- Email: [email protected]
Automated general tolerances for dimensions and features without tolerance indications
Joumal of
Materials Processh g
ELSEVIER
Journal of Materials Processing Technology 68 (1q97~ 251--256
Technobgy
Automated general tolerances for dimensions and features wkhout tolerance indications S.M. Darwish * Mechanical Engineering Departmet~t, King Saud Universit.v, P.O. Box 800, Riyadh 11421, Saudi Arabia Received 26 November 1995
Abstract
The intense global competition in the manufacturing of high quality products has led production engineers to consider tolerances as the key parameter in the achieving of their goal. Thus, all features on component parts should have a toleranced size and geometrical shape, and nothing should be left to judgement in the workshop or in the inspection department. In the present work, the process of specifying general tolerances for dimensions and features left without individual tolerance indications has been automated. The work is designed to suit any system of units; that used here is the ISO standard. A test sample based on ISO is given also. ~_~1997 Elsevier Science S.A. Keywords: CAD/CAM; Straightness; Flatness; Circularity; Symmetry: Run-out
1. Introduction
To maintain its competititivness towards other manufacturing techniques, any industry must be able to combine high demands on mechanical properties with maintained or even improved close tolerances of its products, keeping in mind that tight tolerances result in excessive process cost, whilst loose tolerances may lead to increased waste and assembly problems [1-15]. Special attention has been directed towards the analysis of dimensioning and tolerancing in manufacturing to ensure product quality and economy of production. In the last two decades, much work has been done in the area of tolerance techniques such as the dimensional tolerance chain technique, statistical and probabilistic methods in tolerancing, geometrical modeling in tolerances, and the modeling of geometrical tolerances with processing inaccuracy [5-15]. The implications of geometric and dimensional tolerances on the mechanical behavior of assemblies has been addressed also [12-18]. Recently, the expert system approach has been implemented to generate alternative process plans for mechanical parts, with their tolerance requirements fulfilled [16-20]. * Fax: + 966 ! 4674254. 0924-0136/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved.
PII S 0 9 2 4 - 0 1 3 6 ( 9 6 ) 0 0 0 2 8 - 3
Obviously, all features or component parts always have a size and a geometrical shape. In order to make sure that the elements of size and geometry of all features are controlled, tolerancing should be complete and nothing should be left to judgement in the workshop or in the inspection department [21,22]. To simplify this task, ISO produced a standard which specifies general tolerances for features and dimensions left without tolerance indications. This is intended to help designers to save time by avoiding detailed tolerance calculations, avoiding arguments between the buyer and the supplier since, in this respect, the drawing is complete~ and helping production planners to concentrate on those dimensions that have individually-indit,ated tolerances and require special attention in production. For dimensions between an unfinished and finished surfaces, e.g. of cast or forged parts, for which no individual tolerance is indicated directly, the larger of the two tolerances in question applies [21,22]. Computerization of the design process can produce quick, accurate and impressive designs. Automated tolerance analysis is one of the most critical problems for computer-aided process planning systems to be applied in the real manufacturing environment [23,24]. Thus, the aim of the present work is to automate the process
S,M. Darwish/Journal of Materials t)rocessing Technology 68 (1997) 251-256
252
GeneralTokmmcesForOime~sion~& "1 FeM~nuW~hou~To~in~ ~ i m ~ (1) LI~ewm4 ~IIU~UOImnsI~,~i 2) General~ T~e~anc~l O) f
~
~-
~
II
6') =
I
c3
I
T--~
-H -H -H -H
I
2
q-I -t-t +l +1
Fig. 1. T h e p r o g r a m flow-chart.
,'q.~ -H -H -H -H
of specifying general tolerances for dimensions and features left without tolerance indications.
2. A u t o m a t e d
O
general tolerances
The present computer-assisted program for specifying general tolerances for dimensions and features without tolerance indications has been designed for use on microcomputers [21,22]. The program was designed as a menu-driven program so that it will be flexible and easy to use. The specification of tolerances is accomplished through the interaction between the user and the program. The program is written in BASIC computer language for easy transfer between computers. The program starts by displaying its main menu, which offers the user two choices, these being whether to specify general dimensional tolerances or general geometrical tolerances. The system flow chart demonstrating the selection menus is presented in Fig. 1. Four sub-routines are involved in the program, a detailed description of each being given below.
-H -H -H -H E E e-
-H -H -H -H v~
+l +l +l +l
o
+I -H -t-I -H
2.1. Linear general dimensional tolerance sub-rout#Te This sub-routine deals with general tolerances for dimensions left without individual tolerance indications, the database of this sub-routine being used to supply the program with the necessary information. The general tolerances for linear dimensions are given in Tables 1 and 2 where four classes of tolerances are specified for linear and angular dimensions [21,22], these being fine, medium, coarse, and very coarse.
tz~
• 0 ._~
m
¢'q
"H -H -H I
S.M. Darwish/ Journal o/ Materkds Processing Technoh,gy 68 (1997) 251-256 Table 2 Permissible deviations for broken edges (external radii and chamfer heights expressed as ram) Tolerance class
0.5 up to 3
Over 3 up ~o 6
Over 6
Fine Medium Coarse Very coarse
+0.2 _+0.2 +0.4 +0.4
+0.s _+0.5 +1 +1
+1 ~ i ±2 +2
253
2.3.2. Circularity The general tolerance on circularity is equa~ to the numerical value o f the diameter tolerance, but it should not be greater that this value.
