Hammond, R., and Bras, B.A., “Design for Remanuacturing Metrics”, Proceedings of the 1st InternationalWorkshop on Reuse, (S.D. Flapper and A.J. de Ron eds.), Eindhoven, The Netherlands, pp. 5-22, November 11-13,1996.

Towards Design for Remanufacturing –Metrics for Assessing Remanufacturability

Bert Bras* and Rick Hammond**

Systems Realization LaboratoryThe George W. Woodruff School of Mechanical Engineering

Georgia Institute of TechnologyAtlanta, Georgia 30332-0405

U.S.A.

ABSTRACT

A growing concern about the environment, and especially about waste and landfill, has spurredresearch into the design of more environmentally benign products. A dramatic reduction inenvironmental impact can be made by product remanufacturing in which, in contrast to materialrecycling, the geometrical form of the product is retained and its associated economical andenvironmental value preserved. Our research goal is to establish design metrics which efficientlyand effectively measure the remanufacturability of product designs. In this paper, metrics forassessing the remanufacturability based on product design features are introduced. Similar likeDesign for Assembly metrics, these Design for Remanufacturing metrics provide a relativelyefficient and effective means for a product designer to obtain feedback with respect to theremanufacturability of a product. The metrics have been applied to various case studies, rangingfrom consumer electronic to automotive products. Feedback from the remanufacturing industryconfirms the remanufacturability assessments obtained using the metrics described in this paper.

* Assistant Professor, corresponding author** Former Graduate Research Assistant

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1 Our Frame of Reference – Metrics for Assessing Remanufacturability

As manufacturers become more and more environmentally conscious, they tend to investigatevarious means of producing their products in such a manner as to reduce environmental harm,while simultaneously keeping their costs down. Some manufacturers are particularly concernedwith the proposed European Automotive “Take-Back” Legislation, which would requiremanufacturers to reclaim their product at the end of its lifecycle and recycle a certain percentageof it (see, e.g., (Congress, 1992, Fiksel, 1996)).

Product reuse, as opposed to material recycling, would seem to be the more profitable means ofproduct disposition, both ecologically and economically, as the reprocessing and manufacturingexpenditures (time, energy, cost, etc...) are avoided (Amezquita, et al., 1995a, Berko-Boateng, etal., 1993, Haynsworth and Lyons, 1987, Navin-Chandra, 1993). Remanufacturing is the practiceof disassembling, cleaning, refurbishing, replacing parts (as necessary) and reassembling a productin such a manner that the part is at least as good as, or better than, new. By remanufacturing aproduct, the product may be returned to service with a reasonably high degree of confidence thatit will endure (at least) another full lifecycle.

The largest gain in enhancing reusability and remanufacturability can be made in design(Congress, 1992). In order to assist the product designer to develop parts which can beremanufactured at the end of their first lifecycle, a system of efficient and effective1 mechanicaldesign metrics is currently being developed in our laboratory. These metrics would objectively,and quantifiably, measure the mechanical remanufacturability of their product, providing thedesigner with immediate feedback as the design progresses. A good example of efficient andeffective metrics in a different domain, which proved successful, are those postulated andvalidated by Boothroyd and Dewhurst regarding the assembly of products (Boothroyd andDewhurst, 1991). Their success lies in the simplicity of the usage of the metrics (e.g., everybodycan count the number of parts in an assembly) connected to the fact that their metrics are validand indeed provide a good measure for the assemblability of a product.

In order to develop a similar system of metrics for assessing remanufacturability, it is necessary todevelop a better understanding of what criteria need to be measured, and to get a feel for howimportant these criteria were, relative to one another. In (Amezquita, et al., 1995a), we identifieddesign characteristics which facilitate remanufacturing from literature and general practice. Wediscussed principal driving factors for remanufacturing, as well as identifying existingremanufacturing guidelines, philosophies, and practices. In (Amezquita, et al., 1995b), weoutlined our research approach taken for the establishment of remanufacturability metrics andgave preliminary list of measurables that affect remanufacturability in the form of a worksheet.Some of the most notable work in remanufacturing was performed by Lund who performed asurvey in the early eighties among remanufacturers. In (Hammond, et al., 1996), we presentedresults from a survey we recently conducted. Among others, it was noted that the automotiveremanufacturing industry has changed since the late seventies due to changes in automotive designpractices by Original Equipment Manufacturers (OEMs).

1 We define efficiency as a measure of swiftness and effectiveness as a measure of completeness and correctness.

3

In this paper, we will present Design for Remanufacturing metrics that we have developed basedon our findings. First we will start with the foundational structure of the metrics, namely,Boothroyd and Dewhurst’s Design for Assembly metrics, followed by a detailed discussion of themetrics and the resulting remanufacturability assessment. The metrics will be applied to a productexample.

2 Intellectual Foundation – Design for Assembly

A good example of efficient and effective metrics which proved successful are those postulatedand validated by Boothroyd and Dewhurst regarding the assembly of products (Boothroyd andDewhurst, 1991). Their success lies in the simplicity of the usage of the metrics (e.g., everybodycan count the number of parts in an assembly) connected to the fact that their metrics are validand indeed provide a good measure for the assemblability of a product. To assess the assemblyindex in the DFA analysis, Boothroyd & Dewhurst assert that the theoretical minimum number ofparts must be determined. This ideal number of parts is allotted 3 seconds each for assembly,which results in an idealized time for assembly. The ideal time is then divided by an estimate ofthe actual assembly time required by the chosen assembly sequence, which results in the efficiencyrating for assembly. According to Boothroyd & Dewhurst, typical assembly efficiencies rangebetween 25-35%.

