Door latch

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Contents 1 Bill of Materials 2 Design for Manufacturing and Assembly (DFMA) 3 Failure Mode and Effects Analysis (FMEA) 4 Design for Environment (DFE)

Bill of Materials

Part Name	QTY	Mass (g)	Function	Manufacturing Process	Material	Image
Door Holder Front	1	13	Secures Door-Latch to Door	Stamping	Steel (Coated)
Door Holder Front	1	13	Secures Door-Latch to Door	Stamping	Steel (Coated)

Design for Manufacturing and Assembly (DFMA)

Performing a Design for Manufacturing and Assembly analysis on our doorknob allows us to assess whether or not designs of the product could be improved in such a way that the cost, ease, or quality of manufacturing and assembly can be improved. In order to analyze the product, we had to dissect the doorknob, so we could at least consider the manufacturing process that went into producing the doorknob.

The main goal of the dissection and the analysis was to identify areas of the product where we believe the designer made good decisions, or where we believe improvements could be made. Did the designer:

1. design the simplest solution?
2. make good cost-saving decisions?
3. design for easy manufacturing?
4. design for easy assembly?

The table below lists guidelines that we followed as well as our findings in this analysis.

Minimize Part Count: Eliminate fasteners, part consolidation	All parts were found to have a function, but for a product with only a few functions, room for part reduction should be considered.
Standardize Components: Take advantage of economies of scale & known component properties	It is interesting to mention that even though doorknobs are meant to look the same on both sides, dissection revealed that the doorknobs were in fact not the same part. Instead, it appears that different molds were used to create the components. In general, we are looking to make the product as symmetric as possible.
Commonize Product Line: Economies of scale and minimum training and equipment	It appears that most of the components are either stamped or cast. Thanks to this small number of types of manufacturing, training can be minimized, and employees become more flexible in terms of position on the production line.
Standardize Design Features: Common dimensions for fewer tools and setups	Again, small differences in the design of the two doorknobs require different molds to produce each doorknob. We believe improvements can be made to use one mold for both doorknobs.
Ease of Fabrication: Choose materials easy to work with	Dissecting the product revealed that the two primarily materials used in production were mostly steel and some plastic. While switching to one material should be considered, some choices were made with a functional purpose. For example, a low-friction plastic piece on the door latch was meant to facilitate the door latch sliding on surfaces.

Failure Mode and Effects Analysis (FMEA)

Performing a failure mode and effects analysis (FMEA) allows us to determine potential areas of concern, particularly ways in which our product can fail. The FMEA also allows us to prioritize each failure mode. After determining the severity (S), the probability of occurrence (O), and detectiblity of failure (D), on a scale of 1-10, the three values are multiplied, which yields a risk priority number (RPN). This number is then used to order the failure modes in terms of importance. The table below shows the results of our FMEA analysis on our doorknob.

Item and Function	Failure Mode	Effects of Failure	S	Causes of Failure	O	Design Controls	D	RPN	Recommended Actions
Locking mechanism	Shaft fails	User cannot lock or unlock	7	User turns locking lever too hard	3	None	5	105
Doorknob	Doorknob fails	Door cannot be opened	8	User turns doorknob to hard	1	None	5	40
Door latch	Latch spring fails	Door inoperable - fails to stay closed	7	Age/wear	1	None	5	35

Design for Environment (DFE)