DE10120725C1 - Powder nozzle used for surface treating using a laser beam comprises an inner part, an outer part, and an expansion chamber for distributing a powder gas mixture flowing into an annular gap - Google Patents

Abstract

Powder nozzle comprises an inner part (1); an outer part (2); and an expansion chamber (4) for distributing a powder gas mixture flowing into an annular gap (8). A diffuser (5) is arranged on the inner part in the expansion chamber. The annular gap is arranged coaxially to the spreading axis of the laser beam (10). Preferred Features: The diffuser is a rod or ball diffuser. An adjusting unit (3) is provided opposite the inner part for finely adjusting the outer part.

Description

Technical field

The invention relates to a powder nozzle for surface processing according to claim 1. Die Thanks to its compact design, the powder nozzle allows it to be accessed even in difficult-to-access areas Place a powder nozzle with a coaxial powder gas supply. The invention Powder nozzle combines the advantages of nozzles with lateral powder gas supply, i.e. good ones Accessibility of hard-to-reach places, and the advantage of nozzles with coaxial Powder gas supply, i.e. the possibility of direction-independent processing.

State of the art

The processes of dispersing, alloying and coating using laser radiation (also as Laser cladding or laser generation) are used for Surface treatment and for generating components with filler materials used.

A melt pool is created on the surface of a component with a laser beam, into which a powdery filler material is injected via a powder nozzle using a conveying gas  becomes. The filler material melts on and by moving the component relative to Laser beam creates a layer on the surface of the component that matches the base material is fused over the connection zone. In addition, a is created in the base material HAZ. The powder feed plays an important role in this process. there one differentiates essentially between three possibilities to supply the powder. The The first option is the side powder feed, where the powder is below a certain level Angle is injected into the weld pool from only one side. The second option the powder is made up of several partial beams positioned around the laser beam, injected.

In addition, the coaxial powder supply is also known, in which the powder under one certain angle is injected into the weld pool in a ring.

The coaxial powder nozzle systems have the advantage over the side systems that that the machining result in the plane is less directional. Let it through 3-D components can also be produced by laser beam generation. With the coaxial Powder nozzle systems can also achieve significantly higher powder efficiency are as with the side powder feed systems. The powder efficiency gives this Ratio of the amount of powder made available to the molten bath to the ins Amount of powder injected into the molten bath.

A coaxial powder nozzle is known from US Pat. No. 4,724,299, in which the powder flows horizontally an annular distributor is passed. From here, the powder passes through boreholes first in a swirl or mixing chamber and then in one, under one certain angle tapered, annular gap. From the outlet of the Annular gap, the powder gas jet is coaxial to the laser beam into that generated by the laser beam Melting bath injected. For better shielding of the melting bath from the Atmosphere is an additional protective gas shower around the coaxial powder nozzle arranged. The coating head is water-cooled in the upper area and is directly attached below the processing optics.  

An improvement of the coaxial powder nozzle described in US 4,724,299 is in the Find WO 95/20458. The powder is at a steep angle to the horizontal injected through three powder nozzles into an annular tapered cavity that is arranged coaxially to the laser beam. The powder is injected into the weld pool analogous to the manner described in US 4,724,299. In improving the second The nozzle was focused on a more compact and slim design as well the higher suitability for continuous use. In addition, the nozzle tip cooled with water.

Both systems have a far-lying inner part for powder jet shaping which protects the inner part from reflected laser radiation. Through this constructive measure, a powder gas jet focus less than 3 mm cannot be set. For These systems are therefore only conditionally used for machining small track widths can be used because the powder efficiency decreases sharply as the weld pool becomes smaller.

No. 5,418,350 presents a coaxial nozzle in which the coaxial powder gas jet passes through an additional coaxial gas jet can be influenced and that on the nozzle front is water cooled.

A coaxial powder nozzle with high powder gas jet quality is described in DE 199 09 390 C1 described. With this system, the powder is fed via two or optionally four individual nozzles injected into a swirl chamber to create a uniform and coaxial powder gas cloud to generate the laser beam. To calm this powder swirl, i.e. H. to generate The powder gas mixture becomes a quasi-laminar flow through specially shaped channels guided and guided in a flow direction parallel to the laser beam axis. About one adjustable annular gap of the hollow powder cone. With the in DE 199 09 390 C1 described coaxial powder nozzle can have a diameter of the powder gas jet focus 1 mm can be generated. This means that even when coating with small melt baths higher powder efficiencies can be achieved than with the above-mentioned coaxial Powder nozzles.  

