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DFM - Designing An Affordable Electric Dog Door
DFM - Designing An Affordable Electric Dog Door
This project was designed for MCEN 5045: Design for Manufacturability, the second part of the Product Design specialization series.
The goal of this project was to design a cost-effective electric dog door with principles we learned from class. Electronic dog doors on the market today can reach prices of well over $200. Our goal is to design a product that significantly undercuts this price without sacrificing quality. We accomplish this by using the methods of manufacturing and design for assembly to create a consumer-friendly product that allows for easy installation and could be manufactured at a low cost.
The goal throughout this investigative and analytical process was to gain an in-depth understanding of the design and manufacturing considerations required to create such a product. The process was categorized into four phases of work: product decomposition, component and system modeling, design for assembly analysis, and product redesign.
A complete redesign was necessary for the final design iteration, which utilized commercial of the shelf (COTS) parts to reduce manufacturing processes necessary, while also considering simplification of manufacturing processes for those that were necessary. Material and process selection analyses were performed for key components of the design that were designed to ensure that the final product would be well suited for a consumer while also being practical to manufacture. The DFA metrics from the initial design to the redesign support those design changes since the efficiencies increased while the DFA metrics decreased across the board.
Product Decomposition:
Black Box Diagram
Glass Box Diagram
Fishbone Diagram
Material Analysis:
Door Frames
Requirement:
Low thermal conductivity.
Withstand high wind speeds.
Assumptions: Based on Colorado's wind speed and area of the door, we found a force of 23.05 Newtons.
Young's modulus of 1.969 MPa.
Low-cost.
Material Recommended:
Considering the price per unit volume and manufacturing of each polymer, Polypropylene PP would work best for these parts. Another alternative would be Polyethylene PE.
PP is inexpensive and easy to access, and due to its semi-crystalline property, it possesses a high flexural strength.
When injection molding, polypropylene is easy to mold despite its semi-crystalline nature, and it flows very well because of its low melt viscosity.
Servo Stopper
Requirement:
Withstand applied force on the door.
Assumption: the force from the door acts as a point force on the centroid of the lock.
A force of 11.525 Newtons & min. Youngβs modulus of 0.02015 GPa.
The maximum deflection of this part will be 0.05 inches.
Low-cost.
Material Recommended:
After reading the FEA results and comparing the Ashby chart, polypropylene PP would work as the best option if the product needs to be inexpensive. It would allow manufacturers to avoid using a variety of materials and all parts can be injection molded.
There are many metals that would work according to Ashby Chart. If the manufacturing unit has metal scraps that are readily available for manufacturing purposes, they may be used.
Design Modifications:
Living Hinges incorporated in the Battery Compartment - combining two parts.
Using the Thumb Tab feature to fix Battery Compartment into the Inner Frame - eliminating the use of fasteners.
Use of two unique fasteners in the entire assembly
Provided Sliding Slots for proper alignment of the frame during the assembly process.
Incorporation of Press-Fit design to eliminate the use of screw
Spring with the inactive coil to avoid tangling during the assembly process
Design for Assembly (DFA) Analysis:
Number of Unique Parts: 22
DFA Complexity: 48.06
Theoretical Efficiency: 60.6%
Practical Efficiency: 63.6%
OTHER DFA METRICS:
1.] Error Proofing: 0.10
2.] Handling: 0.15
3.] Insertion: 0.45
4.] Secondary Operation: 0.45
Cost Analysis:
Order of Magnitude Cost Estimate
Depending on:
Material cost for each part
The volume of material required
Material density
Purchased Parts Cost
Taking into account, electronic components including screws, a servo, an RF transmitter and receiver, and a PCB. needed to be purchased.
Online Cost Estimation
ProtoLabs would result in a price lower than that estimated by the order of magnitude cost estimation. This likely means that ProtoLabs is able to manufacture our parts for less than we estimated.
All Manufacturing & Part Costs per unit
Following Assumptions were used to calculate a Unit's cost
The total cost of tools is equal to those required by ProtoLabs
Tooling life of 200,000 units
Labor costs of $25/hour
Production rate of 45 units/hour
Factory overhead of $60/hour
Capital equipment cost of $1,000,000
Capital write-off time will be 5 years
Load fraction constants will be equal to 1
Selling Point & Profit
Assuming 100% markup per unit, we get a sales price of $85.72
Whereas the existing product which is currently available in the market range from $200 - $400 dollars.
Fixed costs for our purposes will be equal to tooling costs, factory expenses, and depreciation. The overall value of our fixed costs is approximately $200,000 ($175,000 for tools, $25,000 for factory expenses, and depreciation).
Variable costs are equal to the material and labor costs which total $9.54.
ππ = $200,000/ ($85.72 β $9.54) = 2, 626 π’πππ‘π
This metric indicates that we will need to sell around 2,626 units before we are able to turn a profit. This should not be a difficult number to reach since our product is less than half the price of many other products on the market today.
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