Multitalented Machine Tools
They do everything but make the coffee
By Robert B. Aronson
The path to survival in the face of overseas competition favors those companies that can provide added value to a product. That means more precise, complex products. At the same time small companies are looking for greater product diversity, but without major investment. And this has favored the development of multifunction machine tools.
Here are some of the pluses:
- Fewer, sometimes single, setups.
- Complex parts don't have to be made on several machines.
- Minimized part handling.
- Fewer machines--don't need as much costly floor space.
Machine tool manufacturers have approached this expanding market in two ways. The most obvious is to be able to do more than one process. Machines are now available that offer a combination of milling, drilling, tapping, turning, grinding, welding, and balancing.
The other less obvious way to be more versatile is to make the machine more productive by improving or accelerating part handling, chiefly through the addition of robots or part-handling mechanisms within a single machine or cell.
Another factor promoting interest in multifunction machine tools is the trend of major auto and aerospace manufacturers to minimize their own manufacturing, and instead require suppliers to deliver ready-to-assemble modules. Analysts see large companies faced with warranty issues and aging equipment getting away from high-volume precision work. Some high-volume jobs are now being broken into smaller lots and given to a number of suppliers.
Here are a few examples:
Grinding is now part of the machine tool cell. Makino (Mason, OH) has concentrated on developing grinding technology. Initially they offered plated CBN grinding wheels in conventional machining centers. But, according to Makino's Mark Waymouth, "This technology has been greatly expanded. In addition to grinding with plated CBN, grinding with vitrified grinding wheels is now being done with machining centers. When machining hard nickel-based alloy materials, grinding has now become the primary roughing operation, in addition to the traditional final finishing operation. This has been a dramatic transformation and offers the flexibility of having both machining and grinding capabilities in one machine.
"We take a standard machining center platform and offer unique grinding option packages. In addition to plated CBN wheels we now offer a grinding option package that enables the use of vitrified wheels. Plus, we have added special coolant circuits and wheel dressing capabilities to support the grinding functionality. A second spindle carries a diamond dressing roll to support continuous dress grinding.
"That includes both continuous and intermittent dress systems that are mounted within the machine tool's work zone. The ability to supply continuous dress improves productivity and quality because sharp abrasive is continuously exposed and the wheel has very good form-holding capability. The wheel profile can be changed simply by calling up a different dressing roll and grinding wheel from the tool magazine, analogous to the way in which a machining center performs a tool change.
"The single most important aspect to control is coolant application. If too much is applied, the wheel hydroplanes; too little and you not only reduce the cutting rate, you are likely to burn the part. There is a separate set of nozzles for milling, plus through-the- spindle coolant, where needed.
"We can position a high-pressure nozzle 360º around the grinding wheel. Utilizing this programmable nozzle, high-pressure coolant is injected into a porous wheel ahead of the grind. Centrifugal force pushes the fluid out of the wheel. There is enough fluid to flush the swarf from the wheel and keep the part cool. With this system and continuous dressing we can remove up to 12 in.3 [33 cm3] in hard nickel alloys."
Modular design is critical. Emag (Farmington Hills, MI) is unique in that it is vertically integrated and makes virtually all of its own machine tool components. "We have a number of basic machine platforms that can be modified to meet specific requirements," says Vice President Gary Hulihan. "Most of our machines are custom-built using add-on modules. For example, one of our best-selling machines is the vertical- spindle chucking machine. With it we can do green turning, hard turning, grinding, hobbing, hardening, assembly, and laser welding."
When they get an order, designers first derive a solution for the customer's production situation, then create a machine or line of machines that can do the work. This may be a single-purpose (grinding, milling, etc.) machine. But more often it requires a multifunction design that can include: milling, drilling, turning, grinding, thread rolling, hobbing, tapping, welding, gaging, and part balancing in one machine. "We don't get the easy jobs!" says Hulihan.
Key design features include:
- Short strokes. That is, minimal travel between the part and cutting element.
- Ambient cooling. The machine is kept at ambient temperature, not at some arbitrary value. The best results will be achieved if the part being made and the machine are at the same temperature. An internal system circulates fluid to all heat sources within the machine, including motors and bearings.
- Minimized vibration. The base and columns are made from a high-grade polymer granite called Mineralit. The vibration dampening properties of Mineralit compared to conventional materials results in a better surface finish and longer tool life. In addition, all the power equipment is out of the way above the work area. It's mounted on top of a rigid box-like structure of the machine tool
A band of hydrostatic cells surrounds the spindle, which minimizes spindle deflection under load and damps vibration.
The VSC machine the company offers is said to be the world's first turning machine design in which the workpiece moves while the tools remain stationary. This arrangement is the basis for all multifunctional production centers, as it allows for a number of tooling systems for different machining processes to be integrated into the machining area of the same machine. All this led to the transformation of the "simple" vertical turning machine into the multitasking/multifunctional production center. Emag has delivered more than 5000 of these machines.
