New machine combines accuracy, flexibility for deep hole boring.
According to Dr. Philip Szuba, director of research and new product development at Lamb Technicon, the BOA system, Boring with Optimal Accuracy, permits the user to machine distinct parts with varying bore sizes and bore locations without the need for changeover or retooling.
"We're seeing that a lot of our customers are tending toward developing flexible solutions to their deep boring problems," Dr Szuba says. "Often they'll buy a CNC machine, or a series of CNC machining units and link them together with some type of transfer automation to develop what we refer to as a flexible manufacturing system, or FMS.
"The problems associated with this approach," Dr Szuba continues, "show up when they begin to machine certain features on the parts, especially long bores, or small holes that require gun drilling or line boring. In this type of operation, the typical CNC machine is not capable of holding the proper tool. Neither is it capable of generating the tolerances required by many of these applications.
"But even after they spend a lot of time and money developing these flexible systems," Dr Szuba points out, "eventually many of them still end up buying a dedicated station to do gun drilling or cam boring. The problem with that is the solution really isn't flexible."
What engineers at Lamb Technicon set out to design into the BOA system was a solution to the need for a flexible machine to provide accurate line boring operations. "We knew our customers wanted to be able to change both hole diameter and location," Dr Szuba says. "Those are two features of the BOA machine that make it unique, when it's compared to all other line boring stations. It's a flexible machine, capable of moving the bore to anywhere within a 350mm window. And it's capable of changing the size of that bore to any dimension between 1" and 3" dia. What we developed is a flexible line boring or deep hole boring machine that is capable of very high tolerance, with the flexibility required to meet the needs of what we consider to be our served market-primarily the automotive industry."
As evidenced by broad interest shown in the prototype unit at IMTS, this type of machine also has the potential to serve similar needs in various other manufacturing sectors, such as aerospace components, compressor housings, pumps, and some military applications, as well as certain needs in agricultural and farmtype equipment.
Sizing the machine
"The machine that visitors to IMTS saw in our booth was an experimental prototype machine developed to prove the theory behind changing boring bars and holding tolerance," Dr Szuba says. "We looked at the typical V6, VS. and in-line 6 cylinder engines currently being used by the automotive industry to develop specifications for the prototype BOA.
"If we were to put the fully retracted boring bar in the exact center of the work zone, we would be able to move it from that center point, a distance of 175mm toward the front or back (X-axis), 175mm toward the top to bottom (Y-axis) and 1250mm (40") toward or into the workpiece along the Z-axis (perpendicular to the X-Y plane). So basically, we have a 350mm square window, and we can move the tool a distance of 1250mm 'out' from that window. This gives us a work zone equal to a rectangular box 350mm high by 350mm wide by 1250mm deep."
If the customer has a very big engine that requires a longer stroke, the Z-axis on the machine can be increased. "We didn't realize how excited the diesel people were going to be over this machine," Dr. Szuba says. "They were the ones who really showed a lot of interest at the show. In some bigger applications, we would have to increase both the stroke and the size of the tool. We're talking about some bores up to 6" or 8" in diameter.
"In terms of a production model, we're now looking for a couple of beta-site customers," Szuba reports. "What we want to do is refine the engineering based upon their applications, and provide them with a machine under some kind of business agreement that will enable us to obtain operating data and feedback on what they thought of the machine. Our product development cycle is: experimental prototype, beta field test, and then production build. This means we would not sell a production version of this machine on the open market until later next year."
"With a typical boring machine, as the tool is fed into the part, it has a tendency to droop due to gravity," explains Dr Szuba. "What we have on the BOA machine is an ability to tilt the boring bar and the spindle by means of two y-axis ball screws, so we're actually changing the angular orientation of the boring bar as we feed it into the part. That's something that we think is novel in our industry."
Dr Szuba explains that droop compensation can be calculated and programmed into the control, or it can be measured and corrected in real time. "We can put a part program or a subroutine into the part program based upon, say, CMM data that we obtain from finished parts. For example, let's say we cut five parts and we see that we have some droop. We can 'comp it out' via programs, or we can have sensors on the spindle that will keep it level--or intentionally put it out of level--it can be done either way."
Accuracy also is enhanced by using a series of guide pads--carbide pads that support the spindle by resting upon the previously machined journal. "What amounts to a hydrodynamic layer of cutting fluid builds up between the carbide pad and the machined journal surface," Dr Szuba explains. "We're putting high pressure coolant through the end of the tool as well as through the guide pads so there is a lot of lubrication inside of the bore.
"Without intermediate supports," Dr Szuba points out, "the tool would lose precision as it went further into the part. This might be acceptable in some other industries, but doesn't provide the accuracy that usually is required for cam and crank bores. At IMTS we showed how this machine is capable of boring up to a 30" depth using a 1" dia tool and maintain accuracies of [+ or -]5 microns. The 30-to-1 ratio at [+ or -]5 micron accuracy is characteristic of this type of machine. And, while the maximum stoke on the prototype machine at IMTS was 1250mm, on custom applications, the range can be very, very long--up to several meters, if needed.
The boring tool can be changed between parts by the programmable tool changer that sits underneath the Z-axis. "We can do that easily while parts are being swapped out," Dr Szuba says. "We didn't exactly show how to change parts at the show, but that can be done in one of two ways. Either we could add the machine to a transfer line and have the transfer bar bring a part in every so often, or we could change parts with a pallet swapper. Typically this would be a rotary swapper. While one part is being machined, the operator is loading a fresh part onto the turntable. When the machine is ready for a new part, it just rotates 180 deg and it is ready to go. Either method would work."
Cycle time for a part probably would be less than a minute, according to Dr Szuba. Typically a borer will do two parts in one sequence and cycle time generally is less than one minute for a V-8 engine part. "This may not be quick by transfer line standards, Dr Szuba says, "but it is quick by job shop type requirements."
The machine architecture, as well as the droop compensation feature is covered by US patent applications. The BOA is engineered in Warren, MI, and will be built in one of the firm's three Greater Detroit-area manufacturing facilities.
|Printer friendly Cite/link Email Feedback|
|Comment:||New machine combines accuracy, flexibility for deep hole boring.|
|Author:||Dobbins, Donald B|
|Publication:||Tooling & Production|
|Article Type:||Brief Article|
|Date:||Nov 1, 2000|
|Previous Article:||More than 114,000 view the wonders of IMTS.|
|Next Article:||EDM comes of age.|