CN105160133A - STL triangular patch top-point isometric offset based incrementally formed support body generation method - Google Patents

Abstract

The invention discloses an STL triangular patch top-point isometric offset based incrementally formed support body generation method which is a method for generating a curved surface of a support body model by adopting an STL model for the external surface of a part. A top point of each triangular patch in an STL file is isometrically offset by the thickness of an original plate in a negative direction of a Z axis, thereby providing basis for incrementally forming and processing and quickly and automatically generating a reasonable curved surface of a support body. The method has the beneficial effects that the reasonable curved surface model of the support body is obtained according to the thickness change of the part, thereby effectively ensuring the processing quality of the part; a reasonable gap between a tool head and the support body in different forming angle positions is ensured; it is only required that the generated STL file is read and all Z coordinates are isometrically offset, so that the operation is simple and convenient, and the use is convenient; and the design of the reasonable curved surface of the support body can improve the processing quality of the incrementally formed part and contribute to popularization and application of an incremental forming technology.

Description

Based on the progressive molding supporter method of formation of STL triangular plate summit iso-metric offset

Technical field

The present invention relates to the automatic generation method of supporter model needed for the positive formed machining of a kind of sheet metal component progressive molding, be specifically related to a kind of progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset.

Background technology

Plate progressive molding be the one that proposed by the Leszak of the U.S. sixties in last century without mould flexible forming technology, the nineties is made further research this technology by the luxuriant husband in Songyuan City etc. of Japan, causes the attention of scholars gradually.Progressive molding technology is a kind of based on computer technology, advanced manufacturing technology on Numeric Control Technology and plastic forming technology basis, it adopts the thought of rapid prototyping technique " Layered manufacturing ", serial two-dimensional contour shape is become by discrete for three-dimensional model, the flexible freeform fabrication of one of part global shape is obtained by local plastic shaping accumulation, there is high flexibility, low cost, the features such as high-level efficiency, required plastic force is little, equipment energy consumption is low, vibrate little, noise is low, belong to green processing, the forming limit of sheet material can be increased substantially simultaneously, it is development in recent years a kind of sheet material forming technology rapidly.

In progressive molding, the overall flow of metal material is not obvious, expects that the thinning principle of the cosine law is followed in thick change, i.e. t=t ₀* cos θ (forming angle θ is that Working position method is vowed and the angle of Z axis), like this when work piece surface is curved surface, different its thickness of position of forming angle is not identical yet.As shown in Figure 1, when positive formed machining, suppose that the gap between tool heads and supporter is Δ, the wall thickness of workpiece is Δ s, then, as Δ < Δ s, tool heads and supporter will produce strong extruding to plate, cause plate excessive thinning, unnecessary material is extruded by from tool heads surrounding, is stacked into the front of forming tool, produces severe marking at surface of the work; As Δ > Δ s, plate and supporter cannot be fitted, part easily occur the demoulding rock and unstability thus cause local wrinkling; Only have as Δ=Δ s, plate and supporter fit tightly, and blank periphery just may not occur to extrude phenomenon, therefore rationally determine that clearance delta will become the key improving work piece surface quality.

About the determination of supporter curved surface profile size in progressive molding, the scholars such as Zhu Hu propose a kind of by carrying out the biased algorithm of Unequal distance to part STL model, and detailed process first the normal vector of each tri patch be connected from summit and offset or dish is divided into groups according to the different of its difference degree; Then in each grouping, adopt weighted calculation method to calculate bias vector and the offset or dish on summit, and summit is biased to each grouping biased direction; Finally fill by the gap of the multi-direction biased generation on summit with triangle gridding, although this algorithm has certain innovation, but first there is very large uncertainty to triangular plate grouping, adopt weighting algorithm to obtain summit bias vector in each group in addition, the size of weighted value is bad to be determined; Finally because summit is carried out multi-direction biased, the topological relation on triangle gridding summit can be changed when the later stage fills with triangle gridding the gap produced owing to being biased, in surface fitting, there is very large uncertainty, the experiment of author oneself also demonstrates the supporter gap obtained according to this algorithm between actual value and theoretical value, there is larger error; This method comparison is complicated simultaneously, in actual operation, there is great difficulty.

