Haas Automation VF Series, Книга управления

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101
January 2004
When running a program, an attempt to move outside of the travel limits will cause an alarm prior to starting the
motion and the program will stop. An exception is a circular motion which starts and ends inside of the travel
limits but moves outside of the limits during the motion. This will cause an alarm to occur part way through the
motion.
Travel limits apply even when running a program in Graphics mode. An alarm is generated and the program will stop.
H
IGH
S
PEED
M
ACHINING
High speed machining makes it possible for an increase in the removal rate of material, improve surface finish,
and reduce cutting forces. This will reduce machining costs and extend the life of the tools. An additional
advantage to using high speed machining is to utilize the more current tool cutting edge materials and tool
coatings that are available. The only limitation to high speed machining is the need for rigid, powerful machines
capable of the required speeds and feeds, and having a fixture strong enough to hold the workpiece.
Recommended Tooling
Balanced tools and tool holders are a must to maintain excellent machining conditions. Vibrations during chip
cuttings relate directly to early tool failure, poor part finish and even possible spindle damage. Therefore the
design of the tool holder increases in importance as the speed increases.
The items necessary for proper high speed machining are toolholder taper cone accuracy, concentric relation-
ship of the cutting tool pocket to the tool holder cone, and actual size tolerance of the tool pocket. The fit
between the tool holder and the spindle is the starting point for the machining center. An improved fit for these
two items is essential for hi-speed machining success. Size and tolerance of toolholding features such as bore
or pilot size should not exceed two or three ten-thousandths of an inch. Concentricity of the toolholding feature
(bore or pilot) relative to the tapered shank this should also be within two or three thousandths of an inch.
Where possible use the minimum collet envelope relative to bore size. In other words use the largest bore size
for the smallest collet envelope to achieve high grip force with reduced tool holder mass. This also helps in
keeping the amount of centrifugal force low and will allow the highest speed possible in relation to the balance
specification limitations.
The tool assembly must be balanced to a degree of accuracy that matches the machine spindle requirement.
This means a balancing operation will have to be performed, or check the balanced condition of the assembly,
each time there is a new tool assembly created or a significant change is made to the existing tool assembly.
A significant change could be adjusting cutting tools, changing any part of the tool holder, regrinding or altering
a cutting tool, or changing to a new cutting tool or a new tool holder. In order to thoroughly balance the tool
holder the retention knob and cutting tool must be in place. Commercial balancing machines give accurate
measurement regarding the balance of the tool assembly. Such equipment would be necessary for the initial
balancing and eventual rebalancing operations.
The tool holders should be an AT-3 or better with a nylon backup screw. The tolerances maintained in the AT-3
design are the minimum that would be recommended for a high speed process. The nylon backup screw
increases collet grip on the tool and creates a better seal to aid in coolant transfer.
Use single angle collet chucks and collets for best grip and concentricity. These collet systems are made up of
a long single angle located in the holder. The angle per side should be eight degrees or less for best results.
Avoid double angle collet systems when maximum rigidity and close tolerance are dictated. It is recommended
that minimum engagement of 2/3 of the full length of the bore in the double split single angle collet. However for
better results 3/4 to full engagement is preferred if possible.
Collet envelope is the combination of the maximum bore size and the outside shape designation.
Consult the tool holder manufacturer for the current specifications and capabilities of their tool holders. This
would include the AT rating and maximum RPM that the tool holder is rated for.