DE10123274A1 - Temperature regulation of metal extrusion press, by generating input function and axial bar temperature so that temperature and press speed is constant and at set value - Google Patents

Abstract

By evaluating the press cycle that has just occurred, the variation with length of an input function uk+1(l) and the axial bar-temperature ThetaBk+1(l) of the subsequent cycle is generated such that the temperature of the metal section is as constant as possible and equal to a set value, and the press speed remains as constant as possible and equal to a predetermined value. The calculated input function is fed in by following the variation with time of the calculated input function.

Description

1 Introduction

The present invention relates to a method and a device for regulating or optimizing a Extrusion press for metals, by evaluating past press profiles to find a suitable profile for the operator input or pressing speed and generated for the bar temperature profile in this way and is automatically or semi-automatically fed by the surgeon that for a given, almost constant, pressing speed the temperature of the generated profiles when leaving the Die as constant as possible throughout the entire process and on the basis of quality predetermined maximum temperature is maintained to increase the productivity of the extruder maximize and ensure the quality of the generated profiles.

Extrusion presses are generally used for the production of extruded products made of metal, glass or Plastic used. In this process, which in process engineering is the hot forming processes is assigned to maximize productivity and homogenize product quality Mastery of the thermal household is desirable.

When extruding metals, such as. B. of aluminum, to which reference is made below, aluminum bars are heated in an oven to 400 to 500 ° C and then in a sensor (Recipients) loaded. This is closed on one side by a die, the breakthrough of which Cross section of the resulting profile strand corresponds. From the opposite side is stamped under Exposure to a very large force (<10 MN) of the block except for a small remnant through the die pressed. At the end of a cycle, a new block is loaded and the pressing process can be repeated.

The balance of the thermal household results from the difference in the thermal energy supplied and mechanical work and the energy dissipated by heat conduction. The resulting one The temperature of the emerging profiles when leaving the die can be influenced by the preheating temperature the ingot and the pressing speed are specifically influenced. The press speed in turn is used in older systems by the operator input for the adjustment of the oil flow rate of the hydraulic system influenced. The operator input is the setpoint for the swivel angle a swivel angle pump or for the valve position. In modern facilities, the press guide gives the desired course for the speed. A speed control ensures that the actual pressing speed is the same as the target The pressing speed is provided that the pressing pressure remains within its limits. In general, the Speed control with a programmable logic control system (PLC) implemented.

The inventor proposes a method and a device for generating and feeding an optimal one Trajectory for the operator input or press speed for a given bar temperature profile in front. The optimal trajectory is fed into older extrusion press systems (without Cruise control or programmable logic controllers) by following the The surgeon has drawn the optimal course of the input on a monitor.

In addition, he suggests for plants with ingot furnaces where the axial temperature profile (taper) is specifically adjustable, a method and a device with which isothermal extrusion constant press speed can be achieved. In this case, that is for achieving the desired constant outlet temperature at the desired constant pressing speed,  the required ingot temperature profile is calculated and given to the ingot furnace temperature control. In front When the bar is loaded into the recipient, the bar temperature profile actually achieved is recorded and the associated operator input history is calculated and fed.

2. State of the art

It is known in process engineering that the maximum productivity is reached when if possible during the entire press cycle with the maximum permissible strand exit temperature is pressed. Furthermore, this temperature has a significant influence on the metallurgical Properties of the products, which is why a considerable one for quality assurance reasons There is an interest in specifying them in a defined manner and keeping them constant during the process. If fulfilled this condition is called an isothermal extrusion process [1, 2, 3].

The realization of the isothermal extrusion of aluminum is, however, considerable, technological insufficiently solved problems, which is why so far mainly a theoretical one Dealing with the topic in the technical literature is done, the use on a broad level in the Industry has failed to materialize.

In the literature [4, 5, 6, 7] a) is the simulated isothermal extrusion, b) controlled isothermal extrusion presses and c) the cyclical control of extrusion presses is known.

