CNC Knowledge: Feeding methods, insert types, terminology… Do you know all the key knowledge in wire processing?

The main processing methods of metal cutting threads include turning, milling, tapping, etc. Today, the editor has brought you important technical knowledge to share with you the most common lathe threads in production.

1. Important basic knowledge of thread processing

1. Definition of terms

①Tooth base ②Tooth side ③Tooth top

Spiral angle:

– The helix angle depends on the diameter and pitch of the thread.

– Adjust the clearance angle of the sides of the blade by changing the shim.

– The angle of inclination of the edge is γ. The most common edge angle is 1°, which corresponds to a standard shim in the tool holder.

Cutting forces when entering and exiting the thread:

– The highest axial cutting forces during threading operations occur when the cutting tool enters and exits the workpiece.

– Too high cutting parameters can cause unreliable clamped insert movements.

Tilt the blade for clearance:

The edge angle can be adjusted using a wedge under the blade in the holder. Refer to the tool catalog table to choose which shim to use. All tool holders come with standard tool blocks with edge angle set at 1°.

Select the tool wedge based on the edge tilt angle. The diameter and pitch of the part will affect the edge angle. As shown in the picture below, the workpiece diameter is 40mm, the pitch is 6mm, and the required tool wedge should have a tilt angle of 3° (standard tool wedges cannot be used).

Markings of threaded inserts and shims:

Thread forms and their applications:

2. Threaded insert types and clamping solutions

1. Multi-tooth blade

advantage:

– Reduce the number of meals

– Very high productivity

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– Requires stable clamping

– Sufficient retraction space is required after thread machining

2. Full profile blade

advantage:

– Better control of wire shape

– Less burrs

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– One type of insert can only cut one type of step

3. V-shaped blade

advantage:

– Flexibility, the same insert can be used to process several steps.

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– May cause burrs to form and require removal.

i-LOCK clamping solution:

– Extremely rigid thread with fixed position inserts

– Guided by the guide rail, the blade is positioned in the correct position

– The screw pushes the insert back onto the guide up to the radial stop at one of the contact surfaces (red contact surface) in the insert holder

– Reliable insert interface ensures longer tool life and superior thread quality

Different knife handles:

3. 3 different types of cutting methods

The cutting method can have a significant impact on the threading process. This affects: cutting control, insert wear, thread quality, tool life.

1. Improved side feed

Most CNC machines can use this approach via cycle programs:

– Chip compared to traditional turning type – easier to form and guide

– Axial cutting forces reduce the risk of vibration

– The chips are thick but only in contact with one side of the insert

– Reduced heat transfer to the blade

– First choice for most threading operations

2. Radial feed

Most common method – the only method older non-CNC lathes can use:

– Produces hard “V” shaped chips

– Same blade wear

– The insert holder is exposed to high temperatures, which limits the penetration depth

– Suitable for processing fine wires

– Possible vibration and poor chip control when machining large threads

– First choice for work hardened materials

3. Alternative diet

– Recommended for large teeth

– Uniform insert wear and maximum tool life when machining very large pitch threads

– The chips are guided in two directions and therefore difficult to control

4. Methods to improve treatment results

Cutting depth decreases layer by layer (left) and cutting depth is constant (right)

1. Cutting depth decreases layer by layer (chip surface remains unchanged)

Capable of achieving a constant chip area, this is the most commonly used method in CNC programs.

– The first passage is the deepest

– Follow the recommended values ​​on the power table in the catalog

– More “balanced” chip area

-The last pass is actually about 0.07 mm

2. Constant cutting depth

Regardless of the number of passes, the depth of each pass is the same.

– Have higher requirements for blades

– Ensures optimal chip control

– Should not be used when the pitch is greater than TP1.5mm or 16TP

Use extra margin to finish the crest of the wire:

Instead of turning the blank to the exact diameter before machining the thread, use the allowance/additional material to refine the crest of the thread. For finishing ridge inserts, 0.03 – 0.07 mm of material should be left from the previous turning process to allow the ridge to be properly formed.

Recommended feed value for external threads (ISO metric):

Make sure the workpiece and tool are aligned:

Use a maximum centerline deviation of ±0.1 mm. If the cutting edge position is too high, the clearance angle will be reduced and the cutting edge will be scratched (broken); if the cutting edge position is too low, the thread profile may be incorrect;

5. Successful thread application skills

1) Before threading, check whether the workpiece diameter has the correct machining allowance and add 0.14mm as peak allowance.

2) Precisely position the tool in the machine tool.

3) Check the adjustment of the cutting edge in relation to the original diameter.

4) Make sure you are using the correct insert geometry (A, F or C).

5) Ensure sufficiently large and uniform clearance by selecting the appropriate shim (insert-tilt shim) to obtain the correct sidewall clearance.

6) If the thread is not qualified, check the entire tightening including the machine tool.

7) Check available CNC programs for thread turning.

8) Optimize feeding method, number of passes and size.

9) Ensure correct cutting speed to meet application requirements.

10) If the thread pitch of the workpiece is incorrect, check whether the pitch of the machine tool is correct.

11) Before cutting the part, it is recommended to start the tool at a minimum distance of 3 times the pitch.

12) High precision coolant can extend tool life and improve chip control.

13) The quick change system ensures quick and easy tightening.

When selecting tools for thread turning operations, you should consider:

– Check overhangs and possible clearances (e.g. shoulders, counter spindles, etc.)

– Minimize tool overhang for quick setup

– For less rigid clamping, choose an insert with a lower cutting force

– High precision coolant extends tool life and improves cutting control

– Easily connect coolant with plug-and-play coolant connections

– In order to ensure productivity and tool life, the first choice is multi-tooth type inserts, the second choice is single-edged full tooth type inserts, and the choice with The lowest productivity and shortest tool life is V-tooth type inserts.

Blade wear and tool life:

Feeding method, optimize feeding method, number of passes and depth

Angle of inclination of the blade to guarantee a wide and uniform space (paver inclined by the blade)

Insert geometry, make sure you are using the correct insert geometry (A, F or C geometry)

Blade material, choose the right material according to the material and toughness requirements

Cutting settings, change cutting speed and number of passes if necessary.