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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.