INTRODUCTION
Overview
Wire Electrical Discharge Machining (WEDM) is an advanced electro-thermal machining process that employs a single strand of electrically conductive wire to make precise cuts in metal workpieces Utilizing a dielectric fluid, this non-contact cutting technique relies on electric discharges, or sparks, to melt and vaporize the material, ensuring high accuracy and intricate designs.
The wire-cutting process utilizes a thin wire electrode with a diameter of 0.1mm to 0.3mm, while the workpiece is mounted on a CNC worktable This method avoids direct contact between the wire and the workpiece, ensuring precision without distorting the wire's path or the material's shape The wire is quickly charged to the desired voltage, and when it reaches the appropriate level, a spark bridges the gap, melting a small area of the workpiece Surrounding the wire with deionized water helps cool and flush away debris, maintaining a gap of 0.025mm to 0.05mm between the wire and the workpiece.
When it comes to the origin of WEDM, this machining method first developed in
In 1943, scientists Butinzky and Lazarenko in the Soviet Union laid the groundwork for wire-cutting machining, which underwent a significant transformation in the 1970s due to advancements in high-power pulse generators, innovative cutting wire types, and effective dielectric purging methods.
Reasons for topic selection
The continuous advancement in science and technology has led to rising quality standards in mechanical engineering products, prompting the development of precision-enhancing processing techniques such as Wire Electrical Discharge Machining (WEDM) This method is crucial in the manufacturing sector, especially within the aerospace, defense, automotive, and general engineering industries WEDM is extensively used to create intricate two- and three-dimensional shapes and high-precision components from conductive materials.
One of the most extensively studied areas in manufacturing is the modeling and optimization of process parameters to achieve high-quality products at reduced production costs As a result, many researchers have investigated ways to enhance machining settings across various materials Recognizing the advantages of Wire Electrical Discharge Machining (WEDM), the authors chose to focus their capstone project on examining the impact of cutting parameters on surface roughness and dimensional deviation when machining quenched SKD61 steel using WEDM.
Related topic research
Phan Hung Dung's master's thesis, titled "Optimizing Technological Parameters on EDM Wire Cutting for Stainless Steel," was published in 2008 at Thai Nguyen University of Industrial Technology The research focuses on optimizing key parameters such as Pulse on Time (Ton), Pulse off Time (Toff), and Servo Voltage (Ui) while utilizing 5mm-thick ANSI 304 stainless steel as the workpiece material The study investigates the experimental ranges of Ui (70-90), Ton (0.1-0.7), and Toff (8-16) to analyze the impact of individual parameters and their interactions on productivity and discharge gap during the wire cutting process.
In their research titled “Strategic Optimization and Investigation Effect Of Process Parameters On Performance Of Wire Electric Discharge Machine (WEDM),” authors Atul Kumar and Dr D.K Singh explore the optimization strategies and the impact of various process parameters on the performance of WEDM This study was published in the International Journal of Engineering Science and Technology (IJEST), Volume 4, Issue 06, in June 2012, spanning pages 2766 to 2772.
In this experiment, a 0.25 mm diameter brass wire was utilized as a cutting tool on a CHMER-CW64GS WEDM machine, with a Skd 61 alloy steel plate measuring 100mm x 80mm x 10mm Specimens sized 12mm x 10mm x 10mm were cut following the Taguchi L18 design The study aimed to identify the factors with the most significant impact on cutting speed, surface roughness, and dimensional deviation Results indicated that for cutting speed, the Pulse off time at level 1 (Toff = 22) had the greatest influence, while for surface roughness, the Open Voltage at level 1 (OV = 5) was the most impactful Additionally, the Pulse on time at level 2 (Ton = 10) significantly affected dimensional deviation.
The research conducted by Manish Saini, Rahul Sharma, Abhinav, Gurupreet Singh, and Prabhat Mangla focuses on optimizing machining parameters in wire EDM for 316L stainless steel Utilizing the Taguchi method, ANOVA, and grey analysis, their findings were published in the International Journal of Mechanical Engineering and Technology (IJMET), Volume 07, Issue 02, in March-April 2016.
The study focuses on cutting 20mm x 10mm x 10mm pieces of 316L stainless steel using zinc-coated brass wire with a diameter of 0.25mm To analyze cutting speed (CS) and surface roughness (SR), the authors employed Taguchi, ANOVA, and Grey Analysis methods The findings indicate that the cutting speed significantly influences surface roughness, with Ton being the most critical factor affecting the results.
