Advanced Electrical Discharge Machining and TRIZ

By Professor V.S. Sreebalaji and Dr. R. Saravanan

Abstract

Electrical discharge machining (EDM) is a non-traditional process based on thermoelectric energy between a work piece and an electrode. A pulse discharge occurs in a small gap between a work piece and an electrode, and removes the unwanted material from the parent metal through melting and vaporization. The electrode and the work piece must have an electrical conductivity in order to generate a spark. Dielectric fluid acts as a spark conductor, concentrating the energy to a narrow region. There are various types of products that can be produced and finished using EDM such as moulds, dies, aerodynamic parts, automotive and surgical components. This research reveals how vibration can be incorporated into EDM through modeling an advanced design called the ultrasonic electrical discharge machine (UEDM) using the Theory of Inventive Problem Solving (TRIZ).

Introduction to EDM

In 1770, English scientist Joseph Priestley first detected the erosive effect of electrical discharges on metals. More recently, during research to eliminate erosive effects on electrical contacts, a pair of Soviet scientists, Boris Lazarenko and Natalie Lazarenko (husband and wife), decided to exploit the destructive effect of an electrical discharge and develop a controlled method of metal machining. In 1943, they announced the construction of the first spark-erosion machining device. The spark generator used is known as the Lazarenko circuit. It has been used for years in power supplies in EDM and in an improved form it is used today in many applications.1

The EDM process can be compared to a conventional cutting process. In this case a suitable shaped tool electrode with a precision controlled feed movement is used in place of a cutting tool. The cutting energy is provided by means of short-term electrical impulses. The EDM application of hard metals or alloys (electrically conductive) cannot be easily machined through conventional methods. This plays a major role in the machining of dies, tools, etc., made of tungsten carbides, stellites or hard steels. Alloys used in the aeronautical industry include hastalloy and nimonic, which also could be machined conveniently by the EDM process. The EDM process also is used to machine exotic materials, refractory metals and hardenable steels. This process offers the added advantage of being capable of machining complicated components and making intricate shapes. Most surgical components such as surface quality (SQ) are machined by this process since EDM is one of the unconventional processes used to produce better SQ.

Limitations of EDM

There are a number of problems that still need to be solved in order to enable the process for adoption through an extensive process. Some limitations include:

  1. Lower material removal rate (MRR) and poor SQ. The real time EDM process objectives are to maximize the MRR and minimize the surface roughness value.11
  2. The wear rate on the electrode is considerably higher. Sometimes it may be necessary to use more than one electrode to finish a job.
  3. The work piece should be electrically conductive for machining.
  4. The energy required for the operation is more than the conventional process and will be more expensive.
  5. The ignition of spark discharge in a contaminated die electric fluid is another real time process limitation since contamination of the dielectric fluid will affect machining accuracy. The die electric is fresh, meaning it should be free from eroded particles; eroded particles from the work piece can contaminate the die electric fluid. The die electric fluid should be filtered before reuse to ensure that contamination will not affect the machining accuracy.1

Introduction to TRIZ

The Theory of Inventive Problem Solving (TRIZ) is a method based on logic and data. It accelerates one’s ability to research and creatively solve daily problems including impossible-to-solve problems. The Theory of Inventive Problem Solving also provides repeatability, predictability and reliability due to its structure and algorithmic approach. Genrich Altshuller and his colleagues developed the method between 1946 and 1985. Altshuller discovered that the evolution of a technical system follows predictable patterns. Inventiveness and creativity can be taught. TRIZ has helped solve thousands of difficult technical problems and several Fortune 500 companies are successfully applying TRIZ.

Given a good inventive technique, the impossible becomes the possible. The TRIZ approach is included in a rather rigorous step-by-step process, somewhat similar to an algorithm, although not as rigorous as a formal mathematical algorithm. This problem solving algorithm is called ARIZ (algorithm for inventive problem solving). For the past 60 years the research on the algorithm has unfolded in several stages.

