DESC:FIELD OF THE INVENTION:
This invention relates to the field of mechanical engineering,

Particularly, this invention relates to the field of 3D printing equipment.

Specifically, this invention relates to a post processing equipment required for jobs printed by Rapid Prototyping using Fused Deposition Method.

More specifically, this invention relates to a vapour polishing apparatus for 3D printed jobs.

BACKGROUND OF THE INVENTION:
3D printing, also known as additive manufacturing (AM), refers to processes used to synthesize a three-dimensional object in which successive layers of material are formed under computer control to create an object. Objects can be of almost any shape or geometry and are produced from digital model data 3D model or another electronic data source such as an Additive Manufacturing File (AMF) file. This method is named ‘Additive manufacturing’ due to the fact that instead of removing material to create a part, the process adds material in successive patterns to create the desired shape.

Though the printer-produced resolution is sufficient for many applications, printing a slightly oversized version of the desired object in standard resolution and then removing material with a higher-resolution subtractive process can achieve greater precision.

Some printable polymers such as ABS , allow the surface finish to be smoothed and improved using chemical vapour processes based on acetone or similar solvents.

Existing additive manufacturing technology FDM (Fused Deposition Method) is the most widely used due to its cost effectiveness. A plastic filament is supplied to a heated extrusion nozzle. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a computer-aided manufacturing (CAM) software package.

FDM (Fused Deposition Modeling) is additive manufacturing technology by which one can print complex shaped parts in layer by layer fashion with the use of STL file format. Thermoplastic materials such as ABS, PLA, Nylon, HIPS, etc. are used for printing the parts. Due to the layer by layer manufacturing process, the printed parts come up with serration marks, staircase effect on outer surface causing rough surface which hampers its surface finish and overall aesthetic look. FDM printed parts generally have porous structure which limits its use in the applications where liquid or gaseous material is to be carried or transported and also this limits the FDM printed parts to be electroplated. These problems demands post processing operation like Vapour Polishing to be performed on FDM printed parts to get finished and non-porous part.

The parts produced using FDM also have some lacuna like poor surface finish, porosity and it is not possible to avoid these problems during manufacturing of parts. So, it is necessary to go for post processing of FDM printed parts.

Post-processing techniques are processes by which quality of printed parts are improved after completion of printing of the part such as polishing, support material removal, cleaning, etc.

There are several post processing techniques available in market viz. abrasive grinding, direct dipping of part into solvent solution, vapour polishing, painting, electroplating etc. Out of these methods, electroplating and painting are time consuming and costly. Direct dipping and abrasive grinding may damage the fine details of the part.

There are various applications where the polishing technique plays important role which are listed below
i. Casting: To make good quality casting, the mold should be of good quality. For this, the pattern needs to be properly finished.
ii. Electroplating: To have better electroplating on FDM printed parts, the parts should be smooth and the outer surface of the parts should be completely sealed i.e. non- porous. Because surface roughness of printed substrate is reflected even after electroplating and the porous surface of printed parts allows the electroplating chemical to enter into the part which is not desirable.
iii. Painting: In this process the workers apply body filler on the printed parts which is to be finished. Then worker sand all surfaces of the part and spray on primer. Again sanding of all surfaces is required, then finish the part with a coating of primer.

This surface roughness is because of small gaps generated between two adjacent layers of printed part. The surface roughness on a printed part is mainly affected by layer height, nozzle diameter, and accuracy during XYZ movement of nozzle. By maintaining accurate movements of nozzle and small layer height and nozzle diameter, it can minimize the surface roughness. The surface roughness on the printed part is nothing but small undulations due to each layer on the surface of the printed part. There will be a crest at the line where new layer is started and trough on line of middle of any layer. This pattern is repeated at interval of one unit layer height on the surface. These serration marks are perpendicular to the axis of build. These serrations are even more prominent on the curves when compared with plane surface.

Surface roughness due to serration marks is one of the problems associated with parts printed with FDM technology. Improper Staking of layers and improper bonding between two adjacent layers creates micro pores and gaps between the layers. Such gaps in the printed parts leads to disqualification in some applications. When liquid is poured in the printed part, it leaks out. Improper sealing of the surface leads to infiltration of chemicals while being electroplated.

Vapour polishing using solvent solution for the material used for part printing can be used to have relatively improved surface finish with less cost and time. There is a need for an apparatus and method which uses solvent vapour polishing for post processing of a 3D printed object.

