The Manufacturing Process Design

INTRODUCTION


At first glance, manufacturing of certain products may seem extremely simple. However, the manufacturing process design behind every simple product is fundamentally distinctive and requires the integration of several topics that are related to the processes. The crucial aspects to understand a product involve design, fabrication, assembly, and qualifying results. The designs of current products are very optimized and benefit from today’s innovative technology. The design and the product itself have to be innovative and have a high demand in the market.
The design of any product is an extremely significant step in the manufacturing process. The design stage has three important phases that include conceptual design, embodiment design, and detailed design. The conceptual design phase is where a general list of functions and requirements are determined, which also include the processes and strategies that will be used to manufacture the product. The second phase is the embodiment design that begins at the principle solution and is continued according to the technical and economic criteria. Lastly, the detailed design phase is where design refinement takes place and specifications are created, which include prototypes creation and procurement plans. Moreover, material selection is often studied during the design stage, refer to Figure 1, and each material is selected based on a number of factors including cost, properties, and functionality.

Figure 1. Material Selection at Each Design Stage

The selection of manufacturing processes is a vital phase of the design stage. Choosing the correct manufacturing process for the job means minimizing labour cost, reducing production time, and minimizing materials cost. Also, simplifying the design is a good method to reduce the overall cost and to reduce the number or processes used in order to product the product. However, there are many processes to select from, but selecting the most optimal process for the manufacturing of the various components is the ultimate goal. Casting is one of the important manufacturing processes, it is where a fluid is poured into a mold and then it is cured to obtain the shape of the inner mold. Other simple, essential processes will be used to attain the finished product, which include drilling, bending, and joining.
A pick and place robot is an automation process that is usually used in industrial places to speed up the process of picking parts up and placing them in another location with the purpose of increasing production rate, lowering cost, and increasing the safety of the workplace. The hydraulically controlled ‘pick and place’ robot consists of various parts that allow it to have the capability of gripping objects. The parts include a hydraulic control system, main structure, a gripper, and fasteners. The hydraulic control system uses pressurized hydraulic fluid to power the hydraulic robot; this allows the energy to transfer from flow and pressure. Medical syringes are used as the hydraulic cylinder and clear tubes filled with coloured fluids is be used to guide the control the system. This will allow for the creation of pressure that will operate the hydraulic arm. Additionally, the main structure consists of a base, two rigid bodies (base arm and middle arm), a gripper arm, and a gripper.


OBJECTIVE

The pick and place robot has been designed and fabricated by utilizing a hydraulically controlled system. It includes four control motions, a rotary support base, a set of linkages (two control mechanisms), and a gripper (one control mechanism). The selected raw materials will undergo a number of manufacturing processes in order to product the finished product. The raw materials and manufacturing processes are selected while keeping in mind the importance of cost minimization and optimality.


METHODS & APPROACH

There were a lot of different methods, materials and tools that were used in the hydraulic arm project. The hydraulic arm consists of five main components. The components include the base that holds the arm, the base arm, the middle arm, the gripper arm and the gripper. The process that the team took in order make these components were planned out in a specific way. This approach allowed the hydraulic arm to work correctly. The first objective of this project was to make a prototype of the arm, and to make the arm be able to lift up an object. During this first process of building the prototype, it was realized that a lot of parts of the hydraulic arm needed to be modified. If prototype were not created, the team would have not been able to recognize the modifications that were needed in order to make the hydraulic arm work properly. After this discussion, a brainstorming session took place to discuss many ideas to make the arm as efficient as possible by minimizing costs and resources to be used. The methods and approach that was taken was critical in creating the project.
One of the important aspects to the project are the tools that the team decided to use, which helped with using the proper technique in creating the hydraulic am. There were numerous tools used in the process of creating the hydraulic arm. The tools used throughout this project were very important in creating the arm, which allowed the hydraulic arm to function the way that it does now. One of the tools used was the Mitre Saw (Figure 2). This tool allowed for cuts in a variety of different angles. The Mitre Saw was useful because it allowed for cutting the box for the mold, which similarly allowed for cutting the plastic joints, as well as the plexiglass.