3 roughness outcomes; the ideal parameter configuration is Toff = 45, Ton = 106, SV 50, IP= 90, and WF= 5
+ Research by the authors Shivkant Tilekar, Sankha Shuvra and P.K.Patowari
“Process Parameter Optimization of Wire EDM on Aluminum and Mild Steel by Using Taguchi Method” was published in Procedia Materials Science 5, 2014, pp 2577 –
The analysis using the ANOVA method revealed that for aluminum and mild steel, spark-on time and input current significantly affect surface roughness and kerf width For aluminum, the most effective parameter for surface roughness in the longitudinal direction is Ton, achieving an efficiency of 98%, while Toff is more effective in the transverse direction at 83% The optimal experimental settings for aluminum are Ton = 25, Toff = 6, Ip = 1, with Wf = 80 for longitudinal and Wf = 85 for transverse directions In contrast, for mild steel, the input variable Ip is the most critical factor for surface roughness in the transverse direction, with a significant influence of 99.98%, and 83% in the longitudinal direction According to the Taguchi method, the best parameter combination for mild steel in the longitudinal direction is Ton = 39, Toff = 6, Ip = 1.
= 85 For Transverse direction, Ton = 25, Toff = 8, Ip = 1, Wf = 75
In their study titled “Experimental Investigation of Wire EDM to Optimize Dimensional Deviation of EN8 Steel through Taguchi’s Technique,” researchers Pradeep Singh, Arun Kumar Chaudhary, Tirath Singh, and Amit Kumar Rana explore the optimization of dimensional accuracy in EN8 steel using Wire Electrical Discharge Machining (EDM) methods The research employs Taguchi’s technique to systematically analyze and improve the machining process, aiming to enhance precision and reduce deviations in the final product This investigation contributes valuable insights into the effectiveness of Wire EDM in achieving superior dimensional control in steel machining applications.
Research Journal of Engineering and Technology (IRJET), Volume: 02 Issue: 03 | June-
In a study conducted in 2015, the electrode wire used was a brass-copper alloy with a composition of 90:10 and a diameter of 0.25 mm The dielectric fluid employed was low-conductivity water, while the workpiece was a block of EN8 steel measuring 200x100x21 millimeters Through the analysis of Taguchi and ANOVA, the researchers determined that the optimal settings for minimizing dimensional deviation were the second level of wire feed (A2), the first level of pulse off time (B1@), and the third level of servo (C3) The findings revealed that servo voltage had the most significant impact on dimensional deviation, followed by pulse off time and wire feed.
In their research titled "Optimization of Dimensional Deviation: Wire Cut EDM of Vanadis-4E (Powder Metallurgical Cold Worked Tool Steel) by Taguchi Method," D Sudhakara and G Prasanthi explored the effects of various parameters on the dimensional accuracy of Vanadis 4E tool steel using an ELECTRONICA ULTIMA 1F WEDM machine The study involved a 100mm x 98mm x 24mm tool steel plate and utilized a coated brass wire electrode with a diameter of 0.25 mm By applying a Taguchi method with an L27 orthogonal array, the authors analyzed six input parameters—pulse on time, pulse off time, peak current, spark gap voltage, wire tension, and water pressure—each at three levels Their findings revealed that pulse on time significantly impacts dimensional deviation, followed by pulse off time and peak current.
The analysis of S/N data indicates optimal parameters for Wire Electrical Discharge Machining (WEDM) on quenched SKD61 steel, revealing a Ton of 118, Toff of 63, Peak Current of 13, and a Water Pressure of 2 This research highlights the importance of adjusting cutting parameters to enhance precision, surface roughness, and machining speed across various steel types The study aims to support professors and students at the University of Technology and Education in Ho Chi Minh City in their exploration of these optimization techniques The focus is on understanding the impact of cutting parameters on surface roughness and dimensional deviation during the machining process.
The urgency of the research
Achieving precise and high-quality surface roughness is essential when selecting optimal technological parameters for machining Currently, most machining parameters rely on default settings provided by manufacturers, which may not be suitable for all materials Quenched SKD61 steel, commonly used across various mechanical applications, requires further investigation into machining techniques This research focuses on optimizing technological parameters for Wire Electrical Discharge Machining (WEDM) specifically for quenched SKD61 steel.
Scientific and practical significance
This study utilizes the Taguchi method for experimentation and parameter optimization to enhance the wire-cutting process of WEDM machines The findings will provide a foundational reference for machining quenched SKD61 steel, focusing on varying technological parameters to achieve optimal product quality.
