Thread manufacturing Process (Blog by Samarth Bhaganagare,Krishna Bharadiya,Gaurav Bhoye,Aniket chaudhari,Pavan Chavan)

Thread manufacturing Processes

Introduction:

• A thread is a ridge of uniform cross section in the shape of a helix that is provided on the outside or inside of a cylindrical or conical surface. 
• Functionally fasteners are threaded to keep the component in place.
  
• Thread manufacturing is a major manufacturing activity due to the strong need for high-precision fastening devices and power transmission systems.

Elements Of Screw Thread

• Major Diameter
• Minor Diameter
• Pitch Diameter
• Pitch
• Helix angle
• Thread angle
  

Methods of Thread manufacture:

Thread cutting on Lathe:

• The principle is to feed the tool longitudinally while the work piece is rotating to create a helical groove on a cylindrical or conical surface.
• Steps to follow:

1. Selection of a cutting tool
2. Workpiece and cutting tool mounting
3. Establish a relation between the cutting tool's longitudinal movement and the rotation of the work piece.
4. Thread cutting
5. Tool feeding and thread catching 

The following points highlight the top nine methods used for making threads,

the methods are :

1. Chasing
2. Self-Opening Die Heads
3. Tapping
4. Milling
5. Grinding
6. Rolling
7. Casting
8. Whirling

Thread Chasing:

Ø It is a method of thread cutting that employs a multi-point cutting tool known as a thread chaser. 

Ø Chaser types include:

o  Hand Chaser 

o  Threading device Chaser

Ø During operation, the hand chaser is operated manually by hand with appropriate assistance.

Ø The Flat type and the Circular kind of threading tool chaser are both useful. Both are fixed in a tool holder and used in large-scale production to cut thread.

Ø This group of chasers is made up of Cutting teeth are used for cutting and sizing teeth are used for finishing.

Arrangement of Thread Chasing on Turret Lathe:

Ø In the machine, the lead screw is rotated by the machine's head stock via shifting gears.

Ø A feed nut and tool slide are mounted on the shaft, and they can be engaged and disengaged with a lead screw using a hand-operated lever.

Ø Die threading is the process of cutting external threads on a cylindrical or tapered surface using solid and self-opening dies.

Ø Die sets resemble nuts, however they are constructed of Hardened Steel or HSS and have sharp cutting edges.

Ø This die rotates around the blank in a coaxial fashion.

Ø Die Types 

1) Solid die

Ø Spring dies allow for an elastic reduction in bore and the cutting of threads in a reduced number of passes.

Ø Split dies are dies that are constructed in two sections. One is fixed, while the other rotates within the wrench's hollow.

2) Self opening die

 

ØWhen you disconnect from w/p, it automatically opens.

 ØTurret lathe and special threading machine use these dies. 

ØAll dies have four sets of multi point cutters or chasers that can be adjusted.

Working: Mounted in turret and advances towards w/p; when length measurement is complete, the die is automatically pulled and opened for free returns.

Tapping:

Ø  Internal threads are produced by tapping, which is a thread cutting procedure.

 Ø Multipoint cutting (Tap) is similar to die threading, and it can be done by hand or by machine.

ØThe technique is identical to manual tapping in the machine, except that the feed is automatic and the threads are highly exact and uniform.

Ø During machining, features such as rapid tool retraction, automatic loading or unloading, and the utilisation of several spindles will significantly boost the machining rate.

Ø Solid taps and collapsible taps are the two types of taps.

 

Solid Taps:

Ø  It is made of one piece and has four flutes to give cutting edges, comparable to a threaded bolt.

Ø It is used for tiny diameters and is manually operated. As a result, it's sometimes referred to as hand taps.

Ø Solid taps include the Taper tap, Plug tap, and Bottoming tap.

Ø The beginning of the taper tap is tapered for six threads to make entrance easier.

Ø After removing the first tap, the plug tap is chamfered a little for a few threads and utilised as a second tap.

Ø After the second tap, the bottoming tap is used to cut the thread all the way to the bottom of the hole.

 

 

Collapsible taps:

Ø It is a tool that automatically collapses inwards when the thread is finished, allowing for return without unscrewing. As a result, the operation's pace has enhanced.