Hirt, Saturday such as a lot of scholar's research such as, Mao Feng think, progressive molding is mainly detrusion, and cosine rule δ=δ is followed in the change of workpiece thickness ₀(θ is forming angle to cos θ, i.e. the normal vector of this position and Z axis angle; δ ₀for sheet material original thickness).As shown in Figure 2, the ABCD region of original plate is deformed into the A of workpiece at tool heads effect down cut ₁b ₁c ₁d ₁region, although the sheet material of distorted area along Surface Method to direction vector thickness by δ ₀become δ, but according to detrusion principle, in distorted area, each position is along the thickness δ of Z-direction ₀do not change, such supporter just can be regarded as by the upper surface of part model along the biased original gauge δ of Z axis negative direction ₀obtain.

Stl file form is the interface protocol formulated in 1988 by 3DSYSTEMS company, be a kind of three-dimensional picture file layout for rapid prototyping technique service, be now widely used among the technology such as visualization in scientific computing, animation, virtual reality and Quick-forming.Stl file is with triangle surface set expression object external outline model, and the definition of each triangle surface comprises the three-dimensional coordinate on summit and the law vector of triangle surface.

Summary of the invention

For solving the deficiencies in the prior art, the object of the present invention is to provide a kind of progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset, adopt part outside surface STL model generation supporter surface model, each tri patch summit in stl file is utilized along Z axis negative direction iso-metric offset original plate thickness, to process the rational supporter curved surface of fast automatic generation for progressive molding and provide foundation.

In order to realize above-mentioned target, the present invention adopts following technical scheme:

Based on a progressive molding supporter method of formation for STL triangular plate summit iso-metric offset, it is characterized in that, comprise the steps:

1) determine part progressive molding principal direction, make each position forming angle θ be no more than the forming limit angle θ of sheet material _max;

2) extract the upper surface of part model, generate corresponding STL formatted file;

3) redundancy vertex data are carried out to stl file, simplification merger is carried out on redundancy limit;

4) validity of STL model data and STL model encapsulates are checked;

5) according to the stl file generated, each tri patch apex coordinate (x is read _i1, y _i1, z _i1), (x _i2, y _i2, z _i2), (x _i3, y _i3, z _i3), keep x, y coordinate figure on triangular plate summit constant, z coordinate value is along the biased original plate thickness δ of Z axis negative direction ₀, any triangular plate apex coordinate after biased is (x _i1, y _i1, z _i1-δ ₀), (x _i2, y _i2, z _i2-δ ₀), (x _i3, y _i3, z _i3-δ ₀);

6) according to step 5) curved surface of the biased stl file matching generated as the upper surface of supporter model, generate supporter solid model, process supporter.

The aforesaid progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset, is characterized in that, described step 2) in, STL formatted file generates with certain triangle tolerance, adjacent tolerance grade at CAD platform; The triangle tolerance chosen and adjacent tolerance are chosen based on experience value.

The aforesaid progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset, is characterized in that, described step 4) in, validity check content comprises the geometrical defect whether model exists crack, isolated limit; The content of closure inspection comprises the solid whether all STL triangles surround an interior outer closure.

The beneficial effect that the present invention reaches: obtain rational supporter surface model according to part thickness change, effectively ensure the crudy of part; This invention ensures that tool heads and the supporter reasonable clearance at differing formed Angle Position; All Z coordinates are also carried out iso-metric offset by the stl file only needing reading to generate, easy and simple to handle, easy to use; Reasonable supporter curved design can improve progressive molding part crudy, contributes to promoting the use of of progressive molding technology.

Accompanying drawing explanation

Fig. 1 is supporter schematic diagram;

Fig. 2 is progressive molding thickness shear deformation principle figure;

Fig. 3 is the biased signal in triangular plate summit.

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described.Following examples only for technical scheme of the present invention is clearly described, and can not limit the scope of the invention with this.

A kind of progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset that the present invention relates to, comprises the steps:

1) determine part progressive molding principal direction, make each position forming angle θ be no more than the forming limit angle θ of sheet material _max.

2) extract the upper surface of part model, generate corresponding STL formatted file; STL formatted file generates with certain triangle tolerance, adjacent tolerance grade at CAD platform; The triangle tolerance chosen and adjacent tolerance are chosen based on experience value.

3) redundancy vertex data are carried out to stl file, simplification merger is carried out on redundancy limit.

