10 Questions You Should to Know about Indexable Drill Inserts

U drill, one of the most commonly used tools for hole processing, is usually called by different names, such as shallow hole drill, water jet drill, violent drill, fast drill, T-drill, insert drill, etc. The standard name should be indexable insert drill or machine chuck drill. The term “U-drill” originates from the Sandvik Coromant T-MAX U-drill, which was then widely circulated in the industry and gradually evolved into a common name.

Link to Guangzhou Ruiyi Technology Co., Ltd.

What are the types of inserts used in U-drills?

There are several common types of SPMG, SOMT, WCMT, WCMX, the specific data can refer to the following table.

Types WC, SP and SO are the most commonly used U drill inserts in metalworking. Drilling operations are well suited for the use of indexable insert drills because they reduce the time required for tool changes. The technique of using u drills as roughing is very successful. Deeper cavities or holes can be created by making multiple axial cuts with a drill or milling cutter. This method is particularly suitable for roughing. Since the main cutting forces are concentrated axially along the spindle, it is energy-efficient, effective and reduces the requirements on the machine spindle. Drilling holes for the insert drilling tool is the first step in the internal insert milling process. The unique chipbreaker has a one-of-a-kind design incorporating corrugated edges. This ensures both high edge strength and effective chipbreaking.

Tips for machining with U drill inserts

Irregular surface drilling

• Use shortest drill possible to minimize vibration tendencies and decrease the effects of deflection
• Recommended start values for cutting speed and lowest recommended feed
• Not recommended for 6–7×DC when concave radius is same or smaller than drill radius

Pre-drilled holes

Cross hole drilling

Drilling inclined entrances/exits

Generates uneven and excessive forces acting on the cutting edges

• Intermittent cutting as the drill enters/exits the workpiece
• Increases chance of vibration
• Can distort the drilling profile
• Causes more tool wear than conventional drilling

General recommendations:

• Stability is crucial. A small length to diameter ratio will help to keep the tolerances
• Milling a small flat surface is recommended when entering workpieces with a large inclination

Angled or inclined surfaces, entry

Angled or inclined surfaces, exit

Drilling asymmetrically curved surfaces

How U drill inserts work and what applications they have

The U drill, also known as a drill with indexable inserts, is a tool primarily used for high-efficiency hole drilling in various materials. Below is a detailed explanation of how a U drill works:

1. Components and Structure

• U Drill Body: This is the main part of the U drill, typically made from a robust material. It has two insert seats: one near the center and one at the periphery. These seats hold the replaceable inserts (cutting edges).
• Inserts: U drills use two indexable inserts: the center insert and the peripheral insert. The center insert cuts the material at the core of the hole, while the peripheral insert cuts the outer edges. The outer insert generally does more work as it handles a larger cutting surface.

2. Cutting Process

• Dual Cutting Action: As the U drill rotates at high speeds, both inserts engage the workpiece simultaneously. The center insert cuts the inner part of the hole, and the outer insert cuts the outer diameter. This combination makes the U drill highly efficient because the cutting load is distributed across two inserts.
• Coolant System: U drills are typically designed with internal coolant channels. Coolant flows through these channels and directly cools the cutting zone, reducing heat and friction. It also helps to flush chips out of the drilled hole.

3. Drilling Operation

• Alignment and Positioning: Before drilling, the workpiece is firmly clamped on the machine table or fixture. The U drill’s center is aligned with the intended hole location, either through CNC programming or manual positioning.
• Initiating the Cut: The machine spindle rotates, and the U drill begins to move into the workpiece. The center insert starts the cutting by drilling the core, followed closely by the peripheral insert. As the tool penetrates deeper, both inserts continue to remove material efficiently.
• Chip Evacuation: As material is cut away, chips are generated. These chips are expelled from the hole by the combined action of the rotating inserts and the internal coolant, which helps clear the chips and prevents clogging.
• Completion of Drilling: Once the U drill reaches the programmed depth, the tool retracts, leaving behind a finished hole. Due to the high precision of the inserts and the tool body design, the hole is usually accurate and requires no further reworking.