Figure 2: Mitre Saw used to cut the mold box, plexiglass, plastic and wooden joints
Another tool used in this process was the disk grinder (Figure 3). This tool is used mainly for deburring and grinding. This grinding machine is equipped with abrasive-coated disks revolving at a high speed, which allow for accurate deburring and grinding of the work piece. The disk grinder was used to cut all the stainless-steel rods to the sizes that were needed for the hydraulic arm. These stainless-steel arms were used for the middle arm and gripper arm, a very important part in our project (refer to Appendix, Figure 20).

Figure 3: Cut pieces of the metal rods, the above rod is freshly cut with burrs and the bottom rod has been deburred
Another important tool used was silicon glue. The team decided on silicone glue, as it was the best fit for the arm. The silicon glue was used for gluing the base arm and the syringe bracket. This glue allowed for a very fastened fit, and created an adhesive bond between two objects, refer to Appendix Figure 21.
Another tool used in the project was the Drill Press. This tool is a machine that allows for drilling holes into objects. This tool was chosen as it provides a precise hole, which is needed for the arm. These holes that were created permitted our turning methods, which allowed for holes to be made for the joints. It also permitted our joining methods, because this drill endorsed the base arm to fasten to the base. Without these holes, connecting the parts would not be feasible. The drill press also allowed for making holes in the Plexiglass, specifically; a fillet was created for the ball bearing to be laid in (refer to appendix Figure 22 & 23). Additionally, the drill press was used to drill semi-circle holes for the control unit. In addition to the other tools used, M12X1.0 was used bolt and nut. This bolt and nut was used in order to screw down the base arm, which kept the base arm together. This allowed for it to be strongly banded together. Lithium grease was used in order to lube the ball bearing that was later used in the base arm (refer to Appendix Figure 24). This stage was important to allow for the arm to be able to move and rotate. In addition to lithium grease, silicone grease was also used. This silicone grease was used in the approach to lube the joints and gripper shaft. When these joints and gripper shaft are able to move and rotate, which was an important part for the arm to work. The difference between the two greases is that lithium is a metal on metal’ contact grease where silicon grease is best used for all other purposes such as metal on rubber or rubber on rubber contact. Overall, all of these tools were critical when making our hydraulic arm, as it allowed for us to create the arm to fully function the way that it does, and to complete the goal of lifting an object.
The team’s decisions to use certain materials were also under close observation. Using certain materials and tools lead us to the final product, and to allow it to work with the technique it has. Some of the decisions we made about what to use helped us to allow the hydraulic arm to work the way that it does. For example, plexiglass was used because it has many different advantages that other glass does not have. It is shatter resistant, which would make our arm stronger and unable to break as easily as other types of glass. Another example of materials we decided to use was plastic. We originally had planned to use wooden joints, but then the team came to a conclusion that using plastic would be a much better option. Using plastic allowed for the joints to be a lot stronger, since wood has the potential of cracking or breaking. Overall, there were a lot of different decision in our methods and approach, which lead to our final product, a fully functioning hydraulic arm.
SYNTHESIS, ANALYSIS & TESTING
Innovative designs and alternatives are greatly used for various components. Generally, they are not required, however, they bring more engineering and creativity the project. To create a small-scaled replica or alternative of an industrial hydraulic arm, only a few components are required to design. The following are the real parts and alternative components; the assumptions and their contexts for this project.
Hydraulic System
The alternatives for hydraulic cylinders are 10ml plastic medical syringes, which follow the same principle for creating hydraulic pressure. Vinyl tubing will be used for the hydraulic lines, which is exceptional for this project since the hydraulic pressure is low. The fluid in the hydraulic system went under experiment using water or a low viscosity oil. Water is denser than oil, making it optimal for pressurizing. However, this caused the robotic arm to move much more rapidly, perhaps a better approach would be to use oil for a much smoother motion. Various weight of oil was used based on the workload under each syringe. The base and middle arm syringe had to the most workload, so a 20w-50 (motorcycle oil) was use since the viscosity was high enough to maintain a higher pressure. The gripper arm and base rotator used a lightweight 0w-20 (automobile oil), giving them a fast and smooth motion. Finally, the gripper itself also used 10w-40 weight (gear oil) so it has a firm grip on the object it grabs. The different weights of oil played a colour role additionally, having different colour oils made it easier for the user to identify which syringe on the control system to use to control which part of the hydraulic arm.