4) validity of STL model data and STL model encapsulates are checked; Validity check content comprises the geometrical defect whether model exists crack, isolated limit; The content of closure inspection comprises the solid whether all STL triangles surround an interior outer closure.

5) according to the stl file generated, each tri patch apex coordinate (x is read _i1, y _i1, z _i1), (x _i2, y _i2, z _i2), (x _i3, y _i3, z _i3), keep x, y coordinate figure on triangular plate summit constant, z coordinate value is along the biased original plate thickness δ of Z axis negative direction ₀, any triangular plate apex coordinate after biased is (x _i1, y _i1, z _i1-δ ₀), (x _i2, y _i2, z _i2-δ ₀), (x _i3, y _i3, z _i3-δ ₀).After this step calculates, the topological relation between each triangular plate after biased is still constant.

6) according to step 5) curved surface of the biased stl file matching generated as the upper surface of supporter model, generate supporter solid model, process supporter.

Embodiment is as shown in Figure 3: set the outer-normal direction of any triangular plate as n _i, it is respectively n at x, y, z three-dimensional component _ii, n _ij, n _ik, then according to right-hand rule, triangular plate apex coordinate and outer method vow to there is following relation between component:

$\left\{\begin{array}{c}{n}_{ii}=(v_{1y}-v_{3y})(v_{2z}-v_{3z})-(v_{1z}-v_{3z})(v_{2y}-v_{3y})\\ n_{ij}=(v_{1z}-v_{3z})(v_{2x}-v_{3x})-(v_{2z}-v_{3z})(v_{1x}-v_{3x})\\ n_{ik}=(v_{1x}-v_{3x})(v_{2y}-v_{3y})-(v_{2x}-v_{3x})(v_{1y}-v_{3y})\end{array}\right.$

Can find out, when any tri patch is along Z axis negative direction iso-metric offset, v in triangular plate apex coordinate _ix, v _iy(i=1,2,3) remain unchanged, and only have v _iz(i=1,2,3) are unified becomes (ν _iz-δ ₀), can find out triangular plate be biased after normal vector will remain unchanged, so also can regard that former triangular plate has done overall iso-metric offset along normal vector direction as, if triangular plate normal vector and Z axis forward angle to be regarded as the forming angle of this position, then its distance biased along triangular plate normal vector direction is δ=δ ₀cos θ, just meets the progressive molding thickness cosine law.Each triangular plate summit so just can be utilized all along the iso-metric offset of Z axis, obtain the thickness gap of differing formed Angle Position.

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and distortion, these improve and distortion also should be considered as protection scope of the present invention.

Claims (3)

1., based on the progressive molding supporter method of formation of STL triangular plate summit iso-metric offset, it is characterized in that, comprise the steps:

(1) determine part progressive molding principal direction, make each position forming angle θ be no more than the forming limit angle θ of sheet material _max;

(2) extract the upper surface of part model, generate corresponding STL formatted file;

(3) redundancy vertex data are carried out to stl file, simplification merger is carried out on redundancy limit;

(4) validity of STL model data and STL model encapsulates are checked;

(5) according to the stl file generated, each tri patch apex coordinate (x is read _i1, y _i1, z _i1), (x _i2, y _i2, z _i2), (x _i3, y _i3, z _i3), keep x, y coordinate figure on triangular plate summit constant, z coordinate value is along the biased original plate thickness δ of Z axis negative direction ₀, any triangular plate apex coordinate after biased is (x _i1, y _i1, z _i1-δ ₀), (x _i2, y _i2, z _i2-δ ₀), (x _i3, y _i3, z _i3-δ ₀);

(6) according to step 5) curved surface of the biased stl file matching generated as the upper surface of supporter model, generate supporter solid model, process supporter.

2. the progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset according to claim 1, is characterized in that, described step 2) in, STL formatted file generates with certain triangle tolerance, adjacent tolerance grade at CAD platform; The triangle tolerance chosen and adjacent tolerance are chosen based on experience value.

3. the progressive molding supporter method of formation based on STL triangular plate summit iso-metric offset according to claim 1, is characterized in that, described step 4) in, validity check content comprises the geometrical defect whether model exists crack, isolated limit; The content of closure inspection comprises the solid whether all STL triangles surround an interior outer closure.