The research results in optimizing the cutting parameter when machining Quenched SKD61 steel using WEDM have practical significance as well as in manufacturing as follows:
− Contributing to improve product quality and reducing product costs
− Achieving high productivity when machining Quenched SKD61 steel in production, even in batch production
Objectives and research scope
This research aims to analyze the effects of input technology parameters in the Wire Electrical Discharge Machining (WEDM) process on quenched SKD61 steel, focusing on optimizing these parameters Additionally, it investigates the relationship between input parameters and output metrics, specifically surface roughness and dimensional deviation.
− Processing parameters: Servo Voltage (SV) with 3 levels 30, 40 and 50 (V) Pulse
On Time (TON) with 3 levels 6, 10 and 14 (às) Pulse Off Time (TOFF) with 3 levels 10,
14 and 18 (às) Wire Tension (WT) with 3 levels 6, 12 and 18 (N)
− Design of machining process for quenched SKD61 steel
− Measurement of surface roughness and dimension of machined parts
− Determination of optimal cutting parameters using Taguchi method.
Research Methods
The team's experimental methods and data analysis techniques are:
− Learn how to operate the machine
− Compare and distinguish between G, M code in CNC milling against G, M code in WEDM
− Investigate the cutting of fundamental profiles such as straight lines, arcs, and taper
− Research on programming according to a common standard, subprogram
− Refer to publications pertaining to WEDM machining techniques and use the acquired information Collecting references from scholarly journals, books, textbooks, and the Internet
− Utilize the Mastercam 2021 programming software for machining
Utilize Minitab to evaluate and process data in order to identify the ideal set of parameters for the machining process
THEORETICAL BASIC
WEDM Overview
Wirecut electric discharge machining (WEDM), introduced in the late 1960s, was a revolutionary technology that initially struggled with accuracy despite its capability to process hard materials Over the past few decades, significant advancements have been made in WEDM technology, leading to the development of more sophisticated machines that now offer high efficiency and precision.
Wire cutting, also known as wire EDM (Electrical Discharge Machining), utilizes a continuously wound thin wire as an electrode to follow a predetermined machining path The advancement of NC/CNC technology has significantly accelerated the development of spark machines that employ metal wire electrodes, leading to the rapid evolution of wire EDM machines, commonly referred to as spark wire cutters.
The same basic idea underlies a wire cutter, which is also referred to as a wire EDM
An electrically charged electrode generates a spark when it approaches conductive materials, leading to their wear In wire cutting applications, this electrode is specifically made of copper wire, which is the primary difference in the process.
The wire electrode is maintained at a precise gap of 0.002 to 0.003 inches (0.051 to 0.076 mm) from the workpiece using a DC or AC servo system This servo mechanism enables the machine to progress while shaping the material, ensuring that the wire electrode does not short against the workpiece Wire EDM is a non-contact cutting process, allowing for stress-free operation as the wire never touches the workpiece.
A wire electrode, typically made of brass or a brass-zinc alloy with a thickness between 001 and 014 inches (.025 to 357 mm), is commonly used, although tungsten or molybdenum wire may also be employed To ensure precise gap accuracy and repeatability, new wire is continuously fed into the system.
Figure 2.1: Path of Wire Electrode [9]
2.1.3 The Step – By – Step Wire EDM Process
− A Power Supply Generates Volt and Amps:
Figure 2.2: The wire electrode is surrounded by deionized water while the power supply generates volts and amps to produce the spark [9]
Deionized dielectric fluid surrounds wire electrode and workpiece
Voltage and amperage control the spark between the wire electrode and workpiece
− During On Time Controlled Spark Erodes Material:
Figure 2.3: The material is precisely melted and vaporized by sparks [9]
− Off Time Allows Fluid to Remove Eroded Particles:
Figure 2.4: The pressurized dielectric fluid immediately cools the material and flushes away the eroded particles during the off cycle [9]
− Filter Removes Chips While The Cycle Is Repeated:
Figure 2.5: A filtering system removes and separates the eroded particles [9]
In addition to WEDM, there are other EDM processing such as:
Die sinking EDM, also known as Ram EDM, utilizes an electrode submerged in an insulating liquid to erode the workpiece into the desired shape The electrode, shaped to match the intended cavity, is connected to a power supply that guides the machining process This precise method is essential for creating mold cavities, with the operation's speed influenced by factors such as material type, machining area, and conditions.
