Published 1/1/2000

EDM in the Millenium

A number of recent EDM developments offer significant solutions to obstacles facing the moldmaking industry in the millennium.

Lack of Skilled Labor

Despite the current softness in the moldmaking market, there is an ongoing unmet demand for about 20,000 skilled moldmakers, diemakers and precision machinists in the U.S. The lack of an adequate quantity or quality of these skilled professionals has a direct impact on delivery, cost structure and even the ability to obtain and use the newest technologies. Recent developments in EDM, especially in CNC EDM in late 1999, offer dramatic productivity improvements. These advances allow U.S. shops to both stretch the available pool of moldmakers across a much larger volume of work and to train new EDM operators more rapidly to a higher level of efficiency.

Compressed Delivery Times

Shortened product development cycles have severely compressed the time available to design and build molds, in some cases cutting 50 percent off of traditional cycles. At one time, EDM was one of the bottlenecks in the moldmaking process. But now the combination of high-performance graphite electrode milling and the newest highly adaptive CNC EDMs means dramatic reductions in the EDM portion of the delivery time. Additionally, increased use of wire EDM allows for more unattended machining, fewer mold components and easier assembly.

Competitive Pricing

The most common moldmaker com-plaint cited in the NTMA Report concerned severe price competition - especially from developing countries that pay low wages. U.S. shops need to reduce labor costs/price so that the remaining price gap is justified by quality, convenience, language, confidence, ease of parallel engineering, etc. The recent developments in EDM, especially CNC RAM EDM, offer dramatic cost savings. For the most difficult applications, on a per unit output basis, labor costs during machining are reduced by 75 percent and capital costs by 28 percent. These savings are based on cutting speeds in excess of all previous EDM technologies in difficult flushing applications and all with totally unattended machining.

Advances in EDM Performance

Processes such as high-performance milling and rapid tooling are competing for some of the applications traditionally produced with EDM. Despite the technical strides that these processes have made, EDM has maintained a dominant position in moldmaking. This is largely due to vast improvements in the RAM and wire EDM processes. In fact, in the U.S. market, EDM sales have risen from one-half percent of total machine tool sales in 1960 to six percent in 1998. CNC RAM EDM, which is primarily used in the mold and die cast industry, has increased sales even more rapidly than total EDM sales for the last 15 years.

Wire EDM

Wire EDM's improvements during the past 20 years bring to mind the price/performance improvements achieved in the computer industry. Specifically, the process improvements for wire EDM since 1976. Most relevant to moldmakers are the simultaneous increases of: 800 percent in cutting speed, 500 percent in maximum workpiece volume and 9,000 percent in taper capability - all achieved while the inflation-adjusted price of the machines fell by 75 percent .

Other Benefits

Wire EDM enables the machine to cut internal corners with the minimum radius based on wire diameter. It becomes easy to cut square openings without segmentation of the mold. Mold inserts or core pinholes can be cut up to 20 inches thick after heat treating to insure maximum location accuracy. The wire EDM process is predictable and repeatable in accuracy and surface finish because the path program can be stored and re-used, if necessary. This means less downtime in case of modification or repair, and therefore lower associated costs. Wire EDM electrodes in the diesinking process make honeycomb or other rib shapes easily. Deep and thin walls in copper or graphite also are mastered easily. Complex shapes can be cut in order to reduce the number of electrodes needed for the mold, and therefore the time and cost to build it.

Under-Utilization of Wire EDM

Despite wire EDM's process improvements and the multitude of applications, many mold shops are still under-utilizing wire EDM. There still are many shops with more than three manual EDMs or one or more CNC EDMs, but with no wire machine. Generally, these shops outsource the minimum amount of wire and design away from wire EDM. When a shop does opt to purchase a wire EDM, it typically goes through the following phases:

Phase I - Work previously jobbed-out is done in-house.
Phase II - Some work is shifted from grinding, milling or die sinking to wire.
Phase III - Molds are redesigned to have fewer, but more complicated inserts that are wire-cut. The resulting inserts are more accurate and more easily assembled. Total mold costs are thus reduced, while mold accuracy and delivery times are improved.
Phase IV - Another wire EDM is purchased.

Wire Case Study

Verifying the Improvements and Savings
When Osley & Whitney, Inc./Express Tool - part of the Infinite Plastics Group, a Westfield, MA-based mold shop - decided to upgrade its wire-cutting capabilities, they needed a total package.

