All cool kids are doing this now, or more like years: if you don't mind doing repairs and upgrades yourself, you can buy a laser cutter for songs-you know, as a hacker. The downside is that some failures can really ruin your day. This is what happened to [Erich Styger] and his knife, which is just over a year old. This week's failure focused on the mysterious death of the CO2 laser tube.

This is the infamous K40 laser cutting machine. Our own [Adam Fabio] just accepted one a few months ago, and [Erich] even cited Hackaday's report on the K40 Whisperer project as the reason for his purchase. We have been following his blog because he purchased the knives and upgraded them in the process, but after an estimated 500 hours of use, the machine made a terrible scream of gritted teeth. [Erich]'s reaction was to press the emergency stop button; this is of course the reason for its existence.

Tracking down the problem is a good story, but as is the case in these FotW articles, the ultimate cause of the failure is not fully understood. We would love to hear your thoughts in the comments below.

The investigation started with the power supply of the laser, but no answer was obtained. Next, he moved to the pipe and noticed that the wire connection to the anode of the pipe was not welded. The anode is an unknown material, he suspects it is graphite, and he found a video showing the "welding" process of connecting wires. (We added quotation marks to this because the video he linked doesn't actually weld anything, but the wrapped strand itself.) The solution he found is a great hint to learn from the story. This is a socket of TE Connectivity, and he solders the wires to the socket. Assuming that its power meets the task's rated value and will not drop during normal operation, this is a good method.

But we digress. Even if the connection is made, the old pipe must be replaced with a new pipe. It is also worth noting that when the new tube is black like the outside part, the anode part inside the broken tube is orange. Does this imply the cause of the death of the tube, and can this be avoided? If you have insights, please comment below to help us learn from this failure.

The anode may be tungsten.

Looking at the picture, I guess the connection between the anode and the metal ring is poor, causing an arc between the two (this can explain the orange deposits on the anode), and the arc causes local heating, which may rupture the tube, causing it to kaput.

A link to an eBay tube with the same orange anode was obtained, which was not used. https://www.ebay.com/i/123085591606?chn=ps This is not the culprit.

Orange is actually a sealing alloy that has the same thermal expansion/contraction and wetting properties as glass.

nvm I see the orange you are talking about.

The new tube has the same color of Dumet wire as the old tube. I suspect this is simple, because the old connector failed, arcing and overheating of the lead on the anode caused micro cracks in the seal to damage the tube.

The inside of the glass is orange because it is a Dumet seal or the like.

Some observations from a few users of "cheap Chinese lasers". First of all, most (if not all) of the HV connections on the pipe are just wrapped around the post. This is not uncommon, nor is it a common point of failure. Secondly, as we all know, the tubes that come with "k40" lasers are very cheap, usually not real 40-watt tubes, so they are usually over-driven, leading to premature death.

For the connection, I will be satisfied immediately and only use alligator clips.

It will take you a while, but eventually you will get rid of the obsessive-compulsive disorder of this world.

If I am in a hurry, I will use screw terminals. A crimp connection may be better because the pins may become hot due to the heat of the laser tube.

Step 1: Find one of the previous laboratory glassware wizards. Step 2: Find the necromancer. Step 3:? ? ? Step 4: Profit.

Oops, beyond snark, which means that I think the old SAMS laser FAQ has some tips on restoring the laser tube.

If the connection overheats (causing cracks), it may be time to find a way to use a large heat sink to dissipate heat. The more the mass of the heat sink, the more heat will be absorbed, and the problem will be solved. Just thinking out loud here. I bet that the idea of ​​an alligator clip would be terrible, just because there is only a small metal surface in contact with the lead, so only a small amount of heat can be removed... You need a "Tim Taylor" way to remove heat, which means big The heat sink, and the large contact surface between the probe and the wire.

But first... Tim Taylor will try liquid nitrogen!

The tube is borosilicate glass, so it will not be sealed by Dumet, it is only used for soda lime (soft) glass. It is most likely tungsten, which gives this color. It also explains the difficulty of soldering to it.

Failure Mode: Crazy China

Getting a conductor through a glass enclosure has been an engineering challenge in the past few days.

