Author's Note: Hello friends, my name is Karan and iam a mechanical engineer. For those who are not aware about the concept of 3D printing. This article will let you understand what exactly 3D printing is and how it works. I have intentionally tried to explain it with simple words and have used some content from other blogs so that you get everthing in one place. so basically it is for students keen to learn about this technology and hopefully it would help them in their academics.
INTRODUCTION:
Previously when computer technologies were not so advanced as of now, manufacturing industries had to test their product relying on trial and error basis. But this process consumed lots of time and material was also wasted. Hence there was a need of a process that could rapidly and easily produce prototypes of a product using relatively cheaper material which could resemble to the characteristics of final product. Rapid prototyping is the fast fabrication technique of a physical part, model or assembly using 3D computer aided design (CAD). The creation of the part, model or assembly is usually completed using additive manufacturing, or more commonly known as 3D printing.
3D printing is an additive manufacturing process. Basically it is the construction of a three-dimensional object from a CAD model or a digital 3D model. The term "3D printing" can refer to a variety of processes in which material is deposited, joined or solidified under computer control to create a three-dimensional object, with material being added together (such as liquid molecules or powder grains being fused together), typically layer by layer. In an additive process an object is created by laying down successive layers of material until the object is created. Each of these layers can be seen as a thinly sliced cross-section of the object. 3D printing is the opposite of subtractive manufacturing which is cutting out / hollowing out a piece of metal or plastic with for instance a milling machine. 3D printing enables you to produce complex shapes using less material than traditional manufacturing methods.
CLASSIFICATION:
There are basically two main types used in a 3D printing technology.
- Liquid jetting (FDM based) Technology: It is probably the most popular printing method due to the number of printers available on the market. FDM is an affordable 3D printing process compared to other 3D printing technologies. This process works by material being melted and extruded through a nozzle to 3D print a cross section of an object each layer at a time. The bed lowers for each new layer and this process repeats until the object is completed. Layer thickness determines the quality of the 3D print. Some FDM 3D printers have two or more print heads to print in multiple colours and use support for overhanging areas of a complex 3D print. This process is widely used for building prototypes out of plastics and for small scale production of plastic article.
- Binder Jetting (SLS based) Technology : This type is similar to Laser sintering process but the only difference is instead of laser, a binding agent is used to bind the powder in definite contoured shape layer by layer. The process most notably facilitates in the creation of complex and interlocking forms. Most of the 3D printers use this technology for production of products using alumide (mix of polyamide powder and fine aluminium particles.) and plastic.
CONSTRUCTION:
Let us study the construction of most basic form of a 3D printing mechanism.
2. The printer head is attached to a tank filled with liquid binder there can also be multicoloured liquid binders fed to the print head so as to obtain different colours on the object. The binder is extruded from the nozzle dropwise over the powder layer according to the required shape.
3. At the base it consists of two platforms. Powder delivery platform is filled completely with powdered metal composite initially and below there is a piston which pushes this stack of powder in the upward direction. The displacement of the piston is decided according to the thickness of each layer and with every passing iteration it has to move by the same amount.
4. The powder from delivery platform is transferred to another platform known as build platform with help of a levelling roller every new powder layer is placed over the build platform. There is a build piston placed right below, initially it is at its maximum upper limit but as new layers are formed it displaces downwards by the amount of the thickness of new layer.
5. The print head hovers over the build platform and drips the binder on each powder layer according to the required shape of each layer. Once the printing process is completed the build piston moves upward so as to reveal the final output of process.
WORKING:
A new layer of powder from the powder feed platform is swiped over the build platform with help of the levelling roller.
2. The ink jet head moves in X-Y directions according to the STEP program fed to it. As it moves to cover the specified contour of a particular layer it drips in the liquid binder throughout its trace.
3. This liquid binder fuses the metal compound powder together and binds them together to endorse rigidity in the produced layer. The liquid binder is preheated to provide proper binding of powder with each other.
4. Once a layer is completed the build platform moves downward by the amount of the thickness of the proceeding layer and the delivery platform raises the powder stack by the same amount and again the entire process is repeated.
5. These iterations continues until the last layer is formed and once the entire program is executed the build platform moves to its top position and all the loose unused powder gets separated from the binded product and final product is then sent for final finishing process where the supports are removed by machining and surface finishing is also done to achieve the required tolerance of the product.
6. The entire process is controlled by a program module which is executed by MCU (machine control unit). This has the functions of controlling the print head movement over the powder layer, jetting of specified coloured binder with a controlled feed rate, movement of the pistons and to synchronise the process according to the running program.