• a) In simulated extrusion [5], the extrusion temperature is based on a thermal Simulation model can be calculated in advance and by reversing one regarding this model optimal press speed curve can be calculated. The extrusion process, the one represents thermal system with distributed parameters, but is hardly with analytical methods and can only be described imprecisely with numerical methods, which is why this method is not suitable provides peaceful results.
• b) With controlled extrusion [4], the extrusion temperature is measured, whereby predominantly Radiation pyrometers are used. The basic structure corresponds to a closed one Control loop, which is a constant comparison of setpoint and actual value during the process Stellgrössee calculated for the press speed. Since the contactless measurement of Strand exit temperature, especially on aluminum, is likely to cause regular disturbances, uncontrolled system behavior cannot be excluded. Consequently, this has Strategy proven not easy to apply in practice.
• c) The European patent EP 0615 795 B1 [6] specifies the cyclical control of extrusion presses [7, 8].
  • 1. The process begins with the measurement of the axial bar temperature profile before it is loaded into the recipient.
  • 2. The course of the press speed as a function of the stamp position 1 is calculated and specified by a digital computer before the start of each press cycle. The speed control loop ensures that the actual speed curve matches the specified target curve.
  • 3. The pressing takes place. The actual press speed and the strand exit temperature are measured over the entire press cycle.
  • 4. After the end of the press cycle, the optimal setpoint speed profile for the subsequent cycle is calculated and specified with the aid of optimization algorithms, taking into account the limit values, in such a way that the temperature error, ie the difference between the desired and the actual strand exit temperature, is minimized.

The above Method c) is successful in modern extrusion presses with programmable memories Control systems (PLC) and speed control used and tested [8, 9]. In older ones Cruise control is not available for systems. The entry is made using a rotary knob, with which of the press guides the target angle position for the swivel angle or valve of the hydraulic Systems pretends. The use of a regulation according to EP 0615 795 proves to be expensive. Further the installation of the system requires the press operation to be interrupted.

A requirement in EP 0615 795 B1, which is not always present, is that the bar temperature does not Subject to fluctuations.

In the present invention, a method and a device are proposed with which Isothermal extrusion can be implemented in older extrusion lines without costly Investments such as B. for speed control or interruptions. Changes in the bar temperature are also taken into account.

From an engineering point of view, the extrusion press, with a radiation pyrometer as a measuring sensor for the controlled variable, can be characterized as follows:

• - The setpoint curve for the strand _exit temperature _θaw (t) (0 <t <T _Zyk ) is known before the start of a cycle.
• - The cycle time T _Zyk always has the same order of magnitude.
• - The system behavior is only slowly changing (<< T _Zyk ).
• - The process is non-linear and can hardly be described with analytical methods.
• - The process behavior is determined, is not subject to stochastic parameter fluctuations and is always reproducible.
• - Every cycle has the same initial state.
• - The manipulated variables of the process are limited and cannot be changed as quickly as desired.
• - The acquisition of the controlled variable (strand exit temperature 'a) is associated with considerable errors, Measurement errors and with a dead time, which is why offline processing of the measurement signals is advantageous.

Because of these process properties, a process is described in European Patent EP 0615 795 B1 proposed that deviates from conventional fixed value regulations. It will not, as with one closed control loop, only the local operating point, but always the entire cycle is optimized. Because of the repetitive nature of the process, the experience is generated from a cycle k for the generation the pressing speed curve uses k + 1, which results in feedback from one to the other Cycle is present.

In previous literature, such as [5] and in EP 0615 795 B1 [6], it is assumed that for a given Bar temperature, the pressing speed the immediate adjustable by the surgeon Influencing factor is. Consequently, the methods proposed there calculate the Target press speed curve and specify it. A speed control loop, if one is present ensures that this speed curve is also achieved. The procedures are not applicable if there is no cruise control. This situation is in older ones Attachments. In older plants, the swivel angle is not one, but the swivel angle  Swivel angle or the valve position and thus the oil flow rate is the primary one Operator input size.

In contrast to [5, 6], in the present invention, both the oil flow rate and the Press speed allowed as operator input u. This eliminates the requirement of Presence of a cruise control.

