4. Clamping possibilities for workpieces and tools
Clamping the workpieces
Work-holding devices have the following special functions for
machining on drilling machines:
positioning - fixing of the workpiece position in
relation to the tool
clamping - neutralization of cutting forces during the
machining operation
The clamping elements to be used must both neutralize the
cutting forces (feed and speed) and hold down the workpiece during the machining
operation.
Especially when drilling is made with twist drills the torque
caused by the cutting force is of great importance for a safe clamping of the
workpiece. The torque subjects the tool to torsion and simultaneously tries to
drag along the workpiece.
Therefore, greatest importance shall be attached to
a firm, job-related workpiece clamping according to labour safety
regulations.
The choice of the respective clamping equipment depends on
- the shape, size and number of workpieces to be
machined
- the number of bores in a workpiece and their size
- the angular
position of the bores
- the cutting forces acting on the workpiece
- the
type of drilling machine to be used
- the position, direction and necessary
quality of the bore.
There is a great number of variants of the various clamping
elements and fixtures.
As main variants for clamping workpieces, the following ones are
applied:
Clamping against a stop
for loose workpiece clamping with medium-sized and bulky
workpieces as a safeguard against displacement and distortion.
Figure 14. Clamping the workpiece
against a stop
1 stop, 2 table, 3 work-holding bolt, 4
workpiece
Vice clamping
Loose vice clamping for quickly fixing the workpiece's central
positions in single-piece production or at low cutting pressure. Firm vice
clamping with determination of fixed position in series production or at high
cutting pressure.
Figure 15. Vice clamping
1 vice, 2 workpiece, 3 parallels
Chucking
for clamping rotationally symmetrical workpieces and machining
of their end faces.
Figure 16. Chucking
1 tool, 2 workpiece, 3 chuck
Clamping by means of clamps
for clamping large or bulky workpieces on the table. We
distinguish between flat, U-shaped, fork-shaped and cranked clamps of fixed and
adjustable design.
Figure 17. Clamping by means of clamp
1 clamp, 2 support, 3 work piece
Make sure by means of supports that the clamps are
arranged horizontally.
Clamping in fixtures
for clamping workpieces which due to their geometrical shape can
not or only with considerable effort be clamped with usual clamping equipment
such as vice, stop and clamp. This is the safest kind of clamping ensuring high
quality. It is, however, dependent on the specific workpiece and construction of
the fixture.
Figure 18. Fixture
1 tools, 2 drill bushes, 3 fixture, 4
workpiece
In addition to this, angle-plates, parallel clamps and toe dogs
can be used.
Figure 19. Angle-plate
Figure 20. Parallel clamp
Clamping of tools
The following tool holders are applied:
Taper sleeves
for tools or tool holders with taper shank and for compensating
different tapers per inches between drilling spindle and tool taper.
Figure 21. Taper sleeve
Drill chuck
for chucking tools with parallel shank or cylindrical tool
holders.
Figure 22. Drill chuck
Quick-action chuck
for chucking tools by friction. It makes a quick change of the
clamping of different tools possible and is applied when work-pieces have
different hole contours and hole qualities.
Figure 23. Quick-action chuck
Tap chuck
for drilling of tapped holes with safety clutch preventing
breakage of taps by interrupting the operation when 2/3 of the ultimate torque
of the tap are reached.
Figure 24. Tap chuck
What function do work-holding devices
have?
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What kinds of vice clamping can be
applied?
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