Paper towel dispenser

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Executive Summary

Stakeholders

There are six major stakeholders with regards to the paper towel dispenser: Manufacturer, retailer, customer, user, society. The main needs for the manufacturer are to reduce cost and create a reliable product. For the retailer, it is being able to sell a quality product. For the customer, it is making sure it is an affordable and reliable machine. For the customer, cleanliness and ease of use are paramount. For the maintenance worker, ease of opening and replacing the paper towel are important. Society plays a role with regards to how the use of paper towel affects the ecosystem and earth in general. Listed below are the stakeholders and their respective needs.

Paper Towel Manufacturer

Material cost
Manufacturing cost
Assembly
Transporting
Standardize/minimize parts

Retailer

Cost
Storage
Reliability
Usability
Transporting

Customer

Cost
Mounting
Ease of use
Reliability
Aesthetics
Safety

User

Ease of use / ergonomics
Speed of operation
Aesthetics
Cleanliness
Safety

Maintenance Worker

Ease of towel replacement
Safety

Society

Environment

Usability Study

Assembly Pictures

How it Works

Mechanical Analysis

For the Mechanical Analysis, we decided to determine the amount of force that is required to advance the paper towel roll one sheet. In turn, we can determine the amount of torque that is exerted as a resistance force inside of the paper towel dispenser.

Free Body Diagram

By gradually adding weight to the paper towel, we were able to determine the amount of force needed to overcome the torque of the paper towel dispenser: 1.15 lbs.

Fpull = 1.15 lbs.

Cylinder radius = 1.91 in.

Assume:

Force is perpendicular to cylinder
Paper towel does not slip off cylinder

τ=F x d

τ=1.15 lbs x 1.91 in

τ=2.2 lb-in

Parts List

Part No.	Name	Function	QTY	Weight	Material	Manufacturing Process
01	Front Housing	Protects device from exterior	1	935g	Plastic	Injection Molding
02	Front Housing Clip	Holds housings together	1	13g	Steel	Bending, Punching
03	Front Housing Tab	Secures housing clip	1	<1g	Plastic	Injection Molding
04	Rear Housing	Holds mechanical components	1	986g	Plastic	Injection Molding
05	Paper Towel Holding Arm	Holds paper towel roll	2	40g each	Plastic	Injection Molding
06	Phillips Head Screw (1/8 x 1/4 long)	Secures device to rear housing	1	1g	Steel	Machined
07	Wall Mounting Screw (1/8 x 1.25 long)	Secures housing to wall	4	3.5g each	Steel	Machined
08	Screw Anchor	Holds screw in wall	4	~0.25g	Plastic	Injection molding
09	Paper Guide Tube	Guides paper towel to cutting cylinder	1	55g	Plastic	Injection molding
10	Spring (uneven hooks)	Holds 09 in place	2	2g each	Metal	Extrusion
11	Spring (even hooks)	Holds lever to spindle housing	2	1.5g each	Metal	Extrusion
12	Screw (3/32 x 5/8 long)	holds turning wheel and lever to spindle housing	2	~1g each	Metal	Extrusion
13	Red Screw Cap	Hides screw in turning wheel	1	<1g	Plastic	Injection molding
14	Locking Spring	Ensures correct wheel spin direction	1	4g	Steel	Extrusion
15	Red Turning Wheel	Turns main spindle	1	30g	Plastic	Injection molding
16	Guide clips for 09	Guides paper on 09	2	2.5g each	Plastic	Injection molding
17	Screw (3/32 x 3/8 long)	Holds lever assembly together and spindle housing	2	<1g each	Metal	Machined
18	Lever Arm	Connects spring to spindle	1	1g	Plastic	Injection molding
19	Spring Connector	Connects two springs to lever arm	1	<1g	Plastic	Injection molding
20	Rounded Spring Guide	Angles spring to desired measurement	1	<1g	Plastic	Injection molding
21	Thin Paper Guide	Guides paper out of device	1	24g	Plastic	Injection molding
22	Spindle Housing Front	Final housing before paper leaves device	1	132g	Plastic	Injection molding
23	Spindle Housing Back	Back of spindle housing	1	162g	Plastic	Injection molding
24	Spindle Housing (L)	Left of spindle housing	1	105g	Plastic	Injection molding
25	Spindle Housing (R)	Right of spindle housing	1	105g	Plastic	Injection molding
26	White Spindle Guide	Holds spindle in line	3	2.3g each	Plastic	Injection molding
27	Screw (3/32 x 3/8 long)	Connects spindle halves	2	<1g	Metal	Machined
28	Square nut	For use with 27	2	<1g	Steel	Cast and drilled
29	White Teeth Guide/Arm	Guides cutting teeth in spindle	2	3g each	Plastic	Injection molding
30	Cutting Teeth	Cuts paper towel	1	75g	Steel	Cast, punched and bent
31	Spindle Top Half	Holds cutting tool	1	125g	Plastic	Injection molding
32	Spindle Bottom Half	Holds cutting tool	1	135g	Plastic	Injection molding
33	Metal Key	Helps open housing	1	5g	Steel	Punched

