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Design for Manufacturing

Final Project

Air Compressor Device

Masoud Golshadi

Natalie Ferrari

Timothy Nash

Gregory Feather

Spring 2012

Rochester Institute of Technology

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Table of Contents

1. Introduction………………………………………………………………………………………..……3

2. Project Plan…………………………………………………………………………………………..…3

3. Bill of Materials………………………………………………………………………………………....4

4. Design for Manufacturing Analysis………………………………………………………………..….6

4.1. L-Shape Bracket …………………………………………………………………………...……….6

4.1.1 DFM Analysis…………………………………………………………………………..…….6

4.1.2. Process Plan………………………………………………………………………………...14

4.1.3. Cost Estimation……………………………………………………………………………..15

4.2. Plastic Housing………………………………………………………………………………….....17

4.2.1. DFM Analysis………………………………………………………………………………17

4.2.2. Process Plan……………………………………………………………………………...…21

4.2.3. Cost Estimation……………………………………………………………………………..21

4.3. Gear Holder………………………………………………………………………………………..23

4.3.1. Analysis……………………………………………………………………………………..23

4.3.2. Process Plan………………………………………………………………………………...26

4.3.3. Cost Estimation………………………………………………………………………..……26

5. Design for Assembly Analysis………………………………………………………………………...28

5.1. Assembling Process of the Components…………………………………………………………..29

5.2. DFA Analysis of the Compressor Device…………………………………………………………30

5.3. Time Improvement……………………………………………………………………………...…32

6. Conclusions…………………………………………………………………………………………….34

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1. Introduction

The following is an overall analysis of Design for Manufacture (DFM), Design for Assembly

(DFA), and cost estimation of a Harbour Freight air compressor. This air compressor is a very nice

example of a cheap product of what could be very costly. The market value of this product is

approximately eight dollars while competitor prices range from anywhere between twelve to one hundred

thirty dollars.

The product was strictly analyzed through three main components, the plastic housing, the L-

shape bracket and the gear holder. Using DFM guidelines, these components were analyzed to determine

the overall quality of each part. As it was expected due to the cheapness of the part, the overall quality of

the parts failed to meet many DFM guidelines as a consequence to eliminating manufacturing processes

that in the end, would have added a sufficient amount to the overall cost per product.

Assuming Harbour Freight desired to make 500,000 air compressor products the overall cost

would be approximately 850,000 dollars. With a market value of about eight dollars, and assuming they

sold every single product, this would leave Harbour Freight with a profit of 3,150,000 dollars.

2. Project Plan

The project involves several stages and its process was started by creating a list of component and

parts. Then the parts were modeled into CAD software called “SolidWorks”. In the modeling of the parts,

attention was introduced to all the details and the final CAD files contain components with precise

dimensions. After that, the parts were assembled together to produce the final product and the assembly

animation was then created out of that. The drawings of each components and the final assembly were

made from the CAD models. Three different parts of the compressor were then selected to be analyzed by

design for manufacturing guidelines. The parts were included a main plastic housing manufactured by

injection molding, gear holder and L-shape bracket manufactured by die casting process. The cost

estimation analysis of each component was revealed the total cost of the parts and the features capable of

improvement. Then, design for assembly analysis was employed to estimate the assembly time based on

Boothroyd-Dewhurst criteria. During that analysis, the assembling problems were revealed and based on

the DFA criteria, a better design was introduced.

All these works were done in 4 weeks and in a group of 4 people. The tasks of each person are

presented as follow:

Masoud Golshadi: CAD Modeling, DFA Analysis, Animation, Preparing the Final Report

Natalie Ferrari: Drawings, BOM, DFM Analysis and Cost Estimation (Gear Holder)

Timothy Nash: Drawings, DFM Analysis and Cost Estimation (Plastic Housing)

Gregory Feather: Assembly, DFM Analysis and Cost Estimation (L-Shape Bracket)

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3. Bill of Materials

The bill of materials (BOM) is indicated as the following table:

Item NO. Make/Purchase Description QTY. Picture

1 Make Compressor Housing Side 1 1

2 Make Compressor Housing Side 2 1

3 Make Gasket 1

4 Make Connecting Rod 1

5 Make Piston 1

6 Purchased Pin 1

7 Purchased O-Ring #1 1

8 Purchased Cylinder 1

9 Make Crank 1

10 Make Main Shaft 1

11 Purchased Small Shaft 1

DFM Project Parts List

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Item NO. Make/Purchase Description QTY. Picture

12 Purchased Motor 1

13 Purchased Small Gear 1

14 Make Large Gear 1

15 Make Gear Holder 1

16 Make Bush 1

17 Make L shaped Bracket 1

18 Purchased Spring 1

19 Purchased Plunger Seal 1

20 Purchased O-Ring #2 1

21 Make Casted Screw 1

22 Purchased Intake Plate 1

23 Purchased Long Screw 2

24 Purchased Spring Washer 2

25 Purchased Motor Screw 2

26 Purchased Housing Screw 5

27 Purchased Retaining Ring 1

28 Purchased Sticker #1 1



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4. Design for Manufacturing Analysis

