High-temperature resistant 3D printed items

Abstract

Processes for manufacturing CBAM parts and / or components, including the resulting articles, are disclosed. One process uses a fiber-based binder that has a flash point temperature above a predetermined processing temperature.

Description

[Technical Field]

[0001] REFERENCE TO RELATED APPLICATIONS This non-provisional patent application claims priority to U.S. Provisional Patent Application No. 63 / 481,681, filed January 26, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present subject matter relates to enhanced high temperature capabilities in articles made according to the CBAM processes disclosed herein, including associated systems. [Background technology]

[0003] U.S. Patent No. 10,046,552 (incorporated herein by reference in its entirety) describes a system for creating 3D printed parts. The system operates according to a principle the present assignee hereinafter refers to as Composite-Based Additive Manufacturing (CBAM). In CBAM, a computer model divides the part to be printed into cross-sectional slices. Using a printing technique (e.g., inkjet), a liquid is printed onto a porous sheet in a shape corresponding to one of the object's cross sections. The porous sheet is typically carbon fiber, but can also comprise fiberglass or other suitable substrates. Printing can also occur at the end of a fed roll (or web), with cutting occurring in a downstream step. The printed sheet is then submerged in powder (typically thermoplastic powder) so that the powder adheres to the printed areas and not to the unprinted areas. Unadhered powder is removed from the sheet using various means (e.g., vacuum, vibration, air knife). The sheet then moves to the stacking stage, where it is placed on top of the previous sheet (if present), which has undergone a similar process for the immediately adjacent object cross-section. A stacker uses tapered registration pins to keep the sheets aligned and fit into holes drilled in those sheets during the upstream printing stage. This process is repeated for as many cross-sections as needed to create a build block of multiple substrate sheets, each stacked on top of each other in the predetermined order required to represent all cross-sections of the 3D object. The build block is subjected to subsequent processing in the form of heating and compression, which melts and fuses the powder in the printed areas. After heating and compression, the build block is then subjected to polishing or chemical removal to remove the substrate, for example, weak carbon fiber areas that were not printed and are embedded in the powder. The fused / fused areas withstand this polishing and therefore emerge from this process with the intended shape of the final 3D printed part as defined by the computer model.Advantageously, this use of carbon fiber and thermoplastic powder results in a part that is extremely durable and suitable for the high tolerances required in industrial applications, and is therefore a so-called "composite-based" 3D printed part. The '552 patent describes various aspects of the system described herein above, as well as embodiments of subsystems that perform each step (i.e., material feeding, printing on a platen, powdering, depowdering, layering, etc.).

[0004] As mentioned, CBAM involves heating and compression steps. Certain problems can become apparent when carbon fiber is used as the substrate and a high-temperature thermoplastic, such as polyetheretherketone (commonly known as PEEK), is used as the resin, along with similar materials such as the PAEK family of polymers. By way of example, CBAM processes can use substrates made by various commercially known nonwoven processes, such as wet-laid processes, where carbon fiber or fiberglass is bonded together with a binder. The binder can include thermoplastic resins or starch or other adhesive materials, which can decompose and potentially burn at the melting point of PEEK, approximately 350 degrees Celsius (°C).

[0005] Starch / resin decomposition in conventional nonwoven substrates can be exothermic, burning the heated binder and producing smoke from binder breakdown. Figure 1 shows a plot of temperature over time (two lines for two thermocouple placements within the same build object) for a polyester binder, obtained without external intervention, showing a very rapid rise in temperature from approximately 260°C after about 1 hour and 10 minutes to approximately 755±15°C after about 1 hour and 25 minutes. Binder "ignition" or "combustion" begins at the 260°C transition point. For this reason, it is necessary not only to adequately ventilate (or use smoke extractors) the associated manufacturing facilities, but also to provide a smoke extractor system sufficient to stop combustion, such as that resulting from burning carbon fiber.

[0006] One way to use starch / resin as a substrate binder while solving the runaway thermal effects outlined above would be to insert thermocouples at various locations within the build to continuously measure the build's internal temperature and carefully control heating and compression to reduce the risk of fire. This is difficult and time-consuming because it requires a conscious, skilled, and highly trained operator to continuously monitor the process and intervene appropriately if necessary to reduce the possibility of fire. Because each part can be different, this step is difficult to automate, as each different part requires different procedures and protocols. Indeed, as CBAM parts and components grow in size and height, monitoring and adjustment becomes increasingly difficult. Because 3D printing allows for each part to be different, it is not possible to devise a simple protocol that suits each part.