The three primary findings of this research are as follows:

  1. Problems and solutions are repeated across industries and sciences. The classification of the contradictions in each problem predicts the creative solutions to that problem.
  2. Patterns of technical evolution are repeated across industries and sciences.
  3. Creative innovations use scientific effects outside the field(s) where they were developed.12,13

As an international science of creativity, TRIZ, relies on the study of the patterns of problems and solutions, not on the spontaneous and intuitive creativity of individuals or groups. More than four million patents have been analyzed to discover the patterns that predict breakthrough solutions to problems. Research for TRIZ began with the hypothesis that there are universal principles of creativity and they are the basis for creative innovations for advancing technology. If these principles could be identified and codified they could be taught to people to make the process of creativity more predictable. The idea is: Somebody someplace has already solved this problem (or one similar to it). Creativity is finding that solution and adapting it to this particular problem.

Unified Structured Inventive Thinking (USIT) is an Americanized TRIZ term. It is one of such simplified methodologies developed in the United States. It recommends a simple yet powerful process of problem solving. It is composed of three stages:

  1. Problem definition,
  2. Problem analysis and
  3. Concept generation.14

In Japan, TRIZ has been introduced and promoted by the Nikkei Mechanical Journal, Mitsubishi Research Institute, Sanno Institute of Management,and by professor Yotaro Hatamura’s group at the University of Tokyo and in various pioneering Japanese industries.

The Essence of TRIZ

There are many important principles and methods in TRIZ including:

  1. Altshuller’s 39 generic engineering parameters
  2. The contradiction matrix
  3. The 40 inventive principles
  4. The 76 standard solutions
  5. Trends of evolution
  6. Algorithm for inventive problem solving (ARIZ)

Current Research Trends in EDM Development

There are two kinds of EDM research trends: the modeling technique and the novel technique.2

  1. The modeling technique deals with mathematical modeling, artificial intelligence and optimization techniques like regression analysis, artificial neural network and the genetic algorithm. They are used to validate the efforts of input parameters on output parameters, because EDM is a complicated process. It has controlled input parameters like machining depth, tool radius, pulse on time, pulse off time, discharge current, orbital radius, radial step, offset depth and output parameters. It is similar to the MRR and SQ.2
  2. Novel techniques deal with other (unconventional) machining principles (such as ultrasonic) that can be incorporated into EDM to improve efficiency of the process by offering better MMR and SQ.

A Single Engineering Parameter and Inventive Principles

Sometimes a designer knows only one parameter to improve the system, but does not know – or cannot predict – the corresponding contradiction parameter of the system. There are several techniques in TRIZ that do not require a definition of a contradiction (the system operator, the ideal final result (IFR) and the 76 standard solutions all work without explicit definitions of a contradiction).

An inventive approach for a designer to solve an engineering innovative design problem without contradiction information can be accomplished by using the 40 inventive principles. This allows a designer to use one engineering parameter to improve system performance regardless of whether or not the presence of a contradiction parameter is known. This approach includes three steps:

  1. This method examines all corresponding inventive principles associated with each improving parameter in the TRIZ contradiction table. Particular principles were seen a number of times. This is because the inventive principles will make improvements to a certain improving parameter in the system, possibly corresponding with other parameter types avoiding degeneration. Certain inventive principles appeared more often, indicating that they are good options to try when solving an innovative design problem.
  2. The same procedures were applied to each parameter avoiding degeneration in another dimension of the TRIZ contradiction table. The corresponding inventive principles were examined and were accounted for their number of appearances. The use of these principles by a designer means that she can simultaneously improve a system’s parameters and can avoid the deterioration of certain parameters. Certain inventive principles appear many times. This will give a designer a good start to try and solve innovative design problems.
  3. The combination of both parts, and summing up the number of appearances of all of the principles constructed (for a single engineering parameter and inventive principles), is shown in Table 1. The vertical axis is the 39 parameters of TRIZ that a designer wants to improve. The horizontal axis shows the frequency of appearances of each parameter’s corresponding principles. Table 1 classifies inventive principles into different ranks, such as A (more than 19 times), B (16 to 18 times), C (13 to 15 times), D (10 to 12 times), E (7 to 9 times), F (4 to 6 times) and G (1 to 3 times), according to the number of appearances in the contradiction table for each parameter. Most frequently the appearances of the principles (ranked at A, B or C in Table 1) will have a better chance of success in solving an inventive design problem. A designer, therefore, can solve the engineering innovative design problem without contradiction information by choosing a suitable TRIZ inventive principle based on information shown in the table.

