Icass Stamping Defect Correction

5/16/2018 Icass Stamping Defect Correction - slidepdf.com

http://slidepdf.com/reader/full/icass-stamping-defect-correction 1/13

Intelligent Computer-AidedStamping System (ICASS)

Maximizing Productivity Using Variable Binder Force Technology



THIS PAGE LEFT BLANK INTENTIONALLY



Summary: Sheet metal stamping is a manufacturing process that is widely used in several industries.

Examples of stamped metal parts are doors and hoods of automobiles, domestic appliance housings,

and kitchen sinks. However, the design and construction of dies to make these parts without defects

such as wrinkles and splits is a time consuming and labour intensive process, even today. In addition,

operational variations such as lubricant build-up in the dies, small changes in the material properties

and thicknesses of the sheet metal blanks as well as temperature effects can result in parts being

formed with defects, thus resulting in material scrapping costs of millions of dollars. A new technology

that involves a computerized system to accurately control the forces holding the sheet of metal at

various points in order to eliminate these defects has been developed based on extensive research of

the last 20 years. These systems are now available for shop-floor use as Intelligent Computer Aided

Stamping Systems (ICASS) developed by Intellicass Inc. The use of these systems can result in material

savings of around $1000/hour in a typical stamping plant making car door-sized parts from lightweight

hard-to-form materials such as aluminum.

Introduction: The process of sheet-metal stamping is one the most efficient and widely used metal

forming processes in manufacturing. It is used to form sheet-metal parts in several industries, rangingfrom doors and hoods in automobiles to housings in washing machines, and even kitchen sinks. The

process of sheet-metal stamping (or drawing) involves placing a sheet of metal (the blank ) between an

upper and a lower die, which are cut in the form of the desired part and are geometric negatives of each

other, and driving the upper die (or punch) into the lower die with high force using a press. The sheet of

metal is held between a blank-holder (also known as a binder ) which runs around the die, as shown in

Figure 1, and is stamped into the desired shape by the press.

Figure 1: Schematic of sheet metal stamping

Die design is a complex task, as forming dynamics involve interactions between the sheet-metal blank,

the press, the blank-holder, and the die. In addition, operating conditions such as die lubrication and

temperature significantly affect the forming process. Typical defects that occur due to incorrect flow of

material into the die during the stamping process are wrinkling (caused by excessive compression),



tearing or splitting (caused by excessive tension), and springback (caused by elastic recovery of the

metal), as shown in Figure 2.

Figure 2: Typical defects in stamped parts

Traditional stamping involves using a constant and uniform blank-holder (or binder ) force and shaping a

drawbead (see Figure 1) on the blank-holder to control the rate of material flow into the die. This is a

passive method, and cutting the appropriate drawbead on the binder requires extensive computer

simulations based on Finite Element Analysis (FEA), as well as trial-and-error based grinding or welding.

If the drawbead geometry is incorrect, the blank will not be drawn into the die correctly, and splits

and/or wrinkles will occur. Thus, die try-out, the process in which the die and drawbead geometry are

worked by grinding and welding to correct forming defects (see Figure 3), is very time consuming and

labour intensive. In addition, even when a drawbead is cut correctly for nominal conditions (blank

thickness, die lubrication etc.), part defects can occur when these conditions change (for example, a

small change in blank thickness in material from different suppliers, or lubrication build-up in the die

after a few thousand parts are run), resulting in high scrap rates.

Figure 3: Die-work during try-out to correct stamped part defects



Die-design and try-out problems are compounded with the use of light-weight/high-strength alloys for

making stamped parts. Significantly higher fuel efficiency and safety standards in the automotive

industry are necessitating the use of such materials, and coupled with a highly competitive business

environment, there is an urgent need to improve the efficiency of both the die-making and stamping

processes.

