Research in the Processes for Manufacturing Matrix-body Curved-

profile PDC Bits Using the Method of Fusion and Penetration

Yuwen Xiong

,Tonghong Li

and Quanxin Liu

1. Mechanical Engineering Department, Ezhou Polytechnic, Ezhou, Hubei, China

2. Hubei Province Diamond Tool Testing Center, Ezhou, Hubei, China

Keywords: Matrix-body; Curved-profile bit; PDC; fusion and penetration (impregnation).

Abstract: As integration of the modern 3D printing technology with the traditional mold manufacturing technology, the

method of fusion and penetration is used to produce the matrix-body curved-profile PDC bits. This method

includes mainly such processes as the prototype 3D printing, mold copying, mold and material loading,

fusion and penetration, and after-treatment. This method is capable of effectively using a variety of

materials of special properties at different locations of the bit to ensure it has a reasonable structure and high

dimensional accuracy hence ideal application effect, The manufacturing processes are simple with both

manufacturing quality and manufacturing efficiency improved.

1 INTRODUCTION

Polycrystalline Diamond Compact (“PDC”) bits are

a kind of drilling tools commonly applied in the

geological industry. Main examples are geological

exploration, coalfield drilling (for example, anchor-

rod-type PDC bits, and three-wing PDC bits), and

oilfield exploration. Among them, the PDC bits used

for oilfield exploration are the most expensive and

satisfy the most stringent requirements. They can be

called “the noble” among PDC bits. A PDC bit

consists mainly of the bit body, cutters, nozzles, bit-

body outer-wall wear-resistance reinforcement layer,

and the joint. Traditional PDC bits have a steel body

made of nickel-chromium-molybdenum alloy.

Firstly, the alloy stock is machined into the initial bit

body. Then the initial bit body is heat treated. After

the heat treatment, holes are drilled in the bit body.

And man-made PDC cutters are pressed or welded

to the crown of the bit body. Finally, the tungsten

carbide bars are affixed to the bit-body outer wall for

purpose of wear-resistance enhancement. The steel

body is notorious for low wear and fracture

resistance. Thus the high wear resistance of the PDC

cutters is compromised, with the drilling efficiency

reduced and the repair or replacement interval

shortened. Matrix-body PDC bits as a new type of

PDC bits use different materials from those used in

traditional PDC bits. They have a matrix body that

is made of WC/W2C other than nickel-chromium-

molybdenum alloy. Benefits of the matrix-body

PDC bits include high wear resistance and drilling

efficiency. Using the pressureless impregnation

technology, bronze as binder is applied into the

structure the skeleton of which is formed by

tungsten carbide powder. The matrix body is hence

formed. Then, by brazing, PDC cutters are affixed to

the crown of the matrix body. Natural diamond bars

are attached to the outer wall of the matrix body for

purpose of wear-resistance enhancement. The matrix

body is shown in Figure 1. Recent years have seen a

great change in both quality and variety of matrix-

body PDC bits. For example, engineers have

optimized the interface between tungsten carbide

matrix and PDC cutters. Furthermore, important

breakthrough has also been made in the design and

arrangement of PDC cutters, with their toughness,

abrasion resistance, and thermal stability improved a

lot. Nowadays, adoption of new-type smart

manufacturing technology makes also a huge

contribution to the improvement of the quality of

matrix-body PDC bits. These bits possess much

greater resistance to erosion and impact. In this

paper, the modern 3D printing technology and the

traditional mold manufacturing technology are

combined to put forth new processes for making

matrix-body curved-profile PDC bits. Intention is to

overcome the difficulty in machining the crowns that

are made of super hard materials and have a quite

complex shape. These processes make mass

production of the bits possible. These bits hence can

be more effectively applied in more industrial fields.

Figure 1 Schematic of matrix-body curved-profile PDC

bit.

2 PROCESSES FOR MAKING

MATRIX-BODY CURVED-

PROFILE PDC BITS

Generally, curved-profile PDC bits have a complex-

shaped crown. Two to four cutting wings protrude

from the head platform. Three to five PDC cutters

are welded to each cutting wing. Gates are prepared

in the areas between the cutting wings. Cooling

water circulates through these gates while drilling.

The entire crown has a curved profile. It is more

difficult to manufacture the curved-profile PDC bits.

On the one hand, it is more difficult to control the

machining accuracy of the curved surfaces; on the

other hand, the matrix body is made of the hard

materials WC/W2C. Once the curved surfaces are

formed, it is difficult to machine them. Furthermore,

formation of the cutting wings must ensure the

required dimensional and shape accuracy, and the

gates and the locations for welding the PDC cutters

must be formed during the formation of matrix body.

Taking into consideration the structural and material

characteristics of the bits, the technology of fusion

and penetration (pressureless impregnation) is an

effective solution to the mentioned difficulties.

Figure 2 shows the flow chart of the technology.

Figure 2 Process flow for making the matrix-body

curved-profile PDC bits using the method of fusion and

penetration .