2.3.3. Cylimh'icio' The cylindricity deviation comprises three c o m p o nents: circularity deviation (Table 6), straightness deviation a n d parallelism deviation o f opposite general lines (Table 4).
2.2. General tolerances for angular dimensions
2.4. Geometrical tolerances fi~r related.features
T h e s e c o n t r o l only the general orientation o f line elements o f surfaces and n o t their f o r m deviations. T h e permissible deviations o f a n g u l a r dimensions are given in T a b l e 3.
2.4,1. Parallelism
T h e s e are all specified in three tolerance classes: fine, m e d i u m , a n d coarse.
T h e general tolerance on parallelism is equal to the nmnerical value o f the size tolerance or the flatness/ straightness tolerance, whichever is the greater. T h u s , the user is interrogated a b o u t size tolerance, which is then c o m p a r e d with flatness/straightness tolerances (see Table 4).
2.3. I. So'aighmess and flatness
2.4.2. Pe~pendiculariO'
T h e general tolerances o n straightness a n d flatness are given in Table 4. T h e selection f r o m T a b l e ! is b a s e d o n the case o f straightness o n the length o f the c o r r e s p o n d i n g line, a n d in the case o f flatness o n the longer lateral length o f the surface, o r the d i a m e t e r o f a circular surface.
T h e general tolerances on perpendicularity are given in T a b l e 5. It is w o r t h m e n t i o n i n g t h a t the attention o f the user is d r a w n to the requirement that the longer o f the two sides f o r m i n g a right angle shall be taken as the d a t u m : if the sides are o f equal length then either m a y be taken as the d a t u m .
2.3. Geometrical tolerances .['or s#lgle features
Table 3 Permissible deviations of angular dimensions (length of the shorter side of the angle expressed as mm) Tolerance class
Up to 10
Over 10 up to 50
Over 5t) up to 120
Over 120 up to 400
Over 400
Fine
+ 1°
+0030 '
+0°20'
-+0°10'
+-0°5'
Medium Coarse
+_.1°30'
+ 1°
+ 0030 '
+ 0 ° 15'
+ 0 ° 10'
Very coarse
+. 3°
+ 2°
+ 1o
+ 0°30,
+ 0°20'
Table 4 General tolerances on straightness and flatness (expressed as mm) Tolerance class
Up to 10
Over 10 up to 30
Over 30 up to 100
Over 100 up to 300
Over 300 up to 1000
Over 1000 up to 2000
Fine Medium Coarse
0.02 0.05 0.1
0.05 0. l 0.2
0. i 0.2 0.4
0.2 0.4 0.8
0.3 0.6 i .2
0.4 0.8 1.5
Table 5 General tolerances on perpendicularity (e,:p~essed as mm) Tolerance class
Up to 100
Owr 100 up to 300
Over 300 up to 1000
Over 1000 up to 3000 0.5
Fine
0.2
0.3
0.4
Medium
0.4
0.6
0.8
I
Coarse
0.6
!
1.5
2
S,M. Darwish/ Journal of Materials Processing Technology 68 (1997) 251-256
254 Table 6 General tolerances on symmetry
Tolerance class
Up to 100
Over 100 up to 300
Over 3•'3 up to 1000
Over 1000 up to 3000
Fine Medium V. coarse
0.5 0.6 0.6
0.5 0.6 1
0.5 0.8 1.5
0.5 I 2
2.4.3. Symmetry The general tolerances on symmetry are given in Table 6. The program draws the attention of the user to the requirement that the longer side of the two features shall be taken as the datum: if the features are of equal length, then either may be taken as the datum. The program also draws the attention of the user to the requirement that general tolerances on symmetry apply, where one of the following conditions is to be met: (i) at least one of the features has a median plane (see Fig. 2), or (ii) the axes of the two features are perpendicular to each other (see Fig. 3). 2.4.4. Coaxiality The deviation in coaxiality may be taken, in an extreme case, to be as great as the tolerance value for circular radial run-out (see Table 7). 2.4.5. Circular run-out The general tolerances on circular run-out (radial, axial) are given in Table 7. Here the bearing surfaces shall be taken as the datum, otherwise, the longer of the two features shall be taken as the datum: if the features are of equal nominal length, then either may be taken as the datum.
