Inventor 2010 Tooling: Core & Cavity and Plate Design

Written by Al Dean

Published Tue 12 May 2009

As with many  features and functions within Inventor 2010, the new tooling technology has been public knowledge for some time. However, rather than having been tried, tested and refined on the Autodesk Labs web-site (labs.autodesk.com), the technology has been on test in some of the most hectic tooling-heavy countries in the world - namely, China and Brazil. After all, if you have a new set of tools aimed at such a specific industry sector and working process, it makes sense to test it in an environment in which it’ll see a great deal of usage. 

While those directly involved with tooling design will be aware of many of the processes involved, Inventor’s new tooling technology brings real benefit to those either making their first steps into developing moulds in 3D or those looking to gain a better understanding of the process so it can aid their design for manufacture knowledge. 

There is also the fact that, due to the rising costs and scarcity of many previously low cost and abundant materials (particularly metals), many designers are now engaging in plastic part design for the first time. By combining the new plastic part design tools (see page 23) with the full suite of design to manufacture preparation tools we’re exploring here, Inventor is now offering a capable environment in which to take your first steps into design for injection moulding.

So, with that in mind let’s take a look at how the technology works and the steps you take to get to the point of a completed core, cavity and plate design. 

Stage 1: Placing plastic part or core/cavity

There are two options here: either start with a basic part, designed in Inventor or import geometry from another system. The next step is to load up the new mould template and then position the part. It’s also possible to start with the core and cavity set-up. This is particularly useful if the core and cavity design is supplied by a third-party specialist or client, or there are different team members working on it.

Stage 2: Adjust orientation

The chances are the part will not be designed in the correct orientation for moulding purposes, where the two basic halves of the mould split. To help remedy this the adjust orientation tool provides the capability to rotate the frame of reference for the part to ensure it’s correctly aligned with the mould’s opening angle. 

Stage 3: Select material

With the acquisition of Moldflow, Autodesk gained access to a much richer set of materials information (the company even has its own certified materials testing lab). This is now available within the Inventor Suite. The select material dialog provides access to the fully searchable (by vendor, trade name, property) database of plastic materials, from which the user chooses a suitable plastic. The wealth of information here is incredible and there is access to a world leading source of materials information. The dialog also gives feedback of recycle-ability and an energy use indicator helps assess sustainability.

Stage 4: Core and cavity design

This is perhaps one of the most critical stages in the design process, as it’s here that many of the performance characteristics of a mould are defined (but by no means all). There’s a separate Tab and Panel for Core and Cavity Design, so let’s look at that in stages. 

4a: Gate location: This defines where the material enters the part cavity and the user can either select this manually or use the Moldflow-based tools to make suggestions. While the manual method will be used by those experienced in mould design, the suggestion tool is worth running as it may give a new perspective and offer up previously unconsidered positions. In this example, it is known where the Gate location is, so it’s been added manually.

4b: Part Process Settings: Here the user defines the basic operating conditions for the moulding machine tool. If this is known then they can be added, but if this information is not available then the Moldflow technology can be used to find an appropriate set of inputs. These are ball park figures, rather than specific values, as a machine tool mould team or supplier is likely to have a much higher-level of knowledge and know the intricacy of the hardware and the material and how they can be combined to achieve the desired result.

4c: Part fill analysis: (1 above; 2&3 below) If the user wants to double check the settings, a part fill analysis can be performed to find out how the system thinks the part will perform given the operating conditions, material characteristics and the gating location. Even at this early stage, insight can be gained into how both design and material choices can affect manufacturability. This allows design changes to be made and values adjusted before progressing  too far towards completion.

4d: Part shrinkage: the shrinkage factor of a  mould is used to ensure the desired part dimensions are achieved after accounting for shrinkage of material when cooling. This can be manually input or based on a calculation by the system using a number of different options for reference (time versus end of fill pressure etc). A text report provides indicators for shrinkage and the system can display how that shrinkage affects the form of the part graphically.

4e: Define work-piece setting: Regardless of whether the final mould will have one piece plates or use an insert strategy, this is where the bounding box or cylinder (to which runoffs are built) is defined. The system provides the basic requirement and this can then be tidied up to round dimensions, either for cleanliness or using stock or standard material billets.

4f: Creating patching surfaces and runoffs: These are the surfaces that close out internal open features, commonly referred to as shut-offs (see Figure 4F1 above) and the runoff surfaces (see Figure 4F2 below) that extend from the split line to create the core/cavity closing surfaces. A parting diagnostic can then be run to give an indication of how the core/cavity set performs.





4g: Create core/cavity: This brings this stage of the process to a close, by adapting the form of the part to accommodate for shrinkage, adding the gating location, and using the shut-offs and runoffs to split the core and cavity and create the two solid bodies required. Everything accomplished is available for inspection and editing in the feature tree, so there is a complete record of the work to date. 

Stage 5: Pattern

So far, we’ve discussed creating the core cavity set for a single cavity mould but it’s more than likely that users will be looking to optimise the part product count and make full use of machine time by creating a patterned mould tool. This enables multiple batches of parts to be created in one shot. Inventor Tooling provides tools to pattern the core/cavity set-up intelligently as a rectangular or circular pattern, based on part count required.

Stage 6: Runners, gates, cold wells & cooling

The next few stages allow users to define all of the interconnect between parts in a multi-cavity mould (runners and other components aren’t as applicable to single cavity moulds). The system provides a mix of tools that allow users to define these features automatically or dive in an add the geometry manually.

 

Stage 7: Validation of mould

Here, the user has access to similar mould simulation tools already used within the core/cavity design process, but applied to the whole mould, taking in cavity patterns, runners, gates, cold wells and cooling channels. They show exactly how design decisions can affect the quality of parts and users can adjust parameters at any stage accordingly. Once happy with the plate design, the user can then move on to the next step Mould Base Design