1、BRITISH STANDARD BS3800-3: 1990 General tests for machine tools Part 3: Method of testing performance of machines operating under loaded conditions in respect of thermal distortionBS3800-3:1990 This British Standard, having been prepared under the directionof the Machine, Engineers and Hand Tools St
2、andards Policy Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 28 September1990 BSI03-1999 The following BSI references relate to work on this standard: Committee reference MTE/1 Draft for comment88/74114 DC ISBN 0 580 18141 3 Committees responsible for this Br
3、itish Standard The preparation of this British Standard was entrusted by the Machine, Engineers and Hand Tools Standards Policy Committee (MTE/-) to Technical Committee MTE/1, upon which the following bodies were represented: Advanced Manufacturing Technology Research Institute Cranfield Institute o
4、f Technology Department of Trade and Industry (Mechanical Engineering and Manufacturing Technology Division) Health and Safety Executive Machine Tool Trades Association Ministry of Defence Society of British Aerospace Companies Limited The following were also represented in the drafting of the stand
5、ard, through subcommittees and panels: Coopted members Amendments issued since publication Amd. No. Date of issue CommentsBS3800-3:1990 BSI 03-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Test conditions 1 3 Thermal distortion of structure 1 4 Thermal drift
6、of axis drives 2 Figure 1 Typical set-up for measurement of thermal distortion of the structure of a vertical machining centre 4 Figure 2 Typical set-up for measurement of thermal distortion of the structure of a slant bed lathe 5 Figure 3 Temperature and deflection versus time for warm-up of the st
7、ructure of a machining centre, 4000 r/min spindle speed 6 Figure 4 Typical set-up for measurement of thermal drift of the x-axis drive of a machining centre 7 Figure 5 Typical set-up for measurement of thermal drift of the z-axis drive of a CNC lathe 7 Figure 6 Positional error plot (example 1) 8 Fi
8、gure 7 Positional error plot (example 2) 9 Figure 8 Drift of end point of axis during warm-up and cool-down for a typical CNC lathe 10 Figure 9 Positional error plot (example 3) 11 Figure 10 Positional error plot (example 4) 12 Publications referred to Inside back coverBS3800-3:1990 ii BSI 03-1999 F
9、oreword This Part of BS3800 has been prepared under the direction of the Machine, Engineers and Hand Tools Standards Policy Committee. It is based on a proposal from the Advanced Manufacturing and Technology Research Institute (AMTRI). This British Standard describes methods of testing machine tools
10、 to determine the influence of thermally induced error on workpiece accuracy. The objective of the test is to supplement the information obtained from tests for geometric accuracy in BS3800-1 and for positioning accuracy and repeatability in BS4656-16 (which will be revised and published as BS3800-2
11、). The tests specified are all instrumental tests and do not depend upon measurements of a machined workpiece. Instrumental tests have the ability to quantify the contribution made to the total machining accuracy from a particular source of error. Other Parts of BS3800 will deal with statistical met
12、hods, vibration and noise. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pag
13、es This document comprises a front cover, an inside front cover, pagesi andii, pages1 to12, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.BS38
14、00-3:1990 BSI 03-1999 1 1 Scope This Part of BS3800 gives methods for assessing the contribution to workpiece inaccuracy arising from the thermal behaviour of the machine, due to internal heat sources, in respect of: a) distortion of the structure; and b) drift of the axis drives. The tests for ther
15、mal distortion of the structure are applicable to any machine which incorporates a rotating spindle or spindles supporting the tool or the workpiece. The tests are designed to establish the relative displacements occurring between the tool and workpiece sides of the structure as a result of thermal
16、expansion or contraction of key structural elements. The tests for thermal drift of the axis drives are applicable to numerically controlled (NC) machines only and are designed to quantify the effects on positioning accuracy and repeatability of thermal expansion and contraction of the axis drives.