3. Sample design The automated general tolerances for dimensions and features left without individual tolerance indications include two groups of menus, the first of which is concerned with the general dimensional tolerances, whilst the second is concerned with general geometrical tolerances. The menus involved throughout the general dimensional tolerances are those of linear and angular dimensions, whilst the menus involved throughout the general geometrical tolerances are those of cylindricity, circularity, straightness, flatness, circular run-out, coaxiality, symmetry, perpendicularity, and parallelism. The program has been validated by specifying general tolerances for the dimensions and features of an example set by ISO [22]. Fig. 4 demonstrates the test sample before allocating the general tolerances, the program being found to be in full agreement with the ISO test example. The interactive steps between the user and the program are shown in Appendix A, whilst Fig. 5 shows the test sample after allocating the general tolerances.
4. Conclusions Automated general tolerancing for dimensions and features without individual tolerance it~dications can
I-7I"1
Table 7 General tolerances on circular run-out Tolerance class
Circular run-out tolerances
Fine Mediur.~ Coarse
0. i 0.2 0.5
(a) Datum: loag~funu~ ( / 2 ) ~
D~mens~n8,nnVP, tmelers
72w5
Fig. 2. Where the two features have a median plane.
I ~30~2X/,5" 413HI2(~J)
---N (b) Datum: lons,n're.mm (/2) Fig. 3. Where the two features are perpendicular to each other.
3
:~l~0.1~lAI a ~1 Toletaa~,~ ISO 8015 ~ 180 2?~-mH
Fig. 4. Sample before applying general tolerances (dimensions: mm)
255
S.M. Darwish ,' Join'rod ~" Materials Prm'essing Teclmology 68 (1997) 251 256
Appendix lB. Ty#caJ e×amp|e of specifying ge~era~ geometrical te]erances )
so~'~}
r-== RUN
L/'LO,~)j
~@). ~s'(;'~ ~o~,
.
.
* "
* ]l- F O R L I N E A R A N D A N G U L A R D I M E N S I O N S . * 2- F O R G E O M E T R I C A L FEATURES.
* *
*
=
"---[÷l"o.' @l,~
~rT,:.. ~ .
* C O M P U T E R A][DED TOLERANC~NG F O R D I M E N S I O N S & * F E A T U R E S V / I T H O U T INDIVIDUAL T O L E R A N C E INDICATION
.
.
E N T E R Y O U R CHOICE? 2
o.~
Fig. 5. Sample after applying general tolerances.
produce quick, accurate, and consistent tolerance nomination, which is very critical for computer aided process planning. It also helps to avoid arguments between the supplier and the buyer of manufactured goods.
Appendix A. Typical example of specifying genera~ dimensional tolerances RUN * COMPL~FER A I D E D T O L E R A N C I N G F O R D I M E S I O N S & * FEATURES WITHOUT INDIVIDUAL TOLERANCE INDICATIONS
* *
* 1- F O R L I N E A R A N D A N G U L A R D I M E N S I O N S . * 2- F O R G E O M E T R I C A L F E A T U R E S .
* *
* GEOMETR~rCAL T O L E R A N C E S F O R F E A T U R E S W I T H O U T * 3"OLERANCE I N D I C A T I O N S
* *
* I- S T R A I G H T N E S S & F L A T N E S S * 2- CIRCULARITY. * ' ~ - CYLINDRICITY. * 4- PARALLELISM.
5678-
* * * *
*' 9- D R A W I N G INDICATION.
10- M A I N M E N U
PERPENDICULARITY S ~ Y COAXIALFI~. CIRCULAR RUN-OUT
*
E N T E R Y O U R CHOICE? 6
*
GENERAL TOLERANCES ON SYMMETRY
*
T O L E R A N C E CLASSES:
* * *
I . F I N E (H) 2- ~ D I I . J M (K) 3- C O A R S E ft.)
* '* *
* *
* NOTES: * 1- Applied only when one of the two features has a medtan plane. c 2- A n d t h e a x e s o f t h e t w o f e a m r e s a r e p e r l m n d i c u J a r t o e a c h o t h e r .
*
E N T E R N O M I N A L L E N G T H O F THE S H O R T E R F E A T U R E (MM)? 50 E N T E R T O L E R A N C E CLASS? 1 GEN~::RAL T O L E R A N C E O N S Y M M E T R Y = 5
MMS
F N T E R B A S I C SIZE (0,5 - 4000 M M S ) ? 8 T H E P E R M I S S I B L E D E V I A T I O N = (+/-)
.1
MMS
E N T E R B A S I C SIZE (0.5 - 4000 M M S ) ? 6 T H E P E R M I S S I B L E D E V I A T I O N = (+/-)
1
MMS
E N T E R YOLrK CHOICE? ! * T O L E R A N C E S F O R LINEAR A N D A N G U L A R D I M E N S I O N S
* * * *
J234-
L I N E A R DIMENSIONS (except broken edges). B R O K E N EDGES. A N G U L A R D I M E NSIONS. RETURN TO PREVIOUS MENU.