Because of the proven utility and the familiarity of designers with Boothroyd and Dewhurst’sDFA index, we have chosen to base our metric for remanufacturability on similar concepts as theDFA index. Specifically, we have found it useful to use of the concept of actual versus thetheoretical minimum number of parts needed in the product as a basis for assessing the“goodness” of remanufacturability. For a part to be considered theoretically necessary, it mustmeet at least one of three criteria, according to Boothroyd & Dewhurst. These criteria for anideal part are as follows:1. Only large ranges of motion should be considered (small motions can be accomplished by

incorporating elastic elements into the part)2. The part must be made of a different material, since the properties of that material are

required to achieve design requirements3. The part required to facilitate the process of assembly or disassembly (such as access panels

or housing covers) The theoretical minimum number of parts is a useful concept for providing a comparison betweenideal situations and real ones. Since these criteria were developed by Boothroyd and Dewhurst todetermine only if a part was required for assembly purposes they need to be modified to facilitatethe same decision with respect to remanufacturing. With this in mind, the following criterion hasbeen added to the previous criteria: 4. Is the part required to isolate wear to parts with relatively low intrinsic value

Relative intrinsic value can be somewhat difficult to assess without dealing with transient factorssuch as cost. The intrinsic value of a part is directly proportional to the amount of time, energy

4

and other resources (like scarce materials) that have been invested into the part. For example,complex castings which have been machined are usually considered to have a significant intrinsicvalue, since both the casting and the machining processes require a great deal of time and energy.Conversely, parts made of stamped sheet metal usually are not, since they are typically producedin large quantities in very short amounts of time very little energy expended per part. Parts with asignificant amount of intrinsic value, called Key Parts, are the parts in the product that areimportant to be recovered during the remanufacturing process.

With respect to the remanufacturability metric, manual disassembly and reassembly are the onlydis- and reassembly process options under consideration. Much like Boothroyd & Dewhurst’sDFA analysis, a metric can be subsequently modified in order to accommodate other processes ortechnologies like high-speed automation. However, it is beyond the scope of this paper todevelop multiple assessment techniques for the various technologies and processes which arecurrently available to the remanufacturing industry. We believe that our work will provide thefoundation upon which subsequent research may add to or modify these metrics to accommodatethese changes. With this in mind, manual assembly and disassembly will be used as the basis forthe remanufacturability metric, since it is easily understood and is stable from a technologicalstandpoint. This has the added benefit of allowing the metric to be easily verified, as the majorityof the existing remanufacturing industry uses manual (re)assembly and disassembly.

3 Components of the Remanufacturability Metric

From existing literature as well as surveys distributed to the remanufacturing industry (Amezquita,1996, Amezquita, et al., 1995a, Amezquita, et al., 1995b, Hammond, et al., 1996, Hammond,1996), issues that appeared to have potential to be considered as a part of a remanufacturabilitymetric were identified. Since the metric which we are developing is to be objective and to be usedto assess product designs, we decided to narrow this list of criteria to factual data about thedesign, preferably in such a way as to allow the metric to be assessed by computer, for examplevia software built into a CAD system. Also, we decided to focus the list of criteria to those issueswhich are directly affected by the mechanical aspects of the design. Consequently, issues as coreand parts availability which are really market issues were eliminated from the list. Removing theseissues does not reflect that they do not have any bearing on a part’s remanufacturability. Rather,the removal of a criterion from this list merely indicates that it is beyond the scope ofcomputerized tracking of mechanical remanufacturability or it is not a design driven issue.

Of the remaining issues, several are related to the process of remanufacturing and almost all of theother issues directly affect those processes. For example, corrosion increases the amount ofdisassembly and cleaning time required, permanent fastening increases disassembly times and theamount of refurbishing required and so on. Since each process is more or less independent ofeach other, we deemed it logical to develop the metrics to use the processes as the top-levelissues. From the surveys and literature (e.g., (VDI, 1993)), the following “generic”remanufacturing processes were identified:

5

Assembly CleaningDisassembly InspectionTesting RefurbishingRepair Replacement

However, areas of overlap exist between these eight processes which must be eliminated, suchthat each can be assessed independently of each other. For this reason, the listed processes mustbe combined or partitioned into independent criteria for which a metric can be developed. Basedon our findings, we have refined the list of top-level issues into the following categories for whichsets of metrics have been developed:

• Cleaning• Damage Correction, composed of repair, refurbishment and replacement metrics• Quality Assurance, composed of testing and inspection metrics• Part Interfacing, composed of disassembly and assembly metrics

In Figure 1, the basic organizational structure of our remanufacturability assessment is portrayed.Information flows from left to right and the arrows indicate a combination of inputs. In thestructure, the following distinctions are made between metrics, indices, and categories:

• The column labeled “metrics” in Figure 1 denotes the (eight) key criteria which need to bemeasured in order to obtain a remanufacturability assessment.

• A “category” is a grouping of closely related and inter-dependent metrics. The fourcategories themselves are independent from each other. In essence, a category denotes anintermediate step in obtaining a remanufacturability assessment.

• “Indices” represent numerical values. The indices for the metrics are calculated using theformulas discussed in the following sections. The indices for the categories are calculatedusing associated metric indices times a relative weighting. The remanufacturing index is aweighted value denoting the remanufacturability of the product.

In addition, weights for the metrics and categories are given. These are discussed in detail inSections 3.5 and 3.6. In the following sections, detailed discussions are given on the categoriesand metric formulations and indices calculations.

Level 1Metric Weighting Index Index

Replacement (Key)Disassembly 30.0% RemanReassembly 70.0% IndexTesting 80.0% Category Weighting Index Level 2Inspection 20.0% Interfacing 30.0% IndexReplacement (Basic) 20.0% Quality Assurance 5.0%Refurbishing 80.0% Damage Correction 40.0%Cleaning Cleaning 25.0%

Figure 1 – Structure of Remanufacturability Assessment

3.1 Part Interfacing Category: Metrics for Assembly and Disassembly

It is reasonably obvious that there are many similarities between both assembly and disassembly.As a matter of practice in remanufacture, the disassembly sequence is often the opposite of its(re)assembly sequence. Many of the same tools, techniques and fixtures are used to accomplish

6

both processes. However, assembly and disassembly both have concerns, unique to each, thatcomplicate them. By improving one process, the other does not necessarily improve. Forexample, snap clips can speed up assembly times (vs. screws or other threaded fasteners), butremoving them is more difficult. Because of these differences, it is desirable to quantify assemblyand disassembly separately. However, since they are so closely related, it is desirable to considerthem together when assigning them weights for combination with other metrics.

