Mold & Die Welding Preparation Procedures for Toolmakers
Toolweld, Inc. 1750 Cumberland Pkwy. Unit 8 Algonquin, IL 60102 Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com
Table of Contents Preparing the tool for welding Filler Material Pre-heating Sinks in the weld zone Welding a pre-existing crack Cracking “caused� by welding Laser welding
Toolweld, Inc. is a precision micro-tig and laser welding company located in Algonquin, Illinois. We have 32 years of experience in the welding field. We service mold shops, molders, machining shops, defense companies and aerospace companies from coast to coast. The welding preparation guidelines and comments provided in this book are based upon our experiences in the tool welding industry; the intention is to give the toolmaker a better understanding of the challenges the tool welder faces; in addition, to giving the toolmaker procedures he can use in order to ensure the best welding outcome for his project.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com 2
Preparing the tool for welding Listed below are basic procedures for preparing a piece for welding. Following these procedures will result in the best possible outcome.
Remove all oil and grease.
Grind away rusting 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 results in an unacceptable finished surface. Therefore, 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 weld to remove minor pitting caused by the transferred heat of the welding torch.
General nitriding: Nitriding can be welded, but the welding process will leave blowholes and pitting in the weld area. As a result, a welding touch up of the pitting area may be required after machining.
Carburizing: This treatment is not weld-able. All carburized tools should be surface grounded before welding. Attempting to weld a carburized surface will leave numerous large blowholes.
Plastic: Remove all plastic from cracks, corners and sub-gates that are to be welded. If all the plastic cannot be removed from a crack, then the crack should be ground down deep enough to allow several layers of weld to be deposited. When using to repair procedure, the initial layers of weld will contain blowholes and cracks caused by melting plastic; however, the final layers of deposited weld should result in an acceptable finish.
EDM finish: EDM finish can have a very hard re-cast layer that acts as a barrier to the melting of the steel. As a result, torch heat must be increased substantially to break through this hardened surface layer. This results in difficult to control weld puddle which can cause heat damage to the surrounding detail. Therefore, the re-cast EDM finish can cause major difficulties, especially when welding confined intricate areas. In these situations, grinding down the EDM re-cast layer will result in better weld-ability.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com 3
Filler material Below are some key points when deciding the proper filler material.
Suppliers do not offer individual filler rods that match every die and mold steel on the market. When the exact match is not supplied, 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. The welded area will achieve the same hardness as the base metal when the tool is heat treated.
When welding a hardened tool, there are more choices in filler material. A somewhat softer rod can be used to allow for easier machining.
On larger repair areas, 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 layer can be topped with a moderately harder—or matching hard rod, depending on the customer preference and how the tool is used.
When a mold runs a very 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. Give the specific properties and duty of die steel, a “finished” hard layer must be applied in order for the tool to work properly in service. Otherwise, the welded area will be 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 bond together when welded—there is no difference. That being said, the reason we use 420ss is because it shares the same wear resistance and hardness of most tools we work on. This is why 420ss is used so frequently.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com 4
Pre-heating Pre-heating is one of the most important procedures prior to welding. However, the real reasons for pre-heating are different from what you might have originally thought
It is generally assumed that tool steels should be pre-heated before welding to minimized cracking. While this is accurate, a more defined reason for pre-heating is to prevent the martensitic transformation (excess hardening) around the weld area. This hardened area around the weld area can result in a future problem (heat check cracking), as the mold rapidly heats and cools while in service.
While all tool steels should be pre-heated, the possibility of cracking around or near the welded areas is actually low. Mold steels are quite resilient. However, this does not apply to die steels. Die steels must be properly pre-heated and post pre-heated.
Pre-heating also slows down weld contraction, which allows peening and minimizes sink in the weld zone.
Technically, pre-heating should be at a temperature above the martensitic range, but, below the tempering range. These two ranges can be very close so it is always best to err on the lower side to keep the mold hardness from drawing down.
