IS 11166 : 1993 Indian Standard PERMISSIBLE DEVIATION ON DIMENSIONS, SURFACE ROUGHNESS AND MASS OF STEEL CASTINGS MADE WITH INVESTMENT CASTING PROCESS ( First Revision ) 1 SCOPE LK This standard covers the permissible devi- ations on dimensions, surface rougness anc mass of steel castings made with iayesiment casting process. This standard provides for the following two classes of permissible deviations. Class — Involving a closer contzol over the process and in most eases, a higher cost of manufacture Class 2— Involving normal controls. and in most cases a lower cost of manu- facture 4.2 Normally on the engineering drawing, tole- ances shall be specified on all important dimen- sions, on surface roughness at_ important arcas and on mass of those castings where the mass js. relevani factor. The tolerances thus speci- fied shall normally be in conformity with the values specified against Class | and Class 2, 1.3 With exceptionally close control or with certain additional operations, it may be possible to achieve a level of control closer than Class [ also, ‘The designer may call for such a closer level of tolerances on especially critical dimen- sions, but it is recommended that this be done in consultation with the manufacturer. 1.4 Unless otherwise specified on the drawing orin the enquiry and order, on the untoter- anced dimensions, surface roughness and mass, the deviations mentioned against Ciass 2 shail apply. 2 TERMINOLOGY ‘2. For the purpose of this standard, the folln- wing definitions shall apply. 2.4 Investment Casting ( Lost Wax Process ) This is a casting process in which a consumable pattern of wax or thermoplastic or other maaterial used. The pattern is invested in a fefractory slurry to form a mould. After the mould is dried the pattern is melted or burnt out of the mould cavity. 2.2 Rongh Casting ‘This is the finai product of the inyestment foun« dry after the usual operations of gato removal, ettling, heat treatment, ete, but before any machining operation is curried out. 2,3 Dimensions 2.3.1 Nominal Dimensions The dimension prescribed on_ the production drawing ty which deviation is to be applied (see Annex A). 2.3.1.1 If the suefaces influeacing this dimension ate not provided with machining allowances, the nominat dimension of the final casting is the dimension specified in the drawing, 2.3.1.2 If the surface influencing this dimension are provided with machining allowance, then the nominal dimersion on a casting is equal to the total of the dimension given in the machi- mponent drawing and the relevant ing allowance. 2.3.2 Overatl Dimension ‘The largest measurable dimension of the pacti- cular part of @ casting in which the nominal dimension is located. The overall dimension is to be considered in a plane normal to the nominal dimension ( see Annex A). 2.4 Permissible Deviations 2.4.1 A positive deviation is the difference bet- ween the maximum permissible dimension and nominal dimension. 2.4.2 A negative deviation is the difference between the minimum permissible dimension and the nominal dimension.IS 11166 : 1993 2.5 Machining Allowance This is the stock of extra material, which is provided on the relovant surface of a raw cast- ing, on removing which, in the process of ing, the casting would attain the finish machined dimensions shown in the drawing of machined componeat. Provision of a machi ing allowance, and the consequent machining, are necessary wherever the “as cast’ dimensional tolerances that are attainable are not close enough for a given application and require improvement by the process of machining. ‘Machining is some times also done to eahance the ‘as cast’ surface finish or to alter the shape of a casting to suit a particular application. 2.6 Draft is the taper that is necessary 10 be provided in case. of ail vertical faces ( faces perpendicular to the parting plane ) in a pattern to facilitate its withdrawal from the die/mould. 