Sheet metal forming 1. Apa yang membedakan antara sheet forming dengan bulk forming? Pada sheet forming perbandingan antara luas permukaan area dengan volume tinggi dan biaxial stresses,sedangkan pada bulk forming perbandingannya tinggi dan triaxial stresses 2. Apa yang dimaksud dengan shearing? Metode pemotongan metal dengan mengoperasikan 2 pisau yang memanfaatkan gaya geser 3. Mengapa pinggiran dari hasil shear atau blanked umumnya tidak mulus? Karena kecepatan punch yg menyebabkan panas yg dihasilkan terbatas pada daerah yg kecil dan lebih kecil juga karena adanya efek clearance yg menyebabkan cacat burr 4. Mengapa proses fineblanking lebih rumit daripada conventional blanking? Karena gerakan punch,pressure pad, dan die-nya dikendalikan secara terpisah 5. Apa yang dimaksud dengan proses slitting? Cutting or shearing along single lines to cut strips from a sheet or to cut along lines of a given length or contour in a sheet or workpiece. 6. Apa perbedaan antara piercing dan blanking? Blanking : The shearing of close contours, when the metal inside the contour is the desired part. Punching or piercing : The shearing of the material when the metal inside the contour is discarded. 7. Apa manfaat terbesar dari pembuatan dies sebagai multipiece assembly?
8. Apa yang dimaksud dengan steel-rule die dan apa jenis material yang dapat di potong? Proses umum yg digunakan untuk memotong berbagai lembaran metal kerja termasuk kertas,kardus,karet dan plastik. Selain untuk memotong juga dapat digunakan untuk membuat lipatan, perforasi dan celah. Steel-rule die dibuat dari substrat kayu lapis dan kadang2 juga membutuhkan aluminium atau baja lalu ditambahkan karet ejeksi untuk membantu mengeluarkan material setelah dipotong. 9. Apa perbedaan antara progressive dies dan transfer dies? Line Dies Line dies are tools that typically are hand or robotically loaded. Often each station that forms or cuts the sheet metal represents a single operation die. Hand-loaded line dies usually lend themselves to low-production parts or those that are too big and bulky to handle with automation. Several line dies usually can be placed within a single press. This allows the operator to transfer the parts from die to die to with a minimal travel distance.
Larger line dies often are placed in individual presses close together in a line, an arrangement referred to as tandem line presses (Figure 1). Some line die advantages are: 1. They often cost less than more complicated dies. 2. They can be timed to run together in a common press. 3. The operation's simplicity allows the part to be turned over or rotated in any axis by the operator or robot if necessary. This often allows for more complex geometries to be created. 4. Smaller individual tools are lighter and can be handled with lower-cost die handling equipment. 5. Maintaining a single station does not require removing all the dies. Common line die disadvantages are: 1. They often cannot compete with production speeds achievable with other methods, such as progressive dies. 2. They require expensive robots or human labor. 3. They often require several presses to manufacture a single part. Transfer Dies Transfer dies are special line dies that are timed together and properly spaced an even distance apart in a single press. The distance between each die is referred to as the pitch, or the distance the part must travel between stations. Unlike with conventional line dies, the piece parts are transferred by special traveling rails mounted within the press boundaries. These rails most commonly are mounted on each side of the dies. During the press cycle, each rail travels inward, grabs the part with special fingers,
Figure 2
and then transfers it to the next die.
Transfer Rails
Transfer systems can perform numerous motions. However, the two basic types are 2-D (two-axis) and 3-D (three-axis). Two-axis transfers move inward, grip the part, and slide it forward to the next station. Threeaxis transfers move in, grip the part, pick it up vertically, move it to the next station, and lower it down onto the die. This third-axis movement allows the part to be placed within the
perimeter gauging boundaries. Transfer systems are popular for manufacturing axialsymmetrical (round), very deep-drawn parts (Figure 2). Some transfer system advantages are: Large parts can be handled at fairly rapid speeds. Stamped parts can be turned over or rotated during the transfer process. Servodrive-type transfers can be programmed to accommodate a large variety of parts, press speeds, and stroke lengths. Transfer dies do not tie each part together, often allowing for material savings. Large volumes of parts can be produced in a fairly short time frame. Some transfer system disadvantages are: They often are quite costly. They often require sophisticated electronics and mechanical finger motion to function properly. They require more die protection sensors. They require a blank destacking system. Progressive Dies The progressive die is one of the most common, fastest methods available for producing piece parts. Unlike line or transfer dies, progressive dies tie the parts together by a portion of
Figure 3
the original strip or coil, which is
Progressive Die Strips
called a strip carrier. Different
Sample strips courtesy of SURE Tool.