   Ø Because to the machining, the surface finish is excellent. The taps are equipped with a trip plate that adjusts the thread length to be cut.

Thread Milling:

Ø Threads produced by the milling process- Threads are manufactured on rotating work pieces utilising form cutters (single form cutter and multiple form cutter).

Ø When milling is appropriate: for generating interior threads that are difficult to cut with a tap.

Ø Work on enormous diameters that exceed the die's capability.

Ø When using a single form cutter, the blank rotates slowly and the cutter is accurately moved along the blank's axis.

Ø Threading can be done in one or more passes, depending on the thread depth.

Ø Several annular rows of cutting teeth are formed by flanks or gashes in the multiple form cutter.

Ø The spindle is set parallel to the work axis, similar to a single form cutter, and this procedure is suited for threads with short distances.

Ø Thrilling is a CNC milling procedure that combines threading and drilling with the use of a specific cutting tool. 

 

Thread Grinding:

Ø Thread grinding works in a similar way to thread milling. Grinding is done with grinding wheels that have been specifically dressed.

Ø The grinding wheel can be single or multi-ribbed, and the procedure is suited for hard materials that cannot be threaded using conventional methods.

Ø Types of thread grinding

1)   Pass over grinding

2)   Plunge grinding

3)   Centre-less grinding

Pass over grinding:

Ø It is similar to threading on a lathe, but instead of a single point cutting tool, a grinding wheel is used.

Ø In a single wheel, the rib wheel rotates in the opposite direction of the work, and axial motion is provided by an accurate lead screw.

Ø The thread isn't finished in a single pass. To complete the thread up to a particular depth, multiple passes are required.

Ø 
It is also known as transverse thread Grinding.

Plunge Grinding:

Ø The principle of thread grinding is similar to thread milling. Grinding is done by using specially dressed grinding wheels.

Ø  Grinding wheel may be of single rib type or multi rib type and process is suitable for hard materials for which other methods of thread cutting is not possible.

Ø Types of thread grinding

1)   Pass over grinding

2)   Plunge grinding

3)   Centre-less grinding

Centre less thread grinding:

Ø This process is used to make headless set screws.

Ø Work is fed between regulating wheel and grinding wheel where threads are fully formed.

Ø 
Production rate is 60 to 70 (13 mm long) pieces per minute.

 

Thread Rolling:

Ø External threads on cylindrical w/p are created via a cold forming procedure.

Ø By pushing a thread rolling dice against the blank, threads are produced into a blank.

Ø  
It is more efficient technique of producing

Ø Because skilled labour is not required, it is a cost-effective technique of thread production.

Ø No material wastage due to the lack of chipping.

Ø Threads created by rolling are of excellent quality and precision.

Ø Thread rolling increases the work material's tensile and fatigue strength, however the method is only applicable to ductile materials.

Ø Thread rolling machines are type of machine that is used to roll thread.

o  Reciprocating Flat die machine.

o  Cylindrical two/three die machine.

Flat die machine:

Ø There are two dies in use. One is a stationary bottom die, while the other is a reciprocating die.

Ø The blank is placed on a fixed die, and the moving die is then moved over it. Blanks roll between two dies and threads are produced as a result of this activity.

                                                                          

Cylindrical die machine:

Ø Two or three dies are used in a cylinder die machine.

Ø The work blank is supported between two dies in the case of a two-die machine, as indicated in the image.

ØIn a three-die machine, one die moves radially outward to allow the work blank to pass between the dies, then closes and rotates to roll threads.

 Thread Casting:

Ø Threads are created directly by the geometry of the cavity in the mould or die in casting and moulding.

Ø Sand cast thread is coarse and is only occasionally used in vises and harsh machinery.

Ø In comparison to other casting methods, lost wax produces more precise threads with a better surface polish, but it is a more expensive process.

Ø Cast threads are employed in situations when only a few threads are required over a short length of time due to their poor precision.

 

Thread Whirling:

Ø Thread Whirling is a form of  the Thread Milling process  with the exception that the  cutters are mounted on the  inside of a Cutting Ring or  Cutter Holder rather than the  outside of a milling tool.

Advantages of Thread Whirling:

§  Deep Threads

§  Faster Setup

§  Increased Productivity

§  Increased Tool Life