Figure 4: Control unit with different colour oils
As stated earlier, the gripper arm and base rotator syringe had the same grade of oil, however, to differentiate, the base rotator syringe used old motor (dark brown) oil where the gripper arm used fresh oil (gold colour). Each tube underwent a bleeding procedure to reduce any air bubble in the system; this procedure is critical because air pockets cause an insufficient amount of pressure under operation. An issue surfaced regarding fastening the vinyl tubes and syringes. The syringes had threads for the tubes to fasten in them. The thread’s pitch was fine, however, the thread depth (distance from root to crest) was short. This would cause a loose fit and potential air leaks in the hydraulic system causing the operation to function poorly. To ensure the tubes and syringes was fasten securely, Teflon tape and fuel injector rings (hose clamps) were used on some hydraulic system (refer to Appendix Figure 15).



Main Structure & Gripper

The structure is broken down to 5 main parts, the base that hold the arm, the base arm, the middle arm, the gripper arm and the gripper (Figure 5). The first proposal was to make the structure purely out of plastic; the material is cheap and durable. The second proposal was to use sheet metal as the structure. However, considering the precision, accuracy, and labour, both ideas were too complicated.

One of the main factors to focus on regarding a manufacturing process is the cost. That being said, the structure would have to be made thin and durable to minimize cost. The new idea was to use stainless steel rods and plastic joints for the middle, gripper arm and gripper (Figure 8).

The base arm and base platform are made of polymethyl methacrylate, also known as plexiglass. The rods would require cutting and the joints would be casted; this was an optimal decision of minimizing cost of materials and labour. To cast the joints, a mold would be made for twenty-one pieces all identical and mass produced. The assembly process is much easier when all the joints are identical, this would reduce labour time to assemble the hydraulic arm. The team considered the cost of the silicon mold and tried to minimize the amount of silicon mold used to create the joints. However, a thicker more durable mold was more of a priority, the mold can be used to make multiple casts. After molding, each piece would need to be buffed and cleaned from any imperfections caused in the molding process (figure 6). Aside from the arm structure, the control unit that mounts the other syringes will made of plastic, factoring in ergonomics and mobility, the design will simply be made small enough to fit in the user’s hand.

Figure 6: Joint buffed and ready for drilling
Fasteners


To minimize cost, the hydraulic arm generally used a press fit procedure to fasten to majority of the parts. For this process to work, the holes drilled into the joints and base arm had tight tolerance specs to ensure the steel rods had a snug fit. This idea also makes it easy to disassemble the entire arm. The base arm and the rods that go in between the whole arm structure and joints were fastened by press fit or silicon glue. The base and base arm were fastened using a M10x1.0 bolt, 3 washers, a ball bearing and two nuts, the ball bearing was glued to the base platform to ensure a smooth rotating motion of the hydraulic arm (figure 7). The gripper syringe was secured by grinding slits into two joints and pushing them into the syringe (refer to appendix figure 15).

Figure 7: Base to base arm assembly


As for fastening the arms (base, middle and gripper arm) together the first idea was to use screws and washers. However, to minimize cost, press fit will be used instead. The syringes will be fastened down using zip ties, the idea cannot be too complicated incase the user to needs to perform maintenance or service on the syringe.

