Frequently Asked Questions
What are my Tooling options?
Long gone are the days when the only tooling option was to use steel! These days, a wide variety of materials are used, from SLA resins such as Perform, to silicone, epoxies, aluminium and steel.
Selecting the optimal tool material is dependent upon the quantities of parts required, the moulding material and any potential run-on requirements.
For really low numbers say up to 50, silicone is the obvious option, moulding parts in polyurethane. As quantities rise one starts to look at hard tooling materials, getting progressively harder/stronger all the way up to specialist steels. These hard materials allow the use of injection moulding and the full range of production materials.
Casting or moulding polyurethane into silicone tools is most often done under vacuum and is capable of producing very impressive, complex parts at a fraction of the cost of hard tooling options. However with the lower tooling cost comes a higher piece part cost, which is why higher volumes transition to injection moulding.
Silicone moulds (Soft Tooling)
The primary aim here is reduced cost and increased speed, usually due to the low quantities of parts required either as prototypes or low volumes of production parts.
In order to cast polyurethane, a silicone mould tool is made from a master part, that in turn can be cnc machined or most frequently made by 3D printing. Polyurethane is a thermoset resin, and cures with heat. Depending on the material, it can take anywhere between 1-24 hours to cure. A silicone mould can produce parts with extremely complex geometry, intricate detail and tight tolerances. Part finishing is done by hand.
Silicone moulds are used when a lower volume of parts are needed (1-100) with an approximate tool life of about 25 per cavity. The silicone will replicate the finish of the master, allowing textures to be incorporated at negligible additional cost, and can be coloured or painted resulting in functional cosmetic parts.
Aluminium Tooling (Bridge Tooling)
When aluminium is discussed in tooling applications it is important to differentiate between commercial grades and tooling grades. There is a world of difference.
Whilst aluminium is softer than steel, it can be machined faster, and generally worked more easily, offering the potential to reduce tooling costs and reduce leadtimes. 'Should aluminium be considered as a tooling material?' may be a useful article to look at at this point...
The term, Bridge Tooling is often used for a stage in development where there is a need for moulded parts in production intent materials, but production tooling is not yet available.
The process can be used to ‘bridge the gap’ with motive originating from time saved, early availability of parts or economics. Often on new projects the quantities are far from certain, making justification of tooling spend difficult. Bridge tooling allows that ‘toe in the water’ without the usual higher costs associated with steel tooling.
And those part quantities don’t have to be that low, with 100,000 parts being achievable with care and unfilled materials.
A mould tool that costs less than a production tool, can be up and running in two to three weeks, and has the capability to produce from ten to a few thousand parts….well worth considering don’t you think?
Steel (Hard Tooling)
Production tools are usually made of steel and intended for high volume production programs, or aggressive materials, and can be rated for millions of shots.
The lead-time to cut steel for a hard tool is longer and will often require heat treatment, therefore the upfront cost is much more expensive. That said if the part quantities are really there, multi cavities, full lights out moulding and less maintenance all contribute to savings when production is underway.
Sometimes the geometry or finish will demand the use of steel. This could be due to very thin wall sections or fine features where the materials inherent strength becomes a must have.
Additive manufacturing is starting to impact production tooling by allowing for conformal cooling. This permits waterways to be run more efficiently within the tool that in turn have a beneficial effect on moulding cycle times.
How to decide which type of tooling you need?
* Geometry and complexity – Size drives cost, especially with hard tooling and the associated moulding presses become increasing costly. Complexity likewise can preclude other options.
* Time pressures – Remember a hard tool can take weeks to build, whereas soft tools can be produced in as little as a few days (depending on the complexity).
* Tool life and Quantities – Silicone tools are good for typically 25 shots of a part, aluminium tools can go from 10 to 100,000+, whereas steel tooling can take you into the millions.
* Required Finish – Most surface finishes can be recreated on an aluminium tool, however textured finishes will not last as long and its best to allow for an increased amount of draft to help with this.
* Materials – TPE,PP, ABS, PA, PC, PMMA for example all work well in aluminium, adding glass or ceramic fillers will question the use of steel tooling if the quantities are also there.
* Flexibility – Aluminium is frequently easier to modify, hence its use in bridge or development tooling when the design is less certain. Modifying production tooling should usually be avoided if possible.
Understanding what you need is important when considering what option to pursue. If you have a tight-tolerance part that is critical to the function of your system, cutting corners and cost in the development stage may not always save the money over the long term. Plunkett Associates have the knowledge and experience to advise and support with all your tooling requirements. We can sometimes offer some alternative solutions so please give us a call.
Read more expert articles in our FAQ section where we discuss topics on materials, methods and products.
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