SEJARAH MESIN CNC

Apa mesin CNC itu? "CNC adalah mesin yang dipergunakan untuk pengontrolan otomatis dalam dunia industri. Mesin ini berfungsi untuk mengontrol kinerja mesin-mesin lain yang dipergunakan. Dengan kata lain kita tidak memerlukan operator yang banyak untuk mengoperasikan beberapa mesin yang ada. Cukup dikontrol dengan CNC saja maka mesin yang dikontrol bisa berjalan sesuai dengan keinginan kita," ujar Ir. Oegik Soegihardjo, MA, M.Sc., Dekan Fakultas Teknologi Industri UKP.

"Sebagai contoh, CNC telah banyak dipergunakan dalam industri logam. Dalam kondisi ini, CNC dipergunakan untuk mengontrol sistem mekanis mesin-mesin perkakas dan pemotong logam. Jadi seberapa tebal dan panjangnya potongan logam yang dihasilkan oleh mesin pemotong logam, dapat diatur oleh mesin CNC. Saat ini tidak hanya industri logam saja yang memanfaatkan teknologi mesin CNC sebagai proses automatisasinya. Beberapa industri di bidang lain juga telah memanfaatkannya," lanjut alumnus Teknik Mesin Institut Teknologi Sepuluh Nopember Surabaya. Keunggulan dari CNC sendiri adalah kemudahannya untuk de-program sesuai dengan kebutuhan. "CNC cukup kita program melalui software Fanuc. Melalui software inilah kinerja CNC kita atur, dengan mengatur kinerjanya berarti kita telah mengatur proses automatisasi untuk mesin-mesin industri yang lainnya, karena pada dasarnya mesin ini menjadi pengontrol bagi kinerja mesin lainnya," papar pria kelahiran Kediri, 26 Nopember 1959 itu."Mesin ini bekerja sesuai dengan program yang kita berikan kepadanya. Program yang kita berikan tentu harus sudah sesuai dengan rencana yang hendak kita gunakan dalam suatu perusahaan. Mesin CNC dapat mengontrol beberapa mesin yang dihubungkan kepadanya. Jika kita telah mengubah rencana yang ada dalam perusahaan, kita bisa menghapus program lama yang ada dalam CNC dan kita tuliskan program baru di dalamnya," lanjutnya.Bagi mahasiswa Teknik Mesin, keberadaan mesin ini sangat bermanfaat bagi mereka. Mahasiswa dapat mengaplikasikan mata

kuliah pemrograman mesin-mesin CNC serta praktikum CNC secara langsung. "Kita tidak mengharap dengan adanya mesin ini, mahasiswa Teknik Mesin menjadi expert di bidang CNC. Tapi cukup dengan memahami CNC secara umum saja sudah cukup membawa arti dengan hadirnya mesin tersebut," ucap pria yang memperoleh gelar MA dari Institut Alkitab Tiranus Bandung.

Keberadaan mesin CNC sendiri nantinya juga akan dipergunakan untuk penerimaan order dari beberapa industri. "Penerimaan order itu bisa berupa pembuatan barang-barang dari logam, misal mur, baut. Kami siap menerima order tersebut," tandas pria yang juga staf pengajar Manajemen Industri, Pompa dan Kompresor di Jurusan Tenik Mesin UKP.

Awal lahirnya mesin CNC (Computer Numerically Controlled) bermula dari 1952 yang dikembangkan oleh John Pearseon dari Institut Teknologi Massachusetts, atas nama Angkatan Udara Amerika Serikat. Semula proyek tersebut diperuntukkan untuk membuat benda kerja khusus yang rumit. Semula perangkat mesin CNC memerlukan biaya yang tinggi dan volume unit pengendali yang besar. Pada tahun 1973, mesin CNC masih sangat mahal sehingga masih sedikit perusahaan yang mempunyai keberanian dalam mempelopori investasi dalam teknologi ini. Dari tahun 1975, produksi mesin CNC mulai berkembang pesat. Perkembangan ini dipacu oleh perkembangan mikroprosesor, sehingga volume unit pengendali dapat lebih ringkas.Dewasa ini penggunaan mesin CNC hampir terdapat di segala bidang. Dari

bidang pendidikan dan riset yang mempergunakan alat-alat demikian dihasilkan berbagai hasil penelitian yang bermanfaat yang tidak terasa sudah banyak digunakan dalam kehidupan sehari-hari masyarakat banyak.

