Maintenance science

16-01-23 Mould Maintenance importance

“Mold repair is the second most expensive budgetary item in a plastics molding facility.”

This statement should make everyone stop and pay attention. The only way to change that figure is to change the culture, and we all know that culture change is tough.

We all wish we could just have somebody purchase maintenance widgets that they could just stick in the mold to make things better. But it doesn't work that way. It’s one little piece at a time,. Begin with the process (training organization...), start systemizing things and then people will begin to see it working and experience the payback, so then you can implement a little more and then a little more.”

Specific maintenance systems and process are necessary to end the firefighting culture (desenrascanço in portuguese) of many toolrooms today. There could be a process that allows shops to efficiently produce quality parts on time. Without a process, you are freelancing how you do something, and then it is never done the same way.

Before a toolroom tries to make any changes in the maintenance environment, they figure out how to turn everything they do plus all the issues into money. That will get everyone's attention because that's the equalizer.

Let’s face it, every other aspect of plastics manufacturing has a process that employees must follow from scientific modeling to design guide checklists to simulations, but maintenance is an afterthought most of the time. Maintenance is thrown in the back of the warehouse with a bench, some rags and a five-pound hammer working on a half-million-dollar piece of equipment. This is not the way it is supposed to be.

This attitude makes mold-maintenance training programs a culture shock to many who range from mold repair technicians to processing engineers. “

The Cost
What system, you ask? Well, there’s a lot to it, but it’s also a lot of common sense. For example, everybody has a horror story, like putting cavity blocks in upside-down, forgetting bolts or leaving things out. Then someone places the mold in the press, puts the bolts in and closes the press, causing 500 tons of pressure to crush 50,000 € worth of tooling because they didn’t have the patience to slow down to see what the problem is. The first thing to do is slow down or, “Put down the hammer!”

Little mistakes can cost hundreds of thousands of dollars because people are in a hurry due to the manufacturing urgency that everyone feels. However, a toolroom needs to be accurate, safe and fast. It’s all about a tech’s focus level and his or her ability to work very carefully and measure before starting.

Before you can grind and work in tenths, you need to measure in tenths, which takes a lot of feel and the right equipment. Sometimes, we have a loose connection between the hand and head. Critical areas need to be measured as you're putting moulds back together while you're assembling the tool, especially when working on hot manifold system.

For example, for a technician to truly have command of a tool in his hand, whether it’s a hammer, pry bar, screwdriver, saw or even a precision micrometer, he must read the resistance because when you are trying to measure something within two-tenths (a hair split 10 times) you have to have a delicate feel. You cannot be heavy-handed. Your job is to understand the resistance and how much you should feel, and when it becomes too much, you have to put the tool down and find out where the resistance is coming from. The answer is not always more leverage.

Wwhat a toolroom should do first to get a maintenance process underway? to clean up the shop and get organized! then work on standardizing the language to collect better data for improved documentation.

Maintenance is a process, so as a toolroom equates everything to a dollar, they must also do that within a process of documentation. However, historically that's been very difficult to do because shops use data collection through maintenance stories that use ambiguous, non-standard terminology. You're never going to get any better if you can’t measure to justify what you do. You must standardize first. Maintenance tracking software comes into play. Key software features include track performance metrics along with maintenance and tooling costs for a variety of molds and dies, drop-down menus built on a shop’s standard terminology for accurate reports, consistent instructions and images, and a custom troubleshooting guide to create a specific knowledge base for every mold is key.

Examples (as check list e.g.)

Verify all available cavities are open and those unavailable are blocked
Verify current cavity identification numbers are correct
Air/water check all cooling circuits
Electric test manifolds, heaters, probes and thermocouples
Check knockout rods and components for uniformity, length and condition
Complete repair sheet form and return to the mold maintenance office
Enter repair sheet data into the maintenance system
Tag and place salvageable tooling into appropriate rework bin
Track mold location and status
Stage mold in the appropriate location
Each stage has its own setup steps to follow.

