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Recently I was asked in an email whether NAK 55 can be welded. Below is my reply.
“As you know, Nak55 is a Japanese steel used as a semi replacement (or their version) for P20, although it’s harder, more polish-able, and it can be machined faster. We have a few customers that work on Japanese molds that use Nak55. To answer your question: Yes, it can be laser welded (I have done it), but there some pitfalls you have to be aware of.
NAK 55 has sulfur in it which can interfere which the welding process. What actually happens is that after a long repetition of welding, you will see the sulfur crystallize on top of the weld bead.In addition, the edges of the weld can crumble which it not good when it is going to be polished. I have learned through experience to laser weld in short passes–with narrow beads–and use what I would can a “sink pass” to cover any crumbling. The suppliers for NAK 55 will, of course, insist you use Nak55 filler; however, if its a repair (light welding of shut off areas and such) I use 410ss, which gives me smoother touch. If it’s a heavy buildup, new tool, or a polished surface then I would consider Nak55 filler. I have used 410ss even on polished areas and it’s worked out fine.
TIG welding requires different parameters.My main advice to is the longer you TIG weld Nak 55 the more problems you will have with the sulfur in the steel. You can actually see a white sulfur pit show up at the end of weld passes. This will infer with the weld so you need to take a punch and pop the sulfur off. A way to stop sulfur pits is to weld backwards in small beads, and the manufacturer will most likely suggest this procedure.
Here is the important thing: When you welding Nak 55 you need to immediately follow the post heat procedure (see the link) if the mold has a polished surface. The post heating procedure is imperative to the success of NAK 55, although I think a lot of shops bypass this for the sake of time.”
The short answer is no.
Of course, this requires an explanation. Our definition of micro-TIG welding is using a TIG welder under a microscope via low amperage (1-50 amps) and a small diameter filler (.005″ to .020″). Since copper and aluminum need an incredible amount of amperage to melt, it’s impossible to pre-heat a piece high enough to melt at low amperage. Even if you did pre-heat the piece high enough to achieve the desired amperage range, the piece would lose structural integrity and it would deform prior to welding–there is a fine line between achieving a proper melting temperature and having it be too much. Yes, you could technically use micro-TIG (meaning under a micr0scope with TIG), but you would to use a much higher amperage and it would require at least at .035″ filler. This would defeat the purpose of welding small.
There are some other problems: Copper based alloys and aluminium are suggested to welded under AC (alternating current)–a cleaning action which is critical for aluminium. (There is a tool welder’s trick for welding aluminum under DC–direct current–that I will discuss in a later post.) There are two ways to weld these two alloys: regular TIG and laser welding.
Regular TIG (400 and above amps) will, of course, increase the size of the weld deposit because of the power required to melt. If you absolutely need a micro-weld size, then you have the option of laser welding. Laser welding is a pulsed, concentrating its melting power to a miniature area. Bare mind that laser welding is also timely and it has problems regarding ease of access.
A few years ago there was an article done about us in a trade magazine called Practical Welding Today.
Since there is little to no decent information regarding the tool welding trade, I decided to contact this magazine in the hopes they would do an article about us. Thankfully they did; and here it is.
Some key points as to what filler materials a mold welder uses.
- Suppliers do no offer individual filler rods that match every die and mold steel on the market. When the exact match is not available, the welder will match the same hardness and general composition as close as possible.
- When welding on a new “soft” tool,” every effort should be made to match the composition of the base material. This way the welded area will achieve the same hardness as the base material after heat treating.
- On larger repairs, a base layer of softer rod can be used to give ductility in the weld deposit, which reduces the possibility of future stress cracks in the welded area. This softer base can to topped a moderate, or matching hard rod, depending on the customer preference and how the tool is used.
- When a mold runs abrasive material, the top layer hardness should match the hardness of the base material.
- Die repair welding should always be topped with a “finished” hard layer on all working surfaces. Not doing this will make the working area too soft.
- It is general welding trade “knowledge” that when confronted with an unknown steel type, 420ss can be used as a filler material. Although the bonding qualities of 420ss are exemplary, the truth is that almost all tool steels will bong together when welded–there is no difference. That being said, the reason why welders use 420ss is because it shares the same wear resistance and hardness of most of the molds we work on. This is why 420ss is used so much.