17、2 Test conditions 2.1 Environment Where the temperature of the environment can be controlled, it shall be set to20 C. NOTEThe tests can be carried out at any other ambient temperature. The ambient temperature shall be continuously recorded during the test, the variation not exceeding2 C, although so
18、me machines may require closer tolerance. The machine including all of its services, e.g.hydraulics, shall be completely shut down before the start of the test. Both the machine and the measuring instruments shall have been in the test environment long enough, preferably overnight, to be in a therma
19、lly stable condition before testing. They shall be protected from draughts and external radiations such as those from overhead heaters, or sunlight, etc. If the measuring instrument incorporates compensations for environmental factors such as air temperature and pressure, then these shall be used. H
20、owever, compensations for machine or position feedback temperature shall not be used. If the measuring instrument incorporates facilities by which the measured data can be normalized to the case of that in which the machine or position feedback system is at20 C, then these facilities shall not be us
21、ed. 2.2 Machine to be tested The machine shall be completely assembled and fully operational in accordance with the manufacturers instructions. All necessary levelling operations, geometric alignment tests and functional checks shall be completed satisfactorily before starting the tests. All tests s
22、hall be carried out with the machine in the unloaded condition. Where a machine involves rotating both the workpiece and tool on separate spindles, the test shall be carried out for each spindle with respect to a common fixed point. Where the machine incorporates compensation for thermal errors, the
23、 machine compensation system shall be active. 2.3 Sequence of testing The order of carrying out the two types of test is not significant, provided that both tests commence with the machine thermally stable at a steady ambient temperature. 3 Thermal distortion of structure 3.1 Instrumentation and equ
24、ipment 3.1.1 Calibration. The calibration of all instrumentation used shall be traceable to a national reference standard. 3.1.2 Instrumentation. The following instrumentation shall be provided: a) non-contacting displacement transducer equipment, five channels minimum, with linear output proportion
25、al to measured deflection; b) thermocouple, resistance or semiconductor thermometer with an output proportional to temperature. 3.1.3 Test equipment 3.1.3.1 Data acquisition equipment, such as a multi-channel chart recorder which continuously monitors and plots all channels, or a computer-based syst
26、em in which all channels are sampled at least one per minute, and data is stored for subsequent analysis. 3.1.3.2 Test-mandrel, preferably about50mm in diameter and150mm in length and made in a low-expansion alloy material, e.g.invar, shall be attached to the spindle of the machine. The test-mandrel
27、 shall be set so as to minimize run-out. NOTEWhere significant, the differential expansion of the collet that holds the mandrel may need to be taken into account. 3.1.3.3 Fixture in which to mount the displacement transducers, constructed in a low-expansion alloy material, e.g.invar.BS3800-3:1990 2
28、BSI 03-1999 3.2 Test procedure Figure 1 and Figure 2 show typical measurement set-ups for a vertical machining centre and a lathe, respectively. The fixture in which the displacement transducers are mounted shall be securely fixed to the non-rotating workholding or toolholding zone of the machine, s
29、o as to be able to monitor: a) the relative displacements occurring between the tool and work sides of the machine in the three orthoganol axes parallel to the axes of travel of the machine; b) tilt or rotation in the two axes normal to the spindle axis. The temperature of the machine structure, as
30、close as possible to the front spindle bearing housing, shall be continuously monitored. The test shall commence by running the spindle at approximately0.7 maximum speed. All transducer outputs shall be monitored until the deflection change, over any20min period, in all axes has reduced to less than
31、15% of the maximum deflection registered over the first20min of the test, or until a period of4h has elapsed, whichever occurs first. The machine shall then be allowed to cool down, for a minimum period of1h, whilst monitoring of the transducers is continued. Plot the results in graphs of deflection
32、/temperature versus time, as shown in the example given in Figure 3. 3.3 Interpretation of results The effect of warming up the machine structure on the ability of the machine to maintain the position of the tool relative to the workpiece, can be directly assessed from the deflections versus time gr
33、aphs. 4 Thermal drift of axis drives NOTEThis test is carried out on computerized numerically controlled (CNC) machines only. 4.1 Instrumentation The calibration of all instrumentation used shall be traceable to national reference standards. A laser interferometer system with linear measurement opti
