1. Introduction
Private manufacturing, also referred to as household manufacturing, has a lengthy history in the United States which resulted in the emergence of domestic commerce [
1,
2]. With the development of interchangeable parts, however, came the assembly line, and manufacturing transitioned to standardized high-volume mass production [
3,
4]. Lower variable costs, greater flexibility, and higher average product performance contributed significantly to this transition [
5]. Since then, a global trend toward large-scale, centralized manufacturing and global shipping, particularly for inexpensive plastic products, has arisen alongside growing world consumerism [
6,
7]. Economies of scale provided consumers with more convenient and lower-priced goods than what they could make themselves [
8]. However, the rapid growth of the 3-D printing industry may change this trend.
Additive manufacturing (AM), or 3-D printing, promises to be an emerging 21st century innovation platform for promoting distributed manufacturing for many products [
9,
10,
11,
12,
13]. The compound annual growth rate of worldwide additive manufacturing products and services over the past three years, from 2013 to 2015, was 31.5% [
14]. Although a less centralized model of manufacturing than that currently practiced, the conventional 3-D printing industry is still focused on businesses manufacturing and selling products to consumers or other businesses [
14]. However, with the rise of Internet sharing and open source hardware development [
15], it may provide a more aggressive path to distributed production. Most notably, the self-replicating rapid prototyper (RepRap) 3-D printer [
16,
17,
18] can fabricate more than half of its own parts. Already, RepRaps have significantly reduced distributed digital manufacturing costs for high-end products such as scientific equipment and have enabled economic non-business distributed manufacturing [
19,
20,
21]. The savings for the distributed manufacturing of these high-end products [
22] provide staggering value for the scientific community [
23,
24]. However, distributed manufacturing is not relegated to high-price specialty items.
Preliminary research has already shown that the number of free pre-designed 3-D products is growing rapidly, and low-cost do-it-yourself (DIY) 3-D printers such as the RepRap are already economically beneficial for the average American consumer [
25]. This provides the opportunity for the most radical form of distributed manufacturing. At-home 3-D printing capitalizes on the elimination of product transport, establishing the technology within the realm of distributive manufacturing’s three-tiered modes of operation [
25] (tier 1: central manufacturing distributed to different locations, tier 2: decentralized further to local and agile production sites (e.g., localized manufacturing , fablabs, and makerspaces), and tier 3: at home manufacturing). Nonetheless, in order for this innovative form of localized and customized manufacturing to make a significant impact on the industry as a whole, ease of use and the economic advantage to the average consumer must be better understood [
26]. In particular, the past study by Wittbrodt et al. [
25] assumed that the consumer was technically savvy enough to build a 3-D printer from parts using freely available Internet plans. This may have been an overly optimistic assumption as less than a third of Americans are scientifically and technically literate [
27,
28]. Considering past work in the context of the technical sophistication of the American public, two questions arise: Will 3-D printing be relegated largely to replacing conventional manufacturing techniques and creating the potential for more distributed business-based manufacturing [
29,
30]? Alternatively, can 3-D printing be used to economically manufacture in the majority of American homes of technically illiterate people? In addition, it is worth acknowledging that financial savings provide just one contribution to a consumer’s motivations, so economic analysis must be kept in context.
To probe this latter question of the economic viability of this scale of 3-D printing for home manufacturing in the developed world, this study reports on the life-cycle economic analysis (LCEA) of Lulzbot Mini technology for an average U.S. household. The Lulzbot Mini is a commercialized and fully assembled plug-and-play derivative of the RepRap, which can be used by a consumer with no training and modest technical familiarity [
31]. A selection of twenty-six freely available open-source 3-D printable designs that a typical first-world household might purchase were selected to simulate use over half a year at the average rate of production of one “home-made” item per week. A selection of the parts was printed to determine energy use per mass of material. Printed products were quantified by print time and filament consumption by mass and the experimental masses and printing time were compared to slicer software estimates. The experimental values were converted to the cost to the user and were then compared to low and high market prices for comparable commercially available products. The results of this life-cycle economic analysis provide a return on investment (ROI) for the prosumer (producing consumer), which is compared to other potential investments. Finally, the downloaded substitution value of the selection of designs is quantified to draw conclusions about the future of manufacturing in developed-world economies.
