Product Design Specification

The Product Design Specification (PDS) comprises your quantitative statement of what you want to design prior to starting to design it. In other words, the specifications of the PDS should be largely independent of any specific embodiment of your product, so multiple solution concepts are possible.

The purpose of the PDS is to ensure that your design actually addresses your customer needs. This is essential if your product is to succeed.

Instructions on how to create a PDS are available from Chapters 4 & 5 of the Ulrich and Eppinger text and the customer based design lecture. A good model is available in Ulrich & Eppinger Exhibit 5-8. You begin by defining your customer needs, which are stated in the language of the customer. Your team then converts those needs to engineering specifications.

Each specification consists of a metric, a weighting of importance, units, a marginal value, and an ideal value. The metric is something that you can measure. The weighting of importance is scaled from 1, for low importance, to 5, for essential. Units correspond to your measurement; for example, mm for length or degrees C for temperature. The marginal value states the value, or range of values, for the metric that you feel the customer would be able to tolerate. The ideal value states the target for the metric that you hope your team can meet.

Most ME 4054W projects will have between 20 and 50 specifications.

Your customer needs should be stated so that they are independent of the way that the final design is actually implemented. For example, if your product were a roofing nailer, the needs should not constrain your nailer to be implemented with an electric, a pneumatic, or an explosive power source. Strive to make your PDS independent of implementation, also, wherever possible.

As you approach the end of the design process, the marginal and ideal values are merged into a single column of known values.

We clarify the above guidelines by showing a portion of a Product Design Specification corresponding to a former project. This project developed a heated caul veneer press for making wooden veneered panels.

Here is a partial list of the customer needs driving the product specification (the actual list stated 29 needs):

# Need Importance
1 Veneer press can handle large workpieces 4
2 Veneer press can melt hide glue 5
3 Veneer press won't burn veneer 5
4 Veneer press generates sufficient pressure for good glue bonds 5
5 Veneer press creates flat veneered panels 5
6 Veneer press is easy to store 2
7 Veneer press is easy to load 3
8 Veneer press is easy to set up 3
9 Veneer press can maintain pressure until glue cures 3
10 Veneer press is inexpensive 3
11 Veneer press distributes heat evenly 4
12 Veneer press distributes pressure evenly 4
13 Veneer press is safe 5
14 Veneer press can vary caul temperature 4
15 Veneer press operates on standard household outlet 5
16 Veneer press reaches operating temperature quickly 2
17 Veneer press is reliable 4

Here is the corresponding partial PDS (the full PDS had 39 specifications):

Need #'s Metric Importance Units Marginal Value Ideal Value
1 Panel capacity: width 4 mm 300-635 150-720
1 Panel capacity: length 4 mm 900-1900 300-2000
1 Panel capacity: thickness 4 mm 12-25 6-50
5 Surface flatness 5 mm/m < 2.0 < 1.0
10 Cost 3 US $ < 800 400
15 Power source 5 VAC 120 / 240 120
15 Current draw 5 Amperes < 15 < 6
2,3,14 Caul temperature 5 deg C 55-73 52-79
11 Temperature variation over panel surface 4 deg C < 4 < 2
4 Laminating pressure 5 kPa 50-60 50-100
12 Pressure variation over panel surface 4 kPa < 40 < 20
9 Duration of pressure application 3 hours 0-2 0-24
16 Time to reach glue bonding temp 2 min < 10 < 1
7 Loading height 3 mm 550-920 760-920
17 Cycles to failure 4 integer > 500 > 1E6
7,8 Number of operators 5 integer 2 1
8 Set-up time 2 min < 30 < 10
7 Loading time 3 minutes < 10 < 1
6 Storage volume 2 m^3 < 2 1
6 Storage footprint 2 m^2 < 1.5 1
13 Ground fault protection 5 Binary Yes Yes

The PDS provides the specifications for ranking different ways of implementing your design in the selection chart.

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Adviser's evaluation of deliverables (PDF)