PRIOR ART:
There are various existing solutions are as enlisted below:
a) Smoothing the FDM printed part needs different sand papers of grits from 100 to 600. Firstly one should sand the part with sand paper of 100 to 200 grits to remove the serration marks on part and then gradually sanding with sand papers up to 600 grits to increase the smoothness of the part.
b) According to Stratasys Ltd., chemicals like MEK (Methyl Ethyl Ketone), Di-Methylene Chloride, Acetone, etc can be used for finishing the parts. Printed parts are dipped in bath of these polymer solvents.

(1) Sand paper of different grit size can be used to finish the outer surface of the FDM printed part but it abrades the outer surface Polishing by sand paper releases tiny particles in the air causing pollution and if inhaled, these particles can be very hazardous. This process is time consuming and costly.
(2) The printed parts are dipped in chemical solution and taken out to get finished part. Chemicals like Methyl Ethyl Ketone (MEK), Di-Methylene Chloride and Acetone can be used to minimize the roughness of the printed parts. Chemical treatment is done by dipping the part into chemical for finishing the surface. The surface which comes in contact with chemical gets softened but there may be chances of damaging the important features of the part. MEK takes around 12 to 15 hours for regaining the outer surface to its original strength.
(3) One can use laser for finishing the surface of the printed part. Laser and its associated system are very costly.
(4) Painting the outer surface of printed parts minimizes roughness. Painting does not smooth the surface in single coating.
(5) Electroplating of printed parts deposits a new layer of metal over the outer surface of the FDM printed parts. Different electroplating process setup and methods are required for each different kind of material used. Electroplating is expensive and time consuming process

Therefore, there is a need for an apparatus and a method which ameliorates the prior art processes.

OBJECTS OF THE INVENTION:
An object of the invention is to provide an apparatus for post processing of a 3D printed object or item or job.

Another object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job.

Yet another object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job which is cost effective.

Still another object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job which is not time consuming.

An additional object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job which does not damage the object or item or job.

Yet an additional object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job which arrests porosity of the object or item or job.

Still an additional object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job which reduces surface roughness of the object or item or job.

Yet an additional object of the invention is to provide a vapour polishing apparatus for post processing of a 3D printed object or item or job which provides an improved surface finish.

SUMMARY OF THE INVENTION:
According to this invention, there is provided a vapour polishing apparatus for 3D printed jobs, said apparatus comprises:
- a closed chamber (12) with a heater provided at bed of said chamber;
- a vapour application mechanism (20) configured to apply or direct vapour, of a solvent, towards a part that has been printed and is to be processed;
- heating element at the bed of said chamber, said heating element being configured to maintain ambient temperature inside said chamber above vapourisation temperature of solvent;
- an angularly displaceable indexing fixture (20) configured to be located inside said closed chamber and further configured to receive and locate a part that is to be processed such that there accurate processing of the job, said indexing fixture comprising a plate with an array of spikes (21) and an array of holes, said spikes forming a base for part placement; and
- fans, advantageously located, in said closed chamber for recirculating said vapour;
- thereby said apparatus providing an ambient equi-distributed vapour profile enveloping said part to be finished.

Typically, said vapours are acetone vapours.

Typically, said vapours are solvents for respective thermoplastics vapours.

Typically, said closed chamber is an airtight chamber.

Typically, said chamber is communicably coupled to a vacuum pump to create vacuum inside said chamber.

Typically, said vapour application mechanism comprises:
- a flask to receive and vapourise a solvent to be used for processing said part;
- at least a liquid entry pipe (33) allowing liquid solution to enter into said flask;
- at least a vapour exit pipe (34) connected to said closed chamber to allow vapour to enter said chamber where post processing of said printed part is to take place;
- a first valve (35) controlling liquid flow into said flask (31); and
- a second valve (36) controlling vapour flow out of said flask (31).

Typically, said heating element having temperature sensor feedback to control heating and output temperature.

Typically, said apparatus comprises a heat insulating material placed in the space between a sheet of exterior and interior of said chamber in order to maintain the temperature of chamber.

Typically, said apparatus comprises at least a first temperature sensor attached to a heater of said vapour application mechanism.

Typically, said apparatus comprises at least a second temperature sensor attached with the heater at bed of said closed chamber.

Typically, said apparatus comprises at least a third temperature sensor to sense ambient temperature of said closed chamber.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:

Figure 1 illustrates an isometric view of the vapour polishing apparatus.