EDM Wire Cut Machine

EDM Wire Cut Machine also known as Wire Cut Machine or Wire EDM Machine. EDM wire cut uses a spool of a thin metallic wire as an electrode such as brass wire, zinc coated wire and zinc enriched wire to cut a programmed contour in a electrically conductive material or a metal workpiece. The diameter of EDM wire is between 0.05mm (0.002") to 0.33mm (0.13") and the wire tensile strength is more or less than 900N/mm² (130,000psi) depends on the type of wire.

EDM brass wire

The wire EDM machine is generally used when the cut goes all the way through the workpiece and the electrode will be electrically energized to slice through the metal workpiece. The wire is pulled through the workpiece being cut and cooled by a dielectric fluid or deionized water which acts as a coolant. During machining process, the wire itself will be traveling from wire spool into the wire bin reel and the traveling distance will be controlled by the machine program.

EDM Wire

The electrode and the workpiece are either fully submerged, or flushed with a deionized water. To start machining it is first necessary to drill a hole in the workpiece or start from the edge. When the electrically energized wire approaching the workpiece the electrical discharge or spark will be created. The spark will jump to the workpiece which will erode some small amount of workpiece and flush away by the deionized water to form the spark gap between the wire and the workpiece. The spark gap size can be controlled as small as 0.0127mm (0.0005").

EDM wire cut possible machining shapes

The Wire EDM machine uses rapid and repetitive electrical discharges to create more and more spark gap. The spark gap will allow the wire to advance further until the workpiece is cut through. The EDM is a non-contact cutting process, the wire itself does not touch the workpiece and the actual cut is done by the spark. This eliminates machining forces that can cause distortion. The quality of the product depends on the spark gap size, the smaller the spark gap size, the smoother the surface, but the machining time is much more longer.

EDM wire cut produces excellent dimensional accuracy with a high quality surface finish, suitable for cutting intricate shapes or irregular shapes and tight radius contours to create complex dies and other tools from extremely hard materials. It is ideal for cutting hardened materials above HRC 38.

CNC EDM Wire Cut Machine

Most EDM machines are controlled by computer numeric control (CNC). The CNC wire cut machine is an equipment to produce very fine cuts in the metal workpiece. The cut can be as thin as 0.0127mm (0.0005"). The accuracy of the machine could be as precise that it can produce a tolerance of less than 10 micron. This kind of machine is an essential requirement for making precision dies or moulds. Wire EDM requires no special special fixtures and in most cases the machine can run unattended. This makes the EDM wire cut is one of the most cost-effective process, allowing you to reduce inventory and fast delivery dates. This will contribute to improve cash flow and reduce operating expenses.

What is EDM

What is EDM? The EDM is stands for Electrical Discharge Machining or Electrical Discharge Machine. Other popular name for EDM is Electro Discharge Machine. There are two most popular EDM machine, Ram EDM Machine and EDM Wire Cut. Ram EDM also known as, Sinker EDM, Die Sinker, Vertical EDM or Plunge EDM. Ram EDM divided into two main categories, Conventional EDM and CNC EDM. EDM is a non conventional machining method to remove unwanted material from electrically conductive workpiece or metal. EDM is a machining method primarily used for hard metals, super-tough alloy, hardened materials or cutting delicate cavities that would be impossible to machine with conventional machining method such as milling, drilling, grinding or with other type of conventional machine tools. Some of the EDM applications are machining aerospace alloys such as titanium, inconel, & hastalloy, removing broken taps, drills, & bolts and machining of carbide dies and tools.

Conventional EDM or EDM Ram Type

How EDM works

Basically, the EDM process is simple the unwanted material removes by use of recurrent sparks applied to a hard metal. An electrical discharge is created between an electrode and the workpiece known as spark to create spark gap or spark erosion between the electrode and workpiece. For Ram EDM, a special brass will be fabricated into a desire shape and use it as an electrode. The brass will be attached to the EDM machine and use it to machine the workpiece under carefully controlled conditions. Read this blog post about Wire Cut EDM for more details information.

