WO2020245499A1

WO2020245499A1 - Method and apparatus for the computer-aided manufacturing of a product

Info

Publication number: WO2020245499A1
Application number: PCT/FI2020/050368
Authority: WO
Inventors: Raimo Rajala
Original assignee: Aalto-Korkeakoulusäätiö Sr
Priority date: 2019-06-03
Filing date: 2020-06-01
Publication date: 2020-12-10
Also published as: FI20195467A1

Abstract

The invention relates to a method and apparatus for the computer-aided manufacturing of a product, wherein an end product is fabricated on the basis of a digital model made thereof by making use of a photopolymer material. The casting pattern for an end product to be fabricated by molding in a casting mold is prepared from a photopolymer compound (F), which is first of all exposed to light (R) in a digitally controlled manner in compliance with the model made of the end product, whereafter a photopolymer casting pattern (F') to be used in casting and matching physically the to-be-fabricated end product or one or more parts thereof is prepared by removing an unexposed photopolymer compound (Y) from the photopolymer compound (F).

Description

Method and apparatus for the computer-aided manufac- turing of a product

The invention relates to a method and an apparatus for the computer-aided manufacturing of a product as set forth in the preambles of independent claims di- rected thereto.

First, with regard to traditional "mechanical" manu- facturing, especially when the end product to be man- ufactured is required to have a good shape and dimen- sional accuracy as well as surface quality, the manu- facturing has been traditionally practiced by cast- ing, a notable example of which is conventional sand casting that has been widely used in the manufacture of metal articles but also for the needs of both art casting and industry. In addition, sand casting is also used to manufacture for example decorative and utility articles, tools and machine parts .

The foundry sand for sand casting consists of a fine- ly divided sand-binder mixture which reproduces de- tails even with high precision, depending of course on the sand grain size and the mold filling method. The binder consists typically of a chemical curing resin. In particular, when casting high melting point metals, such as steel, the mold surfaces are treated by painting thereon a refractory dressing to prevent the sand from burning and clinging to metal .

The pattern prepared for casting an article to be manufactured comprises typically two pieces so as to enable the lower and upper segments of a mold to be constructed separately. The pattern is typically con- structed from wood, plastics, light metal, or from e.g. a cellular plastic, in compliance with wear re- sistance and dimensional accuracy requirements im- posed on the pattern. It is also necessary that the pattern be sufficiently robust to hold out without warping in mold preparation and storage.

The lower pattern segment is typically secured to a plate upon which is set a mold frame for mold prepa- ration, i.e. forming. The frame is filled with found- ry sand which is packed, e.g. by vibrating, to ade- quate compactness . The mold frame for an upper pat- tern segment is also provided, prior to filling, with patterns for pouring and gas passages .

Another possibility is to construct the mold with a single-piece pattern, necessitating the mold frame to be filled in two steps and the mold frame to be opened for removing the pattern once the sand in the upper mold segment has solidified. A disposable pat- tern of e.g. cellular plastic can be burned off with- out opening the mold. Particularly in full mold cast- ing, however, the pattern can also be made of a mate- rial other than cellular plastic.

If the cast article to be manufactured is hollow, there will be constructed not only a mold but also a sand core, i.e. a mandrel, which itself is also so- lidified and, if necessary, coated. A complex article involves the use of several mandrels as necessary. Once the foundry sand has solidified, the mold seg- ments are removed from the pattern, followed by coat- ing the mold segments, by positioning possible man- drels in place, and by securing the mold segments to each other. Then, the molten metal is poured into the mold. Once the casting has cooled, the mold will be dismantled and the finished casting removed.

A second notable example of casting technique is plaster casting, which is typically used for manufac- turing small and detailed metal objects . Especially in jewelry sector, it has continuously increased in popularity as a cost effective and rapid manufactur- ing method.

