Post-treatment method for selective laser sintering polystyrene

Abstract

The invention relates to a post-treatment method for selective laser sintering polystyrene. According to the post-treatment method for selective laser sintering of polystyrene, the prototype part is fully preheated, wax permeation of the prototype part in the subsequent wax permeation process can be more uniform, the wax permeation time is effectively shortened, the probability that the prototype part deforms and cracks due to the fact that the temperature difference between the interior and the exterior of the prototype part is too large in the wax permeation process is reduced, and the precision of the part is effectively improved. The prototype part subjected to wax permeation is subjected to heat preservation type cooling, excessive attachment of wax liquid to the surface of the prototype part can be effectively reduced, the influence of the wax permeation process on the part size is reduced, meanwhile, the situation that the inner cooling speed and the outer cooling speed of the prototype part are different can be prevented, and the precision of the part is further improved. And surface defect inspection is performed on the prototype part and the wax mold which are subjected to wax permeation treatment and cooling, and the inspected defects are repaired, so that the precision of the part is further improved. And the surface of the wax mold is ground and polished, so that the smoothness of the surface of the wax mold is improved, and the precision of a workpiece is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of additive manufacturing, and in particular to a post-processing method for laser selective sintering of polystyrene. Background Art

[0002] Polystyrene (PS) is a thermoplastic material with a melting temperature of 100°C. It can be melted and bonded after heating, and can be solidified and formed after cooling. The material has low hygroscopicity and shrinkage, which is very suitable for 3D printing laser selective sintering technology. The prototype parts after laser sintering are then treated with wax infiltration to generate wax molds, which are increasingly used in precision casting of complex structures such as turbines and blades, which can shorten the design verification cycle. The final dimensional accuracy and quality of the parts produced by this technology are closely related to the post-processing process.

[0003] Polystyrene post-processing technology is a complex process involving multiple fields such as material science and chemical engineering. From a process perspective, the polystyrene wax infiltration process mainly uses a specific method to infiltrate wax into the polystyrene part material, thereby changing certain properties of the material or achieving specific functions. However, the traditional polystyrene post-processing process still has problems such as long wax infiltration time and low part precision. Summary of the invention

[0004] Based on this, it is necessary to provide a laser selective sintering polystyrene post-processing method that can shorten the wax infiltration time and improve the precision of the product.

[0005] A post-processing method for laser selective sintering of polystyrene, comprising the steps of:

[0006] Carry out powder removal treatment on the surface of the prototype;

[0007] Placing the powder-cleaned prototype in an oven set at a first preset temperature and preheating for a first preset time;

[0008] The preheated prototype is completely immersed in a wax pool having a wax liquid temperature of a second preset temperature and waxed for a second preset time;

[0009] Putting the wax-infiltrated prototype into an oven set at a third preset temperature and keeping it warm and cooling it for a third preset time; the third preset temperature is lower than the first preset temperature;

[0010] The prototype after heat preservation and cooling is taken out of the oven for natural cooling;

[0011] Check the surface defects of the cooled prototypes and wax patterns;

[0012] If there are cracks on the prototype and / or wax model, use adhesive to bond the cracks;

[0013] If the wax model has an uneven surface or a missing corner, the wax model surface should be repaired by hot melting or filling;

[0014] The surface of the wax model is ground and polished.

[0015] In one embodiment, after the powder cleaning step, the method further includes: placing the prototype after the powder cleaning on a wax infiltration tray; a plurality of liquid leakage holes are formed on the bottom surface of the wax infiltration tray;

[0016] When performing the preheating step and the wax infiltration step, the prototype parts are placed in the wax infiltration tray.

[0017] In one of the embodiments, a plurality of pull ropes are provided at intervals along the circumferential direction on the opening edge of the wax infiltration tray;

[0018] When performing the wax infiltration step, the pull rope is used to adjust the depth of the wax infiltration tray sinking into the wax pool.

[0019] In one embodiment, after placing the powder-cleaned prototype on the wax infiltration tray, the method further includes: supporting at least a portion of the suspended portion and at least a portion of the thick-walled portion of the prototype from the bottom of the prototype using a support structure;

[0020] After the step of taking the wax-infiltrated prototype out of the oven for natural cooling, the method further includes: separating the support structure from the prototype.

[0021] In one embodiment, before the step of performing surface powder cleaning on the prototype, the method further includes: separating the large part into multiple prototypes;

[0022] Perform surface cleaning steps to natural cooling steps on each prototype;

[0023] After the step of taking the wax-infiltrated prototype out of the oven for natural cooling, the method further includes: using an adhesive to bond a plurality of wax-infiltrated prototypes according to the structure of the large part.