The proposed procedure works in two phases.

• a) After each die change, the first cycle is run with the experience of the surgeon. After the end of the first cycle, a mathematical image for the transfer _{behavior of} the extrusion press is first created by evaluating the courses of the input variable u ₀ (t) and output variable _θa0 (t).
• b) The control starts from the 2nd cycle. With the help of the image, the course of the input variable u _{k + 1} (t) in accordance with the methods of the iteratively learning regulations is based on the measured course of the outlet temperature _θak (t) and the operator input curve u _k (t) in the kth cycle [10, 11] determined such that the control error
• c)
  e _{k + 1} (t) = θ _aw (t) - θ _{ak + 1} (t) (1)
  and the actuating effort u _{k + 1} (t) should be as low as possible. In particular, manipulated variable restrictions can also be taken into account. The operator input curve u _{k + 1} (t) is calculated before the start of the cycle k + 1 and is no longer changed during the pressing process.

After the pressing process k + 1 has been completed, the quality of the control is checked to determine whether that mathematical image has to be reproduced. If this is the case, the Input and output curves as determined under i). In the other case, continue according to ii)

This procedure makes it easier to suppress measurement errors because, in contrast to conventional controls, more powerful, non-causal filters can be used, and leads to a safe and robust control system despite difficult boundary conditions. Due to the thermal inertia of the extrusion press, the changes in the boundary conditions (tool or recipient temperature) of successive cycles are negligible, which ensures an optimal process flow. Since the implementation is only possible with a microcomputer, the time functions are scanned discretely. The continuous time t is followed by the discrete time i

t = iT _A , i = 0, 1, 2,. , , (2)

replaced. An alternative is to sample the signals at the times when the stamp is on the way

l = i.ΔL, with ΔL = elementary length and i = 0, 1, 2,. , , (3)

put back.

3. How the new procedure works

It is taken into account that a controllable ingot furnace is available in some extrusion presses  stands, with which the ingot is given a predetermined axial temperature profile, called taper can be. In such systems, isothermal presses are applied by applying the optimal taper achieved constant speed.

The exit temperature of the profile when the stamp has covered the path l in mm since the start of pressing is denoted by θ _a (l). The length l is at the same time the length of the pressed ingot: the outlet temperature, under otherwise identical conditions, depends on the ingot temperature at point l and on the course of the operator input u in the interval (0, l).

Process for systems without the possibility of stamping an axial temperature profile

In this case the bar temperature can only be adjusted gradually. The outlet temperature control is then changed by changing the operator input function (setpoint for the oil flow or for the Pressing speed). Since the temperature of the ingot, just like it from the furnace come out, changes only gradually, there is a quasi-steady state. The temperature of the ingot in the (k + 1) th cycle is approximately the same as that of cycle k.

Figure 1 shows the arrangement of a direct extrusion press with the proposed mobile measuring and automation system for extrusion presses (MoMAS). The bars are heated in the block furnace and led to the extrusion press. The pressing takes place through the build-up of the pressing pressure, which is changed by adjusting the oil flow. In systems without speed control, the input u that the operator specifies is the setpoint of the swivel angle of a swivel angle pump and thus the setpoint for the oil delivery quantity. In systems with a speed control, the input u is the setpoint for the pressing speed. In both cases, the input is made by the position of the potentiometer in Figure 1. The potentiometer position is also sent to the computer as an analog or digital signal via the interface unit. It represents the input function u (l) as a function of the stamp position l. The position sensor detects the current position l of the stamp. In systems with a speed control, the actual pressing speed is determined from the detected position signal. The speed control is implemented by automatically changing the oil flow depending on the difference between the set and actual speeds of the ram. In MoMAS, the current position l is also routed to the computer via the interface unit

The outlet temperature θ _ak (l) is recorded with pyrometer 1 and led to the industrial PC via an interface unit, which is used for electrical isolation and signal processing. Pyrometer 2 (which could also be replaced by a touch thermometer) detects the temperature profile θ _Bk (l) of the ingot.