[0007] Another possible solution to maintaining the use of starch / resin-based binders would be to control the temperature and exclude oxygen from entering the laminate, for example by wrapping the part in aluminum foil. However, this is cumbersome, and because a small amount of oxygen remains in the laminate, it may still be necessary to remove fumes from the air when the foil is removed. Even with limited oxygen, the binder in the bale may decompose, if not burn. However, this approach has advantages because only a limited and controllable amount of combustion occurs, which allows the part to heat up faster and therefore process faster.

[0008] Yet another approach to maintaining the use of starch / resin binders is to heat the parts in a chamber filled with an inert gas, such as nitrogen. However, if the chamber is not airtight and the chamber and stack are not evacuated before introducing the nitrogen, residual air will always be present in the stack, resulting in the same results. Furthermore, if the chamber and stack are evacuated before introducing the nitrogen, this process may not be cost-effective because the nitrogen required to operate the process and its leaks can be quite expensive. As an alternative to the above, the parts may be heated in a complete vacuum. The use of an inert gas or vacuum may serve the purpose of preventing the exothermic reactions mentioned above (see Figure 1) (reactions that require the use of oxygen or other non-inert gases). Of course, even such measures may not completely prevent pyrophoric reactions, as the parts themselves may off-gas when heated, providing the very gases that allow runaway exothermic combustion of the binder.

[0009] Yet another possible approach to controlling the temperature could be to use an inorganic binder such as sodium silicate, however such binders are generally very difficult to harden. Summary of the Invention [Means for solving the problem]

[0010] Applicant has surprisingly discovered an approach that utilizes a preselected polyimide binder. Polyimide ("PI") is a polymer containing imide groups and is a class of high performance polymers with high heat-resistant physical properties. Illustratively, the flash point of polyimide is such that it will not burn (exotherm) at the processing temperatures used to make PEEK parts. No fires are ignited by the exothermic reaction, and the temperature levels are effectively controlled. [Brief explanation of the drawings]

[0011] [Figure 1]Figure 1 is a plot of the temperature rise (shown on the vertical axis) versus time (shown on the horizontal axis) obtained without external intervention for an H&V polyester binder. [Figure 2] Figure 2 is a plot of temperature (shown on the vertical axis) versus time (shown on the horizontal axis) for build blocks using TFP polyimide (Technical Fibre Products, Burneside, UK) as the binder. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present subject matter is directed to high temperature processing of CBAM parts and components. Applicant has unexpectedly discovered an approach to solving the problem of thermal degradation. A binder is used in the substrate sheet that does not undergo an exothermic reaction (unlike conventional adhesives, starches, or resins) over the temperature range typical of build block heating. Preferably, the binder is selected such that no exothermic reaction occurs up to a temperature of about 450°C. More preferably, no exothermic reaction occurs up to a temperature of about 400°C. And most preferably, no exothermic reaction occurs up to a temperature of about 340°C.

[0013] Briefly, one approach is to use a preselected polyimide binder for a given processing step (although the binder selection is not necessarily limited to polyimides). Polyimides ("PI") are polymers containing polyimide groups and belong to a class of high-performance polymers that have high heat, flame, and flammability resistance physical properties. (Preferred polyimide binders include Hydrosize HP1632 and 1432, manufactured and sold by Michelman, Cincinnati, Ohio.) Illustratively, the flash point of the polyimide is such that it will not burn at the processing temperatures used to make PEEK parts.

[0014] A substrate sheet or web can be made using a polyimide (or other suitable heat-resistant) binder as follows: The binder must be "cured" by a heating step during the process of making the nonwoven substrate itself. The fibers used to make the substrate sheet can be carbon fiber, fiberglass, a combination of carbon fiber and fiberglass, or any other suitable nonwoven material that will lead to high-quality 3D parts. The process works approximately as follows, although any manufacturing method known to those skilled in the art is suitable: An aqueous slurry of fibers is mixed with appropriate chemicals and then cast onto a screen, which consolidates the fibers into a mat. The mat is continuously removed from the screen as a web. A liquid binder, in this case polyimide, is then poured in by dropping or, alternatively, applied by foaming, bonding the fibers together. It is then heated to cure the binder, followed by a calendaring step and movement over a heater to remove residual water and compress and dry the web of material.