In keeping with Boothroyd and Dewhurst’s DFA metric, the assembly and disassembly metricsare defined using the number of ideal parts times an ideal part (dis)assembly time score dividedover the actual total time for (dis)assembly (see Equations 1 and 2). Hence, once the times fordisassembly and reassembly have been determined, as well as the theoretical minimum number ofparts (also called the number of ideal parts), both the disassembly and assembly score can bedetermined. Following Boothroyd and Dewhurst, 3 seconds are allotted per ideal part forreassembly. Where disassembly is often much faster than assembly, the DFA analysis can bemodified to allocate only 1.5 seconds per ideal part (rather than 3 seconds) for disassembly.Consequently, the metrics for disassembly and assembly are as shown in Equations 1 and 2. InSection 4, we will show how the number of ideal parts and total times for (dis)assembly areobtained through worksheets using a Kodak Funsaver Camera as an example.

( )( )( )µ

# Ideal 1.5 secTime

DisassemblyD

=

[1]

( )( )( )µ

# Ideal 3 secTime

AssemblyA

=

[2]

3.2 Quality Assurance Category: Metrics For Testing and Inspection

Remanufacturers must be vigilant about maintaining the quality of their products. Frequently,consumers are wary of remanufactured goods, despite the lower cost, because they are concernedthat the remanufactured product is not as capable or reliable as the new one. In order to assuagethese fears or personal biases, the remanufacturers must be able to back up their claims of quality.

Most remanufacturers seem to agree that 100% inspection is essential to ensure that obviouslydefective parts are not reused. This practice serves two purposes: 1) to placate the consumer’sworries, and 2) to provide the remanufacturer with the confidence to issue a warranty on theproduct. Also, since remanufacturers can use higher quality replacement parts, remanufacturedproducts can prevent or alleviate original design flaws, and thus prevent warranty returns.

In addition to visual inspections, the parts and/or assemblies that must perform certain functionsmust be tested to ensure that they perform within specified parameters. Testing, however, is morequantitative than inspection, because the product must perform some function within well definedlimits. For example, automotive water pumps are pressure and/or vacuum checked to ensure thatwater cannot leak from the system. Like inspection, testing helps to alleviate the consumer’sconcerns, as well as confirms to the remanufacturer that the product performs satisfactorily.

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3.2.1 The Metric For Inspection

Inspection refers to the process of qualitatively examining parts for damage - usually by visuallychecking the parts. This is most often performed during disassembly (for parts which do notrequire cleaning) or immediately after cleaning. Every part must be inspected for visible damagein order to ensure that all parts which go back into the remanufactured product have not beendamaged. Of particular interest during this step is to identify any damage which is not due toroutine usage. Frequently, damage which is out of the ordinary is the result of misuse by the user,abusive environments, corrosion, and so on. Occasionally, manufacturing defects which were notidentified by the manufacturer are detected in this step as well. Thus, the inspection process looksbeyond the wear or other damage anticipated during the design of the product.

In cases where checking the condition of a part takes a significant investment of time or resources(like magnafluxing an iron casting to check for cracks) these checks are more similar to testing -and thus are more appropriately accounted for in the testing metric. Instead of using the totalnumber of failure modes to assess the process of inspection, it seems more appropriate to simplyuse the number of parts which have to be inspected - indicated by the total number of parts lessthe parts that are replaced. The ideal number of inspections in this case would be represented bythe theoretical minimum number of parts which do not need to be replaced during refurbishing.Therefore the metric for inspection uses the following formula:

µ Inspection = (# Ideal Inspections)

(# Parts - #Repl)[3]

3.3.2 The Metric For Testing

Testing, unlike inspection, requires usually checking the performance of the product orsubassemblies against predefined performance criteria to ensure that they function appropriately.Another case that is covered by the testing metric is inspections which require additional time,tools and/or fixtures. Magnafluxing is a good example of this kind of inspection. The reason thatthis kind of inspection is considered under the testing metric and not under inspection is that theinspection metric covers quick, visual evaluations made by the inspector. The testing metriccovers performance tests as well as inspections which require the use of additional tools orfixtures to identify parts or assemblies that are not adequate.

Since our metrics are comparisons of actual conditions to idealizations, the next step is to identifyhow to define the idealized time for testing. Once again, it is appropriate to refer to the DFAtemplate. Since these metrics are concerned with products which are manually assembled ordisassembled, it is appropriate to assert that the products are also capable of being manuallytested. That is to say that the products can be picked up and manipulated by the person doing thetesting - without requiring the aid of a machine. Given this assumption, it is not inappropriate toallow a fixed amount of time per test to insert, test, and remove the product, much like the 3seconds allotted for the assembly of each part. Thus the total idealized time for testing is found

8

by multiplying the total number of tests by 10 seconds. This idealization is compared to the totalactual time required time required to perform all tests for the product. Thus the metric for testingis defined by equation 4.

( )( )( )µ =

# Tests 10 secTime

Testing T

[4]

3.3 The Metric For Cleaning

Cleaning is the process of removing anything which is not intended to be present in the part.Also, it involves removing any substances (like oil) which would prevent any remanufacturingprocess to be performed (like applying protective coatings or painting). During this process,many foreign substances are removed from products, including (but are not restricted to): oil,grease, shavings (from worn surfaces), corrosion, dirt, dust, lint, etc.

Cleaning is a very significant phase in the process of remanufacturing, as it often requires a majorinvestment from the remanufacturer. A large portion of this investment comes from having toconform to environmental legislation or waste disposal (solid, liquid and airborne) requirements.Also, for parts which require extensive cleaning (like carburetors or engine heads), cleaning canbe very time and capital intensive. There are many different processes for cleaning parts, and eachhas a different level of investment required for each. For the sake of this paper, these processescan be generalized into four categories: loose debris, dry adhered debris, oily debris (baked) andoily debris (washed & dried).

In order to quantify the cleaning metric, it is necessary to assess the resource requirement for eachcleaning process used during the remanufacture of the product. As with the previous metrics, it isdesirable to assess each part for its contribution to the total amount of resources required to cleanthem. Instead of trying to determine the actual amount of resources required for each part, it ismore useful to create an assessment of each cleaning process and apply the appropriate cleaningscore to each part. To assess each cleaning method, a relative comparison of the general cleaningmethods has been performed, as shown in Figure 1. Despite the large variety of, e.g., washingprocesses available, the investment required for each is very similar from a high level ofabstraction. Consequently, various processes have been consolidated into a single category, inorder to simplify the overall assessment of the relative importance of the cleaning processes.