DFMA Analysis

There are several different manufacturing processes involved. Most of the components in the paper towel dispenser are made of plastic so injection molding is the most common manufacturing process. There are still some metal parts used, those are manufactured through punching, stamping and bending processes.

Design For Manufacture

Housings

The various housings, as with many of the components of the paper towel dispenser, are made out of plastic. Even though the types of plastic are different for the different housings, the manufacturing process is the same: injection molding. As mentioned earlier, injection molding is the primary manufacturing process used in the paper towel dispenser. The evidence for injection molding is quite visible, there are multiple points for the plastic to be injected into a mold as well as vents. Each of the housings would have been molded independently and it does not appear that several of the same type of housing were molded together and then separated. The sides of the housings have been manufactured without any notable imperfections

Most of the housings are produced using sensible methods. The spindle housing (Part 22), however, uses far too much material. For almost the entire lifetime of the dispenser, the spindle housing will not be exposed to anything outside the product because the front housing protects everything on the inside. The front housing is usually removed to change the paper towel roll. When this happens, the spindle housing is also removed, so there is no economically justifiable reason to keep manufacture the spindle housing. If it is absolutely necessary, it should definitely be made thinner to decrease unnecessary material cost.

Springs

There are several springs used in the paper towel dispenser. The springs are most likely manufactured from a separate company and purchased by Kimberly-Clark. Most springs are manufactured by coiling a stiff wire, hardening through heat treatment and finishing the spring by adding connection hooks to the ends. The hooks were produced through a bending or curling process. Seeing as how these springs are mass produced, the entire manufacturing process would be conducted by machinery.

Metal Clips and Cutting Teeth

The metal clips and cutting teeth were punched out of metal sheets and then shaped through a bending or stamping process. The punching process is easy to see as there is visible evidence with rough edges and corners of virtually all metal components. Even though steel is a very strong material, thin sheets are very easy to mechanically bend and stamp. The bending and stamping processes require a considerable force (though this is not a major concern because it is conducted by machinery) they do not jeopardize the physical properties of the material to a point where it would impact the reliability or use of the product.

Punching, stamping and bending are simple and efficient manufacturing processes, in terms of both cost and time, as there is no complicated casting involved and no expensive mold needed. The manufacturing of the metal clips and cutting teeth does not need to be improved.

Intricate Plastic Components

The remaining plastic components are manufactured using injection molding. These components are considerably more difficult to manufacture as they have geometries that can only be produced through injection molding. Since the moldings are not very straight forward, they would be more expensive than the simpler moldings for the housing.

This is a complicated, economically inefficient process and it is the most expensive of all the components manufactured. Several of these components are unnecessarily complex, leading to expensive molds for injection molding.

Design For Assembly

Kimberly-Clark paper towel dispensers are made in the United States of America. The assembly process is not simple. As the Parts List shows, there are many different parts and many different steps required to fully assemble the device. If any of the smaller pieces, such as the springs, are incorrectly assembled the system will not function properly. The customer purchases the dispenser fully assembled (with the exception of the mounting) so it must be in perfect working order. The customer will most likely not attempt to use the dispenser until on-site installation is completed. Customers and users will most likely be unable to fix any mistakes in the assembly process because the device is complex and can be confusing for someone who is not familiar with the device.

It is for this reason that Kimberly-Clark would have decided to assemble the paper towel dispensers in the USA where there is higher skilled labor than east Asia and there will be minimal transport cost as they are distributed from the USA as well.

Even though the mechanisms within the main assembly can be quite confusing at first glance, our team was able to decipher how everything worked after taking it apart. Based off of our groups disassembling experience, an assembly plant worker would be able to confidently assemble the entire product within a day or two of training.

