Plastic Welding Machine

                Plastic Welding Machine

 

 

Metal is not the only substance that can be welded – plastics can be welded also, using an ultrasonic welding machine, and in fact, many of the articles which we take for granted in the modern world are created partly or wholly using this process.

Welding plastics by using an ultrasonic welding machine received a huge boost, ironically, with a failed experiment with an all-plastic car in the late 1960s in the United States.

The plastic car was built successfully using ultrasonic welding but was a complete failure in the marketplace.

However, the ultrasonic welding process was perfected during this minor footnote to the auto industry’s development, and it is in very wide use today.

Ultrasonic welding machines weld plastics and thermoplastics by putting an ultrasonic pulse through them vertically (unlike the ultrasonic welding techniques used on metals, which employ horizontal oscillations).

As is usual in most types of welding, heat is involved in the process, and this heat is generated at the bonding point by several different factors.

The vibration energy of the ultrasound itself contributes to heating, as does the reflection of the sound vibrations, with the friction of the two plastic surfaces as they vibrate against each other providing additional heat.

Heating these facing points on the two plastic surfaces causes them to melt, the molten plastic merges, and the bond is made – generally very cleanly and strongly.

Plastic welding of this kind is most successful when both pieces of plastic have identical melting points.

Some preparation of the surfaces is often carried out as well, although this is not as necessary as with ultrasonic welding of metals.

                                    How the Plastic welding machine works

Most ultrasound welding machines operate on the same basic principle and bear a closer (if somewhat vague) resemblance to a drill press or sewing machine than to arc welders and other welding machines that most people are familiar with.

The two pieces of plastic that are to be joined must be pressed against each other and under pressure as well, so there is a “nest” or “anvil” where the parts are placed, and a press there to bind them together for welding.

The sonotrode is the part of the welding machine that provides the ultrasonic pulse that actually causes the two pieces of plastic to bond together.

The sonotrode must be designed specifically for plastics, because of the necessity for vertical oscillations – an ultrasonic welder built for metals will do absolutely nothing to plastic, since its oscillations are horizontal, just as a plastic welding machine cannot weld metals despite the fact that both use ultrasound.

Plastic welding is carried out with high-frequency vibrations in the 20 to the 70-kilohertz range, which is needed to create enough vibration and friction to melt the plastics.

Some hand-held models of plastic welding machines are available on the market as well, with a sonotrode that fits in the hand and must be held precisely at right angles to the two clamped pieces of plastic that the user is attempting to fuse.

                                                         Uses of plastic welding machines

Plastic items are everywhere in the modern world, and many of the objects that are used in everyday life feature plastic welding because of the security, uniformity, and clean characteristics of the join.

Glue, for example, can get into electronics parts very easily, so plastic pieces close to electronics are often welded with ultrasound for a completely clean join.

Ultrasonic plastic welding is often used for the tiny circuits and other parts found inside computers, as well as medical machinery (which often needs to be free of all potential contaminants such as glues), packaging for combustible or explosive items, water, milk, and juice containers, cell phones, and even panels and ducts in cars.

Ultrasonic welding machines are an excellent example of the clever application of a few basic physical principles to create a clean, durable weld in plastic without the need for glues or high temperates – and these principles can be useful in the home as well thanks to the hand-held units now available.

                                                    Plastic Welding Machines

The electric arc of an ordinary welding machine would vaporize most plastics instantly were it to be applied to them, creating clouds of potentially fatal vapor and doing nothing to join the two pieces together.

Alternately, it might set the plastic on fire. Either way, the desired results would not be achieved.

However, there are many situations where a weld is needed on plastic as well.

As just a single example among many, the plastic in medical devices and containers must often be welded so that life-saving medicines and other substances are not contaminated with glue.

There are many different kinds of plastic welding, adapted to the special needs of this substance, including –

Ultrasonic welding, which operates by clamping the two pieces of plastic between an ‘anvil’ and a “sonotrode.”

The sonotrode emits an intense ultrasonic pulse, which vibrates the plastic enough at a specific point to cause it to become molten.

