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In Focus - Archivo Septiembre 2007
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Micron’s best friend – with precision for precision
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The run-out accuracy – an important factor in machining in order to achieve precise machining results.
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01.09.2007 -
Developers and designers have probably been dealing with the topic of roundness ever since the wheel was invented. Long gone are the times when poor run-out could be detected with the naked eye. Modern machining focuses on attaining run-out accuracy values in the range of thousandths of a millimeter. This topic may be old, but it is still relevant when it comes to the increasing demands for accuracy and the rising performance capability of modern machining centers. More and more often, micron is the decisive factor in determining whether a workpiece really is manufactured with precision. Not only this: Run-out, balancing grade and material behavior at different rotational speeds greatly affect machining costs because these factors decisively influence tool lives and even the service life of the machine spindle itself.
Whether machines are used in drilling, grinding, milling or turning – a shaft rotates around its own axis in all of these machines. Whether it is the workpiece or the tool that rotates is not important at first. In both cases, run-out is extremely important in maintaining the workpiece dimensions and tolerances as well as for protecting the machine and tool.
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First, to the theory: What is run-out?
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Example for the definition of run-out accuracy (see text)
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Technically, run-out is a run-out tolerance within the group of positional tolerances. In the example shown, the concentricity deviation must not exceed t = 0.003 mm (= 3 microns) in any measuring plane perpendicular to reference axis A during a rotation of the shaft around the axis. The undesired offset of two rotationally symmetrical shape elements is called out-of-balance or eccentricity. Its maximum permissible value can be indicated as the run-out tolerance on a technical drawing (refer to the run-out example).
People are most likely to be familiar with out-of-balance in daily life from their cars. If a tire is changed improperly or is subject to a unilateral load, the wheels imbalance will produce out-of-balance. A clear sign of this is a shaking steering wheel at a certain speed or, in more severe cases, vibrations that amplify until they rattle the entire car. However, eccentricity can sometimes be useful as well: in the cam shaft and crankshaft in engine construction or in the eccentric press in machine construction.
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Run-out determines the precision of workpieces
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Of course, many factors play a role in the machining process. The run-out accuracy of the machine spindle and the cutting tool are of crucial importance for the cutting performance. The toolholder is generally the connecting link. If the tool in the toolholder is not centered with respect to the toolholder’s center axis, inaccuracies could arise and the required dimensions on the workpiece might not be achieved. Especially in the production of precision products, toolholders with very high run-out accuracy and repeat accuracy are thus required for optimal quality.
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How is the run-out of a toolholder measured?
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static measuring procedure
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Run-out can be measured in two ways: In the static measuring procedure, the toolholder is accommodated in a device. A dial gauge on the device is used to measure the run-out. For this purpose, a test shaft is clamped and the shaft deflection is measured at a specific projecting length. The projecting length of the shaft is generally 2.5 x D. The toolholder is manually turned in the device.
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dynamic measuring procedure
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In the dynamic measuring procedure, the values are measured directly on the machine. This procedure simulates many influencing factors that occur during the machining process. The great advantage here is that the procedure takes the run-out characteristics of spindle, toolholder and tool into account. The results of this measurement apply only to this specific combination of machine, toolholder and tool. They cannot be generalized. If excellent values are determined on a machine for a combination of toolholder and cutting tool, the results can change significantly when one of the parameters is modified.
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Run-out has a decisive influence on tool wear
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In order to prevail in the competitive market, it is advisable to consider the investement costs over the entire tool life in addition to the quality requirements when selecting toolholder systems. This is the only way to achieve competitive prices in the long run.
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Out-of-balance leads to premature tool wear.
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In machining, the toolholder is the key interface between the machine spindle and the workpiece. The toolholder's run-out decisively influences how uniform the tool can enter the workpiece. If the run-out is poor, the tool performance will count. The VHM, CBN or PDK cutting edges used in modern tools are very sensitive to impact. These materials are also very hard, and they thus lack the toughness to compensate these impacts. The ever-increasing rotation speeds of up to 60,000 rpm achieved by modern machining centers additionally multiply the effects of all these factors. Micro-blowouts occur at the cutting edge, significantly reducing the tools’ service life. Especially if expensive tools are used, this can be a key factor in the process costs.
