Richard P. Vaughn has been working with microfinishing equipment since the early 1960s. It's the type of equipment used to improve bearing surfaces of various components, including crankshafts, camshafts, alternator shafts.Vaughn says, "What's out there is essentially 1950's technology." And he's referring to what's out there right now. To be sure, this may be equipment that is absolutely brand new, but Vaughn explains that the fundamental approach to the process that's performed by the microfinishing machines isn't all that different from what was being sold some 40 years ago. These are machines that use shoes of some sort that wrap around the surface to be processed. The abrasive takes the form of a tape (nowadays it is a plastic). The tape is fitted between the shoes and the workpiece. During the operation of this equipment, the tape is spooled out from one part to the next, thereby providing fresh abrasive. The used abrasive moves to a receptacle near the machine base. The work area is flooded with coolant to help wash the swarf away.
According to Vaughn, when he's talked with people who use this equipment in crankshaft and other microfinishing operations he learned that they (1) find the changing of the rolls of tape to be time consuming and (2) can't easily dispose of the used tape because it has been drenched with coolant.
As is legendary in the computer industry and little heard about elsewhere anymore, Vaughn literally built a prototype microfinishing machine in his garage, a machine that would not be based on the approach to microfinishing technology that was developed when many people who use the equipment weren't even born. Then he hooked up with H.R. Krueger Machine Tool Inc. (Farmington, MI), a builder that produces systems for many automotive power-train installations, so something for engine and transmission parts is right in its area of interest.
Vaughn is now product development manager at H.R. Krueger, and the machine that was initially built in his garage is now a machine tool for bearing sizing and finishing tradenamed the Micro-Fast.
|A new approach to microfinishing from H.R. Krueger.|
One of the more notable features of the Micro-Fast is what it doesn't have: No hard tooling. No ribbon of plastic tape.
Instead, there is simply a long-lived cloth belt with diamond or CBN abrasives on its surface. (Note: multiple heads can be fitted to a machine base; for the sake of simplicity, we'll just be referring to one station.) The belt contacts the part at 36o. The operation—on crankshafts, camshafts, balance shafts, output shafts, input shafts, speed cone gears, alternator shafts, etc.—is performed dry. The workpiece, which is held in a simple headstock-tailstock arrangement, can be oscillated if necessary so that an oil retaining surface can be imparted. In addition to improving the surface geometry, the machine can provide size control, in some cases, providing the ability to go, say, from turning to microfinishing, without an intermediate grinding step.
Let's break this down:
- The abrasive belt. This belt is what does the work. Since there is no hard tooling, the defining factor of the size of the workpiece that can be handled is the capacity between centers and the width of the belt. According to Vaughn, the belt can be changed in a minute or less—a fraction of the time that it takes to change a spool of tape. The tape, which is being developed with 3M, has regularly spaced islands of abrasive. Vaughn says that the tape doesn't readily load with removed material. There is a blow-off unit combined with a vacuum device to pull away the particles that are removed from the workpiece.
- The 36o contact. This is in contrast to the hard tooled setup where there could be a 270o wrap of the workpiece. The benefit of the new design is because there is less contact, there is less heat generated, and as this is a microfinishing operation, heat growth (and subsequent part shrinkage) is something that is best avoided. It is worth noting that the belt generally runs at about 3,000 sfpm and is usually held against the workpiece with just 9 lb. of pressure (once again, the concern with heat and possible part distortion).
- Dry. This eliminates any environmental issues with coolant. In addition to which, there are no hydraulics on the machine.
- Simple headstock-tailstock arrangement. No chucks are necessary. This helps simplify the load-unload operations.
Overall, the Micro-Fast is a simple piece of equipment. Vaughn notes, "There's little that can possibly go wrong with it." And in a period when it is increasingly important to minimize all non-value operations, this designed-in simplicity, which can lead to reliability, is absolutely key.