Mold and die steels all have different martensitic and tempering parameters. This is where the experience of the tool welder comes into play. Basic pre-heat guidelines 420SS H13 P20 S-7
400 to 500 F 600 F 550 F 450-550 F
Real world parameters: When the line is down for a mold, or there is a set up at a mold shop—time becomes paramount. In this situation, the experience of the welder comes into play in knowing how to adjust the heating temperatures to complete the weld in a timely manner and achieve a high quality. Anything welded should be stress relieved by a experienced heat treatment specialist. The procedures a tool welder can use to “push” a job along by no means replace properly timed pre-heating and post-heating.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com 5
Sinks in the weld zone Sinks in the weld zone will always occur to a certain degree. Sinking is the result of metal cooling and shrinking below its original level. Anytime a deep hole or area is filled, the sink will be worse. Going into a deep slot requires more amperage for a proper melt; as a result, there is a greater contraction of the weld zone upon cooling—causing deeper sinks. Below are procedures that should be followed to reduce sink depth.
Proper pre-heat slows down the rapid cooling of the weld zone, thereby reducing sink. It is the contraction of the deposited weld which shrinks and leaves a deepened area in the heat affected zone (HAZ) in a ring like shape.
Using only enough amperage to achieve a melt and keeping overall heat as low as possible. Low amperage is achieved by property pre-heating! When the tool is properly pre-heated, the welder can use lower amperages because he no longer has to compensate for the coolness of the piece.
Peening the hot weld when feasible will push down the material and rise up the perimeter material—reducing sink. Again, pre-heating is an important part because it slows the rapid cooling and the welder is able to peen quickly and efficiently.
Laser welding the area (after tig welding) will eliminate sink. Laser welding the ring of sink is one of the great benefits of laser welding. Under certain conditions this procedure can be applied.
There is a difference between a “sink and an “undercut.” An “undercut” normally occurs when weld on a sharp edge does not clean up to the existing form of the original material after machining. This notch in the steel can be felt by running your fingernail across the weld area.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com
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Cracks One of the most common tasks for a welder is to weld an existing crack on a tool or die. When you have a cracked piece, 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. For a long term fix, cracks should be grounded out to their complete depth.
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 in the weld; this will result in pitting and more cracks. The weld will be unacceptable.
Cracks should be ground out in a “U” shape, not a “V”. 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 is order to reach weld to the bottom of the groove and he uses less filler rod.
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, grind 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 too wide or deep a groove will distort a thin wall alongside the crack. There is a delicate balance here between properly grinding a crack and grinding it too much so that welding could affect the surrounding detail.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com 7
Cracking in tool steels caused by welding Here are two main points about cracking: 
Cracking in the weld area of a pre-heated tool is not a common occurrence. Dies, however, are the exception.

Good mold steel rarely cracks and bad steel cracks despite all precautions taken.
If you discovered a crack after the welding process, there are many reasons why this occurred and below are some of the most common.
1.
There were pre-existing cracks that they were too small to see, but heat generated from welding opened them up.
2.
Something went wrong in the initial heat treating, causing a super hardened area.
3.
Welding a die steel. The reason for this is its high hardness and brittleness. It is imperative that 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 (.060 and higher) is performed, 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). Sometimes EDM re-cast layers can have the same hardness as carbide and welding on this surface will result in a surface crack. Lightly grinding down the re-cast layer can minimize this problem.
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com 8
Laser welding Laser welding is an excellent addition to a welding shop but it’s a slow process. This is the price you pay for precision. The amount of weld deposited in one pass is generally less than .005. Since the laser beam is fixed, the work piece needs to be constantly repositioned to get a straight shot with the laser and to be able to properly feed rod. That being said, there are tremendous benefits to laser welding when used in the right context. Molds are becoming smaller, and, in many cases, laser welding is the only procedure you can use in order to get the optimum results. Laser welding facts:
Minimal heat output virtually eliminates distortion or bending of small detail.
Laser welding leaves no sink around the weld area.
Pinpoint weld deposits (weld right up to an edge without going over).
Little to no discoloration around the weld area.
In many cases, the deposits are so small that a quick stoning of the weld can return a mold to service.
Very small deposits on aluminum and copper alloys (this is the only welding process that is capable of doing that).
Toolweld, Inc. Phone 847.854.8013 Fax 847.854.8015 toolweld@hotmail.com www.toolweldmicro.com
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