types of parts require different carrier designs. Progressive dies can produce as few as seven or eight parts per minute or as many as 1,500 parts per minute. Unlike transfer or line dies, all necessary stations are mounted on a single common die set. These stations are timed and sequenced so that the piece part can be fed ahead a constant given distance called the progression or pitch. Many parts can be tied together allowing many parts to be made with each single press stroke. Progressive dies most commonly are coil-fed, and if they contain the proper sensing system, they often can run unattended. It is not uncommon for a single press operator to run two or
three progressive dies. The coil material typically is pushed through the die; however, systems that can pull and push the coil material through the die are available. Progressive dies usually require the use of a coil feeder and stock straightener (Figures 3 and 4).
Progressive die advantages are: They can produce a great volume of parts very quickly. They often can run unattended. They require only one press. Progressive die disadvantages are:
Figure 4
They usually cost more than line
Progressive Die and Strips
or transfer dies. They often require precision alignment and setup procedures. They require a coil feeder system. They require an open-ended press to allow for the metal to feed into the die. Damage to a single station requires removing the entire die set. They often are much heavier than single-station line dies. The production method you choose depends on many factors. Carefully consider items such as the required volume of parts, your labor rates, and your existing equipment before choosing a production method for your stamped parts.
10. Pada saat membuat bending dari sheet metal, apa yang membedakan dengan bending, forming dan drawing? 11. Mengapa metal umumnya menjadi lebih tipis pada bagian yang di lakukan bending? Karena saat proses bending metal kerja dikenakan gaya tekan pada permukaannya sehingga bagian tersebut menjadi lebih tipis 12. Apa jenis operasi yang dilakukan pada press brake? l e m b a r a n m e t a l a t a u p l a t e d a p a t d i b e n d ( t e k u k ) d e n g a n perlengkapan sederhana menggunakan sebuah tekanan, lembaran atau narrow strips (potongan samping) sepanjang 7 m atau lebih panjang biasanya di bentuk (lekuk) dengansebuah press brake mesin memiliki die yang panjang dalam mekanik atau press hidrolik dan sesuaian khusus untuk produksi. Peralatannya simple dan pergerakannya hanya naik dan turun dan merek a b i a s a n y a diadaptasikan untuk jenis bentuk yang luas, juga proses da pat automatis dengan mudahuntuk biaya rendah, dan produksi tinggi yang terus
menerus material die untuk pressbrake mungkin dapat diantaranya dari kayu keras (untuk tegangan material rendah dan p r o d u k s i k e c i l ) , k a r b i t u n t u k m a t e r i a l k u a t d a n a b r a s i v e d a n j u g a d i p i l i h u n t u k meningkatkan umur die. 13. Untuk aplikasi yang paling sering bagaimanapun baja karbondan gray-iron dies biasanya digunakan. Pada proses press brake 14. Factor apa yang menentukan radius minimum pada bending suatu material? R=
(
) dengan R adalah pengurangan tegangan pada area plat logam
15. Apa perbedaan antara air-bend dengan bottoming dies? Mana yang lebih fleksible? Mana yang lebih reproducible?
16. Apa produk umum dari roll bending? Aplikasinya pada berbagai jenis produk dengan struktur berliku seperti ketel termos 17. Mengapa harga tooling untuk operasi spinning umumnya lebih rendah? Karena dapat menggunakan alat sederhana yg dapat digerakkan dengan tangan seperti alat pembuatan perkakas dari bahan tembikar (tanah liat) 18. Untuk jenis produk yang apa, teknik stretch forming menjadi pilihan utama? Jenis produk yg dibuat dari material dengan ductilitas yg tinggi 19. Apa perbedaan antara shallow(dangkal) drawing dan deep(dalam) drawing? 20. Apa yang dimaksud dengan sheet hydroforming? Pengerjaan lembaran metal yang memanfaatkan tekanan dari fluida pada salah satu sisi atau pada kedua sisi, material yg cocok adalah aluminium foil dan reinforced thermoplastic 21. Apa perbedaan proses hydroforming tekanan rendah dan tekanan tinggi dalam hal tekanan dan deformasi? 22. Apa material dan kondisi proses pada superplastic forming? Materialnya titanium untuk aplikasi luar angkasa ditambah baja atau nikel alluys,kondisi yg dipilih adalah pada diffusion bonded pertama dan yang lain tidak di bonded , menggunakanlayer dari material untuk menghindari bonding . Strukturnya lalu di expand pada mold ,dengan menggunakan argon gas,yang lalu mendapat bentuknya dari mold itu. 23. Apa keterbatasan pada superplastic forming sheet metal? Produknya memiliki nilai stiffness yg tinggi untuk rasio berat karena tipis juga memiliki modulus section. Proses ini umumnya digunakan pada aplikasi luar angkasa sehinnga biaya produksinya juga besar. 24. Apa yang dimaksud dengan diagram forming limit?
