BY CHARLES BATES
Mold parts from Holbrook's Roboform 350 EDM, with GammaTec additive, require little benchworking.
Holbrook hardmills more intricate mold features with its HSM 400 high-speed machine.
RICHARD LOCKWOOD IS HAPPY TO tell you what the key to his moldmaking shop's success is. It's no big secret and is quite simple. Bottom line: Maintain a talented, ambitious workforce, constantly upgrade with new technology and provide extensive customer service. In its beginnings, Holbrook Tool & Molding Inc. (www.holbrooktool.com) opened with two machine tools and a two employees, Lockwood and co-owner Dale Barnard. Today, the shop has 40 employees and more than 50 machine tools. It has had only two years of flat growth since its inception twenty-five years ago and has posted gains in its other 23 years of business.
Like most U.S. moldmaking shops, Holbrook's biggest challenge is staying competitive in delivery and pricing. "We have no time to build anything any more, and we have to compete with job quotes coming from China," says Christopher Knierman, a design engineer at Holbrook.
The shop overcomes competitive challenges by choosing the right machine tools that allow it to take on the high-end work and molds that are too complicated to go to an overseas supplier. In addition, Holbrook furnishes its customers with complete mold packages and service — build, sample and debug. And it always tries to find ways to help its customers improve their part designs, make their molding processes easy and cut costs for their tooling while making that tooling more robust.
At Holbrook, jobs do not end when a mold is delivered to a customer. The company's technicians go to its customers' facilities for mold try-outs, and if there is a problem, they ensure that the mold is fixed. "You are not going to compete financially with overseas mold builders, but being able to load a mold into a truck and personally drive it to a customer so they do not lose production time is something an overseas builder can't do," says Knierman.
Holbrook strives to reduce its costs and those of its customers, and manufacturing techniques and technologies play a key role in doing that. For instance, the shop suggests stack molds for its customers whenever possible, which allow customers to produce more parts without having to incorporate larger molds.
Instead of a 24-cavity tool, a stack mold can provide 48 cavities while fitting in the same size injection molding press. The smaller the press, the less floorspace and electricity is required. Additionally, stack-mold tooling is less expensive to produce compared with two sets of tooling to run the same number of parts.
"I don't know if we are doing anything different than our competition, but I believe we are doing it smarter and better," says Knierman. He adds that having the latest in machine tool technology gives his company its competitive edge.
Most recently, the shop has updated its technology with the acquisition of two Charmilles (www.charmillesus.com) Roboform 350 ram EDMs with GammaTec additive technology and a Mikron (www.mikron-us.com) HSM 400 high-speed machining center. The EDMs generate fine surface finishes faster and over larger part areas than do conventional EDMs, and, more importantly, they slash Holbrook's mold-polishing times by half. Meanwhile the HSM 400 lets the shop mill hardened parts that otherwise would have required EDMing.
According to Knierman, the Roboform GammaTec machines are fast, but their real value is in the intricacy of the burns that they can achieve. Manually polishing can damage the details on intricate features of molds. However, parts produced on the the GammaTecs need little polishing, and detail integrity is maintained. Additionally, part surfaces are consistent, so if a customer calls for a replacement component, the shop can produce an exact duplicate. That is not always the case when parts are hand polished.
GammaTec machines, which Charmilles says cut parts up to three times faster than conventional EDMs, run graphite powder made up of precisely sized flakes that users pour into machine worktanks. These flakes form a bridge between EDM electrodes and workpiece surfaces that allow EDMing sparks to jump and disperse over wider surface areas, instead of one area at a time as in conventional EDMs.
The GammaTec system generates finer sparks to produce finer part surface finishes in less time, and finer sludge particles (EDM waste) that can be easily flushed out of the spark gap to eliminate problems with short circuiting and arcing. GammaTec-dispersed sparks also create gloss-type surface finishes, as opposed to the typical matte finishes of conventional EDMs. Mold tooling with such glossy finishes produce plastic parts that are paintable, allowing plastic injection molding companies to use one color of plastic pellets but still produce different colors of the same part by painting.
Holbrook also reduces mold-cavity machining time with its HSM 400. The machine features a Step-Tec 42,000-rpm spindle and feedrates of 20 meters (787 in.) per minute. In some instances, the machining center is faster than an EDM.
"These aren't just simple cavities, most are intricate and high-speed milled complete in steel parts with hardnesses in the 50-Rc range," says Knierman. "Fifteen years ago, we would not have dreamed of doing such milling jobs as cutting 1-millimeter (0.039-in ) thick ribs 0.500-in. deep in hardened steel, but machines such as the HSM 400 and advances in cutting tools make it possible."
Also according to Knierman, 60 percent to 70 percent of the parts that the shop previously would have machined on a jig grinder are now done on its wire EDM or on the high-speed milling machine. When using the HSM 400 as a high-speed jig grinder, the shop orbits diamond nib wheels and brings holes to size for such things as gates, ejector-pin holes and shutoffs for transfer seals of hot runners. "Jig grinding with the HSM 400 may not always be faster, but it frees operators for other tasks because they don't have to tend the milling machine like they do a jig grinder," says Knierman.