Machining vibration occurs in almost all manufacturing processes. The heavy machines used in manufacturing generate strong vibrations, resulting in poor surface finish and deterioration in dimensional accuracy.
Machine operators have to deal with these unwanted vibrations during various processes such as CNC turning, milling or drilling. However, it is useful to understand machining vibrations, their causes and how to avoid them, as this will help avoid downtime, which is terrible for businesses.
This article explains the definition of chatter, its types, consequences, and how to avoid it.
What is machining vibration?
Machining vibration is the unwanted vibration that occurs when cutting or drilling parts. Vibration is caused by the vibration imbalance of the workpiece and tool repeatedly moving relative to each other. Vibration occurs when the machined part and the cutting tool move in opposite directions, resulting in a different cutting load on the machining tool per revolution.
This may be due to incorrect design for manufacturing or inappropriate tooling. Vibration often produces loud noises and visible ripples on the surface of machined components. Machining vibration occurs in two ways, namely:
- Resonance vibration
- Non-resonant vibration
Non-resonant vibrations arise from the use of tools with uneven wear on workpieces. These vibrations are often constant throughout the machining cycle and have mechanical causes that are easy to investigate.
On the other hand, resonance vibrations occur at certain phases of the tool path, for example when machining concave corners.
Types of vibration during machining
There are two main types of vibration that can occur in CNC machining. This includes the following:
Tool Talk
Generally, CNC milling machines vibrate during the cutting process. They start cutting while transmitting vibration to the piece, adding several functions. As a result, the tool and workpiece begin to slip against each other, causing chatter to increase significantly.
Workpiece conversation
If you incorrectly clamp the workpiece on the milling machine worktable, it can sometimes cause shifting and vibration. As a result, the thin wall of the part may begin to vibrate as it passes through the cutting tool.
It's important to note that some rattling noises are often unavoidable. If the vibration that occurs during machining is greater than 100 µm, your part may suffer surface scratches. However, it would be better if you did something about tool and workpiece vibration to improve the quality of your product. Below we will discuss how to avoid conversations.
What are the consequences of chatter during machining?
If machining vibration is not controlled, it can cause various adverse effects, such as reducing machining efficiency. Here are some of them:
Reduced tool life
Cutting tools cannot withstand the vibratory shock of the tool hitting the workpiece. These shocks can chip and dull the cutting tool, affecting the surface quality of the cut pieces. It also reduces tool life and cutting performance, and tool replacement is expensive.
Reduced machine life
The machine tool used in machining different components is made up of different parts, therefore, when vibrated, these components will vibrate at the same frequency. The spindle and other important elements that create the various axes of motion may wear out more quickly than expected. As a result, a machine's vibration puts excessive pressure on the machine's components. If left unchecked, it may reduce machining efficiency and cause downtime.
Poor surface finish
Chatter during machining affects the aesthetic properties of the part and can reduce its tolerances in extreme situations. One of the most obvious consequences of machine vibration is low surface roughness. Vibration causes visible ripples on the surface, affecting the quality and durability of the part.
Reduced dimensional accuracy
When a cutting tool vibrates during CNC machining, it deviates from the path initiated by the CAM. However, this variation may result in the pieces not fitting together correctly. These pieces may be too tight, too long, too short, or too loose due to inaccurate dimensions.
How can vibration be avoided or minimized during machining?
Manufacturing companies use several methods to minimize vibration during machining operations and ensure that parts and cutting tools are in good condition. Here are some of those steps to reduce vibration in CNC machining:
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In conventional milling, the degree of engagement of the cutter with the part varies. During movement along the path, excessive force is periodically applied to the cutter. Therefore, the best way to reduce chatter is to get regular engagement in the tool path. Alternatively, you can reduce the cutting depth.
Also try rethinking the spindle configuration. For example, if resonant vibrations are the cause of machining vibration, increase or decrease the machine speed by 5% to minimize the resonant vibrations that occur. Note that some CAM software has features that allow you to constantly vary spindle speeds. Most manufacturers use this feature because of its versatility.
