工業用3Dプリンティングの材料選定

~金属粉末焼結(DMLS)、樹脂粉末焼結(SLS)、光造形(SLA)で利用できる材料の特性を知る~

※ This article was edited and created by US protolabs. Some services in the sentence include those not yet deployed in Japan. Design Tips - list of secrets of resin parts design  )

In order to obtain excellent results, materials suitable for the application are necessary. Material properties become increasingly important as products move from concept to functional prototyping and even production.
However, in order to evaluate material properties, the manufacturing process has to be determined. It is because it is a combination of material and process that determines the characteristics. For example, alloys made with die casting have different characteristics from metal injection molded (MIM) alloys. Likewise, the thermoplastic resin has different characteristics between injection molding and cutting processing.

Lamination modeling (AM) such as 3D printing is unique. Because it is different from any other manufacturing process, material properties and the characteristics of the parts to be manufactured will differ even if using the same alloy or thermoplastic resin material. Regarding material properties, it is important to recognize that good or bad is not a problem, but the result is different.

Recognizing that the results are different, the following information will be used to characterize the materials used in the three most widely used industrial 3D printing methods, and finally to material selection It will be useful for both. The three types of construction methods are DMLS (Direct Metal Laser Sintering), SLS (Selective Laser Sintering), SLA (Stereolithography).

Advances in materials

Materials used in 3D printing are making progress as expected. Due to the progress of materials, 3D printing has been used not only for models and prototypes, but also for functional parts for testing, for work sites and for some mass production.
The output result of 3D printing is different from the output result of other manufacturing process. On the other hand, 3D printing may be a suitable choice for direct replacement items. Besides, the merit of 3D printing becomes even bigger as users try their possibilities.

But it is somewhat difficult to try out the possibilities. There are other related differences in 3D printing besides the difference in material properties. For example, material for 3D printing lacks performance data to characterize materials under various conditions. 3D printing users can only use one datasheet with only limited values. These values ​​are mostly obtained from the best scenario based on tests using unused materials (unrecycled powder) etc., for example in the case of powder sintering.

Furthermore, in 3D printing, anisotropy occurs, and it is also a problem that the values ​​differ in the X, Y, and Z axes. The degree of anisotropy differs depending on the shaping technique, for example, DMLS is the method with the lowest anisotropy when comparing the three main types of molding techniques before, but this point always needs to be considered.

However, it is rare for suppliers of materials to disclose specifications of materials that record changes in anisotropy characteristics for each axis. The data underlying these specifications may change not only depending on the material and construction method, but also depending on the type of processing machine.

By designing the 3D printing process and adjusting the modeling direction it is possible to overcome problems of anisotropy and insufficient material properties. For that purpose, we will complement the shortfall in the material property data by utilizing the past project experience or by using the experience of the accredited service organization. If performance is crucial, you should consider testing laminated build material in an independent laboratory.

It is not an exaggeration to say that whether it succeeds or not depends on material characteristics, but that is not the only thing to consider. Features such as maximum size of shapeable parts, dimensional accuracy, feature resolution, surface finish, manufacturing time, parts cost, etc. are influenced by the molding material and shaping process. Therefore, once you select the right materials, we recommend that you select a method of evaluation that can satisfy expectations and requirements regarding time, cost and quality depending on the material.

Selection of materials

Normally, molded materials have one or two material properties that are distinct compared to other materials. For example, if you are seeking the average tensile strength of polyamide (PA) 11, you may choose a photopolymer for SLA rather than PA for SLS. On the other hand, if a higher heat resistance temperature (HDT) is required, the nylon material shaped by powder sintering is the best choice.

When choosing materials for 3D printing, it is recommended to first decide which mechanical properties or thermal characteristics are essential after understanding some characteristic characteristics of each material I will. Next, we examine the choices of materials and find what is suitable. After narrowing down the options, consider the remaining non-critical characteristics in order to determine whether it is appropriate to apply that material in the project.

