Metal deforming – With use of control means energized in response to activator... – Sensing work or product
Reexamination Certificate
1999-06-25
2001-05-01
Tolan, Ed (Department: 3725)
Metal deforming
With use of control means energized in response to activator...
Sensing work or product
C072S018300, C072S037000, C072S342500, C072S364000
Reexamination Certificate
active
06223573
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the hot forming or forging of metals and, more particularly, in one aspect to methods and apparatus for forming metals which are difficult to process by conventional methods as well as those more readily formed metals. The term metal, as used herein, includes both elemental metals and alloys unless indicated otherwise.
DESCRIPTION OF RELATED ART
Numerous methods for the solid state forming of metallic workpieces or blanks into selected shapes include forging and rolling. Press forging and trimming are two widely used techniques in which the metal is worked at an elevated temperature such as for the formation of gas turbine engine blade airfoils. In a typical forging operation, an unformed workpiece is pre-heated to forging temperature and then shaped with a hammer or ram of a forge press. The unformed workpiece is typically a pre-form having an approximate shape to that of the formed workpiece. In a typical trimming operation, the formed workpiece is trimmed while still hot from the forging process and excess metal and/or flash formed during the forging process is trimmed using trimming dies and a hammer or ram of a trim press. The unformed workpiece is typically a pre-form having an approximate shape to that of the formed workpiece.
The hot forming or forging process requires a heated workpiece at a high temperature, typically above 1700° F. The forge dies, though often heated, are at a much lower temperature, typically less than 500° F. or even at room temperature. The large temperature differential and the high thermal diffusivity of the metals being forged causes a rapid heat transfer. The temperature of the workpiece in contact with the die drops in temperature at 100° F. per second or more. The thinner the workpiece the larger the relative effect of this temperature drop is. In the absence of any other reheating methods, the temperature of the workpiece continues to fall in a transient way until the ram of forge press impacts the upper die against the workpiece. Afterwards, the workpiece temperature continues to fall until the workpiece is removed from contact with the metal die or until it reaches the same temperature as the die. The trimming process is similar in that the formed workpiece is at a substantially higher temperature than the trim dies.
The physical properties of the workpiece material at time of impact of the forge press on the workpiece are a strong function of the temperature at time of impact. These physical properties contribute to the results of the forging process in terms of extent of deformation achieved with a specific forge force as well as the flow of material caused by the forge forces. In addition there is heat generated in the material during deformation caused by the plastic deformation which also effects the results of the forging process. A similar situation exists for the trimming process as regards the deformation in terms of change in shape of the workpiece. This deformation is relating minor compared to that during forging. On the other hand, the trim size itself and the orientation of features of the workpiece relative to each other can be significantly effected.
The conditions of the workpiece at the exact instant of impact by the ram are determined by the transient temperature distribution through the workpiece which in turn is determined by the heat transfer from the workpiece to the die. The heat transfer depends on two parameters, (1) the heat transfer coefficient or resistance to the heat transfer from the workpiece to the die and (2) the time of contact with the colder die during which the heat transfer takes place.
Variations in these two parameters during the forging and trimming processes effect repeatability of the processes and hence the consistency of the parts that are forged and trimmed. It is very desirable to have a high degree of repeatability in forging and trimming processes and forged and trimmed parts that are more consistent.
The variation in the heat transfer coefficient and the time of contact causes substantial variations between parts in the temperature profile in the workpiece and thereby causes variation in the shape and form of the product. This variation is significant because the precision required in gas turbine engine and, in particular, aircraft gas turbine engine airfoils. Various corrective actions are currently used in forge shops to reduce these variations. Adjustments of other press and forming parameters, benching and changing the shape of the dies, subsequent cold working and hot working, chemical metal removal are all used to reduce part-to-part variation to meet tolerance requirements. These corrective operations increase the cost of production and inventory and also increase the cycle time for making the part.
Any variation in the temperature of the workpiece at instant of impact during operation of trim and forge presses effects the stress and deformation of the workpiece which then causes a variation in the orientation of portions of the part. In the case of an airfoil of a gas turbine engine blade in addition to the variation in the shape of the part, it also causes variations in the orientation of the airfoil with respect to the dovetail and platform. In the trim process it also causes variations in the chord length of the airfoil. These variations cause difficulty in meeting the tolerance requirement of the component. Subsequent operations to manually bench or deform the part to conform to the orientation required and to grind the chord length add to the cost of the part, time to produce it, and increases inventory. For the precision required in aviation airfoils this variation causes substantial cost increases. For very large variations, the current practice requires adjustments or other press and forming parameters.
Another factor that effects repeatability or part-to-part variation is the additional variability due to operators working at different speeds and variations during the shift of same operator. These differences cause both the time of contact and the heat transfer coefficient to vary with consequent variation in the part geometry. There is a need to reduce part-to-part variation in the forging and trimming processes using presses and improve consistency of hot formed parts made with forge and trim presses.
SUMMARY OF THE INVENTION
The invention includes methods and apparatus for forging and trimming with forge and trim presses.
A method for activating a ram in a press having a lower die and an upper die connected to a ram includes heating a workpiece to a first temperature above an impact temperature, placing the workpiece on the lower die, monitoring the workpiece during chill down of the workpiece from the first temperature, and actuating the ram based upon the monitoring in a controlled manner to effect an impact of the upper die against the workpiece. In one embodiment of the present invention, the monitoring includes measuring a characteristic parameter of the workpiece and the actuating includes actuating the ram after a predetermined fixed value of the measured parameter is measured. The placing of the workpiece on the lower die is done manually in the preferred embodiment.
In a more particular embodiment, the characteristic parameter is a contact time period of the workpiece with the lower die and the measuring includes starting to measure the contact time period of the workpiece with the lower die as soon as contact is made between the workpiece and the lower die, and actuating the ram to effect the impact occur at a predetermined fixed period of time after the contact is made. More particularly, an operator manually places the workpiece on the lower die with a holding tool, has the tool make and stay in contact with a wire near the lower die as the workpiece is placed onto the lower die, and initiates starting to measure the contact time period by completing an electrical starting circuit from the wire through the tool, the workpiece, and the lower die.
In another embodiment, the characteristic parameter is
Couture Richard L.
Demichele Stephen R.
Grewal Sukhminder S.
General Electric Company
Gressel Gerry S.
Hess Andrew C.
Tolan Ed
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