Additive Manufacturing Process Chain
Every manufacturing process passes through a certain sequence of tasks. 3D printing machines emphasize the simplicity of this job sequence. These machines are divided by their cost, simple to use and ability to be placed in an office or home environment. The larger 3D printers are suitable for industrial purposes. It can produce a wide variety of object but it also needs an experienced operator and also careful installation of the machine.
Here we go through the different stages of the additive manufacturing process. The objective is to allow you to understand the difference between the 3D printer, their working method and it helps you to identify the best fit 3d printer for your project.
Before we jump into 3D printing manufacturing process chain, let’s take a quick overview of term ‘additive manufacturing’.
Additive manufacturing is the advanced technology that produces 3D objects by adding layer upon layer of metal rather than a traditional machining process where material is removed. For more information about additive manufacturing, you can check out this link Additive manufacturing
Here we are going to discuss the 8 steps in the additive manufacturing process.
· Conceptualization and CAD
· Transfer and manipulation of STL/AMF file to 3D printer
· Part removal and Cleanup
· Post-processing of part
Above mentioned sequence is generally applied to all additive manufacturing technologies but there will be some variations according to part and its applied additive technology.
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Conceptualization and CAD
The product development process begins with the idea, how the product will glance and function. The concept of the product can be done in many forms, like text, representation of sketches and 3d models.
If additive manufacturing is used, then the product description must be in digital form. 3D printer uses this digital product for final product generation.
Conceptualization and product development is a crucial task, it can cover sub-stages depending on the type of product.
3D CAD model is essential for additive manufacturing, without the 3D model it is not possible to make final output. In additive manufacturing, solid objects are presented on the computer. Initially, this method is used in CNC machining. So we can say that additive manufacturing and CAD/ CAM is interconnected.
The generic process must begin with 3D CAD information. 3D source data can be created by various ways like by design expert via a user interface, using 3D CAD software, by reverse engineering like 3D scanning or a combination of the above method.
Modern solid modeling CAD software generates models without any gaps in the model. But if any case is there any gap in the 3D model, this makes very difficult to make the final product by 3D printers. Such types of problems are generally detected once the 3D model is converted to STL format.
Nearly every 3D printers support the STL file format. The terminology STL was derived from STereoLithograhy, which was the first additive manufacturing technology in the 1990s.
STL is a simple method of representing the CAD model in terms of geometry. STL file format removes construction data, modeling history and feature tree of CAD model. It represents the model surfaces in the series of triangular facets. The triangle size is calculated by the minimum distance between the plane represented by a triangle and the surface it is supposed to represent. In simple language, the minimum triangle offset is smaller than the resolution of the 3D printer machine.
The STL file is automatically generated by CAD software, but there is a little possibility of errors in a complex model. So it is recommended to double-check the file with STL repair tool like Materialise Magics to detect and rectify errors. For complex geometries, it is difficult to inspect the CAD model or STL file. So much software is used for checking before manufacturing the final product.
STL is the unordered collection of triangle vertices and surface normal vectors. STL file does not contain any units, material, color or feature information. This drawback of the STL file leads to the generation of new file format which is ‘AMF’. This format is the international ISO standard format that provides info like color, dimension, unit, material, and feature tree, etc. Although STL is the most used file format at the present time in this industry.
In the STL file, the corresponding triangles must be pointing in the proper direction. The surface normal vector must correctly describe the which side of the triangle is inside and which is outside. The discontinuous and complex geometry may not align properly. This creates gaps in the model. Some 3D printer automatically detects such errors and auto-fill such gaps. Sometimes it possibly adds unwanted material in the autofill process. So in such case software highlight the defected portions.
Transfer and manipulation of STL/AMF file to 3D printer
Once the STL file format is created and checked by STL repair software, it can be sent to the target 3D printer. Basically, it is possible to press the ‘print’ button and the machine will create the final product. But it is necessary to check the number of actions before start printing.
First verify the part which we are going to print is correct. Additive manufacturing software helps to visualize, view and manipulate the part. We can reposition or even change the orientation of the part. This will help when we print multiple parts at the same time in 3D printer to utilize the free space and increase productivity.
Sometimes part needs to make slightly larger or smaller than the original size to compensate for the changes due to shrinkage or coating. In such case scaling of part in additive manufacturing software is necessary.
In some part identification marking is required. It can also be done by embossing characters.
All 3D printers have some set of parameters that are specific to that process or machine. Some 3D printers are designed for specific materials and provide limited options to very thickness and build parameters. These machines have few setup changes to make from build to build. Other machines can run with a wild range of materials and create part quickly. This machine provides numerous setup options. Incorrect machine setup will lead to faulty products.
After setting up machine software parameters, machines need to physically prepared for build. the operator must check build material is properly loaded in the machine. For printers that use powder as raw material, they must check loaded and leveled correctly. For build plate as raw material must be leveled with respect to machine axes.
The first few stages of additive manufacturing are semiautomatic tasks, this needs a sufficient amount of human control in the form of interaction, decision making, and inspection. After that process switches to the computer-controlled building phase. Here layer base manufacturing takes place.
All additive manufacturing machines have a similar sequence of layering, material spreading, layer cross-section formation, and height-adjustable platform. Some 3D printer combines some of above mention processes. 3D printer will repeat the process until the completion of the building process.
Generally object printed from the 3D printer is ready to use but in some cases, it requires some minimal human intervention. Some objects need a sufficient amount of post-processing before using. Parts must be removed from the build platform. Some complex part needs additional extra material to support the original object such excess material is known as support materials. Support removal is a crucial task, it may damage the object or even reject if they don’t do it carefully. Recently some processes are developing for easy removal of support.
In the metal industry, a wire EDM, milling equipment and band saw are required to remove the object from the support. The part removal and cleanup are highly dependent on the skill of the operator.
Post-processing makes part ready for application purposes. Different types of post-processing are carried out on part as per the application of part. Some of post-processing are:
Chemical and thermal treatment
Infiltration and surface coating
This post-processes are required to maintain the good surface finish and precision.
After completion of post-processing, parts are ready for use. The same part with the same material can be manufactured by different methods. In such a case, it is possible that the behavior may differ. Some additive manufacturing machines create part with little voids inside part, this can lead to failure under mechanical stress. In some 3D printer some material not bond, link or crystallize in an optimum way. The rapid cooling in the 3D printer can defer properties than conventional and CNC machining. So the designer should properly decide the manufacturing process by considering all affecting parameters.
