Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
  • B21D22/20—Deep-drawing
  • B21D22/21—Deep-drawing without fixing the border of the blank
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D24/00—Special deep-drawing arrangements in, or in connection with, presses
  • B21D24/10—Devices controlling or operating blank holders independently, or in conjunction with dies
  • B21D24/14—Devices controlling or operating blank holders independently, or in conjunction with dies pneumatically or hydraulically

Definitions

• the invention relates to a method for deep drawing products from a blank. More in particular, the invention relates to an improved method for preventing, at least reducing wrinkle formation in the blank during deep drawing.
• a downholder force exerted on the edges of the blank is, on the one hand, sufficiently great to prevent wrinkle formation in the edges, but is, on the other hand, not greater than is necessary, because this promotes crack formation and, moreover, leads to high frictional forces between the blank and the downholder and die ring.
• DE 4 038 864 discloses a method in which at the beginning of deep drawing the downholder force (FN) is preventively chosen so high that this force is greater than a counterforce (F s ) to be expected in the blank.
• FN downholder force
• F s counterforce
• the downholder force is therefore higher than is necessary because, at the beginning of the method and each time when wrinkle formation occurs, this force is increased to above the counterforce to be expected in the blank.
• the height of the downholder force and the good action thereof is strongly dependent on the accuracy with which the counterforce can be predicted.
• the invention contemplates providing a method in which at least a number of the drawbacks inherent to the known methods are removed. To this end, a method according to the invention is characterized by the measures according to claim 1.
• the downholder force is initially kept relatively low and increased only when this is necessary, that is to say at a beginning wrinkle formation. It is important here that this wrinkle formation can be recognized at an early stage.
• this is achieved by taking into account the thickness trend of the edge of the blank during deep drawing or a magnitude derived from this thickness trend, such as, for instance, the speed of the thickness trend.
• the thickness of the blank edge gradually increases during deep drawing, because the diameter of the blank gradually decreases and, therefore, material in the blank edge must be accommodated on an increasingly smaller surface.
• a method according to the invention is characterized by the measures according to claim 2.
• a parameter relevant to wrinkle formation is measured and the downholder force is increased if this measured parameter exceeds a predetermined critical range or critical value, which range or which value is based on, at least takes into account, the above -discussed thickness increase of the blank or a magnitude derived from this thickness increase.
• the downholder force can be increased stepwise, by a predetermined step size, but can, for instance, also be regulated to a desired value by means of known per se regulating algorithms, such as, for instance, a proportionally, integratingly and/or differentiatingly operating regulation, the measured parameter again being located below the mentioned critical magnitudes (range or value).
• a method according to the invention is characterized by the measures according to claim 3.
• the parameter relevant to wrinkle formation may, for instance, be the downholder opening, defined as the perpendicular distance between the downholder and the die ring.
• the thickness trend or the maximum thickness increase of the blank edge can be entered as critical range or critical value, respectively. For if during deep drawing the downholder opening becomes larger than the momentary thickness or the eventual maximum thickness of the blank edge, this indicates wrinkle formation.
• the thickness trend can be theoretically determined, by means of suitable simulation programs, but can also be measured once, previous to deep drawing of a new series of products. To this end, a constant downholder force is adjusted, at which neither wrinkle formation, nor crack formation occurs, and the downholder opening is measured during deep drawing. Since no wrinkle formation occurs, it may be assumed that the measured downholder opening is substantially equal to the thickness increase of the blank. It is assumed here that the measured thickness increase is independent of the adjusted downholder force, or at least that the influence of the height of the downholder force on the measured thickness increase is negligibly small, within the operative area of the downholder force important to the present use.
• a method according to the invention is characterized by the measures according to claim 4.
• the speed at which this opening changes may also function as critical magnitude. This speed may also be determined by simulation or a testing measurement, in the above - described manner. Then the speed trend may function as critical range or a speed value measured to be highest during this trend as critical value.
• the downholder opening speed trend is more sensitive than the downholder opening trend, so that wrinkle formation can be recognized at an even earlier stage.
• both signals, the downholder opening trend and the downholder opening speed trend may also be used side by side, the critical value or the critical range that is exceeded first being decisive of the control of the downholder.
• a method according to the invention is characterized by the measures according to claim 7.
• the downholder force is regulated, based on a predetermined thickness trend of the blank.
• This thickness trend may, in the same manner as discussed before, be simulated or measured.