Design for manufacturing (DFM) is the general engineering art of designing products in such a

way that they are easy to manufacture. It is the process of proactively designing products to optimize all

the manufacturing functions such as fabrication, assembly, test, procurement, shipping, delivery, service

and repair, and in the other hand, assure the best cost, quality, reliability, regulatory compliance, safety

and customer satisfaction. Since the products can be quickly assembled from fewer parts, following the

DFM criteria can reduce many costs. Designing the parts is for ease of fabrication and commonality with

other designs. Furthermore, DFM encourages standardization of parts, maximum use of purchased parts,

modular design, and standard design features. The result is a broader product line that is responsive to

customer needs. The basic DFM idea exists in almost all engineering disciplines, but with different

variation of rules and details depending on the manufacturing technology. This design practice not only

focuses on the design aspect of a part but also on the production feasibility. If these DFM guidelines are

not followed, it will result in iterative design, loss of manufacturing time and overall resulting in longer

time to market. Hence many organizations have adopted concept of Design for Manufacturing.

Depending on various types of manufacturing processes there are sets guidelines for DFM

analysis. These DFM guidelines help to precisely define various tolerances, rules and common

manufacturing checks related to DFM. In the following sections, the DFM analysis of 3 components of

the compressor device is presented continued by explanation of post-processing steps and cost estimation

of the design. The processes are included the injection molding for the main plastic housing of the

compressor, and die casting of the gear holder and L-shape bracket parts. There are several DFM

guidelines which have been violated in designing of these components resulting in a poor quality and

higher cost. Improving these mistakes can reduce the cost and satisfy the customers need in a proper way.

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4.1. L-Shape Bracket

4.1.1. DFM Analysis

The DFM analysis of the L-shape bracket was done in several stages starting with the preferred

parting line and followed by revealing the existing problems and a solution for them.

Parting edge is colored in blue and purple. The purple line splits the cylinder in half, the top and

bottom will be formed by different molds.

The teal and pink surfaces will require side action slides due to their orientation, which is

perpendicular to the movement of the mold.

There are many surfaces on the L-Bracket which require draft angles. The specific surfaces and

angles will be examined in detail below. The surfaces highlighted in green have a draft angle in the

correct direction for the movement of the top mold. The surfaces highlighted in red are correct for

direction of movement of the bottom half of the mold. The yellow surfaces have no draft angle, whether

one is required or not.

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On the bottom of the part where the seal sits, there is no draft angle. To conform to DFM

guidelines the draft angle should be at least 5 degrees, based on the 0.08" depth.

On the bottom of the part where the air intake flap sits, there is no draft angle. To conform to

DFM guidelines the draft angle should be at least 7 degrees, based on the 0.03" depth.

On the base of the part at the rib, there is no draft angle. To conform to DFM guidelines the draft

angle should be at least 1.75 degrees, based on the 0.1" depth.

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Around the outer edge on the base of the part, the draft angle should be 1.25 degrees to conform to

DFM guidelines, based on a thickness of 0.28".

There is no draft on the selected hole, to conform to DFM guidelines, the draft on the hole should

be 3 degrees based on a depth of 0.28".

The draft on the boss and inside edge should be 3.5 degrees based on a depth of 0.1" to conform to

DFM guidelines.

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There is no draft on the center hole, to conform to DFM guidelines, the draft angle should be 4.5

degrees based on the depth of 0.16".

Since the top third of the hole is tapped, the hole will have a maximum core depth based on its

diameter. Following DFM guidelines the max depth of the cored hole should be 0.727", where as the

actual depth is 1.02". Either the diameter of the hole should be larger to accommodate this depth or the

hole depth should be less. The hole will then also have a draft angle created by the change in radii of the

hole's core.

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The draft on the face (blue arrow) should match the draft on the outer edge (red arrow), which is

1.25 degrees, to allow for a smooth transition and surface.

The draft angle on this edge should be 0.9 degrees based on the depth of 0.49" to conform to DFM

guidelines.

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The draft angle for the outside of the cylinder should be 0.75 degrees based on the depth of 0.9" to

conform to DFM guidelines.

The angle for the wall that the arrow is pointing to should be 1.75 degrees based on a depth of

0.15" to conform to DFM guidelines.

Thickness should be consistent throughout the casted part, in the areas pointed out the thickness is

not consistent and it should be balanced with the rest of the part. Coring or a redesign may be necessary.

