Cutting tool technology has evolved dramatically since the 1980s, when dedicated router tooling began to take shape. This in turn has enabled primary and secondary fabricators in the plastics industry to move from generic tooling to material-specific cutting tools.

However, there continues to be a lot of confusion regarding optimal machining methods and practices In the last issue, we looked at three real-life applications in which fabricating problems and their cutting tool solutions were given. This month, three additional scenarios are presented.

Scenario 4
Material Cut: ABS and extruded Acrylic
Product: Covers for surveillance cameras
Router Type: 5-axis CNC
Feeds & Speeds: 18,000 rpm at 100 ipm
Initial Tooling: Straight flute generic plastic tooling
Problem: Initial call was placed because of consistency problems with current carbide tipped tools.

This scenario is very typical of what happens in many manufacturing and fabrication shops: Tooling users become comfortable with a particular tool and do not continue to look for newly developed or advanced tooling that can increase production and bottom line profits. After an on-site visit with this fabricator and some experimentation, a new tool was found that allowed significantly increased feed rates and at the same time exhibited increased finish quality cutter life.

Using a standard spiral "O" flute with geometry modified to allow it to cut both ABS and soft acrylic, the fabricator was able to increase feed rates from 100 ipm to 250 ipm (decreasing part production cycle times and cost) and was also able to drop spindle speeds from 18,000 rpm to 16,000 rpm (increasing cutter life). This was all accomplished with an improved surface finish on the final part and using 1Ú4-inch diameter and smaller tooling.

A second problem brought to light in this scenario was the desire by the fabricator to use a single tooling style (with various diameters) to handle machining of multiple types of plastic. Normally, this goes against the trend of tooling suppliers who are developing advanced tooling that is very application specific. As feed rates increase and surface finishes become more and more important, there will be a significant decrease in the availability of "generic" plastic tooling.

New tooling is designed for specific applications and it is extremely difficult to find an optimum cutter geometry when multiple materials being cut require different machining parameters. This fabricator was lucky, but this scenario is going to become the exception, rather than the rule, as feed rates and CNC router technology continue to advance.

Scenario 5
Material Cut: Lexan
Product: Fabricated parts for the electrical industry
Router Type: Newly purchased 3-axis router
Feeds & Speeds: 2,500 rpm at 25 ipm
Initial Tooling: Plastic end mill
Problem: The new (and expensive!) CNC router was not paying for itself.

As manufacturers leave the metal-working industry and move into the primary and secondary plastics fabrication market, these problems will occur. CNC mills are designed to machine metals; they are very efficient at it. But 15 years ago or more, their use in the plastics industry began to skyrocket. They were able to make intricate, multi-axis cuts on a large variety of soft and hard plastics and were typically much more efficient and effective than other methods available for producing complex finished parts.

In those days, CNC routers were not readily available and those that existed did not have the multi-axis capabilities and/or rigidity required for complex parts and acceptable surface finishes. With current router technology, feed rates are five to 10 times faster than CNC mills and these feed rates are parameters to be realized, however, proper tooling must be used.

End mills are designed to run at end mill speeds (up to 8,000 rpm and 50 ipm) and do not complement a CNC router that is capable of spindle speeds beginning at 10,000 rpm and approaching 30,000 rom with 500 ipm feed rates or higher. It is impossible to justify the cost and return-on-investment for a machine in which costs can exceed several hundred thousand dollars when run at CNC milling feeds and speeds.

By convincing the fabricator (and the machine operator) that router tooling was designed to perform best at high spindle speeds and feed rates, the cutting tool company was able to show the increased chip extraction available as well as the subsequent productivity and the surface finish improvement.

The end result was the use of a 1Ú4-inch diameter dedicated plastic straight "O" flute with speed rates at 150 ipm and spindle speeds at 16,000 rpm The fabricator achieved an increase of six time greater throughput with a better surface finish.

Scenario 6
Material: Cut: Acrylic and ABS
Product: Vacuum formed parts of various configurations
Router Type: 3-axis CNC
Feeds & Speeds: 18,000 rpm and 90 ipm
Initial Tooling: 3-wing slotting cutter with arbor
Problem: Part damage and programming concerns

This scenario is similar to the first in that the fabricator was unaware of new dedicated plastic tooling that was designed to be an "instant fix" to his problem.

The fabricator was using a slotting cutter designed for wood to remove flash from a variety of formed parts. The geometry of the slotting cutter, as well as the large retaining nut at the bottom, were causing numerous problems such as material melting, scarring and occasional damage when the programmer failed to check for adequate clearance between the retaining nut and the material.

The solution was to use dedicated plastic saws designed specifically to run on a CNC router through the use of an arbor. Tooling such as this is being constantly designed and marketed to prevent plastics manufacturers and fabricators from having to "make-do" with tooling that was designed for another industry or application.

By increasing the tooth count to 10 or 20 teeth (ABS and acrylic respectively) on a 41Ú2-inch arbor mounted saw, the fabricator increased feed rates to 150 ipm and eliminated virtually all post-cutting inspection and rework operations.

The preceding three scenarios all illustrate two important facts about router tooling:

• Router tooling is designed for very specific applications and must be chosen and run accordingly.

• There is continuing advancement in the router tooling industry &emdash; just as there is in the machine industry &emdash; and plastic manufacturers and fabricators must constantly scan the market place for application specific tooling to solve their problems or increase their productivity.

Van Niser is director of Plastic Application Engineering at Onsrud Cutter. Readers are invited to send questions to Van Niser at Onsrud Cutter, 800 Liberty Drive, Libertyville, IL 60048; e-mail: vniser@onsrud.com.

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Plastics Machining & Fabricating
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