Here are some basic procedures for preparing a piece for welding. Following this will result in the best possible outcome.
- Remove all oil and grease.
- Grind away rust and pitting.
- Chrome plating: Flash chrome, in general, does not inhibit the welding process. However, heavy chrome plating will crack and lift from the heat distributed during the welding process. Therefore, in heavy chrome applications, the chrome should be stripped away before welding.
- Nickel plating: In general, light nickel plating is weld-able. However, when welding heavy nickel plating, the nickel will melt away from the heat of the torch causing a sunken area around the border of the welded area. This effect may result in an unacceptable finished surface. Heavy nickel plating should be stripped before welding.
- Titanium nitriding: This treatment is weld-able; however, it can require stoning around the edge of the edge to remove the transfer of heat caused by the welding torch.
- General nitriding: This can be welded, but the welding process will leave pitting in the weld area, which will require a touch up after machining.
- Carburizing: This treatment is not weld-able. All carburized tools should be surface before welding.
- Plastic: Remove all plastic from cracks and corners that are to be welded. If the plastic cannot be removed from a crack, then the weld should be ground down enough to all for several layers of weld. When using this repair procedure, the initial layers of weld will contain blowholes and cracks caused by the mixture of weld and plastic; however, the final layers of weld should result on an acceptable finish.
- EDM finish: EDM finishes can have a very hard re-cast layer that acts as a barrier to the melting of the steel. As a result, the torch heat must be increased substantially in order to break through this hardened surface layer. Therefore, the re-cast EDM finish can cause major difficulties, especially when welding intricate areas. In these situations, grinding down the re-cast layer will result in better-ability.
When investigating cracks, you should keep two points in mind:
1) Cracks in the weld area of a pre-heated tool is not common occurrence. Dies, however, are the exception.
2) Good mold steel rarely cracks and bad mold steel cracks despite all precautions taken.
If a crack is exposed after the welding process, there are many reasons as to why this occurred and below are some of the most common.
1) There were existing cracks already which were too small too see, but the heat generated from welding open them up.
2) Something went wrong in heat treating, causing super hardened areas.
3) You were welding in a die steel. The reasons for this is because of its high hardness and brittleness. It is imperative the dies be pre-heated and post-heated to help lower the amount of cooling contraction during the welding process.
4) When a heavy weld build up is performed (.o60″ or higher), the stress caused by numerous weld passes can result in cracking. Post-heating and peening during the welding process are the best defenses against cracking.
5) Welding into a hard, brittle EDM re-cast layer (especially in corners) can be a problem. Sometimes EDM re-cast layers can have the same hardness as carbide which can result in a cracking nightmare. Lightly grinding down the re-cast layer can minimize this problem.
One of the most common tasks for a welder is to weld an existing crack on a tool or die. When you have a crack in a mold, the first question you should ask yourself is: Why did this piece crack in the first place? By asking yourself the previous question, one can further ask: Will welding the crack solve the problem completely? Fixing a crack by welding is often considered a temporary solution by welders.
Here’s the best way to fix a crack by welding:
- Clean all debris out of cracks. The black soot that develops during welding will keep the welder from seeing the weld detail and the melting debris will result in porosity of the weld; this will result in more cracks later.
- Cracks should be ground out in a “U” shape, not a “V” shape. Grinding a “U” shape allows the welder to use a lower amperage combined with multiple welding passes. When grinding a “V” shape, the welder has to use a higher amperage in order to reach weld to the bottom of the groove and use less filler material.
- No crack is the same and this must be kept in mind when preparing a piece for welding. Cracks must be ground out completely when possible. If a crack is welded without providing a weld channel, subsequent machining will remove most of the weld leaving a thin weld layer which will re-crack quickly. Many cracks are so deep that grinding out the entire depth of the crack would result in splitting the mold in half. In these cases, grinding down the crack to a sufficient depth that will allow several welding passes.
- A crack should not be ground deeper or wider than the thickness of the thinnest wall running alongside the crack. The reason for this is that too wide or deep a groove is, the more it will distort the thin wall along the crack. There is delicate balance here–between properly grinding a crack and grinding it too much–that must be adhered to.
I purchased my laser welding machine in October 2005.