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For a cored hole with the radius of 0.15 in, the maximum depth should be roughly 0.5 inches. The

depth of the shown cored hole is roughly twice that. Either the hole radius should be increased or the

depth decreased to conform to DFM.

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The bosses are attached to the wall and can cause sinks to occur due to the added thickness, the

bosses should instead be connected to the wall by a rib.

The inner and outer edges pointed out have a sharp corner; sharp corners concentrate stresses and

lower die life. Each should have a radius of 1.5 times the thickness.

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The internal threads should be machined after the casting operation is complete, this will result in

more precise threads to seal and be air tight as possible.

4.1.2. Process Plan

The process of manufacturing of the L-shape bracket component is started by die casting. After

the die casting, a trimming machine trims the outside flashes of the part. The center hole is then required

to be taped and threaded. So, another machining process is involved in this stage.

4.1.3. Cost Estimation

The cost estimation of the gear holder part was done by considering the following assumptions:

Machine has a clamping capacity of 100 tons and a shot capacity of 16.5 in3.

The total number of components to be cast = 500,000

Die casting machine cycle time = 60 seconds

The cost of operating the die casting machine (casting+operator) = $35/hr.

The cost of operating the trim press (press+operator) = $25/hr.

The trimming process is fully automated, hence the time to trim any number of parts produced in one

cycle is 15 seconds.

The cost of a single cavity die is $40,000.

The cost of a single aperture trimming die is $20,000.

The material used is Zinc No. 3, and you pay $1.2/lb for it.

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Any material not used in the part itself (e.g. feed system and overflow wells) can be recycled without any

waste.

If temporarily ignore whether or not the die casting machines available are large enough, the

number of die openings for this part to minimize the cost would be specified as follows:

The force of the molten metal which is acting on the die by assuming the 4 for the number of die

openings would be as follows:

The required shot volume of zinc material by assuming the 4 as the number of die openings can be

calculated as follows:

To select the correct press machine, the clamping force needs to be considered and according to

the press specifications and following calculations, the 100 ton press would handle that force. Therefore,

the number of die cavities would be maintained as 4:

Using the same number of die cavities, the die casting process cost (Cdc) would be as follows:

And the cost of trimming (Ctr), using the final number of die openings would be as follows:

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Using the final number of die openings, the cost of the multicavity die (Cdn) can be calculated as

follows:

So the cost of the multiaperture trim die (Ctn) is calculated as follows:

The total alloy cost (Cta) would be:

And finally, the total cost of making the 500,000 L-shape bracket for the compressor is:

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4.2. Plastic Housing

4.2.1. DFM Analysis

The DFM analysis of the plastic housing was done in several stages starting with the preferred

parting line and followed by revealing the existing problems and a solution for them.

Part A:

The purple line indicates the parting line of the plastic housing

Part B:

1. Base

a. Problem: Contains sharp corners

i. Solution: Add a draft of at least 0.5 degrees in necessary locations

b. Problem: Several locations require draft

ii. Solution: Add radii of 1.5 T to sharp corners

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c. Problem: Wall thickness fails to follow uniformity

iii. Solution: Add steps to added thickness to allow for uniformity

2. Ribs

a. Problem: All ribs contain no draft

i. Solution: Add a draft of at least 0.5 degrees to all ribs

b. Problem: Sharp corners

ii. Solution: Add radii of 1.5 T to remove sharp corners

c. Problem: The rib thickness

iii. Solution: Reduce the rib thickness from .06in to a maximum of 0.048in

d. Problem: Height should be reduced

iv. Solution: The rib height should be reduced to a maximum of 3T

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3. Bosses

a. Problem: All bosses contain no draft

i. Solution: Add a draft of at least 0.5 degrees

b. Problem: Sharp corners

ii. Solution: Add radii of 1.5 T to remove sharp corners

c. Problem: The depth to diameter ratio of the hole is too large. Diameter = 0.1in, Depth =

0.7in

iii. Solution: Add steps to the hole or increase the diameter of the hole/decrease the

depth of the hold to provide the bosses with more stability

4. Outer Rib Extrusions

a. Require a draft

i. Add a draft of at least 0.5 degrees to all ribs

b. Sharp corners

ii. Add radii of 1.5 T to remove sharp corners

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5. Casing Indentation

a. Problem: Sharp corners

i. Solution: Add radii of 1.5 T to remove sharp corners

6. Base Ribs

a. Two ribs are too close to each other

i. Relocate a rib at least 2T away from the other or remove rib completely if possible

7. Internal Rib Extrusions

a. Sharp corners

i. Add radii of 1.5T to remove sharp corners

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b. Requires draft

ii. Add draft of at least 0.5 degrees to all ribs

c. The thickness needs to be reduced

iii. Reduce thickness to a maximum of 0.048in

d. Height needs to be reduced

iv. Reduce height to a maximum of 3T

4.2.2. Process Plan

The process of manufacturing of the plastic housing component is done by injection molding.

