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AME says its dovetail vise clamping component is useful for a variety of applications and industries, especially aerospace aluminum milling applications. Precision bushing holes are designed for quick and easy location of the vise, the company says. Other features include ½”-13 SHCS and precision dowel screws, which secure the vise on a 2″ grid system; a 15-degree dovetail angle that holds pre-machined parts securely during machining operations; and a maximum part width of 4″ or 5″. The vise is available in 5″, 8″, 12″, 16″ or 24″ lengths with as many as 12 jaws, depending on the length. Metric locating and mounting hole versions are available on request.

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Abanaki’s compact, disk-type oil skimmer is designed for removing unwanted tramp oils from coolants and parts washers. The skimmer features a 1/2″ × 12″ plastic disk and a 110-V, fan-cooled gear motor. A boomerang-shaped wiper blade extends over the edge of the receiving trough to provide an extra inch of wiping area and increase the capacity of the skimmer. Also, the “no drip” wiper holder system is designed to prevent oil from dripping.

The disk skimmer is constructed entirely of plastic, including the motor housing and frame. The durable, polymer-engineered housing prevents corrosion. Other features include capped troughs that prevent oil drips and a sealed shaft to prevent premature motor wear from oil contamination. The disk skimmers are designed for mounting on drums and in places where the water level does not fluctuate and where small oil-removal capacity is required.

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Skiving is one of the oldest and most efficient methods for producing certain types of parts on screw machines. This operation is suitable for parts that are long and slender, parts with close diameter tolerances and finishes, and parts requiring truly spherical radii. Interestingly, because of a lack of knowledge and familiarity with the principles of successful skiving, most layout and setup personnel and operators seem to go to any lengths to avoid the process. With a proper understanding of the corresponding applications, tool design, manufacture and the availability of toolholders with the necessary features for simple, dependable operation, skiving becomes a simple operation. Any screw machine shop should be able to run skiving jobs routinely with few, if any, problems.
What Is Skiving?

Conventional form tools are mounted so that the formed cutting edge of the tool is on the centerline of the part, cutting radially. Cutting action is determined by the combination of radial clearance angle and top rake angle. Diameters are controlled by advancing the forming tool toward the center of the part. But difficulty can be encountered in forming long parts because the entire form contacts the workpiece at one time. The smallest diameter is formed to its finished size at the same time that all the other diameters are being formed, increasing the likelihood of premature part break-off.

Skive tools are mounted so that the formed cutting edge of the tool is advanced into the workpiece below center, cutting tangentially. Cutting action is determined by the combination of shear angle and lead angle. Part diameters are controlled by raising the tool towards the center, and the form is ground along the full length. The cutting edge is obtained by grinding the shear angle on the end of the tool and the lead angle across the width of the form.

Since only the part of the tool that is in contact with the workpiece at any given time is actually cutting, the part is not weakened until the portion of the tool that forms the smallest diameter of the part actually passes below the centerline. Furthermore, as any portion of the tool passes under the centerline, that diameter is completely formed to size and the tool exerts no further cutting pressure on that area of the part. All cutting action takes place in the area between where the tool contacts the part and where it passes under center.

The shear angle affects the cutting action, but unlike the top rake on form tools, it does not affect the part diameter relationship. This angle can be varied until the best possible cutting action is obtained. Too blunt of an angle will tend to cut hard and deflect the part, causing dimensional errors and poor finishes. Too steep of an angle causes the cutting edge to burn out prematurely, again affecting diameters and finish.

Approximately a 20-degree shear angle and a 20- to 30-degree lead angle are typical starting points, but a little experimentation can produce surprisingly different results in finishes, tolerances, cutting action and cycle times.
Advantages Of Skiving

Since skiving is a freer cutting operation, feed rates can be increased approximately two to three times for ferrous and difficult-to-machine materials. These adjustments offset the increased throw time required because of the lead angle. At times it is possible to grind a double angle to reduce throw.

Another advantage of skiving is that, since skive tools cut tangentially instead of radially, step differentials remain unchanged and angles do not have to be corrected, simplifying tool design. Since diametral corrections are not required (as in conventional tools) skiving is about the only way to be assured of forming a perfectly spherical radius on a workpiece. Diametral corrections flatten radii into ellipses, which are almost impossible to produce with conventional radius dressing equipment.

In addition to being used for long parts, skiving is used successfully for parts requiring close diameter tolerances or finishes. Much closer tolerances can be maintained because part diameters are controlled by raising or lowering the skive tool (as in a shaving operation) instead of feeding the tool against a stop. For the same reason, tool wear does not affect diameter dimensions directly (except through poor cutting action).

Better finishes can also be obtained with skiving. As the formed portion of the tool continues to advance under the center of the part, it produces a shaving or burnishing action of the part. Carbide tipped tools are particularly recommended where very good finishes are required, since carbide does not gall or weld as high-speed steel might.

