Injection molding method of carbon fiber composite wheelchair part, carbon fiber composite wheelchair part and wheelchair

Abstract

The invention discloses an injection molding method of a carbon fiber composite wheelchair part, which comprises the following steps of: drying a special carbon fiber engineering plastic premix, adding the premix into a charging barrel of an injection machine, heating to 267-299 DEG C, injecting the premix into a mold cavity at high pressure under the conditions that the injection pressure is 85-135Mpa and the injection speed is 40-90mm / s, maintaining the pressure under the maintaining pressure of 60-80% of the injection pressure, cooling, curing and demolding to obtain the carbon fiber composite wheelchair part. And preparing the carbon fiber composite wheelchair part. The invention also provides the carbon fiber composite material wheelchair part prepared by the method and a wheelchair comprising the carbon fiber composite material wheelchair part. According to the method, the cost is remarkably reduced, the forming efficiency is improved, compared with the prior art, the fatigue resistance and the service life of the wheelchair are remarkably improved, and the requirements of the wheelchair in different use environments can be met.

Description

Technical Field

[0001] The invention relates to an injection molding method for a carbon fiber composite material wheelchair part, the carbon fiber composite material wheelchair part, and a wheelchair. Background Art

[0002] Carbon fiber composites, due to their strength, rigidity, and lightweight properties, are an ideal material for wheelchair components. Currently, most carbon fiber composite wheelchair components are manufactured using a thermoset prepreg hot press molding process. The process involves laying down unidirectional or woven prepregs based on a thermosetting resin (such as epoxy) or thermoplastic resin (such as PEEK or PPS) according to the design requirements. After preforming, the prepregs are placed in a preheated mold, closed, and pressurized. Thermoset prepregs are heated and cured, while thermoplastic prepregs are first softened and formed by heating, then cooled and solidified. Finally, they are demolded and post-processed.

[0003] However, the prior art has the following deficiencies: 1. High cost: Thermosetting prepreg raw materials are expensive, and the hot pressing process is complex, with high equipment and mold costs. This results in a single wheelchair part cost ranging from ¥500 to ¥3000, which is not conducive to large-scale production and cost control of wheelchairs.

[0004] 2. Low production efficiency: The hot pressing process includes multiple steps such as pre-forming, heating and curing, and cooling, which is time-consuming. The monthly output can only reach 5,000-10,000 parts, which is difficult to meet the large-scale demand of the wheelchair market. Summary of the Invention

[0005] The object of the present invention is to provide a method for injection molding carbon fiber composite material wheelchair parts with low cost and high molding efficiency.

[0006] The technical solution adopted in the present invention is: A method for injection molding carbon fiber composite wheelchair parts, the method comprising: After the special carbon fiber engineering plastic premix is ​​dried, it is added to the barrel of the injection machine, heated to 267-299°C, and injected into the mold cavity by high-pressure injection at an injection pressure of 85-135 MPa and an injection speed of 40-90 mm / s. The premix is ​​maintained at a holding pressure of 60-80% of the injection pressure, cooled and solidified, and demolded to produce a carbon fiber composite wheelchair part. Furthermore, the special carbon fiber engineering plastic premix is ​​dried at 100-110° C. for 3-5 hours; Furthermore, the special carbon fiber engineering plastic premix is ​​a chopped carbon fiber reinforced nylon-based premix, preferably a nylon premix containing 30-40% by mass of carbon fibers, with a carbon fiber length of 10-25 mm, which can be purchased commercially.

[0007] The special carbon fiber engineering plastic premix has the characteristics of high strength, high modulus, and UV resistance, and is suitable for the use environment of wheelchair parts.

[0008] Furthermore, the screw speed of the injection machine is 100-200 rpm, so that the carbon fibers in the special carbon fiber engineering plastic premix are further evenly dispersed in the resin to form a melt with evenly dispersed fibers; The injection pressure and injection speed can be dynamically adjusted according to the mold structure and material fluidity.

[0009] Generally speaking, the limits of injection pressure and injection speed are global guidance values, which mainly refer to the process parameters of the main stage. The actual injection molding machine usually performs segmented injection and is adjusted in specific applications, allowing it to exceed or fall below the range in specific stages (such as gate filling, holding pressure, etc.).

[0010] In practical applications, it is necessary to flexibly adjust the segmentation parameters in combination with the mold structure (such as gate position and wall thickness) and material properties (such as melt viscosity).

[0011] Furthermore, in the present invention, the injection of the injection machine is a four-stage injection, and the process is preferably: Injection pressure: Section 4: 40~45 MPa → Section 3: 65~70 MPa → Section 2: 100~110 MPa → Section 1: 90~95 MPa.

[0012] Injection speed: Section 4: 10 ~12 mm / s → Section 3: 15 ~18 mm / s → Section 2: 55.0~60 mm / s → Section 1: 45~50 mm / s.

