A Linear Way of Thinking

Jan. 19, 2010
For one successful shop, high accuracy, excellent surface finishes and machine longevity all stem from linear motors.
Neu Dynamics hardmilled the surface finish on this H-13 54 Rc mold tool using its Sodick linear motor-driven mill.

The benefits of linear motor-driven machines often far outweigh the advantages of ballscrew-driven machines, especially when it comes to positioning accuracy, part surface finishes and machine longevity. That’s the opinion of Kevin Hartsoe, who calls these the “must have” machine-tool qualities that keep his shop thriving and competitive.

Hartsoe is the president of Neu Dynamics Corp., a shop specializing in building encapsulation molds, optoelectronic and fiber-optic molds and insert molds for the electronics and semiconductor industries. But, the incorporation of linear motor-driven machine tools also has helped Neu Dynamics expand into other markets, like medical equipment and general contract micro machining work.

According to Hartsoe, Neu Dynamics chose linear motordriven machines mainly because 90 percent of its jobs involve extremely tight tolerances and lots of small, finely detailed cavitation work. To illustrate, he cited one cavitation mold that had 2,304 cavities and a top-to-bottom mismatch tolerance of half a millionth of an inch. Parts for the mold measured 1 m-sq by 2-m long, but the shop’s average parts may be as small as 0.8-mm square.

The shop also machines EDM electrodes on the linear motor-driven machine.

Linear motor-driven machines at Neu Dynamics include two sinker EDMs and a high-speed milling machine. The EDMs are an AQ35L and AQ55L from Sodick, and the mill is a HS430L, also from Sodick. Many shops purchase linear motor-driven machines for ruining a part’s surface finish when the machine changes directions,” explained Hartsoe.

Since incorporating the linear motor EDMs into its manufacturing processes, Neu Dynamics is able to burn mold cavities right to size without preliminary roughing operations because of the machines’ accuracies. Eliminating the roughing operation also gives the shop longer electrode life and more even burns around entire cavities.

One of the Sodick EDMs at Neu Dynamics has linear motors driving just its Z-axis motion, while the other machine has them driving the X, Y and Z axes. The main advantage of a linear motor-driven Z axis on a sinker EDM is that electrodes can approach and retract from workpieces extremely fast (1,440 ipm and 1.2 G acceleration).

Moving so quickly creates an even and natural flushing action around the electrode that lets Neu Dynamics burn deeper ribs and deeper wells. It also eliminates the need for external flushing systems, which, in turn, allows Neu Dynamics to more easily run the machines unattended because there’s no need to have an operator standing by to set up flush lines or to adjust flushing pressures.

The shop EDMs a large portion of molds, but it also hardmills them on the linear motor-driven high-speed mill. And, Hartsoe said, the linear drives provide phenomenal finishes and tolerances, again because of the absence of backlash.

“We are really happy with the finishes the milling machine produces. Prior to purchasing the machine, we ran some test parts and compared the finishes done on the linear motor-driven mill to those done on ballscrew-driven machines. The linear mill’s finishes met our requirements, while only one ballscrew machine came close to achieving the needed finishes,” said Hartsoe.

Linear motor-driven Sodick sinker EDMs let Neu Dynamics burn deeper ribs and deeper wells without external flushing systems.

He added that there was a bit of a learning curve when it came to hardmilling on the Sodick machine. “When we purchased the mill, the team here had limited experience with hardmilling. At that time, we estimated the learning curve would be between 8 and 10 months, so to use the machine in the mean time, we opted for a vacuum system for milling graphite EDM electrodes.”

One of the lessons Neu Dynamics learned as it strengthened its hardmilling knowledge was that the process generates heat, especially when machining certain size mold cavities. So, to be on the safe side, the shop keeps cutting tools a bit further away than usual from the finished size when rough machining. Then for the finishing process, it will creep up to the finished size. Plus, the surface finishes are so good that there is no need for manual benchwork to polish out tool marks.

Hartsoe added that the shop also learned a few things about surface finishes, especially concerning the medical jobs it does. Some of these components require a matte finish or light abrasive finish, which the shop would generate in the mold using a secondary EDM operation. With the HS430L linear mill, mold cavity surfaces are hardmilled then simply glass-beaded to the required surface finish, eliminating the secondary EDM step.

When it comes to programming the linear mill, Neu Dynamics discovered that the machine requires CAM software with quite a bit of look-ahead capability. At present, the shop is using MasterCam and has had no problems with “data starvation.”

But, reliability is perhaps the most beneficial aspect of linear motor-driven machines the shop has discovered. “We have not had one problem with any of the machines as far as the linear drives are concerned, none of the problems that typically develop over time with ballscrew machines,” said Hartsoe.

Lights-out machining is a high priority at Neu Dynamics, and on one of its linear motor-driven sinker EDMs, a 24- to 48-position toolchanger keeps the machine running for long periods of time. The other EDM has a standard 8-position changer because the shop runs bigger electrodes on that machine.

For the linear motor mill, Neu Dynamics developed fixturing for stacking multiple jobs. For example, when chining electrodes on the mill, the shop uses four System 3R workholding units. Or when running multiple parts, it uses dual vises.

According to Hartsoe, the linear motor-driven machines have also opened up new markets/business for the shop. By just having the machines, he indicated that “work seems to find Neu Dynamics.”

The shop currently machines electrodes for other mold building companies and does some hardmilling for them, too. “These are shops that have not yet made the investment in either an electrode-milling or hardmilling machine. We also get opportunities from these shops to do cavitation work that, in the past, we never got,” said Hartsoe.

He observed that in the mold industry a shop must either innovate and diversify, or it will perish. “Ten years ago, we were primarily electronics-based. Now, 65 percent of our work is medical. However, we are seeing a growing influx of electronics work coming back from Asia and an increase in low-volume custom work, mainly because overseas shops don’t even want to look at a part program unless it involves at least 1 million parts per month,” commented Hartsoe.

The linear motor-driven machine tools at Neu Dynamics help the shop handle the 120 to 140 projects it gets per year. Not all of this work is mold building, and it can vary from a $2,500 spare parts order to a multiple mold package costing $400,000

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