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Metal injection moulding (MIM) is a manufacturing process that has helped many globalmedical device manufacturers meet the challenges they face when it comes to formingcomplex shapes from biocompatible materials. Sachin Shrikant Malgave of Indo-USMIM tells Medical Device Developments about its major benefits and applications.

Break the

mould

In terms of global manufacturing,

present day technological needs

are being examined both from a

cost standpoint as well as with regards

to added value. Every medical device

manufacturer is looking at the possibility

of having a leaner supply chain without

sacrificing qualitative needs.

Biocompatible materials have in

recent years really begun to shape

the development of medical devices

and expand the potential for developers

and manufacturers as well as, ultimately,

the treatments offered to patients.

However, they have posed challenges

for manufacturers as their contours and

shapes can be complex. Metal injection

moulding (MIM) is a manufacturing

process that has helped many global

medical device manufacturers to meet

those challenges.

The MIM process arms medical

device makers with the ability to design

unique products without the cost

restrictions associated with conventional

metal-forming techniques. Medical

device manufacturers are impressed

with the freedom MIM offers. It suits

their needs and allows them to focus on

identifying new-generation technology

that can help provide cost-effective

solutions, while

keeping quality and

safety requirements

intact. The MIM

process combines

the design flexibility

of plastic injection

moulding with

the strength and

integrity of wrought

metals. MIM

technology has

proven itself to be a

viable method for

the production of

complicated and complex-shaped

contours of metal components used

in diverse applications such as

endoscopic and laparoscopic instruments,

orthodontic, and surgical tools, and

implants. These are made from stainless

steels, cobalt and titanium alloys, and

ceramics. Surveys have also concluded

that the MIM process is sustainable

since it generates comparatively less

CO2

and consumes less water.

The I process

The basis of MIM technology involves

fine metal powders, which are combined

with thermoplastic binders that allow

them to be injection-moulded in a

plastic injection moulding machine.

Once moulded, the part is subjected

to high temperatures in a controlled

atmosphere where the binder burns

away and the metal particles fuse into a

near fully dense solid. Similar to plastic

injection moulding, MIM part geometry

has few limitations, which makes it very

inexpensive to mass-produce highly

complex parts once a tool is constructed.

Metal alloy selections are virtually limitless.

Developed more than 25 years ago,

the MIM process found its first medical

applications in orthodontic brackets.

These tiny complex shapes were ideal

MIM parts or medical applications.

MIM process fow diagram.

1. Feedback preparation

Metal powder Binders

Mixer

Injection moulding machine

2. Moulding 3. Solvent debinding 4. Pre-sinteringand sintering

5. Sintered component

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for the process and today MIM is the

preferred manufacturing method. The

explosion in laparoscopic surgical

procedures in the past ten years has

further driven the use of MIM in medical

applications. Small and finely detailed

parts such as endoscopic graspers are

now economically made via MIM.

Confidence in the MIM process and

materials has grown in the surgical

instrument and implant manufacturing

community. New applications for

instruments, reusable tools to assist in

surgical procedures as well as implants

are now becoming a reality with cost

savings and design flexibility being

key drivers in MIM process adoption.

MIM parts are used widely in the

following medical application areas:

minimally invasive surgery (MIS):

laparoscopic and endoscopic jaws,

graspers, scissors

general surgical:scalpel handles,

nippers, forceps and instrument

mechanism parts

orthopaedic surgery:trauma

plates, screws, spine (implants

and external fixation) and

orthopaedic surgery tools

(power and hand type)

open heart surgery:stabilisers and

positioners and various other parts

orthodontic and dental:

orthodontic brackets, dental

instruments and implants

hearing aids: metal hook, tube

element and various other parts.

MIM can manufacture most of the

medical alloys offered by either the

wrought or cast routes. MIM offers a

wide variety of materials for medical

applications such as stainless steel

(300, 400 series, precipitation-hardened

grades) and its nickel-free grades, Co-Cr

alloys, and titanium and its alloys.

For instruments that require high

strength and wear combined with good

corrosion resistance, solutions can

be found in MIM SS 17-4 PH, 420 and

SS 440C-grade stainless steels. MIM

316L-grade stainless steel is a popular

choice for applications that require high

ductility and excellent corrosion properties.

MIM nickel-free stainless grades are

used for orthodontic applications.

Orthopaedic implant applications are

growing for MIM, and the Co-Cr as well

as titanium alloys with HIP processing

are used for these critical applications.

Parts can be fabricated out of difficult-

to-melt alloys such as tungsten-heavy

solutions. Any tailor-made chemistry

can be formulated by MIM.