*
* * * *
References
E N T E R Y O U R CHOICE ?7 1 * P R E M I S S I B L E D E V I A T I O N S FOR L I N E A R D I M E N S I O N S
*
* TOLERANCE CLASSES: * 1- F I N E ( 0 * 3- C O A R S E (c)
2- M E D I U M (ra) 4- V E R Y C O A R S E (v)
* *
* 5- R E T U R N T O P R E V I O U S M E N U
*
ENTER NO OF DIMENSIONS WITHOUT TOLERANCINGW 5 ENTER YOUR CHOICE ~ 2 E N T E R B A S I C SIZE (0.5-4000 M M S ) ? 72.5 T H E P E R M I S S I B L E D E D V I A T I O N = (+/-) .3
MMS
E N T E R Y O U R CHOICE .9? 2 E N T E R BASIC SIZE (0.5-4000 MMS)? 50 PERMISSIBLE DEVIATION = (+/-)
.3
MMS
E N T E R BASIC SIZE (0.5 - 4000 MMS)? 30 T I l E P E R M I S S I B L E D E V I A T I O N = (+1-)
.I
MMS
APPROPRIATE TOLERANCE CLASS? 1 E N T E R R E L A T E D L E N G T H (MMS)? 45 T H E STRAIGHTNESS ~FLATNE3S TOLERANCE =
.I
MMS
[1] Ulf Engstrom, Caroline Lindberg, Factors influencing dimensional tolerances of high strength PM steels, Sintering Advances in Powder Metallurgy U.S.A. 3 (1992) 317 328. [2] M. Beghini, L. Bertini, E. Vitale, Shrink stress density functions in conical threaded connections as a dimensional tolerances, in: Materials Engineering Proc. Int. Offshore Mechanics and Arctic Engineering, ASME Symposium, New York, vol. 3, 1992, pp. 383- 390. [3] H.C. Zhang, M.E. Huq, Tolerancing techniques: The state-ofthe-art, Int. J. Prod. Res. 30 (9) (1992) 211 213. [4] Delvecchio, N Joseph, A. Soom, Tolerances and available relative motions in bolted connections, Adv. Des. Automat. ASME, Des. Eng. Div. 32 (1991) 177-183. [5] Hong, et al., Computational geometry approach to minimum zero evaluation of straightness, J. Chin. Inst. Eng. 14 i5j (1901) 463 -470. [6] C. Doydum, N. Perreira, Method for selecting dimensions, tolerances and precision for alignment, Int. J. Prod. Res. 29 (51 (1991) 103 - 105.
256
$.M. Darwish/ Journal of Materials Processing Technology 68 (1997) 251-256
[7] Tomiharu Matsushita, Improvement of equipment for close-tolerance forging and extrusion in Japan, J. Mater. Process. TechnoL 22 (3) (1990) 223-238. [8] P. Os~wald, M. Blake, Estimating cost associated wi,m dimensional tolerance, Manuf. Rev. 2 (4) (1989) 277-282. [9] P. Skoglind, Tolerance for P/M cylinder liners, Cahiers d'lnformarion Techniques--Revue de Metallurgie (in English) 86 (1989) 87-92. [10] P. Skoglund, Tolerances for P/M cylinder liners, Met. Powder Rep, 44 (5) (ie;89). [11] P. Gupta, On the geometrical imperfections in cylindrical roller beatings, ASME Tribology Conf. U.S.A., 1987. [12] Ulf Engstrom, Glued powder mixes for improved tolerance control, Verlag Schmid Gmbh Freiburg I (1986) (in German). [13] J. Tengzelius, Ulf Engstrom, Means to improve the dimensional tolerances of P/M steel components, in: Modern Development in Powder Metallurgy, vol. 17, Metal Powder Industries Federation, U.S.A., 1985, pp. 743-765. [14] Joshua U. Turner, New methods for tolerance analysis in solid modelling, IEEE (1988) 306-314. [15] Ernest C. Bernhardt, Computer modeling predicts tolerances of molded parts, Plast. Eng. 46 (10) (1990).
[16] F. Etesami, Mathematical model for geometric tolerances, J. Mech. Des., Trans. ASME 11 (1993) 81-86. [17] G. Abdou, R. Cheng, TVCAPP, Tolerance verification in computer-aided process planning, Int. J. Prod. Res. 31 <1993) 39-41. [18] J. Mei, C. Hong, Tolerance analysis for automated setup selection in CAPP, ASME Prod. Eng. Div. (1992) 211-220. [19] M. Porchet, G. Zhang, incorporating geometrical tolerances and processing inaccuracy into dimensioning and tolerancing, Adv. Des. Automat. 44 (1992) 151-156. [20] R. Weill, Integrating dimensioning and tolerances in computer aided process planning, Robotics Computer-Integrated Manuf. 4 (2) (1985) 41-48. [21] ISO 2768-1, General Tolerances--part h Tolerances for Linear and Angular Dimensions without Individual Tolerance Indications, 1989. [22] ISO 2768-2, General Tolerances--part 2: Geometrical Tolerances for Features without Individual Tolerance Indications, 1989. [23] S. Choi, T. Dean, Computer aided design of die block layouts, Int. J. Mach. Tools Manuf. (1987). [24] B. Tong, D. Walton, A computer design aid for internal spur and helical gears, Int. J. Maeh Tools Manuf. (1987).
