Machinery

Introduction of Mechanical Taps

The tap is the mainstream processing tool used in tapping. So how to choose the tap? Today, I will share with you a tap selection guide to help you choose the right tap.

As a common tool for processing internal threads, taps can be divided into spiral flute taps, blade inclination taps, straight flute taps and pipe thread taps according to their shapes. According to the environment of use, they can be divided into hand taps and machine taps. Divided into metric, American, and British taps.

Tap classification

1. Cutting tap

1) Straight flute taps: used for the processing of through holes and blind holes. Iron filings are present in the tap grooves, and the thread quality of the processed threads is not high. It is more commonly used for processing short chip materials such as gray cast iron.

2) Spiral flute tap: used for blind hole machining with a hole depth less than or equal to 3D, iron filings are discharged along the spiral flute, and the thread surface quality is high.

10~20° helix angle tap can process thread depth less than or equal to 2D;

28~40° helix angle tap can process thread depth less than or equal to 3D;

The 50° helix angle tap can process the thread depth less than or equal to 3.5D (4D under special conditions).

In some cases (hard materials, large pitch, etc.), in order to obtain better tooth tip strength, spiral fluted taps are used to process through holes.

3) Spiral point taps: usually only used for through holes, the ratio of length to diameter can reach 3D~3.5D, the iron filings are discharged downward, the cutting torque is small, the surface quality of the processed thread is high, and it is also called the edge tap or Tip tap.

2. Extrusion tap

It can be used for the processing of through holes and blind holes. The tooth profile is formed through plastic deformation of the material, and it can only be used for processing plastic materials.

Main features of extrusion taps:

(1) Use the plastic deformation of the workpiece to process the thread;

(2) The tap has a large cross-sectional area, high strength, and is not easy to break;

(3) The cutting speed can be higher than cutting taps, and the productivity is also improved accordingly;

(4) Due to the cold extrusion process, the mechanical properties of the processed thread surface are improved, the surface roughness is high, and the thread strength, wear resistance and corrosion resistance are improved;

(5) No chip processing.

Insufficient extrusion tap:

(1) It can only be used for processing plastic materials;

(2) High manufacturing cost.

Two structural forms of extrusion taps:

(1) Extrusion taps without oil groove are only used for blind hole vertical machining;

(2) Extrusion taps with oil grooves are suitable for all working conditions, but usually small diameter taps are not designed with oil grooves due to manufacturing difficulties.

Structural parameters of the tap

Dimensions

Total length: need to pay attention to some working conditions that require special lengthening

Slot length: pass on

Shank: At present, the common shank standards include DIN (371/374/376), ANSI, JIS, ISO, etc. Please pay attention to the matching relationship with the tapping tool holder when selecting

Threaded part

Accuracy: It is selected by the specific thread standard. The metric thread ISO1/2/3 is equivalent to the national standard H1/2/3, but the manufacturer’s internal control standards should be paid attention to.

Cutting cone: The cutting part of the tap has formed a partial fixed pattern. Generally, the longer the cutting cone, the better the life of the tap.

Correction teeth: play an auxiliary and correction role, especially in the unstable working conditions of the tapping system, the more correction teeth, the greater the tapping resistance.

Chip flute

Groove: Affects the formation and discharge of iron filings, and is usually an internal secret of each manufacturer.

Rake angle and relief angle: The tap becomes sharp as it increases, which can significantly reduce the cutting resistance, but the strength and stability of the tooth tip decrease, and the relief angle is the relief angle.

Number of grooves: increasing the number of grooves and increasing the number of cutting edges can effectively increase the life of the tap; but it will compress the chip removal space, which is disadvantageous for chip removal.

Material of the tap

Tool steel: It is mostly used for hand incisor taps, which are not common anymore.

Cobalt-free high-speed steel: At present, it is widely used as tap material, such as M2 (W6Mo5Cr4V2, 6542), M3, etc., and the mark code is HSS.

Cobalt-containing high-speed steel: At present, it is widely used as tap material, such as M35, M42, etc., and the marking code is HSS-E.