The plastic parts therefore merge together at the point where the ultrasound passed through both.

Friction welding machines rub the pieces of plastic together with either a straight-line or circular motion, which causes the contact areas to melt, and then combine as pressure is applied and the plastics cool and harden again.

Laser welding machines are used for everything from cell phones to heart pacemakers to headlight assemblies, and is generally used for plastics such as acrylic, nylon, and polycarbonate.

The parts are pressed firmly together and a laser-absorptive substance is applied to the join, which is then treated with a semiconductor diode laser to produce a strong joint.

High frequency welding machines operate by heating the plastics with high-frequency electromagnetic waves, which, as usual, requires pressure to applied as well to squeeze the plastics together.

The radio frequency welding that can be carried out with these machines is best for PVC and polyurethane, but can be used for other plastics as well.

Hot air welders direct a jet of hot air at the point to be welded, melting the plastics and producing a bond between them.

This method is part of the overall method known as “hot gas welding.” This technique is used for

Other methods of welding plastics exist, but these are among the most commonly used.

Whatever the exact technique, plastic welding produces a strong bond without the use of glues or chemicals.

                                       Resistance Welding Machine

Although it usually requires large, generally immobile, and expensive machines, electric resistance welding, also know as ERW, is a clean and efficient method of joining thin metal parts to one another quickly and solidly.

Electric resistance welding is used for some extremely crucial manufacturing processes, such as the seam welding used for fuel tanks, large pipes, and other containers.

The principle behind electric resistance welding, and hence behind electric resistance welding machines, is straightforward, but can be applied in several different ways.

Resistance welding machines work by clamping the two pieces of metal that are to be joined between two copper electrodes.

A strong electric current is passed through the electrodes and the metal pieces – generally, a current with fairly low voltage but high amperage.

The metal’s resistance to the current converts the electric energy into heat energy, which melts both parts at the place where the electrodes are creating a circuit through them.

The pressure of the electrodes then squeezes the two parts into each other, literally combining their substance at that point, and creating a weld.

The two most common forms of resistance welding are spot welding and seam welding.

Each uses a different type of machine with different electrodes, and is used for very different fabrication processes. Both are most useful with thin metal sheets or plates, however.

                                                                 welding Spot

Spot welding is a type of electric resistance welding that is carried out with two clamping electrodes that complete an electric circuit through the two sheets of metal.

The maximum level of resistance is at the point where the two sheets of metal are pressed against each other, so maximum heating occurs here as well.

Heat increases the resistance, which causes more heat, and so on.

To prevent the electrodes from sinking into the other side of the sheets, the electrodes are water-cooled, so the heat is concentrated at the place where the sheets touch and not elsewhere.

The  two areas of the sheets touching each other become molten and flow together, forming a bond.

As the electrodes continue to clamp down, the heat flows back towards them, then is drained away by their water cooling, hardening the weld.

There is a possibility of damaging the weld at this point if the heat has been built up too quickly, however, and cannot be drained off in time to prevent the electrodes from squeezing out molten metal from the weld point.

Spot welding is quick and cheap, but not very strong. It is used frequently in building cars.

                                                              Seam Welding Machine

For some welding processes, heavy industrial welding devices are necessary, which are generally not available to small operators, whether these are home users interested in welding or independent welders who specialize in small-scale fabrication or repair.

One of the welding processes that needs massive pieces of equipment and a precisely-calibrated manufacturing procedure is seam welding.

Seam welding produces long, extremely tough welds between two pieces of metal (although there is also a secondary branch of ultrasonic seam welding used for plastics).

This type of welding is used in the construction of fuel tanks, pipes, and other metal tubes and cylinders, where a long, tough weld is essential to the stability of the finished workpiece.

A seam welding machine can produce a continuous weld of almost any length, as long as more metal sheeting continues to be fed through it.

There is a practical upper limit to the thickness of the pieces that can be welded together, because seam welding makes use of the electrical resistance principle to heat and fuse the metal.

If the metal were too thick, the electricity would be diffused too much laterally and heat would not be generated properly to effect the weld.

