Selecting the sub assemblies is more a question of availability than a deliberate choice. The Mitchell guides' pages for each car model generally divide the parts and repair time registry into several general sections – these sections are present-ed in Table 13.
The aim is of course to find items and assemblies from as many of these sections as possible while at the same time striving to select only such items and assem-blies that are general enough to be found on each of the car models we've chosen for the comparison.
This forces us to make several omissions already from the beginning. Since all cars in the comparison will not have options such as an electric sunroof or an air conditioning device, no such assemblies can be chosen. Furthermore we must try
not to choose items and assemblies that will differ between the different classes.
A good example would be the drive axle: the first three classes selected consist of front wheel drive cars, but the fourth class of rear wheel or all wheel drive cars.
Thus we cannot in all conscience look at the repair time of either front or back drive axles – the two are not comparable, and whichever we would choose to ob-serve, some class of car would not have the other one.
Table 13. Mitchell collision estimation guides’, sections.
1 A/C / Heater / Ventilation 16 Front door 31 Rear gate
2 ABS/Brakes 17 Front drive axle 32 Rear lamps
3 Airbag system 18 Front fender 33 Rear seat
4 Air cleaner 19 Front lamps 34 Rear suspension
5 Center console 20 Front seat 35 Rocker/pillars/floor
6 Cooling 21 Front suspension 36 Roof
7 Cowl & Dash 22 Fuel tank 37 Seat belts
8 Cruise control system 23 Grille 38 Steering gear
9 Electrical 24 Hood 39 Steering linkage
10 Emission system 25 Instrument panel 40 Steering pump 11 Engine/Trans 26 Quarter glass 41 Steering wheel/column 12 Engine/Trans Mounts 27 Quarter panel 42 Sunroof
13 Exhaust 28 Rear bumper 43 Trans oil cooler
14 Frame 29 Rear door 44 Wheel
15 Front bumper 30 Rear drive axle 45 Windshield
As an additional problem to solve, we also have the fact that the Mitchell guides do not display exactly the same assemblies, items and procedures for each year and for every car model. While the sections displayed in Table 13 are generally present in all five year-sets of the manuals, especially the older manuals may sometimes vary a bit in section content and section division. Certain assemblies are presented in some of the manuals but not at all in the others. The larger as-sembly procedures (discussed in the next section) are also more consistently dis-played in the manuals from 2000 and forward.
The conclusion of all these variances is that subassembly selection is a problemat-ic and boundary restrproblemat-icted task. The only way to achieve a goodly selection of assemblies is to begin by choosing as large a possible amount of items to follow and gradually whittle down the list of assemblies when problems occur. If an as-sembly is consistently presented and accounted for in several of the manuals but not in all, we should omit this assembly from the list. If an assembly is consistent-ly presented and accounted for in even the most of the car models, but not in all, we may still have to omit the assembly. This process can only be done manually
by going through the steps of data collection and finding out what is left to com-pare. Needless to say the remaining assemblies will all be extremely general in nature, and more or less present on any car everywhere.
Mitchell manual outlook
As already mentioned, the Mitchell collision estimating guides are mainly for the use of insurance estimators and repair shops, to estimate how much a certain re-pair will eventually cost in total, before the actual rere-pair is made. For each part and assembly presented in the manuals an estimated part's price and an estimated repair time is given. The part's price is a guideline to how much the spare part will cost, bought new from a licensed dealer. The estimated repair time, which we will mainly be looking at in this investigation, is a guideline to how long it will take to remove and replace said part at the repair shop.
The repair times shown in the guides are given in hours and tenths of hours, thus 0,1 hours represent six minutes. As is also explained in the guides
“[the times] are for replacement with new undamaged parts from the vehicle manufacturer on a new undamaged vehicle… The actual time taken by individual repair facilities to replace collision damaged parts can be expected to vary due to severity of collision, vehicle condition, equipment used, etc.” (Collision Estimat-ing Guide Imported 2005: P3).
While this definition may in fact produce certain unrealistic estimates when talk-ing about the repair of a severely damaged vehicle (bodywork skewed to jam bolts, parts deformed to hinder removal) it is strangely enough an almost ideal setting for assembly analysis. New undamaged parts on a new undamaged vehicle – a similar setting to that of the assembly line.
The manuals' listing for one type of car model is most often about 15–20 pages long, divided into sections which we saw earlier in Table 13. Also most often, each section begins with a sort of summary of the larger procedures connected with the section. These larger procedures outline how long it will take to replace or overhaul an entire section of the car' machinery for body. For instance the front bumper section or subsection starts with estimates of how long it will take to 1) refinish bumper cover, 2) refinish upper filler 3) remove and install bumper as-sembly and 4) overhaul bumper asas-sembly (includes remove and install). Under the larger procedures there is a parts sketch – in Figure 16 we see a rendition of
the type Mitchell’s guides uses in its guides, the dashboard of a European car model from 2005.
Most of the repair times given in the manuals will be for one of the three follow-ing procedures: R&I (Remove and Install), O/H (Overhaul) or Refinish. The most commonly used is the Remove and Install procedure, but sometimes the Overhaul time estimate is given side-by-side since there is a certain difference to the two procedures. The Refinish procedure is mainly used when talking about sheet metal parts. The definitions of each of these procedures are presented below.
(Mitchell International 2005)
Figure 16. Instrumentation panel, Mitchell guide.