Micro EDM is a specialized form of electrical discharge machining (EDM) that focuses on creating intricate features as small as 10 microns (0.0004 inches) using tiny electrodes This technique is particularly effective for machining internal geometries such as holes and slots in EDM sinker and EDM milling processes Typically, the electrodes used in micro EDM are slightly smaller than the features being machined In contrast, micro wire EDM (micro-WEDM) primarily deals with external features, allowing for different machining capabilities.
Figure 2.7: Micro – EDM Examples – 0.1mm brass wire [11]
EDM drilling utilizes a spark generated between the workpiece and the electrode tube to erode tough materials, such as tungsten carbide and hardened tool steel, by producing intense heat This advanced drilling technique is capable of creating precise holes ranging from 0.012 inches (0.3 mm) to 0.118 inches (3.0 mm) in diameter, which traditional drill bits cannot achieve.
Figure 2.8: The drill erodes the material with its sparks [12]
Accutex Wire EDM machine
In this experiment, the author uses the Wire EDM (GE-43S) machine that is provided by AccuteX
Figure 2.9: AccuteX Wire EDM machine
Table 2.1: GE-42S AccuteX WEDM machine specifications [13]
The continuous moving axis mode Move to vertical point
The specified distance moving axis mode
Turn on mode: sparking, running wire, flushing water
Approach workpiece and find the edge Sparking
If JOG mode is on, these buttons determine the moving speed
If ING-JOG mode is on, these buttons determine the moving step (each step is 1mm, 0.1mm,
Control XY - axis/UV - axis moving direction
Control Z-axis moving direction Return to START POINT
Return to BREAK POINT Changes the moving axes of
Fills water from water tank to work tank Lock Z-axis lower limit
Drain water from work tank to water tank Restart cutting
When the light is on, the machine stops when finish running a block Z-axis moves up
Dry run Auto Power-off management
M01 optional stop When running to M01, machine stops
Suction (support manual wire threading)
Pause on short Turn off machine operation
Spark alignment Turn on machine operation
2.2.2 Input parameters of Accutex Wire EDM machine
Input parameters are crucial data points fed into a machine that determine its performance and desired outcomes Understanding these parameters is essential for selecting the appropriate ones This article will explore four key input parameters: Ton (on time), Toff (off time), SV (Servo Voltage), and WT (Wire Tension), while also defining additional input parameters.
+ T on (Pulse On Time) (unit: às)
Increasing the pulse on time in machining leads to higher machining speeds due to the rise in discharge energy However, this increase in pulse on time negatively impacts surface accuracy, as the widening discharge gap between the spark and the workpiece results in reduced precision.
+ T off (Pulse Off Time) (unit: às)
The pulse off time (Toff), measured in microseconds, is the interval between two simultaneous sparks and is crucial for machine tool operation, with a setting range of 08 to 50 in 1-unit increments A lower Toff value enhances sparking efficiency by allowing more discharges in a given timeframe, thereby increasing the cutting rate However, excessively low Toff values can lead to wire breakage, negatively impacting cutting efficiency To stabilize discharge conditions, increasing the Toff period can reduce the average gap current and lower the pulse duty factor.
+ SV (Servo Voltage) (unit: volt)
The spark gap set voltage acts as a reference point for measuring the distance between the workpiece and the cutting wire Current machines operate within a spark voltage range of 22 to 150 volts, adjustable in increments of 1 volt.
+ WT (Wire Tension) (unit: Nm)
The selection of wire length between the upper and lower wire guides is influenced by the wire tension Maintaining a consistent tension ensures that the continuously fed wire remains straight and properly aligned between the guides This tension is crucial for optimal performance and functionality.
14 increases as the project becomes thicker Wire breakage and inaccurate work results from improper tension adjustment The wire tension range available on the machine is
IP, or peak current, is the maximum current flowing through electrodes during a pulse, significantly influencing the discharge mode Increasing the IP value enhances pulse discharge energy, thereby improving the cutting rate Typically, IP is set to 10 for rough cuts, 9 for skim cuts, and ranges from 1 to 8 for surface finishing.
OV regulates the voltage for spark ignition, playing a crucial role in discharge stability For thicker workpieces, a higher OV is often necessary to ensure a larger discharge and prevent wire breakage.
+ AON: Arc On Time (unit:ns)
Arc On Time (AON) refers to the discharge time during a short spark, similar to Pulse On Time (TON), where a higher value indicates increased discharge energy and cutting speed However, excessively high values can lead to wire breakage Typically, AON is smaller than TON.