Since the injection molding provides all the part requirements such as required surface finish and

dimensional tolerances, there is no post-processing stage.


The cost estimation of the plastic housing part was done by considering the following

assumptions:

The total number of components to be injected molded = 500,000


The cost of a single injection mold is $30,000.

The material used is Polycarbonate, and you pay $1.75/lb for it.


waste.

To minimize the cost, the number of cavities for this part would be calculated as follows:

By assuming 2 for the number of cavities, the acting force on the mold would be as follows:

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The required shot volume of Polycarbonate if assume the number of cavities from the previous

calculation would be:

The cost of the mold base can be found as follows:

The processing cost can be calculated as follows:

Therefore, the cost of the multicavity injection mold would be as follows:

The total polymer cost is:

And finally, the total cost of making the 500,000 parts can be found as follows:

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4.3. Gear Holder

4.3.1. DFM Analysis

The DFM analysis of the gear holder was done in several stages starting with the preferred parting

line and followed by revealing the existing problems and a solution for them.

Part A:

The blue line is the identified preferred parting line. The orange and green colors separate the top

half of the die from the bottom half of the die.

Part B:

1. Base Extrude

a. Problem: Sharp corners in dies are hard to maintain, and produce localized stresses and

heat build up

i. Solution: Add a fillet of about 1.5t to all sharp corners

Sharp Edges

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b. Problem: No draft on edges of base. Recommended draft for zinc alloys with a wall

thickness between 0.08-0.15” is 3.5 degrees

i. Solution: Increase draft for top half of base part to at least 3.5 degrees

2. Base Holes

a. Problem: Base holes are not drafted. With a depth of 0.13” it is recommended that the hole

have a 4.5 degree draft.

i. Solution: Add a 4.5 degree draft to the bearing hole

b. Problem: Base holes should have fillets entering and exiting hole to reduce stress

concentrations

i. Solution: Add fillets to sharp edges of hole

3. Back Hole

a. Problem: Back hole is not drafted. With a depth of 0.36” it is recommended that the hole

have a 3 degree draft.

i. Solution: Add a 3 degree draft to the bearing hole

No Draft

Sharp Corners

No Draft on Sides of Base

0.13 “

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b. Problem: Base holes should have fillets entering and exiting hole to reduce stress

concentrations

i. Solution: Add fillets to sharp edges of hole

4. Middle Ribs

a. Problem: Rib is wider than the casting wall thickness

i. Solution: Decrease rib width to that of the casting wall thickness

b. Problem: Sharp corners in dies are hard to maintain, and produce localized stresses and

heat build up

i. Solution: Add a fillet of at least the wall thickness to all sharp corners

No Draft

Sharp Corners

t = 0.03”

t = 0.07”

Sharp corners

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5. Side Ribs

a. Problem: Rib is wider than the casting wall thickness

i. Solution: Decrease rib width to that of the casting wall thickness

4.3.2. Process Plan

The process of manufacturing of the gear holder component is started by die casting. After the die

casting, a trimming machine trims the outside flashes of the part. The two side mounting holes are then

required to be taped and threaded. So, another machining process is involved in this stage.


The cost estimation of the gear holder part was done by considering the following assumptions:

Machine has a clamping capacity of 100 tons and a shot capacity of 16.5 in3.

The total number of components to be cast = 500,000


The cost of operating the die casting machine (casting+operator) = $35/hr.

The cost of operating the trim press (press+operator) = $25/hr.

The trimming process is fully automated, hence the time to trim any number of parts produced in one

cycle is 15 seconds.

The cost of a single cavity die is $40,000.

The cost of a single aperture trimming die is $20,000.

The material used is Zinc No. 3, and you pay $1.2/lb for it.


waste.

t = 0.03”

t = 0.07”

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If temporarily ignore whether or not the die casting machines available are large enough, the

number of die openings for this part to minimize the cost would be specified as follows:

The force of the molten metal which is acting on the die by assuming the 4 for the number of die

openings would be as follows:

The required shot volume of zinc materail by assuming the 4 as the number of die openings can be

calculated as follows:

To select the correct press machine, the clamping force needs to be considered and according to

the press specifications and following calculations, the 100 ton press would handle that force. Therefore,

the number of die cavities would be maintained as 4:

Using the same number of die cavities, the die casting process cost (Cdc) would be as follows:

And the cost of trimming (Ctr), using the final number of die openings would be as follows:

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Using the final number of die openings, the cost of the multicavity die (Cdn) can be calculated as

follows:

So the cost of the multiaperture trim die (Ctn) is calculated as follows:

The total alloy cost (Cta) would be:

And finally, the total cost of making the 500,000 gear holder for the compressor is:

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5. Design for Assembly Analysis

Design for assembly (DFA) is a process for improving product design for easy and low-cost

assembly, focusing on functionality and on assemblability concurrently. DFA recognizes the need to

analyze both the part design and the whole product for any assembly problems early in the design

process. The aim of DFA is to simplify the product so that the cost of assembly is reduced. However,

consequences of applying DFA usually include improved quality and reliability, and a reduction in

production equipment and part inventory. These secondary benefits often outweigh the cost reductions in

assembly.