The conductor must have the following characteristics – 1) Sealed with glass (obviously) 2) Will not oxidize, so oxidation will not wick through the seal and cause gas displacement (leakage) 3) Have an expansion coefficient close to glass so the seal will not follow Rupture due to temperature changes 4) No holes

The obvious solution is to use a precious metal with a coefficient of expansion similar to that of glass-looking at the periodic table and bingo games, the perfect precious metal is platinum. It will not oxidize, is sealed with glass, is non-porous and has a suitable thermal expansion coefficient. You may not get platinum from cost cuts in China.

The next best attempt is nickel-iron alloys, because they can be mixed to achieve the desired coefficient of thermal expansion. However, nickel-iron alloys have the following problems – 1) It is porous, especially when the alloy contains impurities. 2) Air bubbles are generated when the glass is sealed. These bubbles create potential stress (fracture) points, so it is not suitable for high-temperature vacuum tubes. 3) The glass cannot be sealed well, so it will not last longer.

The next improvement is to coat nickel-iron alloys with copper tubes. Copper has a completely wrong temperature coefficient for glass, but it is well sealed with glass, does not produce bubbles when sealed with glass, does not oxidize when sealed with glass, is non-porous, and is a better conductor for higher power applications.

Choose the size of the nickel-iron alloy and copper tube so that the nickel-iron alloy provides a temperature coefficient, and the copper conforms to the expansion/contraction under stress.

Correctly calculating these dimensions is a rather complicated formula. This failure is caused by the inclusion of the following three variables-1) OMG: the cost of copper 2) WTF: the cost of nickel-iron alloy is much lower 3) cost -: manufactured in China

The excess carbon in the remaining part of the contact point also indicates that the quality of the nickel-iron alloy is also very low. Maybe it is actually a nickel-carbon steel alloy.

For a new pipe, if you want to use a non-welded connection, it must have sufficient clamping force and mechanical support to avoid vibration and sufficient contact surface area.

Any arc will quickly carbonize the electrode.

The conductor may be tungsten-I have seen tungsten/borosilicate seals before and they have that color. Copper seals (such as Dumet, or copper-plated Kovar or Fernico) are redder, while common Kovar/Fernico seals are gray.

IMO, when it comes to lighter gases, you don't necessarily think that heavier metals are non-porous. If you build a basketball grid, you can still launch ping pong balls through it.

I have been using Chinese laser for many years. The short life of the laser tube almost always leads to an excessively high power setting. A power setting of 100% will greatly shorten the life of the tube. At 65-85% settings, it will actually cut better. It took me a few years (about 3 100w tubes) to learn this lesson! Make a test grid! The 3 lasers I use all run at a maximum speed of 75%

Steve- As long as you are not at the high end of the power range, will running the laser at the lowest possible power affect the life of the lamp? There is an analog meter on my cutting machine. Some people suggest that 20 mils is 100%. There are very few peaks above 5 on my meter. The analog meter responds slowly, so I think the peak is higher, but the meter can show you the average value very well.

Also, do you think it works better in vector or raster mode? In my mind, I discussed this issue back and forth. In vector mode, the laser is continuously turned on a lot, so I can see it getting hotter. In raster mode, it opens and closes quickly, and I can feel the tube is hard, although I am not sure how.

Thank you for your insights on extending laser life!

Recommendations for establishing a connection-find a small spring with an inner diameter slightly smaller than the column, solder the wire to the spring, and then "rotate" the spring to the column, it will hold itself.

Or try the Wago spring clip connector. The 221 series is dazzling.

I am the one with the broken pipe :-). I used a good industrial chiller with this tube, being careful not to overheat it, running at a maximum of 22°C. I don’t have much control over the maximum current provided by the original (nanoN2) controller, so I replaced the controller with a Cohesion Mini controller (https://mcuoneclipse.com/2018/04/15/upgrading-a-laser- cut -with-cohesion3d-mini-and-lcd/), I limit the PWM to 80%. I believe I have bad luck (or maybe medium) with that tube. I am not a laser expert, but I noticed that the new tube shows a purple color (gas?) in the tube and the old tube does not show this color (more?). So it may be that the old pipe has lost gas (leaking?). My idea is that the tube is curved on the anode side, but I'm not sure what the curved shape is. I will put that old pipe aside, maybe I can investigate it later. But now I am satisfied with the replacement :-).

If you want to process large quantities, I suggest you invest in lasers with ceramic or metal laser tubes. They have a longer service life and a faster pulse rate, so you can get better quality even when processing at high speeds. They are more expensive, but worth it. Another thing related to product life is the size of the motor. Smaller motors cannot support large amounts of laser power.