[0024] In one embodiment, the first preset temperature is 56° C. to 64° C., and the first preset time is greater than or equal to 30 minutes.

[0025] In one embodiment, when the wall thickness of the prototype is ≤10 mm, the second preset temperature is 65° C.

[0026] When 10 mm < the wall thickness of the prototype ≤ 30 mm, the second preset temperature is 63° C.;

[0027] When the wall thickness of the prototype is greater than 30 mm, the second preset temperature is 60° C.

[0028] In one embodiment, the second preset time is 1 minute to 3 minutes.

[0029] In one embodiment, the third preset temperature is 28° C. to 32° C., and the third preset time is 30 minutes to 60 minutes.

[0030] In one embodiment, after the step of grinding and polishing the surface of the wax model, the method further comprises: if there are no surface defects, keeping the wax model in a dry environment at a fourth preset temperature and protecting it from light; and / or

[0031] Before the step of completely immersing the preheated prototype into a wax pool having a wax liquid temperature of a second preset temperature for wax infiltration for a second preset time, the method further includes: obtaining the number of times the wax pool performs the wax infiltration step; when the number of times the wax infiltration step is performed is greater than the preset number, adding new paraffin wax to the wax pool; and / or

[0032] Before the bonding process is performed using the adhesive, the method further includes: performing a roughening process on the surface of the bonding portion.

[0033] The above-mentioned laser selective sintering polystyrene post-processing method can make the prototype part more uniformly wax-infiltrated in the subsequent wax infiltration process by fully preheating the prototype part, and effectively reduce the wax infiltration time, reduce the probability of deformation and cracking due to excessive temperature difference between the inside and outside of the prototype part during the wax infiltration process, and effectively improve the precision of the product. Placing the prototype part after wax infiltration in an oven for heat preservation cooling can effectively reduce the excessive adhesion of wax liquid on the surface of the prototype part, reduce the impact of the wax infiltration process on the size of the part, and also prevent the situation where the cooling speed inside and outside the prototype part is different, further improving the precision of the product. By inspecting the surface defects of the prototype part and the wax mold after wax infiltration and cooling, and repairing the defects found, the precision of the product can be further improved. By grinding and polishing the surface of the wax mold to improve the smoothness of the wax mold surface, the precision of the product can be further improved. Therefore, the use of the above-mentioned laser selective sintering polystyrene post-processing method can shorten the wax infiltration time and make the product more precise. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0035] Figure 1 The figure is a schematic flow chart of a post-processing method for laser selective sintering of polystyrene in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Preferred embodiments of the present invention are provided in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0038] When describing positional relationships, unless otherwise specified, when an element is referred to as being "on" another element, it can be directly on the other element or there can be an intermediate element. It is also understood that when an element is referred to as being "between" two elements, it can be the only one between the two elements, or there can be one or more intermediate elements.

[0039] In the case of using “including”, “having”, and “comprising” described herein, another component may be added unless a clear limiting term such as “only”, “consisting of”, etc. is used. Unless mentioned otherwise, a term in the singular form may include a plural form and should not be understood as being one in number.

[0040] See also Figure 1 The laser selective sintering polystyrene post-processing method in a preferred embodiment of the present invention includes steps S10 to S90.

[0041] Step S10, performing a surface powder cleaning process on the prototype.

[0042] Specifically, dry compressed air is used to blow away the floating powder on the surface of the prototype.

[0043] Specifically, after step S10, the method further includes: machining a local position of the prototype part to ensure the dimensional accuracy of the prototype part.

[0044] Step S20, placing the prototype after the powder cleaning process in an oven set at a first preset temperature for preheating for a first preset time. That is, the temperature in the oven is set to the first preset temperature, and the prototype after the powder cleaning process is preheated for a first preset time when the temperature in the oven reaches the first preset temperature.

[0045] Step S30, completely immerse the preheated prototype into a wax pool with a wax liquid temperature of a second preset temperature for a second preset time. That is, the wax liquid temperature in the wax pool is the second preset temperature. Specifically, the second preset time is 1 minute to 3 minutes. The second preset time is selected based on the fact that there are basically no large number of bubbles on the surface of the prototype.

[0046] Specifically, when the wall thickness of the prototype is ≤10mm, the second preset temperature is 65°C; when the wall thickness of the prototype is 10mm<the wall thickness of the prototype≤30mm, the second preset temperature is 63°C; when the wall thickness of the prototype is>30mm, the second preset temperature is 60°C. In this way, during the wax infiltration process, wax liquids of different temperatures are selected according to prototypes of different wall thicknesses for wax infiltration treatment, so as to ensure the wax infiltration effect while reducing the probability of cracking and other problems caused during the wax infiltration process.

