SMART ADDITIVE MANUFACTURING - MATRIX ... AWS
SMART ADDITIVE MANUFACTURING - MATRIX NANO COMPOSITE (CNT-Alloy Steel)
Executive Summary To participate the Local Motors LITECAR Challenge, we proposed Smart Additive Manufacturing method. It is a new kind of additive manufacturing that sync Finite Element Analysis data, and implement it directly and real time in the structure arrangement by additive manufacturing (SLS 3D printing) method. Material: First, we divide the body/chassis structure into two major part, then we called it the core. The other part is the shell that will be a cover of the core. This two major part then will be permanently bonded together. The core is combination of alloy steel powder and alloy steel-CNT (Carbon Nano Tube) in matrix nano composite shape. The purpose of this combination is to made it possible to manufacture with SLS (Selective Laser Sintering) method. The CNT will improve the material yield and tensile strength significantly (5 to 12 times, depend on the CNT percentages) while maintain its weight. It means that to get the same strength and safety factor as the traditional material, we can only use 20% of the material compared to traditional material. If we would like to improve the safety factor, we can use more material as a stiffener within the structure. For the shell, we choose to use Nylon 6/10 because of its nature. However, it can be replaced with ABS, PP, PLA or any other material which able to manufactured by injection molding. Material Arrangement: The basic idea of smart additive manufacturing is to utilize FEA (Finite Element Analysis) data directly while build the structure of the core part. The percentage of the CNT content was vary along the structure, based on the required strength in the FEA data. The mixer works just like a printer head while mixing the color. It will mix the alloy steel and alloy steel-CNT matrix composite in real time, and build the shape directly with small amount of additional additive content to keep it in shape temporarily. Then, the material will be cured and joined together permanently in particle level by SLS (Selective Laser Sintering). For the shell, we use nylon. Nylon structure will handle the low amount or minor impact and absorb it because of its flexible characteristic, compared to steel or aluminum. When there is high amount of impact, the core structure will handle those impact. Manufacturing Method: There is two major manufacturing method to build the body/chassis structure. The first one is smart additive manufacturing to create the core as described above. It is unique 1
and never been develop before. After the core was built, it will be inserted into the injection mold, and then melted nylon will be injected to build permanent bonding of the core and the shell. The edge of the structure will be thicker than the rest of the structure, and is not covered by nylon for a welding and/or other joining method.
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Weight Reduction Methodology
To reduce the weight significantly, the methodology was to use stronger material that have material density almost the same with the current/commonly used material (assumed that today's car body made out of alloy steel). So, in the same load case we can use less material. No. Material 1. 2. 3. 4.
Alloy Steel CNT (Carbon Nano Tube) Alloy Steel-CNT Matrix Composite (5% CNT Content) Nylon 6/10
Density (kg/m^3) 7,700 1,300 - 2,000 Nano 7,390 1,400
Yield Strength (MPa) 620.4 10,000 - 60,000 3,175 139
Based on the above data, Alloy Steel with additional only 5% of CNT in matrix nano composite shape was more than 5x stronger than usual alloy steel. With this material, we can use only 20% of the material for the car body structure (as a core) to get similar structural strength compared with pure Alloy Steel. If we use 120% content of Nylon as a shell to get good surface finish and absorb low level stress/impact. We can save the weight for up to 60 %. This mean that the end result of the structure is 40% thicker than usual thickness although the weight is only 40%. Simple calculation as follow: 20% of Alloy steel-CNT matrix Nano Composite: 20% x 7,390 = 1,478 120% of Nylon 6/10: 120% x 1,400 = 1,680 So, in total: 1,478 x 1,680 = 3,158 And compared with the common alloy steel:
3,158 : 7700 = 0.4101 = 40.01 %
So, with better or at least equal strength, we can save up to: 100% - 40.01% = 59.99% However, the material with high number of yield and tensile strength is very difficult to be formed into desired shape with traditional forming method (stamping or hydroforming). Other difficulties is also because the structure need to be thin (0.3-0.4mm thickness). So, in this proposal, I would like to propose smart additive manufacturing method ( with SLS or selective laser sintering). The SLS method was commonly used by 3D printer. The other main advantages of smart additive manufacturing method is to control the material composition within the structure. We can control the percentage or combination of the pure alloy steel fine powder and alloy steel-CNT matrix nano composite along the structure.