• the downholder may always be adjusted during deep drawing such that the downholder opening is substantially equal to the predetermined momentary thickness of the blank.
• Such a method according to the invention offers the advantage that during deep drawing the downholder opening and downholder speed need not be measured and compared with a predetermined critical value.
• the downholder force will be minimal, at least not greater than necessary, with all the attendant above-mentioned advantages.
• the invention further relates to an apparatus for deep drawing a product from a blank, suitable for use of a method according to the invention.
• Fig. 1 schematically shows a deep drawing apparatus according to the invention
• Fig. 2 shows a diagram in which the trends of the upper and lower limits of the admissible downholder force are plotted as a function of the deep drawing ratio
• Fig. 3 shows a testing measurement with a downholder force for determining a critical value and/or range in which wrinkle formation occurs
• Fig. 4 a measurement in which the downholder opening and the downholder force are plotted against time, with and without regulation according to the invention
• Fig. 5A shows a simulation of the speed trend of the downholder opening (v 0 ) during deep drawing
• Fig. 5B shows a simulation of he downholder force (FN), regulated on the basis of the speed from Fig. 5A;
• Fig. 6 shows a photograph of a deep drawn product, with and without regulation according to the invention
• Fig. 7 shows a deep drawn product with primary and secondary wrinkles.
• Fig. 1 shows an apparatus 1 for deep drawing products, with which wrinkle formation in those products can be reduced and preferably be completely suppressed.
• wrinkle formation is understood to mean the formation of both primary wrinkles 21 in a flange 6 of the deep drawn product 15 and secondary wrinkles 22 in wall parts 25 of the product 15, as illustrated in Fig. 7.
• the apparatus and method according to the invention are directed to suppressing both types of wrinkles.
• the apparatus 1 comprises a die 2 provided with a die opening 3 and a punch 4 arranged above this die opening 3.
• This punch 4 can be moved by means of suitable positioning means 7 into the opening 3, as shown in Fig. 1 on the right side.
• a blank 5 of starting material placed over the opening 3 is thereby forced into the opening 3 and deformed between the walls of this opening 3 and the punch 4 to a desired final product 15.
• the starting diameter D 0 of the blank 5 gradually decreases during this deep drawing, which is accompanied by an increase in the thickness d of the edge 6 and can further lead to wrinkle formation.
• a ring-shaped downholder 8 is arranged around the punch 4, which downholder can be moved with suitable positioning means 9 towards a die ring 10 extending around the die opening 3 while clamping the edge 6 of the blank 5.
• a downholder force FN exerted on the edge 6 by the downholder 8 will thereby increase according as the downholder opening s 0 , defined as the perpendicular distance between the downholder 8 and the die ring 10, increases.
• the downholder force FN must remain between two extreme limits, a lower limit FN.mm and an upper limit Fornax. These limits are graphically shown in Fig. 2, as a function of the deep drawing ratio.
• a lower limit FN.mm When the downholder force FN falls below the minimum limit FN,min, wrinkles will . be formed in the product, while at exceeding the maximum limit FN.max cracks will be formed in the product 15.
• the downholder force FN is therefore adjusted to a 'safe' distance between both limits, so that a certain safety margin is present, in connection with possible spreading in the starting material (composition, thickness, etc.).
• the downholder force FN is contrarily exactly kept as close to the lower limit FN.min as possible.
• the risk of crack formation will thus be reduced to a minimum.
• this will also limit frictional forces F w occurring during deep drawing between the blank 5 and the downholder 8 and the die ring 10, since these frictional forces are proportional to the downholder force FN.
• Lower frictional forces ensure that less lubricant suffices, that the deep drawing process can take place under lower forces, with less work, and that the whole arrangement can be of lighter design.
• the downholder force FN is adjusted according to the invention to a low value and increased only if wrinkle formation occurs. Then the downholder force is increased to a value necessary to suppress the detected wrinkles. 5
• the downholder force FN will thus always be not greater than necessary to suppress the momentary wrinkle formation.
• the deep drawing apparatus 1 of Fig. 1 is therefore provided with5 measuring means 11, with which the mentioned downholder opening trend So and/or downholder opening speed trend v 0 can be measured.
• These measuring means 11 may, for instance, comprise an optical, capacitive or magnetic sensor.
• the measuring means 11 are connected to a control 12, which is provided with means for comparing the measuring signals with a0 critical value or critical range adjusted for those signals, and which control 12 is further arranged to move, in case of exceeding the mentioned critical magnitudes, the downholder 8 towards the die 2 by means ofthe positioning means 9.
• These positioning means 9 may, for instance, comprise a piston- cylinder assembly, an electrically driven screw spindle, a piezo -electric5 element, or the like.
• the critical values can be determined during a testing measurement, by measuring, during this test, the downholder opening trend s 0 as shown in Fig. 3. It is clearly visible that the downholder opening s 0 initially has a substantially constant value o (range I-II) and then gradually increases at a constant inclination (range II-III) corresponding with a constant downholder opening speed v 0 . From point III, the measured downholder opening trend s 0 shows a bend, and this trend increases more rapidly, which indicates wrinkle formation P. On the basis of this measurement, therefore, the range I-III can be implemented in the control 12 as the sought critical downholder opening range. Instead thereof, bend point III may also be introduced as critical downholder opening value. When a downholder opening trend s 0 measured during deep drawing exceeds the critical range or the critical value, the thickness increase is greater than may be expected on the basis ofthe testing measurement, which indicates wrinkle formation.