Wow, there is a lot of crazy (and unknowing) speculation here!

Fortunately, RÖB and imajeenyus (and some others) got it right.

(1) Orange (copper color) is the correct color when the glass and metal pins are fused. (Two materials that look very similar are used. I really don't know which material is common in laser tubes.)

(2) The dark color is the correct color of the part of the lead exposed to the air. (It's not graphite. Sheesh)

(3) In order to match the characteristics of the metal pins to seal to glass (fuse, temperature coefficient, etc.), compromises need to be made: Unfortunately, the result is that the pins are not easy to solder.

(4) Many tube manufacturers warn customers not to try to solder directly to the pins. (Of course, there are many YouTube videos that did halfway work when trying to weld. Who would you believe? *Materials engineer of the company that made* the tube, or someone in the garage trying to pump up his tube with a laser and cat video YouTube channel?).

(5) The tube manufacturer recommends mechanical contact. Spring, clamp or screw contact.

(6) The heat shrink tube shown in the repair is not suitable for the high pressure of the ignition tube. (Usually around 20KV~25KV...depending on the tube size [varies with length]). This is why all HV Silicone RTVs are encapsulated in the connection.

(7) Normally the heat shrinkable tube seems to work, but when you close the hood, an arc will be generated from the exposed metal chassis connection. (a) Most power supplies are protected by short arcs, but they cannot withstand so many shocks. (b) K40 is notoriously poorly grounded, so when the HV lead arcs to the chassis, you may be at risk of serious electric shock or death. Or destroy your electronic equipment, unless you have strengthened the venue.

(8) The *inner* end of the mentioned pin does not seem to be soldered to the internal anode electrode. That makes sense. Just as *external* pins cannot be soldered, *internal* terminals cannot be soldered either. On some pipes I have seen, this is a mechanical crimp connection. The others seem to be spot welded. In addition, I suspect that the metal in the solder will "poison" the laser tube gas.

(9) It is mentioned that the inside of the tube is made of "purple" color. I am not sure if he is referring to glowing gas (when the tube is activated). However, if you observe a slight pink/purple/purple hue on the inside of the center hole (when the tube is not activated), this is a sign of a better tube with a *catalyst*. Usually this does not exist on 40W tubes, but it is more common on higher power (80W, 100W, etc.). The catalyst helps the CO (carbon monoxide) produced during the laser process to quickly recombine into CO2 (carbon dioxide), which is exactly what we are after. The faster the CO2 recovery, the higher the laser efficiency.

(10). Regarding tube life. The manufacturer warns that overcurrent is the main reason for the short life of the tube. Some of our makerspace users insist on running every project at 100%, although lower power and slower speeds usually produce better results.

(11) Two of our pipes failed very early. After just a few months, we observed that the internal cathode electrode became significantly darker, and the tube output and beam quality decreased in parallel. (Subsequent "autopsy" revealed that an incorrectly calibrated HV power supply drove the tube 30% higher than the manufacturer's specifications. Oops! Our replacement RECI tube is still in operation after 5 years.)

(12) I also suspect that the number of ignitions is related to the tube life, because the voltage of each ignition is much higher than the actual operating voltage, and for each of these events, there will be annoying current spikes. Some higher-end HVPS use pre-ignition bias, which can reduce ignition events and improve combustion quality (especially for fine engraving and general cutting). You really don't have any say in the number of ignitions, but in stores that produce a lot of pulses naturally, this is something worth considering. An online project has a modulator that deliberately pulses the laser quickly, thinking that he has gained more energy. On the contrary, he gained more power in those excessive and uncontrolled ignition events. The tube manufacturer recommends not to do this.

thank you for your information. To clarify, in #12, if you have a choice, you'd better not use a vector-based method instead of a raster-based method? In other words, if you are making a logo with letters, turn on the laser and fill in all the first letters, then turn off the laser instead of moving to the next letter, which is better for the tube than scanning the entire logo one line at a time. Turn the laser on and off hundreds of times per line of pulse? Ignition on the tube is more difficult than continuous operation?

(13). By the way, in some online forums, there are reports that car antifreeze is added to distilled cooling water. It is said that even in diluted amounts, some brands of antifreeze are too conductive and will affect laser operation. The (slightly conductive) water jacket may be capacitively coupled to the laser hole. Some people even claim that this will cause an arc inside the tube. (I need more details to understand this.)

Remember, you need distilled water, not just "pure" water.

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