TWI577488B - Surface processing method - Google Patents

Description

Surface processing method

The present disclosure relates to a surface processing method, and more particularly to a surface processing method for increasing the flatness of a machined surface.

The mold industry is the foundation of the manufacturing industry, and the improvement of the polishing process is a key step in increasing the production speed of the mold. In addition to directly affecting the quality of the mold, the cost of this step is 30-40% of the mold manufacturing. At present, mold polishing mainly uses mechanical or micro-discharge technology plus manual polishing to reduce the surface roughness of the machined surface. However, the precision of fine components (such as high-brightness LEDs and IC package molds) is getting smaller and smaller, and the surface topography is becoming more complex, so the surface roughness requirements are getting smaller and smaller (eg Ra<200nm), while the traditional Mechanical or manual polishing technology cannot meet the needs of the future precision mold industry regardless of processing quality control and processing efficiency. In addition, the use of manpower to operate the polishing operation program, the cultivation and transfer of manual polishing technology is not easy, and it is easy to cause technology loss. In order to accelerate the development of the mold industry, it is imperative to establish a complete automated mold polishing system.

Laser polishing technology is the key technology of international research institutions in recent years. It is regarded as the mainstream of the next generation of automated mold polishing system. Its advantage lies in Technical characteristics such as machining accuracy and high output efficiency of local control. However, due to the large heat-affected zone, the conventional laser will produce a remelted layer on the polished surface layer. This remelted layer will affect the hardness and characteristics of the mold surface, and a molten micro-convex structure will be formed on the surface (as shown in Figure 1). The mechanism generated by the micro-bump structure is caused by the reflow caused by the high and low temperature difference, and these convex structures become the main cause of the difficulty in further improving the surface roughness of the laser polishing.

To achieve flattening in conventional laser polishing, a two-pass laser process is required. The first process first removes the surface undulation by laser melting or stripping mechanism. At this time, the surface roughness of the workpiece can be reduced to several tens of micrometers, but the surface is still grayish or slightly white. Since the light will scatter at a surface roughness of several tens of micrometers, the effect of the bright surface cannot be achieved. In order to solve this problem, Fraunhofer ILT proposed two methods of polishing the process, as shown in Figure 2. First, the first process uses a long pulse laser to planarize the surface of the material. At this time, the surface melting depth can reach 100 μm, and the surface roughness Ra reaches 0.4 to 10 μm. After the first process is processed, another process is continued, and the nanosecond laser is used to re-melt the flat surface to brighten the surface of the workpiece, and the surface roughness is 0.2-0.8 μm (200-800 nm).

The two processes of the Fraunhofer ILT are polished to produce two layers of different thicknesses, as shown in Figure 2, and the surface still has a raised structure. The Fraunhofer ILT technology takes twice as long as the general single-pass laser polishing. There are many additional costs, and the metamorphic layer is thicker and the density is also poor.

The present disclosure provides a surface processing method that increases the flatness of a surface of a workpiece.

The surface processing method of the present disclosure includes at least the following steps: providing a laser processing apparatus for providing first laser light and second laser light, and the first laser light and the second laser The illuminating light is separated by an adjustable variable distance; the laser processing apparatus is moved along the machining direction to scan the workpiece, wherein the laser processing apparatus provides a first laser light to be applied to the workpiece, the workpiece is subjected to Melting at the first laser light irradiation to form a melting zone, and with the movement of the first laser light, the workpiece material in the melting zone is thermally reflowed and forming a convex structure; and in the convex structure Prior to solidification, the laser processing apparatus provides a second laser beam applied to the raised structure, wherein the intensity of the second laser light is lower than the intensity of the first laser light The light pressure of the second laser light flattens the raised structure.

In an embodiment of the surface processing method of the present disclosure, the optical power of the first laser light ranges from 30 to 4000 W, and the scanning speed ranges from 1 to 200 mm/s, and the light of the second laser light The power range is 0.0001~20W, and the scanning speed ranges from 1~200mm/s.

In an embodiment of the surface processing method of the present disclosure, the time interval between the first laser light and the second laser light passing through the same point on the workpiece is between 0 and 200 ms.

In an embodiment of the present surface processing method, along the scan trajectory of the first laser light, the melting zone is defined as a region where the workpiece material is heated above the melting point.

In an embodiment of the disclosed surface processing method, the second mine is The pulse width of the light is less than 1 nanosecond.

In an embodiment of the disclosed surface processing method, the energy of the second laser light is less than the stripping threshold of the workpiece.

