RX8Club.com - Renesis engineering tidbits from an engineering-process magazine

I just received a 3 page article from an engineering magazine (AEI Jan ’04) that may be of interest. The article is entitled, “Mazda Overhauls Rotary Engine Plant.”
Here are a the relevant items:

“Now Mazda is gearing up to produce 60,000 units of the new RX-8 every year. The rotary plant has been completely overhauled, renovated, and largely ditigized…. // the remaining article deals w the up-rated manufacturing processes re the Renesis… Digitally modeled based on Mazda’s veteran rotary craftsmen’s skills and know-how, the manufacturing facilities have been updates and rebuilt to incorporate the latest numerical control technology. …
many of the major components of the new Renesis engine in-house. The engine, which inherits the 13B 2 rotor engine family’s internal dimensions and geometry, is a new design with few carry-over parts. Mazda casts, machines, heat-treats, plates, and finishes the engine’s major components, including die cast aluminum rotor housings, cast-iron side and intermediate housings, and cast-iron rotors. The steel eccentric shaft forging, equivalent to the conventional crankshaft, is supplied by an outside specialist, with Mazda machining and finishing it…….. The peritrochoid profile must be precisely shaped. Previously, a mechanical machine tool (!!!!!!!!!!!!!!!!!!) using the copying-grinder principle was employed. For the new Renesis engine, Mazda designed a CNC five-axis grinding machine that improves machining precision by 60% contributing to the engine’s gas-tightness
For Renesis rotors molten metal is poured centrally versus the previous 13B-REW’s pouring from the corner. Uniform metal distribution and more precise rotor balance are achieved. The cast-iron rotor is one of the 2 heaviest rotating components of the rotary engine. The other is the eccentric shaft, whose motion is nicely balanced compared with the rotor’s planetary motion. The Renesis rotor has shed 5% of it’s mass versus the previous 13-B-REW, and now has a mass of 8.6 pounds. That is still a hefty mass, but the rotor revolves at a third of the eccentric shaft rpm… Molten metal previously was poured into a mold between apices of six rotors, three stacked in 2 pairs. In this casting method, molten metal cooling temperature is not even, causing irregular density in the casting. For the Renesis rotor, molten metal is poured into the center of the mold of the 3 rotors, delivering a more even weight balance and casting density.
Each apex-seal groove corner is induction-hardened. A “pin-point” induction-hardening device was developed by a Mazda heat-treatment expert, winning the government sponsored Award of Excellence in 2002. The new system allows full automation of the process and ensures stable hardening.
For the rotary engine, gas sealing has been by far the most crucial technological challenge in design, development, material and manufacturing….. Mazda relies on it’s former subsidiary, Micro-Techno, now spun off and renamed Koldenschmidt KK, to supply the apex and corner seals.
The rotary engine’s gas seals consist of apex and corner seals in the 3 apices of the rotor, and the side seals and a newly added blow-by cut-off ring seal on each side of the rotor. Previously the side seal was arched and rectangular-sectioned piece w a thickness of .03 in. The new engine’s side port configuration allowed significant enlargement of both intake and exhaust port opening areas. Earlier in the development stage, Mazda engineers experienced frequent breakage and “swallowing” of side seals when they traversed over the ports. A new keystone seal, .05 in thick at the top is adopted to solve this problem.
The keystone seal has a trapezoidal section, thicker at the top and tapering down at 4.5 degrees in its .14 in height. Machining 3 trapezoidal-sectioned grooves on each rotor side was another challenge to the manufacturing team. The cutting tool is subjected to lateral force in addition to vertical because of the tapered groove. A new CNC machining system was developed in-house with improved cutting tool rigidity. The tool cuts .002 in in each of it’s 78 travels (it moves arched sideways in a reciprocating movement) delivering a groove .18 in deep to accommodate the seal.
The whole rotor and eccentric shaft assembly is balanced. The rotors sides must be gas tight; therefore, the previous method of balancing by milling is no longer possible.”