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To achieve the various combination of material within the structure is by using simple method, as we can find in the printer head within the inkjet printer that combine the Red, Yellow and Blue toner (instead of toner, we combine pure alloy steel and alloy steel-CNT matrix nano composite). The process then followed by laser that will melt and joining the particle together to built the shape. Further explanation will be explained in the " Required Manufacturing Process" section Bill of Materials No. 1. 2. 3.
Material Alloy Steel CNT Nylon 6/10
Price /kg (US$) 15-30 150-225 3-10
Required Manufacturing Process There is three major phase on the manufacturing process First Phase (CNT-Steel Alloy Matrix Nano Composite creation) At this phase, we need to combine alloy steel with CNT to get CNT-alloy steel matrix nano composite. In other word, in this process, we enrich the alloy steel with CNT, and build matrix nano composite shape. To achieve it, firstly we need to wash the CNT with acid solution. And then, after the CNT washed with acid solution, it need to dispersed within methanol liquid, following by ultrasonic agitation. While the ultrasonic agitation still running, the alloy steel powder poured 4
into the solution, and then resulting a slurries which contain CNT, alloy steel powder and methanol. The next step was the slurry need to be ball milled for 12 hours, and subsequently dried on an oven. The last step was put the result powder into the spark plasma sintering (SPS), hot pressed at 1273 Kelvin for 3 minutes under 30 MPa pressure. Then we get the enriched alloy steel or CNT-alloy steel nano matrix composite.
Second Phase (Core Structure manufacturing with smart additive manufacturing method) The major part of this phase was we need to create the structure, arrange the content within the structure based on the FEA (Finite Element Analysis) data. There is a component that we call "mixer" which mix pure alloy steel and CNT-alloy steel matrix nano composite in certain combination based on the FEA data. Within this mixer, there is also special adhesive that will be able to cure immediately after it released and temporary bond the material together to make the shape. The special adhesive need to be easy to self-removed by heat. This process is just like a combination between 2D printer (that mix red, green, yellow toner) and 3D printer. Instead of toner, this mixer will release mixed pure Alloy Steel and CNT-Alloy Steel in certain thickness and certain combination of the material. The movement of this mixer is numerical controlled as we can find in the 3D printer. Then, the process is followed by laser that will melt and bond the combined material particle permanently, as well as eliminate the adhesive (removing the temporary adhesive by heat).
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Third Phase (Shell manufacturing with injection mold process)
In the third phase, the core structure that we have done before inserted in between the mold, then melted Nylon 6/10 injected within the mold. The nylon will covering the outer face (top and bottom) of the core structure permanently because the core structure have hexagonal/honeycomb through hole that will enable the nylon to go through into both sides in several area, and blocked or only covering one side in the other several other areas.
Passenger Safety In the passenger safety aspect, since we can control the strength in the structure of the car body directly through FEA (Finite Element Analysis) result, it will enable us to widely examine several impact and stresses and then implement it in the structure directly. Innovative/Safety Component In the picture below, showed that the edges of the structure is not covered by nylon and it is thicker than the structure which covered by nylon. Then, this part of the structure will have high strength number. The purpose of this configuration is to get better joint between the structures on the body/chassis.
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Not only passenger that get the positive result, but also the other person/environtment that may collide with the car. As an example, hitting by hammer with steel material versus hitting by hammer with rubber or plastic material with the same amount of power. The impact of the hammer with steel material will be greater since several force will be absorbed by the hammer itself on the hammer with rubber/plastic material. Potential Challenges The most challenging part on this method is in the creating of the mixer (that works like the today's printer head) that need to be able to mix the pure alloy steel and CNT-alloy steel matrix nano composite in a certain combination, real time. Finding the suitable adhesive to hold the structure temporarily before it cured by the laser is also a challenge. The another challenging part is the laser itself. As we know that today's 3D printer (SLS) has small footprint and a laser that consume huge amount of power. So, in the manufacturing point of view, this proposed method will be expensive for now, until we can find the laser with better efficiency (that I am sure will be found in really near future).
Thank you, Arfi'an Fuadi
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