2.1 Making Silica Gel Prototype of Bit

Using 3D Printing Technology

The primary task for the manufacturing of matrix-

body curved-profile PDC bits is to make the silica

gel prototype using the modern 3D printing

technology. First, the 3D solid model of the bit is

built with the design software (for example, PRO/E,

UG, CAD, or SolidWorks). With the model

modified and analytically optimized, the STL file is

directly outputted. Sectioning is then performed.

Next, the 3D printing (fused deposition modeling

(FDM)) is directly performed to produce the silica

gel prototype. The 3D printing technology applies

the “dispersion/accumulation” principle for gradual

formation. The designers can directly view the

model design, and perform the CAE simulation and

analysis using the simulation software. This is good

for communication, optimization and improvement.

The prototype can be made at the specified speed

and accuracy. The whole process is both flexible and

controllable, removing the need of any tooling. The

steps from design to modeling can be completed

with a dozen of hours. ABS, wax, and nylon

filaments are available for the FDM technique. The

modeling temperature is anywhere from 80 to

120ºC, and the modeling accuracy can be 0.1mm. In

addition, the after-treatment is simple, the cost is

low, and the material utilization rate is as high as

100%. When making the silica gel prototype, Mei

PDC cutter

recombination片

WC matrix body

(Fusion and

penetration of bronze

particles)

Steel

cylinder

Xiaoqin[1] adopted a method which additionally

incorporated the process for intermediate model

conversion. First, she built the 3D model of the bit

using the software PRO/E, and converted the 3D

model into the model of basic parent mold. Then she

got rapidly the basic parent mold using the FDM

technique. Finally, she poured silica gel into the

basic parent mold to get the prototype of the bit. The

process flow of this method is shown in Figure 3.

Advantages of this method are effectively

implementing the bit structural design, and ensuring

the quality of basic parent mold. Disadvantages of

this method are adverse influence on manufacturing

efficiency and manufacturing cost.

Figure 3 Conversion from model to mold .

2.2 Making Sand Mold By Copying 3D

Printed Mold

The silica gel prototype is used for making the clay

mold or the sand mold. WC powder is placed in the

clay mold or the sand mold, then they undergo the

fusion and penetration process in an electric furnace.

The matrix body is thereby obtained. Generally, the

clay mold is made with the pouring method. Diao

Wenqing[2] made the Φ96 matrix body of the PDC

bit with the pouring method. First, he performed the

design, calculation and machining of the graphite

mold casing, and fixed the silica gel prototype. For a

sufficiently long time, he mixed steadily a proper

amount of clay powder with water according to a

certain mixing ratio to get the slurry. Then he poured

the slurry into the assembly, thus the cavity between

the mold casing and the silica gel prototype was full

of slurry. Within half an hour since the completion

of the pouring process, the slurry solidified to gain

certain strength due to reaction between the clay and

the water. He took out the silica gel prototype, to get

the clay mold as shown in Figure 4. Finally, the clay

mold was dried. This mode was to be used in the

fusion and penetration process of matrix body.

Figure 4 Making the clay mold .

The sand mold may also be used in the process of

fusion and penetration of matrix body. Difference in

respect of manufacturing process exists between the

sand mold and the clay mold. The silica gel

prototype is placed in the graphite mold casing.

Then the mixture of emery grit, resin adhesive and

curing agent is put in the assembly, to fill the cavity.

Wait approximately 2 hours for the sand mold

solidification. Then directly take the silica gel

prototype out of the assembly. The sand is quartz

sand with a 200 mesh in grain size, to ensure the

matrix body resulting from fusion and penetration

has an ideal roughness. The resin adhesive is furan

resin or phenolic resin. The mixing ratio of emery

grit, resin adhesive and curing agent is 100:1.2:0.6.

The sand mold can be made faster and more simply.

2.3 Machining of Steel Cylinder

The steel cylinder is the basic component of the bit.

One end of the steel cylinder is tapered, and

machined to have shallow rippled grooves, so that

the WC matrix body can be consolidated with

bronze in the process of fusion and penetration. The

consolidation result is acceptable. The other end of

the steel cylinder is machined to have female

threads, for connection with the drill rod. In case the

bit is worn, it can be easily replaced with a new one.

The steel cylinder is often made of #45 steel. In

addition to machining, it undergoes also the heat

treatment process. Both the outer diameter and the

inner diameter of the steel cylinder must be in

accordance with those of the bit. Inward and

outward taped surfaces are arranged where the

matrix body is connected to the steel cylinder. To

ensure the shape and taper of the outward tapered

surfaces, a steel sleeve with a tapered mouth is

machined along with the steel cylinder. The steel

sleeve will be used in making the clay mold or the

sand mold. See Figure 5.

Figure 5 Combination of steel cylinder and steel sleeve.

2.4 Assembly of Mold and Mold Casing

Fix the steel cylinder at the center of the assembly of

mold casing and clay mold/sand mold. Gates (i.e.

preformed graphite bars) are attached with quick-

action adhesive to the locations in the bit for the

gates. To the locations for the PDC cutters in the

clay mold/sand mold, graphite chips are stuck,

which have the same shape and dimensions as the

PDC cutters. These graphite chips are prepared in

advance, and will be removed with the completion

of the matrix body manufacturing, to make room for

the PDC cutters to be welded. To the inner wall of

the mold casing, polycrystalline diamond bars are

stuck. Through the process of fusion and

penetration, these bars will be affixed to the surface

of the matrix body, serving to enhance wear

resistance. See Figure 6.

