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The present invention relates to metal powder compaction.
The use of metal powder compaction as a process for facilitating the high volume manufacture of components is a well known and established manufacturing method. Metal powder compaction is often used to manufacture articles due to its ability to economically produce a relatively large volume of articles.
Typically, a metal powder is placed in a die set essentially having the finished shape of the article. The powder is then compressed to a “green” state, sintered at an elevated temperature, and then finished to final dimensions.
Compaction presses are built to provide maximum designed compacting forces. For example, common compacting capacities are 50 tons, 150 tons, up to even 1500 tons. The actual allowable force provided by a compacting press is specific to the design and preferences of the manufacturer of the press.
The required compacting force for a particular article relies upon the geometry of the article being produced, the compressibility behaviour of the power being processed, and the desired density of the article. For example, gears may be compacted to have a density within the range of 6.6 to 7.5 g/cc, more typically around 7.0 g/cc. The required compaction force can be determined using knowledge of the projected area of the gear and the compressibility characteristics of the powder used to form the gear. The required compaction pressure can be determined from a powder compressibility curve as shown in FIG. 1.
For the example shown in FIG. 1, to achieve a compacted density of 7.0 g/cc, a pressure of approximately 40 tsi is required. The compaction force may be calculated as:
Compaction Force=Part Area×Required Pressure.
Accordingly, to compact a gear having an area of 1 sq in, the compaction force required would be 40 tons. Similarly, for a larger gear having an area of 4 sq in, the compaction force required would be 160 tons.
In a manufacturing facility it is typically not economically or logistically feasible to purchase and install a different compaction press that is sized for each specific article that may need to be manufactured at the facility. In order to overcome this obstacle, a common practice is to install a press that is capable of pressing at or above the maximum requirements for any particular article being manufactured, which results in sometimes only a fraction of the available compaction force being utilized. For example, to accommodate the above gears requiring 40 ton and 160 ton compaction forces respectively, a press with a maximum capacity of 250 tons may be used.
There exists numerous prior art methods and apparatus for performing metal powder compaction. For example, U.S. Pat. No. 4,183,238 to Maillet teaches a double-acting press for deep-stamping that uses a plurality of passes; U.S. Pat. No. 5,043,123 to Gormanns et al. teaches a method of coaxially compacting dissimilar powders to form a single composite body; and U.S. Pat. No. 5,238,375 to Hirai uses a nest of rams acting against a common base for producing stepped articles.
However, such prior art methods and apparatus do not overcome the above-described disadvantages, in particular, the need to either install different machines for different articles or to utilize a machine at below its capabilities in order that the machine may be capable of pressing other larger articles.
Accordingly, maximum utilization of the machine is not achieved and throughput is limited to the cycle time of the press being used.
It is therefore an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages.
In one aspect, a tooling assembly for forming metal powder components is provided comprising a plurality of punches operating during a single compaction stroke to compress powdered metal contained by a plurality of corresponding die cavities to simultaneously produce a plurality of discrete powdered metal components.
In another aspect, a method is provided for simultaneously forming a plurality of discrete metal powder components. The method comprises the steps of arranging a plurality of punches and a plurality of corresponding die cavities, containing metal powder in the die cavities, and operating the punches during a single compaction stroke to simultaneously compact the metal powder within the die cavities to produce the components.
An embodiment of the invention will now be described by way of example only with reference to the appended drawings wherein:
FIG. 1 is a graph showing a powder compressibility curve;
FIG. 2 is a sectional elevation view of a tooling arrangement for two-part compaction;
FIG. 3 is a schematic sectional elevation view of the die and tooling shown in FIG. 2;
FIG. 4 is a schematic sectional plan view of the lower punches of the tooling shown in FIG. 3 along line IV-IV;
FIG. 5 shows a series of schematic views illustrating operation of the tooling shown in FIG. 3;
FIG. 6 is a plan view of a pair of pressed gears using the tooling of FIG. 2; and
FIG. 7 is a schematic view of another embodiment of a tooling arrangement for two-part compaction.
Referring therefore to FIG. 2, a multiple part compaction tooling assembly is generally denoted by numeral 10. The tooling 10 shown in FIG. 2 is arranged to simultaneously press a pair of parts A, B. However, it will be appreciated that the tooling 10 may also be arranged to compact more than two parts as desired, and may also be used to compact parts individually. In general, the compacting press (not shown) utilizing the tooling 10 may be a mechanical press or a hydraulic press, and shall not be limited to either.
