Cutting by use of rotating axially moving tool – With stopping upon completion of prescribed operation
Reexamination Certificate
2000-03-07
2002-04-16
Tsai, Henry (Department: 3722)
Cutting by use of rotating axially moving tool
With stopping upon completion of prescribed operation
C408S014000, C408S0010BD, C408S017000, C408S095000, C408S097000
Reexamination Certificate
active
06371701
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus having a controllable dwell and, more particularly, to a drilling apparatus having an adjustable dwell mechanism and associated method.
BACKGROUND OF THE INVENTION
The production of components of an assembly, for example, airplane structural components, often requires that holes be drilled in the components to accommodate the fasteners that secure the assembly together. In some instances, the drilled holes may also need to be countersunk. Typically, the countersink has a preferred depth where the diameter of the countersink is matched to the fastener being used. If the countersink is not deep enough, the fastener may protrude outwardly of the component surface. If the countersink is too deep, particularly in a thin-section component, the hole associated with the countersink may be unacceptably large, the structural strength of the component may be adversely affected, and the fastener may not be able to securely fasten the component. In addition, the excess countersink depth, after the fastener has been installed, will define a cavity which may undesirably collect debris or disrupt airflow about the component. Further, since these components are generally fabricated in a manufacturing operation, where multiple holes must be drilled and countersunk in one or more components, consistency of the countersink depth is also typically required.
In some manufacturing operations, drilling and/or countersinking processes may be performed with, for example, portable pneumatic power feed equipment. In these situations, a pneumatic drill motor is used to turn a cutter while a feed mechanism feeds and retracts the cutter over a predetermined distance. The relative positioning of the component or workpiece with respect to the travel of the cutter determines the depth of the hole and or countersink. In practice, the power feed equipment must also incorporate a dwell into the feed/retract cycle of the cutter when the cutter is at the feed limit and before it is retracted. The dwell, or pause in the feed cycle at the feed limit, facilitates consistency in the countersink diameter by allowing a period for the cutter to clean up the countersink surface by removing any extraneous material from the countersink. The dwell also allows a flexible workpiece or other flexible components of the power feed equipment to spring back to their original shape if deformed by the feed force exerted by the feed mechanism feeding the cutter. Thus, obtaining a consistent countersink diameter within specified tolerances using pneumatic power feed equipment generally requires a controllable dwell that is both adjustable and consistently repeatable.
Some typical pneumatic countersinking or drilling/countersinking equipment combine dwell and automatic retract features into the same mechanism. For example, in one instance, a microstop-type adjustable stop is used to control the closing of an air vent port at a point in the cutter feed cycle. The air vent port is generally configured to vent air from a pressurized air source that is also connected to the retract mechanism. As the cutter reaches the feed limit during the feed cycle, the vent port is sealed which causes back-pressure to accumulate. Once the back-pressure reaches a threshold pressure, a spool valve in the retract mechanism is shifted and thereby actuates the retract portion of the feed cycle. In some instances, an adjustable needle valve is included in the dwell and automatic retract mechanism for controlling the amount of air flowing out through the vent port and thereby providing the dwell portion of the mechanism. Generally, an increased restriction of the air flow out through the vent port by the needle valve will result in an increased time between the vent port being sealed and the back-pressure reaching the threshold pressure, thereby providing a dwell between the cutter reaching the feed limit and the spool valve shifting to actuate the retract portion of the feed cycle.
However, this dwell and automatic retraction mechanism may produce unacceptable variances in the amount of dwell between cutter feed cycles. For example, one of the factors affecting the dwell is the relative friction between the spool valve and the bore housing the spool valve. Generally, as the friction between the spool valve and its bore increases, the dwell will also increase for a given dwell adjustment of the needle valve. This friction may further depend on, for instance, the lubrication between the spool valve and the bore or the amount of moisture or particulates in the air supply. These factors, along with the air supply pressure, may vary greatly and frequently in a typical manufacturing environment. Fluctuations in the air pressure will also cause the dwell to vary for a given dwell adjustment of the needle valve.
Another factor possibly adversely affecting the consistency of the dwell is the configuration of the dwell portion of the mechanism. The needle valve controlling the amount of air flowing through the vent port typically comprises a relatively small passage for transporting the air from the air supply. Thus, the needle valve may be sensitive to particulates in the air supply which will tend to accumulate in the needle valve, thereby impeding the air flow and causing the adjustment of the dwell to vary.
Still further, in some instances, if the dwell and automatic retraction mechanism is set for a relatively short dwell, the cutter may be retracted by the retraction mechanism before the feed portion of the feed cycle is fully completed. That is, the feed force generated by the feed mechanism, which is the force that generally feeds the cutter, may not have sufficient dwell time to be transferred to the depth stop at the feed limit before the cutter is retracted. Thus, the cutter may be retracted prematurely, thereby possibly resulting in a shallow countersink in the workpiece.
Thus, there exists a need for pneumatic power feed equipment, particularly equipment used in drilling and or countersinking processes in a manufacturing operation, having a controllable dwell that is both adjustable and consistent between drilling and or countersinking processes. Such a dwell mechanism should desirably be substantially independent of the retraction mechanism and relatively insensitive to fluctuations in the pressure of the air supply as well as to the condition and or purity of the air provided by the air supply. The dwell mechanism should also be configured such that the feed force is transferred to the depth stop before the retraction mechanism can be actuated to reduce the possibility of shallow countersinks.
SUMMARY OF THE INVENTION
The above and other needs are met by the present invention which, in one embodiment, provides an apparatus having a controllable dwell for drilling and or countersinking a hole in a workpiece. The apparatus generally comprises a feed mechanism, a retraction mechanism, and a dwell mechanism. The feed mechanism is configured to feed a spindle from a starting position to a predetermined feed limit during a feed cycle. The retraction mechanism is configured to retract the spindle from the feed limit to the starting position to complete the feed cycle. The dwell mechanism is in communication with the retraction mechanism and comprises a mechanical bias member that stores energy during at least a portion of the feed cycle, wherein the mechanical bias member releases at least a portion of the energy once the spindle reaches the feed limit. The retraction mechanism is only actuated once the spindle reaches the feed limit and the mechanical bias member releases at least a portion of the energy. A predetermined dwell period is thereby provided between the spindle reaching the feed limit and the retraction mechanism being actuated.
In some instances, the retraction mechanism is configured to be pneumatically controlled. The apparatus thus further comprises a pressurized air supply operably connected to the retraction mechanism and to a scalable vent port, wherein the vent port is seal
Blankenship Thomas O.
Fritsche David L.
King Daniel C.
Martinek Brian J.
Morrison James L.
Alston & Bird LLP
The Boeing Company
Tsai Henry
Washington Terrence
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