The automotive industry and transmission manufacturers also employ combined VSC turning and gear-hobbing centers for the turning of raw parts and the subsequent high-speed gear hobbing and deburring operations.
VSC production centers will also transform soft, raw parts into hardened, ground, completely machined components. For instance, VSC machines automatically soft-turn forged steel pistons, then hard-turn, drill, mill, and finish-grind them with CBN/corundum wheels.
Another unique feature available is a welding unit. It is an increasingly important area of application for laser welding used in the manufacture of transmission systems. Many components, such as transmission gearwheels and clutch bodies, are frequently machined individually, then assembled and welded. In the welding station the assembled parts are clamped and the weld joint(s) created. The teeth on both workpieces are also well-protected against weld spatter. The welding station features two spindles. One spindle accommodates the assembly during the welding process, and the second spindle is used to unload the previously welded component and to load the constituent parts for the next assembly. The assembled component is deposited on an exit conveyor and unloaded either manually or automatically.
An expanding market. "We currently offer a Turnmill, Model 1250," explains Gary Mead, Monarch Machine Tool (Cortland, NY). "It combines a VTL-type platform on a gantry frame so it offers machining center functions with up to five axes. The gantry handles the X-Y-Z axes and there is a 59", 80-hp [150-cm, 60-kW] turning/positioning table. There are interchangeable heads to handle turning or 50-taper tools for machining, and a single-axis tilt head to provide the fifth axis. Typical products are large valves and aircraft engine components.
"The multifunction market looks good. We are counting on its continued expansion and are working on both a redesign of existing machines as well as some fresh designs in which our vertical machines can convert the spindle configuration to function as horizontals."
Changing demand. "Our company was initially geared to making machines for very high-volume work, over 100,000 parts," says Paul Vess, manager, Fuji Machine America Corp. (Vernon Hills, IL).
"At those production rates you don't mill or drill with a lathe. Now the demand for lower volume and more complex jobs is prominent. There is a big push by the larger manufacturers to get out of fine machining. They want to assemble modules. This is forcing their suppliers to replace old equipment and reduce scrap rates. To keep expenses down, these companies need simple machines that can perform several operations.
"We had to fill the new needs of the customers. They wanted a machine that could be quickly changed over. They would, for example, run one or two days on one job, change to another part for a half-day run, and so on. To meet this need we offer an introductory mill-turn series, the TN line, designed specifically for the small to midsize shops that are just jumping into multifunction automated manufacturing. It's a conservative design available in one or two-axis versions. With it they can mill, drill, or tap."
Fuji is continuing to adjust to market demands and will be bringing new designs into North America from Japan.
Five-axis popularity. Along with the greater use of mill/turn centers, the popularity of five-axis machining is also increasing to meet the needs of the multifunction market. Mikron Bostomatic (Holliston, MA) offers a range of three-to-five axis machines for this market with spindle speeds up to 60,000 rpm and accelerations over 1g. One of the newest products is the UCP 600 Vario which has a 21.5-hp (16-kW), 20,000-rpm spindle and rotary/tilt table for five-axis, five-sided machining. To ensure accuracy, there are modules for vibration monitoring and intelligent thermal control.
More steel-collar workers. "We provide robots for both stand-alone installations outside the machine tool and within the machine tool enclosure," says Jack Justice, manager, Motoman (West Carrolton, OH). "For these installations, the robots have special seals so that the lubricants and coolants can't get into the robot's critical mechanisms."
In addition to traditional loading and unloading, these robots will take parts to gaging stations, deburring operations, or to a vision system for inspection.
"The biggest advances in robotics have been in the controls that allow more simplified programming and operation," explains Justice. "One example is a visual the operator can call up to be sure the part the robot has is the one to be worked on."
Manufacturing versatility is improved when one robot serves many single-function machines. "The less time human hands are on the part, the better," explains Jack Sebzda Jr., manager, System 3R USA Inc. (Totowa, NJ). "Robots are playing a wider role in increasing the versatility of machine tools."
The main unit provided by the company is the WorkMaster. It's a pick-and-place-type robot that serves up to three machines. In most operations, it moves a part pallet from machine to machine so no additional setup is needed. The company specializes in untended installations.
The main difference in the installation is the software. In about 75% of jobs, the robot is slaved to a machine tool. That is, the machine program signals the robot when to move. In more complex applications, the robot's program controls the machine tools. Using a program called WorkShopManager, the robot's program is the cell controller. Identification chips on each pallet and tool magazine are scanned to trigger the work cycle. For example, the robot program tells the machines what part they are working on and checks offsets.
Despite efforts to standardize, notes Sebzda, "Each installation is an adventure. There are slight differences in every application."
Robots have contributed to versatility. "Not only are they being applied to simple load/unload situations, they have taken on a host of post-machining operations, such as gaging and part verification," according to Kap Choi, program manager, machine tool automation, Fanuc Robotics (Rochester Hills, MI).