In general, each part A, B, is compacted within a discrete die set having a die to define the periphery of the particular part, and a pair of punches to cooperate with the die and compress powder in the die. The die sets may be nested (as shown in FIG. 2), one within the other, where dimensions permit, to form parts A, B such as the gears shown in FIG. 6 or may be arranged adjacent to one another (as shown in FIG. 7). In either case, the individual die sets define individual, discrete components, as will be explained more fully below.
The tooling assembly 10 includes a moveable upper punch portion 12 and a moveable lower punch portion 14. The upper portion 12 includes a removable inner top punch 16 and a removable outer top punch I8 that move in tandem.
In this example, the inner punch 16 and outer punch 18 are concentrically arranged about centerline C and each are formed to transfer a particular profile to the separate and distinct parts A and B, that are ultimately produced. It will be appreciated that any profile may be used as desired, and that the punches 16 and 18 are interchangeable to accommodate different punches for different applications. It will also be appreciated that either or both of the upper punches 16, 18 and lower punches 30, 32 may be formed as necessary, in order to define the finished shape of the desired part. The lower punches 30, 32 may also be referred to as die punches or bottom punches.
The lower portion 14 includes a die platen 20, the upper surface of which defines datum D; a central tool core 22; and an annular central punch 24 disposed therebetween. The central punch 24 connects to support 25 and defines an annular inner die cavity 26 and an annular outer die cavity 28 that are distinct and separate from each other. The inner bottom punch 30, connected to support 31, can slide within the inner die cavity 26 in an axial direction, and the outer bottom punch 32, connected to support 33, can slide within the outer die cavity 28 in an axial direction. The bottom punches 30 and 32 are controlled in the tooling assembly 10, and are held stationary at respective axial positions in order to define the respective sizes of the discrete die cavities 26, 28 for containing the respective quantities of metal powder for each discrete part (see shaded portions of FIG. 2). The die cavities 26 and 28 are individually filled with metal powder (as shown to the left of centerline C) prior to compaction thereof for producing a pair of discrete compacted metal powder components (as shown to the right of centerline C). Accordingly, punches 16 and 30 and die chamber 26 defines one discrete die set, and punches 18 and 32 and die chamber 28 define another discrete die set.
The tooling 10 is arranged to distribute the compaction force of the compacting press between the inner punch 30 and outer punch 32 such that this force equals the force applied by the upper portion 12. The distribution of compaction force depends upon the area of each part, and the desired density of the compacted part. Typically, the outer punch 32 will utilize a greater portion of the compaction force than the inner punch 30 due to the relative sizes of the parts (assuming that they use similar materials and are compacted to similar densities).
A schematic representation of the tooling 10 is shown in FIGS. 3 and 4. A series of views of the portion of the tooling 10 to the right of centerline C, is shown in FIG. 5, illustrating operation thereof. To illustrate the relative movements of the parts, datum D is also shown in FIG. 5.
Referring now to the series of views in FIG. 5, a single stroke of the compaction press causes the tooling 10 to compress each quantity of powered metal in the discrete cavities 26, 28, to produce the inner part A and the outer part B respectively. View (a) shows a fill step, wherein the die cavities 26 and 28 are individually filled with respective predetermined quantities of metal powder. View (b) illustrates a compaction step. In view (b), the inner top punch 16 slides within the die cavity 26 and the outer top punch 18 slides within die cavity 28 under a first compaction force F1, applied by the upper tool set 12. Once the punches 16, 18 are within the cavities 26, 28, the lower inner punch 30 and the lower outer punch 32 counter force F1 applied by the upper portion 12, under second and third compaction forces F2 and F3 respectively. Movement of the tipper portion 12 and the lower punches 30 and 32 compacts the individual quantities of powdered metal into the discrete shapes of the separate articles A and B. Compaction continues until the desired density of the material for each part A, B is achieved The forces F2 and F3 are each a portion of the maximum compaction force Fc of the press, and the relationships F1≦Fc; F2+F3≦Fc; and F1=F2+F3 should be satisfied. For the arrangement shown in FIGS. 2-5, typically F2<F3, since the area of part A is smaller than the area of part B. Once the compaction step is complete, the upper portion 12 is raised as shown in view (c).
