Metalcutting Automation: Some Considerations

For the past several years there has been something of an on-going competition occurring in the metalcutting automation arena as high-volume systems are giving way, in some cases, to more flexible systems, and then the high-volume lines regain ground (or, more specifically, plant floor space). Because Lamb Technicon Machining Systems (Warren, MI), a UNOVA company, provides both types of systems, we decided to ask its Mark Tomlinson, vice president of Technology Integration, to provide some suggestions as to what people ought to take into account when assessing the right automation for their application.

Process Commonality

The first thing that Tomlinson recommends be kept in mind when Although this is a high-volume line for producing V8 cylinder heads—built for DaimlerChrysler's New Mack Engine Plant—its architecture is clearly more modular than high-volume transfer lines of the past. (Photo: Lamb Technicon). considering flexible and high-volume systems is that when it

comes to a given part, the processes will essentially be the same for both
types of systems. That is, if a hole needs to be drilled, then that's the case regardless of the volume of parts to be produced. In conjunction with this is the fact that there is likely to be commonality with regard to the tooling—though, as we shall see, there are some differences.

Hold It
Here's a flexible system for machining auto cylinder blocks. It consists of a series of CNC machiing modules and head changer machines. Note the blocks are not palletized. The robots are rail-mounted and used for load/unload operations. (Photo: Lamb Technicon).
Moving to the fixturing and transporting of the workpiece, we arrive at a point where there are clear system differences. For example, in a high-volume setup, where, generally, a single operation is performed at each station, the forces involved are often considerably different than those in a flexible system, where a multitude of cutting operations will be performed at a station (or, more accurately, within a CNC machine). Consider face milling. In a high-volume system, it is probably going to be done in one pass. In a flexible system, there are probably going to be multiple passes. Consequently, there is a difference in the clamping pressures for each type of system, which means there are fixturing differences. And because a flexible system is one in which there are multiple operations performed on a part in a setup, there are accessibility issues that have to be taken into account (e.g., there may be milling on one face and drilling on another, so there must be an open area where the drill can reach its intended target).

Move It

With regard to part transfer, Tomlinson points out that in the case of high-volume systems, there is a new architecture emerging: "The historic drive at the end of the machine is giving way to modular drives and transfer bars." This is providing the means by which there can be new functions added to an existing line by dropping in machine modules. (This modular approach also facilitates building and testing the line in the first place: since the individual pieces have their full mechanical functionality, there is the ability to assure that everything is as it should be far earlier than if it is necessary to wait for the entire line to be built and the drive at the end of the line engaged.)

In flexible systems, Tomlinson says that the trend is away from automatic guided vehicles (AGVs) and pallets fitted with fixtures. Tomlinson explains that the reason is the need to minimize the "streams of variation" that such devices can contribute to. That is, in the case of pallets, there are benefits realized from clamping once (e.g., in terms of consistent part location and management of cutting forces), but there can be difficulties related to maintaining and monitoring the traceability and repeatability of each palletized fixture, of which there are many in a flexible system running at production volumes. "Managing pallets is more difficult than managing parts on skids," Tomlinson notes. So a trend in flexible systems is to maintain the fixturing in the CNC machine tool and loading, unloading, and transferring parts in the free state.

Optimized Vs. Versatile

Another difference between the flexible and high-volume systems related to the physical characteristics of the tooling and fixturing is that in a high-volume system, a particular station is engineered to do one thing while the flexible system is fundamentally engineered to provide the opportunity to do plenty of things. So, for a high-volume system, the fixture, spindle and tooling are optimized at each station for a particular part. But consider just the spindle in a flexible system: it isn't sized for one specific part or operation; it must be capable of handling a variety. Consequently, there are likely to be tradeoffs, which can lead to processing and/or tooling issues.

Think about, Tomlinson suggests, valve seat and guide machining. In a high-volume system, there is a fixed tool that has the valve seat angles in place and a drawbar is used to put out a reamer to machine the guide. With a single-spindle machine this task can be exceedingly more complicated from the tooling point of view (e.g., a tool that has the seat configuration designed in and a reamer that pops out as a result of centrifugal force). The high-volume approach is simpler.