In an embodiment of the disclosed surface processing method, the spot diameter of the second laser light is between 0.8 and 1.5 times the spot diameter of the first laser light.

In an embodiment of the disclosed surface processing method, the light pattern of the second laser light is a Gaussian distribution or a flat top light distribution.

Based on the above, the disclosed surface processing method utilizes a sequential laser scanning of the surface of the workpiece in the same process, wherein the first laser light melts the surface of the workpiece, and the convex structure formed in the molten region is not used before solidification. The light pressure generated by the second laser light smaller than the first laser light flattens the convex structure, reduces the surface roughness caused by heat reflow during processing, increases the surface flatness of the workpiece, and is generally The surface processing method increases the density of the surface of the workpiece after processing.

The above described features and advantages of the present invention will be more apparent from the following description.

200‧‧‧ Laser processing equipment

210, 220‧‧ ‧ laser source

230‧‧‧beam expander

240, 250, 280, 282 ‧ ‧ angle movable mirror

260‧‧‧Coaxial vision system

270‧‧‧ scan head

284‧‧‧ Objective lens

292, 294‧‧‧ divergence angle adjustment module

P‧‧‧The distance between the first laser beam and the second track applied to the surface of the workpiece

D‧‧‧The distance from the center of the first laser light to the center of the second raised structure

D1‧‧‧Distance of two raised structures

S100~S120‧‧‧Steps

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the surface processing of a workpiece surface to produce a convex structure on the surface of the workpiece due to heat reflow.

Figure 2 is a schematic illustration of a portion of the workpiece after machining the surface of the workpiece in accordance with the Fraunhofer ILT technique.

3 is a flow chart of a surface processing method of the present embodiment.

4 is a schematic view of a surface processing method of FIG. 3.

Fig. 5 is a schematic view of a laser processing apparatus applied to the surface processing method.

Fig. 6 is a schematic view showing another laser processing apparatus applied to the surface processing method.

Fig. 7 is a schematic view showing still another laser processing apparatus applied to the surface processing method.

Fig. 8 is a schematic view showing a periodic convex structure formed on the surface of the workpiece.

Fig. 9 is a view showing the measurement results of the surface roughness after the surface processing of the workpiece, the application of only the first laser light, and the application of the second laser light by the surface processing method of the present embodiment.

Figure 10 is a schematic diagram showing the Gaussian distribution of the light pattern of the second laser light.

Figure 11 is a schematic diagram showing the light pattern of the second laser light as a flat top light distribution.

Fig. 12 is a schematic view showing the surface of the workpiece, the first laser light, the second laser light, and the melting zone when the surface processing process is performed on the workpiece.

Embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The various embodiments of the present disclosure may also be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Specifically, these embodiments are provided for The disclosure is made more thorough and complete, and the concepts of the various embodiments are fully conveyed to those of ordinary skill in the art. In these figures, the thickness of each layer or region is exaggerated for clarity.

It is easy to understand that the same symbols represent the same elements throughout the drawings. The term "and/or" used herein includes any and all combinations of one or more of the associated listed. Other words used to describe the relationship between elements or layers should be understood in the same manner (for example, "between" and "directly between" and "adjacent to" "directly adjacent to", "on", as opposed to "directly on").

It is to be understood that the terms "a", "a", "" The definition of layers and/or sections. These terms are only used to distinguish one element, component, region, layer or section with another element, component, region, layer or section. Thus, a first element, component, region, layer or section that is referred to hereinafter may also be referred to as a second element, component, region, layer or section, without departing from the teachings of the various embodiments.

For ease of description, this article will use space-related terms (such as "below", "below", "below", "above", "above", etc.) The relationship of one element or structural feature shown in the figures to other elements or structural features. For devices or devices that are in use or in operation, space-related terms include different orientations in addition to the orientations shown. For example, if you turn the device or device in the diagram Turning, elements that are "under" or "below" other elements or structural features will become "above" the other elements or structural features. Thus, by way of example, the term "lower" can encompass both the orientations above and below, depending on the reference point. The device can also be positioned in other ways (rotated 90 degrees or other orientations) and the space-related transcripts used herein are understood in the same manner.

The terminology used herein is for the purpose of describing particular embodiments, The singular forms "a", "the", and "the" It will be further understood that the use of the terms "comprises" and "comprising" or "comprises" or "comprises" or "includes" or "comprises" or "comprises" More than one other structural feature, integer, step, operation, component, component, and/or group thereof.

