DD236038A1 - METHOD FOR CONTROLLING AND CONTROLLING FRICTION WELDING MACHINES - Google Patents

Abstract

The invention relates to a method for controlling and regulating friction welding processes, in which the material, the welded part geometry, the impact surface preparation and the cooling speed are taken into account. By means of the invention, the field of application of the friction welding method is increased, in particular with regard to the weldable materials. Furthermore, can largely be dispensed with a prior characteristic determination by Proweissweissungen. This is achieved by, in particular, determining the rate of change of the friction torque and, if this reaches a specifiable, approximately constant value, optionally terminating the friction welding operation or measuring the cooling rate. Depending on the measurement result, the friction process can be continued with suitably modified process parameters until the cooling rate reaches a permissible value.

Description

defined optimal Verschweißzustand a signal to terminate the friction welding process or to set the allowable cooling rate at reduced friction pressure and increased friction speed is given.

For this 2 pages drawings

Field of application of the invention

The invention relates to a method for controlling and controlling friction welding processes, in which the material, the weld part geometry, the impact surface preparation and the cooling rate are taken into account. The invention increases the field of application of the friction welding process, in particular with regard to the weldable materials.

Characteristic of the known technical solutions

It is known that the control of the friction welding process today preferably takes place after the welding time or after the welding part shortening.

These two control variables, assuming reproducible cutting of the welded parts, must be determined experimentally as a function of the material, the geometry of the welded part, the friction pressure and the friction speed. The criterion for the necessary amount of welding part shortening or welding time is the quality-compliant friction welding connection. The inspection of the weld quality is destructive by the bending and tensile test as well as non-destructive by ultrasonic testing. The welding part shortenings and welding times thus determined with great effort are average values. Fluctuations in the surface preparation, the geometry of the welding part and the chemical composition of the material can therefore no longer be taken into account when the working values are set once. The friction welding process is interrupted more or less arbitrarily. A statement about the achieved welding condition of the abutment surfaces and about the axial temperature field can not be made. A regulation of the friction welding process is not possible on this basis.

Another disadvantage of conventional friction welding is that the two rotationally symmetric parts are loaded with a predetermined friction pressure and moved against each other at a predetermined friction speed. As a result, a very narrow zone in the region of the resulting weld is brought to the temperature required for pressure welding. -

A narrow heated zone, surrounded by a large mass of cold base material, causes a large temperature gradient and thus a high cooling rate. The result is the formation of martensite in the area of the weld on the hardenable steels. In order to prevent the formation of martensite in addition to the weld in the conditionally weldable steels, a preheating of the steel is necessary. By preheating by means of fuel gas-oxygen flame or inductor, however, creates an additional technological effort.

The difficulty with the automation of friction welding is that the individual welds run very differently during their initial stages and take these initial stages very different lengths. Therefore, proposals are already known to use the friction welding process itself for controlling a process parameter (eg Reibdurck). So z. B. with a method according to DE-AS 1627466 on the specification of a target torque automatically the friction pressure can be controlled. The starting point of this method is the typical for the friction welding process of the torque required to generate the relative rotation; Shortly after the beginning of the relative rotation, the torque reaches a maximum value to drop relatively steadily to an approximately constant equilibrium value after exceeding the "torque peak." The torque is initially subject to large fluctuations, since the contact surfaces are cold and have not yet adapted to each other ,

The solution according to DE-AS 1627466 is to measure the occurring torque and to use to regulate the size of the contact pressure at least at the beginning of the processing, so that the torque does not the approximately constant duration value, which it assumes during the last processing section significantly exceeds.

The disadvantage of the method, however, is that the target torque to be specified must be determined by trial welds, which must be repeated at each change of the weldment geometry and / or the material. Another disadvantage of the method is that the time course of the friction pressure can not be specified as an independent variable. The spread of the temperature field in the workpiece is therefore only slightly influenced. To avoid the disadvantages of conventional timings for the friction welding process, it is also known to regulate the friction welding by means of an automatic timer. In this case, measuring the load of the drive device (eg torque measurement) provides characteristic points in the welding process, which are used as starting points for a

automatic timing can serve (DE-AS 1627466). _ ..._

According to DE-AS 1627466, e.g. a switch is set to respond to a force value that occurs when the torque has reached its steady state value. In this way, the switch can trigger an automatic timer, which causes the braking of the rotating workpiece and the application of the compression pressure. The disadvantage of this method, however, is that the switch-triggering torque value must be determined by trial welds. In another, known method, the temperature of the abutting surfaces is detected by measurement technology and used to control and quality control of the weld. The aim of this method according to DE-OS 2742788 u. a. It is to limit the extent of the heat-affected zone on both sides of the weld and yet always to ensure that the necessary welding temperature is reached. This is achieved by the deceleration is then initiated when the sensor detecting the impact surface temperature signals the reaching of the predetermined welding temperature

 In addition, this method causes an error indication when

a) the required welding temperature is not reached within a certain preheating time, and

b) the welding temperature in the welding zone remains longer than a fixed period of time.

Such a control of the friction welding process is already known in a similar form from DE-AS 1911040. Again, the impact surface temperature is detected with an optical pyrometer and its temperature-dependent output signal used to trigger the deceleration and compression.

However, both the method according to DE-AS 1911040 and the method according to DE-OS 2742788 require the performance of test welds to determine the predetermined temperature setpoint.

