A car sun visor looks like a simple padded part, and that impression is exactly why visor programmes go wrong. In reality a visor is a multi-layer sandwich — PVC skin, foam core, often a stiffening frame — pressed between matched curved dies, welded around the perimeter and cut to final shape in the same stroke. Two of them hang side by side in every car, so any asymmetry between the left and right part is visible to the customer. This article covers what those three facts mean for machine selection, die design and daily process control.

What the Visor Sandwich Does to the HF Field

A visor is typically a 0.6–1.2 mm PVC skin laminated over a 5–15 mm PU or PE foam core, with a wire or plastic frame embedded inside for rigidity. When the press closes, the HF field heats every lossy layer it passes through: the skins take most of the energy, the foam takes some, and the frame — if metal — is present but neither heats nor welds. The goal of the cycle is a bond line where skin meets skin around the perimeter, while the foam in the middle stays intact and resilient.

This is why a visor is harder than a flat two-ply weld: the same field must be hot where the skins are thin and cold where the foam is thick. That balance is set by die design and cycle tuning, not by turning power up. How each polymer in the stack responds to the field is covered in the material guide to how PVC, TPU and PU behave in HF welding.

Matched Curved Dies Are Where Most Problems Live

A visor surface is not flat — it carries a mirror recess, mounting tabs and a slightly crowned face. The die set is therefore a matched male/female contour, and three failure modes follow directly from that geometry:

• Energy concentration at recess edges. The rim of the mirror cutout is the sharpest feature on the die, and the field concentrates there. This is the classic spark location on visors — the sensitive NL-5557 anti-spark system fitted across the CH range protects the die when it happens, but rounding and polishing those edges is the real prevention.
• Pressure map vs die contour. A flat force reading says nothing about contact pressure on a curved face. High spots over-weld and emboss first while low areas are still cold. Shimming and bluing the die at setup is part of the job, not an optional extra.
• Frame bridging. Where the embedded frame crosses the weld line, the die must compress the sandwich without cutting into the frame — a die detail that only shows up on the first real part, not on a flat coupon.

The broader rules behind die-side energy control are the same as for any HF tooling — see the electrode design guide for the generic version.

Weld and Cut in One Stroke: The Land Decides

Visors are produced by synchronous weld-and-cut: the die welds the perimeter flange and, on the same stroke, the cutting edge trims the skin to final shape. The gap between the cutting edge and the weld bead — the land — is the most consequential dimension on the whole die. Too narrow and the cut tears through material that is still molten; too wide and an unbonded channel remains between weld line and edge, which becomes the path for skin delamination later in the part's life.

Cutting through skin plus foam also demands real force, which is why cutting pressure on this machine class is adjustable from 1 to 20 tons. The right setting is the lowest one that leaves a clean edge: excess pressure crushes the foam at the perimeter and leaves a hard, visible ridge under the vinyl, while insufficient pressure leaves a web that operators cut by hand — at the cost of edge quality and cycle time.

Positioning: ±20 µm Exists Because Symmetry Sells

The machine's stated positioning accuracy is ±20 µm, and for a visor that number is not marketing. The left and right visors in one vehicle are judged as a pair: weld lines must sit at the same distance from the edge, embossing at the same depth, the recess at the same height. A few tenths of a millimetre of drift between hits — from jig wear, material stretch or a die that is not re-seated identically after cleaning — is enough for an inspector or a customer to feel the mismatch.

The practical controls: a dedicated locating jig per part number, registration against the pre-trimmed skin rather than the foam, and a first-off pair check (left + right laid together) at every die change and every material batch change.

Cycle Structure and Cooling

A visor weld runs 3–6 seconds of HF followed by a cooling phase that is usually as long or longer, because the thick foam core releases heat slowly and the weld must be set before the press opens. Release too early and the perimeter springs open; cool too long and output drops for no quality gain. Operation is available as oil-hydraulic plus pneumatic or pure pneumatic — the hydraulic assist matters most on the larger 400 × 600 mm table where the cut force is spread over a bigger die face.

