Multipart Assemblies

While assembling your product may be one of the last steps before it goes to your customer, it should be one of the first things you consider when designing your parts. After all, the longer it takes to assemble, the more expensive your overall product cost will be. That’s why you need to design for assembly when creating your molds.

The Importance of Designing for Assembly (DFA)

It’s easy to see your product as a series of parts. Designing for assembly means thinking about the process of putting all the parts together into a single product. The more pieces there are and the harder they are to put together, the more you will have to pay for labor. Spending time thinking about the assembly process while you’re still designing the injection molds could save your company a fortune down the road.

Tips for Designing Multipart Assemblies

Here are some tips you should keep in mind when designing the molds for each part of your final product and how you can design your product with assembly in mind.

Keep in Mind Designing for Manufacturing Principles

Just because you’re designing for assembly doesn’t mean you can forget about designing for manufacturing (DFM). In fact, the two processes are closely linked and often referred to as the single acronym DFMA. You must still consider things like draft angles, uniform wall thickness, radius design, and other crucial DFM principles.

Look for Symmetry

Often, an assembly that typically requires two unique components can actually be made from a pair of identical parts. If you thoughtfully design the product with bolt holes and bosses or clips and undercuts on both halves of the part, you can use a single mold for both halves rather than doubling the cost of your molds using different designs for each half.

Not only will this save you money on the cost of molding, but it also makes it faster to assemble the product if the person or robot can grab two of the same part rather than one of each different part.

Keep Tolerances Realistic

Parts that need extremely fine tolerances are already more difficult and more expensive to make than those with more realistic tolerances. When you have a multipart assembly, a single off-spec piece can throw off the entire assembly. Using a larger tolerance in each piece reduces the potential for assembly problems.

Use Self-Mating Parts

Using mating clips and hooks reduces assembly time and eliminates parts compared to fastening parts with screws or other external fasteners. Taken a step further, using a living hinge allows you to make your entire product from a single mold, further reducing costs and accelerating the assembly process.

Standardize and Minimize Parts and Fasteners

The fewer parts and fasteners you can use, the better. Avoid left- and right-handed fasteners and choose universal fasteners when possible. Beyond that, you should use off-the-shelf parts rather than designing your own screws or fasteners. Also, try to use the same fasteners throughout the entire product. That eliminates the need for the assembler to switch between tools, saving them time and you money.

Design Parts for Handling

Even when machines are assembling your products rather than people, parts that are small, slippery, oddly shaped, or easily stuck to each other (like springs, cup-shaped objects, or E-clips) increase the difficulty of assembling the final product.

Simplify Components

While it may be cheaper to mold 6 simple parts than it is to design and mold one more complicated part, the time saved during assembly may more than make up for the difference. The fewer and simpler components are required to assemble, the more you’ll save on labor costs.

Use Modular Assemblies

If you have a range of variant devices that can use relatively similar modules, you can improve the efficiency and quality of automated device assembly. Whether you have people or robots assembling your products, efficiency is key.

Minimize Part Flipping and Rotating

The less the assembler has to flip, rotate, or otherwise handle your product, the faster they can assemble it, reducing your labor costs.

Utilize Overmolding

Why use mechanical assembly if overmolding can achieve the same result easier and faster? While you have to find the right combination of materials, overmolding creates a permanent bond with no need for secondary assembly processes.

Include Self-Locating Features

The longer it takes for an assembler to stick a screw, spring, fastener, or another part into a hole, the more labor costs increase. Think about how to design your parts so the features are easy to line up and so that screws and other pieces slide right into place without much trouble.

Choose Universal Plastic Mold

With more than 50 years of plastic injection molding experience, Universal Plastic Mold (UPM) can help you design the most cost-effective multipart assemblies, saving your company money. To get a quote or learn more about UPM, click here or call 1-888-893-1587 today.

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