Micro TIG welding for injection mould repair and modification
What is micro TIG welding for injection moulds?
Micro TIG welding — also called pulsed-arc or micro-GTAW welding — is a precision metal-addition process used by toolmakers to repair, modify and restore injection-mould steel. It deposits filler material in controlled pulses at sub-millimetre scale, letting toolmakers fix worn edges, fill machining errors, close unwanted features or add geometry to existing cavity and core inserts without scrapping the tool.
Nordmould includes micro TIG welding as part of its tooling partner capability, using it to keep moulds production-ready and to turn around engineering changes faster than would otherwise be possible.
How does micro TIG welding work?
The process uses a tungsten electrode and a matching filler rod — typically Ø0.1 mm to Ø2.0 mm — under an argon shielding gas atmosphere, operated through a microscope or high-magnification camera to see the melt pool at toolmaking resolution.
Energy is released in short, controlled pulses (typically 3–40 milliseconds) rather than a continuous arc. Each pulse melts a tiny localised zone; between pulses, the metal cools and solidifies. The operator builds up the deposit in thin layers, working under magnification to place each bead within the required area.
Pulse energy is adjustable — commonly up to 100 joules — so the same machine can handle delicate parting-line work on polished optical-grade steel and more aggressive buildups on structural core blocks.
What are the typical use cases in injection-mould tooling?
| Use case | What is repaired or changed | Typical result |
|---|---|---|
| Parting-line wear | Flashing at seam lines | Restored seal, no flash on parts |
| Cavity edge damage | Chipped or eroded edges | Rebuilt to original profile |
| EDM pit repair | Electrode-sink pits, burn marks | Filled, blended and polished |
| Mis-machined geometry | Dimension cut too deep | Material added, re-machined to drawing |
| Design change — subtract | Feature too prominent | Weld up, re-machine to new spec |
| Design change — add | New rib, radii change, gate relocation | Material added to existing insert |
| Gate modification | Wrong gate size or location | Old gate welded shut; new gate positioned correctly |
| Cooling-channel repair | Pinhole or micro-crack near channel | Sealed without insert replacement |
These repairs and modifications are performed on both aluminium Bridge tooling and hardened-steel Production tooling.
What precision is achievable?
The figures below reflect current professional-grade micro TIG systems of the type used in Nordmould's tooling network. Application-specific achievable tolerances are confirmed at the project review stage.
| Parameter | Typical capability |
|---|---|
| Minimum filler rod diameter | Ø0.1 mm |
| Minimum weld bead width | ~0.1–0.4 mm |
| Pulse duration range | 3–40 ms |
| Maximum pulse energy | ~100 J (adjustable) |
| Deposit height per layer | 0.05–0.2 mm typical |
| Post-weld finish | Ground and polished to match cavity |
Because the energy input per pulse is very low, heat-affected zones remain small. Adjacent cavity geometry, textured surfaces and polished optical areas are typically unaffected when the welding area is properly isolated.
How does micro TIG compare to laser welding for mould repair?
Both processes are used in precision toolmaking; the choice depends on the repair type, mould material and scale of the work.
| Factor | Micro TIG welding | Laser welding |
|---|---|---|
| Equipment cost | Low–moderate (~€2K–€10K) | High (€30K–€100K+) |
| Heat-affected zone | Small (larger than laser) | Very small |
| Minimum bead size | ~0.1–0.4 mm | Sub-0.1 mm possible |
| Build-up speed | Faster for large buildups | Slow for large buildups |
| Flexibility (bench/in-machine) | High — portable equipment | Lower — workpiece moves to machine |
| Post-weld handling | Allow cooling time | Workpiece cool almost immediately |
| Best suited to | Parting-line repairs, larger buildups, in-machine work | Ultra-fine cavities, tight HAZ requirements |
Nordmould's tooling partners hold both capabilities. The appropriate process is selected based on the cavity geometry, repair volume and downstream finish requirements.
Why does micro TIG welding matter for tooling change cycles?
Injection-mould steel is expensive and lead time is a constraint at every stage of product development. When a cavity needs correction, the alternatives to micro TIG welding are: replace the insert (weeks and cost), cut a new mould (weeks and significant cost), or live with the defect (not an option).
Micro TIG welding compresses the repair or modification cycle to hours or one to two days for most work. The mould is brought to the welding bench, the material is deposited, the area is finish-ground and polished, and the tool goes back into the press for trial shots.
Nordmould uses this capability to keep engineering-change velocity high during the Bridge and early Production phases of tooling, which is exactly when design teams are most likely to request dimensional adjustments.
What steels can be micro TIG welded?
Filler rod is matched to the base material. Common mould steels in Nordmould's work include:
- P20 — general-purpose pre-hardened mould steel, widely used in Bridge and Production tooling
- H13 — hot-work tool steel used in cores and ejector systems
- S7 — shock-resisting steel for parting lines under high clamping load
- D2 and A2 — high-wear grades where surface hardness is critical
- Stainless grades — for medical or food-contact applications where corrosion resistance is required
Mismatched filler leads to hardness differences that show in the finished part surface as colour variation or polishing defects. Nordmould's toolmakers specify the correct rod grade as part of the repair process documentation.
Frequently asked questions
What is micro TIG welding used for in injection mould tooling? Micro TIG welding is used to repair worn or damaged mould cavities, rebuild parting lines and edges, correct mis-machined geometry, fill EDM pits, and apply design changes to existing tooling — all without scrapping or replacing the mould insert.
How precise is micro TIG welding? Professional micro TIG systems deposit beads as narrow as 0.1–0.4 mm using filler rods down to Ø0.1 mm. Weld buildups as small as 0.1 mm are achievable, making the process suitable for fine details, thin parting lines and tight-tolerance cavity features.
What steel grades can be micro TIG welded on injection moulds? Common mould steels including P20, H13, S7, D2, A2 and pre-hardened grades are all micro TIG weldable. The filler rod is matched to the base material to preserve hardness and polishability in the finished cavity surface.
How does micro TIG welding compare to laser welding for mould repair? Micro TIG costs significantly less to operate than laser systems (equipment cost is roughly a tenth of laser), handles larger buildups faster, and can be performed on the bench or — in some cases — with the mould still in the machine. Laser welding produces a smaller heat-affected zone for very fine work; Nordmould uses the right process for the damage type and cavity geometry.
Can micro TIG welding be used to implement a design change on an existing mould? Yes. Material can be added to a cavity or core to reduce a dimension, change a radii, close a gate, or alter a surface feature. This is far faster and less expensive than sinking a new insert or commissioning a new mould.
Does the weld affect the hardness or surface finish of the mould? When the filler rod is correctly matched to the base steel and post-weld procedures are followed, hardness is preserved. The weld area is finished by grinding and polishing to match the surrounding cavity, so the repaired zone is invisible in the moulded part.
How does micro TIG welding shorten tooling change cycles? By repairing or modifying an existing mould instead of cutting a new insert, lead time drops from weeks to hours or days. Nordmould builds micro TIG capability into its tooling partner network precisely to keep engineering-change turnaround tight.
What is the difference between micro TIG and standard TIG welding? Standard TIG welding deposits wide, deep beads suited to structural joining. Micro TIG uses pulsed-arc energy at much lower power levels — typically 3 to 40-millisecond pulses — producing a tiny, precisely controlled melt pool appropriate for delicate tool-steel work without distorting adjacent cavity geometry.