1. Manufacturing Processes
Sheet Metal Forming
판재 성형
Associate Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University 1

2. Sheet metal forming (판재성형)
Sheet metal forming is a processes that shape a piece of sheet metal into the desired part through shearing(전단) and deformation(성형).
It is also called pressworking, press forming, or stamping.
Sheet metal can be cut, bent, and stretched into a nearly any shape. Material removal processes can create holes and cutouts in any 2D geometric shape. Deformation processes can bend the sheet numerous times to different angles or stretch the sheet to create complex contours.
Sheet metal fabrication processes can mostly be placed into two categories - forming and cutting. Forming processes are those in which the applied force causes the material to plastically deform, but not to fail. Such processes are able to bend or stretch the sheet into the desired shape. Cutting processes are those in which the applied force causes the material to fail and separate, allowing the material to be cut or removed. Most cutting processes are performed by applying a great enough shearing force to separate the material, and are therefore sometimes referred to as shearing processes. Other cutting processes remove material by using heat or abrasion, instead of shearing forces.

3. Contents
[Shearing]
[Forming]
[Press Die]

4. Cutting with Shearing (전단)
Sheet metal is separated by applying shearing force using punch and die.
Edge fracture & burr.
Punch
Sheet metal
Die F
Clearance
Rollover
Burnish
Fracture
Burr
Cutting processes are those in which a piece of sheet metal is separated by applying a great enough force to caused the material to fail. The most common cutting processes are performed by applying a shearing force. When a great enough shearing force is applied, the shear stress in the material will exceed the ultimate shear strength and the material will fail and separate at the cut location. This shearing force is applied by two tools, one above and one below the sheet. Whether these tools are a punch and die or upper and lower blades, the tool above the sheet delivers a quick downward blow to the sheet metal that rests over the lower tool. A small clearance is present between the edges of the upper and lower tools. The size of this clearance is typically 2-10% of the material thickness.

5. Cutting with shear Shearing - Separating material into two parts
Blanking - Removing material to use for parts
Punching - Removing material as scrap
Scrap
Part
Part1
Part2
Part
Scrap
Shearing
Blanking
Punching

6. Shearing
Shearing cuts straight line to separate a piece of sheet metal into smaller parts.
Shearing a specific cutting process that produces straight line cuts to separate a piece of sheet metal. Most commonly, shearing is used to cut a sheet parallel to an existing edge which is held square, but angled cuts can be made as well. For this reason, shearing is primarily used to cut sheet stock into smaller sizes in preparation for other processes.

7. Blanking Desired part (gears, key) is removed from sheet metal.
Fine blanking, applying 3 separate forces, produces smooth and flat edges with minimal burrs and tolerances.
Punch
Stringer
Upper pressure pad
Blanking is a cutting process in which a piece of sheet metal is removed from a larger piece of stock by applying a great enough shearing force. In this process, the piece removed, called the blank, is not scrap but rather the desired part. Blanking can be used to cutout parts in almost any 2D shape, but is most commonly used to cut workpieces with simple geometries that will be further shaped in subsequent processes. Often times multiple sheets are blanked in a single operation. Final parts that are produced using blanking include gears, jewelry, and watch or clock components. Blanked parts typically require secondary finishing to smooth out burrs along the bottom edge.
The blanking process requires a blanking press, sheet metal stock, blanking punch, and blanking die. The sheet metal stock is placed over the die in the blanking press. The die, instead of having a cavity, has a cutout in the shape of the desired part and must be custom made unless a standard shape is being formed. Above the sheet, resides the blanking punch which is a tool in the shape of the desired part. Both the die and punch are typically made from tool steel or carbide. The hydraulic press drives the punch downward at high speed into the sheet. A small clearance, typically 10-20% of the material thickness, exists between the punch and die. When the punch impacts the sheet, the metal in this clearance quickly bends and then fractures. The blank which has been sheared from the stock now falls freely into the gap in the die. This process is extremely fast, with some blanking presses capable of performing over 1000 strokes per minute.
Fine blanking is a specialized type of blanking in which the blank is sheared from the sheet stock by applying 3 separate forces. This technique produces a part with better flatness, a smoother edge with minimal burrs, and tolerances as tight as ± As a result, high quality parts can be blanked that do not require any secondary operations. However, the additional equipment and tooling does add to the initial cost and makes fine blanking better suited to high volume production. Parts made with fine blanking include automotive parts, electronic components, cutlery, and power tools.
Most of the equipment and setup for fine blanking is similar to conventional blanking. The sheet stock is still placed over a blanking die inside a hydraulic press and a blanking punch will impact the sheet to remove the blank. As mentioned above, this is done by the application of 3 forces. The first is a downward holding force applied to the top of the sheet. A clamping system holds a guide plate tightly against the sheet and is held in place with an impingement ring, sometimes called a stinger, that surrounds the perimeter of the blanking location. The second force is applied underneath the sheet, directly opposite the punch, by a "cushion". This cushion provides a counterforce during the blanking process and later ejects the blank. These two forces reduce bending of the sheet and improve the flatness of the blank. The final force is provided by the blanking punch impacting the sheet and shearing the blank into the die opening. In fine blanking, the clearance between the punch and the die is smaller, around inches, and the blanking is performed at slower speeds. As a result, instead of the material fracturing to free the blank, the blank flows and is extruded from the sheet, providing a smoother edge.
Sheet metal
Die
Lower pressure cushion
Fine
blanking
Blanking
Spoon