FROM INCEPTION TO ACTUALISATION:
The working of the 3D printer that we discussed above includes only the basic fundamentals of the process however the actual process is much more advanced and complicated.
The overall workflow of any 3D printer is oriented towards achieving the goal of converting a 3D design created using software into a hardcopy version. While the methods used by different printer models vary, they’re all based on the same type of workflow. Let’s look at this workflow and then delve deeper into the world of 3D printing by exploring the different types of 3D printers available in the market.
The 3D printing process of any printer can be simplified into a series of basic steps. These steps are independent of the printer’s size, scale, material or design, and are closely adhered to by nearly all printer manufacturers.
Step 1: Just as any 2D digital printing begins as a file in a word processing software or page layout software, 3D printing begins in computer-aided design (CAD) software. The version or degree of the software’s complexity may vary but they all share the same basic attribute of being able to design a three-dimensional object inside the computer’s memory. Depending on the type of software, users can exert various degrees of control over the physical and structural integrity of the final product within the simulated environment of the computer. Data relevant to the product’s real-world attributes, such as material’s property or mensuration can also be accurately depicted using computer-aided design software. The scientific data available to this software is also instrumental in giving users an accurate virtual prototype of their design, allowing them to test how the conceptualised object will behave under a variety of real-world settings. The complexity of any product is limited only by your imagination and CAD skills.
Step 2: The next step on the 3D printing journey is the conversion of the CAD-based models and designs into a language format that’s compatible with that of 3D printers - the STL format. The STL format, or ‘standard tessellation language’ format, is the current industry standard that was developed for the use of 3D printers. It was originally created in 1987 for use on stereo lithography apparatus machines (We’ll come back to this and other types of 3D printers at the end of this chapter). Although STL format files are the primary standard for 3D printers, a small group of other assorted proprietary file formats such as ZPR and ObjDF which require specialised software can also do the job. However, the significant majority of professional as well as Open Source software support STL, so new users don’t need to worry about multiple conversions. As with any machine a little hands-on adjustment is always necessary.
Step 4: This step varies according to the type of the printer. Once the STL file is ready for printing, the machines need to be checked for the required materials and placement configurations, just as a paper printer needs to be checked for ink and tray alignment. In the case of 3D printing, the types of machines vary greatly based on their printing techniques, and accordingly require different types of materials to work with. This includes polymers, binders, adhesives and powders. In addition to this, the placement of the base tray or chemical solution base also needs to be adjusted.
Step 5: The next step is very easy - the machine proceeds to process the STL file and fabricate the object that’s been designed. For most consumer grade 3D printing machines and most designs, the entire printing process is automated. Only in certain rare cases, manual intervention may be called for; E.g. If the printing process requires large material quantities and reloading is necessary or if parts of the design need. The printer creates layers measuring 0.1mm in average thickness. Based on the material, this can be thicker or thinner. Printing objects can take a variable amount of time - from minutes to hours to even days. You may sometimes be required to keep checking in on the printer’s progress to ensure that there are no errors or misalignments.
Step 6: Once the object has been printed, its removal from the printer is an extremely delicate and critical step. In many cases, the printing process leaves the object’s surface hot and malleable, and in certain cases requires additional time to clear off fumes and particulates. Users are advised to take special precautions such as wearing gloves and glasses when removing the object from the printer.
Step 7: The next stage involves processing the item. With most 3D printers, the final object is usually found covered with the remains of the additive materials, or a layer of powder or coarse material. The processing stage requires either dusting off the physical particulates or bathing the object in water to remove water soluble elements. It’s important to note that not all objects taken from a 3D printer are immediately ready for processing. Depending on the material and design configuration used, sometime may be required for the additive material to “cure” and harden completely before it can be processed without risk to the physical integrity of the object. If this is ignored, there’s a significant risk that certain parts of the object will fall apart, dissolve or weaken the overall structure of the object.
The above stated workflow of 3D Printing is common to all models. Once the process is complete, you can use the final object for its intended purpose. Many printers are capable of printing multiple objects allowing users to carry out simultaneous manufacturing tasks for maximum efficiency.
MATERIAL AND SPECIFICATIONS:
Depending on the type of printer and the object being printed, the material used can be liquid, powder, paper, metal or even food based.
Some of the materials used for 3D printing are:
1. Nylon: Nylon’s ability to withstand high temperatures and its durability combine to give it above average abrasion resistance. Thus, it is an excellent material for replacement parts in a manufacturing facility or distribution centre.
2. Nylon CF: Carbon fibre reinforced nylon optimized for high strength to weight ratio, stiffness, and heat resistance making it ideal for structural applications and metal replacements.