Defects We See Most on Visors

Symptom	Most likely cause	Change first
Spark at mirror recess rim	Field concentration at sharp die edge; contamination	Radius and polish die rim; clean/dry skins
Perimeter opens after trimming	Land too wide — unbonded channel at edge	Reduce land width; verify against first-off
Cut edge torn / ragged	Land too narrow or cut pressure too low	Adjust land; raise cut pressure gradually
Hard ridge under vinyl at perimeter	Cut pressure too high — foam crushed	Reduce cut pressure in small steps
Left/right pair mismatch	Jig wear or die re-seated differently	First-off pair check; re-qualify jig
Foam collapses in crown area	Energy too high over high-spot contact	Reduce dwell; shim low spots
Weld brittle in cold weather	Over-weld drove plasticizer out of skin	Shorten cycle; verify with cold flex

The spark system protects the tooling, but the triggers are predictable — sharp die features, moisture in stored skins, printed or metallised logo areas. The routine that keeps these in check is the same as for any HF line: see the guide to reducing defects and downtime in HF production, and the underlying physics in the article on what determines HF weld strength.

Testing That Matches the Product

• First-off pair comparison. Left and right part laid together; check weld-line offset, emboss depth and recess height against the approved master.
• Perimeter peel. Cut four peel coupons at 12/3/6/9 o'clock positions — the crown and the tab areas behave differently from the straight runs.
• Frame-line check. Cut one section through the frame crossing and confirm the die has not cut into the frame and the sandwich is fused on both sides.
• Cold flex. A visor that passed at room temperature can crack at winter temperatures if the cycle overcooked the PVC.

Choosing Between the 8, 12 and 15 kW Models

The CH-8KW-DSRD / CH-12KW-DSRD / CH-15KW-DSRD series shares 27.12 MHz, the NL-5557 anti-spark system and 20-ton maximum pressure; the real differences are the generator, the tube (7T69RB / E3130 / 8T85RB) and the table (300 × 500 mm on the 8 kW, 400 × 600 mm on the 12 and 15 kW). For a single visor die on the smaller table, 8 kW is generally sufficient. Choose 12–15 kW when running visors on the large table, when the sandwich is thick or the skins are heavier, or when the same machine must also handle larger interior panels — the headroom shows up as shorter cycles and a more stable field under load. Where the visor fits among other interior parts is sketched in the overview of HF machine technology and selection.

Related machine pages for the same production family: the HF car mat welding machine for large-format multi-hit mat work, and the HF insole welding machine for full-area weld-and-cut in a single stroke.

FAQ

Why does a sun visor need matched curved dies instead of a flat electrode?

The visor face is contoured with a mirror recess and mounting tabs. A flat electrode would only touch the highest points, so energy and pressure would concentrate there. Matched male/female contours distribute both across the whole face.

What is the land on a visor die?

The distance between the cutting edge and the weld bead. It sets the balance between clean cutting (narrow land) and a fully fused perimeter (wide land). It is tuned per die, not per machine.

Why do sparks keep happening at the mirror cutout?

The recess rim is the sharpest feature on the die and the field concentrates there. Radius and polish the rim, keep skins clean and dry, and let the NL-5557 system protect the tooling when a discharge still occurs.

Can the machine also emboss logos on visors?

Yes, within the same stroke — logo or part-number embossing is usually built into the die crown. Depth is limited by pressure distribution on the contour, so deep embossing needs matching die relief.

Why must left and right visors be checked as a pair?

They hang side by side in the vehicle. Symmetry of weld lines, embossing and recess position is what the end customer actually sees, so a first-off pair comparison is the most meaningful single check.

Oil-hydraulic or pure pneumatic operation?

Pure pneumatic is simpler and suits the smaller table and thinner sandwiches. The oil-assisted mode gives steadier force over the larger 400 × 600 mm die face and on thicker cut stacks.

© Chenghao Machinery — High frequency welding machines and forming equipment for industrial manufacturing.