A flat die is a special cutting tool used for processing taps and bolts. It consists of two square templates on top of a threading machine, one long and one short, with teeth patterns used to mold the screw or bolt into threads.

Flat dies are the most commonly used thread tools in the standard fastener industry for processing screws and bolts. The processing principle mainly uses cold extrusion forming, which has the advantages of high production efficiency, low processing cost, high precision and strength of the produced threads, and good surface quality, and has been widely used.

Flat dies are generally formed by cold rolling and are not processed after heat treatment. During operation, the teeth must withstand severe impact loads and extrusion stresses. After heat treatment, the hardness of the teeth below 3 to 5mm from the tooth root is 58 to 61HRC, the martensite of quenching is less than grade 3, and there is no decarburization on the tooth surface.

Broken points:

• Reduce the inclination angle.
• Grind more material at the feeding end of the grinding machine and less at the output end, causing an increase in feeding and a change in the cutting form.

High stress on thread rolling dies, smoking, and hot screws:

• Maximize the chamfering position for feeding.
• Make the chamfer sharper, with a sharpness of 2-3mm for the short die.

Difficulty adjusting the machine:

• The difference between the centerlines of the short and long dies must be traced back to the original centerline marking method.
• The coordinates of the short and long dies must be consistent during chamfering, and CNC automatic control is preferred.

Dull thread bottoms and peeling:

• The coordinates of the chamfer for the long and short dies must be consistent.
• The anti-skid teeth generally only reach the centerline (they can be appropriately lengthened in the case of different thread lengths).
• The anti-skid teeth must be pressed first and then chamfered or milled with a tool (must be implemented within three years).
• The anti-skid teeth should not be too deep (specifically shown in pictures).

Peeling at the bottom of the pointed threads:

• The milling teeth on the slope are too small or the chamfer on the slope is too large, both of which cause too much material on the slope (CNC programming has a better effect).
• The outer diameter of the thread at the turning line is easily too large, and burrs easily accumulate at the bottom of the thread. In particular, the pointed tail of the machine screw is cut flat, the round tail, and the pointed tail of the machine screw has no teeth.

Blackening and heating at the tip, and easy wear on the slope:

• Increasing the slope can improve the problem.
• Push more material out while grinding the pointed tail, causing a complete change in the cutting method so that the tip is not under stress.
• Open the chamfer on the slope for the 2nd to 4th teeth during feeding, and it is best to use CNC control.

The main heat treatment processes for flat thread rolling dies are tempering heat treatment and carburizing heat treatment.

• Purpose: To achieve higher hardness and strength for screws after cold forming.
• Function: Achieve self-locking attachment of metal, improve mechanical properties of metal components such as torsion resistance, tensile strength, and wear resistance.
• Tempering Heat Treatment (does not add elements to the metal, changes the internal structure of the metal by temperature variation to obtain better mechanical properties): Products with a strength level of 8.8 or higher are all products of tempering heat treatment. The characteristic of this heat treatment is that the hardness is relatively uniform inside and outside.
• When heat treating the same material, the higher the hardness, the worse the toughness. Therefore, there needs to be a safe match to ensure that toughness is guaranteed while meeting the hardness requirements.
• Carburizing heat treatment: adding carbon elements to the metal component to increase its surface hardness, targeting metals with low carbon content. Self-tapping screws basically all require this treatment, which is characterized by a very hard surface and a relatively soft core because it needs to be screwed into a hard iron plate.