Materials Processh g
ELSEVIER
Journal of Materials Processing Technology 68 (1q97~ 251--256
Technobgy
Automated general tolerances for dimensions and features wkhout tolerance indications S.M. Darwish * Mechanical Engineering Departmet~t, King Saud Universit.v, P.O. Box 800, Riyadh 11421, Saudi Arabia Received 26 November 1995
Abstract
The intense global competition in the manufacturing of high quality products has led production engineers to consider tolerances as the key parameter in the achieving of their goal. Thus, all features on component parts should have a toleranced size and geometrical shape, and nothing should be left to judgement in the workshop or in the inspection department. In the present work, the process of specifying general tolerances for dimensions and features left without individual tolerance indications has been automated. The work is designed to suit any system of units; that used here is the ISO standard. A test sample based on ISO is given also. ~_~1997 Elsevier Science S.A. Keywords: CAD/CAM; Straightness; Flatness; Circularity; Symmetry: Run-out
1. Introduction
To maintain its competititivness towards other manufacturing techniques, any industry must be able to combine high demands on mechanical properties with maintained or even improved close tolerances of its products, keeping in mind that tight tolerances result in excessive process cost, whilst loose tolerances may lead to increased waste and assembly problems [1-15]. Special attention has been directed towards the analysis of dimensioning and tolerancing in manufacturing to ensure product quality and economy of production. In the last two decades, much work has been done in the area of tolerance techniques such as the dimensional tolerance chain technique, statistical and probabilistic methods in tolerancing, geometrical modeling in tolerances, and the modeling of geometrical tolerances with processing inaccuracy [5-15]. The implications of geometric and dimensional tolerances on the mechanical behavior of assemblies has been addressed also [12-18]. Recently, the expert system approach has been implemented to generate alternative process plans for mechanical parts, with their tolerance requirements fulfilled [16-20]. * Fax: + 966 ! 4674254. 0924-0136/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved.
PII S 0 9 2 4 - 0 1 3 6 ( 9 6 ) 0 0 0 2 8 - 3
Obviously, all features or component parts always have a size and a geometrical shape. In order to make sure that the elements of size and geometry of all features are controlled, tolerancing should be complete and nothing should be left to judgement in the workshop or in the inspection department [21,22]. To simplify this task, ISO produced a standard which specifies general tolerances for features and dimensions left without tolerance indications. This is intended to help designers to save time by avoiding detailed tolerance calculations, avoiding arguments between the buyer and the supplier since, in this respect, the drawing is complete~ and helping production planners to concentrate on those dimensions that have individually-indit,ated tolerances and require special attention in production. For dimensions between an unfinished and finished surfaces, e.g. of cast or forged parts, for which no individual tolerance is indicated directly, the larger of the two tolerances in question applies [21,22]. Computerization of the design process can produce quick, accurate and impressive designs. Automated tolerance analysis is one of the most critical problems for computer-aided process planning systems to be applied in the real manufacturing environment [23,24]. Thus, the aim of the present work is to automate the process
S,M. Darwish/Journal of Materials t)rocessing Technology 68 (1997) 251-256
252
GeneralTokmmcesForOime~sion~& "1 FeM~nuW~hou~To~in~ ~ i m ~ (1) LI~ewm4 ~IIU~UOImnsI~,~i 2) General~ T~e~anc~l O) f
~
~-
~
II
6') =
I
c3
I
T--~
-H -H -H -H
I
2
q-I -t-t +l +1
Fig. 1. T h e p r o g r a m flow-chart.
,'q.~ -H -H -H -H
of specifying general tolerances for dimensions and features left without tolerance indications.
2. A u t o m a t e d
O
general tolerances
The present computer-assisted program for specifying general tolerances for dimensions and features without tolerance indications has been designed for use on microcomputers [21,22]. The program was designed as a menu-driven program so that it will be flexible and easy to use. The specification of tolerances is accomplished through the interaction between the user and the program. The program is written in BASIC computer language for easy transfer between computers. The program starts by displaying its main menu, which offers the user two choices, these being whether to specify general dimensional tolerances or general geometrical tolerances. The system flow chart demonstrating the selection menus is presented in Fig. 1. Four sub-routines are involved in the program, a detailed description of each being given below.
-H -H -H -H E E e-
-H -H -H -H v~
+l +l +l +l
o
+I -H -t-I -H
2.1. Linear general dimensional tolerance sub-rout#Te This sub-routine deals with general tolerances for dimensions left without individual tolerance indications, the database of this sub-routine being used to supply the program with the necessary information. The general tolerances for linear dimensions are given in Tables 1 and 2 where four classes of tolerances are specified for linear and angular dimensions [21,22], these being fine, medium, coarse, and very coarse.
tz~
• 0 ._~
m
¢'q
"H -H -H I
S.M. Darwish/ Journal o/ Materkds Processing Technoh,gy 68 (1997) 251-256 Table 2 Permissible deviations for broken edges (external radii and chamfer heights expressed as ram) Tolerance class
0.5 up to 3
Over 3 up ~o 6
Over 6
Fine Medium Coarse Very coarse
+0.2 _+0.2 +0.4 +0.4
+0.s _+0.5 +1 +1
+1 ~ i ±2 +2
253
2.3.2. Circularity The general tolerance on circularity is equa~ to the numerical value o f the diameter tolerance, but it should not be greater that this value.