4. Advantages of U Drills

• High Efficiency: Since the U drill uses two inserts to cut simultaneously, it operates at much higher speeds and feeds compared to traditional drills, reducing cycle time.
• Precision: The design of the U drill ensures accurate hole diameters, often eliminating the need for additional finishing operations like boring or reaming.
• Coolant Efficiency: The built-in coolant channels keep the inserts cool during high-speed drilling, reducing wear and extending tool life.

5. Operating Considerations

• Insert Selection: It’s essential to choose the right insert material and geometry based on the workpiece material (e.g., steel, aluminum, cast iron). Using the correct inserts ensures smoother cuts and prolongs tool life.
• Cutting Parameters: The drilling speed and feed rate should be adjusted according to the material and depth of the hole. If the feed rate is too high, it can cause excessive wear or damage to the inserts.
• Coolant Flow: Ensure the coolant system is properly set up and functioning. Insufficient coolant can lead to overheating and premature tool failure.

What Are U Drill Inserts and Why Are They Popular?

U drill inserts are cutting tools used in indexable U drills, specifically designed for high-efficiency hole drilling. These inserts are typically made from carbide or other hard materials, which are capable of withstanding high cutting speeds and temperatures. They are replaceable, meaning once an insert becomes dull, you can swap it out instead of replacing the entire drill, making them cost-effective.

 why U drill inserts are popular:

High Efficiency: U drills with inserts can drill holes much faster than traditional twist drills because they cut using two inserts simultaneously—one for the hole center and one for the perimeter. This reduces machining time significantly.

Cost-Effective: Since the inserts are replaceable, the overall tooling cost is reduced. Instead of replacing an entire drill, you only need to replace the worn inserts.

Versatility: U drill inserts can be used on various materials such as steel, stainless steel, cast iron, and non-ferrous materials. Different insert geometries and coatings are available to suit different applications.

Precision: U drill inserts provide high precision when drilling, often creating holes with minimal need for secondary finishing operations like boring or reaming.

Coolant Delivery: Many U drills are designed with internal coolant channels that cool the inserts during drilling, improving tool life and chip evacuation.

Important Considerations When Using U Drill Inserts

To ensure optimal performance when using U drill inserts, several factors need to be taken into account:

1. Insert Material Selection

Choose the correct insert material (carbide, coated carbide, etc.) based on the workpiece material. Different materials require specific inserts to achieve the best results. For instance, tougher inserts may be needed for drilling through hard steels, while softer materials like aluminum may require a more specialized insert geometry.

2. Cutting Speed and Feed Rate

The cutting speed and feed rate should be appropriate for the workpiece material and insert type. Excessive feed rates can cause insert failure, while too low feed rates may result in poor chip formation or excessive heat buildup.

Consult the manufacturer’s guidelines for recommended speeds and feeds, adjusting based on material hardness and depth of hole.

3. Coolant Management

Ensure that coolant is properly directed to the cutting zone. Coolant helps to reduce heat, prevent tool wear, and aid in chip evacuation. U drills often come with internal coolant channels, but you must ensure these channels are functioning correctly.

Using insufficient coolant or having a blocked coolant passage can lead to overheating, reduced tool life, and poor hole quality.

4. Proper Insert Installation

Make sure the inserts are properly seated and secured in the U drill body. Improper installation can lead to insert shifting, poor hole quality, or even damage to the tool body.

Periodically check for insert wear and replace inserts when they are dull to avoid damaging the workpiece or tool.

5. Chip Evacuation

Monitor chip evacuation during the drilling process. Poor chip removal can cause chips to clog the hole, leading to tool failure, overheating, or workpiece damage.

Adjust feed rates or coolant flow if chips are not being effectively removed from the hole.

