Starting a new project is an exciting adventure. Each stage of the development process brings decisions to be made, and sometimes those decisions can cost you time and money later. Extravagant designs may look great, but often can add unnecessary complication. Over the years we’ve found helpful tips to make designs less complicated, and in turn save a few dollars in the development of your new product. These are the things that you can do to make plastic injection molding parts assembly less complicated while decreasing cost:
Start with a DFMEA Process Sheet
You may have heard the term pokeyoke in a conversation, which is a Japanese term that translates to defense of a foolish act. Or maybe you’ve heard of a fool proof design? In either case, the basic concept is to have a design that doesn’t allow for mistakes, or has taken initiative to prevent an assembly operation from creating a defect or mis-assembly. There a few different ways that designs can incorporate error proofing, and the partner you choose should have a solid foundation in ‘design for assembly’. One way to document the process for error mitigation is with a DFMEA document. It is a document that lists all potential errors at each step of the process, and how the design will prevent that error from occurring. It’s primarily listed in a matrix form with error listed by failure mode, then ranked by severity, and their projected occurrence. It should indicate which error would be most annoying or harmful to your customer and where the design should focus to prevent issues later on.
Use Common Fasteners
One often overlooked option at every assembly involving fasteners is using common fasteners that can reduce the number available and where to use them. In more complex designs, multiple fasteners can be used based on the torque requirements, material requirements, and the driving head shape. The best case scenario would be to use one fastener in every joint on an assembly. That will reduce the errors produced as no other fastener will be an option. Secondary tools won’t need to be purchased for additional fasteners, and you can offset any costs with bulk pricing on the fasteners.
Use Datum Schemes
If you’ve unboxed a new purchase that had written instruction, it probably has a datum scheme designed into the assembly. A datum scheme will indicate which portion of an assembly to connect first, second, third, and beyond. When it comes to fasteners, a datum scheme may translate into hole sizes being smaller, oblong, or oversized based on their sequence. The smallest round hole will dictate a primary assembly point, an oblong could be used a secondary point to limit rotation, and an oversized third hole just simple used for the connection of the parts. How these holes are used as an error prevention is that they typically cause a misalignment when completed out of sequence. The parts shouldn’t fit correctly, assemblies shouldn’t work as designed, and it should clearly indicate a problem at or before the final inspection.
Examine Labor Costs
Human labor may be one of the more expensive investments into your project. Tooling has a large initial cost and may have a small maintenance cost over its life. Skilled and experienced workers can be difficult to find. Paying them a fair and competitive wage earns their loyalty and translates into motivated employees who perform at a high level. This should be expected as part of the cost to manufacture and assemble products.
Eliminate the Need for Secondary Fasteners
Secondary fasteners cost extra money, so the elimination of fasteners such as screws, bolts, or nuts will directly affect the bottom line in a positive fashion. This could also go for the need to have threaded inserts in the assembly to be able to create a fastened joint. If the assembly doesn’t require the option for disassembly, other options like sonic welding, plastic welding, or a snap-fit joint may allow for an attached assembly without a secondary fastener. A simple self-tapping screw could eliminate the need for a threaded insert and fastener combination if designed properly up front.
Keep it Simple Stupid
The K.I.S.S. method seems pretty simple, and in essence it explains itself very well. Keep it simple. Designing for Assembly (DFA) means you have thought about how to manufacture a product with minimal errors, make it so simple that anyone can do it, and reduce the operations, parts, fasteners, and labor needed to save costs where applicable. Some Computer Aided Design (CAD) software includes various built-in tools that can aid designers in prediction, and some of the know-how will come from experience.
When you’re ready to work with an elite team that produces world-class products, call us (425) 339-0288 or email us at mattp@sealectplastics.mystagingwebsite.com. We can offer you advice on the best technology to use, the best materials to meet your product demands, and how to navigate through each development stage with ease.
Matthias Poischbeg was born and raised in Hamburg, Germany. Matt moved to Everett, Wash., after finishing his bachelor’s degree in business in 1995 to work for Sea-Dog Corporation, a manufacturer, and distributor of marine and rigging hardware established in 1923.
In 1999, Matt took over the reins at Sea-Lect Plastics Corporation, a sister company of Sea-Dog and a manufacturer of plastic injection molded products with an in-house tool & die shop. Matthias Poischbeg is also a contributor to Grit Daily.