It often happens in a preliminary mold design meeting that a seasoned mold designer will propose changes to the part design that will improve its production and reduce the cost to produce it. Sometimes this will stimulate a request to detail the proposed changes. Unfortunately in a second meeting when the details of these proposed changes are reviewed the decision will often be to keep the part as originally designed. Then after the mold is in production and there are issues with molding the part, a decision to follow proposed changes is then mandated.
You can take a donkey to the pond, but you cannot force the donkey to drink.
Total agreement that it is important for the design engineer to see the parts being produced. Seeing first hand voids, sinks, and knit lines helps future desigsn. Even if the mold maker can make a mold to produce parts, it is not always guaranteed that a processor can produce quality parts from that mold. A good mold shop will no-quote a design rather than enter into a losing project.
Everything described as “Design Rules” in this article is important, but its only an introduction to part design. As design engineers gain experience, they gain a wealth of knowledge that makes them so much more valuable to their employers. An inter-related skill of part-designer and mold-cavity designer emerges. This skill is often learned, but not often taught. This article is a start in the right direction. When we were struggling through it, we called in “concurrent design”.
Flash-back 25+ years. When I designed my first plastic part as a CAD designer in the early 80’s I knew NOTHING about tool design. Constant wall thickness? Draft? Gate location-? (what’s a Gate?).This is basic stuff, not taught to CAD jocks at the time. Not to mention the “zillion” issues (knit lines, glass content, shrink, fill rates) pointed out by my associates at Phillips in Wisconsin. When that first horrid little part design was reviewed by an experienced tool designer, egos were bruised, but greater knowledge ensued.
The interrelationship of part design with mold design should be a corporate mandate. Any person who designs a CAD database ought to be the same person who sits in the tool design consult at the mold-maker’s office. The concessions can be discussed on paper, before they’re locked in steel. Later, that same Jr. part designer needs to be assigned to review the tool design, to gain understanding from the mold-maker’s perspective. Subsequently, the same person should visit the tool shop, see the tool being built, see it assembled and finally; sampled at press-side. There is no greater education in manufacturing than to take part design geometry the full course; from an awkward CAD concept to the smell of molten Polycarbonate in the pressroom: the proving ground.
These are great tools for plastic part designers. Keeping the wall thickness as uniform as possible definitely helps in the final part quality. Varaiations in wall thickness especially thick to thin to thick again open up the possibility of quality issues like sinks and voids the end of fill.
In multi-cavity molds, it is always best to designate which cavity the part originated from on the part. It is not safe to assume that all cavities produce the exact same part due to flow, pressure, temperature variation, etc...
Phillips' four simple rules gives engineers a lot to go on. Also, Doug's point about making tooling issues and mold design requirements part of the early development process is spot on and can help teams avoid a lot of the rework and time delays resulting from having to make after-the-fact design changes to accommodate tooling. A lot of the CAD/CAE vendors are beginning to address this issue with new modules and capabilities as part of their broader design tool suites.
By experimenting with the photovoltaic reaction in solar cells, researchers at MIT have made a breakthrough in energy efficiency that significantly pushes the boundaries of current commercial cells on the market.
In a world that's going green, industrial operations have a problem: Their processes involve materials that are potentially toxic, flammable, corrosive, or reactive. If improperly managed, this can precipitate dangerous health and environmental consequences.
With LEDs dropping in price virtually every year, automakers have begun employing them, not only on luxury vehicles, but on entry-level models, as well.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
3 
