Quality parts begin in the process tool
designs
Precision measurement is critical to on-machine
control
By Jim Lorincz
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LaserControl NT is a 3rd generation
technology for tool setting and tool breakage control on
machining centers in even the heaviest coolant
conditions.
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Production and quality problems that begin when machining
processes go out of control can be defeated by technology that
makes sure that processes are “in control” as they are
producing parts.
The latest technological
advances from Blum-Novotest GmbH, parent of Blum Laser
Measuring Technology Inc., Erlanger, KY, address the critical
elements of product and process control whether machining is
being done in flexible machining lines for high-volume
production, on the latest high-speed machining centers, or in
unmanned operations.
Developments continue the
company’s work over the last 20 years using lasers for tool
measurement and broken tool detection and touch probes for
locating and measurement in the difficult environment of the
work envelopes of machining centers. Technologies include the
next generation laser control, a multidirectional touch probe,
and enhanced wireless communication with multiple measuring
devices.
At EMO 2003, Blum-Novotest introduced the
Laser Control NT for tool setting and detecting missing or
broken tooling, the TC touch probe family for workpiece
locating and measurement, and the on-machine wireless Bore
Gauge BG40 for high-volume measurement of production parts
with the same diameter. Also introduced was the IC55 Infrared
Transceiver for wireless data transfer.
“One
purpose of our latest developments is to eliminate production
of defective parts before damage is done by broken or missing
tools and parts need to be scrapped,” explains Alexander Blum,
managing director. “For precision measurement, the combination
of on-machine adjustable tools, bore gauges, and laser control
system eliminates the need for a costly post-process measuring
station, which often determines problems only after a lot of
damage has already been done,” says Blum
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Universal TC50 touch probe is designed for
multi-directional measurement in mold and die
production, as well as for precision
machine
shops.
| Lasers
at work
A few relevant facts explain the dramatic
increase in the use of lasers on machining centers to locate
and measure cutting tools. Because the workpiece gets its
geometric shape from the tool, it is imperative to identify
the position and dimension of the cutting edge in the
machining system as precisely as possible. The value of the
laser system for tool setting is that it can measure cutting
edge geometry under nominal speed and in accordance with the
basic parameters of the machine tool system. This is
especially important with the increasing use of high-speed
cutting (HSC) systems in which tool growth with temperature
and speed change can have a dramatic effect on cutting
precision.
The basics of using laser systems in
machining environments are pretty well known. A laser system
in the machine tool is a high-precision light barrier that
generates a trigger signal to the control to measure the
values of the axis positions when the laser beam is
interrupted by a tool. The standard software integrated in the
control of the machine uses the measured value together with a
reference value for precise tool setting and breakage control
in the machine.
Blum explains that laser systems are
able to carry out different functions at any speed of rotating
tools for the following purposes:
• detection of shaft
breakage
• detection of single cutting edge breakage
•
detection of setting and concentricity errors
• measurement
of tool length
• measurement of tool diameter
• form
control (breakout and wear), and
• thermal compensation of
machine axes
The main obstacles to using optical-based
laser measurement systems in machine tools are interference
signals caused by coolant and chips. Blum-Novotest has solved
this problem by sealing the optics against coolant using a
pneumatically-operated mechanical shutter. During the short
time needed for measuring, a barrier of air prevents the
pollution of the optics through coolant mist or
drops.
A second problem results from coolant drops or
chips that can interrupt the laser beam and generate a trigger
signal. A broken drill, for example, might not be detected due
to a false signal just as the coolant drop interrupts the
beam, says Blum. The initial solution to the problem was a
plausibility check that had the side effect of requiring
longer measuring time because of increasing coolant. There is
a limit to the effectiveness of this approach when coolant
flow becomes too heavy.
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TC51 touch probe is designed for
quickly locating parts or fixtures in high-speed
machining
centers.
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High-speed
solution
Blum-Novotest’s patent-pending 3rd generation
of laser control called LaserControl NT eliminates the
interference caused by coolant and allows the user to realize
a reliable and essentially faster tool setting. “With
LaserControl NT, the tool is positioned in the laser beam and
measured when moving out of the beam,” Blum explains. “A
microprocessor integrated into the laser system generates the
trigger signal only when the effective tool radius, that is,
the longest cutting edge has left the beam completely and when
there is no beam interruption for one complete
rotation.”
Another advantage of NT technology is the
variable adaptation of the length of the laser system trigger
signal, says Blum. Until now, the trigger signal had to be
adjusted to a defined period (e.g. 5 ms). As a result, single
cutting edge control (control of every individual cutting edge
of a multiple cutting edge tool concerning breakout and wear)
could be carried out only at a specific
speed.