Since the characteristics of the shaped parts in 3D printing are unique, we do not recommend choosing from the viewpoint of whether it is optimal as a material for casting, injection molding, or cutting. Rather than do so, examine the available material options and find the building material that meets the most important requirements.

Direct metal laser sintering (DMLS)

With Direct Metal Laser Sintering ( DMLS ), metal powders that do not contain binders etc. can be used to produce parts with characteristics equal to or better than those of generally accepted forged metal parts . Dissolution and solidification are performed rapidly at a place where the laser irradiation point always moves within a narrow range, so DMLS may have a difference in grain size and grain boundary as a metal grain structure, which may affect mechanical performance . The particle structure is changed by parameters of laser, heat treatment after shaping, hot isostatic pressing method, and research is still continuing to clarify its characteristics. However, the result is not widely known. Ultimately particle structure differences will be of great benefit if certain manipulations are possible and various mechanical properties are available in parts.

Of the above three types of layered fabrication methods, DMLS can produce parts with isotropic material properties to a considerable level. However, when you measure along each axis, there are some variations in the characteristics. Regarding the material properties of DMLS, tensile strength in Fig. 1, elongation at break in Fig. 2 and hardness in Fig. 3 are visually compared, respectively.

Stainless steel is a material generally used in DMLS. Pro-Labs offers two grades: 17-4 PH and 316L. Selecting 17-4 yields a much higher tensile strength (190 ksi = 1,300 MPa), 316 L with 70 ksi = 480 MPa) and yield strength, hardness (47 HRC, 316 L is 26 HRC). However, because the elongation at break (EB) is much lower than 316 L (8%, 316 L is 30%), it is inferior in malleability. Both 17-4 and 316L are corrosion-resistant, but 316L has better acid resistance. 316L is also superior to temperature tolerance than 17-4. 17-4 can change the mechanical properties by heat treatment. On the other hand, 316 L is provided with residual stress removed.

DMLS Aluminum (Al) is equivalent to the 3000 series alloy used for casting and die casting. The metal composition is AlSi 10 Mg, it has excellent weight ratio strength, heat resistance, corrosion resistance, fatigue resistance, creep resistance, breaking strength. The tensile strength of Al (36 ksi = 248 MPa to 43 ksi = 297 MPa) and the yield strength (30 ksi = 207 MPa to 32 ksi = 221 MPa) are far higher than the average value compared with the aluminum of die cast 3000 series. However, the elongation at break is much lower (1%) compared to the average value of aluminum in the 3000 series (11%).

DMLS titanium (Ti - 64 ELI) is most commonly used in aerospace and defense applications due to its weight ratio strength, heat resistance, acid resistance / corrosion resistance. It is also used for medical applications. Compared to Ti grade 23 (annealed), the mechanical properties are almost the same, the tensile strength is 130 ksi = 900 MPa, the elongation at break is 10%, the hardness is 36 HRC.

Cobalt chromium (CoCr) is one of the two DMLS superalloys and is used especially for aerospace applications and medical applications. CoCr contains a very excellent elongation at break (20%) and has creep resistance and corrosion resistance. Compared with the average value of ASTM F-75 CoCr (depending on heat treatment), the material properties of DMLS CoCr are almost equivalent, the tensile strength is 130 ksi = 900 MPa (95 = 655 MPa to 140 ksi = 966 MPa), the elongation at break is The yield strength is 75 ksi = 518 MPa (65 - 81 ksi = 449 - 559 MPa), the hardness is 25 HRC (25 - 35 HRC) (the value in parenthesis is the value of F - 75), 20% (8 - 20%). Among all metals for DMLS, CoCr has the best biocompatibility (which requires additional biocompatible treatment that does not correspond to protoabs), making it ideal for medical applications such as dental implants.