34、cs, automatic compensation unit or barometer and thermometer, the latter two of uncertainty not exceeding0.5mmHg 1)and0.5 C respectively, shall be provided. 4.2 Test equipment 4.2.1 Computer system, for data acquisition, storage and analysis linked to the laser interferometer system. NOTEManual data
35、 processing is permissible if a computer system is not available. 4.3 Test procedure The laser reflector and remote interferometer shall be set so as to measure the distance traversed by the moving part of the axis under test. Examples of typical test set-ups are shown in Figure 4 and Figure 5. Test
36、 positions shall be selected along the axis under test in accordance with BS4656-16. These are the command positions. To commence, the axis under test shall be moved to home position in the direction in which the traverse to the test positions is to take place. The measuring system shall then be res
37、et, i.e.set to zero. An initial test sequence involving a test of the positioning accuracy and repeatability of the axis shall be performed in accordance with the procedures specified in BS4656-16. This test sequence shall be performed as quickly as possible. The axis shall then be driven at rapid t
38、raverse rate between the two end points, i.e.the positions at each extreme of programmable travel, dwelling at each end point just long enough to record the error, i.e.actual position minus programmed position. The test shall proceed in this manner until the change in the error over any5min period a
39、t both points has reduced to less than15% of the maximum error change over the first5min of the test, or until a period of1h has elapsed, whichever occurs first. The initial test sequence described above shall then be repeated. Finally, the axis shall be positioned at that end of the traverse at whi
40、ch the largest error during warm-up was recorded and shall be left at that position for a minimum of1h, during which the error is recorded at1min intervals. The data corresponding to those parts of the test involving the full accuracy and repeatability tests at the five positions along the axis shal
41、l be processed and plotted in accordance with BS4656-16. Examples of the plots showing the results of the accuracy and repeatability tests before and after warm-up are shown in Figure 6 and Figure 7,and Figure 9 and Figure 10 respectively. The data corresponding to the error at the end points, colle
42、cted during the warm-up and cool-down process, shall be plotted in the form of error versus time plots, an example of which is shown in Figure 8. 1) 1mmHg=133.322 PaBS3800-3:1990 BSI 03-1999 3 4.4 Interpretation of results The effect of warming up the axis drives on the accuracy and repeatability ch
43、aracteristics of the machine is indicated by the difference between the results of the two full accuracy and repeatability tests performed. The results of these tests can be directly compared with the results of the tests carried out to assess the basic positioning characteristics of the machine in
44、accordance with BS4656-16. In particular, the results of these tests can be used to assess the effect of warm-up on the repeatability of positioning of an axis. The results showing the drift in position at the two end points can be used to assess the effects of warm-up on the positioning accuracy of
45、 the axis. BS3800-3:1990 4 BSI 03-1999 Figure 1 Typical set-up for measurement of thermal distortion of the structure of a vertical machining centreBS 3800-3:1990 BSI 03-1999 5 Figure 2 Typical set-up for measurement of thermal distortion of the structure of a slant bed latheBS3800-3:1990 6 BSI 03-1
46、999 Figure 3 Temperature and deflection versus time for warm-up of the structure of a machining centre,4000 r/min spindle speedBS3800-3:1990 BSI 03-1999 7 Figure 4 Typical set-up for measurement of thermal drift of the x-axis drive of a machining centre Figure 5 Typical set-up for measurement of the
47、rmal drift of the z-axis drive of a CNC latheBS3800-3:1990 8 BSI 03-1999 Figure 6 Positional error plot (example 1)BS3800-3:1990 BSI 03-1999 9 Figure 7 Positional error plot (example 2)BS3800-3:1990 10 BSI 03-1999 Figure 8 Drift of end point of axis during warm-up and cool-down for a typical CNC lat
48、heBS3800-3:1990 BSI 03-1999 11 Figure 9 Positional error plot (example 3)BS3800-3:1990 12 BSI 03-1999 Figure 10 Positional error plot (example 4)BS3800-3:1990 BSI 03-1999 Publications referred to BS3800, General tests for machine tools. BS3800-1, Code of practice for testing geometric accuracy of ma
49、chines operating under no load or finishing conditions. BS4656, Accuracy of machine tools and methods of test. BS4656-16, Methods for determination of accuracy and repeatability of positioning of numerically controlled machine tools. BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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