EDM Wire Cut

1. Title: EDM wire cut.

2. Objective

 To examine engineering product of an EDM, wire cut process  To understand wire cutting process

 To understand the process of programming CNC

3. Theory

Electrical Discharge Machining is a process in which the workpiece is connected in a circuit with an electrode. The electrode is placed a certain space apart from the workpiece, this creates voltage buildup and eventually will produce sparks. The spark produces intense heat with temperature ranging from 8000 to 12000 degrees celcius, melting almost anything. The spark is in a controlled manner meaning it is focused onto the surface of the material only. The workpiece is submerged in an insulating liquid more typically oil or, less frequently, other dielectric fluids The electrode shape is in the form of a die or a wire. The die shape is to

erode the material in accordance to the shape of the die. EDM that uses wire is called “Wire cutting”. EDM wire cutting uses a metallic wire to cut a programmed contour in a workpiece. On common wire cut machines the cutting process can only be performed on a x-y axis frame. The wire is fed

by a spool and cuts along a kerf, all of this is preprogrammed by using CAM technology specifically G-Code programming. The work is done under submerged dielectric liquid directing all the spark along the guided kerf. The wire can cut with kerfs as wide as 3 inches and precise positioning. This allow for parts that require precision such as extrusion dies and blanking punches. The cuting process is always through the entire workpiece. To start machining it is first necessary to drill a hole in the workpiece or start from the edge. The wire is usually made of brass or stratified copper, and is between 0.1 and 0.3 mm diameter.

Depending on the accuracy and surface finish needed, a part will either be one cut or it will be roughed and skimmed. On a one cut the wire ideally passes through a solid part and drops a slug or scrap piece when it is done. This will give adequate accuracy for some jobs, but most of the time,

skimming is necessary. A skim cut is where the wire is passed back over the roughed surface again with a lower power setting and low pressure flush. There can be from one to nine skim passes

depending on the accuracy and surface finish required. Usually there are just two skim passes. A skim pass can remove as much as 0.002" of material or a as little as 0.0001". During roughing ( i.e. the first cut) the water is forced into the cut at high pressure in order to provide plenty of cooling and eliminate eroded particles as fast as possible. During skimming (accuracy / finish cuts) the water is gently flowed over the burn so as not to deflect the wire.

Wire Cut Process

G-Code

According to wikipidea; G-code the common name for the most widely used numerical

control (NC) programming language. The main purpose for G-code is too instruct automated machine tools to carry out commands, usually in computer-aided manufacturing process. G-code is sometimes called G programming language.

In fundamental terms, G-code is a language in which people tell computerized machine tools how to make something. The how is defined by instructions on where to move, how fast to move, and

through what path to move. The most common situation is that, within a machine tool, a cutting tool is moved according to these instructions through a toolpath, cutting away excess material to leave only the finished workpiece.

In wire cut the commands used were as follow:  G01 = cut to mentioned coordinate  G02 = clockwise cut

 G03 = counter-clockwise cut

 G41 = offset tool from workpiece, right side  G42 = offset tool from workpiece, left side

4. Apparatus

4.1. Industrial Apparatus

 Excetek’s Wire-cutting EDM V650G

A somewhat similar machine compared to the lab’s EDM wirecut, the V650G uses damping equipment to maintain accurate cuts. It uses a Mono bloc Meehanite cast elements designed using Finite Element Methods (FEM) provide exceptional damping properties and exceptional machining rigidity. To ensure thermal stability, rib location has been designed using Finite Element Analysis, assuring optimised structural rigidity.

Specifications 650G

Maximum workpiece (mm) 1000 x 700 x 345 mm(39.4" x 27.6" x 13.6")

Max. Work piece Weight 800kg(1764 lb)

Travel of X/Y axes 650 x 400 mm(25.6"x 15.7")

Travel of U/V axes 160 x 160 mm(6.3"x 6.3")

Travel of Z axis 350mm(13.8") Option 410mm(16.1")

Wire diameter 0.15~0.3mm(0.004"~0.012")

Number of axes controlled 5 Axis AC Servo Motor

Max taper angle ±30°/ 100mm(±30°/ 3.9") with wide diamond guide and nozzle

Machine size 2520 x 2720 x 2290 mm(99.2" x 107.1" x 90.2") (89")

Machine Weight 4000kg(8818 lb)

 CHMER Submeged EDM wirecut, G53S

Another EDM wirecut with more varying feature. It provides high level of flexibility with low running cost. Also includes the laser alignment and mechanical structure to promote higher accuracy