3 PERMISSIBLE DEVIATION ON DIMENSIONS 3.1 Permissible deviations on the nominal dimensions of castings shall be as_given in Tables J and 2 respectively for the particular class. 3.2 The total change in nominal dimensions due to change in geometrical shape or profile and other reasons should not exceed the deviation indivated in the respective classes. Table 1 Permissible Deviations on Dimenstons, Class 1 ( Clause 3-1) All dimensions in millimetres. ‘Nominal Dimensfons ‘of Rough Castings ‘Overall Dimensions cate Git tal Bel Goh Sob Sab Bole pow ove Up Upeid UPS USO Opes uc BL Gee S200; soi eor2 eo12 mods sols e020 eoas 6 oz kone boas eos som Boas S00 ooo = Sols nots 400020234030 sos «2 = . fom £028 dom 4000 sas Soe s =£ 5 “So Re oe seo son aoe is ©=£ & &£ "> Ha io tes eo @ © 2 2 2 2 8S ae oe woo ‘Table 2 Permissible Deviations on Dimensions, Class 2 (Clause 3.1) Ail Gncnsione rime, Namal Dimwaions roa Die oH cng ae — 7 Gt Soe Ge a Cae eee aE Over ‘Upto Upto10 Uptois Upto30 Upto80 Up te 180 Upto 300 Upto 30 6 © £010 RoI? 2013 402 “028 OM Les EO as a ro ee ee re oe eo» oc 2 “IY gem sem soa cose | woes mom MS Sass hoe 409s Be Doe on wm ms wom4 PERMISSIBLE DEVIATIONS ON CENTRE- TO-CENIRE DISTANCE, Permissible deviations on centre-to-ceatre dis- tance between holes, bosses, ete, shall be as. given in Table 3. Table 3. Permissible Deviations on Centre-to- Centre Distance Between Holes, Bosses, ete. ‘All dimensions in millimetres. ‘Nominal Dimensions ‘Permissible Deviation “Over Upto Gast ‘Class? 6 00 £0125 ‘ » 2000 £0125 10 8 20-10 S015 18 30 £015 £025 30 % £020 £035 0 180 £030 #045 130 300 x 04s £070 300 $00 40-60 = 090 5 PERMISSIBLE DEVIATION ON MASS 5.1 Permissible deviations on mass of a casting shail be as given in Table 4. ‘Table 4 Permissible Deviation on Mass Nominal hase erCusinyse ——Permlsble Deviation, Recent ‘Over upto’ Gast Sia 2 peer) £50 x am #30 240 0 sm) 20 a2s 50100045 220 1 t00 210 ais 5.2 The nominal mass of casting shall be deemed tobe the average of the actual masses of a batch of castings, all of which have dimensions within the permissible deviations. IS 11166 : 1993 5.2.1 By prior agreement, the purchaser and the manufacturer mey choose a different basis of defining the aominal mass and aiso what will constitute a batch of castings. 6 PERMISSIBLE DEVIATIONS ON ANGLES: Permissible deviations on specified angles shall boas follows: Class § Class 2 yet ah “Where the overall dimension governing the concerned faegs or points is over 75 mmo, the permissible deviation in Claes T shall be # 0-7? justend of # 1,2" 7 PERMISSIBLE DEVIATIONS ON SURFACE ROUGHNESS TA Surface roughness determined in accord- ance with TS 3073 : 1979 shall not exceed the following limits: Class 1 Class 2 (Ra pra (Ra pn y* 30 60 Raum = Aritimetical mean deviation from the line profile, in mierometzes, NOTE — Under Ciase i, the actual surface rough- ness is genotslly likely fo lie in the range of 1610 sya 8 MACHINING ALLOWANCE 8.1 ‘The maximum permissible machining allo- wance per surface shall be as given in Tabie 5 8.2 Even though the values given in Table $ are the maximum as far as the manufacturing foundry is concerned, it is open to the pur- chaser to specify higher machining allowances, ithe so desies, at the time” of enquiry and the order. ‘Table 5 Permissible Machining Allowances (Clause 8.1) Nominal Dimensfon ‘Orerall Dimensions (min/face ) Over Upto 6 610 1018 18.0 30.80 80.130 100.300 — 6 03 035 o4 05 o7 10 10 ‘ 10 = 035 04 os 07 12s As 10 18 = - 0s 06 o7 125 15 8 30 = 3 2 o6 oa rw 475 30 0 = - = - 19 16 200 89 480 - = = ~ = 20 235 180 300 - = = 7 = = 300TS 11166 : 1993 8.3 The interpretation of providing machining allowance and its relationship with casting tolerances are as illustrated in Fig. 1 A, 1B. 1C, and 1D, Itisto be noted that a machining allowance specified in Table 5 is the nominal maximum amount that would survive inspite of there occurring