Controlled

In the area of controls for the equipment, there are big differences. Here the advantage is, in Tomlinson's estimation, with the flexible system because there are "standard" CNC controls. The consideration is wholly on the part programming logic. For the high-volume systems, on the other hand, the control architecture isn't as standardized—improved, yes, but standardized, no. Consequently, there is a need to work on both the machine logic and the part processing.

People Needs

There are workforce considerations, too, from the standpoints of required skills and number of people required to staff the systems. In the case of a high-volume system, the required personnel are generally limited to a loader, unloader and maintenance crew (that is either assigned to the line or central to plant operations). A flexible system needs more people. For one thing, the part transport is unlikely to be fully automated, so a number of part handling people may be needed to man the line (robotic handling is certainly a viable option). There must be a maintenance crew (who can be deployed as in the case of a high-volume system). But a big difference that Tomlinson points to is the need to have decision makers who will be able to decide what to do in the event that a cell within the system goes down. A high-volume system is either running or it is down. A flexible system based on work cells can continue to run, but the part flow must be determined. So there is a need for planners, schedulers and supervisors.

Downtime Data

Tomlinson explains that the flexible system introduces some uncertainty—at this point in time, anyway—when it comes to a part flow strategy. There is an abundance of data existing that describes the downtime for high-volume systems; after all, they've been used for decades. This data can be used to determine the number of parts that should be kept in a bank to handle the average downtime. But in flexible systems, this data isn't nearly as deep. What's more, there are many more problems that can arise.

For example, on flexible systems, one of the approaches to minimize downtime related to toolchange time is to have redundant tools in the toolchange mechanism, in addition to the variety of types of tools that are in place to perform the multiple operations. All of which means plenty of toolchanges per hour. But how many times can a toolchanger change before it fails? (And take into account the fact that in a given cell there are multiple machines, each of which has a toolchanger, each of which is changing tools on an on-going basis, so if one toolchanger goes, how long before the others follow?) There is a move toward using more high-speed machining spindles in flexible sys-tems. There are some concerns with the reliability of these spindles in production applications; downtime may be greater. And although CNC controls may be standard, there is still some question about control reliability. With time, these reliability issues will be worked out, just as they have been for the elements of high-volume machines; the high-volume machines simply have the advantage of having been around a lot longer.

Economic Advantage?

This time factor has also resulted in the development of a depreciation philosophy that tends to favor the high-volume approach. Tomlinson posits a situation where there need to be one million parts produced. A high-volume machine can handle it. A flexible system can be engineered to do it—but it may cost three times what the high-volume system does. When it comes to a five-year depreciation, the high-volume system provides what he describes as an "attractive return on capital." But the flexible system won't make the cut—under that metric.

Tomlinson points out that the flexible system can be readily retooled so that it may be able to do three or more programs. He cites a flexible DaimlerChrysler manifold system that has been retooled some six times since Lamb installed it in the mid-1980s. So when it comes to lifecycle costs, the flexible system can clearly be more economic. But unless more than just the sticker price is taken into account, flexible systems may be economically unviable.

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Micro Machining Center operates with zero metal contact

Model Zµ3500 uses temperature-controlled hydrostatic oil in hybrid spindle bearing, static pressure guides, and linear motor cooling system, virtually eliminating thermal distortion saturation time. At 25 hp, spindle reaches speeds of 30,000 rpm. Travels are 13.78 in X-axis and 11.8 in Y- and Z-axes. Positioning is accomplished with cooled scaled linear motors at 0.6 G in acceleration. Near absence of friction and vibration increases precision and reduces noise levels.
NOVI, MI - (May 1, 2006) A breakthrough in micro machining technology, NTC’s revolutionary Zµ3500 operates with zero metal contact, and achieves superior rigidity, accuracy and repeatability.
Traditional machining centers include calculated NC offset functions within the control to compensate for inherent inaccuracies due to backlash and other mechanical tolerance issues. However, functioning without linear guide ways, roller bearings or ball screws, the Zµ3500 overcomes the inertia of conventional technology, as well as the compromised tolerances required for that technology to function.
What’s more, when compared to other machines, where metal-to-metal contactproduces heat from friction, and creates thermal distortion, the Zµ3500’s zero metal contact design eliminates major sources of friction and related thermal distortion. The Zµ3500’s use of temperature-controlled hydrostatic oil in the hybrid spindle bearing, static pressure guides and the linear motor cooling system virtually eliminates thermal distortion saturation time. And, because traditional warm-up time is not required, productivity is enhanced substantially. The near-absence of friction (and therefore vibration) not only increases precision, but also extends tool life and reduces noise levels.
The Zµ3500’s spindle is the world’s first fluid hydro hybrid, incorporating hydrostatic and hydrodynamic technologies that virtually eliminate wear and run-out. At 25 HP, it reaches speeds of 30,000 RPM. The spindle utilizes HSK E32 tool holders. The 12-tool ATC is fully enclosed. Travels are 13.78″ in the X-axis and 11.8″ in the Y- and Z-axes. Positioning is accomplished with cooled scaled linear motors at 0.6G in acceleration.
The Zµ3500 is based on NTC’s extensive experience in building machining centers, grinders, and optics and semiconductor machines.


