There seems to be a lot of urban-myth and folklore about different methods to remove small dings and dents from vehicles and appliances. What’s the straight dope?
Can you reliably use heating followed by cooling to remove a dent? If so, what’s the physics behind this?
How likely are vacuum/pulling mechanisms likely to remove a neat circle of paint instead of the dent?
A lot of the so-called easy fixes are a generally a scam but still may work some. I have removed some pretty large dents from truck tailgates with a toilet plunger but you could still tell there was once a dent of you looked at it intently. However, paintless dent-removal done by specialists does work very well but it requires special tools and lots of skill. Rather than removing entire body panels, bonding, and repainting them, they use special picks and suction devices to remove smaller dings to near pristine condition. I had it done to one of my vehicles for one of the largest dents they would work on (about the size of a man’s foot) and he got it back to 95% and wasn’t apparent to the untrained eye. Smaller dents can be fixed much better than that. It is like a magic trick but it does take lots of skill and training to do it right and a novice wouldn’t have that but the basic idea is sound.
Heating/cooling won’t work. Sorry, if a metal surface, once it has been deformed (stressed to the point of buckling), the deformation is permanent (see #2). Scratches and gouges are caused by removing paint and/or metal. Heating and cooling can’t replace them. For a non-metal surface (fiberglass, carbon fiber, plastic) it depends on the injury. In general, stiff-chain materials held together by a resin (fiberglass, carbon fiber, etc) will either break or not. If they don’t break, you won’t see the damage. If they do, can’t fix it easily. Plastics can sometimes be restored by heating and reforming (think LP’s left in the sun, then made playable by heating gently and cooling between two pieces of glass), but again, it depends on the amount of damage, and the type of plastic.
Vacuum methods work to some degree on metals, but almost always require further work in terms of hammering to smooth the surface again, and probably body filler or at least a new, very detailed paint job. As you intimated, just repairing the ‘dent’ will break the paint (in addition to weakening the actual metal, though slightly), which requires a decent amount of work to repair. Without a proper restoration of the paint (and body prep, and primer, and paint, and topcoat, assuming a vehicle) the defect will always be noticeable.
2a) Vacuum devices (thinking auto-body here) will not ‘suck up a circle of paint’. If they do, then the vehicle manufacturer did an extremely poor job in applying it. They will cause stress fractures around the area of the dent, which isn’t the fault of the vacuum or puller, but just that the paint doesn’t deform well, it cracks and spiderwebs.
2b) “Pullers”, which is actually where a small hole is drilled in the deformation (again, auto-body), and then an expandable probe is inserted, and the deformation is literally PULLED out have the same problems with the paint, but have more issues then using vacuum, as they don’t put the same stress on the affected body panel, and will require more work (body filler) to smooth out the contours.
Khendrask, sorry to contradict you, but both techniques work, in very specific cases, and both need the eye and hand of a (very) skilled worker.
- automotive dents (ie gravel impact) when not too marked, and without the paint layer being broached, can be “pulled” out using glued on plastic “needles” and traction. This is specialist tooling DONT TRY IT YOURSELF. The paint is then repolished with type specific abrasive paste. The result is remarquable, but only a qualified specialist will know exactly which dents can be treated (depth, location etc) , how much traction to use, and the paint polishing is real craftmanship.
Once again this can be a very good solution for an isolated dent not too close to a border (like in the middle of a door panel), in France the charge is about 60 euros (each) still much cheaper than re-painting)
- Restraint is possible for thin metal work, usually after hammering out a dent to absorb the excess length created by the hammering process. Successive passes of the torch and a wet sponge in a circular movement around the hammered part are done and some retraction is created, as well as annealing. Once again, to do this right, hours of training are neccessary.
I brought a car to one of these “Just Dings” shops. I watched one of the techniques as it was performed. Using a small pointed hammer he tapped at specific points all around the ding. After 5 miutes or so of this he accessed the back of the ding with a tool that had small “roller” at the tip. Rubbed on it a bit and the ding just popped out. He told me the hammer taps released the tension on the metal that was induced by the dent.
Last summer my Miata was caught in a huge hailstorm and came out of it with literally hundreds of little dents on the (aluminum) hood and trunk lid. The insurance company said that it was a perfect candidate for paintless dent removal and wanted to try that first. I was somewhat skeptical since I had read that the success of the process was entirely dependent on the skill of the technician.
The guy had the car for a day and a half and the results were perfect.
As others have said, there are ways to repair dents without the classic beat, fill and paint technique, but they’re not a do it yourself type of thing.