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Tolerance level is something that calculates and figures out the exact and correct values for which an investment cast according to the given specification, reaches a maximum point without getting damaged by any means. The tolerance can be specified in many dimensions and in many suitable industrial ways, by which a buyer can deduce and co relate according to the required specification and be assured about the maximum ratings or tolerance accordingly.
We are Micro Melt Pvt. Ltd, an ISO certified 9001:2008 company dealing and manufacturing quality investment casting and metallic shaped instruments according to the given specifications. We have a set of lists, from which a person or a company can correlate the charts so as to match their requirements. The levels and different specified tolerances and its variants are listed below as follows:
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SURFACE
FINISH
As-cast finishes will vary with alloy specified but generally
fall within the range quoted. For a ground finish an allowance
of 0.010 in. (0.25mm) should be made.
Metal |
C.I.A.
value |
Micro-inches |
As-cast |
Machined |
Stainless
Steels |
90-126
60-125 |
Cobalt
Chrome Alloys |
80-100
50-100 |
Carbon
Steels |
90-125 60-125 |
GENERAL TOLERANCES
Shape and alloy selected will influence accuracies achieved
but values given are normally accepted through out the investment
casting industry.
| Dimension |
Tolerance |
| Upto
25 mm |
±0.25mm |
| Above
25 mm |
±0.25mm/25mm |
Closer
tolerance may be held on selected dimensions following design
evaluation.
STRAIGHTNESS
There are practical limits to straightness which can be achieved
but mechanical straightning can reduce variations.
Casting
Length |
As-cost |
Corrected |
25
mm |
±0.50
mm |
±0.25
mm |
50-100
mm |
±0.75
mm |
±0.50
mm |
100-150
mm |
±1.00
mm |
±0.50
mm |
150
mm |
±1.50
mm |
±0.62
mm |
FLATNESS
Flatness is also affected by dimensions of investment casting. Addition
of ribs will minimize bowing, twisting and distortion and
mechanical straightning will reduce variations where necessary.
Casting
Length |
As-Cast |
Corrected |
25
mm |
±0.20
mm |
±0.10
mm |
50
mm |
±0.37
mm |
±0.15
mm |
75
mm |
±0.50
mm |
±0.20
mm |
100
mm |
±0.62
mm |
±0.25mm |
CAST HOLES
Depth (D) and Diameter(d) of hole must allow for adequate penetration
of investment material.
Values given show usual limits for cast holes but pre-formed
ceramic cores allow this restrictions tobe exceeded, although
usually at increased cost.
Through
holes |
Diameter
(d) mm |
Maximum
Depth (D) mm |
3.17-6.35
D
upto 1.5 d |
6.35-12.70 D
upto 3.0 d |
12.70 D
upto 5.0 d |
Blind
Holes |
Diameter
(d) mm |
Maximum
Depth (D) mm |
4.76-12.70 D
upto 1.5d |
12.70 D
upto 2.0 d |
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CONCENTRICITY
The larger the outside diameter becomes, the closer to concentric
an inside diameter can be cast.
Mechanical correction can normally be made where wall thickness
is thin enough to allow plastic deformation.
O.D.(mm) |
I.D.
(mm) |
Eccentricity
(mm) |
As-cast |
Corrected |
18.75 |
6.25 |
±0.100
±0.100 |
25.00 |
12.50 |
±0.125 ±0.125 |
37.50 |
18.45 |
±0.200 ±0.200 |
50.00 |
25.00 |
±0.250 ±0.200 |
ROUNDNESS
For solid bars roundness is affected by solidification stresses
and tolerance required increases nearly in proportion to diameter,
inline with usual 'Lost Wax' tolerances.
Values shown are for as-cost roundness on inside and outside
diameters of tubes of varying sizes. Wall thickness is important
and tighten tolerance can be obtained by mechanical correction
if desired.
O.D.
(mm) |
Tolerance
(mm) |
I.D.
(mm) |
Tolerance
(mm) |
12.50 |
±0.25 |
upto
6.25 |
±0.30 |
25.00 |
±0.50 |
6.25-12.50 |
±0.40 |
37.50 |
±0.60 |
12.50-25.00 |
±0.50 |
50.00 |
±0.75 |
above
25.00 |
±0.50
(per 25 mm) |
MINIMUM SECTION THICKNESS
Wall thickness will depend upon area of casting and alloy selected.
The following values are of guide from general experience.
Material |
Minimun
wall thickness obtainable |
18/8
stainless steels |
1.62
mm |
25/12
stainless steels |
1.50
mm |
Carbon
steels |
2.25
mm |
Cobalt-Chrome
alloy |
1.12
mm |
PARALLEL
SECTIONS
Parallelism can be maintain by adding fire-bars to minimize
distorsions. Values shown are typical tolerances for various
gap-widths between parallel sections per inch cost.
Gap
(mm) |
Tolerance(mm)
As-cast |
Corrected |
6.25 |
±0.075 |
±0.075 |
12.50 |
±0.125 |
±0.100 |
18.65 |
±0.150 |
±0.100 |
25.00 |
±0.175 |
±0.125 |
OTHER FEATURES :
Angles : Angular tolerance to ±1/2° (Closer by mechanical
corrections).
Symbols : Latters, Numbers, etc., can be reproduce in
relief or inset.
Serrations, Splines and Gear Teeth may be cast in certain instances
subject to prior agreement. |
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