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Metal Forming, Fabricating, Lasers, and Gear Generation

Flexibility and innovation drive these fields

Gleason Corp. (Rochester, NY) will be offering several new machines with the goal of more sales in the jobbers market.

Their Genesis vertical hobbing machine optimizes dry machining and reduces floor-space requirements. It's intended for spur and helical gear manufacture.

Gleason will also be offering more equipment for gear metrology applications, through their M&M Precision Systems Corp., a manufacturer of gear inspection and process control systems. One of the newer units in their Sigma series is specifically for small-part measurement.

Lincoln Electric (Cleveland) will emphasize welding of aluminum because of its cosmetic appearance, and the fact that it can be welded quickly. "This is a growth area, and there is a lot of opportunity, particularly from the transplant companies," says Geoff Lipnezicius, application manager.

The company is focusing on custom systems and firsttime users of automatic systems. Also, because of new OSHA pollution regulations, there is a growing interest in fume-recovery systems.

"We are offering a new process, a rapid-arc, single-wire application that can provide welding speeds of 90-100 ipm [2.3-2.5 m/min] in aluminum using the MIG process," says Lipnezicius.

Although vision systems for welding are still used, they have been replaced in many applications with smart sensors on robots that can guide the welding operation.

"Increasingly, people are asking for reach analysis. This allows you to just drop-in new systems.

"Another featured product is the E-cell. A compact robotic system that is plug and play, is suited for job shops, and takes up only 60 x 90'' [1524 x 2286 mm] of floor space. It's a good design for the smaller shop or those just getting introduced to welding."

A broad range of equipment will be shown by ESAB (Florence, SC), with a focus on a new hybrid laser welding system that has been in the works for some time. It consists of a 10,000-W, fiber-laser system mounted on a gantry with a CNC control on a MIG welding system. "This unit is 5-10 times faster than conventional welding," says Jeff Hoffart, general manager and senior vp. "It automatically compensates for difficult fit-up. A laser and MIG unit work together. The laser preheats the work area and the welder fills. It's going to change the way manufacturers view welding. It uses 10% of the welding material commonly used and heat input is much less, so the smaller HEZ allows you to do things that couldn't be done before. This includes use of conventional steel in a wider number of applications, and also easier welding of dissimilar materials."

The sensor system evaluates the joint and makes dynamic changes, including wire feed, arc voltage, wattage, and travel speed. Sensors look at both the front and back of the weld, and send corrective signal to the system control.

Jet Edge (Saint Michael, MN) will feature an abrasive waterjet cutting system with upgraded intensifier pumps and controller.

"We are finding new markets as the industry matures and the pool of customers grows," says Tom Macgibbon, VP. "This process can be applied to any industry, from food to hard metals.

"We will show a new cutting head with a nozzle designed for longer life and greater cut accuracy. In addition, programs and software are improving rapidly as we move toward a plug-and-play capability.

"As abrasive waterjet becomes a more widely accepted process, we have to put greater emphasis on service and maintenance."

A 200-hp (150-kW) hydraulic pump will be featured by KMT. It has more capacity than previous pumps and is capable of delivering water at 60,000 psi (42 MPa) to up to 32 cutting heads.

As to trends:

* More turnkey contracts as waterjet becomes better known for its versatility.

* More installations in which a number of cutting heads are run from one pump.

* Greater ease of use. Many of the calculations and setup requirements of earlier machines have been eliminated.

* Key industries are medical and stone work.