A seam welding machine is an interesting application of electricity’s properties to make a weld that could not be created by standard means.

                Seam welding machines and electrical resistance

Seam welding machines operate in somewhat the same way as spot welding machines – the weld is created by bracketing the two metal parts with electrodes that have a strong current passing between them.

The metal parts resist this current, and its energy is transferred to them in the form of sudden, intense heat throughout their thickness, since the current passes entirely through them, forming a circuit through both the upper and lower electrodes.

A seam welding machine uses two copper rollers or wheels as the electrodes. These rollers are electrified with a charge that is low in voltage, but very high in amperage – as much as 100,000 amperes may be used, depending on the type and thickness of metal pieces that are to be joined.

The two pieces of metal are passed between these rollers, which travel along the seam between the two pieces, guided by precise computer adjustments of the roller position and the metal sheets’ position.

The rollers perform no less than three different tasks at once, all of which, when combined, form the seam welding process.

The electrode rollers or wheels actually move the pieces of metal, sliding them forward so that new areas of the join are continuously brought in contact with the electrodes.

They also squeeze the pieces of metal powerfully together, and they serve as electrodes, passing the powerful electric welding current through the metal in a continuous circuit.

The resistance welding effect of the electrodes is caused by the metal’s resistance to the electricity, which converts some of the electrical energy into heat energy at the point immediately between the upper and lower rollers.

The metal is heated to a semi-molten state, and is simultaneously squeezed together by the rollers. This has the effect of literally squeezing the substance of both pieces of metal into each other – since they are semi-molten, both pieces are mashed together so that they flow into each other and occupy the same space, combined into a single piece by a combination of heat and pressure.

Of course, the seam welding machine does not simply do this at one point.

It continues to roll the metal sheets forward between the electrodes, passing a continuous electric current through them as it does so.

There is no pause in the welding process – the machine welds steadily, forming a constant seam that has no breaks in it and is completely uniform down its whole length.

There are a few variations on this process as well. Some machines perform a rapid series of spot welds in place of using electrode rollers, with each spot weld overlapping the last so that the welds form a continuous ribbon rather than a ‘stitching’ pattern.

Plastic seam welding machines make use of an ultrasonic sonotrode in place of the electrode, with the mechanical vibration of the ultrasound replacing the electric current of the metal-fusing versions.

The principle is largely the same, however – reducing the weld area of both pieces of material to a semi-molten state, then squeezing them so hard that they combine. 

                                                                Seam Welding Machines

Since there are so many different kinds of welding jobs in the world, and so many circumstances that may involve welding, it is perhaps no wonder that dozens of different specialized types of welding machine have been developed to handle them.

Some welding jobs are small, such as fitting together the parts of a cell phone, while others are enormous – constructing a ship hull, building an oil pipeline, or creating an offshore oil drilling platform.

Some are very intricate, with a series of short welds following the lines of complex shapes.

Others are very straightforward, no-nonsense welds that are little more than making a straight welded line.

Indoor welding in a factory or workshop differs from outdoor welding on a construction site, and so on – there are so many different variables that it is impossible to catalog them all.

So, in response to this array of needs and circumstances, a panoply of welding machines has sprung up, been refined, and been expanded on during the past century and more.

Some welding techniques stretch back to the earliest days of arc welding in the 1880s, while others – the more exotic and technological – have sprung up only in the past few decades.Seam welding is a process that makes use of specially designed seam welding machines.

Seam welding machines – or “seamers” as they are familiarly known – are an example of a welding device that is so adapted to a specific task that it can do no other.

Welding a seam is quite simple, in a way – a long, straight, precise weld must be made between two pieces of metal.

However, despite its simplicity, it takes a dedicated design of machine to get the job done properly, quickly, and efficiently – and with enough strength to make the method useful for making fuel tanks, containers, and other metal fabrications that require a long, very even seam.

One of the most common seam welders uses a pair of copper electrodes in the shape of wheels to weld its seam.

The copper electrode wheels turn, simultaneously moving the two sheets of metal through the machine, pinching them together strongly at the weld line, and welding them by melting their contact surfaces and squeezing them together to combine.