Inconel 718 (IN 718 ) is a nickel and chromium superalloy that is used at all times in high temperature conditions, such as aircraft engine parts. Use of DMLS IN 718 parts The durability temperature is amazing (-253 ° C to 704 ° C), and it also has excellent corrosion resistance, fatigue resistance, creep resistance, and breaking strength. The DMLS IN 718 has higher tensile strength (180 ksi = 1,242 MPa, 160 ksi = 1,104 MPa in the conventional product) than the IN 718 processed by the conventional construction method, and the yield strength is also equal (133 ksi = 9, 177 MPa, the conventional product is 160 ksi 1, 104 MPa). However, the elongation at break is half that of IN 718 processed by conventional construction method (12%, 25% for conventional product).

 

 

Powder sintered laminated shaping

For SLS (Selective Laser Sintering, Powder Sintered Lamination), use mainly thermoplastic powder such as polyamide (PA). We can manufacture functional parts with toughness, impact strength, high heat resistance temperature HDT (177 ° C ~ 188 ° C) better than parts made with stereolithography SLA. Instead, SLS can not provide a surface finish or fine shape as obtained with SLA.
Normally, PA for SLS is lower than the average characteristic value of corresponding PA injection molded item, although each HDT value is close, each value of mechanical characteristic is low. DuraForm HST Composite, which contains reinforcing fibers, is exceptional and exceeds mineral reinforced PA 12 in all respects, except tensile strength. For some materials, the degree of anisotropy can be confirmed from the characteristics indicated by PA for SLS. Regarding the material properties of SLS, we compare visually the heat-resistant HDT in Figure 4, the breaking elongation in Figure 5 and the tensile strength in Figure 6, respectively.

DuraForm HST Composite is one of fiber reinforced PA and resembles PA 12 containing 25% reinforced mineral. Due to the fibers contained in HST, the strength, rigidity and heat resistance HDT are greatly improved. Compared with other SLS and SLA options (except ceramic reinforcement), HST has the highest tensile strength, flexural modulus, impact strength and high HDT. Therefore, HST is suitable for functional applications where the temperature may exceed 149 ° C. However, this material is somewhat brittle, EB is 4.5%. Also, please take into account that there are large differences in the value of Z axis, as with injection molded products of fiber reinforcement.

With PA 850 Black , ductility and flexibility are obtained without compromising tensile strength (6.9 ksi) and heat resistance (HDT is 188 ° C), its tensile modulus is 214 kpsi = 1,477 MPa and EB is 51%. Due to these characteristics, the PA 850 is widely used as a versatile material, making it ideal for living hinge materials where the number of tests is limited.
Compared with the average value of injection molded products of PA 11 in the past, PA 850 has high HDT (188 ° C, PA 11 at 140 ° C), tensile strength and rigidity are equivalent. Although EB is the highest among AM resins, it is only 60%, which is lower than the value of injection molded products of PA 11 of the past.
Another characteristic of the PA 850 is its uniform dark black color. Black has high contrast, makes the shape conspicuous, makes dirt, grease, dirt less visible. It is also suitable for optical applications because of its low reflectivity.

ALM PA 650 is an economically superior, well-balanced main material and is used in a wide range of applications. It has higher rigidity than PA 850 (tensile elastic modulus is 247 ksi = 1,704 MPa, PA 850 is 214 ksi = 1,477 MPa) and tensile strength is equal (7.0 ksi = 483 MPa, PA 850 is 6.9 ksi = 48 MPa). Although EB is half of PB 850 (24%), it still has the top class performance in terms of ductility. The PA 650 is nearly equivalent to the average characteristics of PA 12 injection molded parts. Although the rigidity is close, the tensile strength and the EB are about half. However, HDT is much higher than 177 ° C (PA 12 is 138 ° C).

PA 615-GS is a polyamide powder containing glass spheres that increase rigidity and dimensional stability. However, since it becomes brittle due to tempered glass, impact strength and tensile strength are greatly reduced. Also, due to glass spheres, the parts made with this material are much more dense than the parts made from other AM material.
PA 615-GS is very similar to the average value of injection-molded products of glass reinforced nylon. Compared with nylon containing 33% of glass, HDT is as low as 177 ° C (nylon at 254 ° C), tensile strength (80%) and EB (50%) are also much lower values.

