Joining non-woven abrasive web & PU foam sheet

Without any specific information on the abrasive web material(s), it is hard to say, but I'd look into ultrasonic welding/stitching as one possible method. Manufacturers of suitable machines may be willing to run some trials if you'll furnish sample materials to them, in hope of supplying equipment to you if successful. Try to let them (and us!) know more details on the materials to be joined, purpose, thicknesses and overall size, etc. in order to obtain better answers.

web is formed of nylon/polyester . It is 50m in length & 1m in width. This web is later converted into small scrubber pads used for domestic (utensils ) / industrial cleaning. Thickness of nonwoven abrasive web/pad ranges from 10-30mm & PU foam 20mm thick. Since it is a low cost product ,I should go for a simple & economical method..!

web/pad ranges from 10-30mm & PU foam 20mm thick

That may eliminate simple ultrasonic bonding, but I'd still check suppliers for up-to-date information. There are some non-woven or spun-bonded adhesive sheets or films that might be sandwiched between, and activated by heat, ultraviolet, or radio-frequency energy, but I've never worked with any myself, so can't advise further except to say "Look them up." Energy could be supplied after the materials are pressed into contact, or as they are fed into position between rollers (imagine side-by-side rollers, with raw materials coming in from right and left, and the adhesive coming straight down into the "V". If the adhesive is heated even to melting/dripping, it happens as it is going into the gap and so coats the surfaces just as they are pressed together, with gravity helping). Contact-type adhesives could be applied by spraying, or supplied as a sheet, and the two materials pressed into intimate contact between rollers to get a bond; the same suppliers as those for the non-wovens may offer this type as well. It is possible that simply heating one or both of the materials on a very small area just before they meet [again, going into roller pairs] would cause adhesion as the material cooled, but I'm no expert. The only other method that came to mind was actual stitching/sewing, but the thicknesses and eventual purpose don't make that appear a good option.