Variable Binder Force Control: The use of locally varying binder force to eliminate stamped part defects

and improve formability has been extensively studied in the academic research community over the last

twenty years [1-24]. The idea of using variable binder force is conceptually simple: if a split is imminent,

the binder force near the location of the split is reduced, thus reducing the tension on the blank and

preventing the split; conversely, if a wrinkle is starting to form, the binder force is increased, thus

increasing the tension in the blank and stretching out the wrinkle. However, since the stamping cycle is

relatively quick (typically 0.5 – 0.8 sec), and the timing of the force adjustment is critical, implementing

such a system to precisely adjust the appropriate binder force at multiple locations around the blank

presents several engineering and technological challenges. Thus, a large number of studies have relied

on simulation to validate the concept; however, there have been some experimental studies usingsimple part geometries (cups or pans) with hydraulic presses which drive the punch at a constant speed

(see [4, 5, 9, 13, 14, 24, 25, 31], for example). However, more recent work conducted by the University

of Michigan and Intellicass in partnership with Troy Design and Manufacturing (a wholly owned

subsidiary of the Ford Motor Company) ([32-34]) has shown that variable binder force control can

significantly improve the efficiency of die try-out. It can also maintain part consistency in the presence of

operational variations, even for typical automotive parts with deep draws and complex geometries,

while using standard mechanical presses designed for high-volume production. Figure 4 shows a typical

result where simultaneously occurring splits and wrinkles are eliminated using variable binder force

control on a part made with a tailor-welded blank.

Wrinkle

Split

Figure 4: Wrinkle and split corrected using variable binder force

Defects eliminated using

variable binder-force

without die work



Technological Challenges in Developing Variable Binder Force Systems:

1. Design for Mechanical Presses: Hydraulic binder force control systems (also known as

programmable multi-point cushion systems) consist of hydraulic cylinders that deliver the

required force to the appropriate location on the binder. The hydraulic fluid in the cylinder is

compressed by the downward motion of the press ram, and the fluid is metered out through aservovalve that is controlled by a real-time computer system (see Figure 5). Most programmable

hydraulic cushions are designed for hydraulic presses, which have relatively constant ram

speeds, thus allowing relatively simple logic-based or PID control algorithms to be effective.

However, in a mechanical press that is typically used for fast, high-volume production, the ram

speed is high at the top of the stamping cycle and zero at the bottom because of the use of a

crank drive. This non-constant ram speed profile necessitates a much more sophisticated

control algorithm to regulate the fluid flow out of the cylinder to generate the desired binder

force. The Intellicass ICASS uses a patented control algorithm to achieve accurate hydraulic

binder force control in both hydraulic and mechanical presses operating at a range of ram

speeds.

2. Cost-effective reconfigurable design for try-out: The key to effective use of variable binder-force

technology is being able to determine the required binder force profiles during try-out.

Production facilities do not want to waste time and man-power on determining optimal binder

forces. Thus, both die-construction/try-out and production facilities need to have access to cost-

effective variable binder-force systems. Currently, most programmable cushions, which only

have limited spatial and time-based control, are prohibitively expensive for try-out facilities, and

are only found in top-of-the-line presses in production. However, they are rarely used effectively

in production because production facilities do not have the resources to determine the required

Figure 5: Schematic of hydraulic binder-force control system



binder force trajectories. By developing a cost-effective reconfigurable solution that can be used

effectively for any die in any press for try-out, and a complementary system for production,

ICASS provides the means to exploit this technology.

Figure 6: ICASS for try-out ICASS in Try-Out: ICASS has been extensively used in try-out for more than 3 years at Troy Design and

Manufacturing, with several hundreds of parts produced for prototype vehicles. It has been particularlyhelpful to rapidly address defects in hard-to-form parts using tailor-welded blanks (Figure 4) and

lightweight materials such as aluminum. Using the system, try-out time has been reduced 60 – 80%

depending on the part. In Figure 7, the bottom of an aluminum door-inner is shown, with (a) showing

the part made using conventional FEA-based methods and (b) showing the part made using ICASS. In

addition to very effectively reducing wrinkling, it can be seen that ICASS leaves more material outside

the drawbead line, which can be cut from the blank for material saving (as indicated by the dashed

yellow line). Any wrinkling caused by reducing the blank size can be corrected by locally increasing the

binder forces at the bottom of the stroke using ICASS.



(a)

(b)

Figure 7: Wrinkle correction and material savings using variable binder force (features obscured for confidentiality reasons)

ICASS in Production: Besides the obvious requirement that variable binder-force usage in try-out would

necessitate the same capability in production, analysis shows that using variable binder-force

technology in production results in very high levels of cost-savings. Specifically, cost savings stem from:

1. Smaller blank size as detailed in the previous section

2. Reduced scrap when using automatic tonnage correction for lube build-up and for operational

variations

3. Reduced material tolerance requirements because of a more robust stamping process

4. Reduced down-time to correct for defects

5. Reduced maintenance costs due to lower press impact forces (the binder tonnages are built up

from near zero in about 0.1 sec)

6. Virtual elimination of panel bounce due to smooth return of the binder under controlled

hydraulic pressure

7. Capability that exceeds that of the most expensive programmable cushions built by large press

manufacturers at a fraction of the cost provides a strong competitive advantage, leading to

more business

Cost savings from (1) and (2) alone are estimated at more than $1,000/hour for an aluminum part the

size of a door-inner running in a tandem line operating at 10 strokes/min.