2.3.3. Cylimh'icio' The cylindricity deviation comprises three c o m p o nents: circularity deviation (Table 6), straightness deviation a n d parallelism deviation o f opposite general lines (Table 4).
2.2. General tolerances for angular dimensions
2.4. Geometrical tolerances fi~r related.features
T h e s e c o n t r o l only the general orientation o f line elements o f surfaces and n o t their f o r m deviations. T h e permissible deviations o f a n g u l a r dimensions are given in T a b l e 3.
2.4,1. Parallelism
T h e s e are all specified in three tolerance classes: fine, m e d i u m , a n d coarse.
T h e general tolerance on parallelism is equal to the nmnerical value o f the size tolerance or the flatness/ straightness tolerance, whichever is the greater. T h u s , the user is interrogated a b o u t size tolerance, which is then c o m p a r e d with flatness/straightness tolerances (see Table 4).
2.3. I. So'aighmess and flatness
2.4.2. Pe~pendiculariO'
T h e general tolerances o n straightness a n d flatness are given in Table 4. T h e selection f r o m T a b l e ! is b a s e d o n the case o f straightness o n the length o f the c o r r e s p o n d i n g line, a n d in the case o f flatness o n the longer lateral length o f the surface, o r the d i a m e t e r o f a circular surface.
T h e general tolerances on perpendicularity are given in T a b l e 5. It is w o r t h m e n t i o n i n g t h a t the attention o f the user is d r a w n to the requirement that the longer o f the two sides f o r m i n g a right angle shall be taken as the d a t u m : if the sides are o f equal length then either m a y be taken as the d a t u m .
2.3. Geometrical tolerances .['or s#lgle features
Table 3 Permissible deviations of angular dimensions (length of the shorter side of the angle expressed as mm) Tolerance class
Up to 10
Over 10 up to 50
Over 5t) up to 120
Over 120 up to 400
Over 400
Fine
+ 1°
+0030 '
+0°20'
-+0°10'
+-0°5'
Medium Coarse
+_.1°30'
+ 1°
+ 0030 '
+ 0 ° 15'
+ 0 ° 10'
Very coarse
+. 3°
+ 2°
+ 1o
+ 0°30,
+ 0°20'
Table 4 General tolerances on straightness and flatness (expressed as mm) Tolerance class
Up to 10
Over 10 up to 30
Over 30 up to 100
Over 100 up to 300
Over 300 up to 1000
Over 1000 up to 2000
Fine Medium Coarse
0.02 0.05 0.1
0.05 0. l 0.2
0. i 0.2 0.4
0.2 0.4 0.8
0.3 0.6 i .2
0.4 0.8 1.5
Table 5 General tolerances on perpendicularity (e,:p~essed as mm) Tolerance class
Up to 100
Owr 100 up to 300
Over 300 up to 1000
Over 1000 up to 3000 0.5
Fine
0.2
0.3
0.4
Medium
0.4
0.6
0.8
I
Coarse
0.6
!
1.5
2
S,M. Darwish/ Journal of Materials Processing Technology 68 (1997) 251-256
254 Table 6 General tolerances on symmetry
Tolerance class
Up to 100
Over 100 up to 300
Over 3•'3 up to 1000
Over 1000 up to 3000
Fine Medium V. coarse
0.5 0.6 0.6
0.5 0.6 1
0.5 0.8 1.5
0.5 I 2
2.4.3. Symmetry The general tolerances on symmetry are given in Table 6. The program draws the attention of the user to the requirement that the longer side of the two features shall be taken as the datum: if the features are of equal length, then either may be taken as the datum. The program also draws the attention of the user to the requirement that general tolerances on symmetry apply, where one of the following conditions is to be met: (i) at least one of the features has a median plane (see Fig. 2), or (ii) the axes of the two features are perpendicular to each other (see Fig. 3). 2.4.4. Coaxiality The deviation in coaxiality may be taken, in an extreme case, to be as great as the tolerance value for circular radial run-out (see Table 7). 2.4.5. Circular run-out The general tolerances on circular run-out (radial, axial) are given in Table 7. Here the bearing surfaces shall be taken as the datum, otherwise, the longer of the two features shall be taken as the datum: if the features are of equal nominal length, then either may be taken as the datum.
