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In Focus - January 2010
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Modern lathe chucks dispose of a vast safety equipment.
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Lathe chucks should always be evenly lubrified at every lubrication nipple. This safely maintains the clamping force.
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01-12-2010 -
If a workpiece loosens from the chuck on a lathe, it can be dangerous to those working in the manufacturing hall. Because of this, the Employer’s Liability Insurance Associations, Standards and Safety Commitees, do everything in their power, to avoid accidents. But it is also up to the operator to ensure his own safety at the lathe.
Maximum safety is the common goal of the manufacturers of machines and workholding solutions. Even though many safety systems on modern machines work automatically, the operator, shift supervisor, and production manager still take the responsibility for regular maintenance and systems controls. It can be compared with a car: The best ABS brake is useless, if the brake pads are worn out or the brake fluid is old.
Regular greasing maintains the clamping force
In order to assure proper function of the lathe chuck, it must be greased regularly. If not, the risk is high that friction inside the chuck will increase and will result in a loss of clamping force. One glance at the curve of the clamping force shows how the clamping force of a new lathe chuck (continuous curve) changes, depending on the RPM. On the other hand, the lathe chuck, which was greased insufficiently, shows a considerably reduced clamping force (dashed curve). Depending on the type of lathe chuck, the weight of the top jaws and the operating condition, the clamping force drops down to about 50 percent of the nominal clamping force! As a result, a clamped workpiece that was thought to be safe may fall out of the lathe chuck during machining. To avoid this, the manufacturer of the clamping equipment provides maintenance and lubrication intervals, which have to be observed. In addition to the maintenance and lubrication manual, they also define the lapse of time, after which the static clamping force of the lathe chuck has to be controlled.
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Insufficiently greased lathe chucks considerably lose their clamping force.
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Depending on the type of top jaw, weight and shape, the maximum clamping force of the lathe chuck differentiates.
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It makes sense to travel through the whole stroke several times after 500 jaw cycles of the clamping piston. This helps to convey the lubricant to the pressure faces and maintain the clamping force longer.
For lubricating the lathe chucks, SCHUNK recommends a special heavy duty grease. It assures optimum lubrication even in case of high wear, e.g. at high clamping forces, short cycle times or an intensive use of coolants. Improper lubricants however, may negatively influence the proper function of the lathe chuck, reduces clamping force, and increases the coefficient of friction which in turn causes premature wear.
Normally a lathe chuck is equipped with several lubrication nipples. In order to avoid an extreme unbalance, all the lubrication nipples should be greased evenly. For assuring an even distribution of the grease inside the chuck, open and close the jaws several times after the first greasing.
Independent from the maintenance and lubrication intervals, in extremely contaminated environments a chuck can lose clamping force. In this case, the complete chuck has to be disassembled, cleaned and the chuck components have to be inspected for damage. Details for complete cleaning of the chuck and chuck disassembly can be found in the operation manual of the manufacturer.
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Calculation of the centrifugal force - Keeping the invisible risk under control
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Invisible but always present is the centrifugal force. The jaw weight, shape and position, centrifugal force and RPM’s influence the clamping force and the safety during the turning operation. This effect can be tremendous and the maximum speed of the lathe chuck can no longer be achieved. According to DIN, a newly greased lathe chuck with standard stepped jaws operating at nominal speed, has to achieve more than a third of the residual clamping force.
Since the top jaws can be located in various positions on the chuck, every application has to be checked individually. By recalculating every individual set-up, for every clamping situation, the maximum nominal speed can be determined. For detailed information of how to calculate the centrifugal forces of the jaws, please see the individual operation manuals of the lathe chucks, or the latest lathe chuck catalog from SCHUNK. For a rough determination of the maximum speeds, the clamping force - speed curves of various top jaws and power chucks are illustrated there.
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Payload of the guideway - The absolute limit
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The higher the top jaws, the higher the payload of the guideway. In case of high jaws the speed and clamping forces have to adjusted!
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The integrated base jaw and the chuck body are the components of the lathe chuck, which are mainly exposed to wear. The higher the clamping jaws, the higher the transmissible torques at the chuck’s base jaws. Therefore for safe turning operations, the height of the jaws play an important role. Depending on the chuck type (size and length of the base jaw guidance) every lathe chuck is marked with the maximum admissible payload of the guideway.