FMEA Analysis

Failure mode and effects analysis (FMEA) identifies potential problems of every component in the machinery, lists their effects on the system, and finally provides recommended actions to prevent such failures. The methodology for problem identification depends on ratings of Severity of a failure (S), Occurrence of Failure (O), and Detection of Failure (D). These scales are between 1 and 10 and they are rated in a way that less number of ratings indicates less significant problem and conversely higher rating means more serious failure or effect. The results of a FMEA Analysis (RPN) are calculated by multiplying S, O and D to signify seriousness of the problem.

Conclusion

Part No.	Name	Function	Failure Mode	Effects of Failure	S	Causes of Failure	O	Design Controls	D	RPN	Recommended Actions	Responsibility
01	Front Housing	Protects device from exterior	Fractures, Warped	Exposure of internal components Possible injury to customer	7	Improper handling Improper manufacturing	4	Material selection	2	56	Drop test	Reliability
02	Front Housing Clip	Holds housings together	Bends	Housings fell apart	4	Improper handling Improper assembling	2	Material Selection Packaging	6	48	Select a stiffer material	Assembly and Reliablity
03	Front Housing Tab	Secures housing clip	Strips	Housing clip exposed	2	Improper assembling Improper manufacturing	2	Material selection Mold design	8	32	None	Assembly
04	Rear Housing	Holds mechanical components	Fractures	Unable to hold mechanical components	7	Improper handling Improper manufacturing	4	Material Selection	9	252	Drop test Select a stiffer material	Reliability
05	Paper Towel Holding Arm	Holds paper towel roll	Bends	Unable to hold paper towel roll due to misaligned components	6	Improper handling Improper manufacturing Incorrect design	3	Material selection Mold design	2	36	Select a flexible and elastic material	Assembly and Manufacturing
08	Screw Anchor	Holds screw in wall	Fractures	Unable to hold mechanical components Possible injury to customer	7	Improper handling Poor upkeep	6	Material selection	8	336	Select a reliable material	Reliablity
09	Paper Guide Tube	Guides paper towel to cutting cylinder	Failed
10	Spring (uneven hooks)	Holds 09 in place	Deformed	Malfunctioning of mechanical spindle	3	Fatigue	2	Material selection Improper assemblying	5	30	Select a stiffer material Reduce stress on spring	Assembly and Reliablity
11	Spring (even hooks)	Holds lever to spindle housing	Deformed	Malfunctioning of mechanical spindle	3	Improper handling Fatigue	2	Material selection Improper assemblying	4	24	Select a stiffer material Reduce stress on spring	Assembly and Reliablity
14	Locking Spring	Hides screw in turning wheel	Deformed	Unable to confine rotation direction of spindle	3	Improper handling Fatigue	2	Material selection Improper assemblying	4	24	Select a stiffer material Reduce stress on spring	Assembly and Reliablity
16	Guide clips for 09	Guides paper on 09	text	text
18	Lever Arm	Connects spring to spindle	Breaks	Malfunctioning of mechanical spindle	5	Improper handling Improper manufacturing	2	Material selection	2	20	Select a stiffer material	Manufacturing and Reliablity
19	Spring Connector	Connects two springs to lever arm	Breaks	Malfunctioning of mechanical spindle	5	Improper manufacturing Improper assemblying	2	Material selection Mold design	3	30	Select a stiffer material	Assembly and Reliablity
20	Rounded Spring Guide	Angles spring to desired measurement	Breaks	Unable to adjust spring to a desired angle	2	Improper handling Improper manufacturing	2	Material selection	7	28	None	Manufacturing
21	Thin Paper Guide	Guides paper out of device	Breaks	Paper ejected in inconsistent direction User dissatisfaction	4	Improper handling Improper manufacturing	3	Material selection	1	12	Select a stiffer material	Manufacturing
22	Front Spindle Housing	Final housing before paper leaves device	Fractures	User dissatisfaction	3	Improper assemblying Improper manufacturing	2	Packaging Material selection Mold design	6	36	Select a stiffer material	Assembly and Manufacturing
23	Spindle Housing Back	Back of spindle housing	Fractures	User dissatisfaction	3	Improper assemblying Improper manufacturing	2	Packaging Material selection Mold design	6	36	Select a stiffer material	Assembly and Manufacturing
24,25	Spindle Housing (L,R)	Sides of spindle housing	Breaks	Unable to hold spindle	5	Improper assemblying Improper manufacturing	2	Packaging Mold design	6	60	None	Assembly and Manufacturing
29	White Teeth Guide/Arm	Guides cutting teeth in spindle	Breaks	Malfunctioning of mechanical spindle	3	Improper assemblying Improper manufacturing	3	Packaging Mold design	6	36	None	Assembly and Manufacturing
30	Cutting Teeth	Back of spindle housing	Wears,Bends	Unable to cut papers User dissatisfaction	4	Improper manufacturing	2	Material selection Teeth design	2	16	Redesign teeth	Manufacturing
31,32	Spindle	Back of spindle housing	Warps,Breaks	Malfunctioning of machinery	5	Improper assemblying Improper manufacturing	1	Material selection Mold design	3	15	None	Assembly and Manufacturing