3. Sample design The automated general tolerances for dimensions and features left without individual tolerance indications include two groups of menus, the first of which is concerned with the general dimensional tolerances, whilst the second is concerned with general geometrical tolerances. The menus involved throughout the general dimensional tolerances are those of linear and angular dimensions, whilst the menus involved throughout the general geometrical tolerances are those of cylindricity, circularity, straightness, flatness, circular run-out, coaxiality, symmetry, perpendicularity, and parallelism. The program has been validated by specifying general tolerances for the dimensions and features of an example set by ISO [22]. Fig. 4 demonstrates the test sample before allocating the general tolerances, the program being found to be in full agreement with the ISO test example. The interactive steps between the user and the program are shown in Appendix A, whilst Fig. 5 shows the test sample after allocating the general tolerances.
4. Conclusions Automated general tolerancing for dimensions and features without individual tolerance it~dications can
I-7I"1
Table 7 General tolerances on circular run-out Tolerance class
Circular run-out tolerances
Fine Mediur.~ Coarse
0. i 0.2 0.5
(a) Datum: loag~funu~ ( / 2 ) ~
D~mens~n8,nnVP, tmelers
72w5
Fig. 2. Where the two features have a median plane.
I ~30~2X/,5" 413HI2(~J)
---N (b) Datum: lons,n're.mm (/2) Fig. 3. Where the two features are perpendicular to each other.
3
:~l~0.1~lAI a ~1 Toletaa~,~ ISO 8015 ~ 180 2?~-mH
Fig. 4. Sample before applying general tolerances (dimensions: mm)
255
S.M. Darwish ,' Join'rod ~" Materials Prm'essing Teclmology 68 (1997) 251 256
Appendix lB. Ty#caJ e×amp|e of specifying ge~era~ geometrical te]erances )
so~'~}
r-== RUN
L/'LO,~)j
~@). ~s'(;'~ ~o~,
.
.
* "
* ]l- F O R L I N E A R A N D A N G U L A R D I M E N S I O N S . * 2- F O R G E O M E T R I C A L FEATURES.
* *
*
=
"---[÷l"o.' @l,~
~rT,:.. ~ .
* C O M P U T E R A][DED TOLERANC~NG F O R D I M E N S I O N S & * F E A T U R E S V / I T H O U T INDIVIDUAL T O L E R A N C E INDICATION
.
.
E N T E R Y O U R CHOICE? 2
o.~
Fig. 5. Sample after applying general tolerances.
produce quick, accurate, and consistent tolerance nomination, which is very critical for computer aided process planning. It also helps to avoid arguments between the supplier and the buyer of manufactured goods.
Appendix A. Typical example of specifying genera~ dimensional tolerances RUN * COMPL~FER A I D E D T O L E R A N C I N G F O R D I M E S I O N S & * FEATURES WITHOUT INDIVIDUAL TOLERANCE INDICATIONS
* *
* 1- F O R L I N E A R A N D A N G U L A R D I M E N S I O N S . * 2- F O R G E O M E T R I C A L F E A T U R E S .
* *
* GEOMETR~rCAL T O L E R A N C E S F O R F E A T U R E S W I T H O U T * 3"OLERANCE I N D I C A T I O N S
* *
* I- S T R A I G H T N E S S & F L A T N E S S * 2- CIRCULARITY. * ' ~ - CYLINDRICITY. * 4- PARALLELISM.
5678-
* * * *
*' 9- D R A W I N G INDICATION.
10- M A I N M E N U
PERPENDICULARITY S ~ Y COAXIALFI~. CIRCULAR RUN-OUT
*
E N T E R Y O U R CHOICE? 6
*
GENERAL TOLERANCES ON SYMMETRY
*
T O L E R A N C E CLASSES:
* * *
I . F I N E (H) 2- ~ D I I . J M (K) 3- C O A R S E ft.)
* '* *
* *
* NOTES: * 1- Applied only when one of the two features has a medtan plane. c 2- A n d t h e a x e s o f t h e t w o f e a m r e s a r e p e r l m n d i c u J a r t o e a c h o t h e r .
*
E N T E R N O M I N A L L E N G T H O F THE S H O R T E R F E A T U R E (MM)? 50 E N T E R T O L E R A N C E CLASS? 1 GEN~::RAL T O L E R A N C E O N S Y M M E T R Y = 5
MMS
F N T E R B A S I C SIZE (0,5 - 4000 M M S ) ? 8 T H E P E R M I S S I B L E D E V I A T I O N = (+/-)
.1
MMS
E N T E R B A S I C SIZE (0.5 - 4000 M M S ) ? 6 T H E P E R M I S S I B L E D E V I A T I O N = (+/-)
1
MMS
E N T E R YOLrK CHOICE? ! * T O L E R A N C E S F O R LINEAR A N D A N G U L A R D I M E N S I O N S
* * * *
J234-
L I N E A R DIMENSIONS (except broken edges). B R O K E N EDGES. A N G U L A R D I M E NSIONS. RETURN TO PREVIOUS MENU.
