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Here are some design for maintenance tips for your consideration:

Tip #1: Consider the material being used to build a given tool. When choosing this material, first ask the question: What is the expected life of the product? For mold classification purposes, we can say a “Class 101 mold,” but for the investment, just like our vehicles, we want them to last. I compare one million cycles on a mold to 100,000 miles on a vehicle. In the early days, one million cycles or 100,000 miles was a lot, but not anymore. We expect our tool to exceed one million cycles and our vehicle to exceed 100,000 miles; therefore they should be designed accordingly.

Another material question to ask is: What resin are you running and is it abrasive or corrosive? Some materials are harsh and require extremely hard or exotic steels. There is a big difference in tool wear rate on a simple open/shut tool with no action versus a tool that has moving components. When considering those moving parts, material selection is critical. Corrosion can come in the form of water contact, acidic materials and outgassing. Choosing materials that can stand up against these elements is critical for achieving long tool life.

Tip #2: Include front-loading components as much as possible. Disassembling the whole tool is extremely time consuming. For this reason, we attach the fixed components on the parting line side rather than the backside when we can. In the accompanying images, you can see a simple representation of this in action. Cavity blocks bolted from the front; inserts that can be pulled from the front; hot runner gate tips that can be cleaned in the press; angle pins that can easily be removed; and venting with removable vent dumps are all design elements that will reduce the time to do PM.

Tip #3: Standardization of mold components is a great area to focus on. Components that can be easily standardized include springs, switches, angle pins, angle bushings and shot counters. Keeping the required variety of such parts at a minimum helps the PM shop keep less inventory.

Often, we find ourselves building several molds for the same customer. If you are able to standardize across multiple tooling projects and also use off-the-shelf components, sourcing becomes easier and lead times can be dramatically reduced. In many cases, skilled moldmakers are able to order stock blank components and finish them in-house with the detail needed, whether it be cutting them to length or adding other details.

(Source: Design Your Tools for Moldability... and Maintenance)

Here are critical questions a mold builder should ask before sending a mold out for service:

Polishing

• How much material did you leave?
• Where are you finishing?
• What is the required finish and what does that finish mean to you?
• What areas have some leeway (e.g., do all cutter marks need to be removed)?
• What is the part making?
• Are parting lines finished?
• Does everything need to be sharp?
• What are the critical dimensions?
• What is more important: finish or size?

Hot Runner

• Does the job require the entire hot half or hot half components only (manifolds, drops, plates)?
• Are there any flow channel blockages?
• Is the system flooded or leaked? Is this routine maintenance?
• What is the resin and process temperature?
• Are all the heaters working properly?
• Are there any problems with temperature control?
• Will the manifold or drop heaters require rewiring?
• Will you need new thermocouples?
• Are any parts/components damaged?
• Do you want components replaced?
• Do you have spare parts?

Mold Maintenance

• What is the size of the mold?
• How many cavities are having an issue?
• When will the tool be ready to go out?
• When do you need it back?
• Do you have any pictures of the tool and/or the damaged area?
• Do you have any last shots or piece parts?
• Do you have drawings, prints or files?

Laser Welding

• How much weld do you need finished when you can’t see the physical damage and you need to build up a shutoff surface?
• What is the base material?
• Does the order need to be picked up or is it being shipped?
• Was a direct contact provided for the person responsible for answering questions?
• What amount of buildup is needed when finished machining?
• What location needs welding?
• Is blending and polishing to remove the weld needed?

Laser Engraving

• What material is it?
• Do you have a file?
• What is the depth of engraving (is it critical)?
• Will additional stock be removed?
• Do we need to go deeper than the print calls?

(Source: Questions and Considerations Before Sending Your Mold Out for Service)

Properly treating the surface of a mold is the only way to ensure a high-performing mold that lowers the cost of ownership and increases the number of parts produced over time. However, proper surface treatment is not a one-time thing; it must be a part of preventative maintenance and includes more than coating a mold’s surface in a hard metal for wear protection. When a mold is taken out of production because a part run is complete or has a maintenance issue, perform a complete mold cleaning and surface treatment program. 

This program includes a thorough cleaning of the mold, flushing the cooling channels, checking the cooling channels’ flow rates, performing a leak integrity check, coating the cavity, core, pins, and slides for wear protection and coating the cooling channels to prevent scale, rust and leaks.  If you follow this program after the mold is taken out of service, or better yet, before a new mold is put into service, the mold will perform more efficiently and for a more extended period.

(Source: Components of a Complete Cleaning and Surface Treatment Program)

Texture damage is defined as an impact event on the textured tool surface that left a scar. The following methods (listed in order of effectiveness) are used for initial texture damage evaluation:

• Close-up photos of the damage.
• A molded part that shows the damage.
• A review of the damaged tool.

1. Scuff of the micro-texture. If the surface has received damage only to the micro-texture, then a re-gloss using the original sandblast media formula will remove the scuff and return the surface almost back to the original finish. The term “almost” is used to account for the wear that sandblasting can cause to an etched texture. This wear happens every time a texture is sandblasted or re-glossed, so it is a concern.

Most textures can be re-glossed at least once and still maintain 95% of the original profiles, as long as the technician is trained in the process. Overly aggressive sandblasting can and does damage textures.

2. Scrape of the etched texture. When the main etched grain is damaged, the repair will require acid etching to restore the original texture profiles. The area of repair may be prepped by stoning or polishing out the damage, followed by replacing the texture with etchants often engineered specifically for this application.

Many of today’s textures are achieved through multiple layers of etch applications. In the case of repairs, the layers will have to be reproduced. It is important to know the texture specification so that these layers can be reproduced as accurately as possible.

Some of the repair scenarios for damaged textures will require welding to replace the steel that was removed with the scrape or compression event. The tool’s exact steel type must be noted so the weld metallurgy matches as close as possible to the tool metallurgy. Tool steel manufacturers provide specific welding rod recommendations because differences in steel metallurgy will result in differences in texture profiles. 

Weld hardness is another critical factor for successful repair. If the weld is too hard, the micro-texture finish will not match that of the parent steel. This will appear as a gloss differential on the part. Pre-heating the area to be welded and post-weld heating can help minimize this hardness.

3. A gouge that reaches down into the tool. The flatness of a surface is altered when a texture is damaged with a depression, and it is necessary to polish out the texture to facilitate the best texture replacement option.

Etched texture replacement always removes surface stock, which affects surface flatness. With texture repair, it also is common to face situations where stock is removed from a surface, thereby creating a dip or sink on the repair surface. Using a radius, fillet or parting line to tie in the new texture with the original texture is recommended. By using existing profile changes in the tool, the change in surface flatness is hidden. Oftentimes this means that complete texture removal may be recommended for an area much larger than the damaged area to facilitate texture blend.

Sometimes the blend has to be done in the middle of a flat surface because there are no radii or fillets with which to blend. In these cases, the metal removal will be kept to a minimum and the texture will be replaced with a slight dip in the surface. Even if the texture replacement perfectly matches the original texture, the dip on the surface may reflect light, highlighting the area. To eliminate the dip, a weld is applied. Then locally texturing the welded area and blending the repair into the surrounding non-welded area is recommended.

(Source: Understanding Texture Repair)