Table 1: Single Engineering Parameter and Inventive Principles10
Level FeatureA (more than 19 times)B (16-18 times)C (13-15 times)D (10-12 times)E (7-9 times)F (4-6 times)G (1-3 times)
1Weight of moving object352826, 18, 2, 8, 10, 15, 40, 29, 3127, 34, 1, 36, 19, 6, 37, 383, 32, 22, 24, 39, 5, 13, 1112, 21, 20, 17, 4, 30, 16, 14, 25, 23
2Weight of non-moving object3528, 10, 19, 1, 262627, 13, 2, 186, 15, 22, 2939, 32, 9, 14, 40, 5, 8, 317, 25, 30, 20, 16, 11, 36, 37, 24
3Length of moving object1, 291535, 4, 1710, 28, 8, 1419, 24, 13, 2616, 2, 34, 9, 737, 39, 18, 32, 36, 5, 12, 22, 25, 23, 40, 6, 38
4Length of non-moving object3528, 14, 26, 1, 107, 153, 2, 29, 18, 30, 24, 32, 1617, 40, 8, 13, 27, 9, 37, 38, 39, 6, 25, 23, 19, 31, 12, 11, 5
5Area of moving object1517, 26, 13, 210, 29, 30, 41, 14, 19, 32, 34, 28, 318, 39, 16, 357, 5, 25, 36, 33, 22, 40, 11, 6, 31, 38, 23, 24, 9, 12
6Area of non-moving object18, 3539, 3039, 30, 17, 4, 3632, 15, 7, 1, 3828, 26, 37, 22, 9, 29, 3, 14, 13, 27, 25, 23, 19, 31, 6
7Volume of moving object352, 10, 291, 15, 34, 4, 6, 713, 4016, 28, 14, 39, 17, 18, 26, 22, 30, 25, 37, 3624, 38, 11, 12, 32, 19, 9, 23, 27, 20, 21, 5, 3
8Volume of non-moving object35218, 14, 3410, 4, 39, 19, 31, 37, 30, 6, 1, 1625, 17, 7, 24, 15, 26, 27, 3, 9, 32, 38, 40, 8, 28, 22,36, 5
9Speed28, 35133410, 38, 158, 2, 18, 1932, 3, 29, 14, 4, 26, 1, 3016, 21, 36, 24, 27, 6, 11, 12, 5, 33, 23, 25, 9, 20, 22, 7, 40
10Force35, 10, 3637, 1828, 1915, 1, 23, 21, 13, 4014, 26, 16, 17, 812, 11, 34, 29, 9, 24, 20, 5, 23, 27, 30, 32, 38, 39, 4, 6, 25
11Tension/pressure35, 1036, 372, 1419, 3, 18, 40, 16, 15, 13, 24, 27, 2533, 4, 16, 32, 22, 28, 21, 29, 39, 11, 9, 23, 38, 12, 8, 34
12Shape110, 14, 15, 3529, 3432, 13, 40, 42, 28, 2230, 5, 26, 18, 7, 17, 316, 6, 8, 25, 37, 27, 39, 19, 36, 9, 12, 11
13Stability of object3539, 2140, 13, 18, 32, 3027, 15, 3, 22, 2819, 10, 14, 17, 11, 4, 23, 34, 3324, 21, 26, 37, 31, 16, 6, 29, 8, 5, 9, 38
14Strength3, 35, 10, 2840, 1514, 2726, 9, 18, 2, 32, 1, 298, 11, 13, 17, 19, 3034, 22, 6, 7, 37, 31, 25, 16, 5
15Durability of moving object35, 193, 1027282, 6, 1813, 4, 29, 15, 25, 39, 1, 22, 4031, 9, 33, 14, 16, 26, 11, 38, 34, 20, 17, 30, 21, 12, 8, 32
16Durability of non-moving object1635, 101, 4038, 27, 6, 34, 19, 18, 3, 2, 2025, 24, 39, 23, 22, 28, 31, 17, 33, 36, 26, 21, 30
17Temperature35, 1923, 10, 39, 18, 2221, 32, 27, 17, 16, 28, 36, 26, 3824, 30, 4, 14, 15, 6, 4031, 13, 9, 34, 33, 25, 1, 29, 20, 7
18Brightness19, 32, 11315, 35, 2, 26617, 16, 3, 10, 2428, 27, 11, 25, 30, 39, 21, 8, 4, 22
