High Speed Electric Spindle Rigidity Helps Company Meet Quality Challenges

Engraving companies that produce dies used for stamping products with production codes, lot numbers and logos must pay close attention to detail, finish and tight tolerances. To meet these challenges, Durable Engravers Incorporated (Franklin Park, Illinois) uses a variety of vertical machining centers (VMCs), all of which are equipped with high speed electric spindle systems from The Precise Corporation (Racine, Wisconsin).

Durable Engravers produces dies, stamps and other tools used for marking products with images such as lot numbers, dates, logos, codes and recycling information. The company specializes in steel type, mold engraving, hot stamping dies, mold inserts and similar products. Founded more than 50 years ago, Durable Engravers now relies on equipment that includes several computer-driven VMCs to help it create special images that are faithful to the finest detail.

Traditionally, engraving was performed on pantographs that allowed the operator to duplicate artwork or models. It was a manual process in which the machine duplicated the operator's motions as he followed a pattern. Computer-controlled machine tools now simplify engraving by automating the process, and they also minimize the variables to achieve greater consistency and accuracy.

Fine engraving, however, requires small diameter cutting tools that must be driven at high rpm to achieve proper cutting speeds and optimum efficiency. Most machines at Durable Engravers achieve this speed by incorporating high speed electric spindles that can reach speeds as high as 30,000 rpm. The company uses spindles made by The Precise Corporation.

High spindle speed is a necessity, but the rigidity of the spindle is another major factor in achieving quality engraved numbers, letters, logos or other characters. Gary Berenger of Durable Engravers notes that one of the company's VMCs was originally equipped with a different electric-powered spindle that had problems with excessive vibration and runout. He says this caused a certain amount of "shakiness" in the cuts and compromised the quality of the final work. "There weren't too many jobs we could use it on," he explains, "and we were going to sell it."

Instead, the company worked with Numatix/Pro Tech, Inc. (Farmington Hills, Michigan) to retrofit the machine with a Precise SC 50102 Series high speed electric spindle system. Through Numatix/Pro Tech, The Precise Corporation offers complete retrofit services for any type of CNC machine, including installation of a high speed spindle system and new CNC controls. In addition to the 100 mm spindle, the system includes a Precise PCA2 2030 high frequency converter and a RCS 1001 liquid cooling system that dissipates the heat generated by the spindle bearings and motor. The 7 kW (9.4 hp) spindle provides speeds up to 30,000 rpm.

The machine, a Sharnoa rp-25, now is a productive part of the Durable Engravers facility. In one recent job, it was programmed to cut letters 0.030 inch high by 0.004 inch deep in hardened steel. A 1/8-inch diameter cutter was used at 18,000 to 20,000 rpm.

"Now we get a nice clean cut," says Jim Maybach of Durable Engravers. "With the old spindle, it always left a burr, no matter what kind of cutter we used. We've eliminated hand finishing and increased cutter life."

Spindle accuracy of 2 micronmeters (0.00008 inch) maximum T.I.R. at the spindle nose is said to allow the cutting tool to work effectively at high speeds and achieve excellent precision and finish. The light chip load and low tool pressure inherent in high speed machining make it possible to achieve highly accurate results when engraving even the finest characters.

While many of the stamping dies and molds the company engraves are made of steel or aluminum, a substantial portion of the engraving and fine machining is performed on graphite EDM electrodes that are used to produce the final marking product. "We have 10 EDM machines and use the process quite a bit," Mr. Berenger says. "Some of our engraving machines are dedicated for use on graphite."

Among the other VMCs at the company is a Sharnoa SGC-32, which is also equipped with a Precise SC 50102 Series spindle. The spindle is designed to work with the machine's automatic tool changer.

Tooling generally is carbide, although high speed steel also is used. Most tools are specially ground for the purpose at Durable Engravers, using special configurations developed through experience.

The company started with Precise spindles in its early years, and one older machine is a small Kuhlmann engraving machine equipped with a Precise SC 60 Series spindle. It continues to perform well after many years and is used steadily to engrave small characters in graphite EDM electrodes.