At Accurate Gauge in Rochester Hills, Mich., the company motto — “The quality is not in the product, unless the quality is in the process” — reveals the organizational strategy as well as their pride in their work. Machining large ductile iron castings and assembling them into components for heavy truck and military vehicle drivetrain systems demands accuracy at every turn.
Correspondingly, the heavy-duty manufacturing equipment here includes a line of Niigata SPN 701 horizontal machining centers with multiple pallets, used to machine very large, heavy workpieces to accuracy standards that rank among the highest in the global market. As a result, Accurate counts among its customers some of the top manufacturers in that sector, including Meritor, Axle Alliance, Dana and Mack.
The shop machines over 98% of its workpieces from ductile iron and the iron sludge build-up in the coolant tank is a familiar problem for the shop floor personnel. “We approach every machine with a keen eye on machine uptime and an absolute ease of maintenance,” Accurate’s engineering manager Mark Tario explained. “We had experimented with other systems to handle cast ductile iron fines and knew their benefits as well as their shortcomings.”
Tario noted that the shop actually designed two systems in-house to improve the handling of chips and the cleaning of coolant. While the benefits had been appreciable, the operators felt the results were still short of their idea, and so the Accurate team began a systematic search for a better solution.
Mark’s colleagues in the project included Greg Mann, plant manager; Dennis Shepp, maintenance technician; and Jim Weeks, shift supervisor and maintenance technician.
One of the suppliers they identified, Hennig Inc., is well established in that category of machining auxiliaries: Hennig’s chip conveyors and machine enclosures are found on the CNC machines of many builders around the world.
Hennig custom designs and builds machine protection and chip/coolant management products for machine tools. These products protect against corrosion, debris, and common workplace contaminants.
A Better Design
One particular development — a magnetic chip disc filtration system — caught the attention of the team at Accurate because it represented a substantial improvement over traditional drum screen filtration system used on most competing brands. The relative ease of changeover immediately impressed the shop’s engineers, in terms of productivity and maintenance.
“Replacing the drum filter screens is not an easy task,” Tario explained. “In fact, it can be downright miserable. The Hennig disc arrangement seemed to us a much easier system to operate and maintain.
“The incorporation of a rare earth drum and scraper assembly inside the conveyor appeared to be a great solution for minimizing the amount of cast iron fines reaching the coolant tank side of the system,” he continued. Mark also noted that heavier-duty mechanical components and drive chains used on the Hennig conveyor were impressive, providing a greater wear life and reduced downtime likelihood.
An initial order was placed with Hennig for four Chip Disc Filtration (CDF) conveyors to run in tandem with the shop’s Niigata machines. All electrical controls, coolant tanks, pumps, and other hardware were provided by Hennig. Mark Tario and his team worked with the Hennig mechanical and electrical engineers, as well as the Hennig’s local representative, John Kaczmarek of Marathon Industrial Sales in Sterling Heights, Mich., to complete the first installation.
“We have over 40 years of experience in what works and what doesn’t in the machining of cast iron,” Mark said, “so we had a very defined list of needs in all facets of the design, electrical functions, and the very important aspect of machine to auxiliary equipment communication.” He added that the worst scenario in the shop occurs when the machining center is working, but the chip conveyor is not.
Every aspect of the machine-to-conveyor connection was planned out by the Accurate engineering team, including the layout of the coolant tank covers, and the access ports. This attention to detail is something in which the company takes great pride. “The Hennig team was very good on this job and they realized that nothing less than their best efforts would satisfy us,” Tario recalled.
Among the issues Accurate had to overcome, downtime for maintenance was the most prominent. Machining cast iron, by definition, creates considerable problems because of the frequent need to replace conveyor chains, drum screens and other mechanical components that are infiltrated by the iron fines. The machines literally lock up.
For example, the conveyor chains on the Hennig system were found to be stronger than the typical styles used on other designs, which often require adjustment and repairs several times in the course of a year, and usually need total replacement once a year. Depending on the severity of the repair or replacement operation, this situation resulted in many hours or even several days to resolve. Practically speaking, the maintenance personnel would get completely soaked and filthy with the coolant and sludge in the effort.
Easy Maintenance Aids Productivity
By contrast, with the Hennig CDF system the discs can be removed easily and cleaned on a workbench. It’s not necessary for the maintenance engineer rather to reach through narrow access ports to wrestle with a drum style filter. According to Tario, this entire process takes no more than two hours to complete. Simple screen replacements can be done in 30 minutes or less, he noted.
Coolant-related failures are another common problem for the maintenance personnel. On the HMCs at Accurate, a substantial amount of “through the spindle coolant” is used to improve productivity. However, this generous use of coolant can create an immediate and dangerous problem, if the coolant runs low and the machine has no safeguard-warning device, especially when drilling and tapping.
Nearly half the Accurate systems had no such devices, originally, and that led to some damage on the high-speed drills used here. A third of the latter systems used at the shop had a communication device to put the machine’s CNC into a single-block state when the coolant tank ran low, but had no protection to shut off the pump to prevent dry running.
“On our third-generation systems, we changed from a diaphragm style pump to a screw pump, where dry running would be very bad, to say the least,” Tario recalled. “With our fourth-generation Hennig conveyors, however, we have all the protections of the previous generations plus all the necessary controls to shut down the pumps to prevent very costly system component damage.”
Accurate has installed four Hennig systems to date, and recently took delivery of three more. The shop plans to purchase two more shortly, so a total of nine should be in place there soon. All are connected to Niigata HMCs that have an opening in the back with a horseshoe-shaped channel where the conveyor fits. The overall size of each machine size is 10 ft wide by 30 ft long.