19Energy spent by moving object35, 1918, 28, 2, 615, 24, 1, 13, 27, 3216, 12, 38, 17, 29, 14, 34, 10, 321, 25, 26, 37, 5, 8, 31, 11, 23, 22, 9, 30
20Energy spent my non-moving object1, 35, 1918, 27, 4, 37, 36, 31, 2210, 16, 28, 2, 23, 29, 3, 32, 6, 9, 15, 12, 25
21Power35, 19, 10, 232, 6, 38, 1834, 31, 26, 28, 1727, 16, 20, 1, 15, 22, 30, 37, 1412, 25, 36, 8, 29, 3, 13, 4, 24, 21, 11, 40
22Waste of energy35219, 715, 1018, 6, 38, 3213, 28, 22, 14, 17, 1, 21, 26, 23, 25, 3016, 27, 39, 3, 29, 11, 36, 5, 12, 37, 24, 31, 20, 9, 34
23Waste of substance10, 35, 281831, 242, 27, 39, 334, 40, 29, 5, 1338, 1, 36, 6, 30, 14, 15, 33, 23, 1622, 32, 37, 21, 25, 8, 19, 12, 4
24Loss of information103524, 26, 2228, 32, 19, 30, 42, 27, 33, 13, 15, 16, 23, 21, 29, 18, 4, 6, 5
25Waste of time10, 35, 28, 184, 3234, 20, 2629, 24, 51, 30, 16, 37, 17, 6, 15, 36, 19, 214, 22, 3, 38, 39, 21, 27, 25, 9, 7
26Amount of substance35, 3, 29181014, 27, 40, 31, 28, 15, 213, 6, 24, 25, 34, 30, 1, 39, 16, 19, 32, 3633, 26, 17, 38, 4, 7, 23, 22, 21, 20, 12, 8
27Reliability35, 10, 114028, 27, 3113, 24, 8, 2, 32, 2919, 21, 4, 14, 16, 2317.39.26.15.36.06.34.31.09.30.38.25.05.18
28Accuracy of measurement32, 28, 263, 1024, 6, 34, 1, 1335.0216.25.27.11.235, 33, 18, 15, 31, 19, 4, 12, 39, 17, 22, 36
29Accuracy of manufacture3228, 10182, 26, 3531, 25, 29, 30, 36, 24, 27, 23, 4034, 37, 17, 4, 11, 13, 16, 19, 31, 33, 39, 9, 38
30Harmful factors acting on object22, 35, 2133, 2818, 19, 24, 27, 4039, 10, 3731, 29, 21, 13, 34, 17, 15, 2623, 30, 6, 3, 32, 11, 25, 16, 36, 4
31Harmful side effects35, 22, 2, 391, 184021, 24, 17, 1915, 3, 10, 27, 33, 34, 4, 2631, 16, 6, 28, 29, 30, 32, 23, 13, 36
32Manufacturability1, 352827, 132624, 15, 16, 292, 11, 10, 4, 32, 18, 34, 12, 17, 19, 408, 5, 36, 9, 3, 33, 37, 6, 23, 25, 30, 31
33Convenience of use1132, 28, 35, 3212, 15, 34, 2516, 26, 17, 274, 3, 10, 24, 40, 19, 39, 2922, 30, 5, 18, 23, 6, 8, 9, 31, 7, 11
34Repairability1, 10, 21135, 1332, 15, 16, 2725, 2834, 49, 3, 12, 7, 26, 19, 17, 29, 18, 31
35Adaptability35, 15, 12916, 2, 1319, 28, 10, 37, 8, 34, 3, 30, 27, 6, 1732, 31, 14, 4, 18, 7, 26, 11, 20, 22, 24, 5, 25
36Complexity of device126, 28, 10, 13352, 29, 19, 2434, 27, 15, 176, 36, 37, 30, 18, 2212, 4, 2, 40, 14, 20, 3, 31, 39, 25, 23, 9, 11, 7
37Complexity of control352827, 262, 19, 29, 15, 16, 1, 318, 24, 13, 32, 39, 1025, 40, 22, 37, 36, 34, 6, 1711, 21, 30, 4, 5, 38, 31, 33, 23, 12, 8, 9
38Level of automation352, 28, 261, 13, 10, 3418, 2423, 27, 32, 15, 17, 8, 12, 16, 193, 33, 14, 30, 5, 25, 6, 11, 4, 21, 9, 7
39Productivity35, 10, 28118, 2, 37, 26, 34, 14, 15, 38, 29, 1724, 3, 32, 13, 12, 23, 22, 39, 6, 1916, 20, 27, 30, 4, 40, 5, 25, 21, 31, 36

