CN110605392B

CN110605392B - Metal entity printing method for alternately performing outer wall surfacing and internal filling

Info

Publication number: CN110605392B
Application number: CN201910905020.6A
Authority: CN
Inventors: 沈洪垚; 刘冰; 邓荣新; 唐胜; 李顺
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2019-09-24
Filing date: 2019-09-24
Publication date: 2020-06-30
Anticipated expiration: 2039-09-24
Also published as: CN110605392A

Abstract

The invention discloses a metal entity printing method for alternately performing outer wall surfacing and internal filling, and belongs to the technical field of additive manufacturing. According to the invention, the deformation printing is carried out on the region of the workpiece which is easy to generate the hanging flow, so that the problem of hanging flow collapse when certain inclined positions are vertically printed is avoided, and the forming stability is ensured; meanwhile, the non-flow hanging area on the outer wall and the interior of the entity are processed by adopting the traditional three-axis material increase instead of posture change, so that interference can be avoided better, and the complexity of path planning is reduced. In order to avoid interference between a welding gun and the printed outer wall stream hanging area when the workpiece is printed in other areas to be printed, the strategy of alternately printing the outer wall stream hanging area and other areas every 8mm is adopted, and the sustainability of the surfacing process is ensured. By using the printing method provided by the invention, the problem that the hanging flow is generated at certain positions of the workpiece in the traditional triaxial material increase is solved.

Description

Metal entity printing method for alternately performing outer wall surfacing and internal filling

Technical Field

The invention belongs to the technical field of additive manufacturing, and particularly relates to a metal entity printing method for alternately performing outer wall surfacing and internal filling.

Background

Additive manufacturing technology is commonly known as 3D printing, and is a digital manufacturing technology for finally obtaining a required workpiece by adding and stacking materials layer by layer. With the rapid development of metal additive manufacturing technology in recent years, many metal parts which are difficult to process or have high cost by the traditional method can be rapidly realized by a metal additive manufacturing process. At present, metal additive manufacturing technology has been applied in many fields. Among them, the electric arc additive manufacturing has many advantages, such as high deposition rate, short manufacturing cycle, high wire utilization rate, low cost, etc. In addition, the formed piece has high density, uniform chemical components and excellent mechanical properties.

The Chinese patent document with the publication number of CN207642290U discloses a single-metal arc type 3D printing device, which comprises an X-axis linkage mechanism, a Y-axis linkage mechanism, a Z-axis linkage mechanism and a control system for controlling the X-axis linkage mechanism, the Y-axis linkage mechanism and the Z-axis linkage mechanism to carry out three-axis linkage, wherein a welding gun for printing a workpiece is arranged on the X-axis linkage mechanism, and the X-axis linkage mechanism is arranged on the Z-axis linkage mechanism and can drive the welding gun to realize the movement in the X direction and the Z direction; and the Y-axis linkage mechanism is provided with a workpiece substrate which can move along the Y direction along with the Y-axis linkage mechanism, and the workpiece substrate is positioned below the welding gun.

However, in the process of electric arc additive manufacturing, the wire becomes in a high-temperature melting state, and if a traditional three-degree-of-freedom printing mode is adopted, serious hanging flow collapse phenomenon can occur when some inclined structures are formed by overlaying welding. Therefore, metal overlay forming is generally performed by a multi-degree-of-freedom robot arm.

However, if the metal entity is printed, the multi-degree-of-freedom variable-attitude printing is adopted in the whole surfacing processing process, so that more interference situations sometimes occur, and the path planning is more complicated, so that the processing efficiency can be greatly improved and the forming stability can be ensured if the traditional fixed-attitude vertical printing and the multi-degree-of-freedom variable-attitude printing are combined in the metal entity printing. However, there is no method for combining the two printing forms for metal forming.

Disclosure of Invention

The invention provides a metal entity printing method for alternately performing outer wall surfacing and internal filling, which solves the problem that certain positions of a workpiece in the traditional triaxial additive can generate hanging flow.