In the prioritization matrix shown in Figure 2, the amount of investment required for each methodis compared with each other in order to generate their relative importance. Since these relativeimportances are based on incremental decisions, as shown in the legend, it is not appropriate totake the exact relative importances as being precisely correct. Therefore, the calculatedimportances are rounded to a set of approximations to the true relative importances. Theseapproximations are then scaled such that the one with the smallest investment - blowing/brushing- is set equal to one. This scaled set is used as the cleaning score for each process. Using thesescores to assess the cleaning investment required for each part, a total cleaning score can bedetermined by adding up the individual part’s scores.

9

Prioritization Matrix Legend5 (row) requires much more investment than (column)3 (row) requires more investment than (column)1 (row) requires the same investment as (column)

1/3 (row) requires less investment than (column)1/5 (row) requires much less investment than (column)

blow

n

abra

ded

bake

d

was

hed

ScoreRelative

Importance

Approximate Cleaning

Score

Usable Cleaning

Scoreblown 1.0 0.3 0.2 0.2 1.7 7% 1.00 1

abraded 3.0 1.0 0.3 0.3 4.7 18% 2.69 3baked 5.0 3.0 1.0 1.0 10.0 38% 5.77 6

washed 5.0 3.0 1.0 1.0 10.0 38% 5.77 626.4 100% 15.23

Figure 2 – Prioritization of Cleaning Processes

In order to create a metric for cleaning, an idealized score must be developed. The first idealsituation which comes to mind is if all of the parts of a product merely needed to be blown orbrushed clean, since this requires the least effort of the cleaning processes. However, to take thisidealization one step further, a more ideal case would be to only have to clean the minimumnumber of parts, which would then only need to be blown free of loose debris. Consequently, themetric for cleaning becomes a comparison of the total cleaning score of each of the parts and theideal number of parts (multiplied by 1 - the minimum cleaning score). The formula used is shownin Equation 5.

( )( )( )µ =

# Ideal 1Cleaning Score

Cleaning [5]

3.4 Damage Correction: Metrics For Part Refurbishing And Part Replacement

Damaged parts must be repaired to like-new condition, or barring that, they must be replaced.One of the main goals behind remanufacturing is to reuse as many of the original parts as possible.Often this is construed as to mean that the parts must be made significantly more durable - whichusually entails a significant additional investment, and often causes the product to weigh more.However, if parts are designed to isolate wear and other anticipated service damage away fromvaluable parts, very little additional investment is usually required. Using this concept, wearshould be isolated to replaceable parts that have very little intrinsic value. By doing so, the mostvaluable parts in the product are protected from damage due to wear, and may not even need tobe repaired at all. Consequently, the reused parts represent the vast majority of the value of thewhole product.

This brings to light two facets of correcting damage done to the parts of a product. The first facetis the more preferable of the two - part refurbishing. Refurbishing is used here to cover the repairof damage (from whatever source) through the reapplication of protective/aesthetic coatings(ranging from rust inhibitors through decorative paint). The second facet is the less desirable

10

alternative to refurbishing - part replacement. This is reserved for those parts which cannot bereused because they cannot be refurbished (without the use of specialized tools or processes).Replacement is much less desirable than refurbishing, as it often requires a more significantinvestment to purchase the replacement parts than to prepare them for reuse.

3.4.1 The Metric For Part Refurbishing

Refurbishing refers to both the repair of damage to the part and the application ofprotective/aesthetic coatings. In the case of damage done to the part, it is irrelevant where orwhen the damage occurred. In particular, it is unimportant at this point whether the damage wasinflicted during the product’s service life or during the disassembly process. The crucial questionis whether the damage can be undone in such a manner as to return the product back to itsoriginal capabilities. If they cannot, the part must be replaced.

There are almost as many different ways to refurbish parts as there are products to beremanufactured. Even generalizing refurbishing into categories, as was done in Section 3.3 forthe cleaning metric, is not practical. There are many types of products which require very uniqueprocesses, specific to the product itself. At a very high level of abstraction, however, it is possibleto determine how much investment is required to refurbish a product by simply identifying howmany parts need to be refurbished. Even though this does not account for the actual, specificinvestment required to perform the various refurbishing processes, it does provide an indication asto how many parts require an investment. An underlying assumption here is that regardless of thespecific process, there will be - at the very least - a moderate investment of time, energy and/orresources to refurbish a part.

Given that the number of parts which need to be refurbished accounts for the actual portion of themetric, the idealized case must be determined. Ideally, there would be no refurbished parts - allparts in the product would go back into the part without needing to be refurbished. As with theother metrics, the ideal case is approached as the metric nears 100%. This would seem to indicatethat as the parts that do not require refurbishing approach the total number of parts, the idealsituation is approached. Since the number of parts which do not need to be refurbished isequivalent to the total number of parts less the number of parts which do require refurbishing, theformula for the refurbishing metric becomes:

( )( )µ = 1 - # Refurb# Parts

Refurbish

[6]

3.4.2 The Metrics For Part Replacement

Part replacement is the last resort for those parts which cannot be conventionally refurbished.Occasionally, several key parts in the product (ones which embody a significant amount ofintrinsic value) cannot be refurbished or reused, and must therefore be replaced. If several ofthese key parts must be replaced, remanufacturing the product impractical, since it requires a verylarge (financial) investment to replace these parts. Since replacing several of the key parts in a

11

product has such a significant affect on the remanufacturing process, it makes sense to separatethe metric for replacement to account for the key parts which must be replaced, and for theremainder of the parts (those which do not include key parts).

The part replacement metrics developed are similar in nature to the refurbishing metric. That is tosay that the number of parts to be replaced is compared with a total number of parts. Thismaintains the focus on the design of the product, and not the market conditions. The metric forthe replacement of the key parts in a product is given in Equation 7. Every part will have at leastone key part - often more. The ideal situation would be not to replace any of the key parts. Sincethis is very close to the situation with the refurbishing metric, the metric for key part replacementcan be defined as follows:

( )( )µ = 1 -

# Key Replaced# Key

KeyRepl

[7]

Similarly, the metric that accounts for the remainder of the non-key parts, called basic parts, thatrequire replacement are compared against the total number of parts less the key parts. Again, theideal situation, which approaches 100%, occurs when there are no basic parts replaced. Theformula for the basic part replacement metric is as follows:

( )( )µ = 1 -

#Repl - #Key Repl# Parts

BasicRepl

[8]

3.5 Combining the Metrics into a Remanufacturing Index.

Combining the preceding metrics into a single remanufacturability assessment index can beaccomplished in several ways (Hammond, 1996). The aim is to ensure that the combined indexsatisfies the following criteria:• The magnitude criterion which ensures that the result of combining the metric indices is

approximately of the same general order of magnitude as each of the indices that make it up.The resulting remanufacturability index should not be significantly larger or smaller than themetric indices. Also, given that the metric indices are normalized, and as such have amaximum value of 100%, the remanufacturability index should not exceed 100% itself.