+ AOFF: Arc Off Time (unit: às)
Arc Off Time refers to the duration of rest between short sparks during cutting processes Similar to TOFF, a higher Arc Off Time value results in increased intervals between sparks, which can lead to a slower cutting speed Properly adjusting the Arc Off Time is crucial for achieving stable cutting, particularly when working with thin materials or when a flush cut is not ideal.
The wire feed rate, which refers to the speed at which the wire-electrode moves along the guide route for sparking, should ideally be set to its maximum for optimal performance Maximizing the wire feed reduces wire breakage, enhances machining stability, and slightly boosts cutting speed, with adjustments typically made in increments of 1 meter per minute The maximum wire feed achievable is 2 meters per minute, with a general range from 1 to 20 meters per minute.
WA refers to the step number in the watering flushing process, which is essential for effective cutting Higher input water pressure is necessary when using greater pulse power and when cutting thicker materials, while lower pressure is suitable for thin workpieces and trim cuts The input pressure range typically falls between 1 to 8.
It is the percentage % of the moving speed It is used to adjust speed according to a base preset value The range is 1% ~ 300% [13]
It is the base reference value of cutting speed The real speed is affected by F, SV and FT, SG The range is 0.1mm 2 /min~500mm 2 /min [13]
FT is the cutting mode M90(G95) is servo control mode and M91(G94) is fixed federate mode In servo control mode, the cutting speed is determined by F, SV and SG
In fixed-feedrate mode, the cutting speed is determined by F and SV But the spark energy (TON/TOFF/AON/AOFF) still determines the maximum cutting speed [13] + SG: Servo Gain
This determines how sensitively the servo control works The bigger the value the faster the response of servo control is The range is 0.1~99 Usually, it ranges from 1~35
M98 Subprogram Call Call subprogram from main program
M99 Subprogram Return End of subprogram and return to main program M00 Program Stop
G01U_V_; (only with MEM and TAPER B)
The G01 command will force each axis to move in a straight line, seen in figure 2.11 Absolute Command
The X and Y commands control the movement of each axis, indicating the position of the arc's endpoint Meanwhile, the I and J commands define the circle's center by specifying the distance from the starting point to the arc's center, with I and J representing the vector values in the X and Y directions.
17 respectively As demonstrated in, G02 (clockwise) and G03 (counterclockwise) control the arc's direction as shown in figure 2.12
Wire diameter compensation is crucial for maintaining the correct dimensions of a machined workpiece It ensures that as the wire travels along the programmed path, its center remains at a specified distance from the nominal route OFFSET plays a significant role in this process, enhancing precision in machining operations.
The distance between the nominal route and the actual path is crucial, as implementing a finish cut requires adjusting the OFFSET for each cut This adjustment, along with the modification of parameters, is essential to ensure precise dimensions.
Figure 2.25 depicts the correlation between different compensation levels and the programming route, highlighting the concept of Offset Cancel, which occurs when the wire center shifts along the program route This state is usually the default condition following a machine's power-on or reset Furthermore, the G40 command serves to eliminate any offsets from the G40 block or the subsequent block.
Material of cutting wire
WEDM (Wire Electric Discharge Machining) effectively cuts through any conductive material, including hard alloys like carbide and even diamond The process utilizes strong copper wire that does not make contact with the workpiece surface, allowing for precise cuts in small internal corners and narrow slots This non-contact method requires minimal cutting force, making it ideal for processing thin materials.
EDM cutting wire, also referred to as high-tension copper wire for EDM circuit breakers, has been utilized since the 1960s in machining processes This technique involves the EDM cutting wire and the workpiece acting as two electrodes submerged in demineralized water, where electrical discharge occurs between them During machining, corrosion affects both electrodes, but this corrosion is asymmetrical By carefully selecting parameters such as polarity, thermal conductivity, melting temperature of the material, and pulse intensity duration, it is possible to achieve a wear rate of 99.5% for the electrodes and only 0.5% for the instrument electrodes.
The following section describe the key physical properties of EDM wires and they related to real world cutting:
Conductivity, often expressed as a percentage of IACS (International Annealed Copper Standard), is a vital factor in EDM wire performance, as it influences the efficiency of power transfer from the power feed to the cutting point This is particularly important when using "open guides" for cutting, as the distance can be substantial, leading to voltage drops and energy losses if the wire conductivity is low Given that many modern power supplies can deliver peak currents exceeding 100 amps, the impact of conductivity on performance is significant.
The tensile strength of EDM wire is crucial for its ability to withstand the tension required for vertical cutting Measured in N/mm², the tensile strength indicates the wire's hardness level: wires with a tensile strength of 900 N/mm² or higher are classified as "hard," while those around 490 N/mm² are considered "half hard." Wires with a tensile strength of 440 N/mm² or lower are classified as "soft." Understanding these classifications is essential for selecting the appropriate wire for various applications in wire EDM processes.
