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THREAD FORMING TAP - A Different Way Of Producing Internal Threads :
Also known as COLD FORMING TAP OR ROLL FORMING TAP produce internal threads by an action similar to Thread Rolling a novel method of cold forming of threads by displacement of materials rather than by chips removal. These taps have neither flutes nor cutting edges and it is just like a screw and in the end view and cross section, the major and minor diameters follow a CONTOUR. The fluteless taps are "Screwed" in the predrilled work piece with proper feed rate and the thread profile is gradually press formed (Please refer to figure)

 
It is a chip less technology and any materials having ductility co-efficient of 10% or less (Tensile strength less than 1000N/mm2) can be machined perfectly.

 
ADVANTAGES OVER CONVENTIONAL THREAD CUTTING TAPS :
  • No chips are produced since threads are produced by cold forming process and hence the chance of tap breakage is minimized. (Chip entrapment/clogging has been identified as the major cause for tap breakage and poor quality of threads).
  • Easier Blind hole tapping because there are No chips to clog or jam at the bottom of the hole which consequently eliminate tap breakage.
  • Strong Threads because grain fiber are not cut but thread is formed by displacement of materials Fig (2).
    The Pull test or Torque Tension Tests demonstrate that the threads produced by Roll form taps are stronger (by an average of 35% more than threads produced by Thread cutting taps.)
  • Better control of tapped hole size (Thread cutting taps may cause to cut over size holes due to excessive downward pressure.)
  • Better surface finish and absolute accuracy of thread is guaranteed because of Cold Forming.
  • No Threads Pitch Errors-Thread cutting taps may cause tearing of threads, which may cause pitch error while reversing.
  • Faster tapping speed and increased productivity. (Tapping speeds can be more than those recommended for Cutting Taps).
  • Increased tool life due to strong core area.
  • Consistency in tapped hole sizes from the first to the last due to continuous forming action and accurate lead.
  • Plating failures reduced because there is no chip to stick at the bottom of blind holes or on the threads.
  • The tap has greater rigidity and better strength (Core portion) because there are no flutes and less risk of breakage especially in small sizes resulting in reduction in cost per tapped hole resulting in increased production.
  • Application in wide range of materials like Aluminum, Steel, Stainless steel, Copper (soft) Brass (long chipping) Magnesium, Zinc alloys etc.

 
EQUIPMENT :
Conventional tapping equipment can be used. Forming taps works very well in NC and CNC Machines, drill, lathes, lead screw tapping equipment and on many standard tapping heads.
OIL GROOVES:
For tapping depths more than two times the tap diameter, Roll Taps with Oil grooves are recommended. These grooves provide a passage for lubricant and also for the escape of air and oil to avoid a piston effect in blind holes.
HOLE SIZE:
The pretapping hole size required for forming taps is larger than in conventional tapping. Accurate pretapping hole is desirable while tapping with fluteless taps. This size depends on the forming property of the material, desired depth of the thread, stripping strength requirement etc. For the conventional thread cutting tap the hole size is identical to minor dia of the tapped internal thread, but in the case of Fluteless tap the hole size is calculated as per following formula.

HOLE SIZE = BASIC TAP OD ( 0.0068 X 65 X Pitch)

The general formula for determining the hole size has been given above but if necessary fine tuning may be required after performing some actual trials etc.

We are giving hereunder profiles of threads formed by M10 x 1.5 fluteless taps with different hole sizes.
 
TORQUE :
The torque requirements for forming taps are more than those for cutting taps. The actual torque experienced will vary with the material to be formed and some experiments may be required if torque is a limiting factor. We are giving a graph showing effect of hole on driving torque while tapping with M10 x 1.5 fluteless tap.


 
THREAD FORMS:
Metric Coarse, Metric Fine, UNC, UNF are always available in ready stock. Other thread forms like BSW, BSF, BSP etc. are against orders.
RANGE:
1.6 mm to 24 mm and 1/8 to 1.
COATINGS :
Surface coatings like TiN, TiCN, TiALN etc. are available to improve the tools life and suit different work material applications.
LUBRICATION :
Proper lubrication is very important in thread forming with fluteless taps. Lubrication prevents material from building up on the high points of thread flanks and ensures that the torque during thread forming process does not increase. Therefore continuous flow of lubricant is necessary. Oils having presence of graphite such as those used in rolling processes should be preferred.

CHECK LIST WHEN USING ROLL FORM TAPS:
  • Proper selection of the correct drill size for pre-tapped holes.
  • Countersink or chamfer the hole to avoid possible deposit of displaced burrs at the mouth of the holes.
  • Use a cutting oil (Sulforized or chlorinated) than a coolant.
  • Surface coating of taps is advisable for best result and higher productivity.
  • Tapping speed-please get our advice, depending upon your application.
  • Torque requirement for Roll Form tap is higher than those for thread cutting taps and hence suitable machines should be selected.
  • While using multi spindle tapping machines please check if enough torque is available.
  • For short blind holes caution has to be exercised that the tap does not hit at the bottom and break or chipoff.