The technical scheme of the invention is as follows:

a metal entity printing method for alternately performing outer wall surfacing and internal filling is characterized by comprising the following steps of:

(1) acquiring an STL model of a workpiece to be processed, and setting printing parameters, wherein the printing parameters comprise the layer height of an additive process, the wire feeding speed, the printing speed and the welding bead spacing;

(2) horizontally slicing the whole model according to the set additive process layer height to obtain a slice outline line segment set A, and filling the inside of a slice outline line to obtain an internal path line segment set S;

(3) analyzing the workpiece STL model to obtain a model outer wall hanging flow area and an outer wall non-hanging flow area, and acquiring a model height H;

(4) for the slice contour line segment in the set A falling in the stream hanging area, deleting all other contour line segments except the lowest contour line segment, selecting the lowest contour line segment as a base line, and carrying out continuous equidistant bias on the outer wall curved surface by the additive layer height to obtain a bias contour line segment set B;

(5) sequencing the line segments in the set A, B, S to form an additive path of the model;

(6) constructing a plane z 1-h and z 2-0, wherein the value of h is less than the dry elongation of the wire;

(7) sequentially selecting line segments positioned between the planes z1 and z2 in the set B and the set A ∪ S to form an additive printing sequence;

(8) judging the relation between z1 and H, if z1< H, updating the values of z1 and z2, wherein z1 is z1+ H, and z2 is z2+ H, returning to the step (7), and otherwise, executing the step (9);

(9) generating a model additive path according to the obtained additive printing sequence, wherein line segments in the set B are printed in a variable posture, and line segments in the set A ∪ S are printed in a traditional fixed posture;

(10) and alternately carrying out variable-attitude outer wall surfacing and fixed-attitude internal filling printing processes on the additive manufacturing platform.

The invention uses the variable-attitude printing workpiece outer wall hanging flow area to ensure the forming stability, and meanwhile, the outer wall non-hanging flow area and the solid interior adopt the traditional three-axis material increase instead of adopting multi-degree-of-freedom variable-attitude processing, thereby better avoiding interference.

In the step (3), the division standard of the external wall hanging flow area and the external wall non-hanging flow area is as follows: and (3) collecting all positions of the normal vector on the outer wall of the workpiece under the XY plane of the space to be divided into outer wall hanging flow areas, and collecting all the positions of the outer wall of the workpiece except the hanging flow areas to be divided into outer wall non-hanging flow areas.

In the step (6), because the dry extension of the welding wire is about 12mm generally, in order to ensure that the welding gun does not interfere with the part of the printed and formed outer wall flow hanging area when the contour line segment of the outer wall non-flow hanging area is printed and the inside is filled in the fixed posture, the value of h is preferably 8-10 mm. Further, the value of h is 8 mm.

In the step (7), in a vertical height interval h from a plane z1 to a plane z2, the contour line segment of the outer wall of the convection area in the height interval is printed firstly, then other areas of the outer wall are printed layer by layer and internal filling is completed, and an additive printing sequence in the height interval is formed.

In the step (9), the printing direction D with the variable posture is obtained by the cross product N × T of the normal N of the surface of the workpiece at the point and the tangential T of the base line or the offset line at the point, and the printing direction with the traditional fixed posture is the vertical Z direction.

Compared with the prior art, the invention has the following beneficial effects:

according to the metal entity printing method for alternately performing outer wall surfacing and internal filling, disclosed by the invention, the deformation printing is performed on the region of the workpiece which is easy to generate the hanging flow, so that the problem of hanging flow collapse when certain inclined positions are vertically printed is avoided, and the forming stability is ensured. Meanwhile, the outer wall hanging flow area and other positions are alternately printed, so that interference is avoided, and the continuity of surfacing welding is ensured.

Drawings

FIG. 1 is a schematic flow chart of a method for printing a metal entity by alternately performing outer wall surfacing and inner filling according to the present invention;

FIG. 2 is a schematic view of a selected workpiece model according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of an embodiment of the present invention, in which a workpiece model is horizontally sliced according to the additive layer height to obtain a slice contour line segment and then filled to obtain an internal path line segment;

fig. 4 is a schematic diagram of a bias contour line segment obtained by continuously and equidistantly biasing the outer wall flow region according to the embodiment of the present invention;

fig. 5 is a schematic diagram of plane z 1-8 mm and plane z 2-0 mm constructed by an embodiment of the present invention;

FIG. 6 is a schematic diagram of the embodiment of the present invention in which the welding gun does not interfere with the outer wall sagging area when the alternating height is set to 8 mm.

Detailed Description

The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention without limiting it in any way.

As shown in fig. 1, a method for printing a metal entity by alternately performing outer wall surfacing and inner filling comprises the following steps:

step 1, obtaining an STL model of a workpiece to be processed, and setting the layer height of an additive process to be 2.0mm, the surfacing additive speed to be 0.011m/s, the wire feeding speed to be 5.0m/min and the welding bead spacing to be 4.0mm as shown in figure 2.

The printing material selected in the embodiment is ER5356 stainless steel welding wire with the diameter of 1.2 mm. The protective gas is a mixed gas of 2% oxygen and 98% argon. The guard flow was set at 20L/min.

And 2, horizontally slicing the whole model according to the height of the additive layer, as shown in fig. 3, obtaining a slice outline line segment set A, and completing filling to obtain an internal path line segment set S.