Taper cuts with angles exceeding 50° are generally performed using half-hard or soft wires, as hard wires resist bending at the guide pivot, leading to inaccurate cuts Moreover, unless a machine is specifically designed for these types of wires, half-hard and half-soft wires are often unsuitable for automatic threading.
Elongation refers to the plastic deformation that occurs in wire just before it breaks, calculated as a percentage of the gauge length used in testing This property is often linked to the wire's brittleness, with hard wires exhibiting significantly lower elongation compared to half-hard wires In the context of Electrical Discharge Machining (EDM), where wires endure high tension and are subjected to numerous sparks that erode their cross-section, elongation becomes a vital characteristic A more ductile wire can tolerate temporary overloads by deforming slightly, allowing it to continue cutting, while a brittle wire is prone to snapping under similar conditions.
EDM, or electrical discharge machining, is a spark erosion process where the melting point of the wire electrode is not usually specified However, it is crucial that the wire is designed to resist rapid melting from the intense sparks generated during the process.
Another crucial element of EDM wire that is rarely specified but is essential for successful auto threading is straightness [16]
Flushability is an essential characteristic that significantly influences a wire's cutting efficiency, although it is not usually specified for individual wires This property is primarily linked to metallurgy, specifically the alloy components and sublimation temperature of the wire In simpler terms, improved flushability leads to faster cutting performance.
Cleanliness is a crucial yet often overlooked characteristic of EDM wires, as contaminants like drawing lubricants, residual metal powder, or added paraffin can render the wire "dirty." This contamination can lead to significant operational issues, such as jammed guides, power feeds, or slipping belts and rollers, ultimately disrupting your workflow.
"Plain" EDM wire refers to wire that is made from a single, uniform material without any coating or composite construction This type of wire is categorized based on its lack of additional coatings or materials.
Initially, copper was the preferred choice for EDM wire due to its excellent electrical conductivity However, its low flushability and tensile strength led to the adoption of brass wire, especially with the advancement of 2nd generation pulse type power supplies Despite this shift, copper wires are still used in specific applications where zinc, found in coated or brass wires, is considered an undesirable contaminant.
Brass wire, an alloy of copper and zinc, has largely replaced copper wire and remains the most commonly used wire today due to its cost-effectiveness, reasonable conductivity, high tensile strength, and improved flushability While the addition of zinc reduces the conductivity of copper, hard brass wire typically retains only about 20% of the conductivity of pure copper wire The primary alloys that constitute brass wire are essential for its widespread application.
Some manufacturers now produce "high zinc" brass with a composition of Cu60%Zn40%, enhancing the flushability of brass wire This higher zinc content can accelerate cutting speeds by up to 5% in optimized applications, although users with standard settings may not experience a noticeable difference Additionally, it is important to consider that a significant brass deposit may occur in certain situations.
Removing the residue left on the workpiece after cutting can be quite difficult Additionally, cold drawing wire with more than 40% zinc content is not feasible, leading to the development of coated wires.
A special alloy wire is created by incorporating a small percentage of aluminum into brass wire, significantly enhancing its tensile properties This alloy can achieve tensile strengths of up to 1,200 N/mm² while maintaining elongation, making it less prone to breakage compared to standard brass wire However, the usage of this wire has declined, leading a major manufacturer to announce plans to cease its production.
Workpiece
SKD61 is a versatile middle carbon tool steel known for its exceptional hardness and wear resistance, making it ideal for various applications After heat treatment, it exhibits high hardenability and thermal fatigue stability, allowing it to endure substantial heat and mechanical stress during repeated use Commonly used in the manufacturing of cutting tools, such as drilling cutters and scissor blades, as well as dies for cold and heat work, SKD61 is also essential for components like diesel engine pistons, valves, and ejector sleeves, which operate under high-temperature conditions.