6. Hole Depth and Accuracy

U drills are ideal for producing holes quickly, but accuracy can vary depending on the setup and material. For deep holes, ensure proper alignment of the U drill to avoid deviation, which can lead to tapered or out-of-round holes.

7. Insert Wear Monitoring

Keep track of insert wear during use. Worn inserts can negatively affect hole quality and may also cause excess heat, increasing the risk of breakage or damage to the workpiece.

Regular inspections and timely insert changes are essential to maintain hole quality and extend tool life.

By following these guidelines and using the right insert for the application, you can maximize the efficiency, cost-effectiveness, and precision of U drills in your machining operation

Conclusion

The U-drill is a drilling tool containing carbide inserts characterized by ease of use and cost-effectiveness. In order to facilitate the machining of a wide range of materials, ONMY U-drill inserts are available in a variety of types and sizes.ONMY U-drill inserts offer an energy-saving and efficient solution, in addition to a high metal removal rate. For high quality U-drill inserts, contact ONMY! Contact us and we will be happy to answer any questions or concerns you may have.

Coolant supply tips and tricks

Having a correct coolant supply is crucial in order to achieve successful performance in drilling. The coolant supply influences:

• Chip evacuation
• Hole quality
• Tool life

The coolant tank volume should be between 5-10 times larger than the volume of coolant that the pump supplies per minute. It is important to have sufficient coolant flow.

The volume capacity can be checked using a stop-watch and a suitably sized bucket.

Pressure-diameter relationship in cutting fluid supply
(pressure in red, diameter in yellow, volume in blue)

Check the volume coming out from the drill

• Soluble oil (emulsion) should always be used with EP (extreme pressure) additives. The mixture of oil and water should be between 5-12% oil for best tool life (10-15% for stainless steels and heat resistant alloy materials). When increasing percentage of oil in cutting fluid, always check with the oil distributor to be sure to not exceed recommended percentages of oil
• Internal coolant supply is always favourable, when applicable, as compared to externally applied
• Neat oil improves lubrication and is beneficial when drilling stainless steels. Always use with EP additives. Both solid carbide drills and indexable insert drills work well with neat oil
• Compressed air, mist cutting fluid or MQL (Minimum Quantity Lubrication) can be successful under favourable conditions, especially for some cast irons and aluminium. Reduced cutting speed is recommended due to elevated temperatures which in turn can negatively impact tool life

Internal coolant

Internal coolant is always preferred to avoid chip jamming, especially in long chipping materials and when drilling deeper holes (>3 x DC).

A horizontal drill should have a flow of coolant coming out of the drill without any downward drop for at least 30 cm (11.81 inch).

External coolant

External coolant supply can be used when chip formation is good and when hole depth is shallow. To improve chip evacuation, at least one coolant nozzle (two if drill is stationary) should be directed closely to the tool axis.

Dry drilling tips, without coolant

Dry drilling is generally not recommended.

• Can be used for short-chipping materials at hole depths up to 3 times the diameter
• Preferably in horizontal applications
• Reduced cutting speed is recommended
• Tool life will be reduced

It is never recommended to use dry drilling for:

• Stainless materials (ISO M and S)
• Exchangeable-tip drills

High pressure coolant (HPC) (~70 bar)

The benefits to using high pressure coolant are:

• Longer tool life due to improved cooling effect
• Improved chip evacuation and possibly tool life in long-chipping materials such as stainless steels
• Improved security due to better chip evacuation
• Provides sufficient flow for a given pressure and hole size to maintain delivery

Chip control tips

Chip formation and chip evacuation are critical issues in drilling and depend on the workpiece material, choice of drillI/insert geometry, coolant pressure/volume, cutting data.

Chip jamming can cause radial movement of the drill and consequently affect hole quality, drill life and reliability, or drill/insert breakages.

