An overview of nested tooling, its requirements, advantages and disadvantages.
The Challenge
For the purposes of this case study, nested tooling is defined as the ability to make variations of the same basic part from a single mould tool, made up of a matrix of inserts. That is a part with the same basic geometry but with outlets or ports located on different parts of the final moulded part. This case study was devised to outline the advantages and disadvantages of nested tooling versus standard conventional tooling.
The Process
All the fundamental principles of plastic injection moulding still apply. First, we must understand the construction elements of the tooling. Figure 1 is a diagram showing the different parts that go into the making up a mould. A part is created by two or more tools moving together to create a closed volume, into which plastic is injected under pressure. In a 2-part tool, the cavity (on top of the product) creates the quality outer surfaces and the core
(underneath) creates inner details. These are also the same parts that are required for a nested tool.
The two key elements to note here are the stationary (or fixed) plate and the moveable plate.
Pictured at Figure 2 is the Fixed Plate with cavity plate in place. Figure 2 shows this without these inserts and Figure 3 shows these inserts in place. This is one of several nested tools that we run and maintain in Thormac on behalf of three different customers.
The design of the tooling to meet the requirements of all the parts is a critical step in the development of nested tooling. At Thormac, we saw the need for nested tooling given the number of versions of the same basic part we needed to produce for the product range the customer required.
In short, we would have had to make over 150 tools. But with the use of careful mould flow analysis and product design we were able to make one tool with multiple inserts. The tool pictured is capable of producing over 150 parts with the same basic geometry.
Pictured in Figure 4 are some examples of the inserts required for the matrix laid out on the tooling workbench.
Each insert was designed with in Autodesk Inventor and populated into the tooling framework to ensure continuate of fit and function.
The Figure above shows a section of some of the variants we have produced using a single nested tool. Each is the same basic part, but with small variations – hence the need to use inserts instead of constructing a different mould for each variation.
Advantages
- There is a substantial cost saving using the same tooling as opposed to individual tooling. The tooling in this case study can produce 150 different variations of the same part.
- In production the tool setup is the same in relation to machine setup of pack height {tool height} ejector bar, and cooling lines, for all product variants.
- The speed of tool setup from one product to next is much faster.
- It allows for different size variation of product within pocket allocation size.
- There is only one purchase of one hot tip or hot runner system for all versions.
- It dramatically reduces the level of tool storage required for multiple versions of tooling for parts.
- It also reduces the scheduled maintenance dramatically due to the repeated use of the main tooling elements.
Disadvantages
- There is an increased set up time to change multi cavity inserts when measured against the time to change the complete tooling.
- There is an increased possibility of human errors being made during insert changes of tooling, thus producing incorrect or unusable parts.
- The risk of shot size being oversized for smaller insert parts.
- The failure of the hot runner will stop production of all versions in product.
- The tooling downtime of part replacement can negatively effects lead time of product.
- Tooling life cycle is decreased given the variances being used on the tooling.