In this experiment, the authors used SKD61 steel (JIS G4404) as the workpiece material for processing because of the following advantages:
− Less thermal deformation, this is a suitable factor for WEDM machining because during the machining process will generate a large amount of heat
− High polishing ability due to a large amount of Chromium
Table 2.6: Chemical compositions of SKD61 Steel (Unit: %) [25]
− Carbon (0.35-0.42%): which decreases the deformation of steel caused by impact during manufacturing and is the crucial element of hardness
− Chromium (4.80-5.50 %): increase rust resistance and decrease the oxidation from the environment
− Molipden (1.00-1.50 %): enhance wear resistance and toughness
Table 2.7: Physical properties of SKD61 steel [26]
Table 2.8: Mechanical properties of SKD61 steel [26]
Taguchi method
In experimental planning, selecting the appropriate experimental design is crucial as it significantly impacts both the process and outcomes of the experiment While controlling the number of experiments is straightforward for single-factor qualitative or quantitative studies, it becomes challenging in more complex experiments that involve multiple factors In such cases, relying on a single-factor experimental model is inadequate; instead, a multi-factor model must be employed to effectively determine the number of experiments and facilitate proper planning.
The experimental model aims to identify parameters that closely align with desired values while considering various influencing factors and reducing the number of experiments required The Taguchi method, developed by the renowned Japanese engineer and statistician Genichi Taguchi (1924 – 2012), effectively addresses this challenge.
The Taguchi method employs an orthogonal array as a multi-factor model, adhering to a rigorous procedure that necessitates fewer experiments while delivering more reliable data.
The idea of the Taguchi method is to determine the technological factors necessary to achieve the highest efficiency by detecting and minimizing the effects of disturbances
A factor (input variable) that affects the result in two directions – the effect that makes the result closer to the goal – is a useful signal, called a "signal." The effect that causes
The "credit-to-noise" ratio (S/N) is a key performance criterion used to evaluate and select parameters, with results indicating that moving away from the target generates "noise." To achieve optimal performance, it is essential to identify parameter sets that yield a large S/N, ensuring the selection of the most effective parameters for maximizing results.
− According to the problem form, there are 3 methods to calculate the ratio S/N: + Minima Problem (Smaller better):
+ Specific value problem (Target better)
− u – the order of tests; n – the number of tests in experiments
− Regardless of the type of problem, the optimization goal is always the maximum of the ratio S/N
2.5.2 Steps to optimize technological parameters according to the Taguchi method
To optimize technological parameters according to Taguchi method, including 7 basic steps
+ Step1: Select independent variables (or Factor, Control Variable) and response variables, objective function
In Step 2, assess the impact of each factor on the objective, identify potential interconnections among these factors (Degree of Freedom), and categorize the complete range of variables into distinct levels.
+ Step 3: Create a structure (orthogonal array): Columns are variables; rows are experiments
+ Step 4: Conduct experiments to collect data
+ Step 5: Analyze the data according to S/N and determine the optimal value of the parameters
Step 6 involves conducting an Analysis of Variance (ANOVA) to assess the impact of various factors on the output This step serves as a supplementary analysis since Step 5 has already considered the influence of these factors using the signal-to-noise (S/N) ratio It is important to note that performing ANOVA does not alter the optimization results obtained in previous steps.
+ Step 7: Recalculate the objective function according to the optimal set of parameters and test it experimentally [20]
Analysis of variance by ANOVA method
ANOVA, or analysis of variance, is a statistical method used to test the significance of differences among group means in various fields This technique allows researchers to determine if there is a statistically significant variation between the results of different experiments.
An analysis of variance (ANOVA) involves key components such as degrees of freedom (D.O.F), total squared deviation (SS), and the P-value, which reflects the reliability of the experimental process.
The analysis of variance (ANOVA) was conducted on both raw and signal-to-noise (S/N) data to identify significant and insignificant variables affecting the response characteristics Subsequently, response curves were generated for both data types to evaluate the parametric influences on these characteristics Ultimately, the optimal values for significant process parameters were determined by analyzing the ANOVA results and the response curves.
Programming on Mastercam
Programming the wire cutter in Mastercam 2021 is a simple process that requires a thread point and a profile with defined start and end points to fulfill the programming needs for wire cutting.
To create a thread point, Choose Wireframe tab, Click Point Position
Then Choose Thread point and we have a point like this
Mastercam 2021, like other CAD software, has basic drawing commands such as Line, Circle, Rectangle, and SPline,… allowing you to freely create whatever profile you need
Choose Machine tab, then move a mouse cursor to Wire Module, then click to choose
Figure 2.33: The Machine ‘s Post processor
The Machine's Post Processor allows users to select any desired machines, enabling the choice of one default machine and a 4-axis machine However, since the AccuteX machine module is unavailable in the post processor, the authors opted for the MITSUBISHI machine module as an alternative.