Thicker and stiffer chips SpeedMore open due to less friction Feed

Chip formation is acceptable when the chips can be evacuated from the drill without disturbance. The best way to identify this is to listen during drilling. A consistent sound means that chip evacuation is good, but an interrupted sound indicates chip jamming. Check the feed force or power monitor. If there are irregularities, chip jamming can be the reason. Look at the chips. If they are long and bent, instead of curled, chip jamming has occurred. Look at the hole. If chip jamming has occurred, an uneven surface will be visible.

A hole with good chip evacuation

A hole affected by chip jamming

Tips to avoid chip jamming:

• Make sure the right cutting data and drill/tip geometry is used
• Inspect chip form – adjust feed and speed
• Check the cutting fluid flow and pressure
• Inspect the cutting edges. Long chips can be caused by damages/chipping on the cutting edge when the entire chip breaker is not engaged
• Check if machinability has changed due to new workpiece batch – adjust cutting data

Excellent, acceptable and unacceptable chips

Indexable insert drills

The central insert forms a conical chip that is easy to identify. The peripheral insert forms a chip similar to that formed by turning.

Central stripPeripheral chip

Excellent

Excellent

Acceptable

Acceptable

Chip jamming

Chip jamming

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Solid carbide drills

One chip is formed from the centre to the periphery of the edge.

Excellent

Acceptable

Chip jamming

Start chip

Note: The start chip from entering into the workpiece is always long and does not create any problems.

Exchangeable-tip drills

Excellent

Acceptable

Unacceptable, risk for chip jamming

Tips and tricks for feeds and speeds

vc (m/min)

fn (mm/r)

Effects of cutting speed – vc (m/min(ft/min))

Cutting speed is the main factor, along with material hardness, that affects tool life and power consumption.

• Cutting speed is the largest factor determining tool life
• Cutting speed affects the power Pc (kW) and torque Mc (Nm)
• Higher speed generates higher temperature and increased flank wear, especially on the peripheral corner
• Higher speed is beneficial for chip formation in certain soft, long-chipping materials, i.e. low carbon steel
• Too high cutting speed:
  - Rapid flank wear
  - Plastic deformation
  - Poor hole quality and bad hole tolerance
• Too low cutting speed:
  - Built-up edge
  - Bad chip evacuation
  - Longer time in cut

Effects of feed – fn (mm/r(in/r))

• Influences chip formation, surface finish and hole quality
• Affects the power Pc (kW) and torque Mc (Nm)
• High feed affects the feed force Ff (N), to be considered when conditions are unstable
• Contributes to mechanical and thermal stress
• High feed rate:
  - Harder chip breaking
  - Less time in cut
  - Less tool wear but increased risk for drill breakages
  - Reduced hole quality
• Low feed rate:
  - Longer, thinner chips
  - Quality improvement
  - Accelerated tool wear
  - Longer time in cut

When drilling a thin/weak component, the feed rate should be kept low.

Tips for achieving good hole quality

Chip evacuation

Make sure chip evacuation is satisfactory. Chip jamming affects hole quality and reliability/tool life. Drill/insert geometry and cutting data are crucial.

Stability, tool set-up

Use the shortest possible drill. Use a rigid and accurate tool holder with minimum run-out. Make sure the machine spindle is in good condition and is well-aligned. Ensure component is fixed and stable. Establish correct feed rates for irregular, angular surfaces and cross holes.

Tool life

Check insert wear and establish pre-determined tool life program. The most effective way to supervise drilling is by using a feed force monitor.

Maintenance

Change insert-clamping screw regularly. Clean the tip seat before changing insert and make sure to use a torque wrench. Don’t exceed maximum wear before regrinding solid carbide drills.

Drilling tips and techniques for different materials

• Low carbon steel
• Austenitic and duplex stainless steels
• CGI (Compact Graphite Iron)
• Aluminium alloys
• Titanium and Heat Resistant Alloys
• Hard steels

Drilling low carbon steel tips

Issue: Chip formation can be a difficult issue with low carbon steels, which often are used for welded components. The lower the hardness, carbon and sulphur content of the steel, the longer the chips are that will be produced.