Powder metallurgy high-speed steel: used as a high-performance tap material, the performance is greatly improved compared with the above two, and the naming methods of each manufacturer are also different, and the marking code is HSS-E-PM.

Cemented carbide materials: usually select ultra-fine particles, good toughness grades, mainly used to make straight-groove tap processing short chip materials, such as gray cast iron, high silicon aluminum, etc.

The taps are highly dependent on materials. The selection of good materials can further optimize the structural parameters of the taps, making them suitable for efficient and more demanding working conditions, and at the same time have a longer life. At present, the major tap manufacturers have their own material factories or material formulas. At the same time, due to cobalt resources and price issues, new cobalt-free high-performance high-speed steels have also come out.

Tap coating

Steam oxidation: the tap is placed in high-temperature water vapor to form an oxide film on the surface, which has good adsorption of coolant, can reduce friction, and prevent the adhesion between the tap and the material being cut. It is suitable for Processing mild steel.

Nitriding treatment: The surface of the tap is nitrided to form a surface hardened layer, which is suitable for processing cast iron, cast aluminum and other materials that have a lot of tool wear.

Steam + Nitriding: Combine the advantages of the above two.

TiN: Golden yellow coating, with good coating hardness and lubricity, and good coating adhesion, suitable for processing most materials.

TiCN: Blue-gray coating, hardness is about 3000HV, heat resistance up to 400°C.

TiN+TiCN: dark yellow coating, with excellent coating hardness and lubricity, suitable for processing most materials.

TiAlN: Blue-gray coating, hardness 3300HV, heat resistance up to 900°C, can be used for high-speed processing.

CrN: Silver-gray coating, excellent lubricating performance, mainly used for processing non-ferrous metals.

The coating of the tap has a very obvious effect on the performance of the tap, but at present, most manufacturers and coating manufacturers cooperate to study special coatings, such as LMT’s IQ, Walter’s THL and so on.

Factors affecting tapping

Tapping equipment

Machine tool: It can be divided into vertical and horizontal processing methods. For tapping, vertical processing is better than horizontal processing. When horizontal processing is externally cooled, it is necessary to consider whether the cooling is sufficient.

Tapping tool holder: It is recommended to use a special tapping tool holder for tapping. The rigidity and stability of the machine tool are preferred to use the synchronous tapping tool holder. On the contrary, the flexible tapping tool holder with axial/radial compensation should be used as much as possible. Except for small diameter taps .

Cooling conditions: For tapping, especially for extrusion taps, the requirement for coolant is lubrication>cooling; in actual use, it can be adjusted according to the conditions of the machine tool (when using emulsion, the recommended concentration is greater than 10%).

Workpiece

The material and hardness of the workpiece: the hardness of the workpiece material should be uniform. Generally, it is not recommended to use a tap to process workpieces exceeding HRC42.

Tapping bottom hole: bottom hole structure, choose a suitable drill bit; bottom hole size accuracy; bottom hole wall quality.

Processing parameters

Rotation speed: The basis of the speed setting is the type of tap, material, processed material and hardness, and the quality of the tapping equipment.

Usually selected according to the parameters given by the tap manufacturer, the speed must be reduced under the following working conditions:

  • Poor machine rigidity; large tap jump; insufficient cooling;
  • Uneven material or hardness of the tapping area, such as solder joints;
  • The tap is lengthened, or an extension rod is used;
  • Lying plus, cold outside;
  • Manual operation, such as bench drills, radial drills, etc.;
  • Feed: rigid tapping, feed = 1 pitch/revolution.
  • When flexible tapping and tool holder compensation variables are sufficient:
  • Feed = (0.95-0.98) pitch/revolution.

6 basic elements for tap selection

  • Type of thread to be processed, metric, imperial, American, etc.;
  • Type of threaded bottom hole, through-hole, or blind hole;
  • The material and hardness of the workpiece to be processed;
  • The depth of the complete thread of the workpiece and the depth of the bottom hole;
  • The required precision of the workpiece thread;
  • The appearance standard of the tap (special requirements need to be specially marked).
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