8. Punching Scrap(Hole, slot) is removed from sheet metal.
Piercing - cylindrical punch
Slotting - rectangular holes
Perforating - large number of holes
Notching - edge of sheet
Lancing - partial cut to be bent
Slitting - straight line
Parting - separating a part
Cutoff - separating a part
Punching is a cutting process in which material is removed from a piece of sheet metal by applying a great enough shearing force. Punching is very similar to blanking except that the removed material, called the slug, is scrap and leaves behind the desired internal feature in the sheet, such as a hole or slot. Punching can be used to produce holes and cutouts of various shapes and sizes. The most common punched holes are simple geometric shapes (circle, square, rectangle, etc.) or combinations thereof. The edges of these punched features will have some burrs from being sheared but are of fairly good quality. Secondary finishing operations are typically performed to attain smoother edges.
The punching process requires a punch press, sheet metal stock, punch, and die. The sheet metal stock is positioned between the punch and die inside the punch press. The die, located underneath the sheet, has a cutout in the shape of the desired feature. Above the sheet, the press holds the punch, which is a tool in the shape of the desired feature. Punches and dies of standard shapes are typically used, but custom tooling can be made for punching complex shapes. This tooling, whether standard or custom, is usually made from tool steel or carbide. The punch press drives the punch downward at high speed through the sheet and into the die below. There is a small clearance between the edge of the punch and the die, causing the material to quickly bend and fracture. The slug that is punched out of the sheet falls freely through the tapered opening in the die. This process can be performed on a manual punch press, but today computer numerical controlled (CNC) punch presses are most common. A CNC punch press can be hydraulically, pneumatically, or electrically powered and deliver around 600 punches per minute. Also, many CNC punch presses utilize a turret that can hold up to 100 different punches which are rotated into position when needed.

9. Punch Force
The punch force is product of shear strength of sheet metal and cross-sectional area being sheared.
Punch force : F ≈ (0.7σu)tl
σu = ultimate tensile strength
t = thickness
l = total length of the sheared edge t l F

10. Punch press machine Punch press bending tool
AMADA
LVD

11. Ex) Calulation of punch force
Estimate the force required in punching a 25 mm diameter hole through a
1.8 mm thick 5052-O aluminium sheet at room temperature. Ultimate tensile strength of it is 190 MPa.
Solution
F = ( Mpa) (1.8 π 25 mm2) = 18.8 kN

12. Forming (성형)
The sheet is bent or stretched into various shapes by tensile forces in the plane of the sheet.
Bending
Deep Drawing
Stretch forming
Roll forming
Spinning

13. Bending (굽힘) of Sheet and Plate
A force is applied to a piece of sheet metal, causing it to bend at an angle and form the desired shape.
In bending, recovery is called springback. σy Ri Rf t θi θf
Bending is a metal forming process in which a force is applied to a piece of sheet metal, causing it to bend at an angle and form the desired shape. A bending operation causes deformation along one axis, but a sequence of several different operations can be performed to create a complex part.

14. Ex) Springback of bending
A 20-gage ( cm) steel sheet is bent to a radius of 1.27 cm. Assuming
that its yield stress is 276 MPa, calculate (a) the radius of the part after
it is bent, and (b) the required bend angle to achieve a 1.57 rad bend after
springback has occurred.
Solution
The appropriate formula is
and
Hence,
b. Required bend angle is

15. Bending die V-bending die Wiping die
Acute angle die; Gooseneck die; Offset die; Rotary bending die w
(a) V-die
Punch
Die w
(b) Wiping die
©갈창우, GNU

16. Press brake Laser Cutting Press brake (Bending)

17. Deep Drawing
Flat sheet-metal blank is pressed, using punch, into the die cavity.
Bank is held in place with a blankholder under a certain force.
Die
Punch
Blankholder
Blank
Deep drawing is a metal forming process in which sheet metal is stretched into the desired part shape. A tool pushes downward on the sheet metal, forcing it into a die cavity in the shape of the desired part. The tensile forces applied to the sheet cause it to plastically deform into a cup-shaped part. Deep drawn parts are characterized by a depth equal to more than half of the diameter of the part. These parts can have a variety of cross sections with straight, tapered, or even curved walls, but cylindrical or rectangular parts are most common. Deep drawing is most effective with ductile metals, such as aluminum, brass, copper, and mild steel. Examples of parts formed with deep drawing include automotive bodies and fuel tanks, cans, cups, kitchen sinks, and pots and pans.