Figure 8: Stainless steel rods and plastic joint design
Coatings
The paint job was intended for the joint only, the rods could not be painted since the joint was need to slip onto the rods which could potential peel the paint. The painting process became an issue because the primer and rust paint would not stick to the plastic joint. Theoretically, even after rough sanding each joint, there was an adhesion issue; both coats of paint would not leave an appealing surface finish. The paint was later stripped using Versol (paint thinner). Each joint went through quick a paint-thinning bath because excessive time may have caused damage to the plastic.
The outcome was a red rustic look for each joint, it may have not been a priority choice; however, the joints have some character now (refer to Appendix Figures 16&17).
Design & Calculations
Platform
The platform for the hydraulic robotic arm is measured to a precise length of 470mm. More specifically, the measurement is from the bottom most joint to the top joint just before the gripper. To scale the robotic arm correctly, the length of each arm was divided by a percentage of the platform length. Extra lengths were considered when calculating the arms since the joints would be above and below where they are fastened together on the arms (refer to Appendix Figure 19). For example, the gripper arm of the platform, was approximately 115mm plus 74mm of extra length (Figure 9). The benefit of using rods and joints was that it was easy to adjust the joints to match the platform specifications. If the hydraulic arm was off by a few millimeters, the joints could be adjusted to match specification by sliding the joints around. The following chart summarizes the lengths of each arm for the platform (table 1).
Table 1: Hydraulic arm measurements
Part Percent (%) Length (Joint to Joint) (mm) Extra Length (mm) Total Arm Length (mm)
Base Arm ————– 190 190
Gripper Arm 35 110 79 189
Middle Arm 50 280 10 290
Gripper 15 80 10 90
Total 100 Total Platform Length: 470 159 759

Figure 9: Sketches and measurements of the hydraulic arm structure
Stability
As said previously, the main structure is made of metal rods and the base and base arm are made of plastic. The gripper will be shorter than the main structure and have felt tape so it will be capable of picking up various objects. Another design feature was to keep the center of gravity closer to the base, so the base arms were offset back a few millimeters create arcs instead of linear arms (Figure 8). The gripper arm with have extra material behind it to counter the weight of the gripper and the object the gripper will be holding. The base dimension was determined based on the length of the arms in a cantilever position the result of dimensions is 300mm x 300mm. The base will square shaped extending to half to the structures arm length, which is approximately 172.5mm.
Joints
When experimenting with joints, the design is to have parallel rods when fastening the arms with the plastic joints. Each joint in the design has a purpose, it will either be put in place to hold a syringe or fasten an arm to another arm. Additional joints were added to the bottom of the base, the purpose of this was to elevated the hydraulic arm off the floor so there would be clearance for the bolt holding the hydraulic arm. The joints will also be using as the gripper arms. The dimensions were around 37.5mm by 17.5mm with a tolerance of 0.3mm plus or minus in a rectangular prism shape (Figure 10).

Figure 10: Joints with a width on 17.50mm ± 0.3
Angle Range
The range of angles varies between parts. Based on the measurements and design from the figure above the syringes cause the arms to move to limited lengths. The base is capable of moving left and right 45 degrees. The hinge connecting the base syringe will be positioned an inch away from the arm giving the base a wider range of motion. The middle arm was designed as the “reach” arm for the structure, so a wide range of angles had to be considered. Based on how the hydraulic syringe was positioned, the middle arm can range from 30 to 180 degrees in reference to the ground. Because of this wide range designed for the middle arm, the gripper arm could be simplified to a short angle range from 45-135 degrees.
Gripper
This gripper will have a one arm fixed while the other is capable of opening and closing by sliding within two rods at a range of 70mm. The gripper was a simple design to keep the components from failing later on. The original design had elbow like arms that both open and close, however, through testing, the elbow design was not capable of keep a grip to the object it was holding. With our shaft design, the syringe controlling the gripper would not need to be held constantly since a cumulated force would be exerted on the object once in the grippers grasp (Figure 10).

Figure 11: Gripper with one side free to move along the shaft while the other is fixed to the gripper arm
Control & Hydraulic System
The control system should be easy to understand, comfortable and simple. For ergonomic purposes, the control system will be shaped like a cylinder with the syringes around each other, a mount will be created to integrate them all. This design will be easy to hold in the hand and have extended tubes that go to the robotic arm for mobility reasons (figure 11). The vinyl tubes for the hydraulic system were cut into pieces that will eventually all come the control unit as equal lengths. The gripper arm and gripper had excessive lengths of tubes to ensure clearance and avoid and pinch or bench when the hydraulic arm was in operation.