Light shaping

For SLA (Stereolithography), use photopolymer which cures with UV (ultraviolet light) light, ultraviolet curable resin. Material choice is the widest, tensile strength, tensile modulus, flexural modulus, EB also vary. Impact Strength and Heat Resistance For HDT, it is usually much lower than the value of general resin injection molded products. Also, you can choose the degree of color, transparency, opacity etc from among various materials. For SLAs that provide excellent surface finishes and high feature resolution, you can produce parts that are similar to injection molded parts in terms of both performance and appearance.

Since photopolymer is hygroscopic and has UV photosensitivity, dimensions and performance of parts may change with the passage of time. Exposure to moisture or ultraviolet rays will change the appearance, size and mechanical properties. Regarding the material properties of SLA, we compare visually the heat-resistant HDT in Fig. 7, the elongation at break in Fig. 8 and the tensile strength in Fig. 9, respectively.

Accura Xtreme White 200 is widely used material for SLA. In terms of flexibility and strength, since it is located between polypropylene and ABS, it is suitable for snap fit, master pattern and demanding applications. Xtreme is a material for SLA with excellent durability, has very high impact strength (1.2 ft. - lb. / in. = 6.3 kJ / m 2) and high EB (20%), strength and rigidity are moderate is. However, HDT (47 ° C) is the lowest value among materials for SLA. Compared to the average value of ABS injection molded products, the tensile strength of Xtreme is somewhat higher (7.2 ksi = 50 MPa, ABS: 6.0 ksi = 41 MPa) but EB is slightly lower (20%, ABS is 30%). At bending load, the stiffness of Xtreme is reduced by 26% and impact strength is reduced by 70%.

Somos WaterShed XC 11122 is unique in that it has low hygroscopicity (0.35%) and transparency close to colorless. Secondary processing is necessary to make this material completely transparent, in which case very light blue color remains. Suitable for a wide range of applications and pattern creation, WaterShed is most suitable for flow visualization model, light pipe and lens.
WaterShed's tensile strength and EB are the highest among 3D printing materials resembling thermoplastic resins and are excellent in toughness and durability. Compared to the average ABS injection molded product, the tensile strength is slightly higher (7.8 ksi = 54 MPa, ABS is 6.0 ksi = 41 MPa), EB (20%, ABS is 30%) and heat resistant HDT ° C, ABS is 102 ° C) is inferior.

RenShape 7820 is another alternative to traditional molded parts when you want to use ABS injection molded parts as a prototype. It not only resembles the functional properties of ABS, it has a dark black color and has a glossy surface as seen from the top, so it has an appearance like an injection molded part. On the other hand, when viewed from the side, layer lines may be visible. Also, since the RenShape 7820 has low hygroscopicity, parts are relatively stable in size.

Compared to other materials for SLA, any mechanical characteristic value is "medium" value. EB (18%, ABS is 30%) and HDT (51 ° C, ABS (30%)), although the tensile strength is slightly higher (7.4 ksi = 51 MPa, ABS is 6.0 ksi = 41 MPa) than the average value of the conventional ABS injection molded article Is 102 ° C) is below the ABS value. The most different from ABS is the impact strength, which is as low as 0.91 ft. - lb. / in. = 4.8 kJ / m 2.

Accura 60 is a substitute for RenShape SL 7820 and WaterShed XC 11122 when rigidity is required. Like the RenShape SL 7820, this material creates sharp and vivid detail. In addition, translucency like WaterShed can be obtained. However, instead, the ductility is low, the EB is 29 to 36%, and the impact strength is 10 to 44% lower. Also, Accura 60 has a high hygroscopic rate, which may affect dimensional stability.

