Manufacturers
are eternally seeking ways to maximize efficiencies throughout their production
process. The first thought that usually comes to mind is to upgrade existing
capital equipment under the assumption that a new
machining center’s slightly higher speeds and faster cycle times
are the best solution. In some cases this may be true, however, another
much less expensive investment is often overlooked while trying to streamline
the production process.
Needing a Presetter
Most machining centers are actually cutting less than 50 percent of
the time during a typical day or shift—the rest of the time
they sit idle while operators are preparing the workholding and tooling
for the next cycle, essentially wasting valuable spindle cutting
time. Reducing spindle downtime is the key component to maximizing
production efficiency, and these results can be partially achieved
by simply investing in a tool presetter and modifying toolroom management
standards. This can all be done with a minimal investment, an excellent
alternative to buying all new expensive machine tools.
An entire set of tools is being prepared on a high precision
modular tool presetting system. Once these tools have been preset,
measured and stored in memory, the entire set will be taken to
the machine tool and is ready for cutting. All of this is taking
place while the machine tool is running a different job. |
Increase
Production, Reduce Setup Time and Minimize Spindle Downtime
The
greatest potential for savings and productivity is in tooling setup
reduction. Unfortunately, many shops continue to use the machine
tool spindle as a presetter, costing hundreds of thousands of dollars
in
machine time annually.
Consider, for example, a shop running four CNC mills for two
shifts per day at a shop rate of $40 per hour. If each operator takes
only
one hour per shift on each machine for tool setup, the shop is losing
about $320 per day, or $80,000 per year, to spindle downtime. If
this allotted setup time isn’t sufficient to ensure optimal cutting
conditions, short tool life and scrapped parts will quickly erode
profits. A presetter will virtually eliminate these factors.
In many shops, operators are required to gather all necessary tools
from a centralized tool crib, then begin setting them up. The acquisition
of a tool presetter will allow the tool attendant to shift focus from
inventory management to acquiring a better understanding of the machining
process, fixturing, measuring tool lengths/diameters and other setup
procedures. Operators can preset cutters with adjustable cutting edges
for a balanced chip load, rather than setting these indexable tools
on the machining center. Offline adjustment of boring-bar length and
diameter can reduce tool-changeover time at the machine spindle from
15 minutes to less than one minute. The machine operator will be able
to acquire a completely qualified set of tools to a machining center,
get them loaded and go directly into production, thus minimizing non-cutting
time on the machine tool.
Proven Results
One company purchased a tool presetting system and started presetting
all required tools before machining began on a job. The newly implemented
system dramatically reduced setup scrap and allowed the company to
identify if, and when, additional tooling needed to be ordered before
a job was even started.
The company shared analysis of a 100-piece job to show the impressive
savings. Historically, the job averaged between 60 and 100 hours of
setup. The presetting system cut setup to less than 34 hours.
An example of a contact presetter. An easy-to-use, high precision
digital tool measuring and presetting station, suitable for any
workshop environment. |
Selecting a Presetter
There are many tool presetters on the market, so it is very important
to choose the one that will best complement a company’s processes.
To find which presetter will best suit the company’s needs,
first determine the maximum tool length (z-axis) and diameter (x-axis)
to
be measured. This will determine the presetter travel capacity
necessary to measure the full range of tools used in-house. If
future growth
is likely, select a system that is slightly larger than currently
required by the facility and has the capability to be upgraded
and adapted to
meet future demand.
It also is important to consider the tolerances that must
be held during machining operations. How accurate and repeatable
does the presetter
need to be? Precision within 0.0001” is available, but isn’t
necessary for every shop’s operation requirements.
Another aspect to consider when selecting a presetter is the different
tool shanks used during operations. The presetter should be fixtured
for the shanks that are run, whether they are standard V-flange, DIN-standard,
BT-flange, NMTB or lathe tool shanks. Keep in mind that as job requirements
change, so may your machine tool and the spindle connection. For this
reason, presetter manufacturers offer adapters for a variety of tool
shanks and tool holding systems besides the type that is supplied standard.
