DFM - 9 Things 20 Minutes

Ok
You are working on a demanding program
Time is scarce
You get a DFM for an important part

AaaaaaggggHHHhhhh !!
Where will you get the time to do a full review?

Here’s an option
Take twenty minutes
Run through these nine things
Keep things rolling

1.Residence Time

Residence time. First thing to check in your DFM report.

Do the general calculations look ok?

It may be worth plugging the numbers into the calculator to double check.

Remember . . .

Residence time can be both too long, and too short.

Don’t get too excited about residence time at initial DFM review. Relax, it's gonna be ok.

Why? Because there are many strategies available to manipulate and improve things.

A quick sanity check of Residence Time is valuable at the initial DFM review stage.

It gives you a feel for related risk at this early stage.

And design actions to take to resolve.

2. Material

Is the correct material grade specification applied in the DFM?

Check with your Materials and GSM team to assess the material supply planning.

Does the mold-flow have the right resin grade?

You will be surprised how many times there are assumptions made.

“We don’t have the exact UDB file, so we used this one instead”

Red alert. Make sure you are using the correct material . . . even in simulation.

Watch out for the “local brand” material equivalent.

Always, always use material from a known and reputable source.

“Local brand” requires more due diligence and control. Important to avoid surprises.

Material surprised are never pleasant.

3. Material Weight

Another numbers check and cross reference.

Scan the runner and part weight entries in the DFM tool.

Is the overall weight suitable for the machine and barrel?

You may need to dig deeper into the machine details.

Is the runner undersized?

Sometimes, the vendor will undersize the runner in an attempt to save material. There is an optimal size for every runner based on material, MFI, cavitation and runner length.

Look at all the weight information in the DFM tool.

Cross reference with your Moldflow report.

Are there pressure drop risks?

Are there freeze-off issues?

Be careful under-sizing runners.

Make sure all weight calculations add up.

4. Cavitation

Look at the part size, the drawing dimensional specification and the cosmetic requirements.

Is the cavitation suitable for the accuracy and finish requirements?

For high accuracy and cosmetic consistency across cavities: less cavities is better.

Then ask . . and this may sound counter intuitive.

Is there an opportunity to have more cavities?

This is a mental exercise.

It helps you assess the maximum and minimum options.

The discussion of both scenarios may reveal other potential holes.

5. Runners

Quick self query when looking at runners in your DFM.

Do you see any pressure drop transition issues?

Check the sprue to runner transition. This area has a big pressure wobble potential.

Full round is the best runner section.

Sometimes its not possible to have a full round. I hear you.

Most times runners are machines into one tool half, for ease of machining reasons.

Is this detail included in the DFM?

f not, what is the reason? Get it in there.

Are there runner overruns to capture gas and other potential nasties?

Did the tool designer consider venting in the feed system?

Dedicate some MoldFlow byte power to focusing on the runner system. Too. much time gets focused on the part only.

Check pressure, speed and shear details in the MoldFlow report.

6. Tool Steel

Check the steel grade and hardness used on your tooling?

Have you a reliable and reputable steel supply source?

Does the vendor have ability to check and test material integrity?

Again, watch out for the “local stuff”.

Who is the supplier?

Is it the “local brand” equivalent?

Yikes. Be careful.

Polish-ability is huge.

If you are polishing to a mirror type finish, then pop polish-ability to the top of your criteria list.

It’s not all about harness and corrosion resistance.

Dig into the steel recommendations based on your resin selection.
Simple example: glass filled materials usually require specific steel types that are fully hardened.

7. Inserts

A good tool design is loaded with options in the form of inserts.

Inserts for fill, venting, machining and maintenance.

Do the tricky features and areas of the tool have inserts?

Any unresolved design issues that an insert can help resolve later?

Too many inserts can affect cooling design and efficiency.

Inserts are your friend.

It’s ok to overkill with inserts in your proto tool.

8. Ejection

Ejection layout should look tidy and balanced.

A high level design will always look correct. If the ejection looks random and messy, this is an alert for you to dig deeper.

Are there too many small ejectors?

Small ejectors are a maintenance risk.

Yes, many parts need small ejectors.

Keep their quantity to a minimum.

Requirements for blade ejectors can be questioned.

Again, blades tend to break more often than round ejectors.

Can a stripper plate be used?

Maybe the addition of a slide will improve the ejection story.

Is ejector positioning hindering cooling access?

You may need to remove ejectors in order to have better cooling.

There are many such trade offs in tool design.

9. Cooling

It’s easy to see when insufficient cooling is designed into the tool.

This looks too simple and fails to cover enough of the working tool area.

Are there any hot spots in the tool?

Which areas need dedicated and individually controllable cooling?

Your MoldFlow can help you assess.

Is there an option to add more cooling later if needed?

Keep your options open.

Do you need to add baffles, bubblers or 3D printed inserts to get cooling to required areas?

It's good to add cooling to bolster plates and support plates.

May not need this extra cooling but it's handy to have as an option.