Figure 2 illustrates a top view of the vapour polishing apparatus;

Figure 3 illustrates a schematic view of the indexing fixture;

Figure 4 illustrates a schematic view of the indexing fixture, with a motor;

Figure 5 illustrates a schematic of the vapour application apparatus;

Figures 6a and 6b illustrates a flowchart of the steps of the process of this invention; and

Figures 7a, 7b, 8a, 8b, 9a, 9b, 10a, and 10b illustrate various exemplary case studies’ related jobs.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a vapour polishing apparatus for 3D printed jobs. It is very difficult for us to achieve the desired accuracy in the parts which are produced on different rapid manufacturing processes. The major reason regarding accuracy is the function of multiple factors, some of which can be interdependent. The factors that most influence RP accuracy are basic STL files and material used. In FDM machines the CAD model is employed in the standard STL input file format. It approximates the surface of the three dimensional CAD model by triangles. Facets are hard to avoid on curved surfaces and can sometimes appear on the final model. The accuracy of STL files can be controlled at the time of their generation by modifying the chord height and the angle control factor. But still the printed part comes up with serration marks on the outer surface and the parts having staircase effect. This results into bad surface finish which can be improvised by using polishing method.

Figure 1 illustrates an isometric view of the vapour polishing apparatus.

Figure 2 illustrates a top view of the vapour polishing apparatus.

In accordance with an embodiment of this invention, there is provided a closed chamber (12). This is an airtight chamber. In vapour polishing process, an FDM printed part is kept in this closed chamber. A vacuum pump can be used to create vacuum inside the chamber before polishing to allow solvent vapours to be in the purest form. Also, a vacuum pump can be used to take out the vapours from the closed chamber after completion of finishing operation. A heater is provided at the bed of closed chamber to maintain the vapourised solvent in vapour phase.

According to a preferred embodiment, the chamber is a metal chamber with a glass opening - used for clear vision of the part. Reference numeral 17 refers to vapour application mechanism chamber. Reference numeral 19 refers to electronics’ chamber where electronics is housed.

Figure 5 illustrates a schematic of the vapour application apparatus.

In accordance with another embodiment of this invention, there is provided a vapour application mechanism (14) configured to apply or direct vapour towards a part that has been printed and is to be processed. The vapours, according to an embodiment, may be acetone vapours. Vapours are directed towards part by heating acetone above its boiling temperature. After some time, printed part get finished. Fan blades (16) are used to recirculate the vapours inside chamber. DC motors along with fan blades are used for circulating the solvent vapours inside the chamber for better finishing results.

In at least an embodiment of the vapour application mechanism, a conical flask (31) made up of sheet metal, is welded to the centre of thick stainless steel plate. A volumetric flask with measurement marks is used to deliver correct amount of liquid solvent inside the flask. The flask (31) is used to heat the chemical or solvent and convert it into vapours. The flask is of conical shape which has fixed with a cap at the neck. The fit does not allowing the vapours to escape. The cap has two nozzles fixed to it. A liquid entry pipe (33) allows liquid solution to enter into the flask. A vapour exit pipe (34) is connected to closed chamber to allow vapour to enter the chamber where post processing of the printed part is to take place. Both the flask and cap are made up of metal. A first valve (35) controls liquid flow into the flask (31). A second valve (36) controls vapour flow out of the flask (31).

The chemical is poured into the flask via the pipe, which opens at the top of the machine. A small funnel like part can be fitted onto top of it. Other end of the pipe is attached on one of the nozzles which is fixed on flask cap. In similar fashion, second pipe connects nozzle attached on top of cap to the one fixed on the side sheet of closed chamber. The flow of fluid through these pipes is controlled via valve attached in midway.

In accordance with yet another embodiment of this invention, there is provided a heating element (32) configured to form vapours. A controller circuit is provided to control temperature range for such heating. This temperature control is for temperature inside chamber and that of heat bed. A heater plate is used as heating element which can be used to heat the solvent to form vapours. A chamber heating coil is provided to ensure that the ambient temperature inside the chamber will be above vapourisation temperature of solvent. A temperature sensor is used to sense the temperature and feedback to microcontroller. A relay circuit is used for each AC heater coil, which will cut off the circuit and heating will stop to maintain the desired temperature range. Depending upon the input from microcontroller, it switches off or on the circuit of heating coil. A digital thermometer with display is used to sense and display temperature inside the chamber.

It is important that there is an ambient equi-distributed vapour profile enveloping the target product to be finished.

A heater plate (32) will heat the flask above the temperature of the boiling point of the chemical solvent which is poured into the flask. This heater is used to convert the liquid solvent into vapours. The temperature of the heater is controlled within a close interval by using feed back from temperature sensor.

An additional heater is required to install on the bed of closed chamber. This heater will heat the condensed vapours which are deposited at the base of closed chamber 12. This heater will also heat the cold vapours accumulated near base of closed chamber. Similarly this heater is also having temperature sensor feedback to control the heating and output temperature.