Under the parts sketch each part is listed with number, VIN code, replacement time and estimated parts cost:
Part name VIN Time (H) Cost $
Panel Assy, Intrument 30722602–7 6,5 302,17
Procedure definitions
The definitions of the terms are stated in the collision estimating guides:
“Remove and Install (R&I): Remove a part or assembly, set it aside and reinstall it later. The time shown includes the alignment that can be done by shifting the part or assembly.” (Collision Estimating Guide Imported 1991: P3).
The term Remove and Replace (R&R) can be used almost synonymously, since in that case, the part is removed and replaced with a new replacement part. In both cases, there is no damage to the part being removed and installed.
“Overhaul (O/H): Remove an assembly, disassemble, clean and visually inspect it, replace needed parts, reassemble and reinstall on the vehicle making any nec-essary adjustments.” This is a more time consuming process than Remove & In-stall, and certainly one where DFA should be apparent.
And finally Refinish – the process where a certain panel is removed, prepared, repainted and re-installed on the vehicle. This is a procedure where the principles of DFA are not as clearly visible – most of the time goes not to removal and in-stallation, but rather to the paint job – and as such should be considered an inferi-or indicatinferi-or to the other two. However, finferi-or comparable vehicles, there is a certain amount of information to be gleaned even here.
In general, the ranking of the three indicators is such that Overhaul can be consid-ered a better indicator of DFA than Remove and Install, which in turn is a better indicator better than Refinish. This because more time is actually used to disas-semble parts and asdisas-semble them, and the basic design come into play – an assem-bly designed to the principles of DFA should make this process faster.
Final assembly selection
Selecting as many subassemblies and items as possible, taking care to select only those that are most general and present on the largest amount of cars, we arrive at the list of 53 possible assemblies. However, after the gradual whittling down of
the list to arrive at something that is commonly shared by all the selected car models, we arrive at a final selection of 44 subassemblies and items. These selec-tions are presented in Table 14.
Table 14. Final assembly selection.
1 A/C/Heater/Ventilation; Motor, Blower 23 Front Suspension; Arm, Lower Control 2 Air Cleaner; Housing, Air Cleaner 24 Front Suspension; Bar, Stabilizer 3 Back Window; Glass, Back Window 25 Front Suspension; Hub Assy
4 Center Console; Console Assy, Center 26 Front Suspension; R&I Suspension (One Side)
5 Cooling; Fan, Cooling 27 Fuel Tank; Pump assy, Fuel 6 Cooling; Radiator Assy 28 Fuel Tank; Tank, Fuel 7 Electrical, Alternator 29 Grille; Grille Assy
8 Engine/Trans; Pan Assy, Engine Oil 30 Hood; Cable, Hood Release 9 Engine/Trans; Pulley, Crankshaft, R&I 31 Hood; Panel, Hood
10 Engine/Trans; R&I Engine/Trans Assy 32 Instrument panel; Panel, Main Instrument 11 Exhaust; Manifold, Exhaust 33 Quarter Panel/Side body; Panel, Outer
Quarter
12 Front Bumper; Cover, Front 34 Rear Body; Panel Assy, Rear Body 13 Front Door; Panel Assy (Interior), Door
Trim
35 Rear Bumper; Cover, Rear
14 Front Door; Panel, Door Repair 36 Rear Lamps; Lamp Assy, Combination 15 Front Door; Shell Assy, Door 37 Rocker/Pillars/Floor; Pillar Assy, Hinge 16 Front Fender; Fender (Left) 38 Roof; Headliner (w/o Sunroof)
17 Front Inner Structure; Apron Assy 39 Roof; Panel, Roof (w/o Sunroof) 18 Front Inner Structure; Crossmember, Front
Suspension
40 Seat Belts; Belt Assy, Seat 19 Front Inner Structure; Support Assy,
Ra-diator
41 Steering Wheel/Column; Column Assy, Steering
20 Front Lamps; Lamp Assy, Combination 42 Windshield; Glass, Windshield 21 Front Seat; Cushion, Seat Bottom 43 Windshield; Tank Assy, Washer 22 Front Steering Linkage/Gear; Gear Assy,
Steering
44 Wiper System; Motor Wiper
The assemblies omitted include highly common components such as steering pump, rear shock absorbers, muffler (exhaust), brake caliper, steering wheel as-sembly, etc. All are found on a majority of cars but are unfortunately not present-ed in the manuals for certain models or simply presentpresent-ed as a part of different assemblies.
If we look at the list of assemblies selected in Table 14 we can see that it is quite a diverse collection with parts and assemblies from all the sections of the car. Mo-tor parts, suspension, cooling, lamps, sheet metal, interior, electrical equipment – as close as we can come to an overall representation of the car's parts in total, working within the boundaries and limitations of the data source and car selec-tion. Most of these parts should in addition be relatively insensitive to the class of the car.
Now, it should of course be said that several of the subassemblies are quite simple in their design and as such can probably not benefit much from redesign with as-sembly in mind. The stabilizing bar in the front suspension is an example of such a simple component. However, this is not necessarily the point of the whole exer-cise. We must consider that to remove even this simple component other compo-nents must be shifted, and for the larger collection of simple compocompo-nents there are still opportunities to implement DFA. Looking at the sum total of the time it takes to remove and install the whole number of individual components we should get an idea about the Design-for-Assembly level of car.