CNC Electrical Discharge Machine / CNC EDM

During EDM process, the current will be switched on and off by moving the electrode up (current off) and down (current on) to control the spark gap. When the current is switched on the spark jumps across the gap and the small amount of unwanted material is removed from the workpiece to allow the electrode to be moved through the workpiece. The electrical spark are very short in duration, approximately 1 microsecond to 1 millisecond each. This process repeats its self over and over again until the electrode is slowly advanced deeper and deeper into the cut. The path of the electrode is typically controlled by a numerical controller (NC) for NC EDM

machine or computer numerical controller (CNC) for CNC EDM machine, which allows a desire shapes to be produced.

The spark always takes place in the dielectric of deionized fluid which acts as a coolant and when the current is switch off the deionized fluid will flushes away the eroded particles from the workpiece. In fact, the electrode itself does not touch the workpiece being cut because the actual cutting is being done by the electrical discharge or spark created between the electrode and the workpiece.

WIRECUT EDM

The Process

Wirecut EDM (Electrical Discharge Machining) is a thermal machining process. Sparks discharged from a small-diameter, tensioned wire erode the workpiece without any contact between the tool and the part produced. This process, also called traveling-wire EDM, produces a straight, narrow-kerf cut. The slowly moving wire brings a fresh, constant diameter electrode to the cutting gap, thereby enhancing kerf size control. Usually a programmed or numerically controlled motion guides the cutting, while the width of the kerf is

maintained as a constant by the wire size and settings on the spark discharge controls. The dielectric is deionized water under pressure, introduced through concentric nozzles at the top and bottom of the workpiece. In a wirecut EDM system, the wire feeds from a spool, travels over tension rollers, along upper and lower guides, over electrical contacts and into a takeup reel. Note that the EDM wire must be threaded through a starter hole in the workpiece. These holes are normally created for the wire by drilling before parts are hardened.

As the wire discharges sparks for thermal machining, the table on which the workpiece is mounted moves to generate X and Y coordinates. Here, small pulse increments (on the order of .00004") assure accurate cutting. For tapered cuts, some wirecut EDM machines use U and V axes on the upper wire guide. These axes can be used to generate tapers up to 30 degrees per slide. Wirecut EDM can be up to a five-axis process.

History

Conventional EDM equipment first appeared in the early 1950s, and performed simple machining utilizing the phenomenon of electrical spark but utilizes five heads mounted above discharge. Wirecut EDM machines a single table. The ability to stack came on the market in the early workpieces under each head to depths 1970s. The first five-head wirecut EDM arrived in the United States in December, 1980.

Until then, wirecut EDM had generally been used only for tool and die manufacture, prototype parts or intricate machining jobs that could be accomplished in no other way. Typical tolerances of +/- 0.0002" have made the process highly attractive for precision machining. The reduction in machining steps has also reduced production times and costs for many operations.

The programmer provides dimensional data to a computer via a keyboard. Then the software within the computer will automatically generate either a punched paper tape or cassette, which will drive the wire EDM machine.

High Production Now Possible

A five-head wire EDM system operates on the same single program, but utilizes five heads mounted above a single table. The ability to stack workpieces under each head to depths of seven inches further multiplies the time-efficiency of the process. It increases production by 400 percent, allowing the wirecutting of five workpieces in the time it used to take to produce one piece, and at half the cost.

This innovation often makes wire EDM the most cost-efficient machining method available. Fewer machining steps, no special cutting tools and lower scrap rates combine with the faster production of five-head equipment to make EDM highly attractive, especially for jobs involving precise tolerances, intricate shapes or exotic materials.

Wirecut EDM has advanced into every industry by offering the reliability, cost efficiency and versatility that challenge conventional machining methods, including low-volume stamping. Manufacturing, aerospace, automotive, jewelry, communications and other high-tech industries which have utilized wire EDM have generally found it to be one of the most effective precision-cutting methods for producing intricate tooling, dies, molds and prototype parts.

