Manufacture: tolerances, variation and inspection
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| tolerance/ˈtɒlərəns/ | sai số cho phép |
| clearance/ˈklɪərəns/ | khoảng trống |
What would explain this observation?
- Two parts can each match a nominal drawing yet fail to assemble if allowed variation has not been considered. Manufacture produces a range of dimensions.
Build the model
- A tolerance 公差 specifies an allowed dimensional range around or beside a nominal value.
- Precision concerns consistency of repeated measurements or production, while accuracy concerns agreement with a reference.
- Process selection must consider material, geometry, quantity, surface finish, waste and achievable variation rather than appearance alone.
- tolerance: The allowed range of variation in a specified dimension.
- clearance 间隙: The dimensional space between mating parts under the stated model.
Which dimensions determine the minimum worst-case clearance?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Worst case pairs the extremes that squeeze the gap: the clearance is smallest when the hole is at its smallest and the shaft at its largest. The other pairings give the maximum clearance or no clearance at all.
Match each technical term to its precise meaning.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- For a worst-case clearance model, subtract the largest shaft from the smallest hole for minimum clearance, and the smallest shaft from the largest hole for maximum clearance.
- The calculation assumes the stated dimensional limits and ideal geometry.
- Shape, alignment, temperature and measurement uncertainty can affect actual assembly.
In the lab: Use safe school-made models or a provided dimension dataset. Specify dimension units, nominal values and limits before testing. Measure with an appropriate calibrated instrument at agreed positions, record every result and classify against the specified range. Retain rejected pieces and explain whether the problem concerns the design limits, process variation or measurement method.
Which two habits make the investigation or model in this case more defensible?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a hole is 10.0±0.2 mm, giving 9.8–10.2 mm; a shaft is 9.5±0.1 mm, giving 9.4–9.6 mm.
- Minimum clearance is 9.8−9.6=0.2 mm and maximum is 10.2−9.4=0.8 mm.
- This model predicts positive clearance across the stated limits.
- It does not establish strength or fitness for a safety-critical application.
Your turn: A hole ranges from 12.0 to 12.4 mm and a shaft from 11.5 to 11.8 mm. Calculate minimum clearance.
A hole ranges from 12.0 to 12.4 mm and a shaft from 11.5 to 11.8 mm. Calculate minimum clearance.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The result is 0.2 mm. Known: hole 12.0-12.4 mm; shaft 11.5-11.8 mm. Minimum clearance = smallest hole - largest shaft = 12.0 - 11.8 = 0.2 mm. Maximum clearance = 12.4 - 11.5 = 0.9 mm; the fit stays loose across the stated limits.
Check the conclusion and its limits
- A tighter tolerance can increase cost, inspection time and waste, and may not improve the user outcome.
- A measuring instrument with a fine display does not automatically have the accuracy required to accept a part near its limit.
Not true: A finer instrument display guarantees sufficiently accurate dimensional inspection. Display resolution is not accuracy: an instrument can show 0.001 mm while being systematically off by far more. Inspection near a tolerance limit needs a calibrated instrument with proven accuracy.
- A tolerance specifies an allowed dimensional range around or beside a nominal value.
- For a worst-case clearance model, subtract the largest shaft from the smallest hole for minimum clearance, and the smallest shaft from the largest hole for maximum clearance.
- Watch for: A tighter tolerance can increase cost, inspection time and waste, and may not improve the user outcome.
Write from a minimum clearance of 0.1 mm
- A hole ranges from 20.0 mm to 20.3 mm. A shaft ranges from 19.6 mm to 19.9 mm.
- Find the minimum and maximum clearance. The limits do not prove strength.
A finer instrument display guarantees sufficiently accurate dimensional inspection.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Display resolution is not accuracy: an instrument can show 0.001 mm while being systematically off by far more. Inspection near a tolerance limit needs a calibrated instrument with proven accuracy.
The allowed range of variation in a specified dimension: write the technical term.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
tolerance means The allowed range of variation in a specified dimension.
A hole ranges from 20.0 mm to 20.3 mm and a shaft ranges from 19.6 mm to 19.9 mm. What are the minimum and maximum clearances, and what do they not prove?
Minimum clearance is the tightest assembly of the stated limits. Maximum clearance is the loosest.
What is the minimum clearance?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The smallest hole minus the largest shaft is 20.0 minus 19.9, which is 0.1 mm. Other options — 0.7 mm (the maximum clearance); 20.0 mm (the smallest hole).