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The high run-out accuracy of SCHUNK precision toolholders ensures long tool life. This saves money in the long run.
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Tests comparing precision toolholders to conventional collet chucks demonstrate that the considerably better run-out can greatly extend the tool life when precision toolholders are used. Toolholders with high run-out accuracy ultimately save a lot of money despite their higher purchase price. In many applications, it is thus becoming increasingly worthwhile to consider the use of precision toolholders instead of conventional standard toolholders.
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Run-out protects the spindle
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Another cost factor, which is not obvious at first, is decisively influenced by the toolholders’ run-out: When machining is performed using toolholders with a low balancing grade or poor run-out, vibrations are transferred directly to the spindle bearings of the machine. Over time, constant vibrations cause premature wear on this expensive machine component and thereby lead to high costs and unnecessary machine failure.
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Quality details are decisive
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Inner values determine the true performance capability of a toolholder. With the TENDO hydraulic expansion toolholder, maximum quality requirements ensure excellent results
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SCHUNK employs many measures to refine its precision toolholders in order to maintain run-out accuracy values of less than 0.003 mm. This begins with the selection and treatment of the steel, because only excellent raw material and appropriate processing know-how can ensure lasting, uniform precision of the toolholder. SCHUNK pays great attention to achieving the best possible uniformity of all interfaces of the toolholder. This applies to both the contact areas between the toolholder and the spindle on the machine side and between the toolholder and the tool on the workpiece side. However, the highly uniform clamping of the tools in the shaft also plays a crucial role. The precision toolholders from SCHUNK are fine-balanced as standard for use on HSC machines. The balancing grade is G 2.5 at 25,000 rpm.
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With toolholders, just as with products in everyday life, all these quality characteristics can not be noticed at first glance. However, long-term use on the machine shows the real benefits. Decades of know-how in development and production, a pioneering spirit and ongoing development of mature products ensure SCHUNK’s leading role in the toolholding market. The precision toolholders from SCHUNK are manufactured in Lauffen according to the strictest quality directives – Made in Germany.
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Large selection of precision toolholder systems
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The TOTAL TOOLING program from SCHUNK includes several precision toolholding systems that all feature a decisive characteristic: maximum run-out accuracy of less than 0.003 mm.
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TENDO hydraulic expansion toolholder
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The TENDO hydraulic expansion toolholder is a universal toolholder for precision machining. The clamping force is hydraulically applied to the tool shaft. In addition to the high run-out and repeat accuracy of 3 microns or less, it offers a perfect balancing grade and excellent vibration dampening characteristics. The set-up time couldn’t be shorter: tools can be exchanged or readjusted in just a few steps using nothing more than an allen wrench – generating unique added value in particular for smaller companies.
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TRIBOS Polygonal Clamping Technology
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TRIBOS Polygonal Clamping Technology is another patented development by SCHUNK. In various sizes and versions , it covers a very broad range of applications. TRIBOS allows everything from micro-machining with shank diameters as small as 0.3 mm up to rough machining applications. The applications range from the automotive industry to precision machining and the medical industry. For the TRIBOS system the run-out accuracy is less or equal than0.003 mm as well.
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CELSIO heat shrinking technology also masters more specialized tasks in poorly accessible workpiece areas requiring small interfering contours. The comprehensive program includes all commonly used sizes of heat shrink toolholders.
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12.2007
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11.2007
Patented and very impressive: the SCHUNK multi-tooth guide
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10.2007
Micro-handling
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09.2007
Run-out Accuracy of Toolholders
Micron’s best friend – with precision for precision
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08.2007
Service Robotics
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07.2007
Tool Clamping
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06.2007
Hygienic Design
High-tech creations for culinary delights
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05.2007
Reduction of set-up costs with the quick-change pallet systems
Savings potential of up to 90 percent
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04.2007
Minimum quantity lubrication - MQS
- For minimum costs and maximum protection of the environment
A possible solution in searching for the optimum lubrication system
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In Focus - 2013
In Focus - Archivo 2012
In Focus - Archivo 2011
In Focus - Archivo 2010
In Focus - Archivo 2009
In Focus - Archivo 2008
In Focus - Archivo 2007
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