CNC machining Tools, as the ultimate executing components in modern manufacturing, play a crucial role in the CNC machining process. The quality of their performance directly determines the machining quality and efficiency, which, in turn, affects the improvement of labor productivity and cost control in the manufacturing industry. Therefore, their significance in modern manufacturing is highly prominent.
Lathe cutting tools are tools used in the cutting process during the manufacturing of CNC machining shops. The cutting tool manufacturing industry refers to the production of interchangeable cutting tools for manual or CNC machines. Common components such as bearings and gears are inseparable from the use of lathe cutting tools, and in conjunction with CNC machining centers, they can complete the production of various precision equipment.
What are Lathe Cutting Tools?
Lathe cutting tools are tools with cutting portions used for CNC turning. They are one of the most widely used tools in CNC machining. The working part of lathe cutting tools is the section responsible for generating and processing chips, including the cutting edge, the structure for breaking or curling chips, space for chip evacuation or storage, and channels for cutting fluid.
Types of Lathe Cutting Tools
Based on their purpose, lathe cutting tools are essentially divided into two types:
- According to the method of tool usage.
- According to the method of feed.
A) According to the method of tool usage.
Thread Cutting Tools
- External Thread Cutting Tools – External thread cutting tools, also known as thread cutting tools, are defined as tools used for machining external threads on workpieces.
- Internal Thread-Cutting Tools – Internal thread-cutting tools are defined as tools used for machining internal threads within workpieces.
Chamfering tools can be defined as tools used to create bevels or grooves on bolts. These tools are employed to chamfer the corners of workpieces. When a significant amount of chamfering work is required, specific chamfering tools with side cutting angles are used.
Roughing turning Tool – Roughing turning tools are used to rapidly remove a large amount of metal within the shortest possible time. They feature a clear-cutting angle and can withstand the maximum cutting forces.
Finish turning Tool – A finish turning tool is used to remove a small amount of metal. The cutting angles are also polished to produce a very smooth and precise surface.
Grooving tools are essentially defined as tools used to create narrow slots of a certain depth on the conical, cylindrical, or flat surfaces of a part. In this case, the specific shape of the grooving tool is chosen based on the geometry of the groove being cut, whether it’s square, circular, and so on.
Face Milling Tools
Face milling tools can be defined as tools used for cutting the plane perpendicular to the axis of rotation of the workpiece. These face milling tools are supported by a tool holder fixed on the machine frame. They are used to reduce the length of the workpiece by providing a cut that is perpendicular to the lathe axis. The cutting edges of the tool should be set at the same height as the center of the workpiece.
Boring tools are lathe tools used for enlarging holes. When you need to widen an existing hole, you use a boring bar. Boring bars can easily enter a pre-drilled hole and increase its diameter. They are used to quickly enlarge holes to the correct size for proper installation of other components.
Forming tools can be defined as tools used to create different types of workpiece shapes. In this case, special types of inserts or holders are used to secure the forming tools. This allows us to perform various types of operations, such as creating inner radii, outer radii, and more.
Back Boring Tools
Back boring tools can be defined as tools used for enlarging and locating the socket head of a screw or bolt. This tool has two radii: A) Creating pre-drilled holes B) Boring on the workpiece
Reaming tools are defined as tools used for precision machining and ensuring dimensional tolerances on holes that have been drilled or bored.
Bottom cutting Tools
Bottom cutting tools are similar to grooving tools. In this case, bottoming tools are used to bore larger holes within a fixed distance from the hole’s end. Bottoming cutting is primarily performed on internal threads to achieve clearance.
Drilling tools are also crucial tools in a lathe. Drilling tools are primarily used for machining cylindrical holes in a given workpiece. In this case, the workpiece is secured on the faceplate, and the drill bit is fixed in the tailstock drilling frame, with the hole being completed through the movement of the tailstock spindle. This is suitable for workpieces with regular shapes.
B）According to the method of feed
Round Nose Tools
Round nose-cutting tools can be defined as tools used for finishing machining. Round nose tools have no side or back angles and can perform cutting in various directions. They usually have three types, Round nose grooving, round nose turning, and Round corner Forming.