Mold maintenance training, (workshop highlights)

Mold Design
Plastic parts are getting more complex (more detail, functionality and specialized plastic materials), simplify part design and use standardized mold components when possible to reduce costs and lead time.
Gate location and gate type is the most important consideration for any injection mold.
Use software to simulate the result of gate location and note what happens when you change gate type and location.
More gates always result in more weld lines.
If at all possible, use only one gate.

Processing
Look at plastic through the eyes of a process engineer. Simplify the process and establish process outputs that correlate to an acceptable part.
Ensure the best mold quote by presenting the moldmaker with a model of the part that you wish to produce. Identify critical features and dimensions so that the mold can be constructed to accommodate.
Scientific molding is simply short shot molding — shifting from velocity to pressure when the mold is filled 90-95 percent.
Match the outputs of the process to yield the same part every time. Perfect process outputs equal a repeatable part.
Use a setup sheet and capture process outputs. Revise your existing setup sheet to include process outputs. This will ensure part consistency.

Venting
You can never over vent an injection mold.
Vent everywhere — sprue and runners, inserts, cores, ejector pins and blades, slides and lifters.
Be certain that you are venting to atmosphere and relieve pass the seal-off area. Utilize the correct vent depth to avoid flash.
Always check clamp tonnage. Determine when the part flashes by dropping tonnage. Once the part starts to flash, add 10 percent to accommodate process variation.
With poor venting, the vents will begin to build up residue. In extreme cases when the entrapped gas cannot get out, you’ll experience dieseling (explosion).

Tonnage
Determine minimum tonnage and add 10 percent for variation. This will maximize venting effectiveness.
Measure tie bar stretch with family molds to see if it is even and to determine if tonnage is affecting the press/machine (not just the mold).
Use dial indicator and measure the stretch of all four tie bars.
Understand mold size and tonnage, or you will damage the toggle mechanism. The footprint of the mold is important. Too little and you will damage the platens. Too big and you may damage the toggle.

Maintenance
Every mold has a weakness. Create a PM plan around that weakness.
No more duct tape maintenance books or files of work orders. Today proper mold maintenance requires software.
Share knowledge to maintain repair and maintenance consistency
Avoid under or over maintenance. PM mode is replacing things at a certain number when that number comes up. That’s good as long as that number is right.
Following the eight stages of PM: preparation, disassembly, troubleshoot, corrective action, clean, assembly, final check and stage/rack.
Follow the system. Cleaning is number five for a reason: you are wiping away all the clues, which will make it difficult to troubleshoot.
Clean cooling channels.
Chart mold wear to help create a PM plan.
Doing a mold positional analysis to remedy runner imbalance (lineal vs. rheological balance)
Always look for wear defects.
Identify the controlling features of each mold.
Determine where your maintenance dollars are going.
Collect data points at the press to identify root causes.
Use data to convince someone in the corner office that you want to improve efficiency.
Don’t use brass or aluminum hammers during assembly because they chip.
Listen to your hot runner. Look for cable issues, loose pins/damaged cables, gate insert problems, and incorrect flow.
Check tip “l” heights (distance from the front of the manifold plate to the top of the tip) because short tips cause a temperature increase.
Check hot tip systems as tips erode.
Follow the proper start up and shut down procedure (waiting for the hot runner to soak out; 30 minutes or so).

The Impact
One assistant manager of plastics maintenance in tool and die for Toyota Motor Manufacturing in Georgetown, Kentucky has recently moved to the tool and die side of the business, so this workshop was perfect timing to broaden his experience and knowledge of mold design, setups and various mold components. Lance is now armed to tackle documentation tracking, which he knows is key to helping the toolroom get out of firefighting mode.

Whether you want to work on molds, manage molds or design molds, you need to understand how these systems work and what is necessary to take them apart to clean them up. Proper mold maintenance is not difficult, but it is an exercise in patience, professionalism, accountability and discipline to do the right thing without someone looking over your shoulder. “That is what separates the pounders and apprentices from the journeymen. It is that person who can do all that without constant supervision,” Johnson says.