2. Materials and Methods
For this analysis, it was critical that the methods of manufacturing and materials were relevant and accessible to the average consumer. A Lulzbot Mini [
31] was selected due to the ease of use, high resolution capabilities, support of open-source hardware and software, and the ability to work with a variety of operating systems, as well as its relevance in the 3-D printing community following other similar products [
32]. To be used by the Mini, 3-mm poly lactic acid (PLA) was selected as the filament because it is the most common household printing material. PLA has gained prominence, as not only does it demonstrate less warping during printing than other materials such as the second most common 3-D printing plastic (ABS), but the emissions during printing are less pungent [
32,
33]. Furthermore, PLA is made from corn-based resin, making it non-toxic, biodegradable, and able to be produced in environmentally friendly, renewable processes [
34,
35]. It should be noted that because the ABS filament costs are roughly equivalent to PLA and the melting temperature is not that much higher, the results from this study can be extrapolated to ABS.
Twenty-six items were selected from open source 3-D printable design repositories after searching for open source design files indexed on Yeggi.com, which is a 3-D design file search engine. The twenty-six items are summarized in the
Supplementary Materials including the source of the design, and the low and high price URLs for roughly equivalent products. Items were selected to represent the average American consumer’s use over the course of half a year of printing one product per week. Three criteria were used in the selection of products: (1) printable by a Lulzbot Mini in PLA (e.g., having an appropriate build volume, resolution, and material requirements); (2) widely considered to be a common product purchased (or class of product purchased) or owned by the average American consumer; and (3) has a commercially comparable alternative available for purchase online. The concluding analysis was mindful of the difficulty in quantifying the print quality, however the items included in this study met the authors’ expectations for acceptable quality (e.g., z-level print lines are observable using the high-quality quick print settings, but not unacceptable for general consumer use).
One of the most challenging areas in 3-D printing technical knowledge for new users is optimizing the slicer settings that determine the tool path of the 3-D printer. To avoid this challenge, all parts were printed in PLA using the QuickPrint settings in the Lulzbot version of Cura [
36] to demonstrate ease of use.
Figure 1 shows the Lulzbot Mini mid-print using PLA and Cura Quick Print settings. The estimated and actual mass, filament length, and estimated and actual printing time were recorded. All parts were weighed on an electronic balance with an error of ±0.02 g.
In order to apply a cost per hour for each printed item, the print time and energy consumption was recorded by a multimeter (±0.02 kWh) for complex, simple, and average geometric complexity. Greater print complexity demonstrated a higher level of energy consumption primarily because of the operation time per unit mass. The average was found to be about 0.01 kWh/g, which is higher than that reported in the Wittbrodt et al. study [
25] due to the additional energy consumed by the heated bed of the Mini. The average consumption of 0.01 kWh/g was applied for all prints included in the study.
High and low commercial prices for each product was found primarily on Walmart.com and supplemented using Google Shopping. Associated shipping costs were excluded from the analysis for both purchasing and distributed manufacturing (e.g., no shipping charges included for the plastic filament). The operating cost for the Lulzbot Mini (
OL) was calculated using the electricity and filament consumption during printing. The average electricity rate in 2015 in the United States is $0.1267 per kWh for the residential sector [
37] and the cost of a 1 kg spool of 3-mm PLA was found to range between $23/kg and $25/kg [
38,
39], so $24/kg was used here. This operating cost was calculated as follows:
where
E is the energy consumed in kWh,
CE is the average rate of electricity in the United States in USD/kWh,
CF is the average cost of the PLA filament in USD/kg, and
mf is the mass of the filament in grams consumed during printing. Thus, the total cost (
CT) to the average consumer using the selected printer an average of once per week is the following:
where the operating cost is summed over
T years and
CL is the cost of the Lulzbot Mini itself. It should be noted here that the capital costs were not considered because it is assumed that the prosumer is not financing the cost of the capital equipment because the Lulzbot Mini cost is only $1250.00 [
40]. It should be pointed out that if the 3-D printer were purchased on a credit card, which is the only feasible method of financing a consumer purchase such as this, this would need to be included in