In this project the Boothroyd-Dewhurst criteria has been employed. The Boothroyd-Dewhurst

DFA evaluation centers on establishing the cost of handling and inserting component parts. The process

can be applied to manual or automated assembly, which is further subdivided into high-speed dedicated

or robotic. An aid to the selection of the assembly system is also provided by a simple analysis of the

expected production volume, payback period required, number of parts in the assembly, and number of

product styles.

Regardless of the assembly system, parts in the assembly are evaluated in terms of “ease of

handling” and “ease of insertion”, and a decision is made as to the necessity of the part in question. The

findings are then compared to synthetic data, and from this a time and cost is generated for the assembly

of that part. The opportunity for reducing this is found by examining each part in turn and identifying

whether each exists as a separate part for fundamental reasons. These fundamental reasons include

relative movement of the part with respect to the other assembled parts, isolation or material difference

and the necessity to have a separate part from all those already assembled.

The second stage of the analysis is to examine the handling and insertion of each component part.

For manual assembly, a two-digit handling code and a two-digit insertion code are identified from

synthetic data tables. The tables categorize components with respect to their features for handling such as

size, weight, and required amount of orientation. For insertion, there are categories for part alignment, the

type of securing method, and whether the part is secured on insertion or as a separate process. These

codes are then cross-referenced to identify the time for that operation from the table.

5.1. Assembling Process of the Components

The process of assembling the components of compressor device is started with press fitting the

bush inside the gear holder. Therefore, the gear holder is set inside a press machine and then the bush is

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press fitted inside the hole. Since the bush has axial symmetry and because several burs can be observed

at the part, easy alignment with resistance in insertion was chosen. The small gear is then fitted at the

motor shaft by press fitting and the motor is mounted to the gear holder by two screws. The small shaft

and the large shaft are secured into the crank due to a small tolerances and press operation. After that, the

motor sub-assembly is grasped and the large shaft is inserted into the bush and the large gear is then

secured at its position by a retaining ring. The piston sub-assembly is included the connecting rod

mounted to the piston by a pin. At the top of the piston, there is an o-ring which provides sealing for the

compressed air inside the cylinder. The piston sub-assembly is also set at its position into the motor sub-

assembly and then the cylinder is introduced to the complex.

Now, a spring is grasped and the plunger seal is put on one side of it. Then the L-shape bracket is

picked up and oriented to locate the spring with plunger seal its head. Casted screw is positioned at the

top and it is tightened afterward. The L-shape bracket is then rotated by 180 degrees to reach the bottom.

Now, its o-ring is mounted and then the intake plate is secured at its place. Since the intake plate is very

thin and difficult to grasp, and because it requires tweezer to locate it at the its position, the proper

insertion and handling code has been selected. The L-shape bracket sub-assembly is then introduced to

the top of the motor sub-assembly and by the help of two long screws and their spring washers, it is

mounted to the top of the complex. Now, the entire mechanical sub-assembly is located at its position on

one of the plastic housings and secured by an elastic gasket. The other half of the main housing is then

introduced and secured by the notches on the housing and mounted by five screws. The stickers are the

last parts to be added and since there are 3 stickers on 3 different outer sections of the compressor

housing, the orientation operation is required to reach the correct position of them.

5.2. DFA Analysis of the Compressor Device

The following table illustrates detailed DFA analysis of the system based on the Boothroyd-

Dewhurst criteria.

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Part or Operation DescriptionNo. of

Items

Alpha

Symmetry

Beta

Symmetry

Tool Acquired

Time

Handling

Code

Handling

Time

Insertion

Code

Insertion

Time

Total

Time

Gear Holder Set the Gear Holder onto a press machine 1 360 360 - 30 1.95 30 2 3.95

Bush Grasp the Bush 1 180 0 - 01 1.43 - - 1.43

Press Operation Fit the Bush into the Gear Holder by press machine 1 - - 3 - - 07 6.5 9.5

Motor Set the Motor onto a press machine 1 360 0 - 10 1.5 - - 1.5

Small Gear Grasp the Small Gear 1 180 0 - 01 1.43 - - 1.43

Press Operation Fit the Small Gear into the Motor shaft by press machine 1 - - 3 - - 07 6.5 9.5