A heat insulating material in placed in the space between the sheet of exterior and interior of the machine. It maintains the temperature of chamber. Minimum heat loss will ensure minimum energy utility.

Temperature sensors are provided in this device. Preferably, at least three temperature sensors are located at three different positions; one is attached with the flask heater, second is attached with the heater at bed of closed chamber, and the third one is located at a random position to sense the ambient temperature of the closed chamber. All these three temperature sensors will sense the heat and send feed back to the microcontroller.

Figure 3 illustrates a schematic view of the indexing fixture.
Figure 4 illustrates a schematic view of the indexing fixture, with a motor.

In accordance with still another embodiment of this invention, there is provided an indexing fixture (20) configured to be located inside the closed chamber and further configured to receive and locate a part that is to be processed such that there accurate processing of the job. Typically, fixture was developed to minimize the contact between parts to be finished and base which avoids damage of part. Ideally, the fixture is built to have free contact between solvent vapours and printed part.

In at least one embodiment, the indexing fixture is made up of a plate with an array of spikes (21) for part placement. It may have an array of holes. These holes will allow vapours to pass through.

The plate is attached to the shaft of a motor (22) with low RPM. The fixture is rotated through motor for uniform polishing in every direction. The part to be subjected to the vapours should be placed on the spikes of the plate. The spikes ensure minimum surface contact with the part. It also ensures that the bottom surface of the part not stick to the plate. Also, with this design, the texture of the base in not imprinted on the part. The holes allow the vapours to pass through. Such an arrangement will finish even the bottom side of the part. Close placement of the spikes ensures that even smallest part (or the part with minimum base contact) is able to be finished using the machine.

Fans are advantageously placed in the closed chamber for recirculating the air, vapour, and electronics.

A heatsink is provided at the base of flask heater sheet. The heat sink will help in loosing extra heat generated due to flask heater. It will prevent the heat to pass on to other components in the system. A fan is used for releasing the heat at faster rate.

A temperature sensor is being used to show the ambient temperature inside the glass chamber on digital display.

Figures 6a and 6b illustrates a flowchart of the steps of the process of this invention. Parts get finished with glossy appearance.
1. After printing the part using FDM technology, please remove unwanted support material. Make sure that the part is clean, free from dust and other foreign particles.
2. Make sure the mount for placing the part and chamber are clean.
3. Place the part on the mount. Check that the part is well within the boundary made out of spikes and the part should be stable while rotating the mount.
4. Close the Chamber door, ensure the air seals are properly placed and chamber is air tight. Check that the valve for solvent and vapour solution channel/pipe are locked (or in OFF position).
5. Start the Vacuum pump to remove all the air present in the chamber. Check the pressure gauge indicator showing pressure inside the chamber. There should be approximate vacuum inside the chamber.
6. After reaching to approximate vacuum, stop the vacuum pump. Close the valve on exhaust pipe connected to vacuum pump.
7. Open the valve for pouring solvent into heating flask. Pour the measured volume of solvent into the conical flask and close the valve.
8. Start both the heaters for heating conical flask and chamber bed. Set the temperature range according to the physical properties of the solvent used (such as boiling temperature)
9. Wait for some time after reaching in desired temperature range, to allow uniformly distribution of the temperature.
10. Switch on the rotary table motor fans inside the chamber.
11. Open the valve of vapour channel, allowing vapours to fill into the closed chamber. Let the valve of vapour channel be remain open. Start the timer to measure polishing time.
12. After completing the determined time for vapour polishing, Switch off both the heaters and close the vapour channel valve.
13. Open vapour exhaust valve and start vacuum pump.
14. If suction of the vapours from closed chamber is completed, close the exhaust valve.
15. Open the Closed chamber, leave the part on the rotary pan for a while (Till the temperature of the closed chamber is equal to or nearly equal to the room temperature.
16. Remove the part and let it cool at its own to the room temperature.
17. Analyze the finish of the part.

The TECHNICAL ADVANCEMENT of this invention lies in providing a set up for vapour polishing which allows post processing of a part printed by FDM. This set up is built for minimum part contact with controllable parameters. Surface roughness and porosity of the part can be easily minimized using this technique.

EXPERIMENTAL DATA:
Experiments are conducted on FDM printed parts by considering input process parameters like temperature, time and amount of acetone. Surface roughness of each part is analyzed after polishing which considered as output process parameter.
Geometrical accuracy of vapour polished parts is carried out.
i. Firstly a three dimensional part is modeled in CAD package. The modeled part is printed using FDM technology.
ii. The printed part is scanned with three dimensional scanner and its point cloud data is superimposed on CAD model. This will give us the dimensional accuracy of the FDM printing process.
iii. The printed part is to be finished using vapour polishing setup. Then the finished part is to be scanned again using three dimensional scanner and the point cloud data will be superimposed on cad model, which will show the dimensional accuracy after vapour polishing.
iv. Comparison of point cloud data before and after polishing is checked for effect of vapour polishing on dimensional accuracy.

