DESIGN GUIDE & TOLERANCES:
The ultimate success of the casting design depends on the communication
between the designer and foundry engineers. When the foundry is properly
informed of part requirements, there is usually a compromise of specifications
that will allow for maximum compliance to print specifications and
finish part design. 1. Standard Linear Tolerance(mm)
Dimensions |
Normal |
Premium |
Up to 10 |
±0.12 |
±0.10 |
10 to 15 |
±0.20 |
±0.13 |
15 to 20 |
±0.25 |
±0.15 |
20 to 30 |
±0.30 |
±0.20 |
30 to 50 |
±0.40 |
±0.25 |
50 to 75 |
±0.50 |
±0.35 |
75 to 100 |
±0.65 |
±0.45 |
100 to 125 |
±0.80 |
±0.60 |
125 to 150 |
±1.00 |
±0.70 |
150 to 175 |
±1.20 |
±0.80 |
175 to 200 |
±1.50 |
±0.90 |
200 to 250 |
±1.80 |
±1.10 |
over 250 |
±0.80% |
±0.50% |
2. Angularity
As-cast tolerances of angles is mainly a function of the part design
and their ocation in casting. They range from +/- 1/2 degree (considered
minimum) for well supported positions to +/- 2 degree where existing
distortion could be expected. Inclusion of gussets and ribs normally
minimizes distortion and many sections can be mechanically straightened.
3. Flatness, Strengteness and Roundness
Section Thickness |
Possible Thickness Section
Sink per Face of Casting |
Normal |
Premium |
Up to 25 |
0.20 |
0.10 |
25 to 50 |
0.40 |
0.20 |
50 to 100 |
0.60 |
0.30 |
100 to 150 |
0.80 |
0.40 |
Straightening adds cost, but sometimes cannot be avoided. The
actual straightening costs are often dependent on the tightness
of the tolerance specified, so do not specify tighter flatness,
straightness, roundness, or other requirements than you actually
require. (Cheonseng typically straightens parts using die sets that
will be included in your tooling price.)
4. Size and Weight Range
Size and Weight. Part size and weight are the most critical factors
in determining part cost because mold capacity is limited by both
size and weight. The more pieces that can run on a mold, the lower
the part cost. Unnecessary mass should always be removed by correct
engineering practices to reduce part weight.
Items |
Size |
Premium |
Outline Dimention |
1000×620×380 |
up to 100 |
Weight(kgs) |
0.005 - 100 |
0.10 to 1.50 |
Min. Wall Thickness |
0.50 |
5 to 10 |
5. Surface Roughness
80 to 120 RMS are average.
6. Hole Length
Making a good hole in a casting is dependent on the integrity of
the shell. The ratio of holediameter to length is important in determining
what can be offered. Blind holes must have aradius at the top and
the bottom of the hole to insure that a strong core is built for
castingpurposes and to insure the best possible casting
7. Number of Gates
When possible, parts should be designed so that a single gate can
feed the part. This will generally yield more pieces per mold and
reduce the pour weight per mold.
Cheonseng builds gate grind fixtures for virtually all parts produced
that require gate grind. When possible, the part should be designed
so the gate can be put on flat surface rather than curved surface.
Gate grind tolerances are listed from least to greatest cost.
1. Break-off witness (same alloys)
2. 0.20-0.50mm high witness
3. Flush grind
8. Heat Treatment
Heat treatments are used to control hardness, mechanical properties,
corrosion resistance, and surface treatments. Unless otherwise indicated,
all alloy steels are quoted with a normalize or anneal. All 300
series stainless steels and 17-4PH are quoted with a solution anneal.
9. Gaging
Cheonseng performs a 100% visual inspection, However, if dimensional
verification is required, a sampling plan and process control is
less expensive than 100% gaging of each part. Fixed gages such as
"go-no-go" are less expensive to use than gages with dial
indicators. (Important: Whenever custom gages are used, there should
be identical gages at Cheonseng and at the customer's plant.)
10. Non-destructive Testing
All sample investment castings are non-destructively tested in
order to establish first article quality. However, this is generally
not required on production commercial investment castings; doing
so will add costs. The following non-destructive tests are listed
from least to greatest cost:
1. Magnetic Particle
2. Fluid Penetrant
3. X-Ray
11. Certification
Chemical Certification can be provided at no extra cost. Mechanical
Property Certification adds to cost, so it's best to consider a
combination of Chemistry and Hardness Certification instead. Marking
each casting with heat number also adds to the cost. Investment
casting in lot numbers may be a good tracability option for commercial
parts.
12. Tooling & Cavities
If the design contains features that will raise scrap or rework
rates (and the piece price), the Cheonseng Estimating Engineer will
recommend design modifications to keep the piece price down.More
cavities means higher tooling cost, but lower piece price. Configurations
that do not allow metal cores to be drawn must be treated in one
of the following ways:
1. Collapsible Cores - Lowest piece price, higher tooling cost.
2. Loose inserts - Best for low volume parts.
3. Multipiece Wax Assemblies - Best for certain configurations,
but tolerance control suffers.
4. Soluble Cores - Requires additional die and labor.
5. Pre-Formed Ceramic Cores - High cost for specialized shapes.
13. Alloy Grade
Alloys are listed from least to greatest cost:
1. Carbon and Low Alloy Steels
8620, 4140, 1020, 1035are best choices
2. 17-4PH and 400 Series Stainless Steel
17-4PH & CA-15 (410) are most frequently poured
Do not specify 416 unless necessary for machinability
3. 300 Series Stainless Steel
CF-8 (304), CF-8M (316) are best choices
Do not specify CF-16F (303) unless necessary for machinability
4. Tool Steels
Costs vary widely depending on grade
5. Nickel Base Alloys
Alloy C and X are best choices
6. Cobalt Base Alloys
All grades pour well - Choice is based on end use and cost |