MIM materials have advantages such

as homogeneous microstructure and

isotropic material properties with no

interconnected porosity. Hence, MIM is

the most suitable manufacturing process

for complex medical parts, with part

performance and material properties on

a par with the wrought and cast route.

Spinal surgery application

The various parts of orthopaedic surgery

instruments, such as trauma plates,

blades, screws, spine (implants and

external fixation) and orthopaedic surgery

tools (power and hand), are successfully

manufactured by the MIM process.

The critical requirement of orthopaedic

surgery equipment parts are: complex

geometry; high length to thickness

ratio; good dimensional consistency and

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close tolerances for proper assembly and

function; material with high hardness

and good corrosion resistance; and clean

manufacturing process to meet the

specified cleanliness in the final component.

One recent application developed for

MIM is a retractor blade and ring set

used in a spinal surgery procedure.

Manufactured by Indo-MIM for a leading

orthopaedic implant manufacturer, MIM

resulted in a dramatic reduction in

manufacturing costs without sacrificing

product quality or function. Made in

three lengths, the retractor blades offer

the surgeon easy access in order to insert

the fixation rod during the procedure.

Previously made from wrought 17-4PH

stainless steel bar stock, both parts

required extensive multi-axis CNC

machining as well as wire electrical

discharge machining (EDM) to achieve

the intricate detail. Indo-MIM was

able to produce the products with its

MIM technology in the 17-4 PH alloy

and achieve the required mechanical

properties and biocompatibility

requirements. Indo-MIMs cost-effective

tooling and product development

resources were able to tool up the three

blade lengths and ring quickly, while

still being economically viable for

small-series production volumes.

IS instruments

MIS has been widely adopted for

certain surgical procedures and

manufacturers are looking to design

new devices that will allow open

surgeries to be converted to minimally

invasive procedures. MIS devices are

highly complex, yet they need to be

cost-effective in low to moderate

production volumes.

The following

should be noted:

Laparoscopy

and catheters

are popular MIS

procedures.

MIS is

expected to

further reduce

invasion

and be

used for

microscopic operations

in narrow spaces.

Laparoscopic jaws and graspers for

MIS instruments are successfully

produced by metal injection moulding.

Laparoscopic jaws, endoscopic

jaws, graspers, scissors and

instrument bodies for MIS have

been widely manufactured by MIM.

Tight tolerances are necessary for

proper fit, form and function for the

mating parts in the final assembly,

and material with high hardness

and good corrosion resistance is

required for these applications.

The clean manufacturing process to

meet the specific cleanliness level

in the final component is must.

Indo-MIM produced the products

with its MIM technology in the

17-4 PH alloy, and achieved the

required mechanical properties

and biocompatibility requirements

at a significant saving.

MIM has incorporated all of the

critical features and geometry of

the parts in the injection mould,

avoided the machining, and

produced the net-shape components.

Fixation plates

Another potential MIM candidate is the

family of plates used in the plating

system for the treatment of fracture

fixation, reconstruction or arthrodesis

of small bones, including those in the

forefoot, midfoot and hindfoot. The

characteristics of the plate call for a

profile that allows fixation in various

profiles as per a contour customised to

specific anatomy to facilitate fusion or

fracture reduction, and stabilisation. As

the plate is compressed to bone, the

plate will further contour to the specific

anatomy of the patient.

Many of the plates also incorporate

a slot used to assist this compression

and they need to have a matching

profile to house the head of the special

screws. MIM meets the challenge of

biocompatibility as well as complexity

owing to its unique capabilities. It

manages to meet the low-volume,

high-variety requirement of such an

application, thereby allowing the surgeon

to offer problem-free treatment.

MIM has been used as a successful

manufacturing process for complex parts

for various medical products, meeting

high quality and regulatory requirements

with a variety of medical materials.

Sachin Shrikant algaveSachin Shrikant Malgave is deputy manager, R&D Group, for Indo-MIM.

He has nine years experience in metal injection moulding, mainly in the

area of materials and process development. Malgave is certied as Six

Sigma black belt from the American Society for Quality (ASQ).

MIM parts for MIS application.

Typical medical grade materials processed by I

Stainless steels

Austenitic 304L, 316L

Martensitic 410, 420, 440C

Precipitation-hardened 17-4PH

Duplex structure 2205

Specialty alloys

Titanium alloys CP Ti, Ti-6Al-4V

Co-Cr alloys F-75

Refractory Tungsten-Ni-Fe

Ceramics Alumina, Zirconia -