The key technology for reducing scrap and enabling a more robust production run is the use of process

control for stamping. This concept has also been actively studied in academia [27 – 42] and is based on

using real-time feedback of a quantity that provides information on part quality and consistency, such as



material draw-in, punch force or friction force, to actively adjust the binder forces to compensate for

operational variations such as lubrication build-up in the die, or small changes in sheet metal material

properties. Several academic publications have validated this concept using simple part geometries and

hydraulic presses [25 – 31]. A significant amount of research has also been conducted on development

of sensors for real-time feedback [35 – 40]. However, technology jointly developed by Intellicass and the

University of Michigan utilizes existing tonnage monitors to provide total press-force feedback for

process control, and has been tested at two facilities, namely Troy Design and Manufacturing (for try-

out/prototype) and Ogihara America Corporation (for production). Figure 8 shows a graphical

representation of process control using tonnage monitor feedback, while Figure 9 shows tonnage

monitor readings that capture operational variations, thus demonstrating that these readings can be

used to adjust binder forces and reduce the scrap rate.

Figure 8: Process control schematic

Process Control

System

Hydraulic Binder

Force System

Stamping

Process

Operational variations

(lube build-up etc.)

Tonnage monitor feedback

Figure 9: Tonnage monitor data capturing operational variations for process control feedback



Figure 10 shows wrinkles caused by excessive lubrication (a) automatically corrected using process

control (b).

Figure 10: Wrinkles caused by excessive lubrication (a) and corrected by process control with variable binder force (b)

Cost-savings Estimate: The estimate given below is based on a production run of door-sized panel made

from draw quality aluminum. The assumptions are as follows:

1. Press tandem line runs at 10 strokes/minute, or production of 600 parts/hour

2. Differential between cost and scrap recovery rate per blank is $35

3. Current scrap rate is 8%

From test data, it is estimated that the use of ICASS results in material savings from blank size reductionof 2% and scrap reduction from 8% to 4% with process control. Thus, total material savings of 6% are

achieved or in dollar terms = 0.06 x $35/part x 600 parts/hour = $1080/hour.

Other benefits include reduced try-out time for launching dies, reduced down-time for die work, lower

press maintenance costs, and lower costs for production delays. With a utilization of 1000 hours/year,

each ICASS in production generates savings of more than $1 million per year.

For try-out, ICASS significantly reduces the time required for die work. In one test case, a good part was

produced using ICASS with 2 man-hours of effort. The die was then worked based on material flow

information obtained from deploying ICASS, and it took 32 man-hours to get a comparable part using

traditional methods. Thus, a reduction of 93% in try-out time was realized. However, on an average, try-out time is reduced by 60 – 80% with ICASS.

Furthermore, FEA simulation time can be reduced, as a basic drawbead design can be enhanced using

variable binder force control. Thus, extensive simulation to design precisely engineered drawbeads is

not required. Combining FEA simulation time savings with reduced try-out time leads to faster time to

production.

(a) (b)



Conclusion: The sheet metal stamping process can be significantly enhanced by the use of variable

binder force technology, specifically be generating material savings in production and reducing try-out

time. The technology has been the subject of extensive academic research and has now been

transitioned to shop-floor use by Intellicass. The potential for cost-saving using these systems is very

high (estimated at around $1000/hour for a typical automotive application). The technology can is non-

disruptive and can be easily integrated into existing facilities, and is expected to be transformative in the

world of sheet metal stamping.

References

[1] Herderich, M.R. (1990). Experimental Determination of the Blankholder Forces Needed for Stretch

Draw Die Design. SAE Paper. No. 900281 53-61.

[2] Ahmetoglu, M.A. Altan, T. Kinzel, G.L. (1992). Improvement of Part Quality in Stamping by Controlling

Blank-Holder Force and Pressure. J. of Materials Processing Tech. Vol. 33 195-214.

