How Surgical Instruments Are Made: From Forging to Passivation

A reusable steel instrument such as a hemostat or a pair of scissors goes through many separate steps before it reaches a hospital. Some steps happen in large factories, some in small specialist workshops, and some at outside suppliers. This guide sets out the usual sequence, from steel bar to packed instrument, and explains what each stage does. It is a general overview. Every manufacturer has its own process, and the details for a given product are set by its drawings and its quality system.

The process at a glance

Industry and training sources describe broadly the same sequence for reusable stainless steel instruments:

1. Material selection
2. Forging the blank
3. Trimming the excess metal
4. Machining and milling (box locks, ratchets, serrations, teeth)
5. Fitting and assembly
6. Heat treatment (hardening and tempering)
7. Grinding and sharpening
8. Polishing or surface finishing
9. Passivation
10. Marking, inspection, cleaning and packing

The order is not fixed. Some parts are machined after hardening, and inspection happens throughout rather than only at the end. A study of the Sialkot cluster in Pakistan by the Ethical Trading Initiative (ETI) and the Pakistan Institute of Labour Education and Research (PILER) found that a reusable instrument can involve up to 40 production processes, while a disposable instrument made from lower-grade steel involves about 20.

1. Choosing the steel

Most reusable surgical instruments are made from stainless steel. A lesson plan published by the US Healthcare Sterile Processing Association (HSPA), adapted from material by Aesculap, explains that the 300 and 400 series are the most common grades. The 400 series is used for cutting instruments and many non-cutting ones. The 300 series is used for some non-cutting instruments.

The grade matters because it decides whether the part can be hardened. Martensitic stainless steels, the family that includes the 400-series grades used for blades and jaws, can be hardened by heat treatment. Austenitic grades in the 300 series are not hardened this way, and are chosen where corrosion resistance matters more than hardness.

Manufacturers usually work to recognised material standards. KLS Martin’s published delivery terms for its suppliers, for example, require approved materials under DIN EN ISO 7153-1, the standard for metals used in surgical instruments, and ask for 3.1 material test certificates under DIN EN 10204 to be kept for 30 years after delivery.

2. Forging the blank

Most ring-handled instruments start as a forging. A piece of steel is heated and pressed or hammered between shaped dies, so that it takes the rough outline of one half of the instrument.

Forging is often a specialist trade. In Pakistan, a 2015 Newsweek Pakistan report said that factories in Sialkot mostly source their steel from forges in the nearby city of Daska. In Germany, larger brands also buy in forged blanks. KLS Martin’s supplier terms state that forged parts must be free from folds, voids and discontinuities, which are the typical forging defects that would weaken an instrument.

3. Trimming

A forging comes out of the die with a thin rim of surplus metal, called flash, around its outline. This is cut off in a trimming press, leaving the raw shape. The ETI study lists forging and trimming as the first steps carried out in the informal vendor workshops that supply many Sialkot exporters.

4. Machining and milling

The working features are then cut into the blank. Depending on the instrument this can include:

• the box lock or screw joint where the two halves pivot
• the ratchet teeth on the handles of a hemostat or needle holder
• jaw serrations, cross-hatching or tissue teeth
• slots for tungsten carbide inserts
• finger rings and shanks brought to final shape

Milling used to be done almost entirely on manual machines with jigs. CNC machining is now common for complex parts. A planned Pakistani government skills programme reported by the Associated Press of Pakistan lists CNC machining among the skills it plans to train for in the Sialkot sector, alongside forging, grinding and polishing, electropolishing and passivation.

5. Fitting and assembly

For a jointed instrument, the two halves are fitted together. With a box lock, one half is passed through a slot in the other and the joint is closed and riveted or screwed. Fitters then adjust the halves by hand so that the jaws meet evenly, the tips line up, and the ratchet engages cleanly. This hand fitting is one of the most skilled parts of the job, and much of the difference between a good and a poor instrument is decided here.

6. Heat treatment

Martensitic stainless steel is hardened by heating it to a high temperature and then cooling it quickly (quenching). This produces a hard but brittle structure. The part is then tempered, which means reheating it to a lower temperature to relieve internal stress and restore some toughness. Wikipedia’s article on martensitic stainless steel describes this quench-and-temper route as the standard way of hardening these grades.

