Lucas Method Boothroyd-Dewhurst method is widely used, it is based on timing each of the handling and insertion motions. Although tables of data are available, the most accurate numbers are compiled through time studies in particular factories. The Lucas DFA method was developed in the early 1980's by the Lucas Corp. in the U.K. Unlike the Boothroyd-Dewhurst method, the Lucas method is based on a "point scale" which gives a relative measure of assembly difficulty.

The method is based on three separate and sequential analyses. These are best described as part of the assembly sequence flowchart (ASF): Specification Design Functional analysis (this is the first Lucas analysis). Possibly loop back to step 2 if the analysis yields problems. Feeding analysis (this is the second Lucas analysis) Fitting analysis (this is the third Lucas analysis) Assessment Possibly return to step 2 if the analyses identify problems

Functional Analysis In this analysis, the components of the product are reviewed only for their function. The components are divided into two groups. Parts that belong to Group A are those that are deemed to be essential to the product's function; Group B parts are those that are not essential to the product's function. Group B functions include fastening, locating, etc. The functional efficiency of the design can be calculated as: E d = A/(A+B) x 100% where A is the number of essential components, and B is the number of non-essential components.

Note that the design efficiency is used to pre-screen a design alternative before more time is spent on it. This is different than the Boothroyd-Dewhurst method (which assumes a design is already available). This analysis is intended to reduce the part count in the product. Typically, a design efficiency of 60% is targetted for initial designs.

Feeding Analysis Similar to the Boothroyd-Dewhurst analysis, both the part handling and insertion times are examined here. In the feeding analysis, the problems associated with the handling of the part are scored using an appropriate table. For each part, the individual feeding index is scored. Generally, the target index for a part is 1.5. If the index is greater than 1.5, the part should be considered for redesign.

Overall, all of the product's components should meet a "feeding ratio" defined as: Feeding Ratio = (Total Feeding Index) / (Number of Essential Components) where the total feeding index is the sum of all the indices of all the parts. The number of essential components is the value A from the functional analysis. An ideal feeding ratio is generally taken to be 2.5.

Fitting Analysis The fitting analysis is calculated similarly to the feeding analysis. Again, a fitting index of 1.5 is a goal value for each assembly. However, it should be noted that there is usually greater variance in the fitting indices than in the feeding indices. Again, an overall fitting ration of 2.5 is desired. Fitting Ratio = (Total Fitting Index) / (Number of Essential Components).

The last part of the Lucas method is to calculate the cost of manufacturing each component. This manufacturing cost can influence the choice of material and the process by which the part is made. Although not a true "costing" of the part, this method does help guide designers by giving a relative measure of manufacturing cost. The part manufacturing cost index Mi = Rc Pc + Mc where Rc = Cc Cmp Cs (Ct or Cf) is the relative cost Cc = complexity factor Cmp = Material factor Cs = Minimum section Ct = tolerance factor or Cf = finish factor (whichever is greater) Pc = processing cost Mc = V Cmt Wc is the material cost V = volume (mm3) Cmt = material cost Wc = waste coefficient Values are derived from the following tables. The first step is to determine the envelope type. Then one uses that type to look up various values.

Manufacturing Analysis The last part of the Lucas method is to calculate the cost of manufacturing each component. This manufacturing cost can influence the choice of material and the process by which the part is made. Although not a true "costing" of the part, this method does help guide designers by giving a relative measure of manufacturing cost. The part manufacturing cost index Mi = Rc Pc + Mc where Rc = Cc Cmp Cs (Ct or Cf) is the relative cost Cc = complexity factor Cmp = Material factor Cs = Minimum section Ct = tolerance factor or Cf = finish factor (whichever is greater) Pc = processing cost Mc = V Cmt Wc is the material cost V = volume (mm3) Cmt = material cost Wc = waste coefficient