5. Procedure

1. A design was made in solidwork to gauge the coordinates; the design included both curved and straight features.

2. Design was transferred to a graphing paper

3. The coding was done according to the design on the graph paper 4. Code was inputed into the EDM machine.

5. Code was save in library of the EDM cut CAM software.

6. The program was graphed on the wire cut interface to ensure no error occurs 7. The CNC program is carried out on the EDM wire cut

6. Results

CNC Program

00181 Reference number

N100 G00 G21 G;

N102 G92 X0 Y10; Initial Position

N104 M60; Wire Connection

N106 M83; Water Flow

N110 S1D1 0; Offset from Spark gap N112 G41 G1 X10. Y10.; N114 G01 X26. Y66.; N116 G01 X26. Y63.; N120 G01 X36. Y61.; N122 G01 X28. Y61.; N124 G01 X28. Y57.; N126 G01 X34. Y57.; N128 G01 X34. Y55.; N130 G01 X28. Y55.; N132 G01 X28. Y48.; N134 G01 X26. Y48.; N136 G01 X26. Y45.; N138 G01 X28. Y45.; N140 G01 X28. Y40; N142 G01 X35.5. Y46.; N144 G01 X37.5 Y46.;

N146 G01 X31. Y40.4; N148 G01 X38. Y31.; N150 G01 X35.5 Y31.; N152 G01 X29. Y39.; N154 G01 X28. Y38.; N156 G01 X28. Y31.; N158 G01 X26. Y31.; N160 G01 X26. Y28.; N162 G01 X29. Y28.; N164 G01 X33. Y18.; N166 G01 X37. Y28.; N168 G01 X40. Y28.; N170 G01 X40. Y13.; N172 G01 X38. Y13.; N174 G01 X38. Y25.; N176 G01 X34. Y15.; N178 G01 X32. Y15.; N180 G01 X32. Y15.; N182 G01 X28. Y13.; N184 G01 X26.Y13.; N186 G01 X26. Y9.; N188 G01 X21. Y9.; N190 G03 X15.Y10.I-3.; N192 G01 X10. Y10.;

}

Closing Commands N194 G40 X0.;

N196 M50; N198 M30;

7. Discussion

Precaution

 Precautions when doing the programming are to make sure the correct coordinate is inputted as shown on the graph.

 The programming should be graphed first before running on the CNC to check for errors  The initial position of the tool bit should ideally be from the left or right side of the object

being made and not from the top or bottom as this would cause confusion for the CNC machine.

 The operation should end on the boundary of the work piece or the initial starting position.  Dots should be placed after each x and y coordinate to indicate a correct point.

 A large object can be scaled to fit the work piece dimensions.

 The object should ideally be done on a graphed paper or solid work to ensure proper dimensioning.

In this experiment we encountered several problems with the object. The endpoint of the object won’t match the initial point even though the graphing and size of the object seems right. This resulted in an open looped object. Closed loop object is needed in wire cut process to ensure proper work piece removal. The problem may lie in the programming of the CNC machine.

The solution was to move the y coordinate up by one point in the base region of the object. The result is a slight edge in the initial frame of the object but it can be CNC.

We have concluded several advantages and disadvantages for EDM wire cut

Advantages Disadvantages

1. Suitable for delicate and small parts 1. Closed loop profile only.

2. Accurate and precise dimension. Dimension can be measured in millimeters

2. Not suitable for large and huge parts.

3. Computer automated. Less human errors 3. Skilled labor may be needed in order to operate the machine

4. Cost

5. Slow material removal rate

6. Geometry constrain; sharp corners are difficult due to electrode properties 7. Can only be used in presence of

8. Conclusion

The G-Code programming is an example of Computer-Aided Manufacturing and it is highly suitable in EDM wire cut where the process involves highly fine workpiece and small parts not possibly done by humans. The wirecut machine manage to cut up to 1mm resolution. The product was precise according to the graphed model. The only drawback is the time taken to cut is far too long (one day) and the EDM encountered many problems during the cutting phase.

9. Recommendation

The improvement that can be made on this is the integration of CAD software during the designing process and live feed onto the CAM software of the EDM wirecut machine. This can also skip the graphing procedure and parse the design directly onto the CAM by converting the CAD data into CNC G-Code programming.

10. Reference

Manufturing Engineering and Technology, 7th Edition SI units, Pearson, Serope Kalpakjian, Steven R. Schmid. 2014