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Questions to Ask Your Molder During Mold Design

Know what questions to ask about your new mold during the mold design phase.

What you know and don&#;t know about your mold design can impact the timing, costs, quality, risks, and life of the mold. The mold design phase defines most of the quality of a mold. You need to ask detailed questions about your new mold during mold design, so you can make changes early on.

If your supplier makes meaningful decisions such as shortcuts to save time and money at the expense of accuracy, you should know. Asking these specific questions helps you learn about both your final output and your supplier. The answers help you select the right provider who will extend your mold&#;s performance and longevity to get the most value from your investment.

Q1: CAN I REVIEW THE MOLD DESIGN?

As the owner of the mold, you have every right to review and approve the mold design prior to mold construction. If they decline your request, this raises red flags. Either your supplier does not use a mold design, or they are unwilling to share their design with you. Either way, this supplier introduces extra risks into your project, and you have to ask yourself why. Your goal is to reduce project risks, not introduce more, and this supplier may not be the right fit for you.

We have had clients transfer molds to us that they own. They were surprised to discover that the mold had no cooling lines or ejection because they had never seen the mold before. Maybe you cannot physically review the inner workings of your mold in person. But you can review the mold design which can reveal these types of issues before building the mold.

You want to make sure not to assume that a high-grade mold is automatically a well-designed mold. A Class 101 mold might be made with hardened steel, but that provides little insight into the rest of the mold design. In other words, a Class 101 mold can still have a poor mold design or lack the ability to run automatically. You can read more about mold classifications here.

Even if you do not want to delve into every minute detail, at a minimum you can review parting line assignments, knockout locations, and gate locations to assess the impact on the final part. You can also review inserted areas and venting locations which will also have an impact on the final part.

 

Q2: WHAT SIZE MOLD WILL YOU BUILD?

We have had many molds transferred to us for molding or repairs where the customer wanted a robust, efficient production mold and ended up with a mold which was much larger than necessary. These molds suffered from inappropriate mold designs. Larger molds consume more raw material and produce unnecessary waste.

In general, you are looking for signs that you are getting the right mold. This means the mold design does not include unnecessary waste. You want a lean mold. You determine waste based upon the purpose of your mold. For example, a rushed mold design could result in a mold that requires a 200-ton press versus a 60-ton press.

That might work if you place priority on speed to first parts as your priority. If the mold will produce a low number of parts quickly, the rapid mold design might work best for you. Rapid molds use quick designs by cutting out steps not needed in pursuit of getting a number of samples as quickly as possible.  Building a robust mold with optimized cycle times proves unnecessary with a primary purpose to validate the part design. As Donald Knuth said, &#;Premature optimization is the root of all evil.&#;

As the need for higher quantities of parts increases, a more efficient mold design grows more desirable. If the mold will produce many parts without wasted processing time during injection molding, a smaller, more compact mold works. This means the mold will fit into a smaller press, consume less energy, decrease cycle time, and yield a lower piece price. The smaller press will generally use a lower clamping force and create less wear on the mold. This helps extend the life of the mold.

 

As a consultant, I continually see mold and molding issues that could easily have been avoided. The most common problem has little to do with cutting steel. The problem is failing to consider, obtain and verify all the pertinent information up front&#;prior to the mold&#;s construction.

It&#;s the responsibility of the moldmaker to ensure the mold will produce dimensionally, functionally, and aesthetically acceptable parts for the life of the program. There is no way to achieve that goal without first determining what the dimensions, function, aesthetics, and lifespan requirements are from the customer.

Most clients are not well versed in our industry, but all too often think they are experts. Still, they prefer to work with knowledgeable vendors&#;someone who is looking out for their best interest. It is the moldmaker&#;s responsibility to educate the customer, which also serves to protect the moldmaker. For example, no matter how insistent a customer may be, the moldmaker should never agree to build a seven-cavity hot-runner family mold for parts of various sizes and wall thicknesses in a high-shrink semi-crystalline material.

Don&#;t laugh. This is a real example, and the project is 11 months late and will soon be converted into four molds. The expensive hot-runner system is now a boat anchor. If that wasn&#;t bad enough, the moldmaker agreed to amortize the mold into the piece price, with no down payment. Ultimately, if the molder can&#;t produce acceptable parts, the finger is going to get pointed at the moldmaker.

This tooling checklist is focused on communicating all the pertinent information about the mold from and to the customer.

With all this in mind, I compiled a list of questions that should be asked both internally and to the customer to help avoid any delays or oversights that could affect getting paid for the current mold, as well as any future tooling orders. I am not going to expand on why each question should be asked. If you are an experienced moldmaker, you already know why. None of the questions below are about the details of the mold design, such as the type of interlocks, plate thicknesses, eyebolt holes, etc. The list is focused on communicating all the pertinent information from and to the customer.

If the molder can&#;t produce acceptable parts, the finger is going to get pointed at the moldmaker.

Initial Inquiry Questions

 1.  How did you hear about us?

 2.  What is the end use of the product (medical, automotive, consumer, etc.)?

 3.  Are there any mating parts?

 4.  Do you need any part-design assistance?

 5.  What are the expected annual production quantities?

 6.  What is the expected lifespan of the product?

 7.  Do you have a CAD file of the part? If so, what is the file format?

 8.  Do you have or need a 3D-printed or machined prototype?

 9.  Do you have a 2D dimensioned drawing of the part?

 10.  What is the material type?

 11.  Will the parts be made in more than one type of material or more than one color?

 12.  Do you have any mold-design specifications that need to be adhered to?

 13.  Can we get your molder involved in future discussions?

 14.  Is the number of cavities desired based on the mold cost, part cost, or production requirements?

 15.  If the mold is to be a MUD or other quick-change insert type, is a specific frame size required? If yes, what is the frame size or number?