And 3, analyzing the STL model to obtain a model outer wall hanging flow area and a model non-wall hanging flow area, and obtaining the height H of the model which is 50 mm.

The out-wall flow area is defined as a set of all positions of the normal vector on the outer wall of the workpiece, which are located below the XY plane in space, i.e., an area c in fig. 2. The definition of the outer wall non-sagging region is the set of all positions on the outer wall of the workpiece except the sagging region, i.e., the region a, the region b, the region d and the region f in fig. 4.

And 4, as shown in fig. 4, for the slice contour line segments falling in each hang-flow region in the set a, deleting all contour line segments except the lowest contour line segment, selecting the lowest contour line segment as a base line, and performing continuous equidistant offset on the outer wall curved surface by the additive layer height to obtain an offset contour line segment set B.

And step 5, sequencing and planning the line segments in the set A, B, S to form a model additive path.

Step 6, construct plane z 1-8 mm and z 2-0 mm, as shown in fig. 5.

And 7, sequentially selecting line segments positioned between the planes z1 and z2 in the set B, A ∪ S to form an additive printing sequence.

And within the vertical height variation range of 8mm, firstly printing the outline line segment of the outer wall of the flow hanging region in the height interval, and then printing other areas of the outer wall layer by layer and finishing internal filling to form an additive printing sequence in the height interval. The vertical height variation range is set to 8mm because the dry elongation of the welding gun is generally set to 12mm as shown in fig. 6, so that it can be ensured that the welding gun does not interfere with the printed outer wall flow hanging region part when the contour line segment of the outer wall non-flow hanging region and the internal filling are printed in a fixed posture.

And 8, judging the relation between z1 and H, if z1< H, returning to the step 7 when z1 is equal to z1+8 and z2 is equal to z2+8, and otherwise, executing the step 9.

And 9, generating a model material adding path according to the planning, wherein the line segments in the set B are printed in a variable posture, the line segments in the set A ∪ S are printed in a traditional fixed posture, and generating a robot motion code, wherein the printing direction D in the variable posture is obtained by multiplying the normal N of the surface of the workpiece at the point by the tangential T of the base line or the offset line at the point by N × T, as shown in FIG. 4, and the traditional fixed posture is in the vertical Z direction.

And step 10, alternately performing a printing process of variable-attitude outer wall surfacing and fixed-attitude inner filling on the additive manufacturing platform.

The printing method solves the problem that certain positions of the workpiece in the traditional triaxial additive can generate hanging flow. And the variable-attitude sagging area on the outer wall of the printed workpiece ensures the forming stability. Meanwhile, the non-flow hanging area on the outer wall and the interior of the entity are both processed by adopting the traditional three-axis material increase instead of adopting multi-degree-of-freedom variable-attitude processing, so that the interference can be avoided better. In order to avoid interference between a welding gun and the printed outer wall hanging flow area when other areas to be printed are printed, the strategy of alternately printing the outer wall hanging flow area and other areas every 8mm is adopted, and the sustainability of the surfacing process is ensured.

The embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.

Claims

1. A metal entity printing method for alternately performing outer wall surfacing and internal filling is characterized by comprising the following steps of:

(7) sequentially selecting line segments positioned between the planes z1 and z2 in the set B and the set A ∪ S to form an additive printing sequence, wherein the specific process is as follows:

in a vertical height interval h from a plane z1 to a plane z2, firstly printing contour line segments of the outer wall of a convection area in the height interval, and then printing other areas of the outer wall layer by layer and finishing internal filling to form an additive printing sequence in the height interval;

2. The method for printing the metal entity by alternately performing the outer wall surfacing and the inner filling according to claim 1, wherein in the step (3), the dividing standard of the outer wall hanging flow area and the outer wall non-hanging flow area is as follows: and (3) collecting all positions of the normal vector on the outer wall of the workpiece under the XY plane of the space to be divided into outer wall hanging flow areas, and collecting all the positions of the outer wall of the workpiece except the hanging flow areas to be divided into outer wall non-hanging flow areas.

3. The method for printing the metal entity by alternately performing the outer wall surfacing and the inner filling according to claim 1, wherein in the step (6), the value of h is 8-10 mm.

4. The method for printing a metal entity with alternating hardfacing and infill according to claim 1, wherein in step (6), h is chosen to be 8 mm.

5. The method for printing a metal object with exterior wall deposition and interior filling alternated according to claim 1, wherein in the step (9), the printing direction D with varied attitude is obtained by cross multiplication of the normal N of the surface of the workpiece at the point and the tangent T of the base line or offset line at the point by N × T, and the printing direction with conventional fixed attitude is the vertical Z direction.