The disadvantage of all coaxial powder nozzles in comparison with lateral (off axis) Powder delivery systems, the less accessible because of their larger size Dimensions. Apart from a few, these coaxial powder nozzles are also suitable Exceptional cases only for coating in the plane.

The weight of these coaxial powder nozzle systems is several kilograms each. you Use with small robots and travel units is only limited or at all not possible. For example, trajectory curves can occur due to the high mass of the nozzles can only be driven at low speeds.

The ease of use of the coaxial powder nozzles is compared to that of the side ones Powder nozzles limited because of the known coaxial designs Powder nozzles have multiple inputs for the powder feed, in order to create a homogeneous one To achieve powder gas jet distribution. To do this, either a single dated Powder feeder Powder gas jet coming through the powder hose into several partial jets divided and then fed to the coaxial nozzle or more Powder delivery systems each convey a jet of powder gas to the corresponding one Powder gas entry of the nozzle. In addition, the known coaxial powder nozzles are not sufficiently compact.

Presentation of the invention

The object of the invention is to provide a nozzle in which the disadvantages after State of the art can be avoided.

Solutions are indicated by the features of claims 1 and 3, being advantageous Refinements are specified by the subclaims.  

According to the invention, it was recognized that the problems mentioned are due to a coaxial Powder nozzle with a diffuser in the chamber, which is used to evenly distribute an in is used to dissolve an annular gap flowing powder gas mixture. Under one uniform distribution is to be understood here that the powder gas mixture at the outlet from the chamber has the same concentration of powder in the gas at every point and that the Powder gas flow density, i.e. the volume flowing per time and area, at the exit the chamber is sufficiently the same at all points. The powder gas mixture flows from the chamber either directly into the annular gap or through individual tubes or equivalent devices in the annular gap.

The powder gas mixture coming from the feed lines is fed into the Chamber much better distributed. The diffuser causes that of the supply lines in the powder gas mixture flowing into the chamber is optimally distributed in the chamber. In order to the chamber can be built much smaller.

A particularly suitable variant of a diffuser is a rod diffuser and / or a Ball diffuser. These diffusers are inexpensive to manufacture and have a very positive effect even distribution of the powder gas mixture. Although rod diffusers and Ball diffusers have been found to be particularly suitable, of course, are others Diffusers such as triangular diffusers are conceivable in principle. There are also deepenings conceivable as diffusers in the inner and / or outer wall. Given the general pronounced complexity of fluid mechanical processes can make a Diffuser only through experimental studies with satisfactory certainty be determined.

The good distribution of the gas mixture flowing into the chamber allows a nozzle to be closed construct with exactly one supply line for the powder gas mixture. In the state of the No embodiments are known in the art in which only one feed line for the Powder gas supply is provided. If there are several supply lines, this becomes one source Originating powder gas mixture distributed in several feed lines. Attention must be paid to this  be that the powder gas mixture is evenly distributed in the feed lines. alternative it is also possible to work with several sources for the powder gas mixture. This one for The technical effort required for multiple supply lines is for a nozzle with one supply line not mandatory. A single supply line increases ease of use and enables the nozzle to be used on components that are difficult to access.

For an inexpensive realization of the nozzle, it is favorable to make the nozzle from an inner part and assemble an outer part. It is possible to use the chamber and / or the Form an annular gap between the inner part and outer part. This allows the size of Varying chamber and annular gap. By changing the size of the chamber and / or The flow of the powder gas mixture can be influenced in an annular gap. The nozzle is now ideal for different powder gas mixtures and / or different powder grain sizes used.

The diffuser is attached to the inside and / or outside of the nozzle. With that the Design effort minimized. For the distribution of the powder gas mixture in the chamber the diffuser should preferably be attached to the inside of the nozzle. The through the supply line (s) flowing powder gas mixture initially flows towards the inner part. Therefore one is there attached diffuser suitable to evenly mix the powder gas mixture in the chamber to distribute. However, it often makes sense to have a diffuser on the outer part of the nozzle to attach, since the outer part of the nozzle is also blown by the powder gas mixture.