• The idealization criterion which stipulates that if all of the indices had an ideal score (100%),the remanufacturing index should also be 100%. Since the metrics have been developed bynormalizing them against an idealization, the index for remanufacturing will also be in theform of comparisons of actual to ideal situations. Thus, as with each individual metric, theindex for remanufacturability will approach a score of 100% as the remanufacturability of theproduct approaches the ideal.

• The annihilation criterion which ensures that if one metric approaches zero, theremanufacturability index also will approach zero - regardless of the performance of the otherindices. This is done to ensure that a significant problem which would make a product

12

extremely difficult to remanufacture would not be overshadowed by outstanding performancein other areas.

• The weighting criterion which stipulates that since the metric indices do not contribute equallyto the total outcome, each must be weighted according to its contribution to theremanufacturability index. Therefore, any combination technique must incorporate aweighting scheme to combine the metric indices.

Weighted averaging, a commonly used technique, satisfies all of the relevant criteria except forthe annihilation criterion. Due to the linearity of this technique, a poor response (even a zerovalue) is compensated for by a higher response. Using this technique, it is possible to haveundesirable scenarios such as the following: 30% of the indices are set to zero, and 70% are setto 100%, resulting in a total remanufacturability index of 70%!

Unlike weighted addition, inverse weighted addition is a non-linear additive approach, andsatisfies the annihilation criterion as well. The concept of adding inversely is not uncommon inharmonic series or in the design of simple electronic circuits. In order to identify the equivalentresistance of parallel resistors in an electronic circuit, the resistance’s are added inversely.Equation 9 presents the form that the equation would take to calculate the remanufacturabilityindex.

µRemanufacturability =

Wj µjj

∑

− 1

[9 ]

Due to its importance (see section 3.4.2), it has been determined that, Key Part Replacement willbe considered a “level one” metric in a preemptive structure, and the remaining metrics, called“level two” metrics, are combined using the weighted, inverted addition technique. These twolevels are then combined by direct multiplication. Equation 10 shows the formula to representthis total combinative technique.

µREMANUFACTURABILITY = µ KEY REPL.

Wj

µj

j

7

∑[10]

3.6 Establishing Weights for the Categories and Individual Metrics

In order to determine a weighting scheme for the categories, a prioritization matrix has been setup (shown in Figure 3), similar to that used in Section 3.3. The weightings for the individualmetrics contained under each category have been listed in Figure 1. Since there are only twometrics under each category (due to its significance, the Key Replacement Part metric is not partof the damage category), the weightings were approximated directly, based on feedback fromremanufacturers.

13

Prioritization Matrix Legend10 (row) requires much more investment than (column)5 (row) requires more investment than (column)1 (row) requires the same investment as (column)

1/5 (row) requires less investment than (column)1/10 (row) requires much less investment than (column)

Inte

rfac

ing

Dam

age

QA

Cle

an

ScoreExact

ImportanceApproximate Importance

Interfacing 1.0 0.2 10.0 5.0 16.2 32.5% 30%Damage 5.0 1.0 10.0 5.0 21 42.1% 40%QA 0.1 0.1 1.0 0.1 1.3 2.6% 5%Clean 0.2 0.2 10.0 1.0 11.4 22.8% 25%

Figure 3 – Prioritization of Metric Categories

Therefore, the process to obtain a remanufacturability assessment is as follows:1) Obtain the values for each of the eight metrics using Equations 1 through 8.2) Evaluate the Category Indices by combining the appropriate metrics using

weighted inverted addition.3) Evaluate the second level index by combining the category indices using weighted

inverted addition.4) Evaluate the Remanufacturing index by multiplying the first level (Key Part

Replacement) and second level indices to combine them.In Figure 4, all pertinent formulae to calculate the remanufacturability index are given.

4 An Illustrative Example - Evaluating A Kodak Funsaver Camera

1 10da70% 30% (7d + 3a)

a d

1 5it80% 20% (4i + t)

t i

1 5rf80% 20% (4r + f)

f r

k40% 30% 25% 5%

D I C Q

20CDIkQ5DIQ + 8CIQ + 6CDQ + CDI

100aCdfikrt21Cdfirt + 25adfirt + 9aCfirt+ 32aCdirt+ aCdfrt+ 8aCdfit+ 4aCdfir

Reman =

)+( )+()+( )

=

=

I =

Q =

D =

))+(

))+(

))+(

=

=

=

(

(

(

(

SymbolsMetric/Category Indecies SymbolDisassembly d

Reassembly a

Basic Part Replacement r

Refurbishing (fixing) f

Testing t

Inspection i

Cleaning C

Damage Correction D

Quality Assurance Q

Part Interfacing I

Remanufacturability Reman

Met

rics

Cat

egor

ies

Figure 4 – Symbolic Formulae For The Remanufacturability Index

14

A Kodak Funsaver Camera is used as an example, to show how the metrics are evaluated. Figure5 contains a picture of the assembled camera, as well as the constituent parts for the camera withthe part numbers used in the analysis. The indices for the metrics are calculated in Figure 6 usingthe formulae given in Figure 4. In Tables 1 and 2, the necessary data gathered for the analysis ofthe camera is presented. Tables 1 and 2 are spreadsheets (a questionnaire and a worksheet,respectively) to be filled in by designers. These tables provide all the necessary information forthe remanufacturability assessment in Figure 6.

In the following, the metric calculations for the Kodak Funsaver are discussed in detail

Disassembly and Assembly – In Table 1, column L evaluates the responses from columns Bthrough E to determine whether each part is considered an ideal part. If any of the criteria (fromB through E) are answered (Y), then the part qualifies as an ideal part - otherwise it does not.The disassembly time TD is assessed for each part as shown in columns B through E in Table 2,and reassembly time TA is assessed in columns F through H. Note that for disassembly, if the partcan corrode (column B), then the amount of time to disassemble that part normally (without thecorrosion) is doubled.

