Forging is a well-known method of making metal parts, such as parts made from aluminum. Modern aluminum forging processes involve providing a round ingot, rolled plate or extruded billet of aluminum, slicing that ingot, plate or billet to make blanks therefrom, then forging each blank into a desired aluminum part shape. The forging step usually involves heating the blank ("hot-forging") and then using forging equipment to shape the part. There are usually several forging steps, which may involve multiple dies, that must be performed in order to form the final shape for the metal part.

Forged aluminum parts have excellent mechanical properties, such as high yield strength and high ultimate tensile strength. In addition, forged parts have excellent strength-to-weight characteristics, which is important to automobile makers, because it means that lighter parts can be used to obtain the necessary strength levels of their heavier steel counterparts. These mechanical properties are crucial especially when the metal parts are used for vital structural members of an automobile, such as control arms. These forged parts, however, are expensive to make relative to cast parts. That is because of the many steps it takes to make a forged part, including casting an ingot, extruding a billet from that ingot, slicing blanks from that billet or other feedstock then performing several forging operations on each blank to transform it into a metal part. In addition, because many times the billet is cylindrical, and because some metal parts have irregular plan view shapes (such as the "Y-shape" of a control arm) there is only about a 30% metal recovery, with metal recovery being defined as a fraction whose numerator is the weight of the final metal part and whose denominator is defined as the initial weight of the blank (times 100% to obtain a percentage).

Until recently, cast metal parts were not used for structural members where high strength was necessary. This is because such cast parts exhibited

unacceptable strength characteristics, due to discontinuities, such as porosity, imparted through typical casting processes. Casting technology has greatly improved over the last decade, however, and cast parts are now starting to rival forged parts in both strength and durability. Because cast parts are less expensive to make, some automobile makers are moving towards replacing forged parts with cast equivalents where possible.

What is needed, therefore, is a method wherein a metal part can be made by a forging process, but which eliminates some of the prior art steps so that forgings can compete with cast metal equivalents with regard to both mechanical properties and cost of production.

The method of this invention has met or exceeded the above mentioned need as well as others. A method of producing metal parts is disclosed in which a shaped metal ingot is provided which has a desired cross-sectional shape substantially in the same configuration of the metal part to be produced. Preferably, the shaped metal ingot is made by a continuous casting method, though discontinuously cast ingot may also be used on a less preferred basis. The desired cross-section of this intermediate part can be non-circular or non-rectangular in shape, and may have shapes resembling an L, Y, V, T, or even C in cross-section.

After providing a shaped metal ingot of this sort, it is sliced to create blank thicknesses having the desired cross-sectional shape. These blanks are then forged into metal parts using minimum tooling, typically just one forging die and significantly less pressure than the multiple die, high pressure forging operations required by the prior art.

The metal part can be made of aluminum such as a 5000 series aluminum alloy (Aluminum Association designation) for example, AA 6061 though it is to be understood that many other alloy forms can be transformed into forged parts in this manner. A representative metal part made in this manner is a control arm for an automobile, or any one of a number of automobile parts.

A full understanding of the invention can be gained from the following detailed description of the invention when read in conjunction with the accompanying drawings in which: Figure 1 is an isometric view of a representative shaped metal ingot

according to the present invention; Figure 2 is a view similar to Figure 1, only showing a blank of the invention being sliced from this elongated metal ingot; and Figure 3 is a top plan view of a control arm showing the sections thereof that were tested for tensile strength, yield strength and elongation as set forth in the accompanying example data.

The Aluminum Association alloy designations herein (AA 6061) are indicated by the preface letters "AA" followed by four numerals, thus in the form "AAXXXX". Reference may be made for compositional details to "Registration Record of International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys" published by The Aluminum Association, Washington, D.C., the disclosure of which is fully incorporated by reference herein. Mechanical properties, such as strength and elongation are as defined in ASTM EG-89, Standard Terminology Relating to Methods of Mechanical Testing and as determined according to ASTM B 557-84, Standard Methods of Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products both disclosures of which are also fully incorporated by reference herein. "Metal recovery" is as defined in the "Background" Section above.