A forming limit diagram, also known as a forming limit curve, is used in sheet metal forming for predicting forming behaviour of sheet metal.[1][2] The diagram attempts to provide a graphical description of material failure tests, such as a punched dome test. 25. Apa keunggulan dan keterbatasan dari mechanical press driver? Hydraulic drives? 26. Sebutkan jenis-jenis umum dari press frames? Jawaban 25 & 26 : Press Drives and Frames
Figure 2 This is the most popular press drive used by contract stampers in the automotive industry. It can be run at continuous speeds down to 28 SPM, although typical press speed range is 40 to 80 SPM. Presses fall into four main categories—mechanical (seeimage at top of page), hydraulic, servo, and pneumatic. Each category derives its name from the drive source that generates the pressure (force) on the die to form the finished stamping. Each category can be further divided into one of two different frame designs: straight-side or C-frame. Each type of press can have single- or double-slide (ram) connections. A low-tonnage press can have a single- or double-ram connection depending on whether the accuracy required justifies the additional cost of a double-ram connection. Straight-side presses have two sides and four to eight guideways for the slide. This reduces the deflection and enables them to handle off-center loads better. C-frame presses are shaped like the letter C or G, and most are manually operated. Because of its open form, a C-frame press is subject to higher deflection under off-center loads than a straight-side press. The slide is guided by two V-guides or box guides. Other types of presses, such as transfer, hydroform, hot forge, and friction screw, are built for special applications. Mechanical Press Drive Transmissions
Figure 3 This drive is used when a continuous production speed of lower than 28 SPM is needed. It is good for heavy-duty applications, especially for stamping high-strength steels. Mechanical presses also can be categorized by the type of drive transmission that exerts force on the die: flywheel, single-geared, double-geared, double-action, link (also called alternative slide motion [ASM]), and eccentric-geared. All are powered by an electric motor that drives a large flywheel. The flywheel stores kinetic energy, which is released through various drive types. For each 360-degree cycle of the press, or stroke, energy in the flywheel is consumed as the part is made in the die. This causes the flywheel to slow, usually between 10 and 15 percent. The electric motor then restores this lost energy back into the flywheel on the upstroke of the press. The press is then ready for the next cycle. If the percentage that the flywheel slows (slowdown), determined in strokes per minute (SPM), is greater than 15 percent, the electric motor will not have enough time to restore this lost energy, and the press will slow down too much. After several strokes, the press will jam on BDC. This occurs when the die tonnage or energy has been calculated incorrectly. To stop and start the press, you use an electronic control to a clutch and brake, which in turn disengages the flywheel to the press drive. Most clutches and brakes are spring-applied and have either pneumatic or hydraulic releases. The stopping time of the clutch and brake is critical in determining both the speed that the press can be run and the safety of the operator and die.
