2 Machining Theory 精密机械工程

2. MACHINING THEORY
2
for machining precision
Various types of measurement:
1.Dimensional precision
2.Form precision
33.Surface roughness
4. Work-affected surface layer
•Laser measurement system -0.01µm resolution at a precision of ±0.1p.p.m.p p p Upper limit in machining precision is 5 times of 0.01 µm or ±0.05 µm 5
µµ
Example of commercial devices
10 μm resolution
6
3 μm resolution
Roundness -e.g. Talyrond by Rank Taylor Hobson. Magnified
out-of-roundness errors 20 times for measurement i h di i i 1i h i d bl assuming a chart division 1 mm is the min. readable unit, Out-of-roundness error is 1/20 000 = 0.5 x 10-4mm =0.05µm can be detected.Therefore the mm 0.05 µm can be detected. Therefore the machining of circular parts, the upper limit of
machining precision is 5 times of the value, giving 0250.25 µm
C .Upper Limit Value for Surface Roughness pp g
Optical surface roughness -non-contact type,
eg WYKO Corp Vertical resolution =03nm eg. WYKO Corp Vertical resolution = 0.3 nm Upper limit in machining precision for surface roughness is 1.5nm .
Example p
The variation in a critical dimension produced by a
manufacturing process follows a normal distribution with mean equal to the set point
(desired dimension) of the process (i.e. there is no "bias"). The standard deviation is 0.002. What minimum resolution would be required of a sensor installed to inspect the products?
The minimum resolution is 5x(.002)= 0.0004
9
are fundamental for high-precision machining.
“giving
up a bearing”g g p g •Stick together –‘wringing’as in gauge block
Only when one mastered the techniques is able to control the 10
Only when one mastered the techniques is able to control the know-how necessary for machining high-precision parts
Use the three-plate method to create a highly precise flat plane.
p g
ËThe tool or workpiece can be translated with high
precision
Typical in a lathe
13
14
for spherical surfaces
17Lens polishing as
the final step
18
f t i l
properties of materials
2122 Built-up edge in machining
p g g
Tool
Work
hi i Machining
MU in mechanical chemical polishing is similar to
o MU in mechanical-chemical polishing is similar to
EEM
2526
Errors are magnified due
to the effects of movements
of movements
such as rolling, yawing, pitching
or heat deformation caused by
uneven heat distribution
Abbe’s principle)
Cutting
point
29
Review
The principle of the upper limit for machining precision
30 defects, impurites, and irregular crystal grains。