The Present Situation of PDC Rock Bits and Its Welding Technology

PDC rock bit is the abbreviation of polycrystalline diamond compact drill bit, which is a commonly used drilling tool in the oil drilling industry. Initially, PDC rock bits could only be used in soft shale formations because hard interlayers would damage the bits.

However, due to the emergence of new technologies and structural changes, PDC rock bits can now be used to drill hard interlayers and long sections of hard rock formations. PDC rock bits are increasingly used by drilling construction teams.

1. Status of PDC rock bit

PDC rock bit is an effective tool for breaking rock, it is composed of bit body, cutting teeth, steel body and upper joint.

Usually, when the steel body is connected with the upper joint by the method of electrode arc welding, the welding quality is unstable, the labor intensity is high, and the welding efficiency is low.

However, when the drill bit works underground, due to the complicated geological conditions, the drill bit has poor working conditions at the bottom of the hole, which is not only affected by the WOB and torque.

Moreover, in the process of rock breaking, it is continuously subjected to impact load, so it is prone to brittle fracture. This puts forward higher requirements and reliability for the welding quality of PDC rock bit welds.

2. PDC rock bit welding process

The PDC drill bit body is combined with the steel body by high temperature sintering in the furnace, and then the steel body (annealed 35CrMo steel) and the upper joint (quenched and tempered 40CrMnMo steel) are welded into a whole.

The main factors affecting the weldability of steel are: chemical composition of steel, welding process, structural design and use conditions. The carbon content of the drill steel body and the upper joint is high, and the hardening tendency is large during welding.

Therefore, it is easy to produce hard and brittle high-carbon martensite in the superheated zone of the welding heat-affected zone.

Large line energy will generate a wide and coarse heat-affected zone, increase the tendency of embrittlement, and also increase the possibility of hot cracks in welds and heat-affected zones.

The use of small line energy reduces the high temperature residence time, avoids the overheating of austenite grains, increases the inhomogeneity of austenite composition, and reduces the stability of austenite;

The strength of the steel is high, so the welding heat affected zone is easy to soften, and the pdc drill cannot be quenched and tempered after welding; the smaller the line energy, the faster the heating and cooling speed, the shorter the heating time, the smaller the degree of softening, the narrower the width of the softened zone.

At present, when the welding of the drill bit adopts the method of electrode arc welding to connect the steel body and the upper joint, the welding quality is unstable, the labor intensity is high, and the welding efficiency is low.

3. pdc drill welding equipment

When manual arc welding is used for circumferential seam welding of the lower body of the PDC rock bit and the upper joint, due to the heavy workpiece, the existing tooling has the problem of uneven pressing force between the lower body of the drill bit and the upper joint, and the welding coaxiality is poor, resulting in unstable welding quality.