The seam welder works through electrical resistance. A continuous current is passed between the upper and lower electrodes.

Since the two pieces of metal are sandwiched between these turning copper wheels, the electricity flows through them as well. The metal resists the electricity, converting part of it into heat energy, which heats up the metal powerfully.

The wheels also serve as heat sinks, ensuring that the outer surfaces of the metal sheets do not become molten.

The contact surfaces between the sheets, however, become heated intensely, melt, and fuse as they are squashed together by the wheels.

Thus, as the wheels continue to roll, they make a single unbroken seam weld between the two pieces of metal.

Some welding machines are best at one job, but are able to handle others as well (perhaps with a loss of efficiency), but others are dedicated to a single task which cannot be properly  accomplished any other way.

The copper wheel “seamer” is an excellent example of this – as well as crucial industrial tool that produces many essential items.

                                                      Spot Welding Machine

Welding is a process to join two pieces of metal firmly together, effectively bonding them into a single piece by using molten metal at the joint – either melting the pieces themselves so that their metal literally flows into the metal of the other piece, or using a molten filler metal to effect the join.

It is one of the most secure methods of joining two pieces of metal together, and many welding methods create a weld along the whole length of the join.

In many cases, however, only a light connection is required between two thin pieces of metal.

In this case, spot welding may be used to fasten the metal pieces together.

Spot welding involves, as its name suggests, welding the metal only at specific spots.

The spot welding machine used for this process is very different from other welders such as arc welders – it is based around a pair of electrodes rather than using a welding gun as the means for creating the weld.

The principle is fairly simple, but the adjustments must be precisely calibrated to get a proper weld for the type and thickness of metal being spot welded.

On the other hand, the simplicity of the idea behind spot welding makes it possible for some enterprising tinkerers to build their own, home-made spot welding machines.

                            What a Spot welding machine is and how it works

The basic mechanism through which a spot welding machine operates is with a pair of copper alloy electrode clamps.These clamps are used to clamp the two sheets of metal to be joined together, placed side by side.

A powerful current is then fired through the electrodes, strong enough to melt the metal at the point where the electrodes are bracketing it.

The molten metal from both pieces of metal mixes together, then cools and hardens into a single metal continuum, effectively fusing the two pieces together at the points where the spot welding has been carried out.

Spot welding is most effective with thin pieces of metal, where the current passes directly between the upper and lower parts of the electrode.

The thicker the pieces of metal, the more of the electricity disperses sideways into the metal rather than traveling through it to complete the circuit.

Thus, greater and greater amounts of electrical power are needed to spot weld thicker pieces of metal.

The practical limit on the thickness of metal that can be fused in this way is 1.25” for steel plate, with other types of metal have thinner limits.Beyond these limits, spot welding is ineffective or impossible.

The best thickness of metal for spot welding is very thin – from between half a millimetre to 3 millimetres.

The time during which the metal is exposed to the electrical current must be carefully controlled if the spot welding is to produce good, solid results.

Depending on the thickness and the type of metal, anywhere from 0.01 to 0.63 seconds of current may be necessary.

Too little or too much can crack the metal, so precise adjustment is usually necessary for anything beyond hit-or-miss results to be attained.

Voltage used is very low – generally no more than 10 volts for the thickest piece of aluminum, and considerably less than that for other kinds of metals.

High amperage is needed for the process, however, with 90,000 to 100,000 amperes being needed to fuse aluminum.

                                                    Portable Spot welding machines

Portable spot welding machines can rarely muster the amperage necessary to weld aluminum sheets together, but are quite adequate for welding thin mild, galvanized, or stainless steel sheets.

Little more than a foot long, featuring a heavy-duty power cord and a pair of tongs at the front which contain the electrodes, these hand-held devices allow anyone to carry out spot welding on metal up to 1/8” thick.

This is enough for most home and light professional users, and the well-designed controls allow these welders to get the weld they need quickly, easily, and safely.

Technology continues to advance and spot welding is now practical on both the large and small scale.

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