Table 2.9: The Process of modeling the workpiece
Machine ‘s Post processor, in the toolpaths bar will appear these parameters, double click to Stock
Click to Display and then click Bounding Box
The Bounding Box dialog appears, then click to the workpiece and click End selection, then click OK
4 Eventually the workpiece has completed
In Mastercam 2021's wire paths area, understanding the two primary strategies—CONTOUR and 4 AXIS—is essential for effectively programming WEDM.
After select a specific Machine ‘s Post processor, here is MITSUBISHI FA-Series 4X The Wirepaths tab will appear, then click Contour in wirepaths box
Identify Thread point and profile by clicking to it
Then click OK in dialog box, the dialog of wirepath contour will appear
2.7.4.2 The meaning of parameter in CONTOUR wirepath
− Wirepath Type: this tab displays a wirepath contour image and allows the chain geometry to be modified
− Wire / Power: This tab contains important parameters affecting the cutting process
+ Pass: Modifying the number of passes cut
+ Wire diameter: modifying the diameter of wire
+ Wire radius: modifying the radius of wire
In Mastercam 2021, the wire overburn parameter, also referred to as spark gap, is crucial for adjusting the stock to leave during arbitrary passes This setting allows for precise modifications to the amount of material left on the workpiece, enhancing the overall machining process.
+ Stock to leave: The same function as Wire overburn However, this parameter just only can modify stock to leave in one-pass cut
The Cut Parameters section in Mastercam 2021 is essential for optimizing the cutting process, featuring four key groups: Cut Before Tabs, Tabs, Cut After Tabs, and Cutting Method These parameters can be adjusted to suit various technological processes, ensuring efficient and precise machining.
In cutting processes, the default setting initiates with a rough cut, ensuring that every cutting cycle begins this way Additionally, the option for extra skim cuts before tab cuts allows for customizable finishing cuts, enhancing precision and quality before the final tab cuts are made.
Tabs are essential in a multi-pass cutting cycle, particularly for core cutting, as they help keep the workpiece intact by preventing it from falling out The thickness of the tab and the number of cuts can be easily adjusted using the Tab width and Number of tab cuts settings When the "Make the cut off move with skim cut" option is selected, tab cuts are performed simultaneously with skim cutting Additionally, the position of the tab can be set either automatically or manually, allowing for flexible placement.
Cutting after tabs refers to the process of removing the tab segment prior to the final skim cut This function is infrequently utilized, as it typically merges both tab cut and skim cut actions at the same time.
The cutting method can be utilized in two modes: One way mode, where the start and end points of the profile remain consistent throughout the process, and Reverse mode, which alternates the wire's direction at the end of each pass instead of re-threading it.
The Auxiliary function "Reset pass number on tab cuts if UNCHECKED" indicates that when this option is not selected, the tab cutting will not adhere to the stock amount specified in the wire overburn and cut number settings In scenarios involving rough and skim cutting based on the designated number of passes, the final tab cut will execute only once rather than according to the set pass count Conversely, if this function is CHECKED, it will align with the installed pass number in PASS Additionally, the option to "Suppress all wire threads and wire cuts" means that the automatic commands for wire cutting and threading will be bypassed, resulting in the omission of M50 and M60 commands during code export.
− Compensation: This tab mainly interferes with the way of wire compensation, namely G41 and G42
The "Stops" feature enhances tab cutting control by allowing individual adjustments for each tab and the first tab in operation It integrates output stop codes, such as M01 and M00, which pause the machine prior to tab cutting, enabling operators to secure parts and prevent dropout Additionally, the settings for "Distance before end of tab" and "After tab" define the stop positions for output code during the tab cutting process.
The "Leads" tab allows for adjustments to the lead-in and lead-out paths during cutting operations Properly managing these wire-paths is essential, as improper angles can lead to marks or burrs when cutting intricate and curved profiles with a straight wire-path, resulting from the spark angle of the wire.
+ Arc radius, Arc sweep: can be adjustable for the appropriate profile
The Overlap function specifies that the distance from the wire profile's endpoint will exceed its starting point by a designated overlap value Additionally, if the Rapid options are left unchecked, the movement from the thread point to the cutting profile, as well as the return from the profile's end back to the thread point, will be executed using the G01 command.
When the "Rapid from Thread Point" option is selected, the movement from the threading point to the cutting profile will utilize the G00 command This means that the G01 command will only be activated once the wire has been cut into the profile It is advisable to check this box only when there is no workpiece present between the threading point and the profile.
When the "Rapid to Cut" option is enabled, the machine will continue to move from the thread point to the cutting profile using the G01 command Once the wire reaches the end of the profile, it will return to the thread point using the G00 command.