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U drills are drilling tools that contain hard alloy cutting inserts. They are characterized by convenience of use and high cost-effectiveness. To facilitate the machining of various materials, we provide U drills of different types and sizes.
Table of Contents
Application Background Of U Drill
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Compared with solid drills,U drillsare tooling that performs hole machining by combining inner and outer cutting edges formed by a center bit (inner edge) and peripheral bits (outer edge). This structural characteristic determines the irreplaceable advantages of U drills over other drilling tools.
Advantages Of U Drill
- The difference between a U drill and a regular drill is that a U drill uses peripheral cutting inserts and a center insert. When the inserts wear out, they can be replaced directly without resharpening. Using indexable inserts is more material-saving than solid carbide drills, and insert consistency makes it easier to control workpiece dimensions.
- U drills have better rigidity and can use very high feed rates. The maximum machining diameter of a U drill is much larger than a regular drill, up to D50~60mm. Of course, due to how inserts are mounted, U drills cannot be made too small.
- For different materials, only the insert type and grade need to be changed. This is more convenient than solid carbide drills.
- Hole accuracy of U drilling is generally better than solid carbide drilling, with better surface finish, especially under insufficient lubrication conditions. U drills can also correct hole positional accuracy, which solid carbides cannot do.
Advantages Of U Drill In CNC Machining
- U drills can drill holes on surfaces with inclination angles of less than 30° without reducing cutting parameters.
- After reducing cutting parameters by 30%, U drills can perform discontinuous cutting such as drilling intersecting, through, or counterbored holes.
- U drills can machine multi-step holes and cored holes, ream, chamfer, and eccentric drill holes.
- Chip formation during U drilling is mostly short and broken chips, which can be safely removed via internal cooling, without needing to clean-cutting residues off the tool. This improves workpiece processing continuity and reduces processing time.
- When standard bore-to-diameter ratios are met, no chip evacuation is needed during U drilling.
- U drills are indexable tools. When inserts wear out, no resharpening is required – only replacement, which is more convenient and cost-effective.
- U drilling produces holes with smaller surface roughness values and tolerance ranges, substituting some reaming operations.
- U drilling does not require pre-drilling center holes. Blind holes have a smoother bottom surface, eliminating the need for bottoming drills.
- Adopting U drilling technology reduces the number of machining tools needed and increases tool life by 10-15 times compared to regular drills since U drills use solid carbide-tipped head inserts. Each insert also has four cutting edges, allowing easy edge changing when worn to further save resharpening and replacement time and improve efficiency by 6-7 times on average.
Techniques For Using U Drill On CNC Machine Tools
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- U drills require high rigidity of the machine tool and tool-workpiece centration, so they are suitable for use on large power, high rigidity, and high-speed CNC machine tools.
- When using U drills, select inserts with good toughness for the center insert, and sharper inserts for the peripheral inserts.
- For different materials, select inserts with different chip slot shapes. Generally for small feeds, small tolerances, and larger bore-to-diameter ratios, use inserts with smaller cutting forces; whereas for roughing, large tolerances, and smaller bore-to-diameter ratios, use inserts with larger cutting forces.
- Always consider the machine spindle power, U drill clamping stability, coolant pressure, and flow rate during use, and control chip removal to avoid affecting hole surface roughness and dimensional accuracy.
- Ensure the U drill center coincides with and is perpendicular to the workpiece surface during clamping.
- Select suitable cutting parameters according to the workpiece material.
- During trial cutting, do not carelessly reduce feed rates or lower speeds to avoid breaking or damaging the U drill insert or tool.
- When inserts show wear or break during use, analyze the reasons carefully and replace them with more tough or wear-resistant inserts.
- When machining multi-step holes, start with larger holes and then process smaller holes.
- Ensure sufficient coolant pressure to flush chips during U drilling.
- Do not mix up inserts for the center and periphery of U drills, otherwise, the U drill shank may be damaged.
- When drilling with a U drill, workpiece rotation, tool rotation, or simultaneous rotation can be used; but linear feed is commonly used with workpiece rotation.
- Consider the machine’s capability during CNC machining and appropriately adjust cutting parameters, usually lowering speeds and feeds.
Common Problems With U Drill In CNC Machining
- Insert breakage or damage occurs too quickly, increasing machining costs.
- Abnormal screaming sounds during machining, indicating an abnormal cutting state.
- Machine tool vibration affects machining accuracy.
Important Points For Using U Drill
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- Pay attention to the correct installation direction – which inserts faces up, down, inside, and outside.
- Center height must be calibrated within a control range of generally 0.1mm depending on diameter. Smaller diameter U drills have higher center height requirements. Improper center height can cause uneven insert wear, oversized holes, and reduced insert life.
- U drills have high coolant requirements – coolant must reach the center and pressure is better with higher pressure. Excess coolant ports can be blocked to ensure pressure.
- Follow manufacturer cutting parameters considerations but also consider different insert brands and machine power. Reference machine load during machining and make suitable adjustments, generally using high speeds and low feeds.
- Inspect and timely replace inserts. Do not reverse inserts.
- Adjust the depth of the cut based on workpiece hardness and insert overhang length. Harder workpieces use greater overhang lengths and smaller depths of cut.
- Do not use excessively worn inserts. Record insert wear vs. machinable workpiece quantities and timely replace inserts.
- Use adequate, correctly pressurized internal coolant. Its primary functions are chip removal and cooling.
- U drills are not suitable for softer materials like purple bronze or soft aluminum.
What Are The Two Most Important Performance Evaluation Indicators For U Drills?
Rigidity and chip removal ability. Rigidity is increased through helical oil groove design, and chip removal is improved by enlarging the inner cutting-edge chip groove and other technologies to enhance U drill performance.
How Can U Drill Rigidity Be Improved?
Manufacturers increase rigidity through designs like helical oil grooves and thicker shanks. The Kyocera DRX series enhances rigidity by 33% using a thicker shank.
How Is Chip Removal Addressed?
Features like varied chip grooves, and the DRV’s focus on micro-cutting outer chips and lightweight inner chips help promote effective chip evacuation during machining.
What Problems Can Occur With U Drills?
Potential issues include bit wear/breakage, heat/friction problems, difficulty with large cuts/clogging, and low accuracy due to lack of rigidity.
Conclusion
U drills combine inner and outer cutting edges via interchangeable inserts. This modularity enables multi-material and size machining. The main advantages are high efficiency, low cost, and ease of use without re-sharpening. U drills provide versatility compared to solid drills through their modular design. When operated correctly, U drills enable efficient and cost-effective homemaking as a CNC tooling option.