1) Aluminium pick-up:

Why it happens: Aluminium builds a thin film on the die bearing due to high local temperature, poor release, or contaminated billet (oxide, oil). Over time this film thickens, burns, and transfers into the profile as streaks.
Factors: inadequate lubricant, low billet taper heat, and rough/pitted die surface.

Solutions:

• Immediate: Stop line, remove and polish bearing & ports to smooth the surface (light stones/paste). Trial.

• Short term: Adjust lubricant type/flow (BN or controlled water-based release), improve billet cleaning.

• Long term: Re-nitride or apply low-friction coating after full refurbishment; consider switching to a PM steel or better surface finish if adhesion frequent.

2) Die lines / scoring / shallow grooves

Why it happens: Mechanical scoring is often from hard inclusions in billet, misalignment (dummy block / container), or abrasive wear from surface particles. It shows as linear lines running along the profile.

Solutions:

• Inspect billet quality and remove suspect heats. Improve billet cleaning and screening.

• Check alignment and dummy-block seating; correct container and die concentricity.

• Polish and, if needed, use EDM to remove localized damage in tight areas where milling can’t reach. Refinish and re-nitride.

3) Poor weld seam in hollow profiles

Why it happens: Uneven flow through bridge/portholes, incorrect billet temperature, or damaged die porthole geometry. Insufficient pressure or poor metal consolidation at the weld causes weak seams.

Solutions:

• Check and equalize billet front/back temperature (taper heat). Increase front temperature slightly if under-weld.

• Adjust bearing distribution or enlarge feeder/bridge land per die-design guidance. Use flow simulation if available.

• Correct die ports with EDM or machining to balance flow; then trial and inspect weld strength.

4) Bearing wear/dimensional drift (profile out of tolerance)

Why it happens: High extrusion ratio, abrasive flow, or prolonged runs without refresh causes bearing length loss. Also caused by incorrect bearing design for the alloy/section.

Solutions:

• Small change: machine (grind) to remove glazing and restore surface; re-measure and trial.

• For dimensional rebuild: weld build-up (TIG) or laser cladding to add material, then finish machine to new dimensions and re-nitride. Validate with trial coupons.

5) Distortion/warpage after correction

Why it happens: Excessive heat input during repair (welding) or incorrect post-repair heat treatment causes residual stresses. Also possible if corrections change metal flow and local stresses.
Fixes:

• Prefer low-heat, low-distortion techniques (EDM, laser cladding) over heavy welds where possible.

• After any build-up, stress-relieve and follow with controlled tempering & nitriding. Always measure straightness before reassembly.