The following approach is used to calculate the optimal input profile for the relationship between the process variables:

where α, β and g _k (l) are selected using data from previous press runs. By discretization with l = i.Δ, i = 0, 1, 2,. , ., N - 1, N.Δ = L = length of the ingot to be pressed, equations (4) (5) become

or in matrix display

The elements of the impulse response matrix G _K are also determined from previous experiments [10, 11]. The optimal course of u _{k + 1} (l) at the beginning of the (k + 1) cycle is calculated as specified in [1] with optimizing iterative learning rules. There is a second possibility for determining u _{K + 1} (l) using linear iterative learning control. Here will

u _{k + 1} = u _K + R [ e _k - α (θ _{B, K + 1} - θ _{B, K} )]

where R is the controller matrix and e T | k = [θ _w ] ^T - [θ _{a, k} ] ^T.

The isothermal pressing is achieved with the above-mentioned automation system with the involvement of the operator in the control loop as follows:
The optimal course of the input function u _{k + 1} (l) for the cycle k + 1 becomes in the pause between the cycles k and k + 1 from the courses of the input function u _k (l) and the error function e _k (l) in the cycle k calculated. The total calculated course is a function of the stamp position at the beginning of (k + 1). Cycle displayed on a monitor. At the same time, the actual operator input is also displayed on the same monitor. The surgeon follows the optimal curve by appropriately pressing the rotary knob for the operator input, and thus he applies the calculated optimal input function profile u _{k + 1} (l) to the extrusion press. In the event that the furnace temperature control does not guarantee a constant ingot temperature, the ingot temperature is measured before the ingot is loaded into the recipient and the measured value is included in the calculation.

The process consists of the following steps:

• a) MoMAS is operated during a cycle determined by the operator - e.g. B. after the second cycle a die change - activated.
• b) The bar temperature is measured  
• c) The operator input u (l), with l = the stamp path, for this cycle is a constant variable u ₀ which the operator chooses and specifies on the basis of his experience and expertise.
• d) After the cycle has ended, the maximum profile exit temperature θ _{max is} automatically determined by MoMAS in this cycle. Usually θ _max occurs towards the end of the cycle. At the same time, the operator checks the quality of the profile. If the profile quality satisfactory, is θ _max, the outlet temperature profile is that you _should ideally and by specifying a suitable surgeon input (L) would achieve over the cycle. Optionally, the operator can choose θ _max or another value for the nominal value of the profile exit _temperature θ _aW .
• e) MoMAS determines the relationship between the operator input, bar temperature, Press speed and the profile outlet temperature from the process variables in the elapsed (kth) cycle.
• f) The bar temperature of the next bars to be pressed in the cycle k + 1 is measured.
• g) The optimal course of the operator input u _{k + 1} (l) as a function of the stamp path l is determined using the knowledge of the course of the process variables in the previous cycle k, as well as the measured bar temperature and the desired outlet temperature, taking into account the permitted limits of the manipulated variables, namely pressing force and punch speed calculated by MoMAS.
• h) The course of the operator input u _{k + 1} (l) calculated by MoMAS is shown on the monitor for the entire cycle at the beginning of the following cycle.
• i) The pressing of the k + 1-th cycle is started. In addition to the curve u _{k + 1} (l) proposed by the MoMAS for the operator input, the monitor also shows the input actually specified by the operator in a different color. The operator now continuously adjusts his input during the cycle in such a way that his input in the display matches the suggested course as closely as possible.
• j) Steps e) to i) are repeated. You can possibly do without step e) and only that Repeat steps f) to i).

For example, a three-stage process can be selected and specified for the operator input the first stage extends over the first 30% of the block length, the second over 40% and the third stage over the remaining 30% of the block length.

In cases of new alloys, profile geometries or setting limits, in which the surgeon does not can rely on his experience, can take advantage of the optimal outlet temperatures the control limits can be determined with MoMAS by gradually increasing the limits until the Optimum is reached.

