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February 11, 2016 5 min read

The process outlined below gives us an idea as to what is involved in the design and manufacturing of Class I Medical Devices, namely Surgical Instruments, all of which is work mainly done by hand. 


Initial design
For the design of new items, this stage is where samples are drawn by hand or on a computer, which may require the consultation of surgeons, nurses, decontamination leads, engineers, techs, craftsmen, distributors and/or sales people.


Prototype

A 3D model of the item is created by hand or computer, taking anywhere between a few hours, to a few months depending on the complexity and its requirements.


Raw material selection

Stainless steel is the name given to a family of steels which contain more than 11% Chromium. The chromium in the steel gives it it's property of being “Corrosion Resistant” and “self repairing”. The chromium reacts with oxygen and forms a “passive” layer, which serves as the protective barrier against corrosion. If a stainless steel instrument receives proper maintenance, the instrument will become more corrosion resistant over time, and have a longer life.

The identification and sourcing of the correct raw material for the devices specific application is crucial. Even though there are many variants of stainless steels manufactured, approximately a dozen out of these are useful in making surgical instruments.

The grades commonly used in the manufacturing of surgical instruments can be found in standards such as ISO 7153, BS 5194 and AISI F899. They are chosen for their specific performance data, often critical to the instruments application. Some factors that they would have considered in the utilisation of these particular grades of stainless steel are its application, hardness, flexibility, tensile strength and malleability.


Austeniticstainless steel is characterised by its high ductility (i.e. its ability to stretch thin when tensile strength is applied, or bend using compressive force) and non-magnetic properties.

eg - AISI 304 : Used for Cannula, Clamps, Holders, Spreaders, suction tubes etc.
Appropriate selection of the material helps in achieving the intended output of the manufacturing processes and the final required specifications.


Martensitic
stainless steel is characterised by its high strength, brittleness and magnetic properties. The hardness of steel is determined by a steels carbon content. Some steels can be hardened to a particular degree, and some simply cannot be hardened at all.

eg - AISI 410 /410 X : Used for Gripping Instruments like Forceps, Tweezers, Dressing forceps, retractors etc.

- AISI 420 A : Used for Cutting instruments like Bone Rongeurs, Chisels, Gouges, scissors with carbide inserts and Needle Holders etc.

- AISI 420 B
: Used for High grade cutting instruments like Scissors, Bone Rongeurs etc.


Die / Mold

A die is a specialised tool used in cutting or shaping material mostly using a press. If a new item is designed, than this is made with the aid of computers. If a current design is being used, then a die or mold for an established pattern is referred to and used.


Drop Forging
This is a process for shaping metal parts through compressive forces in either a hot, or cold state. There are two types of forging processes involved in surgical instruments manufacturing - Hand forging for small quantities orders, and Hammer Forgings for bulk quantities.


Press Work
After getting a crude impression in the piece of metal, the excess material around that shape is trimmed to get a more desirable shape in the form of forgings.


Surface Treatment

The main purpose of this treatment is to clean the surface of the steel parts and if carried out properly, they all increase the corrosion resistance. Pickling is the main technique used to remove the scale formed due to oxidation.


Machining
This process involved the removal of material.

Lathes: are used to create an object with symmetry about an axis of rotation.  
Milling: can create a variety of features on an object by cutting away the unwanted material. Through milling, different features such as serrations, ratchets, the cutting of the male and female parts of a box joint, different types of grooves etc. are produced in surgical instruments. 
CNC: Is a computer aided machine which uses tools to perform milling and lathing. These machines use 3, 4 or even 6 axis.


Filing
This is another material removing processes where different types of grinding wheels and files are used. It is a critical stage in the surgical instrument manufacturing process because the basis for the general shape is produced here, where different types of gauges and initial settings are done.


Injection molding
An effective way to produce complex and precision-shaped parts from a variety of materials without machining, and has the ability to produce parts with complex shapes, superior strength, and excellent surface finish.


Heat Treatment
This is done to change the instruments physical and mechanical properties without changing the original shape and size.

Annealing: is done to soften the material. 
Hardening: is done to produce hardness. 
Tempering: is done to give toughness to the instruments. 

Heat treating is a very useful process to help other manufacturing processes and also improves the performance of the product by increasing strength as well as other desirable characteristics.


Electro Polishing
An electrochemical process that is a super passivator of stainless steel and results in a more passive surface than traditional methods. The surface of the metal becomes bright and its appearance looks fine. Some burr is removed in this process. Phosphoric and sulphuric acids are used in conjunction with a high current to clean and smooth the surface of the steel.


Polishing and Buffing 
These are the metal finishing processes to produce different types of appearances like a mirror finish, or a dull one. Different abrasives are used on a rotary wheel to finalise the finish.


Ultrasonic Cleaning

A process that uses ultrasound to clean the surgical instrument from any foreign matter, such as polish or bits of metal.


Functional Setting and Testing
At this stage, setting the instrument and testing is done to align the instruments and ensure it is functioning properly.


Colour / Powder coatings (Gold, Black, Titanium)



Tungsten Carbide Insertion
Tungsten Carbide is made of a high quality material that withstands rust, and provides a longer lifespan for the instruments while performing the necessary functions efficiently. Usually the tungsten carbide inserts are fixed onto the working parts of the surgical instruments.


Passivation
Is performed when oxide scale, rust, iron particles and metal chips adversely affect the stability of the surface. The process involves immersing the stainless steel instruments in a solution of nitric or citric acid and sodium dichromate, dissolving the imbedded iron particles, which then restores the original corrosion resistant surface by forming a thin, transparent oxide film.


Oiling


Quality Checking

The secret behind affordable-reliable instrumentation lies in the careful selection of raw materials and then the level of effort invested in finishing. It typically takes 20% of the time to make 80% of the instrument, but 80% of the time to finish the other 20% (Pareto's principle).

The entire manufacturing process has its own set of parameters, where each parameter may rely on each customers requirements. 

The combination of the rising price of steel and the level of effort put into finishing an instrument is reflected in cost. Finding the perfect balance between cost and quality takes many years of experience.

If reusable surgical instruments were treated as an investment, they would last a lifetime. When instruments are treated as an everyday consumable item, then some of the risks associated with poorly finished instrumentation (such as contamination) could be eradicated.

Good quality, well finished instrumentation would reduce on-going costs, by lessening the risk of infection / cross contamination, would result in quicker patient recovery times and a reduction in bed occupancy levels.


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