Patent Application
20140260479
Extruded structural tubes are extruded through a die, cut to size and formed in a hydro-forming process.
Vehicle manufacturers are implementing lighter, stronger materials, such as aluminum alloys to meet emission reduction goals, meet fuel economy goals, reduce manufacturing costs, and reduce vehicle weight. Increasingly demanding safety standards must be met while reducing vehicle weight. One approach to meeting these competing interests and objectives is to hydro-form high strength aluminum alloy tubular blanks into strong, lightweight hydro-formed parts.
Aluminum tube types include seam-welded tube, extruded seamless tube, and extruded structural tube. Seam-welded tube and extruded seamless tube are expensive. Seam-welded tubes and extruded seamless tubes are expensive to convert to finished hydro-formed parts. Extruded structural tubes are lower in cost because they are formed in a continuous mill operation having a greater line and material utilization efficiency than extruded seamless tubes and seam-welded tubes.
Extruded structural tubes are formed by extruding an aluminum billet through an extrusion die at a high temperature and at high pressure. Discontinuous material flow across the section of the shape occurs when the flowing aluminum separates in the mandrel plate and re-converges in the cap section. A weld line, or joining line, is created where the flowing aluminum re-converges to form the extruded shape. Extruded structural tubes may have two or more weld lines that are an artifact of the porthole extrusion process.
Hydro-forming complex parts may require a series of bending, pre-forming, hydro-forming, piercing and machining operations. Bending and hydro-forming aluminum tubes is not currently in use in high volume production operations. (i.e. more than 100,000 units/year) Aluminum intensive vehicles (AIVs) are envisioned that use metal forming methods consistent with current conventional automotive manufacturing methods.
In a high pressure hydro-forming (HPH) operation, the tube is inserted in the HPH die before any fluid under pressure is provided inside the tube. The dies are closed that can result in buckling the tube's cross-section. High pressure incompressible hydro-forming fluid, such as water, is supplied to expand and shape the tube to conform to the die cavity. Substantial press tonnage is required to hydro-form parts in HPH processes. Substantial expansion of the tube (circumferential length of line expansion of more than 5%) is necessary to eliminate any tube buckles and produce complexly shaped parts. It is not feasible to form most parts from aluminum tubes with high expansion HPH operations because aluminum seam-welded, seamless tubes and structural extrusion tubes are less formable than mild steel tubes.
The above challenges and other challenges are addressed by this disclosure as summarized below.
According to one aspect of this disclosure, a method is disclosed for forming an extruded structural tube to form a part. The extruded structural tube is first loaded into a hydro-forming die. The hydro-forming die is partially closed and the extruded structural tube is filled with a liquid beginning at a first pressure. The hydro-forming die is then closed with the tube disposed in the hydro-forming die. The level of pressure applied to the liquid is increased to a second level of pressure to shape the extruded structural tube to form the part.
The extruded structural tube may be pre-bent along its length in a rotary draw bending operation or a push roll bending operation and may be pre-formed radially in a pre-forming die. The pre-bending and pre-forming steps precede loading the pre-bent/pre-formed tube into the hydro-forming die. The hydro-forming die cavity has a shape with a circumferential perimeter that is less than or equal to 2% greater than the circumferential perimeter of the extruded structural tube.
According to a further aspect of this disclosure, a method of forming a part comprises extruding an aluminum alloy through a porthole die to form an extruded structural tube. The tube is cut to the desired size and is bent to form a pre-bent tube. The pre-bent tube may be bent in either a rotary draw bending operation or in a push roll bending operation. (As used herein, the term “bending operation” should be understood and interpreted as referring to in either a rotary draw bending operation or in a push roll bending operation.) The pre-bent and pre-formed tube is loaded into a hydro-forming die that is partially closed to radially compress the pre-bent and pre-formed tube. The pre-bent and pre-formed tube is placed in a hydro-forming die and filled with a liquid at a first level of pressure. The hydro-forming die is closed completely and the level of pressure applied to the liquid is increased to a second level of pressure that is greater than the first level of pressure to shape the pre-bent and pre-formed tube into the part.
According to another aspect of this disclosure, a method of forming a part from an extruded structural tube is disclosed that begins with extruding an aluminum alloy to form the extruded structural tube. The tube is pre-bent in a bending operation to form a pre-bent tube. The pre-bent tube is then loaded into a pre-forming die and the pre-forming die radially compresses the tube to form a pre-bent/pre-formed tube. The pre-bent/pre-formed tube is filled with a liquid at a first level of pressure as the hydro-forming die is partially closed. The hydro-forming die is then fully closed against the pre-bent/pre-formed tube and the level of pressure of the liquid is increased to a second level of pressure to shape the tube.
According to other aspects of this disclosure that may be combined with any of the above described methods, the extruding step may further comprise extruding aluminum at a billet temperature greater than 450° C. and less than 600° C. through an extrusion die including a mandrel plate that separates the heated aluminum and a cap section that re-converges the heated aluminum to form the extruded structural tube with a plurality of weld lines being formed where the heated aluminum re-converges. The extrusion die may be a porthole die which may also be referred to as an extruded structural tube die.
According to another aspect of this disclosure that may be combined with any of the above described methods, the step of pre-bending the extruded structural tube is a bending operation that may be performed in a rotary draw bending tool or a push-roll bending tool.
According to other aspects of this disclosure that may be combined with any of the above described methods, the step of increasing the level of pressure may further comprise increasing the level of pressure beginning with the step of filling the tube and wherein the level of pressure is gradually increased to the second level. The first level of pressure may be referred to as a closing pressure and the second level of pressure may be referred to as a calibration pressure. The step of increasing the level of pressure within the tube in the hydro-forming die results in the tube being hydro-formed into the die. The step of increasing the level of pressure within the tube in the hydro-forming die may further comprise hydro-piercing the tube.
The above aspects of this disclosure and other aspects will be described in greater detail below with reference to the attached drawings.
A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention.
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Pressure sequence hydro-forming may be used to form a straight, longitudinally pre-bent and/or transversely pre-formed tube blank 36. The pre-bent/pre-formed tube 44 is placed in the hydro-forming die 40 and is filled with the hydro-forming liquid 48, or water, at a low pressure that may be referred to as the closing pressure before the hydro-forming die 40 is completely closed. As the hydro-forming die 40 closes, calibration pressure is gradually increased to shape the tube in the hydro-forming die 40. The corners of the part are primarily formed during die closing and the tubular blank retains the nominal wall thickness to enable forming materials having lower formability and assure maintaining the structural integrity of the tube 36.
The internal pressure within the tube resists the tendency of the tube to collapse that otherwise may occur upon closing the hydro-forming die 40. The closing fluid pressure in the tube is always greater than zero. The calibration pressure is used to shape the tube 36 and allows the use of lower tonnage presses and results in lower capital costs. In addition, pressure sequence hydro-forming makes it possible to form complex parts having greater structural integrity with improved accuracy.
The pressure sequence hydro-forming process when applied to an extruded structural tube should be performed to minimize expansion. Pressure sequence hydro-forming assures the structural integrity of the part even though the aluminum tubular blank has lower formability than that of steel.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosed apparatus and method. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure as claimed. The features of various implementing embodiments may be combined to form further embodiments of the disclosed concepts.