[0047] Step S40, the wax-infiltrated prototype is placed in an oven set to a third preset temperature for heat preservation and cooling for a third preset time. The third preset temperature is lower than the first preset temperature. That is, during the heat preservation and cooling process, the temperature in the oven is maintained at the third preset temperature.

[0048] Specifically, the third preset temperature is 28°C to 32°C, and the third preset time is 30 minutes to 60 minutes, so as to ensure that the prototype after wax infiltration is slowly cooled in the oven. In practical applications, the third preset time can be selected according to the size of the prototype. The larger the prototype, the longer the third preset time.

[0049] Specifically, step S40 is: placing the prototype on the wax absorbing paper, and putting them together in an oven set at a third preset temperature for heat preservation and cooling for a third preset time. In this way, the excess wax liquid attached to the surface of the prototype can be absorbed during the heat preservation and cooling process.

[0050] Step S50, taking the prototype after heat preservation and cooling out of the oven for natural cooling.

[0051] Step S60, inspecting the cooled prototype and wax mold for surface defects, wherein the surface defects include cracks, surface unevenness, corner defects, etc.

[0052] Step S70, if there are cracks on the prototype and / or wax model, the cracks are bonded with an adhesive. It should be explained that the cracks here refer to a series of cracks, fissures, cracks, etc. formed on the surface of the workpiece. The adhesive can be an adhesive formed by a 1:1 mixture of AB glue, and of course it can also be other adhesive materials that can be used to bond cracks, such as fast-curing epoxy glue.

[0053] Step S80: If the wax model has an uneven surface or a corner defect, the surface of the wax model is repaired by hot melting or filling.

[0054] During the wax infiltration operation, temperature changes, wax liquid purity and other reasons may cause defects such as uneven wax model surface and missing corners. At this time, we can perform hot melt cutting, wax filling and other measures to repair the uneven surface positions to make them flat, and fill the missing corners with wax to repair them.

[0055] Specifically, the uneven surface of the wax model is hot-melt repaired with electric iron, and the corner defect is filled and repaired with wax liquid.

[0056] Step S90, grinding and polishing the surface of the wax model.

[0057] Specifically, step S90 includes the steps of: grinding the surface of the wax model with coarse sandpaper; and polishing the ground surface of the wax model with fine sandpaper.

[0058] More specifically, the wax model is placed on a flat surface, and the surface of the wax model is polished with a coarse sandpaper at a uniform speed and force. In order to avoid damage to the polished surface, direct contact with the polished surface by human hands should be avoided after the polishing process.

[0059] In the above-mentioned laser selective sintering polystyrene post-processing method, by executing steps S10 and S20, the surface of the printed prototype is cleaned and fully preheated to ensure the cleanliness of the surface of the prototype, and the initial temperature of the prototype is closer to the temperature of the wax liquid in the wax pool during the subsequent wax infiltration, thereby reducing the temperature difference between the inside and outside of the prototype during the wax infiltration process, and reducing the probability of deformation and cracking due to excessive temperature difference between the inside and outside of the prototype during the wax infiltration process, making the wax infiltration more uniform, effectively reducing the wax infiltration time, and effectively improving the precision of the workpiece and the reliability of wax infiltration.

[0060] By executing step S40 and step S50, the prototype part after wax infiltration is first subjected to heat preservation cooling and then to natural cooling, which can effectively reduce the excessive wax liquid adhering to the surface of the part and reduce the influence of the wax infiltration process on the part size. At the same time, it can also reduce the occurrence of different cooling speeds inside and outside the prototype part, thereby further improving the precision of the part.

[0061] By executing steps S60 to S90, the prototype after wax infiltration and cooling is inspected for defects and repaired for defects, so as to further improve the precision of the product. Therefore, the use of the above-mentioned laser selective sintering polystyrene post-processing method can not only reduce the wax infiltration time, but also make the product more precise.

[0062] In some embodiments, the first preset temperature is 56°C to 64°C, and the first preset time is greater than or equal to 30 minutes to ensure that the prototype is heated evenly. Thus, it can be seen from the above embodiments that the temperature of the wax liquid in the wax pool in step S30 is usually set to a temperature of about 63°C according to the wall thickness of the prototype, so the first preset temperature is set to 56°C to 64°C, so that the preheating temperature is very close to the temperature of the wax liquid in the subsequent wax infiltration process, effectively reducing the temperature difference of the prototype before and after entering the wax pool, so that the temperature difference between the inside and outside of the prototype during the wax infiltration process is very small, which greatly reduces the probability of cracking of the prototype due to excessive temperature difference between the inside and outside during the wax infiltration process.