Choose the correct working posture
Balanced machine tools are characterized by better fit. Several factors, such as incorrect positions and fixtures, are the main causes of chatter in CNC machining. However, the end-faced tool holder and belt contact helps ensure maximum rigidity during machining. This means that the surface quality of the components is not affected, even at the lowest speeds.
You also need to check that the machine's vise, vacuum table, chuck, or other clamping device applies enough pressure to the workpiece to keep it tight and in place.
However, if you want to use jigs and fixtures to apply the necessary clamping pressure, do not clamp just one end of a long, thin piece. Parts with thin walls have difficulty absorbing shocks. Therefore, filler materials improve its overall rigidity and reduce chatter. A tailstock or similar form of stable support structure is an ideal option for such components.
Use the correct cutting tool
Using the correct cutting tool helps prevent vibrations during machining. Some cutting tools produce more vibration than others. It is not as easy to prevent tool vibrations as it is with a workpiece. Therefore, when choosing a tool, you must consider the following factors:
- Coating a tool
- Correct substrate geometry
- The aspect ratio of a tool
Machinists and engineers generally use the largest appropriate machine tool as long as it meets technical specifications. The more stable a mower is, the less it vibrates. Long or thin tools often bend. Therefore, consider choosing shorter, larger diameter tools.
However, the most effective method for minimizing chatter during machining is to combine different tools with different groove shapes. Also consider reducing tools that protrude from the holder and securing them securely. After this, vibration is less likely to occur in the machine.
Make sure your cutters have sharp blades that minimize the cutting force of CNC routers. You should always consider the stability of the processing environment and timely maintenance of the cutter. It is also important to apply the correct and consistent pressure on the tool so that the chip load is uniform.
Determine the optimal tool path
There are two types of CNC milling operations: up milling and down milling. Applying cutting force in the same direction as the clamping can reduce chatter of curved parts. This is often an essential aspect of the cut that needs to be taken into consideration.
Generally, CNC routers have pre-installed ball screws, which improve the efficiency and accuracy of CNC machine technology. Therefore, you can use a vertical machining center to avoid vibrations during the cutting process.
Machine adjustment and maintenance
As expected, your CNC machine should be installed on a concrete floor without cracks, deformations or inconsistencies. You should know that the layout of your machine plays a crucial role in minimizing vibrations that occur during machining.
This is because elastic, soft, or damaged flow can increase the vibration of a CNC unit. Therefore, you should consider using anchors and leveling feet to keep the CNC unit firm and stable and minimize shaking.
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During machining operations, various small problems such as chatter are always difficult to avoid as they can affect the final result. In these cases, you need a CNC machining expert to help you.
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Chatter is a machining effect that results in significant loss of productivity. It affects machine performance, workpiece quality, cutting tool and machine tool life. Several factors contribute to its occurrence, from the machine installation location to the tool path.
However, if you notice strong vibrations, investigate the problem thoroughly. To effectively eliminate this chatter, ensure that the tool and workpiece are clamped correctly and that the configured machining options are correct.
Common questions
What are chatter marks during machining?
Chatter marks are irregular surface defects caused by a grinding wheel that is out of rotation during grinding. When turning a long workpiece on a lathe, regular marks are created due to machining vibrations.
What causes vibration during machining operations?
The cutting forces created during cutting increase significantly if your machine tool experiences excessive wear. Increased cutting forces typically result in chatter when cutting rigid substrates.
What causes vibrations in rotating equipment?
The most common causes of shaking or vibration in rotating equipment are misalignment, imbalance, wear and play. Imbalance of a heavy area within a rotating component results in vibration as the unbalanced weight rotates around the machine's axis, creating a central force.
How do I recognize vibrations during machining?
Vibration from a CNC machine is often audible. An experienced machine operator can therefore recognize when vibration occurs based on the characteristic noise. Furthermore, chatter during machining leaves visible ripple marks on the surface of the workpiece.