Although a certain amount of this burnishing action is desirable, too much drag can cause the part to spring or deflect. Therefore, most skive toolholders are built with a ¼-degree maximum back taper to prevent excess rubbing as the tool passes under the workpiece. However, while eliminating drag, this back taper causes tapers in the part. In combination with the lead angle, it causes the point at which the tool passes the center of the part to drop away from center, thus increasing part diameter.

The amount of taper per side can be calculated with the following formula. Width of skive tool times the tangent of lead angle times the tangent of back taper angle (usually 0 degree, 15 minutes) equals taper per side. These tapers have, in the past, been overcome by either packing up the holder by this calculated amount or by grinding an offsetting taper on the bottom of the skive tool itself. Both of these methods are hit or miss and are a cause of many operating problems. (Tapers are also occasionally caused by deflection of the part, but this can be overcome by use of an end support on the part.)

Another difficulty encountered has been that most holders are not designed to accommodate extra wide tools and, therefore, necessitate the grinding of T- or L-shaped shanks on the tools. This adjustment shortens resharpenable tool life, increasing the cost of the tools. It also causes rigidity problems in many instances. A further difficulty has been that the depth of form in the tool is limited because of minimal distance between the center of the spindle and the lowest adjustment of the taper wedge in the toolholder.
A Tooling Solution

With these potential problems in mind, Somma Tool Company introduced a new skive toolholder to fit Brown & Sharpes and other machines. The most unique feature of this tool is a rocker-type taper wedge that can be adjusted to offset part tapers, then locked in that position.

Other features include extra wide tool openings to eliminate cutting down of shanks of skive tools; greater distance from the center of the spindle to the lowest adjustment point of taper wedge to accommodate larger part diameters; rugged construction to eliminate chattering; availability in both rear-slide (for forward rotation) or front-slide designs (for those jobs requiring left-hand rotation); and ¼-degree maximum back taper built into the tools to prevent part deflection.

A variety of parts commonly produced in the screw machine industry can see noticeable improvements through skiving. Examples include ballpoint pen tips, hypodermic needle hubs, ornamental lame finials, fireplace andiron parts and ball-type fittings and parts requiring close tolerances and exceptional finishes. Companies should consider adding this operation to their arsenal for producing unusual parts efficiently and economically.

http://www.mmsonline.com/articles/the-forgotten-art-of-skiving.aspx

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Lately, opportunities for growth in the American manufacturing market have shifted away from the smaller, commodity sized parts that everyone can make to parts that are too large, too small or too challenging for most shops to produce. Pursuing the big-part opportunities has prompted manufacturers to buy bigger machines to increase the size of the parts they can process.

Machine tool supplier Mazak recently introduced one such big machine—the new V140N machining center. The company installed this machine in its own Florence, Kentucky, facility.

Seeing how this machine is used there, and speaking with some of the machine tool builder’s personnel who are involved with the machine, revealed some important considerations for using a large machine tool effectively.

Covering the Basics

It almost goes without saying that some basic things are essential to successful machining, regardless of part size. For example, tools typically should be stored, built, and maintained in the tool room and presented to the machine when the setup is complete. Some shops use setup carts for this task, but the ideal tool-chain should be large enough to carry all the tools necessary to run all the parts needed to maintain one-piece flow. Having enough room in the tool chain to carry spare tooling for operations that require it is an added bonus. Tool-life management can help manufacturers utilize spare tooling effectively and maintain process control from part to part.

Fixtures and parts should be stored close by the machine for easy access. Some shops have an FMS system (or a similar system for storage and retrieval), while others use a more manual system. With careful planning, the manual system can be nearly as effective in reducing setup time as an automatic system.

These things are true independent of part size. But for large part machining, some things are different. And to be successful, shops have to develop techniques for doing these things well.

Now the Big Stuff

One thing that is different is obviously the size of the parts. When a part weighs as much as a small car, great care must be exercised in its storage, loading and unloading on and off the machine. When working with smaller parts, safety shoes or other personal protective equipment (PPE) might be sufficient to protect operators should a part accidentally fall. But with larger parts, PPE offers little resistance and drops can be lethal.

The equipment used to load large parts requires more training to use properly. The use of overhead lifting devices such as cranes and hoists requires that operators be aware of their own presence and the presence of co-workers and other traffic in the area. Inspection and maintenance of the lifting equipment must be performed in accordance with all applicable regulations and ordinances. Even storage of the tools required to load the parts requires some thought. Mazak utilizes a system of overhead cranes to safely move large base castings to and from the V140N.

When working with very large parts, some tools will need to be loaded manually because of either excessive weight or excessive size. Automatic tool changer designs accommodate a maximum length, weight and diameter. Tools that fall outside of that range will need to be loaded manually.