When the nozzle is used as intended for dispersing, alloying and coating The machined workpiece is strongly heated by means of laser radiation. This leads to a Heat radiation that heats the nozzle. The nozzle heats up considerably also due to the laser radiation reflected by the workpiece and absorbed by the nozzle. To protect the nozzle from overheating, the nozzles are usually made by one liquid coolant, mostly water. The outer part consists of one Material with a thermal conductivity of at least 300 W / mK, for example made of copper with a thermal conductivity of 384 W / mK, so the heat can easily be cooled  Drain off areas of the nozzle. This allows the areas of the nozzle to be avoided overheating must be minimized. This allows one compact design of the nozzle.

A further miniaturization can be achieved by only the outer part the nozzle has a device for cooling. This can be achieved by Inner part is thermally coupled to the outer part in such a way that the inner part passes through Heat transport from the inner part to the outer part is sufficiently cooled. The Heat transport primarily through heat conduction. In addition, heat radiation can also occur and convection play a role, which is generally subordinate.

The flow of the powder gas mixture in the chamber and in particular in the annular gap can may be sensitive to the geometrical dimensions of the annular gap and Hang the chamber. If there is an annular gap and chamber between the inner part and outer part can be formed by fine adjustment of the inner part and outer part to each other, the flow will be affected. This fine adjustment is advantageous because Inner part and outer part mostly with a comparatively coarse thread be screwed together. In addition, minor manufacturing defects of the inner part and Outer part to be balanced. This can be used in the production of inner parts and Larger manufacturing tolerances are permitted. This allows one cheaper production. In addition, the nozzle and the chamber through the Fine adjustment can be optimized for different flows of powder gas mixtures. The powder gas mixture can have different concentrations of powder in the gas as well as different grain sizes of the powder. In addition, the powder gas stream, i.e. the pro Volume of time flowing through the nozzle, vary. This also requires one Adjustment of the geometrical dimensions of the chamber and the annular gap using a Fine adjustment of the distance between the inner part and outer part of the nozzle.  

For efficient machine-controlled operation, powder nozzles are often on one Telescopic arm attached. To enable a compact design of the nozzle, the at least one feed line for the powder gas supply arranged on the telescopic arm.

Alternatively, the powder nozzle can also be attached directly to an adapter Processing optics are attached. This saves the effort of a telescopic arm is unnecessary in many coating applications

For a compact design of the nozzle, it is useful to have a feed line on the telescopic arm and attach a return line for a coolant.

A space-saving arrangement of the coolant supply and discharge is achieved by the Supply lines and return lines in a common to the axis of the laser radiation vertical plane.

In order to shield the melt as well as possible from the powder gas flow To achieve on the surface to be processed, it is advantageous if the coaxial powder gas jet from the nozzle tip to the focus of the powder gas jet distance to be covered does not exceed 10 mm. In those known in the prior art No nozzles have achieved this so far because of their less compact design have larger surfaces. These larger surfaces take up more heat radiation and reflected laser radiation. To prevent overheating is in the nozzles according to the prior art, therefore, a greater distance from the workpiece, which by the Laser radiation is strongly heated and laser radiation reflects, required.

A compact design is available for machining hard-to-reach surface areas especially required in the laser beam exit area of the nozzle. For this it is helpful that cooling devices in the laser beam exit area can be dispensed with. this will achieved in that the laser beam exit region of the nozzle such thermal Features that sufficient cooling by heat conduction to Laser beam entry area takes place. Adequate cooling occurs when the nozzle  does not get so hot that powder from the powder gas mixture in one is operating the nozzle influencing amount of nozzle parts is melted. In addition, the nozzle must not do so overheated, so that the material from which the nozzle is made warps or even melts. In order to achieve sufficient cooling, it is helpful to remove the Ensure heat, for example by using a material with a high Thermal conductivity, such as copper. The heat input can also be kept low become. This is possible by taking care that the heat radiation exposed areas a low emissivity (and thus low absorption) for the Have heat radiation as well as for the reflected laser radiation.

To reduce the heat input, it is also helpful to design the nozzle so that the area that absorbs heat radiation and reflected laser radiation is minimal.

It is helpful to adapt the nozzle to a wide variety of operating requirements Position the powder jet focus by changing the shielding gas volume flow can.