Intelligent robots add a new dimension to their ability to assist machining operations. We can add force sensing and vision. Our robots can handle variations in part size. They are not limited to gripping a part a certain way, but can work with odd-size parts or handle a family of parts. Instead of gripping a part with a fixed force, the force sensor can modify the grip for each situation."
Robots can also eliminate or reduce the amount of manual labor needed because they can precisely position a part or be programmed to do minor machine tool adjustments such as change chuck size.
"A key is to link the robot's program to the machine tool or cell," says Choi. "This can be challenging in aftermarket situations. Either the system integrator or the turnkey specialist from Fanuc Robotics must be able to link to an existing CNC system. For older units, where the necessary channels are not available, this may require a significant program upgrade."
Multifunction Is Not Just Machining
By Walter Schnecker, PhD
Datron Dynamics Inc.
Many multipurpose CNC machines meet the challenges of machining, but fall flat in addressing the other two thirds of the equation: setup and secondary operations.
Setup is frequently cited by manufacturers as a primary source of inefficiency and frustration. Users often have to call upon their own ingenuity and resources to develop fixturing and workholding solutions. This usually results in limited success with the problems created by the "solution." For example, when spray glue is used to hold the workpiece, a secondary operation is required to clean the machine when the job is completed.
The final phase of machining is a sore spot for many manufacturers. Most parts that come off a machining center must be deburred, degreased, or both. Sometimes another operation is even added in order to improve the surface quality of a given part. In the end, the labor and equipment required for these tasks impact the manufacturer's time-to-market and profitability.
At Datron Dynamics we're tasked with delivering a homogenous solution for the entire process--from setup and machining to secondary operations.
With regard to workholding, our company's focus has been on "modular" designs that leverage the large work area of our machines by allowing for multiple setups, or workstations. One station may accommodate a manual pallet changer, another could have a vacuum table, and a third could have a pneumatic clamping system. Together they inherently provide flexibility, but a single station also provides the manufacturer with agility to adapt to job changes. Our small pallets actually register with a boss-in-cavity system to the machine bed to provide location repeatability. So if a user is in the middle of a batch and an unexpected rush project comes in, one pallet is easily removed and replaced with the new job. When the rush job is complete, the first pallet is returned to its place and the operator can pick up from where he left off. The integrated vacuum tables, on the other hand, were developed in response to the "spray glue" fixturing method mentioned earlier. Plastic foils as thin as 0.001" (0.03 mm) or large aluminum sheets up to 0.250" (6.4 mm) can be swiftly secured to the bed of a machining system. A low cost gas-permeable substrate serves as a sacrificial vacuum diffuser, allowing the cutter to machine through the workpiece without cutting into the table.
Careful setup can still be thwarted by variance in individual blanks. To simplify workpiece setup, "smart features" like 3D probes have been developed to locate parts in the X, Y, and Z coordinates. This includes finding centers of holes and bosses, as well as pre-measuring blanks before the machining process starts. Intuitive machining programs adjust themselves to the particular workpiece on the machining bed in order to maintain consistency regardless of workpiece irregularity.
As for the machining phase, many CNC manufacturers have answered the call by developing multipurpose machines that perform several functions or operations. Datron machines can mill, drill cut, rout and engrave. But, if you frequently use tooling larger than 0.250" (6.4 mm) we're just not a good fit for you. CNC providers that focus on large tools really shouldn't tout the ability to run microtooling because it cannot be done efficiently without breaking tools with their heavy, high-force, low-RPM spindles.
Time-consuming secondary operations face most CNC designers. There are degreasing agents and numerous methods for deburring on the market. But these operations require additional expenditures for materials and equipment. Datron is geared toward high-speed machining with microtooling, which inherently produces better surface finishes and reduces burring. A 60,000-rpm spindle speed reduces the chip load to less than 0.005" (0.127 mm). Such a low chip load significantly reduces the forces between the tool and the material. High-speed/low-force machining develops less heat, reduces tool deflection, and allows machining of thinner-walled workpieces. This results in better surface quality, cooler machining, easier workholding, and better accuracy.
Microtooling needs a lubricating agent with a lower viscosity than water because the coolant needs to make it to the cutting edge of the tool at the high spindle speeds involved. Emulsion-based (oil) coolants have a higher viscosity than water, and thus are less effective as a lubricant for high-speed machining with micro-tooling. Ethanol doesn't need to be disposed of or recycled, because it simply evaporates. The low evaporation point of ethanol makes it a very efficient cooling and lubricating agent for high-speed machining operations. Since it's a natural chemical, there's no negative environmental impact, no waste, no cleanup, and therefore no cost. In addition, ethanol as a coolant does not leave any residue on the machined parts, thus eliminating the costly secondary operation of degreasing the parts.
This article was first published in the January 2005 edition of Manufacturing Engineering magazine.