Southwest Manufacturing News • November 2015 • Production Honing On 4-Axis Machining Center

The complete machining of cylindrical bores from raw part to precise, controllable tolerances in just one setup on HELLER’s H Series machining center dramatically reduces tooling and machine cost as well as machining times, HELLER reports.

Deployed on a 4-axis machining center, HELLER’s NCU out-facing head prepared for honing can adjust the size, taper, surface and tolerance of a bore as it changes the size of the tool during the honing process. A Marposs in-process gauge is incorporated into the head.

HELLER collaborated with DIAHON to program honing cycles that permit helical slide honing. The HELLER H series are designed to create a continuous crossgrind that can otherwise be produced only on advanced honing machines.

“Unlike on honing machines, however, bores with a cylinder form tolerance of just 1 ìm can be produced in one setup over a length of 300 mm, for example, eliminating the typical threepass honing process and minimizing honing cycle time,” said a company spokesperson.

“Combined with a machining center as a standard machine, honing is efficient and cost-effective up to a certain batch size. This is how, in one specific case, we were able to reduce the machine running times from 15 minutes for internal cylindrical grinding to 12 seconds by means of honing,” said Bernd Sihling, Deputy CEO of DIAHON.

“Productivity increases in this range can benefit manufacturers of pump housings, con-rods, cylinder blocks or hydraulic control housings. Cost savings result from the short machining times and the elimination of a special machine for honing. With honing on a machining center, the in-feed motion and the speed of the tool can be adjusted while machining occurs. A high degree of automation is possible, and production capacity can be adjusted as needed,” said a company spokesperson.

“Automotive Tier One manufacturers,” observed Vince Trampus, Heller U.S. Vice President – Sales, “can now avoid investing in dedicated honing systems for engine cylinder bores up to a certain volume production. Machining centers offer the total processing flexibility the industry is asking for, and adding the honing process to machining center capability makes the case even stronger.”

Until now, ‘multitasking’ has not included honing as a process. Once considered a costly, complex process, honing provided little reason to be included in a total part process, and it required expensive machines and tools. The precise machining of cylindrical bores with tight tolerances and complex geometric and topological features tended to be achieved by other processes, such as internal cylindrical grinding.

“There are three distinctly different types of honing: honing by means of a permanently set tool with a defined diameter, honing by means of a tool with a flexible diameter, the hone of which can be expanded by coolant pressure, and path-controlled honing on machining centers,” said Sihling.

HELLER has added honing to the smart technology mix on the H series machining centers. DIAHON has demonstrated - on a HELLER H 2000 with out-facing head for cylinder crankcases, con-rods and control housings- the coolant-expanded honing technologies coolEX, coolEXact and coolEC float, as well as the path-controlled honing technology Xstep. The latter permits conventional honing on a machining center.

While economical, honing on a machining center must also satisfy technical requirements, including the highly precise replication of macroforms (cylinders). Series con-rod machining using coolant-expanded honing technology has also been performed on machining centers for some years now, but not at production volumes.

Honing of coated cylinder crankcases by means of outfacing heads combined with a nonwearing air measuring between nozzles and bore during honing is expected to become a preferred solution in engine construction for the future. High productivity is complemented by high precision (tolerance less than 6 ìm) with specified surface finish, roughness, plateau structures and cross-grind.