Strategies for minimizing tool cost

[Ken Magalnik]

Hello all,
This is my first post. I work for a small niche manufacturer that recently branched in plastic parts. It is company policy to keep as many of the activities in house as possible, and so we design parts and molds, build the molds, and mold the parts in house. My responsibility mainly rests with mold design, with part design being a close second.

Our production runs are extremely limited, from several thousand parts a year to 50k/ year at the most. As such It is important to keep the cost of the tool to as low as possible, often at the expense of cycle time and material cost.

As I'm relatively new to the plastics field, I'd like some advice from more experienced members as to how to best accomplish this. Are family molds a good way to save money? What about selectable, multi cavity molds? Any other strategies?

Thanks,
Ken

[Mauricio.B]

Ken
I find low volume projects more challenging than the large ones because the piece price is very sensitive to the tool cost, machinery cost and change-over and setup costs.

Family tools is definitely something you may need to look into for this type of volumes, but it depends on the quality requirements of your parts. Balancing the tool and deciding which parts are to be produced by the family tool is very important. Most people recommend against family tools, but with those volumes I wouldn't rule them out. Aluminum tools are also something you may want to look into.

Also, wouldn't it be cheaper to outsource your tools to a company specialized in prototype tools rather than making them in house?

Doing some changes to the part design can also help reduce the mould complexity and thus its cost. If possible, eliminate the need of de-moulding mechanisms such as slides and lifters.

Can you provide more information about the type of product (industry), materials and quality, mechanical and dimensional requirements? It will get you better suggestions.

[Ken Magalnik]

Mauricio,

Thanks for the prompt reply. Outsourcing is discouraged per company policy. As I gain experience, I'm starting to see some of the advantages of this philosophy. Besides, I wouldn’t want to do away with my own job

We are in the radiation detection industry. Our products usually carry a heavy price tag, so part cost doesn’t have to be competitive with the consumer market, but it does have to be reasonable, in comparison to say machining parts from stock. We make extensive use of engineered materials, particularly conductive plastics. Aside from that requirement, our products have to be tough enough to withstand abuses in industrial applications, oil fields, and the like. They often have to be fire resistant. Since the total volume is low, material cost is not a great factor in total part cost. Appearance has to be similar to what you see on the consumer market.

A strategy that I have undertaken is to make something similar to a family mold, but with a selector mechanism that directs the plastic to separate cavities. This way the tool cost is similar to a family mold, but without the balancing problem. I don’t know what the technical term for this approach is, but surely I am not the first person to have thought of it.

I've been interested in aluminum molds, but my fear is that the mold is too easy to damage in production; the material is just too soft. Also, we have no way to grind it, which complicated tool making.

With experience, I'm learning ways to avoid undercuts, or at least replace them with undercuts that are easier to mold. Perhaps a better question would be which strategies I should avoid. In particular, is it better to machine the cavity into the mold plates, or cut out an insert which will hold the cavity?

Also, what about three plate molds? It gives more flexibility in positioning the gate, but as I see it requires at least two cavities to keep the mold balanced, in addition to the expanse of extended sprews and roller pullers.

What about mold insert units, as opposed to complete mold bases? It appears that the blank cost of an insert is comparable to the cost of a small mold base, so what is the advantage? Is it just about a quicker change over in the press?

Thanks,
Ken

[Will Call]

Look here: http://www.masterunitdie.com/ You can purchase a frame (or several) and build your mold as individual inserts. When made properly they will last and produce as well as dedicated molds.

[Mauricio.B]

A strategy that I have undertaken is to make something similar to a family mold, but with a selector mechanism that directs the plastic to separate cavities. This way the tool cost is similar to a family mold, but without the balancing problem. I don’t know what the technical term for this approach is, but surely I am not the first person to have thought of it.

I agree. You will have no flow balancing problems. However, the center of area of the projected area will be offset from the center of the machine. This could cause flash and mould maintenance issues as well as higher clamp force (I don't really know how significant) especially if the offset distance is large. Make sure you have enough clamp force in the selected machine in case you need it. Also, if possible make the flow direction mechanism T shaped so that you can have the option of running one or both cavities at the same time.

I've been interested in aluminum molds, but my fear is that the mold is too easy to damage in production; the material is just too soft. Also, we have no way to grind it, which complicated tool making.

Makes sense to me. I would make some experience with non aesthetic, low production, easy flow material parts. If there are small core outs, they could easily bend. Keep the area clear of cooling lines in case you need to insert them in the future or just insert them from the beginning. I have run up to about 10,000 parts in aluminum tools but unfortunately never ran them until they fail or deteriorate. A mould maker told me once that they could guarantee 100,000 shots but I have never confirmed this.