As a third example of casting technique should be mentioned precision casting, based on the use of a ceramic mold and generally used especially for cast- ing small and detailed metal objects . Nowadays, it is also used, among others, in automotive industry. The biggest difference with respect to conventional cast- ing is that the mold is grown on the surface of a wax pattern.

The foregoing traditional casting techniques are la- borious and unfavorable in terms of cost effective- ness, particularly in view of current manufacturing technology-related demands .

On the other hand, "computer-aided" manufacturing has continuously advanced and gained popularity in vari- ous sectors, notable examples of which include stere- olithography and 3D printing by using photopolymer materials . Such methods are based on manufacturing a product in a computer-aided fashion by adding and curing a powdered or liquid photopolymer material layer by layer.

At present, such digitally controlled manufacturing methods are nevertheless still slow in terms of their processing operations and expensive due to their ma- terial costs, further emphasized by a poor efficiency in the use of photopolymer materials because of un- necessarily high loss. On the other hand, the suffi- ciently good surface quality of end products to be produced for specific applications requires the use of very thin material layers, which further slows down production and undermines the cost effectiveness of this particular manufacturing technique.

It is an objective of the present method and appa- ratus according to the invention to provide a deci- sive improvement over the foregoing problems and to thereby raise substantially the available prior art. In order to attain this objective, the method and ap- paratus according to the invention are principally characterized by what is presented in the character- izing clauses of independent claims directed thereto.

The most significant benefits gained by a method and apparatus of the invention should be noted to include the simplicity and efficacy thereof, particularly by enabling traditional casting technique to be enhanced through the utilization of computer-aided modeling and manufacturing of casting patterns. As opposed to conventional digital 3D printing, the invention is based on manufacturing a physically end product- matching object of photopolymer material by exposing a photopolymer material to light and by removing, af- ter the exposure, the unexposed photopolymer com- pound. This makes it possible to increase decisively the speed of 3D manufacturing technique and thereby also the cost effectiveness with regard to manufac- turing both planar, such as e.g. reusable, casting matrices and three-dimensional disposable casting patterns .

Other preferred embodiments for a method and appa- ratus of the invention have been presented in the de- pendent claims directed thereto.

It is in the following specification that the inven- tion will be described in detail with reference to the accompanying drawings, in which figs, la and lb show exemplary process charts for manufacturing processes making use of the invention in the fabrication on the one hand of a planar and on the other hand of a three-dimensional end product, and figs. 2a and 2b show an exemplary principle view of the exposure arrangement for an apparatus applying the invention, and an enlarged detail of the rasteri- zation pattern used in photopolymer material expo- sure.

The invention relates first of all to a method for the computer-aided manufacturing of a product, which comprises fabricating an end product on the basis of a digital model made thereof by making use of a pho- topolymer material. The casting pattern for an end product T to be fabricated by molding in a casting mold V is prepared from a photopolymer compound F, which is first of all exposed to light in a digitally controlled manner in compliance with a model X made of the end product to be fabricated, whereafter a photopolymer material pattern F' to be used in cast- ing and matching physically the to-be-fabricated end product or one or more parts thereof is prepared by removing an unexposed photopolymer compound Y from the photopolymer compound F.

In a preferred embodiment for a method of the inven- tion, the photopolymer casting pattern F' is prepared on a principle apparent from fig. 2 in a shielding gas environment Z, S.

In a further preferred embodiment for a method of the invention, the photopolymer material blank F" is ex- posed on the basis of a stereo imaging, grayscale and/or focal area measurement of the end product to be manufactured in the solid, liquid or powdered pho- topolymer compound F. It is further possible that the exposure be preferably carried out in "thin slices" .

In a further preferred embodiment for a method of the invention, the shape and depth of the photopolymer material blank F" in the photopolymer compound F are adjusted by means of a laser and UV exposure R. In a further preferred embodiment for a method of the invention, the exposure of the photopolymer compound F is conducted by utilizing rasterization according to fig. 2, the shape of the photopolymer material blank F" being produced by adjusting both the dot size and the laser and UV luminosity used in expo- sure.