Inspection – In the spreadsheet model, Column O in Table 1 checks Column L and Column N. Ifan ideal part is replaced it is excluded from the number of ideal inspections, otherwise it is added.The total number of parts is calculated by summing up Column A. The number of replacementparts is totaled from Column N.

Testing – The total number of tests is calculated from column A in the testing worksheet in Table2, and the total testing time TT is calculated by totaling column D in that same worksheet. It is

important to note that the testing is not necessarily done on a part-by-part basis. Therefore,

1

23

9

67 5 13 14 16

17

12

8

11

1 9

10

15

18

Figure 5 – A Kodak Funsaver Camera (Without Packaging); Legend to part numbers isgiven in Tables 1 and 2

15

instead of listing all of the parts and noting which need testing, only those parts and/or sub-assemblies are evaluated in the metric.

Cleaning – The calculation of the number of ideal parts has already been done in thedisassembly/assembly calculation. The cleaning score (Cln Scr) is calculated by totaling column Kin the worksheet in Table 2. The values for this are based on those presented in Figure 2, asshown in the Cleaning Score Table shown below the Testing Table also in Table 2.

Refurbishment – The number of refurbished parts is calculated by adding the values in column Mof Table 1. Column M checks columns H through K to determine whether a part needs to bereplaced or not. If any of these are responded to with a ‘Y’, then the part must be refurbished.

Part Replacement – Column M checks columns H through K to determine whether a part needs tobe replaced or not. The number of key parts is calculated by adding the values in column P.These values are calculated, in turn, by checking column F. If column F has a ‘Y’ value, then thepart is considered a key part, otherwise it is not. To find the number of key parts replaced,column Q checks columns P and N. Whenever both columns register non-zero values for thesame part, the part is a key part that must be replaced. If a part has to be replaced, but is not akey part, then it automatically is a basic part to be replaced.

Table 1 – Funsaver Questionnaire and Results Sheet

Please Answer "Y" or "N" To The Following: Questionaire Results

Kodak Funsaver Camera

Num

ber o

f Par

ts

Larg

e R

elat

ive

Mot

ions

?

Diff

eren

t Mat

eria

l Pro

perti

es R

equi

red?

Req

uire

d To

Fac

ilita

te A

ssem

bly

Or

Dis

asse

mbl

y?

Req

uire

d to

Isol

ate

Wea

r?

Sig

nific

ant I

ntrin

sic

Val

ue (R

elat

ive

to

Ass

embl

y)?

Doe

s P

art F

atig

ue?

Will

Par

ts R

equi

re A

djus

tmen

t?

If C

oate

d -

Can

Coa

ting

Be

Rea

pplie

d?

If W

orn

- Can

Wor

n S

urfa

ces

Be

Res

tore

d?

If D

amag

ed D

urin

g D

isas

sem

bly

- C

an

Dam

age

Be

Ref

urbi

shed

?

Theo

retic

al M

inim

um N

umbe

r of P

arts

Num

ber o

f Ref

urbi

shed

Par

ts

Tota

l Num

ber o

f Rep

lace

d P

arts

Num

ber o

f Ide

al In

spec

tions

Num

ber o

f Key

Par

ts

Num

ber o

f Key

Par

ts R

epla

ced

Metric DataPart # Part Name A B C D E F G H I J K L M N O P Q # Parts 22

1 Camera Body 1 N N Y N Y N N 1 0 0 1 1 0 # Ideal 182 Internal Aperature 1 N N N N N N N 0 0 0 0 0 0 # Refurbished 13 Firing Lever 1 Y N N N N N N 1 0 0 1 0 0 # Replace 24 Spring - Firing Lever 1 N Y N N N N N 1 0 0 1 0 0 # Key Parts 45 Cam Follower 1 Y N N N N N N 1 0 0 1 0 0 # Key Repl 06 Trigger Catch 1 N N N N N N N 0 0 0 0 0 0 # Tests 37 Film Advance Wheel 1 N N Y N N N N 1 0 0 1 0 0 # Ideal Insp 178 Film Advance Cam 1 Y N N N N N N 1 0 0 1 0 0 Clean Score 259 Film Winding Wheel 1 N N Y N N N N 1 0 0 1 0 0 TD 36

10 Film Position Wheel 1 Y N N N N N N 1 0 0 1 0 0 TA 6511 Top Cover 1 N N Y N N N N 1 0 0 1 0 0 TT 4012 Flash Assembly 1 N Y N N Y N Y 1 1 0 1 1 013 Shutter 1 Y N N N N N N 1 0 0 1 0 014 Shutter Spring 1 N Y N N N N N 1 0 0 1 0 015 External Apeture 1 N N N N N N N 0 0 0 0 0 016 Lens 1 N Y N N N N N N 1 0 1 0 0 017 Front Cover 1 N N Y N N N N 1 0 0 1 0 018 Film Spool 1 Y N N N N N N 1 0 0 1 0 019 Film 1 N Y N N Y N N 1 0 0 1 1 020 Back Cover 1 N N Y N N N N 1 0 0 1 0 021 AA Battery 1 N Y N N Y N N 1 0 0 1 1 022 Camera Wraping - Cardstock 1 N N N N N N N N 0 0 1 0 0 0

16

Kodak Funsaver Disposable Camera Study

Kodak Funsaver Camera - Panoramic 35mm (24 Exposure)

Level 1Metric Weighting Index Index

Replacement (Key) 1.000 1.000Disassembly 30.0% 0.758 RemanReassembly 70.0% 0.832 IndexTesting 80.0% 0.750 Category Weighting Index Level 2 0.829Inspection 20.0% 0.850 Interfacing 30.0% 0.809 IndexReplacement (Basic) 20.0% 0.909 Quality Assurance 5.0% 0.768 0.829Refurbishing 80.0% 0.955 Damage Correction 40.0% 0.945Cleaning 0.720 Cleaning 25.0% 0.720

Figure 6 – Summary Of Metric Indices for Kodak Funsaver Camera

From the data, it becomes apparent that this camera design is relatively simple to disassemble andreassemble, since the times are somewhat low (see Table 2). Consequently, the metrics calculatedfor each in Figure 6 are fairly high. Also, the parts in the camera need very little cleaning, whichresults in another high metric. There is very little that requires refurbishing, so that index alsorates very high. This study represents an outstanding design with respect to beingremanufacturable from perspective of its design. Does this mean that the camera is or should beremanufactured? Not necessarily - although the camera is occasionally reclaimed, reloaded andsold again, the economic value of the camera itself is a matter of a few cents - more than whatwould be paid to maintain the infrastructure to reclaim these products. The remanufacturingindex merely indicates that if we seek to remanufacture this product, the product design lendsitself well to remanufacture.

