So you have plastic injection moulding project that requires some design resource? There are number routes to choose from: in-house, freelancer, design studio or your injection moulding partner design resource. Later on in this article we advise selection criteria for you to consider but first here is a quick overview of types of design, stages, file types and how to manage your intellectual property.
Types of design
These days most design is done with computer aided design software (CAD) in 3D, these data files are used directly to design the injection mould tools around. 2D design is still used for concept visuals and engineering drawings although the latter can also be done with annotated 3D files.
Stages
Briefly, there are some basic stages to a design project – concept, design detail of components and assembly packaging, prototyping and design validation (this can include computer simulation processes such as Finite Element Analysis, FEA), production release, sample evaluation and final production approval.
File types and managing your intellectual property
There are many 2D and 3D design packages to choose from and you should always insist on copies of native files for your records and that the intellectual property is yours. For 2D files the most common format of cross platform communication is the PDF format, for 3D CAD STEP or IGES can be opened with a free viewer so your organisation does not need native 3D software.
Some packages can export a format such as ‘e-drawings’ that open without any supporting software so you can view the models or assemblies in 3D and interrogate parts, weights, cross-section etc. Note this format is only for viewing and cannot be used for manufacturing. Where possible always get an assembly of parts as you can see how everything fits together.
Managing your intellectual property should be agreed advance that you own it and your design resource should release copies of the design at the various stages of design described earlier. This should also be supported by a file naming convention with revisions for pre-production (_a/b/c etc) and production release of _00/01/02 etc. It is the production release of 00 onwards that you start tooling with and major capital spend is incurred so each release should be managed with design change notification process and supporting quote of costs before proceeding.
A good way of keeping instant records is to use a shared cloud drive so you instantly have a copy on file and backed up rather than sending files by email that may not get filed. A good tip is also to have a client issue folder of file formats that can be viewed at various design stages.
Levels of design detail to expect
If you are the manager of the injection moulding project you should expect the following levels of details: already mentioned above, copies of all stages of work with a file naming and revision convention, 3D to have all draft angles and route radii, assembly files for packaging and fit checks, material selection, part shot weights, bill of materials (BOM), 2D drawings with component tolerances to ISO 2768 if agreed (your moulder will advise the tolerance class for the selected polymer type), design for prototyping (process type, prototype use, tolerances), design injection moulding (sink, material selection, material fill/injection point, split lines, draft angles, shot face area, tool action design), surface finish and post-moulding operations.
Prototyping pitfalls and tips
With modern day prototyping that virtually prints a 3D file it is very easy to make a file that is not designed for the manufacturing process. The prototyping processes in most cases have a uniform tolerance but injection moulding has shrinkage that is not uniform due to part shape/design and tolerances will vary across the part so don’t be surprised if your prototype has a very good fit and the injection moulding does not at first tool trial. The key is to plan for this in the design and manage the metal safe areas to tune.
It is always advisable to prototype a design so parties can evaluate the design for fit and function. You can’t simulate the effects of gravity in an assembly for example or the ease of assembly and product feel in the hand.
Design resource selection criteria
If you are lucky enough to have in-house design resource the likely most attractive reason for going down this route is it usually does not show as a capital cost but consider the costs of speed to market and right first time design especially if your internal design resource does not have some of the design for injection moulding experience described below. Of course Kavia can support your designer to mitigate this as we have experienced engineers and product designers in our team that help make your internal project a success.
When seeking external resources for design we have the following tips to help you decide. You typically have three design resource routes: University commercial services, freelancers and design studios. The University collaboration can appear to be the cheapest cost and the design studios the most expensive with freelancers somewhere in the middle but it is not the hourly rate that most important in our option. The experience of the designer doing your project is what makes it good value for money, here is some simple criteria to determine their experience in design for injection moulding:
- How many plastic parts have they designed, more than 100 is good experience.
- Have they ever been to an injection mould toolmaker?
- Do they add manufacturing draft into their models at an early stage, consider tool split lines and tool actions?
- Ask for a sample of their 2D component drawing and ask them to explain the tolerance scheme applied. It should exhibit consideration for process variation for dimensional ranges (larger dimensions are less accurate and some materials vary more such as >pp<). Look for ISO 2768 tolerance class and any specific over-ridden tolerances such as CTQ’s (critical to quality) annotations.
- Ask for evidence of how they do pre and post production revision control.
- Have they ever been to a tool trial and done a production approval process?
Kavia Moulded Products does not have an internal design resource but does partner with freelancers and design studios. We offer impartial advice to customers for the best design solution, please contact us as early as possible in your project so we can help with initial scoping, budgeting and approach. We have a great deal of experience with the current engineer team in the business for the last 25 years we have realised a lot of projects into manufacture.
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