DFE Analysis

The production of a product has an environmental impact from the creation of the parts that make up the product, to the time when the consumer throws the product in the garbage. In the Design for Environment, we try to reduce or eliminate any harmful byproducts they may result of the manufacture or use of the product. In our case, we studied the Economic Input-Output Life Cycle Assessment (EIO-LCA) of a paper towel dispenser using Carnegie Mellon's EIO-LCA site. This tool allows us to quantify the data involved with the environmental impact of manufacturing a paper towel dispenser. Specifically, we focused on conventional air pollutants, greenhouse gases, and toxic releases.

Each of the categories below were calculated using $1 million dollars of activity in the sector of "326199 All Other Plastics Product Manufacturing." Since most of the paper towel dispenser is made from plastic parts, we feel that this sector is appropriate. The data are from the Industry Benchmark US Dept of Commerce EIO model from 1997, a Producer Price Model.

We are concerned impact this product has on the environment; specifically, if Congress were to pass a CO₂ tax, would this have a significant impact on the cost of production of the paper towel dispenser?

Conventional Air Pollutants

Below is a table of the release of conventional air pollutants from the top ten contributors in the supply chain, in units of metric tons (mt).

In this chart of conventional air pollutants, you can see that 52% of air pollutants from the production of the paper towel dispenser comes from the generation and supply of energy. In addition, truck transportation plays a smaller, but still significant role in the production of air pollutants.

Greenhouse Gases

Below is a table of the release of greenhouse gases from the top ten contributors in the supply chain, in units of metric tons of CO₂ equivalent(MTC02E).

In this chart, we focused on the emission of CO₂ since this is what the government would tax. The generation and supply of energy plays a large role again, taking producing 46% of the CO₂ emissions. Truck transportation and plastics material and resin manufacturing play a smaller role, but still impact the emissions to the environment.

Toxic Releases

Below is a table of the release of toxic substances from the top ten contributors in the supply chain, in units of kilograms (kg).

The chart below shows that plastics plumbing fixturs and all other plastics products accounts for 45% of the toxic releases. Another significant part is played by plastics material and resin manufacturing at 18%.

EIO-LCA Paper Towel Dispenser

Below is a table showing the effects of production and use of a paper towel dispenser. This is based on an example given by Professor Michalek and thus, we used the example as a template for our project. We ignored the Distribution and End of Life sections. Since the actual use of the paper towel dispenser requires no electricity, the two components are the dispenser and paper towels.

In this example, the paper towels overwhelm the dispenser in terms of CO₂ output. This is because the dispenser only needs to be made once, while the paper towels are constantly being thrown out and replaced.

DFE Conclusion

From the results of the EIO-LCA, we can see that there are many factors that contribute to the release of harmful waste and gases into the environmental. For example, the energy supply causes a large number of CO₂ to be released in the air, this may be reduced by the use of renewable resources such as solar or wind. Truck transportation also plays a detrimental role towards the environment. It is difficult to just make trucks more efficient or burn cleaner, but maybe using a strategic network or green-powered locomotives to transport products can reduce the amount of emissions to the environment. We also realize that since most of the paper towel dispenser is made from plastic, it is not biodegradable and would be better if there were a way to recycle the plastic. Another point, is if it is possible to recycle the paper towels after they are used, instead of being sent to a landfill.

Team Member Roles

Eric Totong: Stakeholders, DFE
Chang Keun Jung: FMEA
James Li-Yang Lee: Usability Study, Assembly pictures, How it works
Nishan Kulatilaka: DFMA, DFA, Parts list

References

Carnegie Mellon University Green Design Institute. (2009) Economic Input-Output Life Cycle Assessment (EIO-LCA) US 1997 (491) model [Internet], Available from: <http://www.eiolca.net/> [Accessed 20 Sep, 2009]