By an engineer with decades of practical manufacturing experience, this book is a complete modern guide to sheet metal forming processes and die design - still . design of dies for sheet-metal forming processes described. metal forming processes, die design, and die manufacturing, it should be evident that it is not. However, we should recall that, at the moment when the die design is carried out, Most problems in sheet metal forming come from a bad control of holding.
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Sheet Metal Forming Processes and Die Design is a complete modern guide to sheet metal forming processes and die design – still the most commonly used. useful in imparting stiffness to parts; can be controlled by proper tool and die design. Quality of sheared edges. Depends on process used; edges can be rough. during sheet-metal forming design. Sheet-metal forming using rigid tools i.e. punch, die enon was possible only for bending processes of the el- ements with.
Since the presence of elastic properties of metals, after the unloading phase, the elastic springback phenomenon always occurs resulting in an off-target formed shape. Springback is dimensional deviation due to the elasticity of a metal sheet during unloading and following forming [ 2 ]. Although it is impossible to eliminate the springback phenomenon, minimizing springback can be done by adopting three approaches.
The first one is based on controlling the blank holder force BHF.
Boljanovic V. Sheet Metal Forming Processes and Die Design
The blank holding force is not fixed, but, as a controlled variable, the blank holding force is known as variable blank holder force VBHF so that the springback can be minimized.
The second approach is by using a hot forming process and the third one is by optimizing die surfaces die compensation to accommodate the springback. A precision binder force control during forming is required, making this process sensitive to any variations in manufacturing conditions such as punch speed, time control, and friction.
The study of springback reduction by the temperature value of tool in hot forming has been investigated [ 6 ].
The experimental investigations in hot forming process can be found in the latest publications [ 7 — 9 ]. Temperature in the springback prediction is becoming a topic that could be improved in the future investigation [ 2 ]. The springback value before and after splitting process is different. This has been studied using split-ring tests for aluminum alloy [ 10 ]. The major advantage of the first strategy to minimize springback is that it is not necessary to modify the tooling surface.
However, there are several implementation difficulties such as implementing the force control or force sensor in the application of VBHF being highly cost sensitive. Similarly, in the hot forming process, it requires additional equipment to control the temperatures of the tools and the blank sheet so that the forming process becomes more complicated and expensive.
In the third method die compensation , it requires many steps of works on tooling design stage, but its potential to compensate springback completely is faster and cheaper even for complex model. Die face adjustment to compensate the springback was done manually in the past, by doing extensive measurements on the prototype or even production tools and refining the tool surface geometry by hand polishing which is time consuming [ 11 ].
Boljanovic V. Sheet Metal Forming Processes and Die Design
Wagoner et al. Finite element FE and numerical and process simulation have gained popularity in the stamping industry due to its speed and low cost, and it has been proven to be effective and efficient in the prediction of form ability and springback behavior [ 12 , 13 ].
The accuracy of springback simulation is not only related to springback analysis itself but also strongly dependent on the accuracy of forming processes. Any calculation error obtained from every simulation step of forming processes will be accumulated. As a result, the accumulated error influence the accuracy of the springback prediction analysis at the last step of the simulation.
Ling et al. The results show a good reduction in springback, but this method is applied and tested in the L-bending only. The bending operations include:.
This is a process of a forming a flat workpiece into a hollow shape by means of a punch, which causes the blank to flow into die cavity. Under this operation, the metal is caused to flow to all portions of a die cavity under the action of compressive forces.
Flanging is a process of bending the edges of sheet metals to 90o Shrink flanging — subjected to compressive hoop stress.
Stretch flanging —subjected to tensile stresses. Sheet metal or plate can be bent easily with simple fixtures using a press.
Long and relatively narrow pieces are usually bent in a press break. This machine utilizes long dies in a mechanical or hydraulic press and is suitable for small production runs. The tooling is simple and adaptable to a wide variety of shapes. Schematic illustrations of various bending operations in a press brake. In beading the edge of the sheet metal is bent into the cavity of a die. The bead gives stiffness to the part by increasing the moment on inertia of the edges. Also, it improves the appearance of the part and eliminates exposed sharp edges.
For bending continuous lengths of sheet metal and for large production runs, roll forming is used. The metal strip is bent in stages by passing it through a series of rolls.
Stages in roll forming of a sheet-metal door frame. In Stage 6, the rolls may be shaped as in A or B. The oldest method of bending a tube or pipe is to pack the inside with loose particles, commonly used sand and bend the part in a suitable fixture.
This techniques prevents the tube from buckling. After the tube has been bent, the sand is shaken out. Tubes can also be plugged with various flexible internal mandrels.
Methods of bending tubes. Internal mandrels,or the filling of tubes with particulate materials such as sand,are often necessary to prevent collapse of the tubes during bending. Solid rods and structural shapes can also be bent by these techniques. The punch is then retracted, the plug returns to its original shape and the part is removed by opening the dies. Water pitchers can be made by this method.
Stretch forming is used primarily to make aircraft-wing skin panel, automobile door panels and window frames. Schematic illustration of a stretch-forming process. Aluminum skins for aircraft can be made by this process. Polyurethanes are used widely because of their resistance to abrasion, long fatigue life and resistance to damage by burrs or sharp edges of the sheet blank.
In bending and embossing sheet metal by the rubber forming method, as shown in the following Figure, the female die is replaced with a rubber pad.
Parts can also be formed with laminated sheets of various nonmetallic material or coatings.
Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die.
This procedure allows close control of the part during forming to prevent wrinkling or tearing. When selected properly, rubber forming and hydroforming processes have the following advantages: Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes.
The hydroform or fluid forming process.
Note that, in contrast to the ordinary deep-drawing process, the pressure in the dome forces the cup walls against the punch. The cup travels with the punch; in this way, deep drawability is improved. This procedure can form simple tubes or it can form intricate hollow tubes as shown in the following Figure. Applications of tube-hydroformed parts include automotive exhaust and structural components. Automotive exhaust and structural components, bicycle frames, and hydraulic and pneumatic fittings are produced through tube hydroforming.
The pressure of this wave is sufficient to form sheet metals.
Advantages Lower strength is required and less tooling costs Complex shapes with close tolerances can be made Weight and material savings Little or no residual stress occurs in the formed parts Disadvantages Materials must not be super elastic at service temperatures Longer cycle times. Types of structures made by diffusion bonding and superplastic forming of sheet metal.
While concentrating on simple, applicable engineering methods rather than complex numerical techniques, the author uses many illustrations, tables, and charts to enhance comprehension and learning. The product requires Adobe Reader or Adobe Acrobat. The CD-ROM should operate with corresponding Windows-compatible hardware, including desktops, notebooks, laptops, netbooks and tablet computers.
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Vukota Boljanovic, Ph. He received his B.Muhammad Yasir. In order to accommodate the springback and to optimize the die based on surface modification, there are two methodologies available called displacement adjustment DA compensation and spring forward SF compensation. By using many of these processes together, sheet metal parts can be fabricated with cutouts and profiles of any 2D geometry. Secondary finishing operations are typically performed to attain smoother edges.
Applications of tube-hydroformed parts include automotive exhaust and structural components.