.... In particular, is it better to machine the cavity into the mold plates, or cut out an insert which will hold the cavity?

Two reasons I can think of to insert the cavity in a pocket in the mould base: one, when the steel will be heat treated as heat treating the large cavity or core plate will deform them and two, for parts that will undergo important design changes in the future so that the insert can be easily modified or just replaced. Cutting the cavities right in the mould base is just faster and easier. I have also used them to reduce the cost of the prototype tool. The production mould base is built with the prototype inserts and later on, the production inserts mounted on the same mould base.

Also, what about three plate molds? It gives more flexibility in positioning the gate,

Other than the gate positioning benefit (is that an issue in your case?), three mould plates are used for automatic ejection and separation of the runner and gate system from the part. This is a benefit for high volumes production. Not your case.

...but as I see it requires at least two cavities to keep the mold balanced, ...

On the contrary. One of the applications of a three mould plate is to allow ONE cavity tools to have the center of area of the part in line with the axis of the clamp unit while being edge gated.

in addition to the expanse of extended screws and roller pullers.

Yes they are more expensive. They also could require a machine with a longer daylight as the shot height is longer and extra spaced needed for runner extraction.

What about mold insert units, as opposed to complete mold bases? It appears that the blank cost of an insert is comparable to the cost of a small mold base, so what is the advantage? Is it just about a quicker change over in the press?

I think that quick change mould bases have more application in high production high change over environments and where part sizes are similar. Because of your low volumes each production run will most probably produce parts for several months. If you have parts that are similar and can use the same ejection system (or easily adapted) I would make inserts and use the same mould base (another use of using cavity insert blocks in the mould base).

[rickbatey]

The trick to aluminum tooling is to place hard steel sleeves in the base and run the steel ejector pins through them. This keeps the steel from eating the softer mold base. There are some aluminum grades that can be air hardened. Gate areas can be inserted with high wear materials for filled resins. MUD bases sound like the best ticket for what you are doing. Rick.

[Al Hall]

Bill & Rick definitely have the right idea. The rest of this is old news that doesn't work in respect to quality and costs. You can make inserts for MUD base out of anything you want. You can build in a hot sprue bushing and speed up cycle time and etc. etc. etc. Flow diverters are nothing new and neither are runner shut-offs. You can build a three plate MUD if you need it. Even some low volume parts can benefit from that. It really has nothing to do with volume but rather where you need the gate. Also remember your toolmakers are working with small components and not wrestling with a family moldbase. You will end up, very quickly, with more holes in your mold base than Swiss cheese. You should spend some time with someone that has been in the business for a while and "been there, done that".

[Bader]

Ken

Just read the whole thread for the first time today.

I also notice Louis famous 'thread-drift' creeping in so i will come to your first question post.
Why do you want to MINIMIZE the tool cost?
How much is your present tool cost ( ? $s for ? Cv) and how much you want to bring down in terms of value or percentage?

In my opinion, nothing is cheap or expensive. It is FEASIBLE or NOT-FEASIBLE.
I learned you are making value added goods and for obvious reasons the volumes have to be low.
I also believe you dont make molds first and than look for a client but you get your quotes approved first and than cut the steel. Right?
If that be the case, your bean counter should be happy with the figures. I cannot understand why would you want to reduce the cost of molds AFTER the project has been approved?

There are three ways to increase the profitability of any company.
ONE: Increase your selling price, keeping volumes and COG (Cost of Goods) the same.
TWO: Increase sales volume, keeping selling price and COG the same
THREE: Decrease COG without touching the other two.

If i were you, i would not spend too much time thinking of reducing my mold cost but rather look for increaeing my number of units sold or get a higher selling price by going into more value added products.

I am not in USA and trust me, this is the FIRST symptom where US companies end up going offshore because they deviate thier attendion from the core business and start looking to reduce the molds cost.

They do so because they may find it EASY and even if you succeed, i dont think you can reduce the molds cost by more than (say) 20-30% where as if same energies are consumed in exploring other avenuew (opportunity cost), the effects on you balance sheet can be very attractive and long lasting too !


Kind regards,


Bader

[markrh]

Ken,
This may seem like a simple question and I notice that you have a lot of good advise already so here is my 2 cents worth. A mold for $1.00 is expensive if it wastes everybody's time and makes no parts, a mold for $100,000.00 is cheap if it makes 50,000 good parts an hour for example. Assuming that you are molding the parts in house and you have all the necessary equipment then the only costs to you will be material for both the mold and the parts, if that is the case then your company would rather spend money in the molding department than the mold making department. A mold is like any other component of the business and should be looked at as a part of the whole cost to produce a part as you would anything else and not as a standalone expense.
Mark