Possible CNC Workpiece Milling Defects and Solutions
CNC milling can result in the development of workpiece defects. This lowers the quality of the final product. Here is a list of a few common examples of defects in CNC workpiece milling and appropriate solutions to fixing them.
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Leftover Material
During the process of CNC milling, the miller leaves leftover material on the workpiece. This leftover material is known as burrs. They commonly form along the bottom edges of the workpiece during milling or drilling. It is additionally commoner in softer materials whose characteristics are low hardness and more plasticity.
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Cause
The last layer of the workpiece material moves away from the milling drill bit as it deforms. Therefore, it becomes impossible to remove this excess material without changing its position. The burrs remain on the workpiece and appear as thin films on the edges. They are sharp and decrease the aesthetic value of the part made.
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Solution
We remove burrs from workpieces through deburring. There exist several ways in how we could remove burrs. One simple way of removing burrs is by doing it manually. We use tools such as a grinding head, files, or sandpaper to polish up and remove the burrs from a workpiece. This simple option does not require much technical expertise but gets the task done. Alternatively, advanced deburring techniques exist that do perform a better job than the manual process. They include thermal and vibratory deburring.
Variable Surface Finish on The Workpiece Surface
A poor surface finish is an important defect resulting from CNC milling.
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Cause
There exist several reasons for a varying or bad surface finish on a workpiece. The first one is due to chatter. This term refers to excessive vibration of the cutter or the machine tool. It causes the development of an uneven surface on the workpiece instead of smooth ones. The main cause of tool chatter is the use of a blunt tool. It leads to the deformation of the workpiece even before the chip becomes detached from the main part. Therefore, holes form resulting in a much lower quality surface finish.
Secondly, is the poor selection of coolant to use during the milling process. Some millers do not acknowledge the importance of selecting the right coolant for the task. They end up purchasing a simple and cheap option coolant that will not protect your tool. A good lubricant increases the quality of the surface finish achievable. Additionally, chances of tool overheating are lower, thus improving the tool life.
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Solution
We need to maintain the sharpness of the tool and use the correct coolant to achieve a smooth finish.
Dents After CNC Milling Tooling
Metals such as copper, aluminum alloys, brass, and bronze at times exhibit dents after tool clamping. It is due to their low hardness level when compared to other tougher metals.
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Cause
The principal cause is usually excessive clamping forces from the tooling. Especially for manual clamps that cannot gauge appropriately the clamping force. Other milling machines use pneumatic or hydraulic cylinders to create this clamping force.
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Solution
A great solution to prevent dents forming is the use of steel plates. We could place them in between the tooling jigs and the workpiece. The plates function in spreading the pressure evenly throughout the workpiece thus preventing part deformation. Furthermore, even with a large clamp force, the dents form on the steel plates instead. Alternatively, we could use special chunks and jigs that are softer. The chances of developing part deformation are much lower with their use.
Burn Marks Along the Surface of The Workpiece
A common defect resulting from CNC milling errors is getting burns on the surface of the workpiece. Burns occur when the workpiece becomes overheated. Sites on the workpiece that exhibit this defect include the material’s corners or edges. It exhibits itself as cutter marks on the surface, rough edges, or raised marks. Additionally, the tool wears faster than normal.
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Cause
The defects occur upon inputting the wrong cutting parameters. Especially choosing an improper combination of feed and speed ratio on the mill cutting machine. It usually results in causing workpiece damage and destruction of the cutting tool. Another cause is the wrong selection of tools for the job. The tool should be appropriate in dimensions, quality, and size for the workpiece.
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Solution
We can easily fix this defect by lowering the cutting speed to feed ratio. It makes the entire machining process slower thus decreasing the heat generated on the workpiece surface. Alternatively, we could increase the rate of cooling on the workpiece during milling. Both of these help in decreasing the chances of causing burn marks on the workpiece. Materials with poor heat conducting properties such as titanium can benefit from a combination of both techniques.
What’s The Final Conclusion?
CNC milling is a complex craft that requires the right partner to achieve a great outcome. Do not ruin your product by gambling on unqualified companies. At Creatingway, we have expert engineers ready to work on your important projects. Simply upload your CAD file to get started. For any inquiries concerning CNC milling services, contact us now.
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