As shown in view (d), the lower die portions 20, 22 are lowered and the outer bottom punch 32 raised in order to provide a flush surface supporting the compacted parts A and B. The flush surface enables the parts A, B to be more easily removed from the tooling 10 using a pushing mechanism (not shown) so that the next compaction stroke may commence. If capable, the press may cause the tooling 10 to use a control scheme to raise both punches 30 and 32 to provide a flush surface along datum D. Therefore, it will be appreciated that any means for removing the parts A and B from the tooling 10 may be used, but preferably, an arrangement that produces a flush surface should be achieved in order to facilitate such removal.
A plan view of a pair of concentrically pressed gears A, B is shown in FIG. 6. To form the gears shown in FIG. 6, the punches 16, 18, 30 and 32 would include profiles defining the gear teeth, desired pitch etc.
Therefore, the tooling assembly 10 enables the production of a pair of discrete, concentrically sized parts A, B using a single compaction stroke and a single compaction machine, without the need to chance dies or punches to accommodate differently sized parts. The central punch 24 maintains separation between cavities 26, 28 in order to press the parts A, B at the same time, but into discrete components. Moreover, each of the parts 40 and 42 may be produced using a portion of the maximum compaction force of the tooling 10 in order to utilize as much of the available compaction force Fc as possible.
In another embodiment shown in FIG. 7, two parts A′ and B′ are simultaneously compacted in a side-by-side arrangement. The tooling assembly 700 includes a moveable upper punch portion 702, and a moveable lower punch portion 704. The upper portion 12 includes a first top punch 706 laterally spaced from a second top punch 708. Similar to the tooling 10 shown in FIGS. 3-5, the punches 706 and 708 move in tandem with upper portion 702, and operate under a first force F1, which utilizes a portion of but not exceeding, the available compaction force Fc provided by the press utilizing the tooling 700.
The lower portion 704 includes a die platen 710, a central tool core 712, and first and second punch cores 714 and 715. The cores 712, 714, 715, and platen 710, define a first annular die cavity 716 and a second annular die cavity 718 for containing metal powder (shaded portions). The tooling 700 operates in a similar fashion to the tooling 10 to produce a first part A′ and a second part B′ using a single stroke of the compaction press, and a distribution of the available compaction force Fc of the press between the two lower punches 722, 720.
Therefore, multiple parts can be simultaneously compacted in various arrangements, including concentric and side-by-side arrangements. However, the concentric arrangement shown in FIGS. 2-5 is preferable in order to encourage a balance of compaction forces and die stresses. The parts produced in the side-by-side arrangement may also be of similar or the same size to balance forces (e.g. as shown in FIG. 7). It will be appreciated that the examples shown herein are for illustrative purposes only and that any arrangement may be used as required by the particular application.
It has been shown in preliminary testing that a concentric arrangement producing an inner (smaller) gear A having an area of 9.4 sq in. and outer (larger) gear B having an area of 15.3 sq in., can be achieved using an 800 ton capacity press with the above-described tooling assembly 10.
In general, the above test broadly applies to the compaction of many grades of ferrous and non-ferrous powders. In particular, a powder blend has been used consisting of commercially available grades of iron powder, copper powder and carbon (graphite) powder. The nominal elemental composition of the powder was 2% copper, and 0.8% carbon, the remainder being primarily iron with a small concentration of unavoidable impurities. Typical lubricant additions were also used. The compressibility characteristics of the blend are represented by the curve of FIG. 1. In the above example, it was desired to compress the gears to a density of 6.7 g/cc. Therefore, according to the curve of FIG. 1, the inner gear A having 9.4 sq in. area required a compaction force of approximately 300 tons (e.g. F2), and the outer gear B having 15.3 sq in. area required a compaction force of approximately 480 tons (e.g. F3).
Accordingly, the combined required compaction force of approximately 780 tons (e.g. F1) to simultaneously compact both parts could be accommodated by an 800 ton (e.g. Fc) compacting press. The simultaneous compaction allows a doubling of the output from the compaction press (increased throughput) while utilizing a greater portion of the available force Fc, thereby favourably improving the economics of the compaction press.
Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.