The Value of a Shop’s Welding Policy
To put the appropriate welding policy in place, you need to choose the right welder—someone who is familiar with tool steel and has a working knowledge of molds.
Most shop owners have a policy for everything from hiring and firing to how many vacations days are allowed to where one can park. However, few shops have a professional tool steel welder or a formal welding policy in place. A welding policy is simply a document—usually a worksheet (see Figure 1)—that outlines exactly what the moldmaker wants done to the mold. This ensures that the welder has all of the information he needs in order to do the job properly.
Often welding is an afterthought—falling by the wayside until a mold needs repair. It makes sense to outsource welding and leave this type of work to the experts who weld day in and day out.
Before a moldmaker can put a welding policy in place or begin the hunt for a professional tool steel welder, he needs to have an understanding of the material he is working with. Many moldmakers are only familiar with a few steels because that is all they work with. The moldmaker needs to read up on the latest materials—
including heat treat manuals and literature published by tool steel manufacturers. He needs to be aware of all of the material’s properties. Then, once the moldmaker has educated himself on the tool steels he works with, he is ready to take the steps outlined below.
Finding a Welder
Before opening the phone book and looking under welding, remember there is a huge difference between welding and welding tool steel, and not many possess complete knowledge of the latter. Before actually using a shop that looks promising, go in there and talk to the welder. If he doesn’t understand what a fit is, tolerancing, parting lines or ejectors, he is a machine operator, not a welder. If he doesn’t have a Rockwell tester then he can’t get the knowledge that will tell him what the preheat is. If he doesn’t have a microscope, he can’t inspect the part. If they don’t have a pyrometer, a digital thermometer or a laser thermometer there is no way he can know what the temperature is. If he doesn’t have an oven, he can’t weld your part. With the sophisticated steels that are available today, this is a necessity.
A mold weld provider should have a fundamental working knowledge of molds, should understand drafts, releases, shutoffs, surface gates, subgates, etc. and their function in relationship to the tool. This knowledge should be weighed on the same level as his knowledge of tool steel and specific heat treat requirements, and some reasonable metallurgical understanding.
The welder also should have an understanding of surface coatings such as hard chrome, titanium nitride and iron nitride, and also color matching and surface treatments such as texturing and polishing. He will have a broader contact base, be exposed to a larger variety of molds and tool materials, and have a range of tool steel weld rods in multiple diameters that are organized and stored neatly. A variety of welding rods on hand means the welder can perform cosmetic welds as well as structural and buildup welds right away, without having to purchase them.
Establishing a Welding Policy
Once you have chosen a welder, your welding policy should be in place so the welder can be a true asset to the shop. The welding policy should formally state what each mold needs in black and white, such as the steel has to be preheated and postheated according to its type, if color match has to be preserved, maintaining Rockwell match, what areas are to be welded, what areas should not be welded, etc.
Once a policy has been established, make sure it comes into play before a mold needs repair. Proper communication is essential even before the mold is in the design phase. Contact the welder for advice on specific materials—what the material is like, if it is repairable, etc. Bringing the welder on-board early in the process will improve the quality of the tool. Once you are on your way, if you make design changes, contact your welder. And, if any problems arise—like a cutter plunge, EDM over-burn, etc.—stop immediately and find out if it should be welded immediately or after the rest of the mold is complete.
The moldmaker also needs to share details of his process with the welder to guarantee the best possible weld. For example, the type of tolerancing the moldmaker generally works with and how crucial it is to his process. These kinds of discussions will help to eliminate misunderstandings.
It is important that the moldmaker develop this policy into a standard worksheet or a form that covers specific needs and requests—including such items as type and Rockwell of material, a designation of where to weld, and a blueprint or a small sketch. Then, the areas to be welded also should be identified on the part. This will increase the welder’s comfort level. This checklist can be fine-tuned between the moldmaker and welder as time goes on and the two grow more comfortable with each other.
Taking Preventive Measures
To avoid problems when it comes to weld work, here are a few pointers. Don’t send sharp corners out to heat treat. Internal sharp corners are supposed to have a radius in there that stops them from cracking. For example, if S7 is sent out for heat treat, and it is brought up to a given temperature, it is pulled out and quenched in oil. This hardens it, but now it is too hard and brittle and one has to draw it. To draw it, it is put back in another oven at a lower temperature left to soak to take out some of the hardness. That is a single draw. A double draw is to leave it at room temperature, and put it back in the oven again. Every time one does a draw it is stress relieving it and there is less tension in the tool. That way, when it is welded, there is less movement and the part is more stable.
Double draws aren’t being done anymore, and that leads to trouble down the road, because there is still stress left on the part. Then the welder comes along and disturbs that stress and he will get more sink than he would if it were a double or triple draw.
When a moldmaker sends a job to a welder, he always wants to know how much sink he is going to have. The welder’s response is what is the material, who made the material, and was a single or double draw performed? These are all determining factors and just one reason why it is essential the moldmaker understand the material(s) he is working with. Often, if a welder knows that just a single draw has been performed, he will send it out for another draw before welding it, to end up with less sink when the mold is complete.
The Follow Through
Reputation is really important in this trade. The welder has one job to do: to give the moldmaker the best weld as quickly as possible at a reasonable price. Follow-up is important. Let the welder know what kind of job he did so he can do an even better job more quickly the next time. With him, a shop can keep broken tools running. The moldmaker wants to continue to build that asset. The more the welder understands the moldmaker’s needs the more help he can be. And—if the welder is performing to his best ability—the results will be evident on the shop floor.
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