• the deep drawing testing measurement may also be carried out at such a high downholder force FN that neither wrinkle formation, nor crack formation will occur.
• This allows for the assumption that a downholder opening trend s 0 measured during this test fully corresponds with the thickness increase of the edge 6 of the blank 5.
• This . measured downholder opening trend may therefore be implemented in the control 12 as critical range. Instead thereof, the maximally measured thickness increase may also be introduced as critical value.
• the speed v 0 at which this downholder opening changes may also be measured during the mentioned testing measurement. This measured speed trend or a speed value measured to be highest during this measurement can be introduced into the control 12 as critical range or critical value for the downholder opening speed trend.
• Fig. 4 shows a measurement of the downholder opening s 0 and the downholder force FN over time, with the thinly drawn hnes representing the trend without regulation according to the invention, while the thickly drawn lines represent the trend when the downholder force FN is controlled on the basis of the critical downholder opening determined in Fig. 3. It is clearly visible that the downholder force FN is step wise increased from the critical value determined in Fig. 3 (bend point III) and thus effectively suppresses (see thickly drawn s 0 line) wrinkle formation (see thinly drawn s 0 line).
• Fig. 4 further clearly shows that the downholder force initially begins relatively low and is increased only if this is actually necessary.
• the force may be increased stepwise, at a predetermined step size, or may be increased proportionally to the measured deviation. Also possible are other known per se regulation techniques, in which, for instance, use is made of integrating and/or differentiating actions.
• the apparatus may also be provided with a self-learning regulation, in which the step size of the force FN is initially adjusted by an operator, and the regulation itself adapts this value in the course of the process, on the basis of fed back measuring data.
• a self-learning regulation in which the step size of the force FN is initially adjusted by an operator, and the regulation itself adapts this value in the course of the process, on the basis of fed back measuring data.
• 5A,B is shown a simulation in which the downholder force is regulated on the basis of the measured opening speed v 0 and a critical speed value predetermined in the above -described manner, which, in the shown case, was approximately 1 x 10" 4 . It is clearly visible how the downholder force FN is increased stepwise, each time when the downholder opening speed exceeds the critical value. It is also visible that the increase of the downholder force FN is greater according as the exceeding of the critical value is greater.
• Fig. 6 shows, on the left side, a flange 6' of a product 15', manufactured with a conventional deep drawing method (see the thinly drawn lines in Fig. 4), while next to this, on the right side, a product 15 is shown, which has been manufactured with a method according to the invention (see the thickly drawn lines in Fig. 4). It clearly appears that the product according to the present method substantially has no wrinkles. It will be clear that the critical values for the downholder opening and the opening speed depend on the starting material and the desired final product. These values are therefore determined again, preferably preceding each new product series. This may be done by means of a testing measurement, as described above. In case of sufficient material data and process data, these values may also be simulated by means of known per se software packages, so that no testing measurements at all need be carried out anymore.
• not the downholder force is regulated on the basis of a measured beginning of wrinkle formation (feed-back regulation), but the position of the downholder and hence the downholder opening are regulated according to a predetermined range, such that the mentioned downholder opening corresponds with the thickness trend of the blank 5 to be expected (forward regulation).
• the thickness trend to be expected may be determined in the same manner as described before with reference to Fig. 3.
• Such a forward regulation has the advantage that during the actual deep drawing no downholder opening or speed need be measured, so that a very simple apparatus, without measuring means and without advanced control, suffices.
• deep drawing may take place in one or more steps.
• the forward position regulation and fed-back force regulation may be combined, the force regulation being able to correctingly act on the position regulation.

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Citations (6)

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• 2002
  • 2002-10-24 NL NL1021738A patent/NL1021738C2/nl not_active IP Right Cessation
• 2003
  • 2003-10-23 AT AT03759078T patent/ATE408465T1/de not_active IP Right Cessation
  • 2003-10-23 DE DE60323658T patent/DE60323658D1/de not_active Expired - Lifetime
  • 2003-10-23 EP EP03759078A patent/EP1554067B1/en not_active Expired - Lifetime
  • 2003-10-23 AU AU2003275734A patent/AU2003275734A1/en not_active Abandoned
  • 2003-10-23 WO PCT/NL2003/000720 patent/WO2004037460A1/en not_active Application Discontinuation
  • 2003-10-23 US US10/532,360 patent/US20050268685A1/en not_active Abandoned

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