Design for Manufacturing Final Project Air Compressor Device Masoud Golshadi Natalie Ferrari Timothy Nash Gregory Feather Spring 2012 Rochester Institute of Technology
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 2
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) 3
3. Bill of Materials The bill of materials (BOM) is indicated as the following table: DFM Project Parts List 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 4
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 29 Purchased Sticker #2 1 30 Purchased Sticker #3 1 5
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. 6
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. 7
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. 8
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. 9
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. 10
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. guidelines. The draft angle on this edge should be 0.9 degrees based on the depth of 0.49" to conform to DFM 11
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. 12
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. 13
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. 14
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 in 3. 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. 15
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 (C dc ) would be as follows: And the cost of trimming (C tr ), using the final number of die openings would be as follows: 16
Using the final number of die openings, the cost of the multicavity die (C dn ) can be calculated as follows: So the cost of the multiaperture trim die (C tn ) is calculated as follows: The total alloy cost (C ta ) would be: And finally, the total cost of making the 500,000 L-shape bracket for the compressor is: 17
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 18
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 19
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 20
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 21
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. 4.2.3. Cost Estimation 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 Die casting machine cycle time = 40 seconds The cost of a single injection mold is $30,000. The material used is Polycarbonate, and you pay $1.75/lb for it. Any material not used in the part itself (e.g. feed system and overflow wells) can be recycled without any 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: 22
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: 23
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 24
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 No Draft on Sides of Base 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 0.13 No Draft b. Problem: Base holes should have fillets entering and exiting hole to reduce stress concentrations i. Solution: Add fillets to sharp edges of hole Sharp Corners 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 25
b. Problem: Base holes should have fillets entering and exiting hole to reduce stress concentrations i. Solution: Add fillets to sharp edges of hole Sharp Corners No Draft 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 t = 0.07 t = 0.03 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 Sharp corners 26
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 t = 0.03 t = 0.07 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. 4.3.3. 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 in 3. 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. Any material not used in the part itself (e.g. feed system and overflow wells) can be recycled without any waste. 27
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 (C dc ) would be as follows: And the cost of trimming (C tr ), using the final number of die openings would be as follows: 28
Using the final number of die openings, the cost of the multicavity die (C dn ) can be calculated as follows: So the cost of the multiaperture trim die (C tn ) is calculated as follows: The total alloy cost (C ta ) would be: And finally, the total cost of making the 500,000 gear holder for the compressor is: 29
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 30
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 subassembly 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. 31
Part or Operation Description No. of Alpha Beta Tool Acquired Handling Handling Insertion Insertion Total Items Symmetry Symmetry Time Code Time Code Time 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 O-Ring Grasp the O-Ring 1 180 0-02 1.88 - - 1.88 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 Plastic Housing 2 Grasp The Plastic Housing 2 1 360 360-30 1.95 - - 1.95 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 Sticker #2 Affix the Sticker to the Plastic Housing 2 1 360 360-33 2.51 31 5 7.51 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 Total Time (seconds) Total Number of Parts 337.7 38 32
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. 33
Part or Operation Description No. of Alpha Beta Tool Acquired Handling Handling Insertion Insertion Total Items Symmetry Symmetry Time Code Time Code Time 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 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 O-Ring Grasp the O-Ring 1 180 0-02 1.88 - - 1.88 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 Plastic Housing 2 Grasp The Plastic Housing 2 1 360 360-30 1.95 - - 1.95 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 2.51 Orientation Operation Rotate the Compressor Assembly 1 - - - - - 98 9 9 Sticker #2 Affix the Sticker to the Plastic Housing 2 1 360 360-33 2.51 30 2 2.51 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 Total Time (seconds) Total Number of Parts 314.14 38 34
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. 35