In a further preferred embodiment for a method of the invention, the photopolymer material pattern F' is constructed from two or more casting pattern blanks to be prepared separately and joined to each other, enabling particularly the preparation of photopolymer material patterns in larger sizes and/or complex shapes .

In a preferred embodiment for a method of the inven- tion, the casting pattern' s desired shape is produced in the exposure of the photopolymer compound F with one or more digitally controlled laser, Full HD, LED UV light sources R and/or by using the like tech- nique .

In a further preferred embodiment for a method of the invention, with reference to figs . la and lb, the photopolymer material blank F" is hardened and re- exposed with UVA and/or UVC exposure. In this con- text, it is further possible to also utilize other finishing and/or surface treatment methods.

On the other hand, the invention relates also to an apparatus for the computer-aided manufacturing of a product, the objective being fabrication of an end product on the basis of a digital model made thereof by making use of a photopolymer material. The appa- ratus is intended for preparing, from a photopolymer compound F, a casting pattern M for an end product T to be fabricated by molding in a casting mold V, the apparatus including, in reference to the accompanying drawings, at least an exposure arrangement R, such as one or more digitally controlled laser, Full HD, LED UV light sources R and/or the like, for exposing a photopolymer compound F in compliance with a model X made of the end product to be fabricated, and a wash- ing arrangement P for preparing a photopolymer mate- rial pattern F' matching physically the to-be fabri- cated end product or one or more parts thereof by re- moving an unexposed photopolymer compound Y from the photopolymer compound F.

In a preferred embodiment for an apparatus of the in- vention, with particular reference to fig. 2a, the apparatus includes a closed process space Z for car- rying out the processing in a manner protected by a shielding gas S such as nitrogen gas or the like.

In a further preferred embodiment for an apparatus of the invention, with reference to fig. 2a, the expo- sure arrangement R comprises light sources Rl, R2 ex- posing the solid, liquid or powdered photopolymer compound F from the opposite sides.

In a further preferred embodiment for an apparatus of the invention, it comprises, with reference to figs. la and lb, a recovery arrangement TO for the unex- posed photopolymer compound Y, by virtue of which it is possible to minimize material loss.

Figs . la and lb illustrate exemplary process charts for manufacturing process making use of the invention in the fabrication on the one hand of a memorial plaque and on the other hand of a three-dimensional decorative object shown at the top left-hand corners of the aforementioned figures. Such processing is im- plementable, with reference e.g. to an exemplary principle depicted in fig. 2a, by means of the expo- sure arrangement R provided with front- and backlight units Rl, R2, whereby the stages presented in the process charts include working steps as follows:

- 1. Exposure of a base part Fc of the to-be-prepared casting pattern, e.g. with a UVA backlight unit R2, on a solid photopolymer compound F provided with a LAMS (Laser Ablation Mask System) protective layer Fa and on its underside with a photopolymer layer Fb,

- 2. Laserization R of a photopolymer compound F" in- to the photopolymer compound F, on the basis of a model X, with a laser, Full HD and/or LED UV front- light unit Rl,

- 3. Exposure of the protective layer Fa, by using e.g. laser and/or UVA light, with the frontlight unit Rl,

- 4. Removal of the unexposed photopolymer compound Y, e.g. by dissolving by means of a washing arrange- ment P,

- 5. Drying of the photopolymer material blank F" e.g. with a thermal radiation arrangement, - 6. Hardening and re-exposure of the photopolymer material blank F", by using e.g. UVA and/or UVC light, with the frontlight unit Rl,

- 7. A physically end product-matching photopolymer material pattern F' , such as a unitary casting pat- tern shown in fig. la and a reusable casting matrix shown in fig. lb,

- 8. Casting in a casting mold, and

- 9. An end product T manufactured by casting.