18. Drawing ration & Punch Force
LDR(limiting drawing ratio) = is the max ratio of blank diameter d0 / to punch diameter dp that can be drawn without failure. 2.7(steel) 2.4(Brass, Aluminum)
Maximum punch force ≈ f (strength, thickness, blank diameter - punch diameter)
Die
Punch
Blankholder
Blank F d0
Blank t dp
Cup

19. Stretch forming (신장 성형)
Sheet metal is clamped and stretched over a die to make double curved aircraft skin panels. σy
Die
Hydraulic force
Sheet metal
Stretch forming is a metal forming process in which a piece of sheet metal is stretched and bent simultaneously over a die in order to form large contoured parts. Stretch forming is performed on a stretch press, in which a piece of sheet metal is securely gripped along its edges by gripping jaws. The gripping jaws are each attached to a carriage that is pulled by pneumatic or hydraulic force to stretch the sheet. The tooling used in this process is a stretch form block, called a form die, which is a solid contoured piece against which the sheet metal will be pressed. The most common stretch presses are oriented vertically, in which the form die rests on a press table that can be raised into the sheet by a hydraulic ram. As the form die is driven into the sheet, which is gripped tightly at its edges, the tensile forces increase and the sheet plastically deforms into a new shape. Horizontal stretch presses mount the form die sideways on a stationary press table, while the gripping jaws pull the sheet horizontally around the form die.

20. Roll forming
Roll forming: Metal strip is bent as it pass through series of rolls.
Roll bending: Cylindrical shaped produced from plate.
Roll forming, sometimes spelled rollforming, is a metal forming process in which sheet metal is progressively shaped through a series of bending operations. The process is performed on a roll forming line in which the sheet metal stock is fed through a series of roll stations. Each station has a roller, referred to as a roller die, positioned on both sides of the sheet. The shape and size of the roller die may be unique to that station, or several identical roller dies may be used in different positions. The roller dies may be above and below the sheet, along the sides, at an angle, etc. As the sheet is forced through the roller dies in each roll station, it plastically deforms and bends. Each roll station performs one stage in the complete bending of the sheet to form the desired part. The roller dies are lubricated to reduce friction between the die and the sheet, thus reducing the tool wear. Also, lubricant can allow for a higher production rate, which will also depend on the material thickness, number of roll stations, and radius of each bend. The roll forming line can also include other sheet metal fabrication operations before or after the roll forming, such as punching or shearing.
Roll forming
Roll bending
SME:
Com:

21. Spinning
A circular sheet metal is held against a rotating mandrel where the tool deforms and shapes it over the mandrel.
The resulting sheet will have a diameter smaller than the blank.
Mandrel
Tool
Blank
Spinning, sometimes called spin forming, is a metal forming process used to form cylindrical parts by rotating a piece of sheet metal while forces are applied to one side. A sheet metal disc is rotated at high speeds while rollers press the sheet against a tool, called a mandrel, to form the shape of the desired part. Spun metal parts have a rotationally symmetric, hollow shape, such as a cylinder, cone, or hemisphere. Examples include cookware, hubcaps, satellite dishes, rocket nose cones, and musical instruments.
There are two distinct spinning methods, referred to as conventional spinning and shear spinning. In conventional spinning, the roller tool pushes against the blank until it conforms to the contour of the mandrel. The resulting spun part will have a diameter smaller than the blank, but will maintain a constant thickness. In shear spinning, the roller not only bends the blank against the mandrel, it also applies a downward force while it moves, stretching the material over the mandrel. By doing so, the outer diameter of the spun part will remain equal to the original blank diameter, but the thickness of the part walls will be thinner.
Al :
Stainless:

22. Hydroforming (Sheet) 1 2 Hydralic pressure applied on sheet.
DRAW RING
BLANK
FLEXIBLE DIAPHRAGM 1 2
CONTROLLED
FLUID PRESSURE
FORMING CHAMBER
Blank is placed on Draw Ring with forming chamber in raised position.
Forming chamber is lowered and initial pressure is applied.
PUNCH
©정하림

23. Die(금형) for Sheet metal
Single operation
Stamping Die
Press Machine
Die is used for multiple station operation of shearing, bending and drawing.
Progressive Die
Transfer Die

