July 24, 2003
F & P Manufacturing Inc., a tier-one automotive components supplier, focused on four areas when it developed a hydroforming line for manufacturing Honda Accord engine cradles. These areas were eliminating end scrap, decoupling the bending machines from the manufacturing line, reducing cycle time, and palletizing parts.
F & P Manufacturing Inc., a Tier 1 automotive supplier, is no stranger to competitive and financial pressures. Unrelenting competitive pressures come from the many other Tier 1 suppliers looking for opportunities to increase their slice of the automotive pie. Financial pressures come from the automobile manufacturers that demand price reductions year after year.
To combat these pressures, the company examined its entire manufacturing process, which involves bending, hydroforming, and material handling.
To successfully manufacture the engine cradle for the Honda Accord®, the company set out to build the most efficient hydroforming line in North America. The company concentrated on four main areas: eliminating end scrap, decoupling the bending machines from the manufacturing line, reducing cycle time, and palletizing parts automatically.
F & P Manufacturing, which has been involved in hydroforming since 2000, drew on its automotive metal forming experience when it developed a plan for turning a straight tube into a finished engine cradle. The part design called for a material with a tensile strength of 440 megapascals (MPa). Because the raw material had such high strength, the company paid particular attention to the material's formability to ensure that the tube wouldn't rupture during the forming process.
|Hydroformed engine cradles typically are made from lengths of straight, round tube.|
A forming limit diagram (FLD) showed a few troublesome spots. The company tweaked the design by changing some of the part's design characteristics, such as corner radii. The company also incorporated a boost assist of 10,000 pounds into the bending process. As the rotary action of the bending head draws the tube into the bender, the boost assist pushes tube into the bend area. The extra tube material pushed into the bender by the boost reduces wall thinning during bending, which enhances formability for subsequent forming processes.
The hydroforming process also relies on feeding extra material. The axial feeding process, as it is called in the hydroforming industry, uses 150 tons of force. The pressure helps to reduce wall thinning as the tube expands in the hydroforming die.
|Before they are hydroformed, the tubes are bent so they will fit into the hydroforming die. The benders incorporate boost assist during bending to reduce OD wall thinning.|
Eliminating Scrap."Eliminating end scrap has a big effect on efficiency," said Murray Mason, chief engineer for F & P.
A conventional hydroformed engine cradle starts out as a round tube but ends up with mostly a rectangular but varying cross section when finished. Round plugs seal the tube for the hydroforming process. After the part is hydroformed, the plugs are removed. The ends, which are round, then are cut off and discarded.
To eliminate end scrap, F & P and Schuler Hydroforming Inc., a manufacturer of metal forming equipment, collaborated to devise a process in which the entire length of tube is absorbed in the hydroforming die. The tube goes through a preforming operation that uses two dies to change the shape of the ends from round to square. Square plugs seal the tube ends for the hydroforming process, which monitors the tube end position during end feeding, and the entire tube becomes the cradle. After the tube is formed, the plugs are removed. Cutting off the ends is not necessary, so end scrap is eliminated.
Decoupling Benders. The manufacturing line was designed with flexibility so that small problems do not stop it. The line has two tube benders, which outpace the hydroforming press, and a one-hour buffer of bent tubes. The benders are decoupled for the manufacturing process so that if a problem arises with one of the benders, technicians can work on the problem while manufacturing continues.
|A finished engine cradle is ready for unloading from the hydroforming die.|
Reducing Cycle Time. Reducing cycle time is critical to the success of any high-volume manufacturing operation. A complete hydroforming cycle consists of loading a part into the hydroforming press, closing the press, developing the clamping force (which keeps the die closed during hydroforming), developing the forming pressure (which shapes the part), forming the part, releasing the pressure, opening the press, and unloading the part.
"Based on our experience with manufacturing similar components and a computer simulation, we determined that a conventional hydroforming press would have had a cycle time of approximately 32 seconds for this engine cradle," Mason said.
Rather than using a conventional press, the company chose a mechanical locking press developed by Schuler. The press uses a mechanical locking feature, rather than hydraulic force, to hold the press closed during hydroforming. This eliminates the time needed to develop the clamping pressure and cuts the cycle time by 25 percent.
Palletizing Parts. A fourth operation—unloading the hydroforming press and stacking the parts—was evaluated for efficiency. This normally is accomplished manually or with an unloading system, which can be expensive, according to Mason.
The company developed its own unloading system. This approach reduced costs in two ways—it eliminated a worker and was less expensive than purchasing an off-the-shelf system.
"This is just one step of many that are needed to push hydroforming further along in the manufacturing industry," Mason said.
"For instance, right now each hydroforming line usually is dedicated to a single part. The next step is to advance hydroforming to a point at which dies can be changed quickly and a hydroforming line can accommodate a variety of parts, similar to what we do on our stamping presses."
Such versatility, Mason said, would prevent a line from sitting idle and would thereby increase the equipment's productivity.
F & P America Manufacturing Inc., 2101 Corporate Drive, Troy, OH 45373, 937-339-0212, fax 937-339-0065, firstname.lastname@example.org.Schuler Hydroforming Inc., 7145 Commerce Blvd., Canton, MI 48187, 734-207-7200, fax 734-207-7222, email@example.com, www.schulergroup.com.
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