Right-Hand Cutting Tools
Right-hand turning tools remove material when moving from right to left (as viewed from above, with the front cutting edge at the top). The name “right-hand tool” is used by analogy to a person’s right hand, where the thumb represents the tool’s feed direction. Therefore, the main cutting edge of the tool is positioned on the left side of the tool.
left-hand Cutting tools
Unlike right-hand turning tools, left-hand tools remove material when moving from left to right (with the front cutting edge visible in the top view). When using the left hand, the thumb represents the tool’s feed direction. Therefore, the main cutting edge of the tool is on the right side of the tool
How to Choose the Right Lathe Cutting Tools
Choosing lathe tools requires an understanding of certain factors related to the equipment. Here are some very important factors you must consider when selecting lathe tools:
Type of Material
The type of material you are cutting is a fundamental factor in determining the types of lathe cutting tools you can use. Important attributes to consider before selecting cutting tools include hardness, wear resistance, toughness, and rigidity. These attributes play a significant role in the types of lathe cutting tools that are suitable. For example, extremely hard materials may require carbide or diamond cutting tools.
The shape of lathe cutting tools is another factor to consider when making your selection. The position of the cutting edge also determines the cutting direction of the tool (right-hand tools, left-hand tools, and round nose tools).
Each type of lathe cutting tool listed under the categories can result in specific shapes. Therefore, you must integrate the desired shape into the required cutting tool. Due to the complexity of most CNC machining projects, you may need to choose a combination of lathe cutting tools.
Composition of Lathe Cutting Tools
The cutting portion of a lathe tool consists of the main cutting edge, secondary cutting edge, front cutting face, primary rear cutting face, secondary rear cutting face, and the tool tip angle. The combination methods of the cutting part and the shank (i.e., the clamping part) of the lathe tool mainly include integral, welding, mechanical clamping, and welding-mechanical clamping types.
Mechanical clamping lathe tools can prevent stress and cracks in hard alloy blades during high-temperature welding, and the tool handle can be reused multiple times. Mechanical clamping lathe tools are generally tightened with screws and pressure plates, and they are used to hold indexable inserts. The blade can be indexed and reused after dulling, and the tool change time is short, which has led to rapid development.
Parameters for Using Lathe Cutting Tools in Engineering
Cutting Speed (Vc)
Definition of Cutting Speed: Vc = N * p * Deff / 1000
Vc refers to the suitable cutting speed value for high-speed machining of a specific workpiece material with a particular tool. It represents the linear velocity of the tool.
Effective Tool Diameter (Deff)
Effective tool diameter and the calculation of effective tool diameter as below picture.
Feed per Tooth (fz)
The definition of feed per tooth is as shown in the picture
Selection of Back Cutting Amount
In rough machining, apart from leaving finishing allowances, the goal is to remove as much material as possible in one pass, but multiple passes can also be used. Finishing machining usually involves smaller allowances and can be removed in a single pass. On medium-power machine tools, the back-cutting amount in rough machining can be up to 8-10 mm; for semi-finishing, a back cutting amount of 0.5-5 mm is typically used; for finishing, a back cutting amount of 0.2-1.5 mm is common.
Determination of Feed Speed (Feed Rate)
In rough machining, where surface quality requirements are not high, the feed speed is primarily chosen based on factors such as the strength and rigidity of the machine tool’s feed mechanism, the strength and rigidity of the tool holder, tool material, tool holder, workpiece size, and the selected back cutting amount. In finishing machining, feed speed is selected based on factors such as surface roughness requirements, tool and workpiece materials, and so on. The feed speed (Vf) can be calculated using the formula Vf = f × n, where f represents the feed per revolution. In rough turning, f is generally in the range of 0.3-0.8 mm/r, for fine turning, it is often in the range of 0.1-0.3 mm/r, and for parting-off, it is typically in the range of 0.05-0.2 mm/r.
Axial and Radial Feed Rates (ap & ae)
The calculation of axial feed rate is as shown in the picture:
In the actual machining process, it is beneficial to have a good understanding of CNC machining and CNC turning processes, along with practical experience. This will make it easier for you to choose the type of cutting tools for your machining needs.
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CNC turning is a versatile and precise manufacturing technique, ideal for various industries and large-scale production. This article has provided you with a comprehensive understanding of the process, enabling informed decisions for your fabrication needs.
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