Reducing the number of parts in a product can save you a huge amount of money, in both direct and indirect costs of the product. The parts that have been omitted can never run out, they don’t need to be repaired and no documentation is required.
In the previous article we discussed these benefits extensively. The following question is: Which parts can be omitted and which can’t? Does each part fulfil a particular function?
In this blog, we will show you a systematic way to determine the minimum number of parts.
Before we can determine which parts are required, we must first understand which function (s) the product should be able to fulfil. The functional requirements of the product can serve as a starting point.
Next, a list must be compiled of all parts of the product. Parts like liquids, glue and lubricants do not count in this analysis.
The assessment of essential parts
To identify which part is essential and which isn’t, we use a roadmap or checklist for each part.This roadmap is divided into four topics: fastening, relative movement, material and assembly. For each part, this step-by-step plan can be used to determine whether or not it is an essential part. The chart below gives an overview of the roadmap.
Fasteners such as nuts, bolts, screws, spacers and rivets can usually be designed out, except when disassembly is required. Fasteners usually represent 5% of the BOM costs, but they generate up to 70% of labor costs during assembly.
1. Is the part used only to fasten or connect others parts?
· If the answer is yes, then this is a non-essential part. If not, go to the next question.
Parts that need to move relative to each other must always be loose. A simple example are scissors, if these were made up of one part, the product could not work, so both halves are essential. Small movements can, however, be made possible by elastic parts.
2. Does the part move relative to all other parts while using the product?
3. Is the movement essential for functioning of the product?
4. Should the part be loose to provide the required movement?
· If Question 2 -4 can be answered yes, then it is an essential part. If not, continue with the next questions.
For some parts, material properties are important for the functioning of the product. These can be different types of properties such as electrical, chemical, magnetic, mechanical, optical, thermal and acoustic. An example is a metal frying pan. The pan itself has to absorb and hold heat while the handles must be thermally insulating.
5. Is the part of a different kind of material and / or isolated from all other parts?
6. Is this material essential for the functioning of the product?
*Only fundamental material properties are acceptable.
7. Should the part be loose to meet these material properties?
· If Question 5-7 can be answered with yes, then it is an essential part. If not, go on with the next questions.
Before and after DFMA
Assembly & Maintenance
Parts that need to be replaced while using the product are of course essential parts that can’t be omitted. For example, take the ink cartridge of a printer or SIM card of a phone.
A product often also has a housing consisting of two halves in which the electronics are located. To assemble and disassemble it is important that the housing consists of more than one part.
8. Should the part be loose because assembly of other parts would otherwise be impossible?
· If the answer is yes, then this is an essential part.
9. Should the part be loose to allow replacement, disassembly, maintenance or repair (of other parts) while using of the product?
10. Are these replacements, maintenance or repairs required?
11. Should the part be separate to enable these replacements, maintenance or repairs?
· If Question 9-11 can be answered with 'yes' then it is an essential part. If not, this is a non-essential part.
What to do with the non-essential parts?
When all parts of the product have been analyzed, a list of essential and non-essential parts can be created.
The non-essential parts can often be combined with another part. For example, in the case of fasteners, screws may be replaced by snap fits or clamps.
Many optimized products have an injection molded base part that incorporates several features in one part. These parts are multifunctional and provide for protection, mounting of different parts and appropriate design.
The number of parts in a product is an important indicator of the design quality. Simple assemblies are usually better priced and more reliable. Therefore, it is important to find the possibilities to simplify the design.
With a simple checklist and functional requirements, we can determine the minimum number of parts of a product. The result of this can then be used as a basis to optimize the product.
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