Further advantages, features and details of the invention result from the im following described embodiments and with reference to the drawings. there demonstrate:

Fig. 1 is a unit for supplying a powder coaxial powder nozzle enveloping a laser beam with a spherical diffuser,

Fig. 2, the unit for the coaxial powder feed of a laser beam enveloping powder nozzle with a rod diffuser,

Fig. 3 is a laser beam enveloping powder nozzle with a spherical diffuser and a unit for the supply of protective gas,

Fig. 4 is a supply line for the powder gas supply and a supply line and a return line for a coolant,

Fig. 5 is a sectional view of the fine adjustment between the inner part and outer part and

Fig. 6 shows the nozzle attached to a telescopic arm.

Fig. 1 and Fig. 2 show a cross section through the unit for the coaxial powder gas supply. This unit consists of an inner part 1 and an outer part 2 . The inner part 1 is screwed into the outer part 2 and is connected to the outer part 2 via a thread. Inner part 1 and outer part 2 are fixed to one another via an adjustment unit 3 consisting of a threaded ring which is screwed onto the inner part 1 .

In the assembled state there is an expansion chamber 4 with a ball diffuser 5 or a rod diffuser 6 inside the nozzle, into which the powder gas flow coming from the powder conveyor is injected through the feed line 7 . This constructive measure distributes the powder gas mixture homogeneously in the expansion space 4 . The homogeneous powder gas cloud that is now present is then conveyed via the annular gap 8, which tapers conically from the expansion space 4, as a coaxial powder gas flow to the nozzle tip 9 , from where a homogeneous coaxial powder gas jet emerges, which is focused at a defined distance from the nozzle tip 9 .

A ball diffuser which is particularly suitable for operation consists of balls which are installed in the side of the inner part 1 facing the expansion space 4 . The balls have a diameter of 3 mm. A total of 40 balls are arranged in this ball diffuser. In the plane of the feed line 7 , the outer radius of the expansion chamber 4 is 20 mm, the inner radius 12 mm

Alternatively, a rod diffuser can also be installed in the expansion chamber 4 with the above dimensions. In a preferred embodiment, 12 rods with a diameter of 3 mm and a length of 7 mm are installed on the side of the inner part 1 facing the expansion chamber 4 . The rods are arranged coaxially with the direction of propagation of the laser radiation.

The laser beam 10 is guided through the center of the nozzle 11 . Then it hits the surface of the workpiece together with the powder gas jet. The powder gas jet is generally preheated by the laser beam 10 before it hits the workpiece. This improves the result of material processing.

The outer part 2 of the nozzle is made of copper and is water-cooled. Since the inner part 1 of the nozzle is not exposed to as high thermal loads as the outer part, it is sufficiently cooled by heat conduction via the thread of the outer part 2 .

For many coating applications only in Fig. 1 and unit for the coaxial Polvergaszufuhr 2 shown Fig. Is needed because the gas used for the powder feed at the same time serves as protective gas.

For coatings in which the protective gas effect of the conveying gas is insufficient, a second unit for a central protective gas supply can be screwed on, as shown in FIG. 3. This unit consists of a housing 12 which is screwed onto the inner part 1 of the unit for the coaxial powder supply. The additional protective gas is fed through the feed line 13 to the machining process through the center 11 of the nozzle. In order to prevent air from being sucked in by the protective gas flow, a protective glass 14 is provided in the housing 12 on the laser beam entry side. Depending on the laser application, the protective glass is transparent for either CO ₂ , Nd: YAG or diode laser radiation.

FIG. 4 shows a cross section of the adjusting unit 3 consisting of a threaded ring with three threads 15 offset by 120 °. Grub screws (not shown) are screwed into the thread 15 . These grub screws allow fine adjustment of the outer part 2 and inner part 1 .

Fig. 5 shows the nozzle laterally attached to a telescopic arm 16 . The telescopic arm 16 is attached to a four-axis positioning unit 17 . With the positioning unit 17 , the nozzle is aligned with the laser beam 10 via the positioning tables located therein. The entire system is laterally attached to the processing optics 18 .

In order to achieve a similarly good accessibility when machining hard-to-reach places as is possible with the known powder nozzles for the lateral powder supply, the connections for coolant 19 , powder 7 and protective gas 13 are designed so that all connections 7 , 13 , 19 run parallel to the telescopic arm 16 , whereby they only expand the space requirement of the nozzle in one direction. As FIG. 6 shows, the diameter of the outer part 2 on the laser beam entry side is the widest point except in the direction of the telescopic arm 16 .