Figure 4 A link drive (alternative slide motion) allows reduced slide velocity during the working portion of the press cycle. Flywheel-drive Mechanical Press. Presses with flywheel drives (see Figure 1) are used for piercing, blanking, bending, and very shallow drawing with progressive dies. The normal press tonnage is between 30 and 600 tons. They run at high speeds—125 to 250 SPM on the low end, to speeds in excess of 1,000 SPM on the high end. Press stroke length is always kept as short as possible, as this affects press speed. The average stroke is 2 inches. If more energy is required at the lower speeds, an auxiliary flywheel can be added to the drive. However, the energy will never reach that of a geared press. A flywheel-driven press normally is rated at full tonnage at 0.062 in. from BDC of the press cycle to BDC of the same press cycle. The flywheel, clutch, and brake are located on the eccentric or crankshaft. As a rule of thumb, full press energy is available between half of the top press speed and the top press speed. However, it is best to check with the press manufacturer for confirmation. You need to check die calculations carefully when the material is thicker than the pressrated capacity. You must become aware of what to do with high snap-through (reverse loads) and press vibration when using ultrahigh speeds. Flywheel presses are designed with dynamic balancing of the upper die and press slide (ram) weight using an opposing force. Without this opposing force, the press would walk around the floor at high speeds. Single-geared Mechanical Press. This is the most popular press drive used by contract stampers in the automotive industry (seeFigure 2). The tonnage ranges from 200 to 1,600, with a two-point connection to the slide. The gear ratio allows the flywheel to run fast,
maintaining energy, while the press speed is much slower than a flywheel machine. Singlegeared presses normally are rated at full tonnage between 0.250 and 0.500 in. from BDC to BDC. The correct rating to choose for your application depends on the die's energy requirement. This rating will make a difference in press price and drive size. A single-geared press is used for progressive stamping with dies having shallow draw or forms with piercing and blanking. This type of press drive transmission can be run at continuous speeds down to 28 SPM. A typical press speed range is 40 to 80 SPM with a 12in. stroke. Remember the rule of thumb regarding energy—full press energy is available between half of the top press speed and the top press speed. Always look for a press with a twin-end drive that has opposing helical gears with an eccentric shaft. This will improve accuracy, reduce deflection, and increase longevity. The single-geared drive can be fitted with an alternative slide motion (ASM), or link drive. Double-geared Mechanical Press. This press is used when a continuous production speed of lower than 28 SPM is needed (see Figure 3). It is good for heavy-duty applications, especially for stamping high-strength steels. The drive gear ratio allows the flywheel to maintain its speed while the press runs slower than both the flywheel and single-geared press. Depending on flywheel size, very high energy can be generated with this type of drive. Press tonnage is from 200 to 1,600, with a two-point connection to the slide. A double-geared press drive is good for transfer die work. Transfers typically run at 15 to 30 SPM. Presses with this drive normally are rated 0.500 in. from BDC to BDC. Some presses have a special drive rated at 1 in. from BDC to BDC; it is used for drawing, forming, blanking, and piercing with transfer and progressive dies. The drive can be fitted with an alternative slide motion, or link drive. Link Drive, or Alternative Slide Motion. This option allows reduced slide velocity during the working portion of the press cycle. It also may allow up to a 25 percent increase in production (see Figure 4). Eccentric-geared Mechanical Press This type of press and drive is used where a very long stroke is required — normally in excess of 24 in. (see Figure 5). All of the features of a double-geared press apply to this drive design; however, accuracy is not as good as an eccentric-shaft press because of the clearance with the arrangement of the gear train and the additional clearance needed in the slide guiding gib adjustment.
Figure 5 An eccentric-geared press and drive is suitable when a very long stroke is required; however, accuracy is not as good as an eccentric shaft. Double-action Slide. This press has two slides—one slide within the other (seeFigure 6). Each slide has two connections to the eccentric shaft. The stroke of each is different and timed so the outer slide is the blank holder while the inner slide completes the drawing operation. A double-action-slide press is used in deep-draw applications, such as beverage cans. In addition, it is the first press in an automotive press line for drawing the outer skin panels of cars. Hydraulic Press Hydraulic presses have advanced dramatically over the years with new technologies and improvements in electronics and valves. They are especially suitable for deep-draw applications, because they can apply full tonnage over the complete length of the stroke. In addition, you can program the velocity that the slide travels as it closes the die. You can program the return stroke for fast return, and you can adjust the stroke to any distance you need, thus achieving the maximum SPM available with the pump design. A hydraulic press is powered by a hydraulic pump to a hydraulic cylinder or cylinders that drive the slide down. Pressure can be preset, and once achieved, a valve can activate pressure reversal so no overload can occur. With this press design and its applications, the die tends to guide the press, so the guiding systems do not have to be as accurate as with a progressive-die mechanical press. Hydraulic press production speeds normally are lower than those achieved with a mechanical press.
Figure 6 A double-action slide drive has two slides, one slide within the other. Each stroke differs and is timed so the outer slide is the blank holder while the inner slide completes the drawing operation.