3. PC ABS: PC-ABS is a strong, engineering-grade material that has both a high heat resistance and high impact resistance. When ABS
does not provide a high enough impact resistance, but high heat resistance is still required, PC-ABS is a great alternative, due
to the addition of polycarbonate.
The degree of complexity and finesse with which a printer can create objects is based on the resolution of the printer. A 3D printer’s resolution is calculated on the horizontal two-dimensional X-Y axis in dots per inch (DPI). The thickness of each layer is generally 250 DPI which is about 0.1 millimetre (100 µm), but can also be as little as 16µm or 0.00016 millimetre. The individual particle or dot size produced by these printers is on average between 50µm to 100µm in diameter.
The materials that can be used for additives are as follows:
1. Polylactic acid-based plastics (PLA): Available in a range of grades, from soft to hard. It’s gradually gaining favour as the more preferred additive type in comparison to ABS.
2. Polyvinyl alcohol (PVA): It’s an essential additive agent used as a dissolvable material, most commonly used to make supports in 3D objects.
3. Polycarbonate (PC): Polycarbonate is a currently experimental additive material being tested with certain types of 3D printers. It’s ejected in liquid state from high temperature ejectors or printer nozzles, similar to inkjet printers.
4. Soft poly-lactic acid (Soft PLA): This plastic is the extreme version of PLAs and has the unique property of being very flexible. However, it’s currently still in limited use due to its basic range of colours and production. And then you have the more resilient and traditional manufacturing materials such as metals and complex polymer. Sturdier additives such as different types of steels, titanium, precious metals such as gold and silver, and other metals are currently not easily available or used in consumer level 3D printers.
FINISHING PROCESS:
The finishing process, as we discussed in the steps, is a careful and delicate process, but usually the fastest in the entire workflow. What’s more, some basic finishing techniques allow for greater quality in the final product. Though 3D printers that can print in high resolution are available, it’s possible to achieve even higher quality through a post-printing subtractive process.
While additive printing is about adding materials together, subtractive printing is the exact opposite. In 3D printing, a slightly larger or oversized version of the item is printed at normal resolution and then subjected to a high-resolution subtractive process, which makes it possible to craft a more accurately sized final object. This is akin to scaling down a larger sized model proportionally to achieve greater precision in detail.
This finishing technique is especially useful when working with 3D printers that use multiple materials in their process. Subtractive printing allows users to flesh out the variances in composition and style especially handy when multiple colour components or parts are printed together. Another aspect of the finishing process is erasing or removing “supports” that are used while printing. In certain designs, it’s necessary to use small components that hold up the orientation or structure of the object during the printing process, after which they’re no longer useful and need to be removed. During the finishing process, these supports are removed either manually or by dissolving them once the object has been printed.
APPLICATIONS:
1. Prototyping and Manufacturing: This was the main motive for which 3D printing was created for in product-based organisations initially to test a new product prototypes can be created by this process.
Medicine: Nowadays 3D printed prosthetics and dentures are widely used since it reduces cost up to a great extent.
Aviation: structural metal components used in aerospace vehicles prefer 3D printed elements since these are light in weight and highly durable.
Automotive: Similar to the aviation industry automobiles nowadays also are equipped with 3D printed elements for reliable and efficient manufacturing.
Jewellery and micro arts: As 3D printing machines can produce objects with submicron level accuracy. it can be used to create artistically detailed designs for jewellery which are very much intricate and small to be developed by any traditional processes.
ADVANTAGES:
1. Wide range of material can be used in this process for both binder and sinter powder.
2. Complex geometrical shapes can be easily manufactured with single step program and the produced object can be made light in weight.
3. Since no extra tools are required hence tool cost and maintenance in eliminated.
4. The process is very much fast and each layer can be produced within seconds with good accuracy.
5. The machine is simple to operate since it relies on computer technology hence not much skills are required to handle the machine
6. There is minimum wastage of material since it is an additive manufacturing process.
7. Multicoloured parts can be created by using different coloured binders.
8. Overall production cost is reduced as compared to traditional process.
9. The produced objects can be accurately scaled and are very much reliable.
DISADVANTAGES:
- Parts produced by 3D printing have relatively low strength since the particles are being binded by the binder hence intermolecular forces are absent.
- Post processing of the produced objects is required in order to achieve the required tolerance so this adds up to the process time and cost.
- There is heavy initial investment in this type of system since the machines and materials both are expensive.
- Size of the component that can be produced is limited to the chamber size of the machine.
- Setting up the machine may require considerable efforts since so many parameters has to be adjusted before starting the process.
Thankyou for reading through the entire blog.
 |
| Karan Gujaran (BE Mechanical Engg.) |
Comments
Post a Comment