[0063] In some embodiments, after step S10, the process further includes: placing the cleaned prototype on a wax infiltration tray. The bottom surface of the wax infiltration tray is formed with a plurality of liquid leakage holes. Specifically, the wax infiltration tray is made of corrosion-resistant and thermally conductive materials such as stainless steel. When executing steps S20 and S30, the prototypes are all placed in the wax infiltration tray.

[0064] Thus, when executing step S20 and step S30, the prototype is stably placed on the wax infiltration tray to facilitate preheating, wax infiltration and transfer of the prototype. The provision of the liquid leakage through hole facilitates the wax liquid in the wax pool to enter the bottom of the prototype, and after the wax infiltration is completed, the excess wax liquid in the wax infiltration tray can flow out to the wax pool in time.

[0065] Specifically, a plurality of pull ropes are arranged at intervals along the circumferential direction on the opening edge of the wax infiltration tray. When executing step S30, the pull ropes are used to adjust the depth of the wax infiltration tray sinking into the wax pool.

[0066] In this way, the setting of the pull rope not only facilitates the placement and removal of the prototype into the wax pool when executing step S30, but also allows the depth of the prototype in the wax pool to be freely adjusted to ensure that prototypes of different sizes can be completely immersed in the wax liquid in the wax pool without being limited by the depth of the wax liquid, thereby further improving the operational convenience during the wax infiltration process.

[0067] Specifically, a contact surface for contacting the wax infiltration tray is selected according to the structural characteristics of the prototype part to ensure that the prototype part is stable during wax infiltration, and to allow residual wax liquid in locations that are difficult to polish (such as small holes, irregular grooves, etc.) to flow out easily to prevent it from solidifying inside and being unable to be handled.

[0068] Furthermore, in some embodiments, after the step of placing the powder-cleaned prototype on the wax infiltration tray, the step further includes: using a support structure to support at least part of the suspended portion of the prototype and at least part of the contact portion between the thick wall and the thin wall from the bottom of the prototype.

[0069] For some prototype parts with larger sizes or larger thin-walled areas, supporting structures are added to the suspended parts to solve the problem of low strength of the prototype parts due to their large size or large thin-walled areas, effectively reducing the probability of cracking of prototype parts with larger sizes or larger thin-walled areas during the wax infiltration process; supporting structures are added to the contact area between the thick and thin walls of the prototype parts to solve the problem of uneven heating and cooling during the wax infiltration process caused by the different thickness of the large-sized prototype parts, further reducing the probability of cracking of prototype parts with larger sizes or larger thin-walled areas during the wax infiltration process.

[0070] After step S50, the method further includes: separating the support structure from the prototype. Specifically, after the prototype is cooled naturally, the support structure is separated from the prototype by using a cutting tool such as a knife and hot air blowing.

[0071] In some embodiments, before step S10, the method further includes: separating the large part into multiple prototype parts.

[0072] Steps S10 to S50 are performed on each prototype. Specifically, steps S10 to S50 may be performed on multiple prototypes at the same time, or may be performed on multiple prototypes in sequence.

[0073] After step S50, the method further includes: bonding the plurality of wax-infiltrated prototype parts according to the structure of the large parts by using an adhesive.

[0074] In this way, for some very large parts that are prone to cracking during wax infiltration and cannot be printed in one go, the very large parts can be first decomposed into multiple prototype parts and molded separately according to the structural characteristics of the very large parts, and then the multiple prototype parts after wax infiltration are bonded to form a very large part, thus realizing the post-wax infiltration processing of the very large parts that cannot be printed in one go.

[0075] In some embodiments, after step S90, the method further includes: if there is no surface defect, keeping the wax mold in a dry environment at a fourth preset temperature and avoiding light. Specifically, the fourth preset temperature is 20°C to 30°C.

[0076] In practical applications, the wax model processed through the above steps S10 to S90 should be made into a metal part as soon as possible to avoid size changes. If the metal part cannot be made for a while, the wax model can be kept in a dry environment at the fourth preset temperature and protected from light after step S90 to reduce the probability of size changes of the wax model during storage.

[0077] In some embodiments, before using the adhesive for bonding, the method further includes: roughening the surface of the bonding area.

[0078] That is, before executing step 70 and bonding the multiple prototype parts after wax infiltration, the surface of the bonding part needs to be roughened to improve the bonding strength.