Intricate Machining Operations

A simple wirecut EDM operation produced an intricate Ampco 45 bronze mount jaw, which requires tolerances to within +/-.0005". The manufacturer saved an estimated $300 on special cutters, and scrap rates dropped from 22 percent for conventional machining to 3 percent using wirecut EDM. Conventional machining techniques would also have required end mills, ground form cutters, deburring and other secondary operations to produce this workpiece.

The finished part features nine different surfaces. Using conventional machining methods, each surface would normally require a separate setup. Drilling, boring and jig grinding would introduce three additional setups and machining operations. Finally, the teeth of the

mount jaw would be cut. This conventional machining process required 4.8 hours per part.

Wirecut EDM made this operation faster and less complicated. First, the workpiece was Blanchard ground. Next, 12 starter holes were drilled, and the workpiece was mounted for wirecut EDM. A parts programmer entered specifications into the computer, which converted those figures into a CNC program for the machine. The unattended machine then produced the mount jaws from five pieces of Ampco bronze blanks.

The same program used to cut the mount jaws also produced a nest type fixture for holding the parts while two starter holes were drilled. These holes were then wirecut to final size in a separate operation. Wirecut EDM also produced the teeth in a final operation. Hole position tolerance was held to .0005" total, the hole size to .0003" total, and tooth position and size to .0005" total.

This procedure would not have been faster than conventional machining without the multiple production capabilities of the five-head equipment. Using five-head wirecut EDM to cut the blanks and fixtures, the process took a total of 2.8 hours per part and produced five parts simultaneously instead of one a 58% reduction in time compared to conventional machining.

Producing Dies and Punches

A major advance in the manufacture of dies and punches has been the use of wirecut EDM. This die is part of a three-unit pierce die assembly. The complete assembly includes 32 dies, 32 punches and 16 stripper plates. Each unit was produced in a single-step wirecut EDM process, eliminating the problem of transfer-error.

Done conventionally, this project would require approximately $600 in special cutters. The close tolerances required to match dies and punches would create additional expenses in scrap. For instance, each pierce die features five dowel pin holes and five slots, which must line

up precisely. However, conventional machining would require jig grinding the holes on a separate machine, making alignment difficult.

The one-step wirecut EDM process aligned holes and slots precisely, resulting in zero scrap. In addition, no special cutters were needed. Wirecut EDM also saved time. Conventional machining would require 544 hours for complete production of the 32 die details. Single-head EDM would take longer, though it would be at a far lower cost than conventional machining. The job was completed using a five-head machine in only 228 hours less than half the time required by conventional machining. By reducing operating costs, wirecut EDM generates added savings for die users.

Machining Extremely Hard Metals

In cases where single-head wirecut EDM is more efficient than conventional machining, five-head is making wirecut EDM technology even more attractive. Parts such as the hammer blanks would normally be made by stamping, but that was highly impractical in this instance. Composed of annealed T15 high-speed steel, the hammer blanks would generate rapid wear on both punch and die. Required tolerances of +/-.0005" would be impossible to maintain. Stamping would also create burrs and jagged edges that were unacceptable for this precision work.

The manufacturer considered fineblanking, but this did not achieve required tolerances and finish. As a result, these blanks were initially made using single-head wirecut EDM, which was able to perform within tolerances.

The single-head completed stacks of 35 hammer blanks in approximately one hour.

The introduction of five-head wirecut EDM has made this process more efficient, multiplying the quantity simultaneously produced to 175, with little reduction in feed rate. Five-head EDM technology allowed an order for 100,000 units to be filled within 2 1/2 months, at a production rate of approximately 2,000 per day. This order would have tied up a single-head wire EDM machine for a year.

Wirecut EDM has proved superior to conventional machining methods for precision cutting of difficult-to machine materials. Spark erosion works on any electrically conductive material, regardless of hardness. This is especially useful for heat-treated parts, since the workpiece may be prehardened, this eliminates the age old problem of heat distortion. Exotic metals machined by conventional methods tend to experience work hardening, which interferes with cutting and reduces overall accuracy. Since EDM involves no contact between tool and workpiece, there is no work hardening with wirecut EDM.