Motor Screws Fix the Motor SA to Gear Holder SA 2 360 0 3 11 1.8 92 5 16.6

Crank Grasp the Crank 1 360 360 - 30 1.95 - - 1.95

Small Shaft Grasp the Small Shaft 1 180 0 - 00 1.13 - - 1.13

Press Operation Fit the Small Shaft to the Crank 1 - - 3 - - 07 6.5 9.5

Main Shaft Grasp the Main Shaft 1 360 0 - 10 1.5 - - 1.5

Press Operation Fit the Main Shaft to the Crank 1 - - 3 - - 07 6.5 9.5

Motor SA Set in fixture 1 180 180 - 10 1.5 - - 1.5

Large Gear Grasp the Large Gear 1 180 180 - 11 1.8 - - 1.8

Crank SA Grasp the Crank SA 1 360 0 - 10 1.5 - - 1.5

Assembling Operation Fit the Large Gear to the Crank SA inside the Motor SA 1 - - - - - 09 7.5 7.5

Retaining Ring Grasp Retaining Ring 1 180 0 3 40 3.6 - - 6.6

Fitting Operation Set Retaining Ring into the Main Shaft end 1 - - 3 - - 07 6.5 6.5

Piston Grasp the Piston 1 180 0 - 01 1.43 - - 1.43

Connecting Rod Grasp Connecting Rod 1 180 360 - 20 1.8 - - 1.8

Pin Grasp the Pin 1 180 0 - 00 1.13 - - 1.13

Press Operation Fit the Pin into the Piston 1 - - 3 - - 07 6.5 9.5

O-Ring Grasp the O-Ring 1 360 0 - 12 1.88 - - 1.88

Fitting Operation Set the O-Ring into its groove in the Piston 1 - - - - - 35 7 7

Cylinder Grasp the Cylinder 1 180 0 - 00 1.13 - - 1.13

Assembling Operation Put the Piston SA into the Cylinder 1 - - - - - 30 2 2

Motor SA Grasp the Motor SA 1 360 360 - 30 1.95 - - 1.95

Piston and Cylinder SA Grasp the Piston and Cylinder SA 1 360 180 - 20 1.8 - - 1.8

Assembling Operation Fit the Piston SA into the Motor SA 1 - - - - - 08 6.5 6.5

Plunger Seal Grasp the Plunger Seal 1 360 0 - 12 2.25 - - 2.25

Spring Grasp the Spring 1 180 0 - 00 1.13 - - 1.13

Fitting Operation Fit the Plunger Seal into the Spring 1 - - - - - 31 5 5

L-Shape Bracket Grasp the L-Shape Bracket 1 360 0 - 10 1.5 - - 1.5


Fitting Operation Set the O-Ring into its groove in the L-Shape Bracket 1 - - - - - 35 7 7

Intake Plate Grasp the Intake Plate 1 180 360 - 53 8 - - 8

Fitting Operation Put the Intake Plate into its place inside the L-Shape Bracket 1 - - 3 - - 11 5 8

Orientation Operation Rotating the L-Shape Bracket 1 - - - - - 30 2 2

Spring SA Grasp Spring SA 1 360 0 - 10 1.5 - - 1.5

Assembling Operation Put the Spring SA into L-Shape Bracket SA 1 - - - - - 30 2 2

Casted Screw Drive the Casted Screw into its place on L-Shape Bracket 1 360 0 3 10 1.5 38 6 10.5

Spring Washer Grasp the Spring Washer 2 180 0 - 09 2.98 - - 5.96

Long Screws Grasp The Long Screw 2 360 0 - 10 1.5 - - 3

Fitting Operation Put the Spring Washer on the Long Screw 2 - - - - - 30 2 4

Motor SA Set the Motor SA into fixture 1 360 360 - 30 1.95 - - 1.95

L-Shape Bracket SA Grasp L-Shape Bracket SA 1 360 360 - 30 1.95 - - 1.95

Positioning Operation Put the L-Shape Bracket SA at the top of Motor SA 1 - - - - - 08 6.5 6.5

Driving Screws Driving the Long Screws SA at the both side 2 360 0 3 10 1.5 39 8 22

Plastic Housing 1 Grasp The Plastic Housing 1 1 360 360 - 30 1.95 - - 1.95

Gasket Grasp The gasket 1 360 180 - 21 2.1 - - 2.1

Assembling Operation Put the Gasket into its place in the Plastic Housing 1 1 - - - - - 35 7 7

Mechanical SA Grasp the Mechanical SA 1 360 360 - 30 1.95 - - 1.95

Assembling Operation Fit the Mechanical SA into the Plastic Housing 1 1 - - - - - 31 5 5


Fitting Operation Fit the Plastic Housing 2 into the Plastic Housing 1 1 - - - - - 09 7.5 7.5

Housing Screws Fix the two housings together 5 360 0 3 11 1.8 38 6 42

Sticker #1 Affix the Sticker to the Plastic Housing 1 1 360 360 - 33 2.51 30 2 4.51