Be sure to investigate the style of adapters offered by the presetter
manufacturer and the simplicity of exchanging them. By supplying information
on lengths, diameters, accuracy and shank style, a quality tool presetter
vendor can help select the most cost-effective measuring system.
Contact Versus Noncontact
Two classes of presetters are available: contact and noncontact.
The magnetic-scale technology of earlier model contact presetters
is outmoded. The newer glass scales and encoders now offer many advantages
and much finer resolutions. Magnetic scales output a digital pulse
and have a fixed resolution (generally 0.0005"). Glass scales
output an analog signal, which allows the manufacturer to select
the resolution on the readout to as fine as one-tenth of a micron.
By using shadow graphs, noncontact presetters provide a view of the
tool profile for both inspection and presetting. Users of these systems
can measure tool length and diameter, calculate nose radii and angles,
and detect damaged or unusable cutting edges.
Noncontact presetters are recommended for most computer-integrated
manufacturing applications, including flexible manufacturing systems
and manufacturing cells, while contact units are more commonly used
in cell-based applications.
Use of a noncontact presetting unit also is preferred for operations
using toolroom management systems to reduce tool management time. Optical
presetting becomes essential for high-speed machining and for operations
where it is important not to touch the tool or where it is necessary
to view and evaluate the integrity of the cutting surface. Given the
state-of-the-art precision available today, user judgment has become
the weakest link in the tool measuring and presetting process. Speroni
vision systems not only eliminate all user judgment from the process,
they further enhance the metrological characteristics of the machine.
A top-of-the-line, noncontact presetting system shown as an
entire tool setting solution. |
Design Criteria
Once a contact or noncontact presetter is chosen, design criteria must
be considered and selected for precision applications. To measure a
tool accurately, it must be held accurately. The presetter’s
spindle should have a high level of rigidity and minimal runout. High-force
retention-knob clamping is essential for the presetter to consistently
duplicate the way the tool sits in a machine tool spindle. A tool presetter
constructed to the standards of machine tool assures the similar accuracies.
Also consider possible damage that can occur in the shop floor
environment—an
enclosed design provides dust protection for sensitive parts and makes
the unit easy to clean. A sealed design may be essential, considering
the coolant mists, welding or iron contaminants and temperature changes
that can interfere with the instrument’s ability to provide repeatable
and accurate measurement.
A tool presetter constructed solely of one material—such as
aged pearlitic cast iron—may appear more costly than other presetters
constructed of steel or aluminum. However, a temperature-stable structure
like cast iron will prevent changes that could cause distortion in
the linear axis or in the positioning of the guideways, thereby assuring
that long-term repeatability and accuracy will not be compromised.
Presetter Features
After selecting the right presetter construction for the shop-floor
environment, determine which system features will best benefit production.
Consider the following list of functions that are important to entry-level
and cell-based users:
- Although it’s always prudent to verify the linear gauge references
when tolerances are tight, machine-axis home position doesn’t
require calibration every time the system is turned on. This is an
added bonus of the more sophisticated readouts that are generally available
only on presetters equipped with glass-scale and glass-encoder technology.
- In
addition to larger numbers and buttons, digital readouts are
now available with data memory for many different
zero points. Rather than
actually performing the calibration for a tool-shank changeover,
a different zero point can simply be selected from the
memory.
- Many presetters
have the ability to switch back and forth from inch to millimeter,
from radius to diameter, and
from
incremental to absolute
measurements from a known gauge point.
- Some presetters
allow fine adjustments of any distance along the z- and x-axis
within the unit’s full range of travel. Others allow
the operator to make geometrical calculations and store
tool data in the presetter’s memory.
- A built-in label
printer or computer connection allows you to print labels
that may be affixed to tools, keep
preset data handy for use
at the machine, or download tool-offset data through
a direct-numerical-control interface system or directly
to
machine tools.
Summary
Whatever a shop’s operations require, a carefully selected tool
presetting system—following the guidelines presented above—will
greatly increase efficiencies and enhance production leading to increased
profits.
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