In accordance with this invention, a shaped metal ingot 10, such as that shown in Figure 1, is provided. The shaped metal ingot 10 shown in Figure 1 is in the shape of a "Y", although it will be appreciated that other cross-sectional shapes such as an "L-shape", "T-shape", "V-shape" or even "C-shape" can be provided. The shaped metal ingot 10 can be any desired length, depending on the manufacturing process used to make such ingots as will be discussed below. The ingot shown in Figure 1 is made of aluminum, such as a 6000 series alloy, for example AA 6061, although it will be appreciated that the invention contemplates any type of forgeable aluminum alloy and indeed, any type of metal.

The shaped metal ingot 10 is preferably made using a continuous casting process in which molten metal is introduced continuously in a mold and solidified therein to form the shaped metal ingot 10. One type of continuous casting process is a level pour process in which molten metal is introduced into a mold that moves downwardly as the molten metal is cast into the mold. Another

continuous casting process that can be used is the known horizontal direct casting (or "HDC") process. Shaped metal ingots 10 can also be formed by still other processes including a vertical continuous cast. For some alloys or alloy compositions, it may prove necessary or even economically beneficial to discontinuously cast ingot shapes according to this invention before slicing and forging the same. Suitable means for making such discontinuously cast ingots include, but are not limited to sand or metal mold processes like: green sand casting, squeeze casting, low pressure casting, die casting, tilt casting, level pour and/or vacuum riserless casting (or "VRC") processes.

One type of preferred caster that can be used for the continuous casting process is a generally vertically oriented caster in which molten metal is introduced into the upper portion of the mold and solidified into the shaped metal ingot 10 in the mold. The shaped metal ingot 10 is then moved out of the lower portion of the mold for subsequent processing. A generally horizontally disposed caster is similar, only with the molten metal being introduced into one side of the generally horizontally-oriented mold and solidified therein. The shaped metal ingot 10 is then moved through the other side of the mold for subsequent processing.

There are several inherent advantages in continuously casting shaped metal ingot 10. First, continuous casting process avoids the steps of traditionally forming an extruded billet from an ingot. In the prior art process, first an ingot must be cast. After this, the ingot must be treated, such as by scalping and homogenization, in order to prepare it for extrusion into billets. The billets are then extruded in a press and readied for slicing. By contrast, molten metal is cast directly into shaped metal ingot 10, in the continuous casting process, thus eliminating the need for extruding a billet, and an extrusion press, for that matter.

Advantageously, shaped metal ingot 10 can be cast with a desired cross-sectional shape that is substantially in the same configuration of the metal part to be produced, such as the "Y-shaped" elongated metal product 10 shown in Figure 1.

Because the shaped metal ingot 10 has a cross-sectional shape in substantially the same configuration of the metal part to be produced, metal recovery is significantly improved. In fact, metal recovery with prior art processes was between about 25-30%. With the present invention, metal recovery increases to

about 60-70%.

Finally, continuously cast shaped metal ingots have more desirable metallurgical properties, such as finer grain size. In traditional processes, the ingot created has a coarser grain size, and then, upon extrusion, these grains are worked and become flattened. A continuously cast shaped metal ingot, on the other hand, has a finer grain size due to its generally smaller cross-section which allows for more even solidification through its cross-section.

In accordance with this invention, shaped metal ingot 10 is next sliced into a plurality of blanks. Figure 2 shows a typical blank 20, which is about 2.5 inches thick. Blank 20 is created by saw cutting the shaped metal ingot 10 along one or more vertical lines. The blanks then have the same cross-sectional shape as the shaped metal ingot 10. After cutting, the surfaces of the blanks are treated, such as by sanding, in order to prepare the blank 20 for forging.