Embodiments of the present disclosure are described herein with reference to the drawings, which are schematic illustrations of idealized embodiments (and intermediate structures) of the various embodiments. As such, variations in the shape of the drawings caused by, for example, manufacturing techniques and/or tolerances are to be expected. Thus, the various embodiments of the present disclosure should not be construed as limited to the specific shapes of the various regions described herein, but should include the shape variations resulting from, for example, manufacturing. Therefore, the various regions in the figures are schematic and are not intended to depict the actual shapes of the regions of the device, and are not intended to limit the scope of the various embodiments.

Unless otherwise stated, all terms (including technical and scientific terms) used herein have the same meaning as in the technical field to which the embodiments of the present disclosure pertain. Commonly understood by people with common knowledge has the same meaning. It will be more readily understood that terms such as those defined in the general dictionary should be understood to have the same meaning as those of the prior art, and should not be construed as ideal or too formal, unless expressly stated herein.

The surface processing method of the present disclosure mainly utilizes a sequential laser scanning provided to a workpiece in the same process, wherein the first laser light is used to melt the surface of the workpiece to form a melting zone, and the heat is reflowed. The convex structure formed in the melting zone flattens the molten convex structure by the light pressure generated by the second laser light to reduce the surface roughness of the workpiece surface due to processing and to increase the density of the surface of the workpiece.

3 is a flow chart of the surface processing method of the present embodiment, FIG. 4 is a schematic view of the surface processing method of FIG. 3, and FIG. 5 is a schematic view of a laser processing apparatus for applying the surface processing method. Referring to FIG. 3, FIG. 4 and FIG. 5 simultaneously, in step S100, a laser processing apparatus 200 is provided. The laser processing apparatus 200 has, for example, two laser light sources 210 and 220 respectively located at two laser light sources 210. Two angle movable mirrors 240 and 250 on the optical path of 220, a beam expander 230 disposed between the laser source 220 and the angle movable mirror 250, a coaxial vision system 260, a scanning head 270, and a coaxial An angle between the vision system 260 and the scan head 270 is a movable mirror 280. Briefly, the coaxial vision system 260, the scanning head 270, and the angular movable mirror 280 are generally arranged in a straight line, and the angular movable mirrors 240, 250, 280 are also arranged substantially in a straight line, but the angular movable mirrors 240, 250 The angles between 280 and 280 are not exactly the same.

Through the above arrangement relationship, the laser light emitted by the laser light source 210 is reflected by the angle movable mirror 240 and then reflected to the angle movable mirror 280, and then After the angle movable mirror 280 is reflected to the scanning head 270, it is projected as the first laser light. The laser source 210 is, for example, a continuous wave (CW) laser, which provides a first laser light having an optical power range of 30 to 4000 W and a scanning speed ranging from 1 to 200 mm/s.

The laser light source 220 is, for example, an ultrafast laser, and the projected laser light is incident on the angular movable mirror 250 through the beam expander 230, and is reflected by the angle movable mirror 250 to the angle movable mirror. 280, after being reflected by the angle movable mirror 280 to the scanning head 270, is projected as a second laser light. The optical power of the second laser light ranges from 0.0001 to 20 W, and the scanning speed ranges from 1 to 200 mm/s. The beam expander 230 described above is a device for changing the beam diameter of the laser light, and the beam adjusted by the beam expander 230 can be used with different optical instrument applications. In the present embodiment, the laser light emitted by the laser light source 220 is converted into a collimated (parallel) light beam after being adjusted by the beam expander 230, and the diameter of the laser beam of the laser light can be adjusted according to the requirements of the beam expander 230. Settings and adjustments. In another embodiment of the laser processing apparatus 200, a divergence angle adjustment module 292 may be disposed between the laser source 210 and the angle movable mirror 240, also in the beam expander 230 and the angle movable mirror 240. A divergence angle adjustment module 294 is provided between them, as shown in FIG. 6, to obtain a fine high power density spot by the divergence angle adjustment module 294. Alternatively, scan head 270 can be replaced with a combination of angular movable mirror 282 and objective lens 284, as shown in FIG. In other applications, a spatial filter may be further disposed in the beam expander 230 or on the optical path of the beam of the laser light to make the asymmetric beam distribution become symmetrically distributed, so that the light energy distribution is more uniform. Capable in the laser processing apparatus 200 The device to be applied can be selected by those skilled in the art according to requirements, and therefore no more examples are given.