[0015] Using a preselected polyimide material as a binder instead of a traditional starch / resin is surprisingly highly advantageous. Traditional exothermic binders significantly reduce the processing time of parts under compression because they initiate an exothermic reaction that quickly gets everything very hot. Conversely, using a non-combustible binder means there's no ignition leading to overheating, and while the temperature level is more controlled, the lower upper limit means that the underlying polymer requires more processing time to melt. The longer the polymer melts, the more degradation of the polymeric aspects of the part due to the effects of prolonged exposure to high temperatures.

[0016] To reduce or eliminate degradation while using advantageous flame-resistant binders, two steps can be taken: the first step of the subject process can be to heat the entire part to a preselected temperature below the melting point of the polymer, and the second step can be to further heat the entire part after it has reached the preselected temperature, raising its temperature to the melting point temperature.

[0017] An alternative approach that may also provide a viable solution to the degradation problem described above is to first heat the entire part more quickly in a first step, for example, at a temperature about 2-8°C above the part's melting point, use two or more appropriately positioned thermocouples to obtain information about when the entire part approaches its melting point, and then reduce the temperature to perform the second step. Such an alternative approach may substantially reduce and / or eliminate heat-induced degradation of CBAM parts and / or components.

[0018] Advantageously, articles made according to the aforementioned steps may find excellent application in aerospace or other fields requiring non-flammable parts because the starch / resin / adhesive of traditional CBAM processing is absent from the part. Thus, the part's flame resistance is much enhanced for the reasons described above that characterize flame resistance during manufacturing. Final parts made using these improved binders disclosed herein have a UL94 flame rating of V0, meaning that any flame is extinguished within 10 seconds after two 10-second flame tests on test specimens.

[0019] Another advantage of this final material is that it has EDS properties, i.e. it is conductive or dissipative, which means that it does not pick up static electricity and can even be used in electronics manufacturing where this is required, for example in solder pallets.

[0020] Another benefit of polyimide binders is that the parts are UL94V-0, which means they will not burn or ignite, which is very important in aerospace applications, for example.

[0021] What has been illustrated and described in this patent application is subject matter directed to the high-temperature processing and manufacture of CBAM parts and components. While the subject matter describing these articles of manufacture and process steps has been particularly disclosed and described in connection with various embodiments (including the present intention and belief), the subject matter is not limited to these embodiments. To the contrary, many alternatives, modifications, and / or variations will become apparent to those skilled in the art upon review of this patent specification and its associated drawings. Accordingly, all alternatives, modifications, and / or variations are considered to be part of the present subject matter insofar as they fall within the spirit and scope of the appended claims.

Claims

1. 1. A method of manufacturing CBAM parts and / or components employing a predetermined processing temperature, comprising: combining effective amounts of each of the fibers fused together by a binder and a preselected thermoplastic material to produce a CBAM laminate; heating the CBAM laminate at a preselected part or component manufacturing temperature to produce the CBAM part and / or component; comprising The method wherein the binder has a flash point temperature greater than the processing temperature.

2. The method of claim 1 wherein the binder is a polyimide.

3. The method of claim 1 wherein the binder is sodium silicate.

4. The method of claim 1 , wherein the fibers are carbon fibers.

5. The method of claim 1 wherein the fibers are a fiberglass material.

6. An article of manufacture made using the method of claim 1.

7. 10. A UL 94V-0 3D printed composite part made employing the method of claim 1.

8. The method of claim 1 , wherein said effective amount of each fiber is bonded together by said binder and said preselected thermoplastic material.

9. The method of claim 8 wherein the binder is a polyimide.

10. The method of claim 8 wherein the fibers are carbon fibers.

11. The method of claim 8 wherein the fibers are a fiberglass material.

12. An article of manufacture made using the method of claim 8.

13. 9. A UL 94V-0 3D printed composite part made employing the method of claim 8.

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