Safe manual loading of tools requires that the table be parked in a safe location and the machine interlocked in such a way to prevent unwanted machine motion during the tool change. For some controls, the interlocking can be a little tricky because turning off the power to drives (to prevent motion) sometimes creates control faults that can cause position information to be lost. With a properly interlocked machine an operator can safely enter the work zone, change the tools, exit and continue in the program without lost machine time. Operators should also pay extra attention when loading machine offsets and other programming during manual tool changes.

Extra care is also required when positioning parts in the fixtures on the machine. Some companies spend a great deal of time at a large surface plate “laying out” castings and adding witness lines to which the machinists make qualifying cuts. Mazak uses a probe to perform this function. Once the parts are loaded into the fixture and the program started, the probe checks to see if the casting is against the primary locators. If the locators are against the fixture properly, the datum structure for all subsequent machining can be established. If the casting is not properly located, the operator is alerted. In the same way, probing the casting can help center-up stock and make alignment adjustments to account for casting variation. At Mazak, lead programmer Jeff Bay works continuously to perfect probing routines that allow the machines to run more automatically.

Offline programming is more efficient than programming at the machine for optimizing tool paths and minimizing tool changes. Due to its size, even a very fast large-part machine can take a lot of time to travel long distances. Any unnecessary motion will add wasted cycle time. Keeping programs backed up via DNC is also a critical step in efficient operation. It is not only a regulatory requirement in some settings to only keep one copy of the program (whether it be in machine memory or on the server) it is also efficient to regularly upload the program to the server making sure edits are kept and any related documentation is updated. Mazak keeps critical machines at its Florence, Kentucky facility tied to its Cyberfactory system to maintain programs that the machines run. This system can even schedule the machine’s next part, which is crucial to saving time between parts.

Five-Axis Time Savers

Some other ways that Mazak saves time in the cut is to machine all the parts that require a particular tool while that tool is in the spindle. Even though the V140N changes tools in about two seconds, the time necessary to move from the cut to the tool change position and back can add up.

After cutting a critical part feature, Mazak can use the probe to determine whether the feature is in print. If the feature needs an extra finish pass, the tool can be reloaded and the pass can be made.

The use of combination tools such as drills that double as thread mills and insert drills that create chamfers around the hole while drilling can be useful when keeping tool change time to a minimum is a concern. Other combinations drill and ream or drill and tap simultaneously. Another variation on the combination tool technology is the use of cutters that can rough and finish at the same time.

Five-Axis Cycle Time Reductions

Since the installation of the V140N in its Florence, Kentucky manufacturing facility, the company has seen cycle time reduced by 50 to 65 percent for parts run on this machine. Part of the difference results from replacing five-face with five-axis machining. Because the machine’s five-axis oscillating head can reach lower to the table than its predecessor, extra machining is combined in a single step. Eliminating extra machining after the fact has improved flow and throughput by 40 to 50 percent. The company can run more parts in a single shift, freeing some much-needed capacity and reducing overtime.

One-Piece Flow

Of all the benefits, perhaps the most valuable has been supporting the company’s long-term goal of implementing one-piece flow on its machining centers. Previously, the batch process left some pieces at operation 10, some at operation 20 and so on, all waiting to be completed. This consumed a great deal of floor space and caused excess handling. The V140N’s five-axis capability reduced the number of milling operations from three to two. Efficient use of the table allowed the company to run both operations simultaneously, completing one set of parts per machine cycle. The machine table also has enough extra space to include a headstock, a saddle, a tailstock, and a cross-slide casting in the same setup. Every time the machine finishes a cycle, all the castings necessary to build a Nexus are completed. The result is a reduction the floor space required to store the in-process castings, not to mention significant reductions in lead-time between machining and assembly.
Five-Face Or Five-Axis, What’s The Difference?

Before installing the V140N, Mazak Corporation used a five-face style of machine to produce castings. Many machines are still designed this way. The five-face concept involves using various attachments, called heads, to enhance the machine’s reach and capabilities. The heads are clamped to the main spindle with an interface that looks like a standard, 50-taper tool holder. Most advanced machine functions are supported in this arrangement (such as through-the-tool coolant and synchronized tapping) although at the sacrifice of speed, accuracy and rigidity.

The vertical head attaches via a standard coupling for use as a typical VMC. One advantage of the attachment system is the ability to develop and use specialty tools to reduce reach problems. For example, extra-long-reach vertical attachments take the place of extra-long tools.

Work along the four edges of the part utilizes a horizontal milling attachment also called a “right-angle” head. The horizontal attachment can index at least every 90 degrees, and some can index every 5 degrees. This limits capability somewhat in anything except box machining, hence the reference to five-face machining.

With five-axis machining, the vertical head and the horizontal heads are actually the same head. The MazakV140N uses a single head concept that allows ±180 degrees of C-axis rotation and ±100 degrees of B-axis rotation. In the case of this machine, the head is not a contouring head, but instead it is a positioning head. This means that it can position to any combination of B- and C-axis travel, but it must be clamped before machining takes place. Traveling the full range of B- and C-axis motion takes less than 2 seconds.

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