Patent Application
20090241625
The invention relates to improvements in progressive forming machines and, in particular, apparatus for detecting angularly misaligned blanks at a workstation in which they are to be additionally formed.
Progressive forming machines typically shape a piece of round wire, hereinafter sometimes called a blank, into a desired shape by striking it with tools and forcing it into dies having configurations corresponding to intermediate and finally shaped blanks or parts. Depending on the character of the part, this forging process can involve separate forging blows performed at multiple successive work stations. Hex head or twelve point head bolts are examples of parts commonly produced in progressive forging machines that can suffer when a blank turns even slightly on its longitudinal axis when it is transferred from one work or forming station to another. Where the blank has a profile that is not both circular and concentric with its axis, rotation of the blank about its longitudinal axis can introduce enough misalignment to prevent the blank from being properly received and formed in a succeeding workstation. This unintended turning, even if relatively small, can result in a misshapen part.
In a high production application, particularly where the unwanted turning of a blank occurs randomly and intermittently, a defective finished part may not be detected by the manufacturer. However, even a small number of defective parts mixed in with a large batch of good parts can cause significant problems for the ultimate user of the part. It can be expected that these problems and their associated costs will ultimately be traced back to the manufacturer resulting in customer dissatisfaction as well as ultimate financial loss to the manufacturer that far exceeds the value of the defective part.
The invention provides a system to detect accidentally turned blanks at one or more workstations of a progressive forging machine. The system utilizes the inherent “go, no go” nature of the blank and tooling at the relevant station. Where the blank is properly aligned with the tooling in an angular sense, the blank will be smoothly received in the tooling. To the extent that the blank is angularly misaligned through accidental turning during the transfer process from station to station, it will resist entering the tooling. The system detects resistance of the blank in entering the tooling and interrupts regular operation of the machine to permit the misaligned blank to be removed from the stream of good product.
In the preferred embodiment of the invention, misalignment between an inadvertently rotated blank at a particular work station is sensed by allowing the tooling to be displaced into its holder in response to forces imposed by the blank on the tool. Displacement, i.e. sliding, of the tool is detected by a proximity sensor which in turn communicates with the machine controller that can shut down the machine operation while the turned blank is removed manually or otherwise.
Referring now to
Precise lengths of cylindrical wire stock, i.e. blanks 27, are formed at a cutoff station 26 and from this station are transferred to successive workstations 21a-21d during a part of each machine cycle. A mechanical transfer device (not shown) known in the art, moves each blank 27 during this transfer movement from one station 21 to the next succeeding station 21. Generally, a blank 27 being moved sequentially from station to station, has a cylindrical portion which is grasped by the fingers of the transfer mechanism. Typically, a forging machine is capable of producing forged parts of a wide variety of configurations. Frequently, these blanks or parts have areas with cross-sections that are not round and/or are not concentric about their longitudinal axis. For purposes of explanation, the longitudinal axis of a blank will ordinarily be understood to be the same as the central axis of its original cylindrical wire shape. There are frequently production jobs where it is important that the profile geometry of an accircular and/or eccentric blank, once formed in one station stay angularly aligned with the tooling in a subsequent station so that properly and accurately shaped parts can be reliably produced. Common examples of such parts are hex head and twelve point head bolts. From time to time, slippage or other mishandling of a blank 27 may occur during transfer of a blank from one station to the next and such slippage can involve some degree of turning, i.e. rotation of the blank about its longitudinal axis. Where the cross-sectional shape of a blank is not angularly aligned with the geometry of a subsequent tool, a misshapen or otherwise defective part is likely to be produced. It is therefore a desired goal of the present invention to detect such turned blanks so they can be separated from the product stream of good parts.
The invention detects turned blanks 27 at a workstation such as the workstation 21c depicted in
A local flat or groove 46 on the case 31 is sensed by a proximity sensor 47 fixed in the holder 33 so that movement of the tool 29 and case 31 in the holder 33 results in a change in a signal from the proximity sensor 47. That is to say, the proximity sensor 47 can detect movement of the tool 29 from the position illustrated in
Operation of the machine 10 can be controlled by a programmable logic controller (PLC) 51 (
The machine 10 is thus controlled to interrupt the flow of regular production blanks 27 when the proximity switch or sensor 47 senses this premature or advanced displacement of the tool 29 and case 31, measured by reference to the crankshaft angle. This control strategy is implemented, by way of example, with a hardwired logic circuit schematically shown in
Once the coil of a relay 54 is turned on, its own contact closes and maintains the coil energized as long as either of relay contacts 56 or 57 are closed. The relay 56 is controlled by the proximity sensor 47 and the relay 57 is controlled by the programmable rotary limit switch 52. In order to initially energize relay 54, a momentary reset signal is applied to the coil of the relay via a push button switch 55. Once the relay 54 is “latched in” through its own contact and either relay 56 or 57 remain energized, a “no fault” signal remains applied to the PLC input (the PLC 51 monitors for the absence of a signal to determine that a fault or turned blank condition has occurred).
The programmable rotary limit switch 52 and associated relay 57 hold the turned blank fault indicator relay 54 energized during a time period or portion of a machine cycle that the tool case 31 is ordinarily displaced by proper engagement of a blank 27 in the tool 29. The relay 57 serves to maintain the fault indicating relay 54 on, i.e. latched in at this portion of a machine cycle. In contrast, the programmable rotary limit switch 52 turns off the relay 57 for a time period or segment of a machine cycle before normal displacement of the tool case 31 and the normal turn off of the related relay 56 to thereby create a check window and detect premature actuation of the proximity sensor 47, assumed to be the result of a turned blank.
As soon as neither relay 56 or 57 is energized, the power to the coil of relay 54 is removed and this relay de-energizes which action also opens its own contact. At the same time, the signal to the PLC 51 disappears which condition the PLC recognizes as a sensed turned blank (TBM fault) and the crankshaft 12 is stopped by the PLC with a signal to the clutch brake 14. In the process of stopping the crankshaft 12, even if either relay 56 or 57 are re-energized, relay 54 will not latch in again until a momentary signal is again reapplied to its coil via the reset push button 55.
A dashed outline 70 on
While, as disclosed, the crankshaft 12 can be stopped from cycling by the PLC 51 in the event that a turned blank fault signal is generated by a shut off of the relay 54 to enable a machine operator to manually retrieve the turned blank from the product stream, it is envisioned that the turned blank can be automatically retrieved after it is ejected from the machine and, in fact, with appropriate controls the turned blank could be withdrawn from the product stream of good parts without stopping the crankshaft 12.
It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.