The blank, such as blank 20, is then preheated to one or more forging temperatures and held at a preferred final forging temperature for a desired period of time. The preheated blank is then forged, often using only a finish-only die.

Because these blanks are formed very near the shape of the final part, less forging pressure is needed to form metal parts from such blanks. Normally, there is no need to use multiple dies so blanks can be formed into metal parts using minimal tooling. After forging, flash is trimmed from the metal part before it is thermally treated, such as by known heat treatments and aging practices specific to the alloy being cast and forged or specific to the part being manufactured therefrom and any desired property characteristics therefor. These post forging operations are well known to those skilled in the art.

It will be appreciated that the process of the invention eliminates many steps of the prior art and thus reduces tooling costs while increasing throughput and metal recovery. It also decreases the amount forging pressure (and thus press size) needed to manufacture forged shapes like these. With this invention, for example, press size reductions of about 25% or more are practical. In other words, if a prior 4000 Ton mechanical forging press would have been needed to make Part X by conventional forging means, a 3000 Ton or less mechanical press would be needed to forge that same part according to this invention.

EXAMPLE A shaped metal ingot in the form shown in Figure 1 was cast with AA 6061 aluminum alloy using a level pour process. This experimental ingot had a total length of about three feet. A blank having a thickness of about 2.5 inches was sliced from this ingot and its surfaces treated by sanding in order to prepare the blank for forging. The blank was then preheated to a temperature of about 850"F before being placed in a die to forge an automotive control arm therefrom. A top view of this control arm 30 is shown in Figure 3. From this, four longitudinal samples (L1, L2, L3, L4 indicated in Figure 3) and three transverse samples (items T1, T2, T3 in Figure 3) were taken and subjected to Tensile-Yield Strength- Elongation ("TYE") tests. Each sample was tested nine times.

The TYE results for the nine tests for each sample are reported below: Yield Ultimate Tensile Elongation L1 Strength (KSI) Strength (KSI) (%) AVG 46.1 49.3 10.2 HIGH 48.4 52.1 13.0 LOW 44.8 47.8 8.0 Yield Ultimate Tensile Elongation L2 Strength (KSI) Strength (KSI) (%) AVG 46.2 49.4 10.2 HIGH 48.2 52.1 13.0 LOW 44.8 47.2 8.0 Yield Ultimate Tensile Elongation L3 L3 Strength (KSI) Strength (KSI) (%) I AVG 47.0 49.8 10.6 HIGH 47.3 50.5 12.0 LOW 46.6 48.8 10.0

Yield Ultimate Tensile Elongation L4 Strength (KSI) Strength (KSI) (%) AVG 45.4 48.8 11.4 HIGH 48.2 52.3 12.0 LOW 43.8 46.6 10.0 II Yield Ultimate Tensile Elongation T1 Strength (KSI) Strength (KSI) (%) AVG 44.9 47.8 13.2 HIGH 48.2 51.4 15.0 LOW 43.5 45.4 12.0 I I II Yield Ultimate Tensile Elongation T2 Strength (KSI) Strength (KS I) (%) AVG 45.5 48.9 13.2 HIGH 47.2 51.3 15.0 LOW 43.7 46.8 12.0 Yield Ultimate Tensile Elongation T3 Strength (KSI) Strength (KSI) (%) AVG 46.6 49.5 9.2 HIGH 48.2 50.5 12.0 LOW 45.6 48.6 8.0 These results compare very favorably with TYE results performed on a similar control arm made by a conventional extruded billet processing.

It will be appreciated that a method is provided of making a metal part by first casting a shaped metal ingot and then slicing a blank from that ingot and finally forging that blank into a metal part. The metal part made by this process has mechanical properties which compare favorably to metal parts made by prior art processes where much larger blanks were sliced from extruded billets made from cast ingots. The method of the invention, however, provides these desired properties by eliminating several steps in the prior art process while at the same time dramatically increasing metal recovery.

While specific embodiments of the invention have been disclosed, it will be appreciated by those skilled in the art that various modifications and alterations to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.