The first laser light and the second laser light are formed in a front and rear sequence along a direction (for example, a processing direction) (ie, the first laser light is in front and the second laser light is behind), and The first laser light and the second laser light are separated by a distance P. The arrangement of the coaxial vision system 260 is used to observe the melting condition of the surface of the workpiece during the surface processing of the workpiece to determine whether the distance P between the first laser beam and the second track applied to the surface of the workpiece needs to be adjusted. In this embodiment, the time interval between the first laser light and the second laser light reaching the same point on the surface of the workpiece is between 0 and 200 ms. In simple terms, after a certain portion of the workpiece is irradiated with the first laser light and the first laser light is removed, after the time interval, the second laser light is illuminated there.

In step S110, the laser processing apparatus 200 is moved along the processing direction, and the first laser light is applied to the workpiece, and the position where the workpiece is irradiated with the first laser light is melted, thereby forming a melting zone on the surface of the workpiece, and As the first laser beam moves, the material of the workpiece that has just been melted in the melting zone moves forward while the first laser beam is moving forward, while the workpiece material in front is melted by heat to create a new melting zone. On the one hand, the workpiece material that is melted in the front is formed on the one hand because the workpiece material in front is solid and forms a barrier wall, so it cannot be moved forward. On the one hand, the material of the workpiece to be melted at the rear is removed because of the first laser light. The temperature of the material to be melted is slightly lower than the material of the workpiece being melted by the first laser light, so that the workpiece is melted ahead based on the characteristics of heat flowing to low temperature. The material flows back and accumulates on the previously melted workpiece material to form a raised structure. Therefore, as the laser processing apparatus 200 continues to move along the machining direction and the first laser light is applied, if no other steps are performed on the raised structure, the raised structure cools and solidifies, thereby forming a periodicity on the surface of the workpiece. The raised structure is shown in Figure 8.

In particular, in order to avoid the formation of a periodic convex structure on the surface of the workpiece, the surface roughness of the surface of the workpiece cannot be expected to be as expected, as in step S120, and therefore, before the solidification of the convex structure, the convexity of the molten state is further exhibited. A second laser beam having a lower intensity than the intensity of the first laser light is applied to the structure to flatten the raised structure by the light pressure of the second laser light, as shown in FIG. Compared with the first laser light applied to the workpiece, the surface of the workpiece is melted to form a melting zone, and the optical power of the second laser light ranges from 0.0001 to 20 W, which is significantly lower than the optical power of the first laser light ( Between 30 and 4000 W), so the second laser light does not provide heat to the raised structure that is still in the molten state and has not yet solidified, causing the convex structure to melt again, but only applying light pressure to the convex structure. Flatten the raised structure down. Fig. 9 is a view showing the measurement results of the surface roughness after the surface processing of the workpiece, the application of only the first laser light, and the application of the second laser light by the surface processing method of the present embodiment. It can be seen from Fig. 9 that the surface roughness Ra of the workpiece is about 450 nm before the first laser light is applied to the surface of the workpiece; and the surface roughness Ra is reduced to about 367 nm after only the first laser light process is performed. After performing the surface processing method of the present embodiment, the surface roughness Ra of the workpiece can be lowered to about 200 nm. Therefore, the condition that the surface of the workpiece is rough is effectively suppressed.

Further, the pulse width of the second laser light applied in this embodiment is less than 1 nanosecond. Moreover, the light pattern of the second laser light may be a Gaussian distribution (as shown in FIG. 10) or a flat top light distribution (as shown in FIG. 11), wherein the Gaussian light type laser light has the advantages of high energy concentration and obvious hot melt effect. The flat top light type of laser light has the advantage of uniform energy distribution to make the processing characteristics uniform. In addition, the spot diameter of the second laser light is between 0.8 and 1.5 times the spot diameter of the first laser light, but is not limited thereto, and those skilled in the art can adjust the second laser light according to requirements. The spot diameter.

The light pressure provided by the second laser light can use the Navier-Stokes equation to calculate the surface tension of the workpiece material in the molten region after the workpiece is melted, and then find out which laser light has a greater light pressure than the melting region. The surface tension of the workpiece material to achieve the effect of flattening the raised structure. The formula used is as follows: 2-D Navier-Stokes equation:

Where μ is the fluid viscosity coefficient, σ is the fluid surface tension and ρ is the solid density.

Then, the light pressure generated by the light of the laser light per unit area E is obtained by the following formula, and the laser light energy of the laser light can be selected to be larger than the surface tension of the workpiece material in the melting zone.

p=h/λ=>p=h υ/c=>pc=E=>p=E/c

Light pressure F=πω ₀ ² P

Table 1 is a comparison table of the surface tension of the workpiece selected for the present embodiment and the force (light pressure) that various lasers can provide.

