Sheet Metal Forming Presses

Transcription

1 Sheet Metal Forming Presses October 15th, 2014 Hyunok Kim, EWI Forming Center Taylan Altan, OSU - Center for Precision Forming (CPF) 1

2 Outline Introduction Classification of presses Mechanical press Hydraulic press Die and Tooling Force, Energy requirement of presses Try-out press, Universal press, Transfer press Servo-drive press (to be discussed separately) 2

3 Introduction Information of presses is useful to: Use the existing capital equipment more efficiently Define the existing plant capacity accurately Communicate with machine builders and work together to improve machine performance Develop in-house proprietary machines, if necessary The press selection should consider: The flow stress and formability of the deforming material Load and Energy requirement The as formed tolerances The production rate 3

4 Load-Stroke Curves and Energy 4

5 Characteristic Data for Load and Energy Available Energy E M Available Load L M (during the ram stroke) Efficiency Factor (losses in electric motor, friction in the gibs and bearings, elastic deflection) L M L p during the stroke E M E p in a stroke (L p = load required by process) (E p = energy required by process) 5

6 Time-Dependent Characteristic Data Machine Capabilities under load Number of strokes per minute, n Contact time under pressure, tp Velocity during deformation, under pressure, v p 6

7 Characteristic Data for Accuracy Unloaded Conditions Clearances in gibs Parallelism between ram and bed (bolster) surfaces Perpendicularity of the slide motion with respect to lower bed Concentricity or in-line positioning of tool/die holders 7

8 Characteristic Data for Accuracy Loaded Conditions Tilting of the ram (ram and frame deflections) under off-center loading Stiffness, c, of the press [i.e., c = L m / deflection(d)] For a given bed and deflection energy, E d = dl m / 2 = L m 2 / 2c Stiffness influences a) Part dimensions b) Contact time under pressure 8

9 Mechanical Press Mechanical presses are powered using electrical motor and forces are transmitted mechanically to the work piece through the slides. Flywheels are used to store the energy. Force required to form the part and fluctuations in the load determines the size of the flywheel. Based on the kinematics of the transmission, mechanical presses are classified as 1. Crankshaft driven presses 2. Eccentric shaft driven presses 3. Knuckle joint presses 9

10 Cross Section of a Mechanical Press / Single Slide Single-Action Mechanical Press with Draw Cushion Courtesy: Schuler Inc. 10

11 Double Slide Press Double-action Mechanical Press Courtesy: Schuler Inc. 11

12 Double Slide Press Stroke versus Crank angle graph 12

13 Crankshaft Driven Press Crankshaft with Gear and pinion drive Advantages: Good stability at high capacities 13

14 Crankshaft Driven Press (Altan, 1983) 14

15 Force, Torque and Energy Permissible Press Force of an Eccentric Press as a Function of Crank Angle Courtesy: Schuler Inc. 15

16 Force, Torque and Energy 16 (Altan, 1983)

17 Knuckle Joint Driven Press A knuckle joint driven press is often used to generate a large force for coining process (Altan, 1983) 17

18 Force, Torque and Energy Eccentric Knucklejoint Eight-Link Displacement-Time Diagram Courtesy: Schuler Inc. 18

19 Frame Primary function of the frame is to contain the forces applied by the press without deforming. Mainly there are two types of frames, Open frame also called C frame and Straight sided frame. 19

20 Open Frame/C-Type Adjustable Bed Stationary Open Back Stationary [SME, 1984] 20

21 Straight Sided Frame Connecting Rod Forces at the Slide in One-, Two- and Four-point Presses Courtesy: Schuler Inc. 21

22 Overloading Protection Mechanical presses are protected from overloading using replaceable or permanent protection units In replaceable units, pins or washers are used, which brake when overloaded Permanent units use hydraulic or pneumatic circuits and switches. When the press is overloaded, the unit collapses. 22

23 Hydraulic Press Hydraulic Press Courtesy: Schuler Inc 23

24 Force, Torque and Energy Displacement-Time Diagram of a Hydraulic Press Courtesy: Schuler Inc. 24

25 Comparison of Mechanical and Hydraulic Presses In mechanical presses the stroke needs to be completed before reversal of the slide and for hydraulic presses the slides can be reversed at any position. Productivity (strokes per minute) of the mechanical press is higher than that of the hydraulic press. 25

26 Comparison of Mechanical and Hydraulic Presses Slide Displacement and Power requirement versus Time in Mechanical and Hydraulic Presses. Courtesy: Schuler Inc. 26

27 Transfer Press In this type of presses, several sheet-forming operations are performed by means of progressive or transfer dies. The blank material is automatically transferred from one operation station to the other. This results in the increase in productivity. The selection of a transfer press has to consider the blank material, the geometry to be formed, and the necessary sequence of operations. 27

28 Tandem Press Line Inter-linkage of Presses with Swing Arm Feeders Courtesy: Schuler Inc. 28

29 Transfer Press Transfer Die Set for a Press with Active Counter Drawing and Fixed Stops Courtesy: Schuler Inc. 29

30 Servo Tandem Line at Suzuka (Japan) Plant (Honda) 30

31 Forming length Slide Position Minimum stroke length Servo-Drive Characteristics Crank or Link press Fixed Motion Cycle time of mechanical press Free motion press Cycle time of Free motion press (6) Synchronize with feeder (1) Variable stroke length Standstill at BDC Time (5) Prevention of noise and shock at contact or breakaway of tools (2) Best speed for materials (3) Improve accuracy by dwelling at BDC (4) Other Process at BDC (Multi Process) The flexibility of slide motion in servo drive (or free motion) presses [Miyoshi, 2004] 31

32 Low RPM - High Torque Servo Motor Drive 2/2 Servo-Press Drive Using Conventional Crank Mechanism [Courtesy: Aida] 32

33 Summary Sheet Metal Forming Presses In sheet metal forming, mechanical, hydraulic and servo-drive presses are used. The understanding of press characteristics (i.e. load, energy, ram speed, stroking rate, stiffness) is very important in selection and use of press. Mechanical press gives shorter cycle time but hydraulic press is more flexible in controlling the ram speed and tool setup. The selection of press type and capacity depends upon part size, material, production volume, and cost. 33

34 Questions & Contacts Taylan Altan Hyunok Kim