24. Stamping Die (프레스 금형)
Lower die
Automotive panel forming process: Drawing → Trimming → Hemming → Punching
Draw die = upper die + lower die + blank holder
Blank holder
Upper die
자동차의 차체 패널은 드로잉(drawing), 트리밍(trimming), 헤밍(hemming), 펀칭(punching) 등 통상
3~4단계의 프레스 공정을 거쳐서 만들어진다.
트림 다이, 피어스다이
중간공정 또는 최종 프레스 공정에서 제품을 필요형상으로 만들기 위하여 전체 둘레 또는 부분
적으로 스크랩(scrap))부분을 절단하는 가공 틀을 트림 다이(trim die)라 하고 가공재료에 구멍을
뚫는 금형을 피어스 다이(pierce die)라고 한다. 피어싱 가공은 상형다이에 펀치 리테이너
(retainer)와 피어스 펀치 (pierce punch)를 설치하고 하형 다이에 버턴다이(button die)를 설치
하여 가공재료에 구멍을 뚫는 작업이며, 뽑힌 부분이 스크랩이 되고 뚫린 구멍이 제품 역할을 하게
된다. 프레스 기계에 의한 피어싱에 있어서는 동시에 여러 개의 구멍을 뚫을 수 있지만 여기에는
제작 조건도 따른다. 이러한 가공들은 가공면이 기울어졌거나 형상에 따라서는 옆에서 절단해야
할 경우에는 고도의 기술을 필요로 하는 전단(shear)가공의 하나이다.
드로우 금형(draw die)의 구조는 제품 성형을 위한 상형(upper die)과 하형(lower die), 그리고 판재를 붙잡아주는 블랭크 홀더(blank holder)로 구성된다.
• 쿠션 핀(cushion pin): 프레스 하부 베드(bed) 위에 위치하여 일정한 압력으로 블랭크 홀더를 밀어 성형이 가능하도록 하는 봉 형태의 핀.
• 핀 후크(pin hook): 금형을 반전 또는 이송하기위해 설치된 구조물.
• 유 클램프(U clamp): 금형을 프레스 장비에 체결하기 위해 사용되는 홈 형태의 구조물.
• 로케이션 슬롯(location slot): 금형의 조립 시 대각선 방향으로 설치하여 공차만큼의 움직임을 주어 금형의 완만한 조립을 돕는 구조물.
• 삼각 리브(triangle rib): 금형 구조에서 취약부위에 보강용으로 쓰기 위해 설치하는 구조물.
• 다이 페이스(die face): 판재의 주름 및 기타 성형불량 현상을 제어하는 면으로서 제품 형상면을 제외한 펀치의 상단면.
• 웨어 플레이트(wear plate): 상형 다이와 블랭크홀더, 하형 펀치와 블랭크 홀더 사이에서 블랭크홀더가 상하로 움직이는 것을 안내하면서 윤활 역할을 하는 부품.
• 가이드 힐(guide heel): 금형의 상형과 하형 또는 상형과 블랭크 홀더를 조립할 때 상호간의 정확한 위치를 잡아 결합시키고, 또한 결합 시 각 금형 사이에 발생하는 밀림을 방지하거나 완화시키기위해 설계되는 구조물.
• 게이지(gauge): 금형에 사용하는 안내판 또는 위치 결정 장치로 패널의 위치를 결정하고 판재(blank)의 투입유무 감지하는 장치.
Press
Draw die

25. Stamping Die
NC machining of die and side panel forming.

26. Press Machine (프레스) Sheet metal / Stamping Die Hydraulic press

27. Progressive Die (순차이송 금형)
Multiple operation such as punching, bending, blanking.

28. Progressive Die
Ring washer production by progressive die.
Ring washer

29. Progressive Die Design
Part analysis (Unfolding)  Strip layout  Punch  Die set

30. Transfer Die (트렌스퍼 금형)
The large sheet metal part is transferred to next station after an operation by transfer machine.
Bar feeder
Finger

31. Design Considerations (설계)
Guidelines for design issues of sheet-metal forming operations:
Punching
Bending
Progressive-die operations
Deep drawing

32. Z-stamp

33. Economics (경제성)
Cup-shaped part can be produced by deep drawing, spinning.
Automotive or aircraft panel can be produced by drawing, stretch forming.
Cost per part
Spinning
Drawing 1
500
1,000
2,000
3,000
4,000
Number of parts

34. References SIMPAC: http://www.simpac.co.kr 프레스장비
삼도프레스: 장비
DieTec: 프레스금형

35. Fast prototyping
Sheet metal fast prototyping : CAD  Tool path  Model cutting  Incremental forming

36. Peen forming Produce curvatures on thin sheet metals by short peening.
Aircraft skin panel.