*
* * * *
References
E N T E R Y O U R CHOICE ?7 1 * P R E M I S S I B L E D E V I A T I O N S FOR L I N E A R D I M E N S I O N S
*
* TOLERANCE CLASSES: * 1- F I N E ( 0 * 3- C O A R S E (c)
2- M E D I U M (ra) 4- V E R Y C O A R S E (v)
* *
* 5- R E T U R N T O P R E V I O U S M E N U
*
ENTER NO OF DIMENSIONS WITHOUT TOLERANCINGW 5 ENTER YOUR CHOICE ~ 2 E N T E R B A S I C SIZE (0.5-4000 M M S ) ? 72.5 T H E P E R M I S S I B L E D E D V I A T I O N = (+/-) .3
MMS
E N T E R Y O U R CHOICE .9? 2 E N T E R BASIC SIZE (0.5-4000 MMS)? 50 PERMISSIBLE DEVIATION = (+/-)
.3
MMS
E N T E R BASIC SIZE (0.5 - 4000 MMS)? 30 T I l E P E R M I S S I B L E D E V I A T I O N = (+1-)
.I
MMS
APPROPRIATE TOLERANCE CLASS? 1 E N T E R R E L A T E D L E N G T H (MMS)? 45 T H E STRAIGHTNESS ~FLATNE3S TOLERANCE =
.I
MMS
[1] Ulf Engstrom, Caroline Lindberg, Factors influencing dimensional tolerances of high strength PM steels, Sintering Advances in Powder Metallurgy U.S.A. 3 (1992) 317 328. [2] M. Beghini, L. Bertini, E. Vitale, Shrink stress density functions in conical threaded connections as a dimensional tolerances, in: Materials Engineering Proc. Int. Offshore Mechanics and Arctic Engineering, ASME Symposium, New York, vol. 3, 1992, pp. 383- 390. [3] H.C. Zhang, M.E. Huq, Tolerancing techniques: The state-ofthe-art, Int. J. Prod. Res. 30 (9) (1992) 211 213. [4] Delvecchio, N Joseph, A. Soom, Tolerances and available relative motions in bolted connections, Adv. Des. Automat. ASME, Des. Eng. Div. 32 (1991) 177-183. [5] Hong, et al., Computational geometry approach to minimum zero evaluation of straightness, J. Chin. Inst. Eng. 14 i5j (1901) 463 -470. [6] C. Doydum, N. Perreira, Method for selecting dimensions, tolerances and precision for alignment, Int. J. Prod. Res. 29 (51 (1991) 103 - 105.
256
$.M. Darwish/ Journal of Materials Processing Technology 68 (1997) 251-256
[7] Tomiharu Matsushita, Improvement of equipment for close-tolerance forging and extrusion in Japan, J. Mater. Process. TechnoL 22 (3) (1990) 223-238. [8] P. Os~wald, M. Blake, Estimating cost associated wi,m dimensional tolerance, Manuf. Rev. 2 (4) (1989) 277-282. [9] P. Skoglind, Tolerance for P/M cylinder liners, Cahiers d'lnformarion Techniques--Revue de Metallurgie (in English) 86 (1989) 87-92. [10] P. Skoglund, Tolerances for P/M cylinder liners, Met. Powder Rep, 44 (5) (ie;89). [11] P. Gupta, On the geometrical imperfections in cylindrical roller beatings, ASME Tribology Conf. U.S.A., 1987. [12] Ulf Engstrom, Glued powder mixes for improved tolerance control, Verlag Schmid Gmbh Freiburg I (1986) (in German). [13] J. Tengzelius, Ulf Engstrom, Means to improve the dimensional tolerances of P/M steel components, in: Modern Development in Powder Metallurgy, vol. 17, Metal Powder Industries Federation, U.S.A., 1985, pp. 743-765. [14] Joshua U. Turner, New methods for tolerance analysis in solid modelling, IEEE (1988) 306-314. [15] Ernest C. Bernhardt, Computer modeling predicts tolerances of molded parts, Plast. Eng. 46 (10) (1990).
[16] F. Etesami, Mathematical model for geometric tolerances, J. Mech. Des., Trans. ASME 11 (1993) 81-86. [17] G. Abdou, R. Cheng, TVCAPP, Tolerance verification in computer-aided process planning, Int. J. Prod. Res. 31 <1993) 39-41. [18] J. Mei, C. Hong, Tolerance analysis for automated setup selection in CAPP, ASME Prod. Eng. Div. (1992) 211-220. [19] M. Porchet, G. Zhang, incorporating geometrical tolerances and processing inaccuracy into dimensioning and tolerancing, Adv. Des. Automat. 44 (1992) 151-156. [20] R. Weill, Integrating dimensioning and tolerances in computer aided process planning, Robotics Computer-Integrated Manuf. 4 (2) (1985) 41-48. [21] ISO 2768-1, General Tolerances--part h Tolerances for Linear and Angular Dimensions without Individual Tolerance Indications, 1989. [22] ISO 2768-2, General Tolerances--part 2: Geometrical Tolerances for Features without Individual Tolerance Indications, 1989. [23] S. Choi, T. Dean, Computer aided design of die block layouts, Int. J. Mach. Tools Manuf. (1987). [24] B. Tong, D. Walton, A computer design aid for internal spur and helical gears, Int. J. Maeh Tools Manuf. (1987).