The following example will illustrate the usefulness and convenience of a single engineering parameter and the inventive principles. In this example, a designer wants to improve a car’s use of road space, especially the engine and engine compartment size, in order to improve the “area of moving object” parameter (during a collision the engine and engine compartment are considered moving objects). The first two corresponding inventive principles for this parameter from Table 1 are dynamicity (#15) and shift to a new dimension (#17). These two principles match the best solution strategies for designing a smart car.

  • Dynamicity (#15) recommends optimal operating condition, adjustable steering wheel and flexible seating arrangement.
  • Shift to a new dimension (#17) recommends moving into a three-dimensional space utilization.10

Problem Context of EDM Research

How to increase the machining efficiency by improving the MRR and SQ.

Problem Discussion

There is a desirable output/characteristic that is needed (in this case MMR). It unfortunately appears to be associated with something costly or unwanted (such as an increase in machining time). In the language of TRIZ, this is called a contradiction.

The identification and resolution of contradictions is a key element of TRIZ. One or more contradictions is found inside a problem. If contradictions are identified and resolved a high quality solution to a problem can result. This is not a better compromise, but an innovative solution that breaks free from the existing constraints and provides a change toward an ideal system. This contradiction is expressed in a simple graph. Figure 1 illustrates how this typically happens:15,17

Figure 1: Contradiction Expression

As an individual tries to improve one parameter (MMR) the other (machining time) becomes worse and vice versa. It is constrained to remain on the line of compromise, which defines the set of possible compromise solutions available. What is best is to move off the line of compromise to a more ideal solution (in the direction shown by the bolded arrow). To achieve this one needs to find a way of resolving the contradiction.

For this particular problem, Figure 2 shows what is being sought:

Figure 2: Contradiction Expression for This Particular Problem

Tackling the Problem

In this case, one of the classic tools from the TRIZ toolkit for solving contradictions can be used via the contradiction matrix. To resolve contradictions, the method is a three-step systematic process:

  1. Step 1: Identify the contradiction(s) in the problem and classify them according to the nature of the contradictory system parameters.
  2. Step 2: From the TRIZ toolkit, use a statistically derived table (the contradiction matrix) to determine which generic inventive principles have been successfully used in the past to resolve contradictions.
  3. Step 3: Take the generic inventive principles suggested in Step 2 and interpret/apply them to a specific problem.17

Through this final step it is possible to generate not just one possible solution, but usually a surprisingly large set of candidate conceptual solutions.

Step 1: Identifying the Contradiction(s)

The Theory of Inventive Problem Solving (TRIZ) deals with two types of contradictions:

  1. Technical contradictions
  2. Physical contradictions

When improving one parameter another gets worse. Consider designing a table – the stronger and more rigid it is made, the heavier it becomes. This is called a technical contradiction of strength versus weight. In this particular case, if one wants to improve MMR, machining time increases.