CL. This would also be true if the prosumer purchased a large amount of inventory filament on credit.
CT was evaluated over a range of years from one to five. The marginal savings on each project,
Cs, is given by:
where
CC is the cost of the commercially available product (which is calculated for both low and high online prices), and the marginal percent change,
P, between the cost to print a product and the commercially available product was calculated as follows:
where
CC is the cost for the commercial product at either the high or low price.
When the cost of the 3-D printer is taken into account the total savings,
S, is given by:
over
T years and all,
A, products.
The simple payback time of the printer (
tpb) was calculated by the following:
An estimated return on investment (
R) was calculated following [
41,
42] assuming a five-year lifetime for the 3-D printer.
Finally, the value obtained from a free and open source 3-D printable design can be determined from the downloaded substitution valuation,
VD(
t) [
23,
24] at a specific time (
t):
This value is determined by the number of downloads (
Nd) on 7 December 2016, where
Cp is the retail cost of the traditionally manufactured product and
Cm is the marginal cost to fabricate it with the Lulzbot mini.
p is the percent of downloads resulting in a print. It should be noted that
p is subject to error as downloading a design does not guarantee its manufacture. On the other more likely hand, a single download could be fabricated many times, traded via email, memory stick, or posted on P2P websites that are beyond conventional tracking. Here, to remain conservative,
p is assumed to be 1 because downloading a design involves effort that is not repaid unless one does the printing. This is equivalent to assuming that if a consumer downloads an ebook that it is read at least once. It is thus reasonable to assume every download resulted in at least one print and the total savings for the random 26 objects can be conservatively determined by:
All economic values are in U.S. dollars (USD), $.
3. Results
Printing twenty-six items to model use over the course of 6 months resulted in a total of 104.18 m of filament consumption with a mass of 737.8 g. An estimated total of 100.18 h, and 7.26 kWh were expended on 3-D printing. This translates to $17.71 worth of material and $0.92 in electricity based on average U.S. electric rates, for a total operational cost of $18.63 over half a year. Thus, at a printing rate of one object per week, operating the 3-D printer costs less than $40 per year.
Table 1 shows the projected cumulative cost of owning and using a Lulzbot Mini as a function of years.
Retail costs for the products totaled $278.57 and $1376.03 for low- and high-priced items, respectively, as seen in
Table 2.
This results in a substantial prosumer savings for each individual product with an average marginal cost reduction of 93.3% and 98.7% when compared against the low and high retail costs, respectively. This results in total savings of $259.94 and $1357.40 for the low and high cost estimates, respectively.
Table 3 shows the projected prosumer profit per year assuming one product fabrication per week using the average of the 26 objects chosen here when compared to low-cost commercially available products and high-priced commercially available products. As shown, profit is realized after the second year of ownership when only low-cost commercially available products are considered in the analysis. When compared to high-cost products, however, profit is realized within the first year of ownership. It should be noted that as many of the objects allow some form of customization, the latter values are a better estimate for comparison.
Comparing the printed objects to the lowest-priced equivalent product, there was a payback time of 2.4 years. In comparison to high-priced items, payback time was only 0.46 years. The return on investment was 25% in year 3 and 108% by year 5 when low-range cost values were considered. Comparing printing costs to high-end commercial prices resulted in a 552% ROI in year 3 and 986% in year 5.
The number of downloads for each item file was used to estimate the total savings for the global 3-D printing community when compared to marginal savings using the high and low commercial prices. These values are shown in
Table 4. When compared to the low-end prices, the 26 printed items saved $803,945.70. Compared to the high-end prices, the savings were $4,033,657.89. The URLs for the designs and the low/high equivalent products are found in
Supplementary Material. Prior research has provided economic justification for quantifying these projected values [
23].