EDM Technical Manual
Poco Graphite, Inc.
Revised February 2013
©1994-2013 Poco Graphite, Inc.
300 Old Greenwood Road
Decatur, Texas 76234
POCO's continuing commitment to the EDM industry necessitated evaluating new machine technology to see how POCO graphites perform and reporting the results to the EDM community.
Poco Graphite, Inc. would like to express appreciation to Mitsubishi International Corporation, EDM Division, for the loan of one of their K series machines (M35K). All of the test cuts needed to accumulate the data for the performance section of the EDM Technical Manual were conducted on this machine. Along with the use of this machine, Mitsubishi also provided set-up, operator training and technical support.
POCO and Mitsubishi felt that a cooperative agreement would provide educational results for both companies. The arrangement allowed this phase of the Objective Comparison Testing Program to be conducted on one of the new technology machines and Mitsubishi was provided with machine performance data using graphite electrodes.
The M35K was equipped with a 32-position tool changer. This tool changer allowed overnight cuts to be made and the machine to run virtually without interruptions. Due to the number of workmetal and graphite combinations and the necessary replications, this program lasted almost four years and has provided valuable data for the EDM community.
There are many electrode materials available for Electrical Discharge Machining (EDM). Material selection should be based on technical data because electrode performance coupled with an operator's skill affects the outcome of any EDM job. Due to the number of brands and grades to choose from, material evaluation and the final material selection can be difficult.
There are some obvious differences in appearance and not so obvious differences in the properties and characteristics of EDM graphites. All of these will ultimately affect an electrode's performance during EDM. The less obvious the differences, the more challenging will be the user's job of selecting the proper electrode material for a particular application.
To aid the EDMer in the selection of electrode materials, POCO has revised the existing EDM Technical Manual and added information from A Practical Guide to Electrode Material Selection. This new publication provides the EDMer with the following essential information:
- EDM fundamentals
- Generic terms for referring to electrode materials, properties and characteristics
- Practical guidelines for choosing the right electrode materials for the job
- An analysis of the factors that influence the choice of electrode materials
- Guidelines for electrode fabrication
- Glossary of EDM terms
- An explanation of POCO's Objective Comparison Testing program
- POCO EDM grade performance graphs
The information contained in this manual can help improve operator skill, efficiency, productivity, and increase your profits.
Graphite as an Electrode
Graphite, a form of carbon, has long been known to most people as a material used in lead pencils and lubricants. However, only since the late 1960's has graphite become recognized as an outstanding EDM electrode material. In the early days of its use little was known about the differences in properties and characteristics of graphite materials or how these would affect their performance as EDM electrodes.
In 1964, Poco Graphite, Inc. introduced to the EDM industry our isotropic graphite electrode material whose unique characteristics were ultrafine particle size, high strength, and uniform structure. POCO scientists had determined that these graphite materials of unprecedented quality might be useful in the still developing EDM industry. Both POCO and the EDM industry were astonished at the remarkable improvement the new graphite made in EDM performance and capabilities.
Five years later, POCO established an EDM test laboratory and embarked upon a full-scale testing program for our own grades of graphite and other types of electrode materials. POCO's methods were unique and objective. Objective testing demands that the investigator carefully control the operating parameters to insure that valid comparisons can be made. Often, tests are conducted without adequate controls. Such nonobjective tests do not yield useful data.
More than 20 years and over 20,000 tests later, questions still remain. But POCO has amassed what is probably the world's most extensive data base of comparative electrode test data, and the answers to the puzzle of just what happens when the electrode meets the workpiece is becoming better understood.
In 1974, POCO published the EDM Technical Manual, the first document in the field based on laboratory testing of EDM electrode materials. Many other exciting things have happened in the years since the first appearance of the EDM Technical Manual. Engineers have fully integrated EDM into the design process. The characterization of EDM as "Nontraditional Machining" appears to be nearly a thing of the past. EDM technology has exploded with new ideas and applications, requiring nearly constant study just to keep abreast.
At POCO, our laboratory has maintained an intensive research and development program in addition to the objective comparison testing program. This R & D program led to the addition to our product line of new graphite grades excellent enough to bear the POCO name. POCO offers a full line of electrode materials for virtually every EDM application.
POCO's commitment to the Objective Comparison Testing program is ongoing. As we desire to continue to manufacture and market the world's finest EDM electrode materials, we feel it is our responsibility to advance the technology of EDM and share this knowledge with the EDM community. It is our hope that all involved in the EDM industry will find the information and data recorded in this book useful in making sound judgments when choosing electrode materials that will yield predictable and profitable results.