At the time, it was considered the new technology, and I thought long and hard about purchasing one. I had read about laser welding a few years before and I found some things: although it produces impossibly small welds, I was stymied by the cost and the time it takes to produce such a small weld. Would our customers want it? Would it be a waste of money? In certain parameters it’s at least 5 to 6 times longer than micro-tig welding; most of my customers would never go for something that could take a hours to do. I asked some customers about laser welding and they told me they would have no use for it.
My questions of necessity was answered by the summer of 2005 some competitors bought a laser welding machine and our sales started to drift south. Apparently, there as a need for it and I had to upon it, thus my life in laser welding begin. After some phone calls, detailed questions and a lease agreement from the bank, my machine was delivered. I got 3 days of “training” from a technical representative, and I was off. Frankly, I had to learn most things on my own. What I learned from the training was that laser welding could take longer than I even imagined. The techniques shown to me had some initial uses but I found them to be impractical in the long term. In order to achieve no undercuts on an edge, I was instructed to lay a “.015 to “.020 rod on the side of an edge and just use pulse to seam both pieces together; the next step was to add rod on the seam for the build up. Yes, the procedure works, but the problem is that it’s rare to have the room to even do this it — I found this out after the first day. The tolerances were too tight to use it on a constant basis. I had other problems in the impracticality of techniques and I needed a solution.
After a few weeks, I determined that I needed a new game plan. I decided that I needed to approach laser welding as a tool-welder and the first thing on my list was to find a way do a bead on the a edge without putting rod on it. It took a week of practice in order to accomplish and feat — and my results were quite less that I hoped for. However, I kept at it, out of necessity since the jobs I had coming in weren’t getting any easier. My results were slow going but my welding speed increased over the next few years. Looking back from 2005 to now, I surmise that my welding speed increased about 50% as I got more confident and experienced.
Unfortunately, there was hiccups along the way — one of them being inherent nature of “pitting” in laser welding which I fought a battle with. “Pitting” in laser welding is a fact, although most don’t want to admit it. When something has “pitting,” it means there is porosity in between the weld beads, meaning air gaps. In most forms of welding, this doesn’t matter; however in mold welding it’s unacceptable. The problem lies in the fact that the laser gives a certain amount of small power, and the optimum rod is “.010. Trouble begins when I have large buildups with impatient customers: then I “cheat” by using .015 to .020 to order to complete the job. The majority of my “pitting” was with .015 to .020 rod. I know what you want to say now: Do use thicker rod?! I completely agree with you, until the moment a customer comes in and “needs” to wait for a job with a large buildup. A conundrum. I done a lot of reading and experimenting in order to fight “pitting” and I’ve come up with some solutions. One solution is to turn my machine power up to least 15-20% higher than I normally would; in addition, I increased the timing of the laser pulse and use back-passes on pulse only when I finish a bead. I also use some other tricks in angling. Using these procedures I can greatly reduce “pitting.”
To have a laser welding machine is a great benefit for a tool-welding shop; but like everything else, it takes time to learn to properly.
Differences Between Micro-tig and Laser Welding
Yes, I started a blog. This will explain things from tool welder’s prospective. The topics will be varied, of course; much like the jobs we do everyday. The tool-welding shop is often treated like an emergency room: meaning you crash something and we fix it. It seems simple on the surface, unfortunately there are pitfalls. When a plastic injection mold is not running, the molder is losing money; when a mold shop makes a mistake, they can’t go on until it’s fixed; when an engineering change needs to be made, the concept of time is throw out the window. These are the jobs that end up at the tool welder for repair.
Here at Toolweld, we do micro-tig and laser welding. Both procedures give you the same result; however, both are vastly different in it’s approach from a tool-welder’s prospective. Before the laser, micro-tig welding was the only way to produce tiny welds. Micro-tig welding makes for low sink, and less machining time; it’s still the option for most repairs. Recently, laser welding took form, which provides for even smaller welds and less sink. Noticeably, mold and inserts are getting smaller and smaller, so it makes sense to have equipment that can effectively go smaller. However, there are some major differences between micro-tig and laser welding: laser welding is a slower process. The beam is in fixed position for laser welding, so one has to position the part and filler rod to the area you work on; it’s not flexible like a welding torch. In addition to being a slow process, laser welding some materials such as powered metals are not recommended for laser welding according to the manufacturer. So course, one tend to break these rules when servicing the customer, but it still stands as a general rule.