Somos 912 0 is the optimum SLA resin if parts with properties similar to polypropylene are required. This material is the most flexible among SLA options, the flexural modulus is 210 ksi = 1,450 MPa, and ductility is also highest at 25% EB. Moreover, it has the second highest impact strength (1.0 ft. - lb. / in. = 5.3 kJ / m 2) among SLA materials. The tensile strength (4.7 ksi = 32 MPa), the tensile modulus of elasticity (212 ksi = 1,463 MPa), the flexural modulus (210 ksi = 1,449 MPa), the impact strength (1.0 ft.- lb. / in == 5.3 kJ / m 2) are all the same degree. The only difference from PP injection molded parts is that the EB is 75% lower.

With Accura SL 5530 , you can create parts with high strength and rigidity and high temperature resistance. Furthermore, it is possible to raise the HDT from 55 ° C to 250 ° C with the thermal post-cure option. The tensile modulus (545 ksi = 3,760 MPa) and flexural modulus (527 ksi = 3,636 MPa) are the highest among the materials for unfilled SLA and the second highest tensile strength (8.9 ksi = 61 MPa) is available. However, post-cure reduces durability, impact strength is only 0.4 ft. - lb. / in. = 2.1 kJ / m 2, EB is only 2.9%. If thermal post-cure is not applied, tensile strength is maintained, flexibility is increased, and EB also increases by 50%.

Compared to thermoplastic resin injection molded products, it is most similar to polycarbonate containing 10% tempered glass. When thermal post-cure is applied, the tensile strength and flexural modulus of Accura SL 5530 are equal (compared with the average value), and the heat resistant HDT is 66% higher. However, in that case the impact strength and EB are greatly reduced (81% and 72%, respectively).

MicroFine Green is a material specially developed by Proto Labs to achieve the highest level of fineness (0.5 mm features can be molded) and the strictest tolerance with SLA material. Normally it is used to create small parts with a volume smaller than 2.5 cm X 2.5 cm X 2.5 cm.

Regarding the mechanical properties of MicroFine Green, the tensile strength (6.5 ksi = 45 MPa) and the tensile modulus (305 ksi = 2, 105 MPa) are average values ​​among the SLA materials, and the impact strength (0.46 ft.-lb ./in.= 2.4 kJ / m 2) and EB (6%) are at low levels.

Although the rigidity (329 ksi = 2,270 MPa) and tensile strength (6.5 ksi = 45 MPa) of MicroFine Green are close to ABS injection molded articles (333 ksi = 2,298 MPa and 6.0 ksi = 41 MPa respectively), HDT is 59 ° C., It is a value lower than 102 ℃ of ABS.

In Pro-Labs, we also offer another proprietary material, SLArmor. By applying nickel plating to the Somos NanoTool parts, it becomes an alternative to aluminum die casting. The tensile strength of NanoTool improves to 14.5 ksi = 100 MPa to 29 ksi = 200 MPa by plating (physical properties depend on the amount of metal). HDT is greatly improved than NanoTool, and it is possible to obtain a value from 50 ° C up to 269 ° C. On the other hand, HDT of aluminum die casting exceeds 260 ° C and tensile strength is 43.5 ksi = 300 MPa.

Decision tree
Summary

From metal to thermoplastic resin and ultraviolet curable resin, 3D printing can utilize various materials, so it is possible to obtain similar characteristics, or at least similar characteristics of materials processed by conventional methods. Because the basic process is different, it is impossible to create a part completely identical with the conventional construction method, but since the degree of freedom of shape that can be molded is higher than any construction method, the most appropriate material and material By choosing a combination with a modeling method, the possibility of achieving the goal will be high.
The key to success is to look at the difference with the conventional construction method, recognize this difference, and utilize 3D printing. In addition to this, you will be able to take advantage of the inherent merits of providing 3D printing only by supplementing the missing data with expert support, familiar with 3D printing.

Source: ulprospector.com  and vendor data sheet 

Design Tips - secrets of resin parts design article list