It is also known a method (DE-OS 1627482), in which the friction welding process is influenced by a schedule control of the rotational speed. It is assumed that a rotation of the parts to be welded above a certain speed range mainly leads to heating of the parts. In contrast, a rotation of the parts below a certain speed range causes mainly a strong plastic deformation of the friction zone. This effect is used to to achieve by periodically changing the rotational speed that the heating propagates radially over the abutment surface. This operation is particularly advantageous when parts with large diameter and consequently high speed gradient are to be welded, because only then a relatively uniform radial temperature distribution can be achieved. Unfortunately, this method also has the disadvantage that the optimum temporal course of the rotational speed to be predetermined must be determined by means of complex test welds.

Another known effect is that the temperature profile in the vicinity of the abutting surfaces can be influenced by the choice of the friction pressure. This is used in the method according to DE-AS 2220898 in order to generate a temporary increase in temperature during deceleration, in that already during deceleration the friction pressure is increased to a value corresponding to the compression pressure. As a result, the temperature of the resulting weld is maintained at a sufficiently high level immediately after completion of the workpiece rotation and delays the cooling. However, the application of this method requires that elaborate test welds are performed to determine the welding parameters. Furthermore, it can be observed that the reduction in the cooling rate to be achieved with this method is often insufficient to ensure the required quality of the welded joint in hard-to-weld iron materials.

Object of the invention

It is an object of the invention to provide a method for controlling and regulating the friction welding process, which eliminates the disadvantages of known methods and ensures friction welds always consistent quality.

Explanation of the essence of the invention

The invention has for its object to provide an uncomplicated method for controlling and regulating the friction welding process which takes into account the composition of the material, the welding part geometry and the abutment surface preparation, which ensures an optimum welding state and a suitable cooling speed independently of previous test welds.

According to the invention the object is achieved in that the time required to produce the relative rotation of the weldments and characteristic of the friction welding process time course of the friction torque (Figure 1) is measured during the friction process. Upon reaching the conditions

- ^M R1> ^M R2 ⁽¹⁾

^dM R '

- -rrr- ft * const

 dt

defined process state is a signal to terminate the friction welding process or, in conditionally weldable steels, for measuring the axial temperature distribution T = T (x) from which the cooling rate can be calculated triggered. Depending on the measurement result, when the condition is met

the friction welding process is completed or continued with reduced friction pressure and increased friction speed until the cooling rate has reached the permissible value Vz.

It has been found that the condition (1) is necessary and sufficient for the reason that a deep impact surface activation takes place by the rubbing process, which in turn is a prerequisite for quality-compliant friction-welded joints. The condition (1) includes in particular the occurrence of a maximum friction torque Mri at a time t-i after the beginning of the friction process and the subsequent decrease of the friction torque below this maximum value.

This time course can be used to control and regulate the friction welding process. In this case, the rate of change of the friction torque is determined and the reaching of that process state is signaled, in which, according to condition (2), the rate of change assumes a predeterminable, approximately constant value. Thus, the optimal weld state of the abutment surfaces can be largely determined without previous characteristic value determination by trial welds. The time for the completion of the friction welding process or for the preferably previously performed measurement of the cooling rate can thus be fixed from the course of the process.

A further advantage of the invention is that the cooling rate can be influenced as a function of the measured values determined without additional heat sources.

embodiment

The invention will be explained below using an exemplary embodiment. In the accompanying drawing shows

Figure 1: the schematic representation of the temporal Reibmomentverlaufes, Figure 2: the block symbol representation of the control and regulation of Reibschweißprozesses.

In the course of the described process, the following reference quantities result:

- the process independent variables

ν friction speed,

U Mdtorspannung,

ρ friction pressure,

W material,

G weldment geometry

- the controlled variables

^X 1 ⁼

-The guide sizes

S ζ

1*

^M R1

- the manipulated variables

^y i ^{= X} 1 - ^W 1 '

^y 2 ^{= X} 2 "

^{= X} 3 -

^y 3.2 ^{= P} min - ^{p =} * ^ ^P '

To control and regulate the Reibschweißprozesses the control machine three reference variables are given (Figure 2), which are well measured and resulting from the laws of friction welding process regardless of the type of material and the weld geometry and the amount of friction pressure and the friction rate itself:

= const

W ^Mr 1

W ₂ =

^W 3 ~ St - ^a 3> _χ 2 = ^V z

During the friction process, the friction torque is constantly measured, for example, with a torque meter, and communicated the result to the control machine. The optimal welding state of the abutment surfaces is achieved when the measurement result coincides with the reference variables W ₁ and W ₂ . At the same time, during the rubbing process, the temperature is measured axially at several points, for example thermovisually. The control unit calculates the cooling rate from these measurements and compares it with the reference variable W ₃ *, which was taken from a ZTU diagram to set the required toughness of the welded joint. If it is less than or equal to then the friction welding process can be terminated. If the cooling rate on reaching the reference variables Wi and W _{2 is} greater than the permissible, then there are several options for setting the required axial temperature distribution:

1. The friction welding process is continued at the same friction pressure and unaltered friction speed until the required temperature field has set. Very large weld part shortenings are the result.

2. The required temperature field is provided by the reduction of the friction pressure while increasing the friction speed. When the allowable cooling rate is reached, the friction welding process can be completed according to the technology provided.

The additional weld part shortenings are very small

 As proof of the weld quality, the following expression of the control automat is used:

M _R =. f Ct)

te and ^ xt for -

Claims (2)

Invention claim: Method for controlling and regulating the friction welding process, characterized in that the time profile of the frictional torque M _R = M _R (t) and the axial temperature distribution T = T (x) are measured and upon reaching the conditions "2> ² d = aj-Uv (3)