Machining workpieces with long and slender shapes, such as shafts, is known to be prone to reduced dimensional accuracy, chatter, and vibration due to their low rigidity. Additionally, the chips generated during machining often wrap around the workpiece, leading to potential damage to the workpiece and cutting tools. This article explains the challenges of shaft turning and discusses key points to address these challenges for achieving high-precision shaft machining.
In the turning of shafts, challenges include the wrapping of chips around the workpiece, chatter and vibration, and variations in diameter dimensions.
When machining long workpieces such as shafts, chips generated during turning are prone to wrapping around the workpiece. This chip wrapping can lead to damage to the cutting tools and scratches on the workpiece, resulting in defective products.
With slender and long workpieces, the lack of sufficient rigidity leads to the occurrence of vibration and chatter. These can degrade the finish surface quality and reduce machining accuracy. In severe cases, it may even cause tool breakage or damage to the equipment.
In turning operations of low-rigidity, long workpieces like shafts, it is difficult to maintain stable machining, leading to variations in diameter dimensions and tapering at different measuring points. If the targeted dimensions and shapes cannot be achieved, it results in defective products, making it a challenging machining process from the perspectives of cost and productivity.
When turning difficult workpieces such as long, small-diameter shafts, it's necessary to select machining conditions tailored to the workpiece rather than using the same equipment and conditions as for other workpieces. For example, adopting measures such as using steadies, tailstock centers, high-pressure coolant, and selecting tools that consider chip management while minimizing cutting resistance that causes chatter are crucial. To resolve the challenges in shaft turning, the following points need to be considered:
To solve chip wrapping, using high-pressure coolant, selecting the right insert, and revising the machining path are effective measures.
Chips generated during turning that remain long and near the tool can cause wrapping around the tool. Adopting high-pressure coolant ranging from 7MPa to 15MPa can fragment the chips and remove them from near the tool, making tool wrapping less likely.
Various inserts are selected for turning, including those that can effectively fragment chips. By changing the breaker on the insert, chips can be shaped and fragmented.
Reviewing the machining path can also effectively avoid chip wrapping. For example, repetitive step machining or "low-frequency vibration cutting," which vibrates the tool synchronously with the spindle rotation in the cutting direction, can achieve chip fragmentation and efficient removal.
Solving chatter and vibration can be approached by selecting the right insert, reviewing cutting conditions, and using steadies or tailstock centers.
To suppress the machining resistance at the cutting point, which is a starting point for chatter and vibration, it's necessary to select the appropriate turning insert. Features of such inserts include positive inserts with relief angles, small nose radii, small edge angles, and inserts with low-resistance breakers.
Using steadies or tailstock centers is effective when machining long workpieces to prevent effects due to low rigidity. Steadies can prevent workpiece deflection in addition to chatter and vibration, contributing to improved dimensional accuracy.
Chatter and vibration can potentially be improved by reviewing cutting conditions. Important points during the review include reducing cutting speed and depth of cut to suppress vibration sources and monitoring spindle rotation changes during machining.
Solving variations in diameter dimensions at different measuring points when machining long workpieces can be effectively achieved through program corrections or adjusting rotational balance.
By measuring workpiece dimensions during machining and modifying the initially set program accordingly, it's possible to correct for variations in diameter dimensions.
Measuring the deflection that occurs when rotating the workpiece and adjusting the rotational balance based on these measurements can make variations in diameter dimensions less likely to occur.
This article explained the challenges during shaft turning and key points to achieve high-precision shaft machining. Shaft machining, being a difficult operation for slender and long workpieces, requires various adjustments including equipment and insert selection, machining conditions, programming adjustments, and the use of steadies or tailstock centers. By appropriately implementing these measures, it's possible to control challenges such as reduced accuracy, chatter, and vibration, allowing for successful shaft turning according to the target.