According to a first exemplary case study, as shown in Figures 7a and 7b of the accompanying drawings, a cube of 20mm×20mm×5mm was polished using vapour polishing and the surface roughness before and after polishing was noted. Figure 7a illustrates a rough part and Figure 7b illustrates a finished part using the apparatus of this invention.

Table 1, below, illustrate surface roughness measured before and after vapour polishing.
Sr. No. Ra value before polishing (µm) Ra value after polishing (µm)
1 6.993 0.464
2 8.609 0.228
3 4.986 0.433
4 3.577 0.326
5 5.720 0.417
6 5.051 0.447
Average 5.823 0.3858

According to a second exemplary case study, as shown in Figures 8a and 8b of the accompanying drawings, a Similar vapour polishing experiment was carried out on Lord Ganesh Idol to verify its effect on complex geometry. Figure 8a illustrates a rough part and Figure 8b illustrates a finished part using the apparatus of this invention.

According to a third exemplary case study, as shown in Figures 9a and 9b of the accompanying drawings, different types of finish on similar part when exposed to vapours for different duration. Figure 9a illustrates a rough part and Figure 9b illustrates a finished part using the apparatus of this invention.

According to a third exemplary case study, as shown in Figures 10a and 10b of the accompanying drawings, vapour polishing experiments were carried out on the parts shown in figure 10 which were then electroplated with copper. Figure 10a illustrates a copper coated part which was finished using the apparatus of this invention and Figure 10b illustrates a copper coated part which was finished using the apparatus of this invention.

While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

,CLAIMS:WE CLAIM,

1. A vapour polishing apparatus for 3D printed jobs, said apparatus comprising:
- a closed chamber (12) with a heater provided at bed of said chamber;
- a vapour application mechanism (20) configured to apply or direct vapour, of a solvent, towards a part that has been printed and is to be processed;
- heating element at the bed of said chamber, said heating element being configured to maintain ambient temperature inside said chamber above vapourisation temperature of solvent;
- an angularly displaceable indexing fixture (20) configured to be located inside said closed chamber and further configured to receive and locate a part that is to be processed such that there accurate processing of the job, said indexing fixture comprising a plate with an array of spikes (21) and an array of holes, said spikes forming a base for part placement; and
- fans, advantageously located, in said closed chamber for recirculating said vapour;
- thereby said apparatus providing an ambient equi-distributed vapour profile enveloping said part to be finished.

2. A vapour polishing apparatus as claimed in claim 1 wherein, said vapours being acetone vapours.

3. A vapour polishing apparatus as claimed in claim 1 wherein, said closed chamber is an airtight chamber.

4. A vapour polishing apparatus as claimed in claim 1 wherein, said chamber being communicably coupled to a vacuum pump to create vacuum inside said chamber.

5. A vapour polishing apparatus as claimed in claim 1 wherein, said vapour application mechanism comprising:
- a flask to receive and vapourise a solvent to be used for processing said part;
- at least a liquid entry pipe (33) allowing liquid solution to enter into said flask;
- at least a vapour exit pipe (34) connected to said closed chamber to allow vapour to enter said chamber where post processing of said printed part is to take place;
- a first valve (35) controlling liquid flow into said flask (31); and
- a second valve (36) controlling vapour flow out of said flask (31).

6. A vapour polishing apparatus as claimed in claim 1 wherein, said heating element having temperature sensor feedback to control heating and output temperature.

7. A vapour polishing apparatus as claimed in claim 1 wherein, said apparatus comprising a heat insulating material placed in the space between a sheet of exterior and interior of said chamber in order to maintain the temperature of chamber.

8. A vapour polishing apparatus as claimed in claim 1 wherein, said apparatus comprising at least a first temperature sensor attached to a heater of said vapour application mechanism.

9. A vapour polishing apparatus as claimed in claim 1 wherein, said apparatus comprising at least a second temperature sensor attached with the heater at bed of said closed chamber.

10. A vapour polishing apparatus as claimed in claim 1 wherein, said apparatus comprising at least a third temperature sensor to sense ambient temperature of said closed chamber.

Dated this 15th day of January, 2018.

CHIRAG TANNA
of INK IDEE
APPLICANT’s PATENT AGENT