Process for systems with the possibility of stamping an axial temperature profile

In this case, a temperature profile can be stamped on the ingot, and the temperature can also be adjusted quickly in the furnace. This gives you the option of specifying a constant pressing speed and a constant outlet temperature, and to achieve this by suitably regulating the bar temperature profile. The setpoint curve of the bar temperature profile is determined using the method of the optimizing iterative learning control or the linear iterative learning control with the help of Eq. (8) calculated, where u the input is replaced by v the pressing speed and G by G ^* . G ^* represents the impulse response matrix in the event that the press speed is considered as the input and the outlet temperature as the output. Since i. Gen. However, if the bar temperature curve deviates from the target curve, the actual bar temperature profile is measured before the bar is loaded into the recipient. Using this data, the target course for the operator input is calculated and specified. This gives higher priority to keeping the outlet temperature constant than keeping the pressing speed constant.

The process consists of the following steps:

• a) MoMAS is operated during a cycle determined by the operator - e.g. B. after the second cycle a die change - activated.
• b) The bar temperature is measured
• c) The operator input u (l) with l = the stamp path, for this cycle there is a constant variable u ₀ , which the operator chooses and specifies based on his experience and expertise.
• d) After the cycle has ended, the maximum profile exit temperature θ _{max is} automatically determined by MoMAS in this cycle. Usually θ _max occurs towards the end of the cycle. At the same time, the operator checks the quality of the profile. If the profile quality satisfactory, is θ _max represents the outlet temperature profile, which one _should ideally and by setting the billet temperature profile and a suitable operator input (L) would achieve over the cycle. Optionally, the operator can choose θ _max or another value for the nominal value of the profile exit _temperature θ _aW .
• _to e) The operator inputs the desired values ν and θ _aW for Pressgeschwindikeit or for the outlet temperature before.
• f) MoMAS determines the relationship between operator input, bar temperature, Press speed and the profile outlet temperature from the process variables in the elapsed (kth) cycle.
• g) The target temperature profile for the ingot furnace for the cycle k + 2 is calculated and specified.
• h) The bar temperature profile of the bar to be pressed in the next (k + 1-th) cycle becomes measured.
• i) The optimal course of the operator input u _{k + 1} (l) depending on the stamp path l is determined using the knowledge of the course of the process variables in the previous cycle k, as well as the measured bar temperature and the desired in cycle k + 1, taking into account the permitted limits of the manipulated variables, namely press force and punch speed, calculated by MoMAS.
• j) The course of the operator input u _{k + 1} (l) calculated by MoMAS is shown on the monitor for the entire cycle at the beginning of the following cycle.
• k) The pressing of the k + 1-th cycle is started. In addition to the curve u _{k + 1} (l) proposed by the MoMAS for the operator input, the monitor also shows the input actually specified by the operator in a different color. The operator now continuously adjusts his input during the cycle in such a way that his input in the display matches the suggested course as closely as possible.
• l) Steps e) to k) are repeated. You may be able to go to step e) and / or f) dispense.

designations

e _k

(l) Control error depending on the stamp position
e control error
g (t) impulse response of the linearized model of the route with the operator input as input and and outlet temperature as output
G

Impulse response matrix
l punch position = pressed bar length
t time (continuous)
T _A

sampling
T _Zyk

Duration of a press cycle
u Operator input: setpoint for swivel angle or press speed
u _should

(l) Course of the target course of the operator input as a function of the stamp position
u _k

(l) At the beginning of the k. Cycle suggested and displayed course of the operator input as a function of the stamp position l
ν pressing speed
ν _k

(l) pressing speed in k. Cycle at punch position = extruded bar length l
ΔL elementary length in the discretization of the stamp position
θa strand exit temperature
θ _aw

Strand outlet temperature (setpoint curve)
θ _max

Maximum outlet temperature
θ _ak

(l) strand exit temperature (actual value curve in cycle k) as a function of the punch position l
θ _Bk