[0013] More preferably, the process of four-stage injection is: Injection pressure: Section 4: 40 Mpa → Section 3: 65 Mpa → Section 2: 100 Mpa → Section 1: 90 Mpa.

[0014] Injection speed: 4th segment 10 mm / s → 3rd segment 15 mm / s → 2nd segment 55 mm / s → 1st segment 45 mm / s.

[0015] Furthermore, the holding time is generally 3 to 5 seconds.

[0016] Furthermore, the packing phase usually requires additional material to compensate for cooling shrinkage.

[0017] During the cooling and solidification, the mold temperature is maintained at 80-100° C., and a mold temperature controller can generally be used for heat preservation.

[0018] Furthermore, during the cooling process, the resin's volumetric shrinkage may cause part dimensional changes. Compensating for this dimensional deviation during curing shrinkage during mold design is necessary to ensure part dimensional accuracy. Based on the mold shrinkage of specialty carbon fiber engineering plastic premixes (0.10-0.20%), a corresponding shrinkage allowance is reserved during mold design. This is a well-known method for compensating for curing shrinkage by allowing for shrinkage during mold design.

[0019] During demoulding, the demoulding force should be controlled within the range of 300 - 800 N to avoid damage to the parts.

[0020] The demoulded parts can be further post-processed, including one or more of trimming, surface treatment or painting, to improve the appearance quality and corrosion resistance of the parts to meet the final use requirements.

[0021] Preferably, the post-processing includes grinding and polishing the surface of the part to achieve a surface roughness Ra of 0.8~1.6 microns to improve surface smoothness and aesthetics; then performing plastic spraying to form a protective coating to enhance the appearance quality and corrosion resistance of the part and extend its service life.

[0022] The plastic spraying treatment can spray a protective coating that meets the requirements of the wheelchair usage environment, such as a protective coating that enhances weather resistance and wear resistance.

[0023] The thickness of the protective coating is generally 50-80 μm.

[0024] The present invention also provides a carbon fiber composite material wheelchair part prepared by the method.

[0025] The present invention also provides a wheelchair comprising the above-mentioned carbon fiber composite material wheelchair parts.

[0026] The beneficial effects of the present invention are: 1. Significantly reduce costs The use of specialized carbon fiber engineering plastic premixes and an optimized injection molding process effectively reduces raw material costs and process complexity. Compared to traditional hot press molding, the cost of individual components is reduced by 90%, significantly reducing costs. This significantly enhances the competitiveness of wheelchair products in the market and facilitates their widespread market promotion and adoption.

[0027] 2. Greatly improve molding efficiency The injection molding process is continuous and highly automated. Compared to existing hot press molding methods, this process significantly shortens production cycles and improves production efficiency. A single injection molding machine can produce up to 1,200 parts per day, effectively meeting the large-scale market demand for wheelchairs.

[0028] 3. Improve product performance and quality By precisely controlling various process parameters, such as material drying conditions, injection pressure, temperature, and cooling time, we ensure uniform dispersion of the carbon fibers in the resin matrix and high-quality molding of the finished parts. The resulting wheelchair parts exhibit excellent properties such as high strength, high modulus, and good consistency, meeting and exceeding national standards. This significantly improves fatigue resistance and service life, while also providing excellent surface quality and high dimensional accuracy, meeting the functional and safety requirements of wheelchairs in various usage environments. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] Example 1 1. Material preparation stage A special carbon fiber engineering plastic premix (commercially available chopped carbon fiber reinforced nylon-based premix, with a carbon fiber content of 33% and a nylon 66 content of 67%, with carbon fiber lengths of 10-25 mm) was placed in a drying machine and dried at 110°C for 3 hours. A wheelchair front fork component was manufactured with dimensions of 63 mm in length, 130 mm in width, and 190 mm in height. A mold was designed based on this. Based on the premix's mold shrinkage (0.1-0.2%), the mold cavity dimensions were designed to allow for appropriate shrinkage margins.

[0031] 2. Plasticization and melting stage The dried premix was added to the hopper of the injection molding machine. The heating cylinder temperature was set to 270°C and the screw speed was 150 rpm to plasticize and melt the material and evenly disperse the carbon fibers in the resin.

[0032] Storage ejection setting: Storage positions: three sections (55.8mm), four sections (85.8mm), five sections (185.8mm).

[0033] Storage pressure: 145 MPa in each section, speed 65.8 mm / s, back pressure 3 MPa.

[0034] Retraction mode: After storage, the retraction distance is 3.8mm, and before storage, the retraction distance is 8.8mm.

[0035] 3. Injection molding stage The molten material is injected into the mold cavity, and the molten material fills the cavity under pressure. The specific injection process parameters are as follows: Injection pressure: Section 4: 40 Mpa → Section 3: 65 Mpa → Section 2: 100 Mpa → Section 1: 90 Mpa.