In the present embodiment, the material of the selected workpiece is, for example, SKD61, stainless steel, die steel, etc., after being irradiated by the first laser light, the melting zone ranges from the first laser light to the Within a range of about 800 microns after the first laser light, and the shape of the molten region assumes a shape like a tail drag (as shown in FIG. 12), and the center of the first laser light is second to the next. The distance D of the center of the raised structure (shown in Figure 1), the distance between the two raised structures is about the diameter d1 of the first laser beam (shown in Figure 1), and the second laser is in the same A laser beam is applied in the melting zone at D-d1 (shown in Figure 1), wherein the surface tension of the molten workpiece material is about 4.397*10 ^-4 N, and the nanosecond mine can be seen from Table 1. Both the shot and the continuous laser provide less light pressure than the surface tension, while femtosecond lasers and picosecond lasers provide a light pressure greater than the surface tension to flatten the raised structure.

In addition, the energy of the second laser light needs to be smaller than the stripping threshold of the workpiece to avoid that when the second laser light is applied to the workpiece, the energy of the second laser light is strong enough to cause the workpiece to be partially peeled off. . The stripping threshold of the workpiece will vary with the material of the workpiece, so the energy of the second laser can also vary with the material of the workpiece; of course, the energy of the first laser will also vary with the material of the workpiece. Different adjustments.

The surface processing of the workpiece by the surface processing method of the present disclosure differs from the conventional laser polishing in that the thickness of the altered layer is different, and the modified layer of the workpiece processed by the surface processing method of the present invention is thinner, and the surface convex is improved. The structure is problematic and the structure density is better. Compared with the method of Fraunhofer ILT, the workpiece processed by Fraunhofer ILT will produce two layers of different thicknesses. The thickness of the metamorphic layer is thicker, the density is also poor, and the surface still has a convex structure. Therefore, the surface roughness cannot be effectively reduced. In addition, Fraunhofer ILT's technology is based on the first laser light after the first laser beam is applied to the surface of the workpiece, and then the second laser light is irradiated, so it takes twice as long as the general single-pass laser polishing. Add a lot of extra cost.

In contrast, the surface processing method of the present disclosure is to sequentially apply two laser beams in the same process, that is, after the first laser light irradiation, the second The ray light is applied to the unsolidified convex structure in the melting zone immediately after the appropriate time interval, so the processing time of the laser light is shorter than that of the Fraunhofer ILT, and the laser processing device can be applied for a certain period of time. The number of artifacts. On the other hand, the surface flatness of the surface formed by the surface processing method disclosed by the present invention is improved, the metamorphic layer is thin, and the density is high, so that the hardness and wear resistance of the surface after processing are improved.

Furthermore, the components of the laser processing apparatus for performing the surface processing method are simple to set up, and the field personnel can select suitable devices for the laser processing apparatus according to requirements without greatly adjusting or changing the old processing optical path. Upgrade to effectively control the upgrade cost of the laser processing unit.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

S100~S120‧‧‧Steps

Claims (8)

A surface processing method comprising: providing a laser processing apparatus for providing a first laser light and a second laser light separated by a variable variable distance; moving the laser along a machining direction a processing apparatus, wherein the laser processing apparatus provides the first laser light to be applied to a workpiece, the workpiece being melted by the first laser light to form a melting zone, and along with the first track Movement of the laser light, the workpiece material in the molten region is thermally reflowed and forms a raised structure; and the laser processing apparatus continues the first laser light along the processing direction before the raised structure solidifies Providing a second laser light applied to the raised structure after moving forward, wherein the intensity of the second laser light is lower than the intensity of the first laser light to The light pressure of the light illuminates the raised structure. The surface processing method according to claim 1, wherein the first laser light has an optical power range of 30 to 4000 W, and a scanning speed ranges from 1 to 200 mm/s, and the second laser light The optical power range is 0.0001~20W, and the scanning speed ranges from 1~200mm/s. The surface processing method according to claim 1, wherein the time interval between the first laser light and the second laser light passing through the same point on the workpiece is between 0 and 200 ms. The surface processing method according to claim 1, wherein the melting zone is defined as the workpiece material along a scanning trajectory of the first laser light. Warm up to a region above the melting point. The surface processing method of claim 1, wherein the second laser light has a pulse width of less than 1 nanosecond. The surface processing method of claim 1, wherein the energy of the second laser light is less than a stripping threshold of the workpiece. The surface processing method according to claim 1, wherein the spot diameter of the second laser light is between 0.8 and 1.5 times the spot diameter of the first laser light. The surface processing method according to claim 1, wherein the second laser light has a Gaussian distribution or a flat top light distribution.