i think need to quote back what i said coz still many professional welders here, hu...hu...

erm, if not mistaken, prtn already used one piece door stamping gen2, tailor welded blanks door saga,exora, and preve i think, door sash + doorpanel,  using double spot, robotic plasma welding, new n latest for prtn, better weight, better design for sash n better strength.

I thinkla :-), dengor2 khabar anginla, ingress corp supply the door to prtn preve. So, better ask them lah, ha...ha...

The door sash is made using roll forming method, only using this method, u can used advance high strength steel(ahss) aka ultra high tensile steel(uhss) as the material coz in cold forming method, its really hard to shape ahss to complex shape coz of its rigidity.

Then the door structure is normally used high strength steel low alloy(hsla), and the trapezoidal impact beam, unique to proton n lotus, start in satria neo n upward(not tabular impact beam as some others using) inside the door also ahss using roll forming.

So, combining the door sash n door panel is using robotic(not human, unless humanoid :-)) plasma welding, double spot, for strength n better corrosion resistant. Ops, forget to mentioned, all high strength steel using in car are galvanised steel(corrosion resistant coating steel), yup, the whole body n panel, deep into pool, electro charged, the pool is in tanjung malim, maybe u can visit for swimming n diving training :-). Plus, its painted in white(thats why they called it body in white as the preve chasis during power of one event), then another layers of colors paint.

So, in other words, using this method, the door will enhance its strength by combining two type of steels(ahss for door sash n hsla for door structure), n door sash is stronger than before as in using tailor welded blanks. Coz previously, only being protected by ahss impact beam inside the door, but door sash still not as strong as ahss(trip or dp), but now, the whole door has the same strength. Yup, i think better they (prtn)conceal with rubber or plastics next time, so that people will not do their own professional analysis coz they only familiar with house grill welding, not robotic plasma welding.

I think better those who curious just google for image using plasma welding, spot, how is it look like, the marks from plasma welding.