Orientation Operation Rotate the Compressor Assembly 1 - - - - - 98 9 9


Orientation Operation Rotate the compressor assembly 1 - - - - - 98 9 9

Sticker #3 Affix the Sticker to the bottom of Compressor Assembly 1 360 0 - 13 2.06 30 2 4.06

337.7

38

Total Time (seconds)

Total Number of Parts

33

5.3. Assembly Time Improvement

There are several features which can be improved under DFA perspective. Since the steel bush in

the motor sub-assembly is a separate part and is a seat for the main shaft, it takes several minutes to align

and install it inside the gear holder by press fitting. If the prepared hole inside the gear holder contains

enough machining allowance and after die casting, machining operation makes a smooth and proper place

for the main shaft, two assembly processes would be eliminated. Although, eliminating that bush could

increase the manufacturing cost but it can decrease the assembly cost and save 10.93 seconds during the

assembly.

In the other hand, the small shaft can be casted in the crank and by doing that, press operation for

fitting the shaft into the crank would be removed. Because dimensions of the shaft doesn’t require high

accuracy and a die casted cast iron can provide enough surface finish for this purpose, combination of

these two parts are feasible. This elimination can reduce the assembly time by 10.63 seconds.

Sticking the labels on the plastic housing is another place for saving time. One of the stickers has a

specific place to seat but the other one should be attached without any seating position. It means that the

operator needs to pay more attention to install this sticker in a correct position and orientation. Thus,

adding a notch or a small pocket to the plastic mold can help the operator during the final assembly stages

and save almost 3 seconds.

The following table shows the improved version of the DFA analysis which requires 23.56

seconds less than the previous one to finish the assembly.

34

Part or Operation DescriptionNo. of

Items

Alpha

Symmetry

Beta

Symmetry

Tool Acquired

Time

Handling

Code

Handling

Time

Insertion

Code

Insertion

Time

Total

Time

Gear Holder Set the Gear Holder onto a press machine 1 360 360 - 30 1.95 30 2 3.95

Bush Grasp the Bush - - - - - - - - 0

Press Operation Fit the Bush into the Gear Holder by press machine - - - - - - - - 0

Motor Set the Motor onto a press machine 1 360 0 - 10 1.5 - - 1.5

Small Gear Grasp the Small Gear 1 180 0 - 01 1.43 - - 1.43

Press Operation Fit the Small Gear into the Motor shaft by press machine 1 - - 3 - - 07 6.5 9.5

Motor Screws Fix the Motor SA to Gear Holder SA 2 360 0 3 11 1.8 92 5 16.6

Crank Grasp the Crank 1 360 360 - 30 1.95 - - 1.95

Small Shaft Grasp the Small Shaft - - - - - - - - 0

Press Operation Fit the Small Shaft to the Crank - - - - - - - - 0

Main Shaft Grasp the Main Shaft 1 360 0 - 10 1.5 - - 1.5

Press Operation Fit the Main Shaft to the Crank 1 - - 3 - - 07 6.5 9.5

Motor SA Set in fixture 1 180 180 - 10 1.5 - - 1.5

Large Gear Grasp the Large Gear 1 180 180 - 11 1.8 - - 1.8

Crank SA Grasp the Crank SA 1 360 0 - 10 1.5 - - 1.5

Assembling Operation Fit the Large Gear to the Crank SA inside the Motor SA 1 - - - - - 09 7.5 7.5

Retaining Ring Grasp Retaining Ring 1 180 0 3 40 3.6 - - 6.6

Fitting Operation Set Retaining Ring into the Main Shaft end 1 - - 3 - - 07 6.5 6.5

Piston Grasp the Piston 1 180 0 - 01 1.43 - - 1.43

Connecting Rod Grasp Connecting Rod 1 180 360 - 20 1.8 - - 1.8

Pin Grasp the Pin 1 180 0 - 00 1.13 - - 1.13

Press Operation Fit the Pin into the Piston 1 - - 3 - - 07 6.5 9.5


Fitting Operation Set the O-Ring into its groove in the Piston 1 - - - - - 35 7 7

Cylinder Grasp the Cylinder 1 180 0 - 00 1.13 - - 1.13

Assembling Operation Put the Piston SA into the Cylinder 1 - - - - - 30 2 2

Motor SA Grasp the Motor SA 1 360 360 - 30 1.95 - - 1.95

Piston and Cylinder SA Grasp the Piston and Cylinder SA 1 360 180 - 20 1.8 - - 1.8

Assembling Operation Fit the Piston SA into the Motor SA 1 - - - - - 08 6.5 6.5

Plunger Seal Grasp the Plunger Seal 1 360 0 - 12 2.25 - - 2.25

Spring Grasp the Spring 1 180 0 - 00 1.13 - - 1.13

Fitting Operation Fit the Plunger Seal into the Spring 1 - - - - - 31 5 5

L-Shape Bracket Grasp the L-Shape Bracket 1 360 0 - 10 1.5 - - 1.5


Fitting Operation Set the O-Ring into its groove in the L-Shape Bracket 1 - - - - - 35 7 7