The company is working on a new head design that will minimize the erosion caused by the abrasive.

"We've seen an increasing level of interest in cutting with shop air to reduce the cost per part," said Burke Doar, vice president Trumpf Inc. (Plymouth Township, MI). "New technology makes compressed air a viable and cost-effective alternative to oxygen and nitrogen as laser assist gasses. This Trumpf process is well suited to a variety of applications for sheet metal fabricators."

At the IMTS show, Trumpf will focus on "air cutting" on the TCL 2510. In this air-cutting technique compressed air is used as a laser assist gas to cut steel, stainless steel, galvanized steel, and aluminum. Air cutting is faster and more cost-effective than cutting with oxygen and nitrogen, and offers an edge finish with much less oxidation than an oxygen-cut edge.

Cutting with compressed air works differently than cutting with oxygen or nitrogen as assist gasses. Cutting with air generates a plasma. Laser energy brought to a tight focal position and the introduction of compressed air creates a plasma ball at the surface of the material. An advantage of cutting with this plasma is that the heat is transferred more effectively than by the laser beam itself. In fact, the cutting speed is often increased to avoid over-melting the material edge.

In addition, the high-speed laser-cutting TCL 2510 machine is designed to run untended. It has integrated, compact, load and unload capabilities for automated production. All of the components were designed to offer users a cost-effective option for automated laser production. The flying-optic design achieves high processing speeds and consistent accuracy independent of material weight. Optimal cut consistency is assured by integral mounting of the laser resonator to the machine frame. The integrated material-handling system reduces manual labor requirements and frees up the operator to concentrate on other tasks or operate another machine.

Mitsubishi will present its equipment in industry-specific areas: aerospace, medical, tooling, and EDM. The booth will define more clearly which machines have the features needed for a specific project. And this year the company will introduce their waterjet system. Prompted by a growing number of medical applications, the company will show how waterjet married to EDM can reduce production time.

"The two processes often compliment each other, with the waterjet used to remove large quantities of material and EDM doing the finishing work," explains Patrick Simon, manager, Mitsubishi EDM, MC Machinery Systems (Wood Dale, IL).

As to company trends,according to Michael Zakrzewski, executive vice president and general manager, cutting and bending will be featured at the Bystronic, (Hauppauge (NY) booth.

"Our goal is to focus on the highend precision metal markets. Overall, the waterjet is still in a strong growth position. Off-line software programming is getting easier. It's now simple to integrate one of our bending machines with the waterjet, and blend the operation with a CAD/CAM package. Our design keeps a balance between ease of use, and performance flexibility. The company also plans to introduce some larger machines in the US.

The biggest change is in the software, which gives better control over the cutting variables, such as abrasive flow and water pressure. "This gives the benefits of improved edge cut quality, tighter motion control, and improved cutting speed," explains Zakrzewski.

The Bystronic waterjet systems can be linked with a shuttle table to give speedy material handling, so the user can handle material while a plate is being cut.

One trend that Fanuc Robotics (Rochester Hills, MI) will feature at IMTS is the use of intelligent robots, particularly for welding. Intelligent robots are able to perform advanced applications previously considered too complex for robots. They can also make existing applications more cost-effective. For example, intelligent robots with vision eliminate the need for expensive part fixtures.

Fanuc Robotics' exhibit at IMTS will include a wide range of robotic vision applications. In some cases, 3-D vision will allow the robot to find loosely located parts that can be offset in three dimensions. In other cases, the robot will use 2-D vision if the parts only vary in 2-D space (X, Y, and roll). The new Fanuc R-J3iC robot controller will demonstrate the ability to perform vision tasks without the need for an external PC or any additional hardware. All Fanuc robots come standard with vision, and only require a software option and a camera.

Delicate six-degrees-of-freedom force sensing will be used to perform assembly applications that previously required tactile feedback. One example is a robot that will assemble the gearbox of another robot.

Another trend is the use of a single controller to drive multiple robots. In one case, four arc welders will operate from a single controller. In another case, two material-handling toploader robots will use a single controller, demonstrating very precise coordinated motion. In a third demonstration, one material-handling robot will present the workpiece to another assembly robot.

The products that follow this article will be shown in the Metal Forming, Fabricating, and IMSCT pavilion at IMTS. -Roben Arunson


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