A physical contradiction, on the other hand, is characterized by having the contradiction derived from the same system parameter. An umbrella, for example, needs to be both large (when in use) and small (when not in use).

What is an Engineering Parameter?

There are 39 generic engineering parameters. When combined in opposing pairs, they can define any engineering contradiction. The parameters describe both the things one wants (or inputs that must be made) and the consequences (the things that are not needed).

To use the matrix, one has to match the problem to the parameter and then be able to ask the right question such as, which of the 39 parameters describes the contradiction?

Step 2: Using the Contradiction Matrix

Before the contradiction matrix can be used it is necessary to map the specific problem parameters (MMR and machining time) onto the generic parameters used by the contradiction matrix. An appropriate mapping can be:

  • Parameter 26, amount of substance matched well with MRR.
  • Parameter 25, loss of time matched well with increase in machining time.

The full description of each of these parameters includes:16

Parameter 26, amount of substance: The number or amount of a system’s materials, substances, parts or subsystems, which might be changed fully or partially, permanently or temporarily.

Parameter 25, loss of time: Time is the duration of an activity. Improving the loss of time means reducing the time taken for the activity. Cycle time reduction is a common term.

What is the Contradiction Matrix?

The contradiction matrix is based on a statistical analysis of a large number of existing patents. Each patent was found to solve a problem using one (or more) of a limited number of generic inventive principles (from 40). The matrix maps the inventive principles according to the generic contradictions (defined by opposing engineering parameters) that were most frequently solved by them. The 39 generic matrix parameters are shown in Table 2:

Table 2: The 39 Generic Matrix Parameters
Weight of moving objectSpeedTemperatureLoss of timeEase of operation
Weight of stationary objectForceBrightness (jargon)Quantity of substanceEase of repair
Length of moving objectStress or pressureUse of energy by moving objectReliabilityAdaptability
Length of stationary objectShapeUse of energy by non-moving objectMeasurement accuracyDevice complexity
Area of moving objectStability of object’s compositionPower (jargon)Manufacturing precisionDifficulty detecting and measuring
Area of stationary objectStrength Loss of energyExternal harm affects the objectExtent of automation
Volume of moving objectDuration of action by moving objectAmount of substanceObject generated harmful factorsProductivity
Volume of stationary objectDuration of action by
stationary object
Loss of informationEase of manufacture

This contradiction is used with the contradiction matrix to obtain suggested inventive principles.

Contradiction to Improve MMR

  • Improving parameter:Amount of substance (MRR)
  • Worsening parameter (undesired):Loss of time (increase in machining time)

These two parameters are used to cross-index the contradiction matrix to obtain the following four inventive principles that (statistically) have been found to be the most successful in obtaining better MMR without more machining time.

Step 3: Inventive principles

The following principles that are most frequently used are listed in the contradiction matrix between the parameters; amount of substance and loss of time.

Mechanical vibration, 18
Parameter change, 35
Partial or excessive action, 16
Strong oxidants, 38

Application of Suggested Inventive Principle(s)

After deriving suggested inventive principles, apply the principles to the particular problem. A recurring theme in TRIZ is that the sequence follows a chain like specific problem-general problem and general solution-specialized solution to specific problem.

The next step is to understand the suggested inventive principles and to understand the full definition of each principle before attempting to apply them.16 In this case, here are the four suggested generic principles:

Principle 18, Mechanical Vibration

A.Cause an object to oscillate or vibrate.
B.Increase its frequency even up to the ultrasonic (distribute powder with vibration).
C. Use an object’s resonant frequency.
D. Use piezoelectric vibrators instead of mechanical ones.
E. Use combined ultrasonic and electromagnetic field oscillations.

Principle 38, Strong Oxidants

A. Replace common air with oxygen-enriched air.
B. Replace enriched air with pure oxygen.
C. Expose air or oxygen to ionizing radiation.
D. Use ionized oxygen (ionized air to trap pollutants in an air cleaner).
E. Replace ozonized (or ionized) oxygen with ozone (speed up chemical reaction by ionizing the gas before use).