(l) Course of the bar temperature in the k. Cycle as a function of the stamp position
indices
i Time index (discrete), location index
k cycle

literature

[1] Ruppin, D. and Strehmel, W .:
Direct extrusion with constant exit temperature - use of variable pressing speed
Aluminum magazine, 1977, pp. 543-548
[2] Ruppin, D. and Strehmel, W .:
Automation of the pressing process in direct extrusion of aluminum materials (I)
Aluminum magazine, 1983, pp. 674-678
[3] Ruppin, D. and Strehmel, W .:
Automation of the pressing process in direct extrusion of aluminum materials (II)
Aluminum magazine, 1983, pp. 773-776
[4] Ingvorsen, J.
Closed-loop isothermal extrusion
Proc. Intnl. Extrusion Technology Symposium, pp. 549-558, Chicago (2000)
[5] Biswas, K .; Repgen, K. and Steinmetz, A .:
Computer Simulation of Extrusion Press Operation - Experience with CADEX
A New Computer Aided Process Optimizing System
5th International Extrusion Seminar, Chicago 1992, p. 149-155
[6] EP 0615795
Temperature control of an extrusion press
[7] Pandit, M. Baqué, S. Deis, W., Müller, K .:
Implementation of Temperature Measurement and Control in Aluminum Extruders
Extrusion Technology 2000, Chicago, 15-19. 5. 2000
[8] Pandit, M., Buchheit, K.,
Isothermal Extrusion of Aluminum ", Part I, Aluminum, Issue 4 (1995), pp. 483-487, Part II, Aluminum, Issue 5 (1995), pp. 614-619
[9] Pandit, M.
Trends and Perspectives concerning temperature Measurement and Control in Aluminum Extruders
Aluminum, 76, H. 7-8, July-August 2000, pages 564-573
[10] Hillenbrand, S
Iterative learning regulations with a reduced sampling rate
Dissertation, Department of Electrical Engineering, University of Kaiserslautern, 2000
[11] Isermann, R .:
Identification of dynamic systems, Vol. 1 + 2
Springer Verlag Berlin 1988

Claims (7)

1. A method for regulating the temperature of an extrusion press for metals, by evaluating the just past pressing cycle k, a curve for the input function u _{k + 1} (l) and the axial billet temperature θ _{Bk + 1} (l) of the following cycle (k + 1 ) are generated and specified in such a way that the temperature θ _{ak + 1} (l) of the profiles when leaving the die is as constant as possible and equal to the specified target value θ _aw , and at the same time the pressing speed is as constant as possible and equal to the specified value ν _{k + 1} remains, and the calculated input function u _{k + 1} (l) is fed in by following the course of the calculated input function shown on a monitor. 2. A method according to claim 1, characterized in that the actual bar temperature curve θ _{Bk + 1} (l) is measured, and from this the optimal input function curve is calculated and from the beginning to the end of (k + 1). Press cycle is displayed on a monitor, on which the input function manually entered by the operator is also displayed in such a way that the operator impresses the optimal input function profile by following the optimal course of the press control. 3. A method according to claims 1 and 2, characterized in that the setpoint θ _{aw to} be specified by the operator is automatically selected as the maximum of the outlet temperature of a previous cycle, the operator ensuring that the quality of the profile is satisfactory. 4. A method according to claim 1, characterized in that the determined bar temperature curve θ _{Bk + 1} (l) is transmitted to the furnace temperature control and is set there. 5. A method according to claims 1 to 4, characterized in that the optimal courses of the input function u _{k + 1} (l) and the axial bar temperature θ _{Bk + 1} (l) are determined with the aid of a simulation model and the algorithms of the iterative learner control , 6. A method according to claims 1 to 5, characterized in that the determination of the Input function required impulse responses g (t) or g (l) of the linearized model of the Extrusion press by evaluating the input function and the outlet temperature of the past Cycles can be used. 7. A method according to claims 1-6, characterized in that the billet temperature θ _Bk (l) is automatically lowered successively, so that the regulation of the ride temperature intervenes via the input function, thereby automatically increasing the pressing speed and thus reducing the pressing time, whereby if the bar temperature is too low, it is automatically recognized that the pressing force has been at its upper limit for too long to initiate a possible increase in the bar temperature, so that the pressing time is shortened.