Generally speaking, the top jaws should be as low as possible. However, if high chuck jaws should be required, the clamping force and speed have to be individually adjusted to the application. Similar to the calculation of the centrifugal force, the actual payload of the guideway can be determined or controlled for every application. If due to an overload, or wear, a base jaw should break, the integrated safety mechanism of the modern lathe chucks prevents the base jaw from being thrown from the chuck.
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Control the clamping force regularly
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On every lathe chuck the maximum admissible actuation forces or torques, the maximum static clamping force and the maximum speed has to be marked.
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Only a regular inspection assures optimum safety. Therefore SCHUNK generally recommend that before starting a production run, and also between individual maintenance intervals, the clamping force should be inspected with a clamping force tester. Here the clamping force should be always measured in the same chuck condition, which comes up to the latest clamping application. If stepped top jaws are used for example, it has to be measured at the steps, where the workpiece will be clamped. If high RPM’s are planned, (due to the centrifugal force a loss of the clamping force has to be expected), the nominal clamping force should be tested with a dynamic gauging.
Checklist for maximum safety
Those who consider the following six points daily, can be sure of maximum safety on the lathe:
- Never actuate the power chuck, if the safety equipment is not installed and functioning properly.
- Inspect the power chuck at least once per shift for visible externally damages and defects.
- Grease the lathe chuck at least once a day with an appropriate grease.
- Try to use light and low profile jaws, which are not welded.
- Report every change of the operating behavior immediately to the responsible department/ person and switch off the machine in the meantime. Do not start the machine again, until the malfunction is cleared.
- After a crash, please return the lathe chuck to the manufacturer for complete inspection.
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2010-07
Pick & Place Solutions in Comparison
In order to assemble components fast and precisely, operators can choose between many different Pick & Place solutions. The performance features of the systems vary from each other. To find the best solution, the advantages and disadvantages of each system should be compared.
 more...
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2010-06
Energy efficient gripping
In the best of case scenario, energy-efficient automation modules should reduce energy consumption of the handling system and increase cycle times and output. It helps conserve the environment and saves money if you focus both measures.
more...
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2010-05
Factor of Success Engineering -
With virtual simulations to the optimum clamping solution
How does a component deform during the clamping process and machining? Which clamping solution assures that the workpiece has the exact dimensions? How can an existing clamping device be ideally used? Virtual simulations are giving valuable answers to these and simular questions. By means of the Finite Elements Method (FEM) deformations and component payloads can be calculated, which allows a comparison of the individual clamping options and how to optimize them. In turn, process and investment reliability are increased, development times shorten, the selection of the suitable clamping device is easier and costs are lowered.
more...
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2010-04
Magnetic Clamping Technology - efficient at a variety of tasks
Magnetism is one of the most fascinating and influential force of our universe. Engineers and technicians use this same force in order to clamp workpieces, or to reliably lift components. Magnetic clamping technology is well-established in various areas, such as grinding, milling, turning, mobile lifting units in production, and for huge crane constructions. Most engineers now know that magnetic clamping solutions reduce set-up times by about 80 percent, that workpieces are clamped without any deformation, and even coils can be reliably transported.
more...
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2010-03
EU-funded project pushes on the service robots
Experts predict an increase in the pursuit of service robotics. This is no surprise: Modern robot applications offer an enormous potential to the economy and society. Pilot applications already show how robots might become more and more the intelligent helpers of humans. In addition to universities and other research institutes, industrial enterprises should focus on development in this sector, and make it a reality. Therefore the European Union has decided to subsidize the transfer of knowledge between research institutes and industry financially support this pursuit as well.
more...
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2010-02
Flexible packing and palletizing
Adaptive handling systems provide dynamics and profitability if comprehensive ranges and frequent changes in assortment are given.
Every week a new product generation replaces the previous one. These products, which provide new impulses in trade, are a real challenge for the packing process. Faster, process reliable, and flexible automated solutions are in constant demand. They help to keep the handling costs under control, even at an increasing product variety.
more...
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2010-01
How operators "play it safe" during turning operation
If a workpiece loosens from the chuck on a lathe, it can be dangerous to those working in the manufacturing hall. Because of this, the Employer’s Liability Insurance Associations, Standards and Safety Commitees, do everything in their power, to avoid accidents.
more...
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In Focus - 2010
In Focus - Archive 2009
In Focus - Archive 2008
In Focus - Archive 2007
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