Get your cutting right, and it will improve sample quality and save you time in the next step in the process. Follow these simple tips to significantly improve the precision, reproducibility and speed of your cutting and sectioning.
Cutting is the foundation of a good quality control process and any mistakes can jeopardize your verification result. By improving your cutting, you can increase your speed and consistency, and so reduce the need for time-consuming grinding and polishing. In this article, our materialographic specialists troubleshoot the six most common materialographic mistakes – and tell you how to avoid them.
1. Eliminate burrs to speed up your preparation process
A burr is a raised edge or small piece of material that remains attached after a specimen has been sectioned. Burrs need to be removed before sample analysis, which adds time-consuming grinding and polishing to your preparation process. Here’s how to avoid them.
Clamp on both sides
A great cut starts with good clamping. If you clamp only one side of the sample, a burr will often form as the material separates. Clamp on both sides of the workpiece and your problem is solved.
Slow down your feed speed
When sectioning manually, it can be difficult to keep the feed speed low just before leaving the workpiece, which means burrs are likely to occur. The solution? Use an automatic cut-off machine with controlled feed speed.
Example of a burr in titanium
Clamping from both sides
2. Improve sample quality by avoiding thermal damage
Thermal damage is a burning in the material’s surface caused by incorrect sectioning. It usually leaves a visible discoloration and changes the micro-structure of the material to a certain depth. Thermal damage has to be removed through a time-consuming grinding and polishing process before analysis. Here’s how to avoid it.
Change your cut-off wheel
One of the most common causes of thermal damage is using the wrong cut-off wheel for the material. Selecting the right cut-off wheel will not only improve your preparation quality – it will also save time and consumables by reducing the need for plane grinding and ensuring you get the most cuts per wheel. As a result, you can produce more samples in a shorter time and at a lower cost per sample.
Selecting the right cut-off wheel requires a number of considerations, including the type of material and size of cut.
Go automatic
Like burrs, thermal damage is often caused by high feed speeds. You can solve the problem by using an automatic cut-off machine with an adjustable feed speed. Reducing feed speed will help to avoid thermal damage.
Remember the cooling liquid
Keep your sample cool. Check the cooling system and the level of cooling liquid, and make sure that the nozzle is positioned optimally over the cutting section.
Thermal damage due to faulty cutting conditions
3. Improve reproducibility by avoiding cracks in brittle materials or coatings
Cracking typically occurs in brittle samples or samples with layers, and usually means the sample has to be cut again, adding extra time to your cutting process. This extra time can be avoided by following these simple tips.
Make a simple adjustment to your cutting technique
When sectioning a coated material, the base material acts as support, so always cut into the coated side of the workpiece.
Support your material
Support is important to stop cracking. If your specimen is small enough, mount it. For extra support, apply an epoxy resin during vacuum-impregnation. This will ensure the epoxy resin penetrates all pores, cracks or openings in the coating to give it full support during sectioning.
Use an automatic cut-off machine
Feed speed is a common cause of cracks. It is very difficult to get the speed right in brittle and layered materials when cutting manually, so the best solution is to use an automatic cut-off machine with adjustable feed speed.
Change your cut-off wheel
Choosing the correct cut-off wheel can vastly improve the cutting process, by reducing the need for polishing and grinding and ensuring the get the most cuts per wheel. When it comes to workpieces with coatings, if the coating is thick, choose a cut-off wheel to suit the coating; if the coating is thin, choose a cut-off wheel to suit the substrate.
Cutting best practice
Bring cut-off wheel into the coated/treated surface first enables the substrate to act as support to layer
Cutting bad practice
Bringing the cut-off wheel into the coated/treated surface last severely increases the risk of delamination
Selection of the right cut-off wheel
Less than 10-20 % coating area use a cut-off wheel for substrate
More than 10-20 % coating area use a cut-off wheel for coating
4. Protect your cut-off wheel by avoiding pinching
Workpieces of hardened steel tend to build up internal stress during longitudinal cuts. The workpiece will then pinch the cut-off wheel, which can cause it to get stuck or break. At its worst, pinching will deform the workpiece , which stresses the material and means any sample cut from it is no longer representative of the whole – invalidating your analysis. There’s a simple way to avoid these issues.
Use pinch-reduction clamping tools
Easily adjustable and compact, pinch-reduction tools limit deformations from the cut to minimize pinching and protect your cut-off wheel.
Example of a pinch reduction clamping tool. A tool that reduces internal stress during longitudinal cuts.
5. Learn how to clamp and cut irregular shapes
An irregular shaped workpiece can be difficult to clamp for sectioning, slowing down your cutting process. If the workpiece is not held well enough, movement during sectioning may mean the sample has to be re-cut. Here are three solutions.
Use support blocks
For larger workpieces, set up support blocks to support the workpiece during sectioning and prevent it from overturning.
Mount in resin
By mounting smaller workpieces in resin before sectioning, you make them much easier to clamp with standard tools. RepliFix resin is an excellent solution for irregular shaped workpieces.
Go custom-made
If you often cut similar workpieces, a custom-made clamping tool will save you a great deal of time and significantly improve your reproducibility and quality.
The vertical clamping tool is specifically designed for multi-purpose clamping of irregular work pieces.
Adjustable support blocks for clamping of irregular shaped workpieces
6. Don’t cut the work surface
Many of us have accidently cut into the cutting table by mistake. How can you minimize the chances of cutting the table?
Use a lower feed speed
The mechanical impact of a high feed speed can bend the cut-off wheel and cause it to veer off into the table. Choose a slower cutting speed for better stability.
Switch to a softer cut-off wheel
If your cut-off wheel is too hard for the material, it may deflect off into the table. If you don’t want to change your cut-off wheel, you can try a lower RPM.
Improve your cutting today
Contact our application specialists to improve your quality control, failure analysis, material science, or academic research. Or if you have a specific question about a preparation method, a material or an industry related issue. We are here to help you.
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