[0036] Injection speed (set in stages): 4th section 10.0 mm / s → 3rd section 15.0 mm / s → 2nd section 55.0 mm / s → 1st section 45.0 mm / s.

[0037] In the technical solution, the setting range of injection pressure 85-135Mpa and injection speed 70-90mm / s is the theoretical optimal window. The actual production adjustment is the result of dynamic adaptation of the process. In the embodiment of the present invention, four-stage gradient injection is specifically implemented, and the average value of the actual segmented parameters still falls within the broad coverage interval of the above range.

[0038] Holding pressure stage: The holding pressure is 70% of the injection pressure (about 70 MPa), and the holding time is 5 seconds.

[0039] Mold temperature: 80-100℃ (remain unchanged).

[0040] Holding stage: The mold temperature controller maintains the temperature to prevent uneven shrinkage of the material due to large temperature differences. Material is added during the holding stage to compensate for cooling shrinkage.

[0041] 4. Demolding and post-processing stage The mold opens, and the part is ejected using an ejector pin with a demoulding force of 600 N. The part is then ground and polished to a surface roughness of Ra 0.8-1.6 microns, and then sprayed with a weather-resistant protective coating (50-60 μm thick) to improve the part's appearance and corrosion resistance.

[0042] Comparative Example 1: The same parts were prepared using conventional thermosetting methods: The specific process parameters are as follows: raw materials 1. Resin matrix: epoxy resin 2. Reinforcement material: carbon fiber fabric grade 700 3. Prepreg form: unidirectional prepreg tape or plain fabric Process steps and parameters 1. Cutting 2. Preforming: Temperature: 60-100℃; Time: 15-30 minutes 3. Hot pressing curing: temperature: 135-165℃ (epoxy resin curing temperature); curing pressure: 5-15MPa; time: 30-45 minutes 4. Cooling: Natural cooling to below 80℃; time: 10-15 minutes 5. Post-processing: burring 5-10 minutes / piece; machining: 0.8-1.5 hours / piece; gluing: baking at 120°C for 1 hour; painting: primer + topcoat; baking temperature: 80-120℃; time: 3-4 hours The performance test comparison results of the wheelchair front fork parts prepared by the method of the present invention and the traditional thermosetting method are shown in Table 1 below: Table 1: Performance test comparison The method of the present invention is used to prepare wheelchair front fork components. Although the strength is slightly reduced, it still meets the national standard requirements. However, by optimizing the material dispersion and process parameters, the key performance such as impact strength and fatigue life are significantly improved, and the front fork components successfully pass and exceed the requirements of GB / T 18029-8. The GB / T18029-8 national standard requires that under a load of 100KG, the wheelchair must pass 200,000 double-roller tests and 6666 drop tests in sequence. The present invention passes 600,000 double-roller tests and 19,998 drop tests in sequence under a load of 150KG, fully meeting and far exceeding the national standard requirements for the function and safety of wheelchair components.

[0043] Furthermore, the cost of a single front fork component is reduced by 90%, and a single injection molding machine can produce up to 1,200 parts per day. By comparison, using traditional thermosetting methods, the average daily production capacity per person is only 20. This invention significantly reduces production costs and improves production efficiency, making it highly suitable for industrial application and promotion.

Claims

1. A method for injection molding of carbon fiber composite wheelchair parts, characterized in that The method is: After the special carbon fiber engineering plastic premix is ​​dried, it is added to the injection machine barrel, heated to 267-299°C, and injected into the mold cavity under high pressure. The injection pressure is 85-135 MPa and the injection speed is 40-90 mm / s. The pressure is maintained at 60-80% of the injection pressure. The material is cooled and solidified, and demolded to produce carbon fiber composite wheelchair parts.

2. The method according to claim 1, wherein The special carbon fiber engineering plastic premix is ​​dried at 100-110° C. for 3-5 hours.

3. The method according to claim 1, wherein The special carbon fiber engineering plastic premix is ​​a nylon premix containing 30-40% by mass of carbon fibers, and the carbon fibers have a length of 10-25 mm.

4. The method according to claim 1, wherein The screw speed of the injection machine is 100-200 rpm.

5. The method according to claim 1, wherein The holding time is 3 to 5 seconds.

6. The method according to claim 1, wherein During the cooling and solidification, the mold temperature is maintained at 80-100°C.

7. The method according to claim 1, wherein According to the mold shrinkage rate of special carbon fiber engineering plastic premix, corresponding shrinkage allowance is reserved when designing the mold.

8. The method according to claim 1, wherein The demoulded parts are subjected to post-processing, which includes one or more of trimming, surface treatment or painting.

9. A carbon fiber composite wheelchair part prepared by the method according to any one of claims 1 to 8.

10. A wheelchair comprising the carbon fiber composite wheelchair part according to claim 9.

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