[3] Kergen, R. Jodogne, P. (1992). Computerized Control of the Blankholder Pressure on Deep Drawing

Process. SAE Paper. No. 920433 51-55.

[4] Siegert, K. Hohnhaus, J. Wagner, S. (1992). Combination of Hydraulic Multipoint Cushion System and

Segment-Elastic Blankholders. SAE Paper. No. 98007 51-55.

[5] Hardt, D. E., (1993). Modeling and Control of Manufacturing Processes: Getting More Involved.

Journal of Dyn. Systems, Meas., and Control, Vol. 115, pp. 291 –300.

[6] Hardt, D. Fenn, R. C., (1993). Real-Time Control of Sheet Stability during Forming. In: Trans. ASME, J.

Eng. Ind., Vol. 115 301-308.

[7] Hosford, W.F. Caddell, R. M. (1993). Metal Forming: Mechanics and Metallurgy. 286-308. PTR

Prentice- Hall. 2nd Edition.

[8] Adamson, A. Ulsoy, A.G., Demeri, M. (1996). Dimensional Control in Sheet Metal Forming via Active

Binder Force Adjustment. SME Trans. Vol. 24, pp. 167-178.

[9] Sunseri, M., Cao, J., Karafillis, A.P., Boyce, M.C. (1996). Accommodation of Springback Error in

Channel Forming Using Active Binder Force: Control Numerical Simulations and Experiments. J. of Engin.

Materials and Tech. Vol. 118.

[10] Cao, J. and Boyce, M.C. (1997). A Predictive Tool for Delaying Wrinkling and Tearing Failure in Sheet

Metal Forming. J. of Eng. Materials and Technology, Vol. 119.

[11] Obermeyer, E.J. Majlessi, S.A. (1997). A Review of Recent Advances in the Application of Blank-

Holder Force towards Improving the Forming Limits of Sheet Metal Parts. J. Materials Proc. Tech. Vol. 75

222-234.



[12] Ziegler, M. (1999). Pulsating Blankholder Technology. SAE Paper. No. 1999-01-3155 1-5.

[13] Kinsey, B. Cao, J. Solla, S. (2000). Consistent and Minimal Springback Using a Stepped Binder Force

Trajectory and Neural Network Control,’’ J. Eng. Mater. Technol., 122, pp. 113–118.

[14] Siegert, Klaus. Haussermann, Markus. Haller, Dirk. Wagner, Stefan. Ziegler, Michael. (2000).

Tendencies in Presses and Die for Sheet Metal Forming Processes. J. of Materials Processing Tech. Vol.

98 259-264.

[15] Cao, Jian. Kinsey, B.L. Yao, Hong. Viswanathan, Vikram. Song, Nan. (2001). Next Generation

Stamping Die – Controllability and Flexibility. Robotics and Computer Integrated Manufacturing. Vol. 17

49-56.

[16] Doege, E. Elend, L. -E. (2001). Design and Application of Pliable Blank Holder Systems for the

Optimization of Process Conditions in Sheet Metal Forming. J. of Materials Proc. Tech. Vol. 111 182-187.

[17] Hardt, D. (2002). Forming Processes: Monitoring and Control. Mechanical Systems Design

Handbook. (O. Nwokah and Y. Hurmuzlu (Ed.)), 105-119. CRC Press

[18] Manabea, Kenichi. Koyama, Hiroshi. Yoshiharab, Shoichiro. Yagami, Tetsuya. (2002). Development

of a Combination Punch Speed and Blank-Holder Fuzzy Control System for the Deep-Drawing Process. J.

of Materials Proc. Tech. Vol. 125 –126 440 –445.

[19] Viswanathan, V. Kinsey, B. Cao, J. (2003). Experimental Implementation of Neural Network

Springback Control for Sheet Metal Forming. J. of Engin. Materials and Tech. Vol. 125 141-147.

[20] Sheng, Z., Jirathearanat, S. and Altan, T. (2004). Adaptive FEM Simulation for Prediction of Variable

Blank Holder Force in Conical Cup Drawing. International Journal of Machine Tool and Manufacture, 44,

pp. 487-494.

[21] Yagami, T., Manabe, K., Yang, M., Koyama, H. (2004). Intelligent sheet stamping process using

segment blank holder modules. J. of Mat. Proc. Tech. Vol. 155 –156, pp. 2099 –2105.

[22] Wang, L., Lee, T.C. (2005). Controlled strain path forming process with space variant blank holder

force using RSM method. J. of Mat. Processing Tech., Vol. 167, pp. 447 –455.