As with any thermal machining process, however, a recast layer of hardened material is created when sparks, which are pure heat, vaporize a miniscule portion of the workpiece. Typical recast layers for wirecut EDM are approximately .0001" to .0005". A proprietary process developed by our company corrects this recast layer. This proprietary process removes the recast metal, leaving the exposed surface totally undisturbed. It remains just as the metal was produced with the same grain structure and stresses that were inherent in the virgin material. The ability to eliminate the recast layer while controlling tolerances as close as +/-.0001". This has made production of aerospace components possible and cost-effective using wirecut EDM.

Engineering know-how and computer-controlled wirecut EDM technology have provided almost limitless solutions to intricate precision machining problems. The ability to produce work to required levels of accuracy, increased productivity and bottom-line cost efficiency results in a very competitive manufacturing environment for wirecut EDM.

JENIS-JENIS CNC MESIN

Mesin CNC Turning

Mesin CNC Miling

WIRE CUT PRAGRAMME

Wire Cutting is a type of an electrical discharge machining. It is a thermal mass-reducing manufacturing process by using a continuously moving wire. A thin single-strand metal wire is fed through the work piece, occasionally occurring submerged in a tank of dielectric fluid or being continuously sprayed by dielectric fluid. This process is used to cut plates that are too thick or too difficult to cut with other methods. The wire, which is constantly fed from a spool, is held between upper and lower guides.

A method for cutting a plurality of holes in a work piece using a wire electrode comprising the steps of:

(a) cutting a first portion of a first of said holes to be cut in said workpiece, said first portion being less than an entire portion of said first hold to be cut;

(b) cutting said wire electrode when said first portion has been cut in said workpiece;

(c) repeating steps (a) and (b) for each of the remaining holes;

(d) moving said wire electrode over the first portion of said first hole without cutting said workpiece;

(e) cutting a second portion of said first hole, wherein the sum of said first portion and said second portion is equal to the entire portion to be cut for the first hole; and

(f) repeating steps (d) and (e) for each of the remaining holes.

5. A method as claimed in claim 4, wherein step (a) through (c) and steps (d) through (f) are performed using the same computer program operating in a firs mode or a second mode, respectively.

6. A method of machining a workpiece using a wire electrode, said method comprising the steps of:

cutting a cutting path in a cut leaving mode according to a computer program by moving said wire electrode and said workpiece relative to one another along said cutting path;

stopping said cutting step in response to a first machining instruction provided prior to cutting of an entire part to be cut and leaving a remaining portion of said part to be cut;

moving said wire electrode and said workpiece relative to each other along said cutting path without cutting said workpiece according to said computer program; and

cutting said remaining portion of said part to be cut in response to a second machining instruction provided during said moving step.

7. A method of machining a workpiece using a wire electrode as claimed in claim 6, wherein said cutting steps are performed using said computer program operating in a first mode or a second mode, respectively.

] Process Characteristic

The process of wire cutting is basically utilizing a traveling wire. Wire cutting removes mateterial by rapid, controlled, repetitive spark discharges. By using a dielectric fluid you can flush removed/cut particles, control discharge, and cool wire and workpiece. This

process is performed on electrically conductive workpieces and can produce complex two-dimensional shapes.

Process Schematic

A moving wire electrode travels from the supply reel through the workpiece to a take-up reel. The wire is gradually advanced between the reels to compensate for the wear that occurs at the point of cutting. A delectric fluid is supplied to the top and bottom of the workpiece. Proper gap length and desired shape are easily achieved using a numerical control system for moving the workpiece.

ADVANTAGES AND DISADVANTAGES

Some of the advantages of EDM include machining of:

complex shapes that would otherwise be difficult to produce with conventional cutting tools

extremely hard material to very close tolerances very small work pieces where conventional cutting tools may

damage the part from excess cutting tool pressure. There is no direct contact between tool and work

piece.Therefore delicate sections and weak materials can be machined with out any distorsion.

Some of the disadvantages of EDM include:

The slow rate of material removal. The additional time and cost used for creating electrodes for ram

/ Sinker EDM. Reproducing sharp corners on the workpiece is difficult due to

electrode wear. Specific power consumption is very high.