the maximum permissible negative deviation in case of an external dimension (see Fig 1 a) or the maximum possi- ble positive deviation in case of aa internal dimensions (zee Fig. 1b). Hence a particular casting may have a total machining stock, for example, in case of an internal surface, equal to the machining allowance specified in Table 5 plus the maximuin negative deviation permis- sible in accordance with Tables 1 and 2 (Class 1 and Class 2 ) as tbe case may be plus the pormi- sisble draft in accordance with Table 6. Thus when jt is stated that a machining allowance given in Table 5 is the maximum, it means that itis the maximum value allowed over and above the corresponding applicable dimensional devi- ation as per Tables Lor 2 plus the corresponding applicable draft as per Table 6. 3.1 1f 2 surface requiting machining has a inkage or a reference with more than one point or surface, then greater_distance shall be taken as acminal dimension for the purpose of deriving the appiicable machining allowance. 9 DRAFT 9.1 The maximum permissible draft per surface shail be as given in the Table 6. Table 6 Draft (Clauses 8.3,9.1 and 9.2 ) Hicight of Face va ‘Draft ia mua (Max) “Over Upto” "Cass = 25 oe 25 50 02 10 80 0635 80 120 os 120, 180 ons 180 250 10 250 350 130 350 500 475 ot Fete IC Machining of Step Dimension Fie, cr. g D ‘UNMACHINED FACE cr ° 10 Machi ing on One Side ILLUSTRATION OF MACHINING ALLOWANCS AND It's RELATIONSHIP WITH. CastinG TOLERANCE AND DRAFT NOTE Re raw casting dimension, F = finished dimension. AMA = machine allowance ( see 2,5 and 8 ), €F = casting tolerance range as per Tables 1, 2 o: D = draft ( See 26 and 9) (in this illustration « epresents the + ve draft ag referzed to in 9.4.2). 49.2 While it is theoretically possible to elimi- nate draft in all cases by suitably splitting the die or by any other means, these methods are often unfeasible, as they would substantiatly raise the cost of the die. Thus in case of some faces a certain degree of draft becomes un- avoidable. The amount of such draft would vary depending upon noi only the length of face but also upon such other factors like the depth to dia ratio in case of a hole whether the hole is through or blind, etc. While i would be logical from the foundry point of view to account for all these factors, it would not be reasonable to expect a purchaser of castings to be familiar with all such aspects and be uncertain of the amount of draft the casting ought by him, may actually have, depending on such factors, Hence to avoid confusion, and as measure of simplification the permissible extent of draft over a given leneth is based only on the class of accuracy, Table 6 for draft is drawn up accordingly. 9.3 The draft provided can be of any of the following 3 types — 4 ve, + ve, — ve draft. This differentiation is illustrated in Fig. 2A, 2B and 2C. siz a z 2A ve Draft IS 11166 : 1993 9.4 Tho following basis is ordinarily followed in chosing the type of draft, 9AM ot ve draft This type of draft is used when the design of a casting does not allow an increase or decrease of the nominal dimension more than 50% of the specified value of the draft, over and above ‘the applicable dimensional deviation. DAD + ve draft This type of draft is most commonly used and is applicable wherever the concerned face is machined or where it is not machined but the casting desion and application do not permit an increase in the concerned nominal dimension in case of an external surface, and a decrease in casc of an internal surface, 94.3 ve draft This type of draft is used where the concerned casting surface remains unmachined and the casting design and the application do not per- mit an increase in the concerned nominal dimension in case of an external surface, and a decrease in case of an internal surface, a 2B + ve Draft NOMINAL DIMENSION 2C ~ ve Draft Fic. 2. Iurustration or Dirreent Tyres or DRAFT