Table 2 – Kodak Funsaver Worksheets

Disassembly Reassembly Cleaning

Kodak Funsaver CameraN

umbe

r of P

arts

If P

art C

an C

orro

de -

Is P

art P

rote

ctiv

ely

Coa

ted?

Man

ual R

emov

al T

ime

Per

Par

t

Man

ual H

andl

ing

Tim

e P

er P

art

Dis

asse

mbl

y Ti

me

(sec

onds

)(A

* f(

B) *

[C +

D])

Man

ual H

andl

ing

Tim

eP

er P

art

Man

ual I

nser

tion

Tim

eP

er P

art

Ope

ratin

g Ti

me

(sec

onds

)(A

* [F

+ G

])

Cle

anin

g C

ode

Cle

anin

g S

core

Per

Par

t( f

(I) )

Tota

l Cle

anin

g S

core

(A *

J) Kodak Funsaver

Camera

Part # Part Name A B C D E F G H I J K Tests In Assembly A B C D1 Camera Body 1 1.0 1.0 1.0 1.0 D 6 6 Shutter Snap & Wind 1 5 52 Internal Aperature 1 2.1 2.1 1.7 1.7 A 1 1 Flash Assembly 1 15 153 Firing Lever 1 1.8 1.8 2.2 2.2 A 1 1 Battery Check 1 20 204 Spring - Firing Lever 1 1.0 1.0 1.8 1.8 A 1 15 Cam Follower 1 1.3 1.3 2.5 2.5 A 1 16 Trigger Catch 1 0.8 0.8 2.7 2.7 A 1 17 Film Advance Wheel 1 0.8 0.8 1.4 1.4 A 1 18 Film Advance Cam 1 1.2 1.2 3.0 3.0 A 1 19 Film Winding Wheel 1 0.5 0.5 1.2 1.2 A 1 1

10 Film Position Wheel 1 0.5 0.5 1.5 1.5 A 1 1 3 4011 Top Cover 1 3.3 3.3 3.7 3.7 A 1 1 # Tests T T

12 Flash Assembly 1 2.5 2.5 6.2 6.2 A 1 113 Shutter 1 2.3 2.3 2.0 2.0 A 1 114 Shutter Spring 1 2.1 2.1 4.5 4.5 A 1 115 External Apeture 1 0.5 0.5 0.8 0.8 A 1 116 Lens 1 0.5 0.5 1.0 1.0 0 017 Front Cover 1 2.7 2.7 2.8 2.8 A 1 1 Cleaning Score Table18 Film Spool 1 2.1 2.1 1.9 1.9 A 1 1 Debris Type Process Code Score19 Film 1 1.0 1.0 15.0 15.0 A 1 1 Loose - Powder/Dust Blown/Brushed A 120 Back Cover 1 5.6 5.6 4.2 4.2 A 1 1 Stuck - Paint/Corrosion Abraided/Buffed B 321 AA Battery 1 2.0 2.0 3.8 3.8 A 1 1 Wet - Oil/Dirt/Debris Baked C 622 Camera Wraping - Cardstock 1 4.9 4.9 10.0 10.0 0 0 Wet - Oil/Dirt/Debris Wash & Dry D 6

40.5 74.9 25.0T D TA Cln Scr

17

In Table 3, a summary is given of other case studies for which a remanufacturability assessmentwas obtained using the metrics described in this paper. Some notable issues are as follows:

• For the clutch disks and cover case studies, as well as the alternator case studies, directfeedback was obtained from remanufacturers after the assessments had been performed. Theremanufacturers independently confirmed that the Chrysler clutch disks and covers were easierto remanufacture. The major difference between the disks is that the GMC disk is used fortrucks, whereas the Chrysler disk is primarily used on passenger vehicles or light trucks.Correspondingly, the GMC clutch disk is much larger in diameter than the passenger vehicleclutch disk, and as such, requires more rivets to secure the friction surfaces, hence, the lowerscores in dis- and reassembly, as well as for basic replacement parts (rivets).

• For the three alternator case studies, the Delco 10 SI scored highest and it was confirmed byits remanufacturer that this was the most easily remanufacturable alternator of the threechosen for the study. The difference in remanufacturability between the Delco CS130 and theChrysler roundback is insignificant, even though the designs are very different. Initially, theChrysler roundback was chosen by its remanufacturer as being representative of a difficultalternator, so when it scored as well as what he perceived as being an average alternator (theCS130) he was somewhat concerned. However upon reflection, he noted that, despite theadditional assembly and disassembly times needed, the roundback has almost the same numberof parts as the CS130 (fewer than the 10SI), and does not require the disposal of any valuableparts. After considering this situation briefly, the remanufacturer agreed that because of thetradeoff between the additional labor investment and investing in replacement parts, the twoalternators were actually very similar in terms of overall remanufacturability.

• It is interesting to see that the older Funsaver design is slightly worse than the newer designs,which is to be expected given the fact that Kodak is continuously improving the design withrespect to reusability.

• The Jeep Grand Cherokee four wheel drive transfer case rates fairly low due to the (assumed)replacement of some gears which were assumed to be key parts, as well as a large amount ofcleaning needed and poor dis- and reassemblability. This case study also contained the largestnumber of parts (74 total with 45 being deemed the ideal number of parts). Nevertheless,these transfer cases are being remanufactured due to their high value, but the assessmentindicates that product design improvements can be made in dis- and reassembly, as well as(perhaps) in cleanability.

