AMT | Application of Powder Metallurgy Structural Parts in Dental Applications

Date：2025-08-04   Views：1003

Metal injection molding (MIM) is a technology that uses metal powders as raw materials and employs plastic injection molding processes to manufacture metal parts. It was initially used to produce ceramic parts with oxide powders (such as Al₂O₃), hence the term ceramic injection molding (CIM). Since both MIM and CIM use powders as raw materials, they are collectively referred to as powder injection molding (PIM).

MIM is a new metal parts forming technology combining powder metallurgy with modern plastic injection molding. It emerged in the late 1970s, initially for manufacturing lightweight weapon components. In the 1980s, this technology drew attention from the U.S. medical device industry. Consequently, medical and dental markets hold a significant share of the U.S. MIM parts market. From 1998 to 2008, in the annual MPIF (Metal Powder Industries Federation) Design Competitions, 14 medical and dental powder metallurgy parts won awards, 12 of which were MIM parts. This indicates that MIM parts have gained widespread acceptance in the U.S. medical and dental industries, with production technology reaching advanced levels. Below is an introduction to the 14 products that won awards in the MPIF Powder Metallurgy Design Competitions from 1998 to 2008.

Laparoscopic Surgical Scissors

These laparoscopic surgical scissors, manufactured using MIM with 17-4PH stainless steel powder, feature cauterization capabilities. They are composed of a spiral gear and two individual scissor blades, with a density of 7.5 g/cm³. The 20-tooth spiral gear is produced using a unique "floating cavity" mold. The blades are precision-machined and heat-treated to achieve the desired curvature and edge. Compared to machined spiral gears, MIM reduces costs by 80%.

Figure 10-17 Laparoscopic surgical scissors

Endoscopic Scissors

The endoscopic scissors, used in minimally invasive cardiac, general, and reconstructive surgeries, are manufactured via MIM with 17-4PH stainless steel powder. They have a density of at least 7.5 g/cm³, a yield strength of no less than 966 MPa, and a tensile strength of no less than 1069 MPa. The parts are straight after forming and sintering, with the customer shaping them to the required curvature. Compared to machined parts from 303 stainless steel, MIM offers significant cost savings.

Figure 10-18 Endoscopic scissors

Needle Driver and Distal Clevis

These parts, manufactured using MIM with 17-4PH stainless steel powder, have a density of 7.68-7.72 g/cm³. The distal clevis has a hardness of 35-38 HRC, an elongation of 10%, and a yield strength of 1100 MPa. The needle driver has a hardness of 38-42 HRC, an elongation of 8%, and a yield strength of 1070 MPa. These parts are used in the daVinci robotic surgical system for minimally invasive procedures, offering high precision and dexterity.

Figure 10-19 Needle driver and distal clevis

Laparoscopic Jaws

These laparoscopic jaws, manufactured using MIM with 17-4PH stainless steel powder, consist of upper and lower jaws, a retainer, and an I-beam. They are used for high-compression applications in laparoscopic procedures. The sintered parts have a density of 7.6 g/cm³ and feature thin walls and complex geometries. The design allows for high compression, crucial for rapid melting of containers without thermal effects.

Figure 10-20 Laparoscopic jaws

Suturing Jaw

This complex-shaped part, manufactured using MIM with 17-4PH stainless steel powder, is used in medical suturing devices. It allows for one-handed operation to achieve secure and uniform suturing. The part has a density of 7.7 g/cm³, a tensile strength of 897 MPa, and a yield strength of 731 MPa. Additional operations include drilling three holes, reshaping, and finishing.

Figure 10-21 Suturing jaw

Intravenous Infusion Pump Latch

This complex-shaped part, manufactured using powder metallurgy with 316 stainless steel powder, is used in medical injection pump handles for intravenous solutions. It has a density of 6.7 g/cm³, a tensile strength of 448 MPa, a yield strength of 290 MPa, and an elongation of 11.5%. The latch must withstand high loads and repeated operations without wear or breakage. Switching to a powder metallurgy latch saves $100,000 annually.

Figure 10-22 Intravenous infusion pump latch

Biopsy Instrument

The biopsy instrument features eleven parts manufactured using MIM with 316L duplex stainless steel. They have a density of at least 7.52 g/cm³, a tensile strength of 503 MPa, a yield strength of 296 MPa, an elongation of 40%, and a hardness of 70-80 HRB. The instrument is designed for one-handed operation under ultrasonic guidance and offers cost savings of over 50% compared to machined parts.

Figure 10-23 Biopsy instrument

Bevel Gear

The bevel gear, manufactured using powder metallurgy with 304 stainless steel powder, is used in the drive mechanism of a surgical fiber cutter. It has a typical density of 6.6 g/cm³, a yield strength of 207 MPa, and a hardness of 63 HRB. Previously made by welding two machined parts, the PM gear reduces costs by 70%.

Figure 10-24 Bevel gear

Orthodontic Buccal Tube System

This series consists of 32 MIM brackets and 2 MIM slides in 17-4 PH stainless steel, heat-treated to achieve a tensile strength of 1276 MPa, a yield strength of 1103 MPa, an elongation of 7%, and a hardness of 38-42 HRC. This is the first all-metal Damon self-ligating appliance to adopt such a buccal tube system, with an annual production of over 12 million parts.

Figure 10-25 Orthodontic buccal tube system

Dental Manifold

This complex part, manufactured using MIM with 17-4PH stainless steel powder, is used in a manual fiber-optic dental device. It has a density of 6.7 g/cm³ and features 19 critical dimensions with tolerances of ±0.076 mm or smaller. Five of these dimensions have tolerances of ±0.0254 mm. The part is drilled in the green state due to the small drill diameter and has seven datum features. Switching to MIM eliminated machining scrap and improved yield from 60% to near 100%.

Figure 10-26 Dental manifold

Orthodontic System Bracket, Slide, and Hook

These three parts, manufactured using MIM with 17-4PH stainless steel powder, are used in the Damon 3 MX self-ligating orthodontic appliance. They have a density of 7.5 g/cm³, a tensile strength of 1186 MPa, and a yield strength of 1090 MPa. The parts are heat-treated, then tumbled and brazed by the customer just before assembly.

Figure 10-27 Orthodontic system bracket, slide, and hook

Functional appliance

This appliance, manufactured using MIM with nickel-free stainless steel, consists of two parts: one with a ball-ended rod and a socket, and the other with a hook. After sintering and polishing, the ball is press-fitted into the socket. The parts have a density of 7.6 g/cm³, a tensile strength of 659 MPa, a yield strength of 552 MPa, and an elongation of 22%. This design significantly reduces production costs compared to precision casting.

Figure 10-28 Functional appliance

Articulation Gear

This complex, tight-tolerance hook-and-gear assembly is produced by MIM in one piece, eliminating secondary operations. It has a density of over 7.65 g/cm³, a tensile strength of 900 MPa, a yield strength of 730 MPa, and a hardness of 25 HRC. MIM reduces production costs by approximately 70% compared to machining from bar stock.

Figure 10-29 Articulation gear

Pin Shroud

The pin shroud, manufactured using MIM with 316L stainless steel powder, is used in the shoulder-repair implant. It anchors sutured tendons to bone in arthroscopic labral repair. The part has a density of 7.85 g/cm³, a tensile strength of 538 MPa, a yield strength of 200 MPa, and an apparent hardness of 69.4 HRB. MIM near-net-shape production replaces three wire-EDM parts that were previously laser-welded, reducing final assembly time from 15 minutes to 5 minutes per unit.

Figure 10-30 Pin shroud