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The purpose of this article is to explain the principles of intaglio cutting, as well as consumables and parameters that affect cutting results.
Metallographic cutting or slitting is often the first step in the preparation of metallographic specimens. In most cases, this is necessary because the part or object is too large for subsequent laboratory scale metallographic grinding and polishing steps. Depending on the geometry of the part and the hardness of the material, as well as the analysis method used, different cutting methods and consumables are used.
Wet milling is the most commonly used method of materialographic analysis in mechanical sectioning because it causes minimal deformation during cutting. Suitable for thin cutting of hard materials, suitable for almost all solids. The exceptions are very soft polymer or rubber materials, but even then there are potential applications.
As a rule, a small zone of plastic deformation is observed in abrasive sections, usually at a depth of 200 μm below the cut surface. This means that the grinding and polishing steps can be significantly reduced as less material needs to be removed to achieve a true microstructure.
However, curved cuts or complex geometries cannot be obtained with this method; in these cases, saws, mainly wire or band saws, can be used. For thin incisions, there is a technique called microtomy. This method, which is standard in the polymer industry and biology, has limited applicability to hard and brittle materials due to the use of a particular blade for cutting.
Cutting very soft and malleable materials as well as very hard and brittle materials can be optimized by choosing the right cutting wheel. In general, the following principles apply: soft bond wheels are suitable for cutting harder materials, and hard bond wheels are suitable for cutting soft materials.
To begin the wet abrasive cutting process, the part is placed and secured in the torch’s clamping device. The user must then select the appropriate consumables, set the correct parameters, and set the cutting wheel in place. Therefore, the user must initiate an automatic or manual partitioning process. Once the sample has been sliced, it can be removed and cleaned before it is ready for use.
1. Manually or automatically move the work stage with the pre-fixed workpiece onto the fixed cutting wheel.
The workpiece to be processed is firmly fixed on the cutting table. The cutting wheel is then guided manually or automatically from top to bottom into the stationary workpiece.
The workpiece is cut not in one cutting step, but in layers (step by step). This cutting method is particularly suitable for cutting large and thick hard material.
The workpiece is cut not in one cutting step, but in layers (step by step). This type of cutting is particularly useful for cutting large, thick, hard material (sheets, angles, etc.) where the edges must be pinched.
In the case of diagonal cuts, the table moves backwards (X-axis) and the cutting disc moves downwards (Y-axis). This type of cutting is especially useful for cutting asymmetrical workpieces or for compensating for wear on the cut-off wheel to achieve a consistent depth of cut.
The workpiece is cut not in one cutting step, but in layers (step by step). A zigzag cut is made in the middle of the part.
In manual cutting, the clamping table (X-axis) moves back and forth until the cutting is completed. It starts with forward and backward movement. This type of cutting is particularly suitable for workpieces requiring clean cutting edges and material-friendly processing (temperature, deformation) due to the smallest possible contact surface.
This process is most commonly used on precision cutting machines. With the appropriate rotating sample holder, it can also be used for large workpieces. The sample is rotated clockwise or counterclockwise relative to the cutting wheel. A quarter or half turn is also possible. For round workpieces with a diameter of 50 mm, a cutting distance of only 25 mm is required.
Wear (i.e. wear resistance), service life and cutting performance are critical to the quality of a cutting wheel. Abrasives (aluminum oxide, silicon carbide, diamond, cubic boron nitride (CBN), etc.) and bonds (metal, synthetic resin or rubber) characterize the composition of the wheel.
The grain size of the abrasive in the cutting wheel is an aspect that cannot be ignored when cutting metallographic specimens. It should be between 45 and 180 microns. If all parameters are met, this will allow you to get an optimal cut surface, which should facilitate further preparation. When using thin cut-off wheels, a very fine grit is recommended. Fine grain size is also important if burr-free cutting is required.
The hardness of the cutting wheel for wet abrasive does not depend on the hardness of the grain, but on the hardness of the bond, i.e. the ability of an individual grain to resist the destruction of the binder.
Figure 1. QATM Al2O3 cutting wheel with rubber bond (left) and synthetic resin (right) Image credit: QATM
Optimal cooling is critical in the cutting process. Excessive heat generated during cutting can damage the specimen and cut-off wheel. The purpose of an anti-corrosion coolant is to protect the machine and specimen from corrosion and to increase material removal by providing proper lubrication during cutting. A pH of 9 to 10 is usually suitable for this purpose. To improve cooling efficiency, QATM coolant has a higher boiling point than water.
The most common anti-corrosion coolants are aqueous solutions with moderate cooling properties and acceptable ability to carry abrasive residue.
All QATM cutting machines are available with various clamping tools and systems. Specimens and materials of any size can be held securely for precise cutting with our clamping fixtures. Our clamping tools include:
The main mistake that users should avoid in wet abrasive cutting is excessive heat generation due to insufficient cooling. In this case, the heat generated leads to an unpredictable and unacceptable change in the microstructure of the material – it no longer represents the original structure of the material. This happens in the example shown in Fig. 43 left. The intense faded color is noticeable when compared to the correctly cut sample in the image on the right.
Other cutting artifacts can be found in our guide to intaglio specimens called “Expert Guide to Intaglio/Intaglio”. The links below contain samples to read and information on getting expert guides.
This article is an introduction to the principle of metallographic sampling (cutting). For more information, see our guide to metallographic sampling called “The Expert’s Guide” to help you deepen your knowledge on this subject.
ATM (January 5, 2023). Basic knowledge of materialographic sectioning. AZ. Retrieved January 14, 2023 from https://www.azom.com/article.aspx?ArticleID=21933.
ATM “Fundamentals of materialographic sectioning”. AZ. January 14 …
ATM “Fundamentals of materialographic sectioning”. AZ. https://www.azom.com/article.aspx?ArticleID=2 (accessed 14 January 2023).
ATM 2023. Fundamentals of metallographic section. AZoM, accessed 14 January 2023, https://www.azom.com/article.aspx?ArticleID=21933.
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Post time: Jan-14-2023