Principle 16, Partial or Excessive Action (application of principle #3 and #9)

A. Change an object’s structure.
B. Make each part of an object function most suitable or conditioned to its operation.
C. Make each part of an object fulfill a different and useful function (multi-function tool).
D. Replace with anti-actions to control harmful effects (buffer the solution to prevent harm from extreme pH).
E. Create stresses in an object beforehand to oppose undesirable working stresses.

Principle 35, Parameter Change

A. Change an object’s physical state.
B. Change the concentration or consistency.
C. Change the degree of flexibility.
D. Change the temperature.

At this point in the problem solving process, an appropriate problem and technological domain knowledge is important. The final solution derived from these principles was used to validate the previousresearch findings and to justify how well this novel approach to TRIZ can be used in emerging engineering and technological research in order to reduce the research time, cost, and to provide the right direction and solution to the research.

Validation of TRIZ

Principle 18, Mechanical Vibration

Kamlakar Rajurkar, author of the Handbook of Design, Manufacturing and Automation, indicated some future trend activities in EDM based on advanced materials, the mirror surface finish (using powder additives) and the introduction of ultrasonic vibration to the electrode; these are used to expand the application of EDM and to improve the machining performance on difficult machine materials.3

Z.N. Guo, one of the authors of A Study of Ultrasonic Aided Wire Electrical Discharge Machining, proposed that the higher efficiency gained by the employment of ultrasonic vibration is mainly attributed to the improvement in die electric circulation, which facilitates the debris removal and creation of large pressure changes between an electrode and a work piece, as an enhancement of molten metal ejection from the surface of a work piece.4

Hitoshi Ogawa, one of the authors of a Study of Micro Machining of Metals by EDM with High Frequency Vibration, proved that the depth of micro-holes by EDM with ultrasonic vibration increases about two times without the ultrasonic vibration and machine rate increasing.5

Minoru Kunieda, one of the authors of the Improvement of Dry EDM Characteristics, introduced an improvement of dry EDM characteristics using piezoelectric actuators to help control the gap length to explain the effects of the piezoelectric actuator where an EDM performance simulator was developed to evaluate the machining stability and MRR of dry EDM.6

Principle 38, Strong Oxidants

Kunieda, who was also one of the authors of Improvement of EDM Efficiency revealed a new method to improve EDM efficiency by supplying oxygen gas into a gap. The authors found that the stock removal rate is increased due to the enlarged volume of a discharged crater and more frequent occurrences of discharge.7

And Q.H. Zhang, one of the authors of Ultrasonic Vibration Assisted EDM in Gas found that oxygen gas can produce greater MRR than air.8

Principle 16, Partial or Excessive Action

This principle is an application of principle 3 (local quality) and principle 9 (preliminary anti-action).

Principle 3 suggests a change in an object structure, Zhang proved this suggested principle through his investigative work titled: Ultrasonic-Assisted Electrical Discharge Machining in Gas with thin-walled pipe electrodes (tube electrode).

Principle 9 suggests that an action be done with harmful effects – buffering a solution to prevent harm. Zhang proved and validated this suggested principle by introducing gas in UEDM by avoiding the use of electrolytes.

Principle 35, Parameter Change

Zhang studied the ultrasonic EDM in gas. The gas is applied through the internal hole of a thin-walled pipe electrode.

Using TRIZ for Better MMR in EDM

The suggested principles have led to brainstorming to propose a new design.

Principle 18, mechanical vibration, recommends increasing its frequency even up to the ultrasonic. An example is to distribute powder with vibration. This leads to a new design of EDM with supply of various types of powder additives to the die electric fluid with respect to mechanical properties like particle size, density, thermal conductivity and electrical properties like resistivity. They may be used according to thermal, physical properties of a work piece and an electrode material for better MRR and lesser tool wear rate (TWR) during a machining process. With the domain knowledge in EDM, it is suggested that the introduction of powder additives into the die electric in micro-EDM will play a vital role in making a smaller crater shape.