[0079] In some embodiments, before step S30, the method further includes: obtaining the number of times the current wax pool performs the wax infiltration step; and when the number of times the current wax pool performs the wax infiltration step is greater than a preset number, adding new paraffin wax to the wax pool. Specifically, the preset number is 5 to 6 times.

[0080] When performing batch wax infiltration post-processing on prototype parts, before each wax infiltration treatment on the prototype parts, the number of times the current wax pool has performed the wax infiltration step must be obtained. If the current wax pool has performed the wax infiltration step a preset number of times, then new paraffin wax needs to be added to the wax pool to ensure the quality of the wax model; if the number of times the current wax pool has performed the wax infiltration step is less than the preset number, then the wax infiltration step is performed directly.

[0081] It should be noted that the number of times the current wax pool performs the wax infiltration step refers to the number of times the wax infiltration treatment is performed without adding new paraffin to the wax pool. If new paraffin is added to the wax pool, the number of times the current wax pool performs the wax infiltration step needs to be recounted.

[0082] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A post-processing method for laser selective sintering of polystyrene, characterized in that: Includes steps: Carry out surface powder cleaning on the prototype; Placing the powder-cleaned prototype in an oven set at a first preset temperature and preheating for a first preset time; The preheated prototype is completely immersed in a wax pool having a wax liquid temperature of a second preset temperature and waxed for a second preset time; Putting the wax-infiltrated prototype into an oven set at a third preset temperature and keeping it warm and cooling it for a third preset time; the third preset temperature is lower than the first preset temperature; The prototype after heat preservation and cooling is taken out of the oven for natural cooling; Check the surface defects of the cooled prototypes and wax patterns; If there are cracks on the prototype and / or wax model, use adhesive to bond the cracks; If the wax model has an uneven surface or a missing corner, the wax model surface should be repaired by hot melting or filling; The surface of the wax model is ground and polished.

2. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: After the step of cleaning the powder, the method further includes: placing the cleaned prototype on a wax infiltration tray; a plurality of liquid leakage holes are formed on the bottom surface of the wax infiltration tray; When performing the preheating step and the wax infiltration step, the prototype parts are placed in the wax infiltration tray.

3. The post-processing method of polystyrene after laser selective sintering according to claim 2, characterized in that: The opening edge of the wax infiltration tray is provided with a plurality of pull ropes at intervals along the circumferential direction; When performing the wax infiltration step, the pull rope is used to adjust the depth of the wax infiltration tray sinking into the wax pool.

4. The post-processing method of polystyrene after laser selective sintering according to claim 2, characterized in that: After placing the powder-cleaned prototype on the wax infiltration tray, the method further includes: supporting at least a portion of the suspended portion and at least a portion of the thick-walled portion of the prototype from the bottom of the prototype using a support structure; After the step of taking the wax-infiltrated prototype out of the oven for natural cooling, the method further includes: separating the support structure from the prototype.

5. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: Before the step of performing surface powder cleaning on the prototype, the method further includes: separating the large part into a plurality of prototypes; Perform surface cleaning steps to natural cooling steps on each prototype; After the step of taking the wax-infiltrated prototype out of the oven for natural cooling, the method further includes: using an adhesive to bond a plurality of wax-infiltrated prototypes according to the structure of the large part.

6. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: The first preset temperature is 56° C. to 64° C., and the first preset time is greater than or equal to 30 minutes.

7. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: When the wall thickness of the prototype is ≤10 mm, the second preset temperature is 65° C. When 10 mm < the wall thickness of the prototype ≤ 30 mm, the second preset temperature is 63° C.; When the wall thickness of the prototype is greater than 30 mm, the second preset temperature is 60° C.

8. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: The second preset time is 1 minute to 3 minutes.

9. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: The third preset temperature is 28° C. to 32° C., and the third preset time is 30 minutes to 60 minutes.

10. The post-processing method of polystyrene after laser selective sintering according to claim 1, characterized in that: After the step of grinding and polishing the surface of the wax model, the method further includes: if there are no surface defects, keeping the wax model in a dry environment at a fourth preset temperature and away from light; and / or Before the step of completely immersing the preheated prototype into a wax pool having a wax liquid temperature of a second preset temperature for wax infiltration for a second preset time, the method further includes: obtaining the number of times the wax pool performs the wax infiltration step; when the number of times the wax infiltration step is performed is greater than the preset number, adding new paraffin wax to the wax pool; and / or Before the bonding process is performed using the adhesive, the method further includes: performing a roughening process on the surface of the bonding portion.

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