A System for Automated Fixture Planning with Modular Fixtures

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In a future plan with overhead clamps, each clamp is assumed to apply the Same amount of damping
force. The minimized due of the objective function is the necessary clamping force. In a fixture pIm
with a vise. the necessary clamping force for a movable jaw is 3 times the clamping force at a point contact.
If the magnitude of the clamping force at the active contact is within the maximal clamping force of a
clamp (or vise), the fixme plan is valid. ?he least required clamping force to hold the prt rigidly during
machining is the largest clamping force among the least clamping forces necessary to maintain the part’s
equilibrium for each cutting force.
3.4.3. Remarks
Force analysis is computationally expensive, and it is not possible to considex evay force direction along
each cutm path. Often, a mup may inciude multiple feaMes to cut In order to estimate the clamping
force with the milling operaiions, various directions of culling forces may be considered. Thus. a few
represenmtive force directions at each milling cuter path can be used to speed up the computation.
3.5. Checking part deflection
Part deflection during machining can deteriome part accuracy and cause dynamic problems such as
chatters in the cutting tod and vibrations in a padfixture assembly, a. Far example, when drilling a hole
in il poorly-supported thin part, severe part deflection not only causes the prt to vibrate, but also may break
the drill (see figure 3-11).
support
Figure 3-11: Part detktion due to driUig
When a candidate fixture plan is mth the damping force at every clamping cornpent, it IS
necessary m check whether pan deflection due to dampmg force or cutting force s acceptable. The sues
applied on the contact area between the clamp and the part c, can be estrmated by
F
Q- A
where F is the clamping force and A is the contact area been the clamp and the pan For example, let
us assume that a swing clamp driven by hydraulic power can apply up to l0,OOO lbs force. If the contact