Since small hole drilling is becoming more popular for production applications in aerospace, medical, electronics, and other sectors that require very small, extremely accurate holes with good surface finish, Makino is seeing a growing demand for machines that can produce these holes consistently and repeatably. Here are some test results that were produced by the Makino EDM Applications Department in Auburn Hills, MI.
The Applications Department performed this test to prove the repeatable accuracy of the EDGE2 Fine Hole machine. A series of 15 holes, 0.010" (0.254mm) diameter, was made on the machine using 0.008" (0.203mm) diameter copper pipe to predrill each hole, then a solid copper rod was used for finishing. The holes were measured for entrance and exit size, and also shape accuracy on an OGP Quest Vision System.
There are several factors that determine the accuracy and speed at which the 0.010" (0.254mm) diameter holes can be produced. When the 0.008" (0.203mm) diameter copper tube is at full length, the machining time is longer and a greater taper is produced from entrance to exit for the solid finishing rod to remove. This is indicated by the values shown for holes 1 through 9. As the roughing pipe electrode becomes shorter, the machining speed and break-through at the bottom of the holes are much faster. The roughing process produced a slight taper of 2 ~ 4 tenths (5-11 micron) which was removed during the finishing process. It was critical to perform these tests in a climate controlled room, and to use only the highest quality copper tubes available to reach these results and times. To maintain the better results shown in holes 10 through 15, the electrodes should be purchased in a maximum of 6.0” lengths. All 15 holes where roughed and finished in approximately 60 minutes for an average of 4 minutes to include dressing between holes.
Hole # Entrance Exit Difference 1 0.010032” 0.010432” 0.000400” 2 0.010090” 0.010242” 0.000152” 3 0.009993” 0.010127” 0.000134” 4 0.010033” 0.010131” 0.000098” 5 0.010048” 0.010145” 0.000097” 6 0.010040” 0.010320” 0.000280” 7 0.010065” 0.010569” 0.000504” 8 0.010025” 0.010348” 0.000323” 9 0.009994” 0.010336” 0.000342” 10 0.009962” 0.010039” 0.000077” 11 0.009966” 0.009984” 0.000018” 12 0.009956” 0.010038” 0.000082” 13 0.010052” 0.010064” 0.000012” 14 0.010056” 0.010066” 0.000010” 15 0.009996” 0.010004” 0.000008”
Cpk Results of Entrances Based on specific pre-defined requirements for these holes, Cpk is 1.82. This Cpk is considered exceptional based on the following scale: 0 to less than 1.0 is unacceptable - sometimes called "not capable" Greater than 1 to 1.33 is fair Greater than 1.33 to 1.66 is acceptable Greater than 1.66 is exceptional These Cpk values and ratings are per QualityAdvisor.com
Hole Shape and Location
The holes shown above were photographed at 166x magnification on the OGP Quest Vision System. Pitch between center of holes was programmed at 0.0250” (0.635mm)
The two photos shown above were taken at 403 magnification. Back light shown at left, surface and back light shown at right.
For more information on these test results or the Makino Edge2 Fine Hole EDM machine, send an email to either jeff.kiszonas@makino.com or bill.paul@makino.com.