The target hardness depends on the job. The HSPA lesson notes that sharp instruments need more hardness, while instruments such as clamps need less. Hardness is normally specified on the drawing. KLS Martin’s terms say that where the drawing gives no value, DIN EN ISO 7153-1 applies, and name the standard Vickers and Rockwell test methods used to check it.

Many factories send heat treatment to specialist firms with vacuum or controlled-atmosphere furnaces. In the ETI study’s description of Sialkot, heat treatment, die making and polishing were among the steps more often kept in the formal factory sector.

7. Grinding and sharpening

After hardening, the steel is ground to its final dimensions. For scissors this includes grinding the blade edges and setting the blades so that they meet along their length. For forceps and hemostats it means bringing the jaws and tips to their final profile and removing any scale left by heat treatment. Edge-sensitive instruments are often sharpened and tested by hand.

8. Polishing and surface finishing

The surface is then finished. Instruments are usually either polished to a bright, reflective finish or given a satin (matt) finish that reflects less light. The finish is applied by polishing wheels, brushing or blasting, and some makers also use electropolishing.

A good finish is about more than appearance. KLS Martin’s supplier terms require surfaces free of pores, cracks, grooves, burrs and residues of grinding and polishing agents, and set a maximum surface roughness of Ra 0.5, measured across the brushing direction. Sharp edges must be broken unless they have a special function.

9. Passivation

Stainless steel resists corrosion because chromium in the alloy forms a thin, protective chromium oxide film on the surface. Machining, grinding and polishing can leave free iron and other particles on that surface, which can later rust. Passivation is a chemical treatment that removes these contaminants and helps the protective layer form.

The HSPA lesson describes passivation as dipping the instrument in nitric acid to remove carbon and steel particles left from manufacturing. ASTM A967, a widely used specification for chemical passivation of stainless steel parts, covers treatments in nitric acid and citric acid solutions as well as electrochemical methods, and sets out tests to verify the result. The oxide layer continues to thicken over time, and protecting it is the basis of correct instrument care.

10. Marking, inspection and packing

Finished instruments are marked, usually by laser or etching, with details such as the manufacturer’s name or logo, catalogue number, and a lot or batch code. These marks allow an instrument to be traced back to its production batch.

Final inspection typically checks dimensions, alignment, jaw closure, ratchet action, cutting performance for scissors, and the surface for defects. KLS Martin’s terms also ask for instruments to be delivered oil-free, with joints and moving parts lubricated with medical paraffin oil. Reusable instruments are normally supplied non-sterile, and must be cleaned and sterilised by the hospital before first use according to the maker’s instructions.

What this means for buyers

Because so many steps are involved, one instrument may pass through several workshops before it carries a brand name. The ETI study found that in Sialkot most production is outsourced to small vendors, and that the location of each manufacturing stage is often not documented. If you are sourcing instruments, it is reasonable to ask a supplier:

• which steel grade and material standard are used, and whether material certificates are available
• which steps are done in-house and which are subcontracted
• how heat treatment is controlled and how hardness is tested
• whether passivation is carried out and to which specification
• which quality management certification covers the site, such as ISO 13485

Our guides on how to check a medical instrument supplier and on company roles such as manufacturer, OEM and exporter explain how to follow up on the answers. You can also browse the surgical instrument database to compare patterns and materials, or look at producer countries such as Pakistan and Germany. Suppliers of components, materials and manufacturing services exhibit at trade fairs such as COMPAMED.

Sources

• Healthcare Sterile Processing Association (HSPA): Spry, C. and Aesculap Inc., “Processing and Care of Surgical Instruments”, CIS Self-Study Lesson Plan CIS 294, Process, November/December 2022 (PDF hosted by Purdue University)
• KLS Martin Group: Technical terms of delivery of surgical instruments
• Ethical Trading Initiative and PILER: Labour standards in Pakistan’s surgical instruments sector, a synthesis report
• Newsweek Pakistan: “Sialkot’s Sweatshop Scalpels”, Louise Tickle, January 2015
• Wikipedia: Martensitic stainless steel
• ASTM A967/A967M-25: Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts (scope via SNV)
• ISO 7153-1:2016 Surgical instruments: Materials, Part 1: Metals (catalogue entry)
• Associated Press of Pakistan: Govt plans Rs 2.8 bln initiative to modernise Sialkot surgical instruments sector