Intake Plate Grasp the Intake Plate 1 180 360 - 53 8 - - 8

Fitting Operation Put the Intake Plate into its place inside the L-Shape Bracket 1 - - 3 - - 11 5 8

Orientation Operation Rotating the L-Shape Bracket 1 - - - - - 30 2 2

Spring SA Grasp Spring SA 1 360 0 - 10 1.5 - - 1.5

Assembling Operation Put the Spring SA into L-Shape Bracket SA 1 - - - - - 30 2 2

Casted Screw Drive the Casted Screw into its place on L-Shape Bracket 1 360 0 3 10 1.5 38 6 10.5

Spring Washer Grasp the Spring Washer 2 180 0 - 09 2.98 - - 5.96

Long Screws Grasp The Long Screw 2 360 0 - 10 1.5 - - 3

Fitting Operation Put the Spring Washer on the Long Screw 2 - - - - - 30 2 4

Motor SA Set the Motor SA into fixture 1 360 360 - 30 1.95 - - 1.95

L-Shape Bracket SA Grasp L-Shape Bracket SA 1 360 360 - 30 1.95 - - 1.95

Positioning Operation Put the L-Shape Bracket SA at the top of Motor SA 1 - - - - - 08 6.5 6.5

Driving Screws Driving the Long Screws SA at the both side 2 360 0 3 10 1.5 39 8 22


Gasket Grasp The gasket 1 360 180 - 21 2.1 - - 2.1

Assembling Operation Put the Gasket into its place in the Plastic Housing 1 1 - - - - - 35 7 7

Mechanical SA Grasp the Mechanical SA 1 360 360 - 30 1.95 - - 1.95

Assembling Operation Fit the Mechanical SA into the Plastic Housing 1 1 - - - - - 31 5 5


Fitting Operation Fit the Plastic Housing 2 into the Plastic Housing 1 1 - - - - - 09 7.5 7.5

Housing Screws Fix the two housings together 5 360 0 3 11 1.8 38 6 42


Orientation Operation Rotate the Compressor Assembly 1 - - - - - 98 9 9


Orientation Operation Rotate the compressor assembly 1 - - - - - 98 9 9

Sticker #3 Affix the Sticker to the bottom of Compressor Assembly 1 360 0 - 13 2.06 30 2 2.06

314.14

38

Total Time (seconds)

Total Number of Parts

35

6. Conclusions

Overall the Harbour-Freight compressor was designed to be inexpensively manufactured, to do

this many guidelines were ignored or deemed unnecessary. The guidelines that were ignored may not

affect the functionality of the part; however the life expectancy and reliability of the compressor will

more than likely suffer. Also the manufacturing moulds will also have lower life expectancy due to sharp

edges and missing draft angles.

The plastic housing appears to already suffer damage from the cheap manufacturing process. The

bosses used to connect the two housing pieces together are already warped due to the thin plastic material

used to help assemble the part together. Harbour Freight created the housing assuming no costumer would

in fact take the product apart as it is clearly noticeable that the inside has no surface finishing. The

locations of each ejector pin are clearly identifiable along with some remnants of flash around some holes

and sides of the part.

The gear holder shows an attempt to perform some surface finishing. There is evidence of what

used to be a draft angle near its base. There are tool marks throughout the entirety of the top of the base.

There are also tool marks near some of the ribs of the part in what can be assumed as a process made to

remove sink marks near those ribs. The gear holder fails to remove some flash near the slot of the main

gear and that of the motor. It seems that this flash was neglected as it does not interfere with the rotation

of the two gears near the slot. The main gear itself also seems to have neglected flash in the five holes as

it does not seem to interfere with the actual function of the product. This part also contains a lettering

indentation of the number one. It appears to be that a similar product is created alongside the gear holder

in an effort to reduce the overall manufacturing cost of casting.

The L-Bracket, like many other parts from this product contains many sharp edges and is missing

very important draft angles. It is another example of actions made by Harbour Freight to reduce the cost

of the die.

After analyzing the list of parts, there are more bought parts than there are manufactured in house.

By buying many parts in bulk, therefore eliminating to pay for moulds, operating costs and tooling cost,

the cost of the part appears to be reduced as well as reduces the production cost.

In conclusion, the Harbour Freight air compressor is a very cheaply designed product with more

thought put into creating a large profit from selling the parts rather than an engineering aspect and the

effectiveness of the part.

design for manufacturing final projectnatalieferrari.weebly.com/uploads/6/1/3/9/6139829/dfm... ·...

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