The company wanted a sophisticated machine that was fast, accurate, ran submerged, had a large taper cutting capability, used a familiar control, included a reasonable maintenance schedule and was capable of operating unattended for extended periods.

As mentioned, one of the capabilities that Osley & Whitney sought was more speed. "With the advanced cutting technology in the submerged wire EDM, the machine runs at least three times faster than the one it replaced," says Roger Beauregard, Osley & Whitney's vice president of manufacturing. "And the larger workpiece capacity speeds up our shop floor operations even more. Also, the accuracy is very good, and the finish is far superior to what we were getting - even though it's running up to 80 hours a week."

Roger Poirier, vice president of sales and engineering at Osley & Whitney, adds, "We verified the speed improvement and cost savings by running a distributor cap replacement job as a test. This design features two mating parts and a parting line that actually forms the outside shape of the part. Basically, this is a cone-shaped part that's larger on the bottom than at the top. It is loaded with fillet radii and scallops that ultimately produce a smooth exterior surface - and it serves as a good test of a wire machine's abilities.

"When we ran the job in our old wire machine, it required 16 hours per cavity. When we ran the same job again on the new submerged wire EDM, it took just four hours per cavity. And we know from checking the results that, whether we run this job just once or 1,000 more times, each time the machine will produce exactly the same shape. We also are able to generate the radii and put in the fillets, notches, and scallops - all at the same time."

John Monaghan, president, adds, "Most of the tools we build are large and complex. It doesn't matter if the customer needs multiple cam action, two-stage ejection, scrolling or the workpiece weighs 2,000 pounds - we're equipped to do one or 100."

CNC RAM EDM

RAM or diesinking EDM achieved its first practical commercial applications in the mid 1950s and soon became an essential moldmaking process. The key eras of RAM EDM development can be thought of as: manual, manual with orbiting, early adaptive generator CNCs, fuzzy CNC and the current era, which is characterized by CNC EDMs with highly adaptive generators.

The highly adaptive generator models achieve their advantages over early adaptive generators and fuzzy technology by optimizing the process and controlling the aggressiveness of the machining. The highly adaptive control changes the pulsation-frequency and pulsation-length according to the actual cutting depth, improving cutting performance in difficult flushing conditions.

The new motor servo control and a two micro-second machining loop-time allows a faster retraction of the electrode during pulsation. The new control software monitors each individual spark and cuts out bad sparks immediately.

The system also adapts the current density during the rough cut automatically. This feature dramatically improves the performance on free-form electrode shapes. During finishing, the control software monitors the cut to insure the best and most consistent surface integrity using a contamination sensor that reacts 10 times faster than the previous generator technology.

Clear Advantage Over Fuzzy

An article in the October 1999 edition of MoldMaking Technology reviewed the advantages of fuzzy logic in achieving improved EDM automation, reduced operator skill requirements and faster cycle times. For some types of generators, complete reliance on fuzzy is necessary to bring performance up to the levels of a good late 1980s adaptive generator. The new highly adaptive generators clearly take another large step in performance - beyond early adaptive or the newest fuzzy generators. As an additional example, based on the best available data, for the three "rib" electrodes in the October article, a comparison of the total cycle time for one each of the three ribs is shown below:

Total Hours

"Fuzzy/Normal Burn Time"
8.89 hours
"Fuzzy/High-Speed Jump Time"
7.22 hours
Highly Adaptive Generator
4.78 hours

CNC RAM Case Study

Diamond Mold Corp., a precision plastic mold shop, obtained the first highly adaptive CNC in the U.S. in September 1999. President Albert Lobrillo says that the new machine cuts 30 percent faster than the best he has ever seen before and operates 24 hours a day, six days a week. Lobrillo has the experience to make a sound comparison since Diamond has a total of 15 EDMs - including three wire EDMs and four CNC EDMs. He anticipates ordering a second, highly adaptive CNC EDM soon.

"We've had a lot of success with the highly adaptive die-sinking EDMs running very close tolerance work, which is 90 percent of our business. We just finished two, four-cavity very intricate mold - all on highly adaptive die-sinking EDMs - and every one passed inspection. I don't know if we could have gotten that out of any other machine - they're great machines," Lobrillo said.

Conclusion

The ever-changing face of technology looks to play a valuable part in resolving some of the current dilemmas in the EDM industry. Enhanced machining speed and unattended operation are solutions to the problems of compressed delivery times, competitive pricing and lack of skilled labor.