Thread Turning Tools: Characteristics And Selection

Thread processing plays a certain role in machining, especially for some pipe fitting connection processing, such as meter and inch thread processing, petroleum pipe thread processing, taper thread processing and so on.

(1) Characteristics and application scope of thread turning tool

Common thread turning tools include: Welded carbide turning tools, carbide single edge machine clamp thread turning tools, carbide machine clamp indexable thread turning tools, prismatic thread turning tools, round thread turning tools, etc.

Prismatic thread turning tools and circular thread turning tools are generally used for multi tooth thread processing, with the characteristics of high efficiency and high precision.

However, these thread turning tools have the disadvantages of slightly complex structure and difficult manufacturing and grinding.

They are only used for large screw hole processing of ring sleeve parts.

At present, these thread turning tools are gradually replaced by comb thread milling tools.

(2) Structure and basic dimensions of thread turning tool

1. Structure and basic dimensions of single edge machine clamp thread turning tool

The national standard GB/T10954-2006 specifies the structure of mechanically clamped carbide thread turning tools.

The blade type used is shown in fig. 3-57.

thread turning tool specified in national standard

Fig. 3-57 thread turning tool specified in national standard

a) External thread turning tool

b) Internal thread turning tool

2. Structure and basic dimensions of machine clamp indexable thread turning tool

At present, there is no national standard for the machine clamp indexable thread turning tool. Refer to Fig. 3-58 for its structural form and basic dimensions.

The indexable blade used is shown in Fig. 3-59.

machine clamp indexable thread turning tool

Fig. 3-58 machine clamp indexable thread turning tool

indexable blade for machine clamp thread turning tool

Fig. 3-59 indexable blade for machine clamp thread turning tool

Typical clamping structures of indexable thread turning tools for machine clamps include screw type (see Fig. 3-60), wedge type (see Fig. 3-61) and up pressing type, which can be selected according to specific conditions.

screw clamp indexable thread turning tool

Fig. 3-60 screw clamp indexable thread turning tool

1 – knife pad

2 – cutter pad clamping screw

3 – blade clamping screw

4,5-wrench

wedge clamp indexable thread turning tool

Fig. 3-61 wedge clamp indexable thread turning tool

1 – knife pad

2 – center pin

3,5 – wrench

4 – wedge assembly

Machining of machine clamp indexable thread turning tool is shown in Fig. 3-62.

thread machining

Fig. 3-62 thread machining

(3) Selection of cutting parameters for clamp type thread turning tool

1. Feed rate

The size of the feed rate and the number of tool paths have a decisive impact on the machining quality and cutting efficiency of the thread.

During thread processing, in order to obtain the best tool life, the workpiece diameter shall not exceed 0.14mm of the outer diameter of the thread, and the feed rate shall not be less than 0.05mm/r.

The machining method generally adopts the feed decreasing method, and the last tool can be an empty tool without feed, so as to eliminate the influence of elastic deformation in the cutting process.

The size of the actual feed rate and the number of tool paths shall be determined by test or according to the actual situation, and can also be selected by referring to the cutting parameters provided by different tool manufacturers.

2. Feed mode selection

There are three feed modes in thread turning: radial, lateral and alternate.

In practical application, workpiece material, blade groove shape and screw pitch determine the choice of feed mode.

(1) Radial feed: the most commonly used feed method, with soft chip forming and uniform blade wear, is suitable for small pitch threads.

When machining large pitch thread, the chip control is poor and the vibration is large.

It is the first choice for work hardening materials (such as stainless steel, etc.).

The processing diagram is shown in fig. 3-63.

radial feed

Fig. 3-63 radial feed

(2) Side feed: this feed mode can lead the chips to one direction and better control the chips.

It is suitable for cutting large pitch threads and internal threads that are prone to chip removal.

In order to avoid poor surface quality or excessive wear of the flank due to friction at the rear edge, the feed angle shall be 1 ° ~ 5 ° smaller than the thread angle.

The axial feed amount of lateral feed can be simply 0.5 × Radial feed calculation.

The lateral feed mode is shown in fig. 3-64, and the schematic diagram of chip flow direction (see fig. 3-65).

lateral feed

Fig. 3-64 lateral feed

chip flow direction

Fig. 3-65 chip flow direction

(3) Alternate feed: mainly used for cutting large teeth.

This method has uniform tool wear and long tool life.

The schematic diagram of alternate feed is shown in fig. 3-66.

alternate feed

Fig. 3-66 alternate feed

(4) Common problems and Solutions

See table 3-26 for common problems and solutions in thread turning.

Table 3-26 common problems and solutions in thread turning

Question

reason

measure

Early wear

 

 

Cutting speed too high

Reduced cutting speed

Improper tool material

Switch to a tool material with better wear resistance

Too many cuts

Reduced number of cuts

Uneven wear of left and right cutting tools

Cutting speed too high

Reduced cutting speed

Improper tool material

Switch to a tool material with better wear resistance

Too many cuts

Reduced number of cuts

Collapsing blade

Cutting speed too high

Reduced cutting speed

Improper tool material

Switch to a tool material with better wear resistance

Too many cuts

Reduced number of cuts

Crack generation

Cutting speed too high

Reduced cutting speed

Improper tool material

Switch to a tool material with better wear resistance

Too many cuts

Reduced number of cuts

Large plastic deformation

Cutting speed too high

Reduced cutting speed

Improper tool material

Switch to a tool material with better wear resistance

Too many cuts

Reduced number of cuts

Poor machined surface

Cutting speed too low

Increase cutting speed

Blade is higher than center

Adjust center height

The spiral Angle is not correct.

Select the appropriate tool pad

Incorrect thread shape

The thread profile angle is incorrect.

Use the external butterfly blade for internal thread machining, or vice versa.

Use the correct tools and blades

Center height is incorrect.

Adjust center height

Insufficient thread depth.

Check the back cutting depth and correct it.

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