Why is the Manufacturing Method so Important and How to Choose the Best Method
In previous blog entries we have repeatedly noted how important it is to keep the manufacturing methods as a key focus of your design process. We mentioned DFM/DFA (Design for Manufacturing and Design for Assembly) and commented that a good design effort will be typified by bearing these two disciplines throughout the design process. Why do we keep harping on this?
There are several key points to consider. Let us assume that whatever your product is, that you will be making a bunch of them. That means that whatever initial work you put into the design and manufacturing processes will get replicated through each one you make. There are many ways to design any given product and there are many ways to make that same item. Let’s talk about the design input for a moment. Take for instance a part of a mechanism that is intended to provide friction. It does this by rubbing on another surface. You decide that the actual contact surface should be a polymer. There are two ways to carry this out. You can make the entire part from the chosen polymer or you can make another piece and fasten the friction polymer to that second piece. Either method would work, but the second method would have more cost both in labor and in part cost. It also may lead to reliability problems. Each time you add a component (and fasteners) you increase the chance of problems occurring during the use of the product. The time to consider these design issues is in the beginning, not after you are in production as you now have foolishly baked a lot of extra cost and problems into you product. Remember, it gets replicated with each one you make!! We are big on part reduction. One of our rules of thumb is if there are two parts next to each other and neither part moves relative to the other, then you probably have one more part that you need.
The considerations about the manufacturing and assembly methods follow a very similar thought process. Let’s take the example of a plastic assembly. You have two housing components that you have to join (Yes, we know that two housing parts violate our “no relative motion” rule but housings quite often are the exception to rule as you have to contain other parts within the housing). Let’s consider two ways of joining these two housing parts. You can use fasteners or you can use ultrasonic welding. If you use fasteners you have baked in the cost of the fasteners and the labor to install them (Sure, if the housing needs to capable of disassembly then the fasteners are an option). If you choose ultrasonic welding, then you have no fasteners (and you have the option of getting a water resistant seal without adding a separate gasket). You just minimized the cost of each product you ship out the door. Once again, in the design phase is the time to make these choices. One additional note here is that in the design process, each individual component of the complete product should be designed so that it can only be put together one way. This will be a tremendous aid to the manufacturing operation. Also if you can work this in, design your components so that if any one of them is missing, other components will not fit or function correctly. This allows you to catch errors in the assembly process prior to the product being completed and you are forced to toss it in the trash.
How do you choose the best manufacturing method? This is a text book in itself and would be much too lengthy to cover in detail here. However here some guidelines:
- The method should meet the requirements dictated by the design intent of the product or part. That is, don’t use polymers where the structural needs demand steel.
- The method you choose should be the minimum cost method that satisfies your requirements. Note that amortizing tooling cost in this is a key part of your analysis.
- Once you choose a method, make certain that you qualify the supplier that will be executing that process. Do they know what they are doing? What is their experience with this process?
- The method should be consistent. This means that every part that goes through the process should be treated identically to all of the others.
- The method should be a commonly accepted practice. In other words ideally the method you use will be available at other suppliers. This reduces that chance of you being held hostage by a supplier or allows you to move your manufacturing for other reasons.
- If you plan on implementing this method in your own internal processes, allow time for a learning curve if it is new to your production methods.
Not making wise decisions upfront regarding manufacturing and assembly will be a long term cost and possibly reliability burden to you.