capabilities such as board making, circuit design, and component use.
At present, the concept and the laboratory are in progress simultaneously.
Considering the development difficulty, time and help for subsequent development, the author's topic is finally determined to realize wire cutting
The basic functions of the machine tool, complete the follow-up development of
CAWEP
software, so that it can realize the real
CAM
function,
Realize the control of each module of the machine tool, so that the machine tool can run normally, and lay a good software foundation for subsequent development.
hardware base. In order to complete the control of the machine tool, we complete the hardware design from the following aspects:
1
) The movement of the workbench is the core of the system design, and the movement of the workbench is jointly controlled by the software system and the motion controller.
The same completion, the trajectory of the worktable movement is the processing trajectory generated by the software system, we use
Windows
The motion controller of the CE
system, carry out secondary development on the motion controller, and call
the API
function to make the motion
The controller outputs direction and pulse signals to achieve the purpose of driving the motor. The development method of combining software and hardware can
Enough to make the control of the main control system more suitable for the actual working conditions;
2
) The relevant control of the wire walking system, lubrication system and power supply system are all controlled and supervised by the frequency converter.
After completing the connection of the terminals, the inverter can control the variable speed of the wire drum motor and the water pump through the peripheral interface circuit.
Functions such as start-stop and power protection, and the inverter accepts commands from the host computer, and only needs to accept high and low through the wiring terminals
Frequency can be.
3
) The power supply is a high-frequency pulse power supply developed by the laboratory itself, using
stm32
chip as the power supply
The main control chip can adjust electrical parameters such as voltage, current and pulse. For the supervision and control of the power system,
In this paper, the relevant part of the work is also completed through the frequency converter. The hardware control principle of the machine tool is shown in Figure
2-6
.
After completing the above design, this article chooses a motion controller that supports
Windows CE
system to
Complete the control of the movement of the workbench. The design of this motion controller is embedded industrial control (
ARM
architecture) and operation
Combination of automatic control, software and hardware integration scheme. The software operating system is customized and configured to achieve the minimum
Functional
WINCE6.0
operating system, the hardware part adopts
ARM
architecture industrial computer and special motion chip
It not only ensures the stability of the system operation, but also has powerful computing power and output capacity.
This motion controller provides
4-
axis linkage control; the frequency and voltage of the output pulses are fully satisfied
The needs of different stepping drives; support
S-
curve acceleration and deceleration and
T
-shaped acceleration and deceleration interpolation control, allowing developers
Design the control type by yourself during the development process; support any
2-4 axis
linear
interpolation and circular interpolation; provide
The DLL
library and part of the source code can call related functions to complete related activities.
The motion control functions provided by the motion controller include the following types: control of pulse output mode;
Speed curve setting, including
S
-curve and
T-curve; displacement control; detection of the motion state of the specified axis; axis
running stop; change the current running speed during single-axis running; change the target position; single-axis continuous movement; specify
Axis acceleration, deceleration and stop, including emergency stop, slow stop, etc., motion conditions; set the origin signal and limit signal
Effective level; interpolation motion setting, there are options for linear, circular interpolation and interpolation axes; gap compensation value setting
place. Reasonably calling the function can perfectly meet the motion control requirements of the wire cutting table. motion controller master
The board is shown in Figure 2-7.
In this paper, the three-phase motor of the wire transport system of the machine tool, the start and stop of the water pump of the working fluid system, the power supply protection and the discharge control are all
It is completed by the frequency converter. This project chooses
the special frequency converter
SY-AX2 Xin dual-source wire cutting, as shown in
Figure 2-8 .
The frequency converter has complete functions, easy operation and abundant interfaces. Its functions are introduced as follows:
1.
The inverter is equipped with input and output signals such as left and right strokes with adjustable polarity, processing start and stop, switching high-frequency power supply, etc.
number switch. The user can choose the normally open or normally closed state to adapt to the machine tool requirements of different manufacturers and the host computer
Design of control signals;
2.
It comes with a complete internal power supply system. In the broken wire detection circuit, there is no need for external power supply, and the lead-in
When the feet are connected to the corresponding position, safe and reliable broken wire detection can be completed;
3.
In the debugging state, it has a signal shielding function, which can control the motor to switch to a low-speed state, easily
Finished threading;
4.
The acceleration of the motor can be adjusted in a large range, making the commutation faster and the efficiency of the machine tool higher. Using
3
signals
The 8- stage speed control
is carried out on the number line
, so that the machine tool can meet different speed requirements and meet the processing requirements of the workpiece, from
To improve the processing quality of machine tools;
5.
Integrated design of function control and frequency conversion adjustment. The inverter only needs to directly connect the relevant signals to the corresponding
All controls can be realized through the interface. Compared with general-purpose inverters, it saves a lot of parameter settings and is easy to install and use.
Single convenience.
2.4 Summary of this chapter
This chapter introduces the principle and characteristics of WEDM, according to the composition and characteristics of WEDM
Based on the analysis of system function requirements, the overall design scheme of wire electric discharge machine tool control is proposed. in software design
Using
Windows CE6.0 system
to further develop the
existing
CAWEP software, the combination of software and hardware
The development mode enables a better combination of software development and hardware use; in hardware selection, the use of
ARM
The microprocessor is used as the main control board, and the motion controller supporting
Windows CE6.0
system is selected, and the controller is
Carry out secondary development, control the movement of the worktable, select the special frequency converter for wire cutting as the auxiliary control device, and turn the electric
The control of the source system, the working fluid system and the wire system are all handed over to the frequency converter.