Lead-Free Materials in Precision Turned Parts: What the Transition Actually Involves

Lead has been a valued alloying addition in turned parts manufacturing for decades. It significantly improves machinability: chips break shorter, cutting forces decrease, and tool life extends. CuZn39Pb3, the classic free-machining brass, and leaded free-cutting steels such as 11SMn30Pb were therefore the standard in high-volume precision turned parts production for the better part of a century.

Whatever the outcome of ongoing discussions about transitional arrangements, one thing is clear: the importance of lead-free materials will only grow in the years ahead.

Switching to lead-free materials is not a simple like-for-like substitution. It changes machinability characteristics, tool wear behaviour, surface quality — and with them, process parameters and unit costs.

What lead does in machining and what changes without it

Lead forms soft inclusions in metal alloys that cause the chip to break during machining. This reduces cutting pressures, improves heat dissipation and prevents the formation of long, continuous swarf that can damage tooling and disrupt automated manufacturing processes. Short, broken chips are a precondition for fully automated bar-fed production.

Lead-free alternatives behave differently. Depending on the application, the most commonly used lead-free materials are:

• Bismuth brass  —  Good machinability  /  Higher material costs
• Silicon brass  —  Suitable for drinking water applications  /  Higher tool loading
• Lead-free free-cutting steel  —  Established standard  /  Less favourable chip breaking

What the material change means in practice

The effects of a material change on the manufacturing process are considerable and should not be underestimated:

–   Tool life decreases: Lead-free alloys are tougher in the cutting zone. Cutting edges wear more rapidly, regrinding intervals shorten, and tool cost per part increases.

• Cutting parameters must be re-optimised: Cutting speed, feed rate and depth of cut all need to be reset. This means test runs, process optimisation and a ramp-up period.
• Cycle times may increase: Those who have pushed cycle times to the limit with leaded materials will often need to run at lower cutting speeds with lead-free alternatives in order to keep tool life economically viable.
• Surface quality changes: Surface roughness values and the tendency to form burrs both change. For components with tight surface finish requirements, the target values need to be revalidated.
• Material certificates change: New alloys require new material data sheets, new heat certificates and, in regulated sectors such as medical technology and automotive, new approval processes.

What this means for procurement: a material change is not a change order. It is a development project with process qualification, first article production and an approval cycle — with the corresponding investment of time and cost.

How design and material selection influence manufacturing costs

Those designing a component for lead-free manufacture can influence the economics of the process through targeted design decisions:

• Tight tolerances only where functionally necessary: Lead-free materials are more sensitive to variation in cutting forces. The tighter the tolerance, the higher the scrap rate on processes that have not been fully optimised.
• Geometry designed for chip control: Undercuts, recesses and abrupt changes in geometry increase the risk of swarf build-up with tougher materials. Chamfers and radii are the simplest countermeasure.
• Agree material selection with the manufacturing partner at an early stage: Whether CuZn21Si3P, CuZn40Bi2 or another alloy is the right choice depends on the application, the medium, corrosion requirements and the manufacturing process. This decision belongs in co-engineering — not in purchasing when the delivery date is already pressing.

In summary: Lead-free is a process decision, not a materials decision.

The transition to lead-free materials is technically achievable. It does, however, require new process parameters, new tooling strategies and — depending on the sector — new approval documentation. Treating it as a simple raw material substitution underestimates what is actually involved. For that reason, design, material selection and manufacturing process should be considered together from an early stage in the project.

The right choice of replacement material depends on the application, the medium, corrosion requirements and the manufacturing process. That decision should be made in co-engineering — not in purchasing when the delivery date is already running.

If you are facing a material transition, designing a new turned part for lead-free manufacture, or have specific questions about lead-free materials, please do not hesitate to get in touch.

A material change demands not only a new approach to the process, it also places high demands on long-term process control.

Further reading:

Why Series Stability in Precision Turned Parts Matters More Than Unit Price

Frequently Asked Questions (FAQ)

Can an existing component simply be manufactured using a lead-free material?

Not always. Even if the geometry remains unchanged, machinability, tool wear behaviour and surface characteristics all differ. Adjustments to manufacturing parameters are frequently necessary, and in some cases minor design optimisations are required as well. A material change should therefore always be assessed in close collaboration with the manufacturing partner.

Do unit costs inevitably increase with lead-free materials?

In most cases, yes — though the extent depends on the alloy, the geometry and the batch size. The additional costs arise from higher raw material prices (particularly for bismuth), shorter tool life, longer cycle times and the process optimisation effort during the changeover. In high-volume series on well-optimised machines, the difference can be reduced to a few percentage points. In smaller series or with complex geometries, it may be considerably higher.

Does a material change affect the existing component approval?

Yes, as a rule. A change of raw material is treated as a significant change in most quality management systems — particularly under IATF 16949, ISO 13485 and comparable standards — and requires new first article production, process validation and re-approval. Underestimating this effort risks delivery delays and quality problems at launch.

Can a material change be made on a live component without a new series approval?

No, not without agreement from the customer and an update to the approval documentation. Even if the new material is technically equivalent, a material change requires updated first article documentation, a new material certificate and, in regulated sectors, renewed qualification. Making such a change without prior agreement constitutes a breach of the obligation to inform the customer.

Who are Häni + Co. AG?

Häni + Co. AG is a Swiss family business based in Arch in the canton of Berne. Founded in 1939, the company has manufactured custom precision turned parts for demanding industrial applications for over 80 years. Its capabilities encompass conventional and CNC-controlled single-spindle automatics, multi-spindle machines and rotary transfer machines, together with in-house finishing operations including centreless grinding, honing, vibratory finishing and roller burnishing. Häni + Co. AG holds certifications to ISO 9001, ISO 14001, ISO 13485 and IATF 16949, and supplies customers in building services, medical technology, interconnect technology, sensor technology, robotics and automotive. Diameter range: Ø 1 to 65 mm.

Which sectors does Häni + Co. AG supply?

Building services, medical technology, interconnect technology, sensor technology, robotics, fluid technology and automotive. Typical components include shafts, axles, bushings, pinions, valve spindles, contact pins and connector elements. Swiss Precision since 1939.