“This is a distinct disadvantage for
high-speed cutting (HSC) spindles as the tool length can vary
considerably under different speeds due to thermal growth and
lower pre-tensioning of the bearings,” says Blum. The
technology developed by Blum-Novotest allows the variable
adaptation of the output signal length. Single cutting edge
control can be carried out at any speed and the machining
accuracy with HSC spindles can be increased. With this 3rd
generation control and its “intelligence,” Blum says that the
laser can now also be used for other applications, e.g.
turning and grinding operations and with new measuring
strategies.
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The wireless BG40 Bore Gauge is designed for
measuring high-production parts with the same diameter
on machining centers and transfer
lines.
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Touch probes
Blum-Novotest’s new TC probe family
offers solutions for precision measurement, fast part and
fixturing locating in high-production applications, and
specialized measuring capabilities in the Z-axis.
• The
TC50 model is a universal touch probe with multi-directional
capabilities for precision measurement of workpieces,
particularly in mold and die, as well as precision machine
shops.
• The TC51 model is a high-speed
bi-directional touch probe that is designed for fast part and
fixture location on production machining centers where time is
of the essence.
• The TC51-20 model touch probe
features a special design to allow both pushing and pulling
measurement of grooves, recessed diameter slots, and shoulders
in the Z-axis of workpieces.
Because of its
mechanically-robust design, the TC 50 can withstand fast
acceleration and rapid machine movement without false trigger
signals by deflection of the system or mechanical damage. Blum
explains that a circular measuring system in the
counter-bearing of the housing generates a signal independent
of the direction of the stylus, eliminating the lobing that is
produced by conventional touch probes that use the three-point
measuring contact principle.
Flexible machining
lines and machining centers that dominate high-volume
production of such workpieces as engine blocks, compressor
housings, and bearing journals present their own challenges
for in-process measurement and control. “Most of these systems
are unmanned and require reliable, precision tools to monitor,
control, and compensate for dimensional part errors caused by
tool wear, tool breakage, temperature drift of the machine
spindle and axis, as well as tool deflection,” says
Blum.
His company has developed the Bore Gauge BG40,
which is an on-machine wireless device that is stored in the
tool magazine like any other tool. It is used to measure
precision bores in the machine working area of machining
centers and flexible machining cells accurately and
independently from the machine axis feedback.
The bore
gage is available with two different measuring
capabilities:
• The BG 40 features a floating principle to
measure bore diameter fast and accurately even when the
machine is not perfectly positioned in the bore
center.
• The BG41 features a multiple sensor
principle to measure diameter, bore profile for cylindricity
and roundness, and position.
Contact sensors are used
on both systems, which feature Blum’s proven wear-free
optoelectronic sensor for internal signal
generation.
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BG41 is designed with
multiple sensors to measure diameter, position,
cylindricity, and roundness. |
BG 40 is designed with
floating measuring system for diameter measurement
only.
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Compatible with multiple devices
The BG 40 has
diameter-specific measuring heads for diameters from 3 mm
to 200 mm. The measuring range is 400 µ with a
repeatability of 1 µ. Data transmission is via simple
interface and transceiver to the machine control. All Blum
workpiece probes and bore gauges are compatible with the new
fail-safe Infrared Transceiver IC55. It is also compatible
with the Komet adjustable Boring Bar M 042 that enables
integration of multiple measuring devices using only one
receiver.
A protective air curtain integrated into the
infrared IC55 helps save the installation of cumbersome air
nozzles in the work area. Another characteristic is the common
power supply for all probes using a standard 9V block battery
with low-energy consumption for up to 100,000
contacts.
When the LaserControl system is used in
conjunction with the BG40 bore gage, the laser is used to
check the actual boring bar flight circle at working speed,
runout, and single-edge tool breakage.
The
control process starts after completion of the rough boring
process. The LaserControl checks the finish tool for runout
and the precise flight circle at full speed. Any deviation
from the target will be automatically compensated. After
finish boring of all bores is completed, the bore gage checks
the last bore diameter and, if required, for form and
ovality.
Exceeding the preset limits results in
compensation for the next part. Compensation is done using the
average means and a dampening factor. If maximum tolerance
limits are reached, the spare tool selection macro calls for a
new sister tool that will be checked and compensated, if
required, by the LaserControl.
Sudden diameter changes
outside the tolerance band result in a production stop and
alert the operations staff. Production will continue
immediately with a new tool if the problem was caused by a
broken tool. Expensive workpiece with undersized bores can be
saved by remachining on a separate machine.
The newly
developed Interface IF46 enables bi-directional communication
of the BG 40 Bore Gauge with the machine control. It transmits
the compensation values and has the capability to provide SPC
data, as well.
Blum Laser Measuring Technology
Inc.,
http://www.rsleads.com/402tp-170
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