 16.  Do you know if you want a cold runner, hot bushing, hot runner, valve gate, etc.?

 17.  Are there any interchangeability requirements, such as various versions of the part or engravings?

 18.  Are there any inserts that will be overmolded?

 19.  Are there any secondary operations that might affect the mold design?

 20.  What are the surface finish requirements for the cavity?

 21.  What are the surface finish requirements for the core?

 22.  How many samples will you need initially?

 23.  Are any inspection or testing criteria required for the parts?

 24,  Are there any mold qualification requirements?

 25.  Is there anything else we should know?

 26.  How many other moldmakers are quoting this project?

 27.  Are any of these moldmakers offshore?

 28.  When are you expecting to place the order for the mold?

 29.  How critical is the delivery date?

 30.  If you gave the potential client a ballpark mold cost, what was their reaction?

Questions the moldmaker must ask internally are as important as the questions asked of the customer.

  

Internal Review of the Supplied 3D Model

 31.  Did the model translate well?

 32.  Should the part design be modified to reduce the mold cost or increase its longevity?

 33.  Can the model be modified in-house?

 34.  Are any actions required (cams, lifters, two-stage ejection, unscrewing, etc.)?

 35.  Are there any holes or features requiring shutoffs?

 36.  Does the part have uniform wall thickness?

 37.  Is additional coring needed?

 38.  Is there sufficient draft to prevent sticking or scuffing in the cavity?

 39.  Is there sufficient draft to prevent sticking or scuffing on the core?

 40.  Are there any undercuts?

 41.  Are there radii on both internal and external corners?

 42.  Should any radii be removed to eliminate cavity impression in both halves of the mold?

 43.  Are there any ejection concerns?

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 44.  Are there any gating concerns?

 45.  Are there any filling concerns?

 46.  Should a flow analysis be considered?

 47.  Are there any cooling concerns?

 48.  Should high-conductivity materials, or conformal cooling be considered?
 

Internal Review of the Supplied 2D Drawing

 49.  Does the 2D drawing have everything defined? Everything includes

        a.  Dimensions, 

        b.  Tolerances,

        c.   GD&T requirements (straightness, flatness, concentricity, etc.),

        d.   Surface finish or texture,

        e.   Notes.

 50.  What is the date and revision level of the drawing?

 51.  Are the critical dimensions identified and toleranced?

 52.  Are there any dimensions or tolerances that are not obtainable for tooling or molding?

 53.  Has the material type and grade been specified?

 54.  Does the material contain any abrasive fillers, such as glass?

 55.  Does the material contain any flame retardants or other additives?

 56.  Do any of the notes refer to documents that were not provided?

 57.  Should a prototype tool be considered?

The more steps we take up front to minimize risks, through the collaboration of the concerned parties, the more competitive and profitable we will be.

Part Design Review with Customer&#;Prior to Mold Design

(In addition to any concerns or questions from above.)

 58.  What is the controlling document&#;a 3D model or a 2D drawing?

 59.  Are you familiar with the inherent issues of family molds?

 60.  Are runner shutoffs required?

 61.  Is the intended gate location acceptable?

 62.  Can a gate recess be added?

 63.  Can ejector-pin bosses be added on deep ribs?

 64.  Are samples and 2D drawings of the mating parts available?

 65.  Are alternate material types or grades acceptable?

 66.  Are you familiar with anisotropic shrinkage?

 67.  Who is specifying the shrinkage factor?

 68.  Who is supplying the material and colorant?

 69.  Are the intended molding machine&#;s specifications available?

 70.  Is the molder planning on using a robot or picker?

 71.  Is it acceptable if the engraving is raised on the part?

 72.  Is a recycle symbol, date clock, revision symbol, or cycle counter desirable?

 73.  Do you have artwork for any engraving?

 74.  Are the font type and size specified?

  

Mold-Design Review with Customer

(In addition to any concerns or questions from above.)

 75.  Is the cavity number location, size, and depth acceptable?

 76.  Are the ejector pin locations acceptable?

 77.  Are the witness lines from any actions acceptable?

 78.  Should some areas be left steel safe and adjusted after sampling?

 79.  Should any spare parts be made?
 

Photos by Jim Fattori. Molds built by Lawrence Mold & Tool Corp., Trenton, N.J.

Molding Considerations

If you think molding issues have no effect on the part or mold design, think again. For example, sink and knit lines will affect the gate location. Splay and jetting will affect the gate type, size and location. Flash will affect shutoff considerations, steel types and heat treatment. Sink, warpage, and material type will affect both the part and mold design. Burn marks and shorts will affect the vent types and locations. Color values will affect the part&#;s wall thickness and mold&#;s surface finish.

 80.  What are the limitations on each of the following?

        &#;  Color (L, a, b, Delta E, gloss),
        &#;  Gate vestige,
        &#;  Sink,
        &#;  Warp,
        &#;  Knit or flow lines,
        &#;  Flash,
        &#;  Shorts,
        &#;  Splay,
        &#;  Burn marks,
        &#;  Black specks,
        &#;  Grease or dirt,
        &#;  Other.

Our business is full of risks. The more steps we take up front to minimize these risks through the collaboration of the concerned parties, the more competitive and profitable we will be.
 

ABOUT THE AUTHOR: Jim Fattori is a third-generation molder with more than 40 years of experience in engineering and project management for custom and captive molders. He is the founder of Injection Mold Consulting LLC in Pennsylvania. Contact: ;
injectionmoldconsulting.com

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