It is obvious that the invention is not limited to the embodiments presented or described above, but within the basic concept it can be subjected to a wide variety of modifications, depending e.g. on the end products to be manufactured at a given time and on the fabrication materials thereof. As opposed to the principle shown in fig. 2a, it is also possible to conduct the exposure of a photopolymer material by using e.g. so-called unilateral exposure, a planar exposure surface, or e.g. partially scattered or mov- able light sources, etc. As opposed to the aforemen- tioned laser, Full HD and UV light sources, the expo- sure arrangement may also comprise other technology suitable for the same purpose.

Claims

1. A method for the computer-aided manufactur- ing of a product, which comprises fabricating an end product on the basis of a digital model (X) made thereof by making use of a photopolymer material, characterized in that the casting pattern, which physically matches an end product (T) to be fabricat- ed by molding in a casting mold (V) , is prepared first of all by exposing a photopolymer compound (F) to light in a digitally controlled manner in compli- ance with the model X made of the end product to be fabricated, whereafter a photopolymer material pat- tern (F' ) to be used in casting and matching physi- cally the to-be-fabricated end product or one or more parts thereof is prepared by removing an unexposed photopolymer compound (Y) from a photopolymer materi- al blank (F") made of the photopolymer compound (F) .

2. A method according to claim 1, characterized in that the photopolymer casting pattern (F' ) is pre- pared in a shielding gas environment (Z, S) .

3. A method according to claim 1 or 2, charac- terized in that the photopolymer material blank (F") is exposed on the basis of a stereo imaging, gray- scale and/or focal area measurement of the end prod- uct to be manufactured in the solid, liquid or pow- dered photopolymer compound (F) .

4. A method according to any of the preceding claims 1-3, characterized in that the shape and depth of the photopolymer material blank (F") in the photo- polymer compound (F) are adjusted by means of a laser and UV exposure (R) .

5. A method according to any of the preceding claims 1-4, characterized in that the exposure of the photopolymer compound (F) is conducted by utilizing rasterization, the shape of the photopolymer material blank (F") being produced by adjusting both the dot size and the laser and UV luminosity used in expo- sure .

6. A method according to any of the preceding claims 1-5, characterized in that the photopolymer material pattern (F' ) is constructed from two or more casting pattern blanks to be prepared separately and joined to each other.

7. A method according to any of the preceding claims 1-6, characterized in that the casting pat- tern' s desired shape is produced in the exposure of the photopolymer compound with one or more digitally controlled laser, Full HD, LED UV light sources and/or by using the like technique.

8. A method according to any of the preceding claims 1-7, characterized in that the photopolymer material blank (F") is hardened and re-exposed with UVA and/or UVC exposure.

9. An apparatus for the computer-aided manufac- turing of a product, the objective being fabrication of an end product on the basis of a digital model (X) made thereof by making use of a photopolymer materi- al, characterized in that the apparatus is intended for preparing, from a photopolymer compound (F) by exposure, a casting pattern (M) which matches physi- cally an end product (T) to be fabricated by molding in a casting mold (V) , the apparatus including at least an exposure arrangement (R) , such as one or more digitally controlled laser, Full HD, LED UV light sources R and/or the like, for exposing the photopolymer compound (F) in a digitally controlled manner in compliance with the model (X) made of the end product to be fabricated, and a washing arrange- ment (P) for preparing a photopolymer casting pattern (F' ) matching physically the to-be fabricated end product or one or more parts thereof by removing an unexposed photopolymer compound (Y) from a photopoly- mer material blank (F") made of the photopolymer com- pound (F) .

10. An apparatus according to claim 9, charac- terized in that it includes a closed process space (Z) for carrying out the processing in a manner pro- tected by a shielding gas (S) such as nitrogen gas or the like.

11. An apparatus according to claim 9 or 10, characterized in that the exposure arrangement (R) comprises light sources (Rl, R2) exposing the solid, liquid or powdered photopolymer compound (F) from the opposite sides.

12. An apparatus according to any of the preced- ing claims 9-11, characterized in that the apparatus comprises a recovery arrangement (TO) for the unex- posed photopolymer compound (Y) .