Figure 6 Assembly of mold and mold casing.

2.5 Material Loading

Materials used for the matrix body are mainly WC

or W2C powder, as well as a small amount of

metallic materials added for property modification.

Referring to table 1, the WC/W2C powder must use

a multi-grain-size formula, to ensure the ideal

overall compactness and surface quality of matrix

body from the process of fusion and penetration. A

frequency- adjustable vibrator shall be used for

powder loading. The vibrator keeps vibrating the

mold casing and the mold, so that the powder flows

substantially into the cavity between them.

Generally, a small amount of WC/W2C powder is

first loaded, to a depth of about 5mm from the end

of the steel cylinder. Then more WC/W2C powder is

added until the level reaches the bottoms of the

cutting wings. Finally, copper-based or ferrous

metal-based powder is added to the tapered surfaces

at the roots of the cutting wings. The powder serves

as connection. The subsequent turning process in a

lathe is feasible for these tapered surfaces. See

Figure 7. With the powder loading process

completed, a certain amount of bronze particles and

borax are placed in the clearance between the

uppermost mold casing wall and the steel cylinder.

Then the assembly can be transferred into the

furnace to receive the process of fusion and

penetration.

Table 1 Mass ratios of materials used in matrix body.

Figure 7 Loading powder in the assembly.

2.6 Fusion and Penetration

The matrix body of the curved-profile PDC bit

adopts the technology of fusion and penetration

(impregnation). The technology is in the field of

powder metallurgy. The whole assembly is heated in

the furnace. The heating scheme shall meet the

specification. The first stage is heating to

somewhere from 1000ºC to 1100ºC; the second

stage is temperature holding. All bronze particles

melt, penetrating into the voids of the WC/W2C

powder skeleton. Result is a compact matrix body.

Generally, the heating at the early stage shall be

controlled at a slow rate. First, it is good for reliably

warming the mold casing and the clay mold or sand

mold. Secondly, it is good for slowly volatilizing the

resin adhesive and curing agent off the assembly. Be

sure to prevent the assembly deformation due to

rapid heating rate. The entire process of fusion and

penetration takes approximately five minutes, with

all the bronze particles penetrating the voids of

WC/W2C powder skeleton, and the steel cylinder

integrated with the matrix body.

2.7 PDC Cutters Brazing

With the matrix body obtained from the process of

fusion and penetration, PDC cutters welding is

performed to get eventually the PDC bits. First,

remove the graphite chips, and clean the locations

for welding the PDC bits. These locations shall have

no oil stain or oxidation scales. Then, using the

copper-based or silver-based welding agent, and the

high frequency heating process, weld the PDC

cutters to these locations. Equipment used for

making PDC cutters is a six-acting-face high-

temperature, high-pressure press. Usually, the PDC

cutters have a regular shape, cube, prism, or

cylinder. The welding agent is of copper-based,

silver-based, aluminum-based, or nickel-based alloy,

with a melting point above 450ºC. With the welding

in progress, the fluxing agent is added, such as

borax, boric acid, chloride, or fluoride. The high-

frequency electric induction heating/welding yields a

good many benefits, such as simple operation, being

free of local deformation, high welding strength,

considerable material saving, and excellent

mechanical behaviors.

2.8 After-treatment

The after-treatment processes mainly refer to the

machining of the tapered surfaces of ferrous metal-

based powder from fusion and penetration, and the

finishing of the edges, corners, and surfaces. In

addition, the parts temporarily used for the

formation of the gates must be removed. Machining

methods include turning, drilling, milling, and sand

blasting.

3 CONCLUSIONS

The technology of fusion and penetration used for

making the matrix-body PDC bits consists mainly of

such processes as making the prototype using the 3D

printing technology, making the clay mold or sand

mold by copying the 3D printed mold, material

loading, fusion and penetration, and after-treatment.

As integration of the modern 3D printing technology

and the conventional mold manufacturing

technology, the method of fusion and penetration is

capable of effectively applying a variety of materials

of special properties at different locations on the bit,

to form a gradient mechanical properties system.

Moreover, this method is capable of ensuring the

required structural and dimensional accuracy of

PDC bits. The products are notable for fairly good

application results. Their manufacturing processes

are simple, with the manufacturing quality and

manufacturing efficiency enhanced.

REFERENCES

1. Mei Xiaoqin, Yin Guofu, Xu Jin et al. Technology for

rapid formation of the basic parent mold for matrix-

body PDC bits based on the FDM technology [J].

Drilling Technique, 2012.35（2）:57-59.

2. Diao Wenqing, Tang Dayong. Research in the

sintering process of matrix-body PDC bits used in

oriented drilling [J]. Coal Science and Technology，

2013,41（3）:21-23.