Archive for May, 2009

Assembly Methods for New Product Design

May 26, 2009

What means should I use to assemble my product? When we talk about assembly we are covering a couple of areas. We are referring to the methods we use to fasten one part to another and we are also talking about the processes used in the production of the item. Let’s do this one more time to ensure that we have this clear. In one respect we are considering the means of fastening parts. That is, are we using adhesives or screws? In the second respect we are covering the production process or tools used to perform the actual assembly. Are we using a manual screwdriver or a pneumatic driver with auto feed?

To be sure these two considerations are intertwined, will have a significant impact upon the quality of your product and, like many things we have discussed previously, need to be determined up front. How are they intertwined? Let us assume that your product will have a high production volume. That would drive you to use a fastening method that could be accomplished quickly and efficiently in production. If you have the choice between an adhesive then, or a screw, you would then opt for the screw as it is more conducive to quick, consistent and reliable fastening. (Yes, I know that there are a number of people reading this who are pro-adhesive. I have spent years working with both methods. There is a place for adhesives. They are unique in their application and serve a role that other fastening methods just cannot fill.)

How will the assembly method have an impact on the quality of your product? Let’s look at the use of a screw. There are several ways in which you can install such fasteners. Let’s look at the use of a manual driver as compared to the use of a pneumatic driver with the ability to set torque. As diligent as a person might be, when using a manual screwdriver they simply cannot tighten the fastener as consistently as someone using a settable pneumatic driver or electric. The end result will definitely show in the quality of your output. It should also be obvious by now why the assembly method needs to settled upfront as an integral part of the product design.

OK, what are some of the means we can use to fasten parts of a product together?

• Fasteners such as screws or snap clips

• Adhesives (cold, hot, UV cure, and so on)

• Ultrasonic welding

•Heat staking

•Molded in features such as snaps


Moving these methods to the production realm requires you to consider things such as consistency, reliability and durability (validated through your product testing process), ease of installation and cost. The costs to consider are not only the cost of the fastener itself but also the cost of the assembly equipment. Ultrasonic welding is a good example of this. There is no fastener cost as you are simply bonding the native materials together. But, behind the curtain is the cost of the welder itself, the horn used to focus the weld energy and the cost of the fixture to hold the parts while welding. This can run up to $30,000 and is certainly not the method you would use if you were only making 20 parts a year. Here come the adhesives!!