How Ceramic Extrusion Die Inserts Transformed Copper Tube Production

The Challenge: Deformation, Inconsistency, and Rework Cycles

The manufacturer produces hot-extruded copper alloy tubes for water supply, drainage, refrigeration, and air conditioning systems. In these applications, dimensional accuracy and surface finish directly impact product quality and end-use performance. Their extrusion process operated at high temperatures with significant mechanical forces, creating conditions that pushed traditional tooling materials to their limits.

Metal extrusion dies, whether fabricated from tool steels, hot working steels, or cobalt-based alloys like Stellite, suffered from a fundamental limitation: they deformed permanently under use. The dimensional accuracy of extruded products varied along their length due to unstable ram speed and progressive die deformation caused by high thermomechanical stresses. Temperature, reduction ratio, and lubrication all influenced dimensional outcomes, but in practice, adjusting these parameters couldn’t compensate for the die’s changing geometry during operation.

The consequences compounded throughout production:

• Dimensional inconsistency – Metal dies experienced “turn-in” deformation, in which high stresses caused the inner-diameter configuration to change, making the outer diameter of extruded tubes progressively smaller. Wall thickness decreased periodically while length increased, with variations of up to 6% between extrusions.
• Poor surface finish – Even with lubricants, metal dies produced unacceptable surface quality, requiring additional processing.
• Frequent rework – Metal dies required machining after the first two to three extrusion cycles, then again after approximately thirty cycles, to restore dimensional accuracy.
• Cold drawing operations – Manufacturers had to apply calibration through cold drawing to achieve acceptable dimensional tolerances, adding process steps and costs.
• Short die life – Despite reworking, metal dies had limited service life before complete replacement was required.

The operational costs were substantial: press downtime for die rework, large die inventories to maintain production during machining cycles, machine shop labor for frequent remachining, and ultimately, shorter die replacement cycles. The manufacturer needed a solution that could withstand the extreme conditions of hot extrusion without the progressive deformation that plagued metal tooling.

The Solution: Engineered PSZ Ceramic Inserts and Process Adaptation

Zircoa proposed transitioning from metal dies to partially stabilized zirconia (PSZ) ceramic extrusion die inserts in Composition 2016. However, the solution involved more than simply replacing one material with another; it required understanding ceramic material characteristics and adapting both die design and manufacturing processes to leverage PSZ’s advantages while respecting its limitations.

The transition was framed explicitly as a “learning curve.” Ceramics behave fundamentally differently from metals, particularly regarding tensile and shear stresses. The manufacturer and Zircoa worked collaboratively to optimize die design, establish proper installation procedures, and train manufacturing personnel on ceramic-appropriate handling and press operation.

Design Engineering for Ceramic Inserts

The ceramic insert design utilized the proven geometry from existing metal dies — configurations that had been refined empirically for each specific extrusion process — but incorporated critical modifications for ceramic material requirements:

• Minimized wall thickness – Reducing ceramic insert wall thickness prevented thermal stress buildup while maintaining structural integrity.
• Adapted land length – The die land (the parallel section of the bore) was optimized for ceramic material characteristics.
• Shrink fit compensation – To account for the reduction in inner diameter caused by shrink fitting the ceramic insert into the metal holder, the ceramic bore was increased by 0.5%.
• Metal casing design – The steel die holder was engineered to support the ceramic insert while accommodating thermal expansion differences.

This hybrid design preserved the metal casing’s structural role while positioning the ceramic insert to handle the extreme temperature and wear conditions at the extrusion interface.

Material Performance Advantages

PSZ ceramic delivered several properties that metal dies couldn’t match:

• Non-wetting surface – The ceramic is not wetted by most extruded non-ferrous alloys, preventing material adhesion.
• Superior lubricity – 50% lower coefficient of friction in contact with copper compared to hot working steel, enabling extrusion even without lubricant.
• Low thermal conductivity – At 600°C, PSZ exhibits thermal conductivity of 1.9 W/mK compared to 28.8 W/mK for hot working steel, reducing heat transmission to the metal die holder and allowing it to retain hardness longer.
• Dimensional stability – No “turn-in” deformation under operational stresses, maintaining consistent bore geometry throughout die life.
• Highly polished, non-abrasive surface – Improved surface quality of extruded products.

Process Implementation

Successful ceramic insert adoption required manufacturing personnel to master several critical elements:

• Correct shrink fit procedures adapted for ceramic material
• Careful handling protocols to prevent damage from impact or thermal shock
• Appropriate press operation parameters for ceramic tooling

The manufacturer’s commitment to this learning process proved essential to realizing the technology’s full potential.