18

5 Closure

In this paper, we have described metrics for assessing the remanufacturability of a product design.The approach has been based on the well known Design for Assembly metrics. The resultingDesign for Remanufacturing metrics provide a relatively efficient and effective means for aproduct designer to obtain feedback with respect to the remanufacturability of a product. Themetric has been applied to various case studies and the results correspond with feedback obtainedfrom remanufacturers. By creating a spreadsheet model to calculate the metrics, the designcommunity is provided with a preliminary tool to evaluate the design of a product with respect toits remanufacturability. However, the metrics have the following limitations:• The metrics can only be effectively used during or after the embodiment phase of product

design (e.g., one needs to know how many parts exist in the design)• The metrics only characterize the aspects of remanufacturability that are directly under the

control of the designer - other issues which may have a more significant impact on theremanufacturability of the product (such as the economic motivation or the environmentalpenalties for not remanufacturing or recycling) must be accounted for separately.

• The accuracy of the metrics is limited for products of the same approximate scale - productsthat can be disassembled, reassembled and tested on a workbench using (standard) hand tools.Other types of products (notably larger systems) can be assessed, but tend to score somewhatlower.

Our work in the immediate future will concentrate on• Obtaining more case studies on diverse products for which data can be gathered and the

weightings and timing assumptions can be more robustly validated.• Modifying the interfacing and cleaning metrics to accommodate larger scales and/or

automated assembly and disassembly.• Developing metrics for other facets that characterize remanufacturability need metrics to be

developed. These facets include such issues as economics, geographic influences, socialinfluences, consumer preferences, market conditions, and so on. Due to the transience ofthese type of issues, uncertainty analyses would undoubtedly play a large role in theirevaluation.

• Integration into CAD software, such that as each part is designed, the questionnaire questionsare posed, and the computer keeps track of the analysis routine, instead of having to update a

Table 3 – A summary of other case studies

Product Replac(key)

Disass Reass Test Inspect Replac(basic)

Refurb. Clean RemanIndex

Clutch disk (GMC) 1.000 0.036 0.137 0.313 1.000 0.023 0.977 0.500 0.118Clutch disk (Chrysler) 1.000 0.085 0.335 0.313 1.000 0.053 0.947 0.500 0.239Clutch cover (GMC) 1.000 0.047 0.055 0.073 0.875 0.348 0.652 0.292 0.126Clutch cover (Chrysler) 1.000 0.103 0.071 0.222 0.875 0.348 0.652 0.292 0.179Funsaver camera (no-flash) 0.800 0.708 0.786 0.750 0.882 0.900 1.000 0.739 0.663Funsaver (old version) 0.750 0.536 0.712 0.750 0.824 0.900 1.000 0.889 0.616Delco 10SI alternator 1.000 0.295 0.612 0.447 0.391 0.885 0.865 0.171 0.373Delco CS130 alternator 0.833 0.317 0.571 0.468 0.400 0.857 0.929 0.163 0.304Chrysler roundback alternator 1.000 0.194 0.238 0.280 0.393 0.700 0.900 0.189 0.303Jeep Cherokee fuel pump 0.857 0.179 0.878 0.471 0.654 0.871 0.968 0.452 0.471Jeep GC 4WD transfer case 0.667 0.125 0.199 0.400 0.442 0.784 0.986 0.107 0.143Chrysler LHS door latch 1.000 0.387 0.630 0.800 0.857 0.903 0.935 0.182 0.412

19

spreadsheet separately

Acknowledgments

We gratefully acknowledge Automotive Parts Rebuilders Association, particularly to Mr. PaulLeCour, chairman, and Mr. William Gager, president, for the information, opportunities and otherresources which they generously provided. Similarly, we would like to thank Mr. Bruce Newey,owner of Alstart Alternators and Starters, for the time and information that he contributed.Additionally, I would like to thank those members of the APRA and the remanufacturers in theMetro Atlanta area who contributed to this through the surveys sent out. We also gratefullyacknowledge the Chrysler Corporation for the donation of a Jeep Grand Cherokee and numerousautomotive parts in support of this work. This material is based upon work supported by theNational Science Foundation under Grant No. DMI-9410005. Rick Hammond was supported bythis grant.

20

References

Amezquita, T., 1996, "Lean Remanufacturing in the Automotive Industry," Master of ScienceThesis, G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology,Atlanta, Georgia.

Amezquita, T., Hammond, R. and Bras, B., 1995a, "Characterizing the Remanufacturability ofEngineering Systems," 1995 ASME Advances in Design Automation Conference, DE-Vol. 82,Boston, Massachusetts, ASME, pp. 271-278.

Amezquita, T., Hammond, R. and Bras, B., 1995b, "Design for Remanufacturing," 10thInternational Conference on Engineering Design (ICED 95), Praha, Czech Republic, Heurista,Zurich, Switzerland, pp. 1060-1065.

Berko-Boateng, V. J., Azar, J., De Jong, E. and Yander, G. A., 1993, "Asset RecycleManagement – A Total Approach to Product Design for the Environment," InternationalSymposium on Electronics and the Environment, Arlington, VA, IEEE, pp. 19-31.

Boothroyd, G. and Dewhurst, P., 1991, Product Design for Assembly, Boothroyd andDewhurst, Inc., Wakefield.

Congress, U. S., 1992, "Green Products by Design: Choices for a Cleaner Environment,"Office of Technology Assessment.

Fiksel, J., 1996, "Towards Sustainable Development," Design for Environment – CreatingEco-Efficient Products and Processes, McGraw-Hill, New York, pp. 23-33.

Hammond, R., Amezquita, T. and Bras, B., 1996, "Issues in Automotive Remanufacturing –An Industry Survey," Journal of Engineering Design and Automation, Special Issue onEnvironmentally Conscious Design and Manufacturing, (under review).

Hammond, R. C., 1996, "Development of Design Metrics for Remanufacturing," Master ofScience Thesis, G.W. Woodruff School of Mechanical Engineering, Georgia Institute ofTechnology, Atlanta, Georgia.

Haynsworth, H. C. and Lyons, R. T., 1987, "Remanufacturing by Design, The Missing Link,"Production and Inventory Management, Second Quarter, pp. 25-28.

Navin-Chandra, D., 1993, "ReStar: A Design Tool for Environmental Recovery Analysis," 9thInternational Conference on Engineering Design, The Hague, Heurista, Zurich, Switzerland, pp.780-787.

VDI, 1993, "Konstruieren Recyclinggerechter Technischer Produkte (Designing TechnicalProducts for ease of Recycling)," VDI-Richtlinien (VDI-Standards), VDI-GesellschaftEntwicklung Konstruktion Vertrieb.