LIST OF REFERENCE NUMBERS

1

inner part

2

outer part

3

adjusting

4

expansion space

5

ball diffuser

6

Staff diffuser

7

Powder gas supply

8th

annular gap

9

nozzle tip

10

laser beam

11

Center of the nozzle

12

Shielding gas supply housing

13

Inlet for protective gas

14

protective glass

15

Thread for grub screws

16

telescopic arm

17

Four-axis positioning unit

18

processing optics

19

Connection for coolant

Claims (15)

1. powder nozzle, which has an inner part ( 1 ) and an outer part ( 2 ), for surface processing by means of laser radiation ( 10 ), with an expansion chamber ( 4 ) for a uniform distribution of a powder gas mixture flowing into an annular gap ( 8 ), the annular gap ( 8 ) is arranged coaxially to the axis of propagation of the laser radiation ( 10 ), the expansion chamber ( 4 ) being formed between the inner part ( 1 ) and the outer part ( 2 ), characterized in that in the expansion chamber ( 4 ) on the inner part ( 1 ) a diffuser ( 5 , 6 ) is arranged. 2. Powder nozzle according to claim 1, characterized in that the diffuser ( 5 , 6 ) is a rod diffuser ( 6 ) and / or ball diffuser ( 5 ). 3. powder nozzle, which has an inner part ( 1 ) and an outer part ( 2 ), for surface processing by means of laser radiation ( 10 ), with an expansion chamber ( 4 ) for a uniform distribution of a powder gas mixture flowing into an annular gap ( 8 ), the annular gap ( 8 ) is arranged coaxially to the axis of propagation of the laser radiation ( 10 ), the annular gap ( 8 ) being formed between the inner part ( 1 ) and the outer part ( 2 ), characterized in that an adjustment unit ( 3 ) for fine adjustment of the outer part ( 2 ) relative to the Inner part ( 1 ) is provided 4. Powder nozzle according to claim 3, characterized in that the adjusting unit ( 3 ) has a threaded ring which can be screwed onto the inner part ( 1 ) and with which the outer part ( 2 ) can be fixed, the threaded ring having bores which are provided with a thread ( 15 ) are, wherein the holes are aligned parallel to the nozzle axis in the screwed state 5. Powder nozzle according to one of the preceding claims, characterized in that the chamber ( 4 ) has exactly one feed line ( 7 ) for the powder gas supply. 6. Powder nozzle according to one of the preceding claims, characterized in that the outer part ( 2 ) and / or the inner part ( 1 ) consists of a material with a thermal conductivity of at least 300 W / mK. 7. Powder nozzle according to one of the preceding claims, characterized in that the outer part ( 2 ) has a device for cooling and the inner part ( 1 ) is thermally coupled to the outer part ( 2 ) such that adequate cooling of the inner part ( 1 ) by Heat transfer from the inner part ( 1 ) to the outer part ( 2 ) is possible. 8. Powder nozzle according to one of the preceding claims, characterized in that the powder nozzle is attached to a telescopic arm ( 16 ) on which the at least one feed line ( 7 ) for the powder gas supply is arranged. 9. Powder nozzle according to one of the preceding claims, characterized in that the powder nozzle is attached to a telescopic arm ( 16 ) on which at least one feed line ( 19 ) for a coolant and at least one return line ( 19 ) for the coolant are arranged. 10. Powder nozzle according to one of the preceding claims, characterized in that the powder nozzle can be fastened to an adapter which is mounted centrally under a processing lens ( 18 ). 11. Powder nozzle according to one of claims 7-10, characterized in that the at least one feed line ( 19 ) and the at least one return line ( 19 ) of the coolant lie in a common plane perpendicular to the axis of propagation of the laser radiation ( 10 ). 12. Powder nozzle according to one of the preceding claims, characterized in that the nozzle can be operated such that the distance to be covered from the coaxial powder gas jet from the nozzle tip ( 9 ) to the focus of the powder gas jet is a maximum of 10 mm. 13. Powder nozzle according to one of the preceding claims, characterized in that that the laser beam exit area of the nozzle has such thermal properties has that sufficient cooling by heat conduction to Laser beam entry area of the nozzle takes place. 14. Powder nozzle according to one of the preceding claims, characterized in that the laser beam exit area of the nozzle is designed so that the area that Thermal radiation and reflected laser radiation is minimal. 15. Powder nozzle according to one of the preceding claims, characterized in that that the powder jet focus due to a change in a protective gas volume flow is positionable.