Recommendations: If problems with chip formation occur, increase the speed, vc, and decrease the feed, fn (note in normal steels, the feed should be increased).

Other: Use high pressure and internal coolant supply.

Drilling austenitic and duplex stainless steel tips

Issue: Austenitic, duplex, and super duplex materials can cause problems with chip formation and evacuation.

Recommendations: The correct geometry is crucial as it enables chips to form properly and aids their evacuation. In general terms, a sharp cutting edge is preferable. If problems with chip formation occur, increasing the feed, fn will allow the chips to break more easily.

Other: Internal coolant, high pressure.

Drilling CGI (Compact Graphite Iron) tips

Issue: CGI does not normally require extra attention. It produces larger chips than grey cast iron, but they are well broken. Cutting forces are higher, which affects tool life. Extra wear resistant grades are necessary. Corner wear is typical as in all cast irons.

Recommendations: If problems with chip formation occur, increase the speed, vc, and decrease the feed, fn.

Other: Internal coolant.

Drilling aluminium alloy tips

Issue: Burr formation and chip evacuation can be a problem. Poor tool life can also be present due to adhesion.

Recommendations: For best chip formation, use low feed and high speed.

In order to avoid poor tool life it may be necessary to test different coatings, minimizing adhesion. These coatings could include diamond coatings or certain cases (depending on the substrate) not using any coating at all.

Other: Use emulsion or mist coolant at high pressure.

Drilling titanium and Heat Resistant Alloy tips

Issue: Work hardening of hole surface affects subsequent operations. Good chip evacuation can be difficult to obtain.

Recommendations: When selecting a geometry for titanium alloys it is preferable to have a sharp cutting edge. For Nickle-based alloys, having a robust geometry is crucial. If work hardening is an issue, attempt to increase feed rate.

Other: High pressure (up to 70 bar) coolant improves performance.

Drilling hard steel tips

Issue: Obtaining an acceptable tool life.

Recommendations: Lower cutting speed in order to reduce heat. Adjust feed rate in order to obtain acceptable chips that can be easily evacuated.

Other: Emulsion with a high mixture.

Hole tolerance tips

The dimensions of a hole can be divided into three parameters:

• The nominal value (the theoretically exact value)
• The tolerance width (designated IT acc. to ISO)
• The position of the tolerance (designated by capital letters acc. to ISO)

Dmax minus Dmin is the tolerance width also called IT.

Diameter range, D (mm)

Tool widthD>3-6D>6-10D>10-18D>18-30D>30-50D>50-80D>80-120D>120-180D>180-250 IT50.........020 IT60.........029 IT70.........046 IT80.........072 IT90.........115 IT100.........185 IT110.........290 IT120.........460 IT130.........720

Diameter range, D (inch)

Tool widthD>0.118-0.236D>0.236-0.394D>0.394-0.709D>0.709-1.181D>1.181-1.969D>1.969-3.150D>3.150-4.724D>4.724-7.087D>7..843 IT50......... IT60......... IT70......... IT80......... IT90......... IT100......... IT110......... IT120......... IT130.........

• The lower the IT-number, the closer the tolerance
• The tolerance for one IT class increases at larger diameters

One example:

Nominal value: 15.00 mm
Tolerance width: 0.07 mm (IT 10 acc. to ISO)
Position: 0 to plus (H acc. to ISO)

Hole and axle tolerances

The hole tolerance is often connected to the tolerance of an axle that should fit the hole.

Example:

Axle ø20 mm (0.787 inch) h7
Hole ø20 mm (0.787 inch) h7

Axle tolerance position is designated by lower case letters that correspond to the hole tolerances. The figure below provides a complete picture:

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Most common Hole larger
than axleAxle larger
than hole Running fit |Slide fitDrive fit |Interference Play (bearings)Grip (=negative play (fixed joints)