  • Principle 38, strong oxidants, suggests using ionized oxygen to speed up the process for better MRR.
  • Principle 35, parameter change, suggests a short pulse with more electrostatic force can change the concentration of die-electric with powder additives and may have an influence on improving EDM efficiency.

Ajit Singh, a professor at Punjab University, revealed that for long pulses, where discharge duration is greater than 100 ìs, electrostatic force becomes small and does not play a significant role in the removal of metal. The temperature of an electrode also plays a role in machining since hot tools of present inventions have increased machining accuracy and also prevents the machining area from becoming messy due to the molten state of a work piece surface.2

The proposed new design recommendations may be implemented through real time application in future experimental research.

Inventive Principle(s) for Better SQ in EDM Using a Single Engineering Parameter and Inventive Principles

To improve SQ of work material (Table 1), a generic parameter such as brightness is used. Do not try to find a parameter that fits perfectly as defined by the matrix. Inventive principles suggested by Table 1 for a single engineering parameter and inventive principles include:10

Periodic action, 19
Segmentation, 1
Other way around, 13
Color change, 32

The four suggested generic principles include:

Principle 19, Periodic Action

A. Instead of continuous action, use periodic or pulsating actions.
B. If an action is already periodic, change the periodic magnitude or frequency (replace a continuous with changes in amplitude and frequency).
C.Use pauses in between impulses to perform a different action.

Principle 1, Segmentation

A. Divide an object into independent parts.
B. Make an object easy to disassemble.
C. Increase the degree of fragmentation or segmentation (use powdered welded metal instead of foil or rod to get better penetration).

Principle 13, Other Way Around

A. Invert the action used to solve the problem.
B. Make movable parts fixed and fixed parts movable (rotate the parts).
C. Turn the object or process upside down.

Principle 32, Color Changes

A. Change the color of an object or its external environment.
B. Change the transparency of an object or its external environment.
C. Use a colored additive.
D. Change the emissivity properties of an object subject to radiant heating.

New Design Using TRIZ for Better SQ in EDM

  • Principle 1, segmentation: in order to increase the degree of fragmentation various types of powder additives may be used for better penetration and fragmentation during machining process (and this was suggested in the earlier design).
  • Principle 13, other way around: suggests making movable parts fixed and fixed parts movable and rotate. Rotation may be given to an electrode to have a better SQ. See the block diagram of a new experimental design of EDM, in Figure 3.

Figure 3: New Experimental Design of
Electrical Discharge Machine Using TRIZ

  • Principle 32, color change, was given a direction to use a colored additive to increase the observability of the machining process to recycle or replace with an electrolyte for effective MRR and better SQ. The proposed new design recommendations may be implemented through real time application and the same may be validated in future research.

Further Scope of TRIZ Applications in Modern Machining Processes

The Theory of Inventive Problem Solving may be used to amalgamate various process principles to make hybrid machines. Mullard Research Laboratories in the United States developed a process that combines electro chemical reactions with ultrasonic abrasions; it was found that tool steel can be machined nine times faster than by ultrasonic alone.1 The authors suggest that TRIZ may be used for hybrid ultrasonic with electro chemical machining (ECM) process research and achieving maximum results with minimal effort.

Conclusion

This work reveals how TRIZ has been used in EDM research to help overcome the limitations of existing EDM processes and to lend a new design. As EDM research is concerned, work began in 1996 and research continues on improving the machining performance. Research work that has taken 20 years through trial and error can be accomplished in a few weeks using TRIZ. The Theory of Inventive Problem Solving (TRIZ) is a vibrant methodology. By using TRIZ, EDM research can be achieved with maximum results with minimal effort; this has been validated through previous research findings. It can be used to extend EDM research and the proposed recommendations and design may be implemented in a real time operation.

References

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  15. Darrell Mann, Industrial Fellow Department of Mechanical Engineering, University of Bath, Design Without Compromise, Design for Life, title presented at the U.S. NFPA International Fluid Power Exposition, IFPE, Technical Conference held in Chicago, April 2000.
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