[23] Groche, P. Metz, C. (2005). Active Material Flow Control during High-Pressure Sheet Metal Forming.

Advanced Materials Research. Vol. 6-8 377-384.

[24] Zhong-qin, Lin. Wang, Wu-rong. Chen, Guan-long. (2007). A New Strategy to Optimize Variable

Blank Holder Force towards Improving the Forming Limits of Aluminum Sheet Metal Forming. J. of

Materials Processing Technology. Vol. 183 339 –346.

[25] Siegert, K., Ziegler, M., Wagner, S. (1997). Closed-Loop Control of the Friction Force: Deep drawing

process. J. of Materials Proc. Tech. Vol. 71, pp. 126-133.

[26] Manabe, K. Koyama, H. Katoh, K. Yoshihara, S. (1999). Intelligent Design Architecture for Process

Control of Deep-Drawing. Intel. Proc. and Manufacturing of Materials. Vol. 1 571-576.



[27] Hsu, C.W. Ulsoy, A.G. Demeri, M.Y. (1999). Process Controller Design for Sheet Metal Forming.

American Control Conference. Vol. 1 192 –196.

[28] Demeri, M.Y. Hsu, C.W. Ulsoy, A.G. (2000). Application of Real-Time Process Control in Sheet Metal

Forming. Proceedings of the 2000 Japan –USA Symposium

[29]Hsu, C.W., Ulsoy, A.G., Demeri, M.Y. (2000). An Approach for Modeling Sheet Metal Forming for

Process Controller Design. ASME J. Manuf. Sci. Eng. 122, pp. 717-724.

[30] Hardt, D. Siu, T.S. (2002). Cycle-to-Cycle Manufacturing Process Control. 1st Annual SMA Symp..

Singapore

[31] Hsu, C.W., Ulsoy, A.G., Demeri, M.Y. (2002). Development of process control in sheet metal

forming. J. of Materials Proc. Tech. Vol. 127, pp. 361-368.

[32] Lim, Y.S., Venugopal, R., Ulsoy, A.G. (2008). A Multi-Input Multi-Output Model for Stamping Process

Control. ASME International Symposium on Flexible Automation (ISFA), Atlanta, June 23-26, pp. 1-8.

[33] Lim, Y.S., Venugopal, R., Ulsoy, A.G. (2009). Improved Part Quality in Stamping Using Multi-Input

Multi-Output Process Control. American Control Conference (ACC), Saint Louis, MO, USA, June 10-12,

2009, pp. 5570 –5575.

[34] Lim, Y.S., Venugopal, R., Ulsoy, A.G. (2009). Multi-Input Multi-Output Modeling and Control for

Stamping. J. of Dyn. Systems, Meas., and Control, (in press).

[35] Pereira, Pratap. Zheng, Y.F. (1994). Sensing Strategy to Detect Wrinkles in Components. IEEE

Transactions on Instrum. and Measurement. Vol. 43 No. 3 442-447.

[36] Lo, Sy-Wei. Jeng, Guo-Ming. (1999). Monitoring the Displacement of a Blank in a Deep Drawing

Process by Using a New Embedded-Type Sensor. Int. J. Adv. Manuf. Technol. Vol. 15 815 –821.

[37] Cao, Jian. Lee, J. Peshkin, M. (2002). Real-time Draw-in Sensors and Methods of Fabrication.

Northwestern University U.S. Pat. 6,769,280.

[28] Doege, E. Seidel, H.-J. Griesbach, B. Yun, J.-W. (2002). Contactless on-line Measurement of Material

Flow for Closed Loop Control of Deep Drawing. J. of Materials Proc. Tech. Vol. 130 –131 95 –99.

[39] Doege, E., Schmidt-Jurgensen, R., Huinink, S., Yun, J.-W. (2003). Development of an optical sensor

for the measurement of the material flow in deep drawing processes. CIRP Annals - Manufacturing

Technology, Vol 52, n1, pp. 225-228.

[40] Mahayotsanun, N. Cao, Jian, Peshkin, Michael, (2005). A Draw-In Sensor for Process Control and

Optimization. American Institute of Physics, CP778 Vol. A.

Date post:	18-Jul-2015
Category:	Documents
Upload:	santiago-galvan-v
View:	37 times
Download:	0 times

Icass Stamping Defect Correction

Documents