Figure 12: control system made simple and mobile

RESULTS
The prototype of the first design of the robot was mainly made of steel except that the gripper, which was made of plastic. Theoretically, the gripper of the first design is supported by the gripper arm which was made of two steel plates and the gripper arm again was supported by and the middle arm and the base arm, which were all made of metal plates (Figure 12).
However, the first design had certain disadvantages. For example, the base arm and middle arm of the first design had to be relatively larger than other parts and the base has to be made of steel to increase the weight of the bottom part in order to make the entire robot stable. And as mention earlier, the material used to build the robot was mainly steel (theoretically) which is expensive and as it can be seen from the prototype, most of the material will be spent on base arm and middle arm making the top part heavy. There was a high potential that the robot may fall due to no counter balance in weight, which also made the syringes difficult to control. Furthermore, the first design of the group consists more parts so the group has to do molding for every piece, which is hard to manufacture, and a lot of time would be spent to build the hydraulic arm.
After discussions and considerations, the group changed the overall design and came up with the second design. Figure 13 shows the final design of the second design. Instead of using steel plates, steel rods were used to connect all the parts of the robot with help of plastic as joint conjunctions. Additionally, the gripper was substituted into two steel bars with two plastic joints in the end where the joint pieces can be pushed together to grasp an object using the syringe. One gripper is fixed, while the other moves along the shaft driven by one of the syringes. With this new design, the top part of the robot will not be too heavy because is made of steel bar and plastic pieces and the material spent on the second design is largely reduced. The most important benefit of the second design is it is much easier to manufacture the second design, the manufacturer can mold the same identical joint pieces that are used through the whole assembly, with no unique pieces, this reduced the cost for assembly. The manufacturer just needs to cut steel bars first and drill holes on plastic pieces after casting. In real manufacturing industry, the plastic pieces can be replaced by steel or aluminum to increase stability of the robot.

Figure 14: Final hydraulic arm design
Errors
Errors happened during the manufacturing process. Figure 14 shows the angle of twist on the arm. Bad positioning during the drilling process caused this error to occur. During drilling, some holes on plastic pieces were not drilled dead straight into the piece, a slight angle will offset the rods during the assembly process; the arms cannot be aligned properly with a bad drilled joint piece. The issue could have been resolved by check the alignment of the vice on the drill press, confirm that the vice on the table was leveled.

Another error is that syringe is not a good controller to control the robot because syringe still can’t hold the pressure from the arm while grabbing even though the group has reduced the weight of the arm and the outcome is that the of syringes may pop off under pressure. The solution is that ring clamps are added to the syringes to prevent syringes from popping off.
The second error that occurred was during the coating process. Its possible that the plastic joints have a hydrophobic surface, making it difficult to coat the joints. Once the primer was used, an inconsistent painted surfaced occurred. In theory, the idea was perhaps as long as the entire joint had primer covering the surface the rust paint would have no issue leaving a clean finished coated surface. However, the rust paint has the same issue, this resulted in stripping the paint using paint thinner, which left the joint with a red rustic look. The red rustic look may have not been the choice of texture; however, the outcome gave the joints a unique characteristic.


CONCLUSION

The group faced some struggles before coming up with the second design. The workload of the first design was huge because first design requires a lot of molding, cutting and drilling. The group was worried that the robot may not satisfy the functional requirements when made. It was a very good decision for the group to decide to go with another design, which is much easier to manufacture, and the testing shows the robot of the second design working very well.


The best design is the simplest design that works. During the brainstorming stage, the group was discussing how to make a robot that satisfies functional requirements and also is production friendly at the same time. Finally, the group has come up with a new design that costs less in material and takes less time to manufacture. Despite costs saved from manufacturing time and process, the manufacturer would also save a lot of cost from the material. Therefore, the manufacturer would definitely choose the second design for mass production.
Recommendation from the group is it would be much better if a stronger controller were offered because syringes are weak and cannot hold the pressure from the arm while grabbing. The performance of the robot can be increased by applying stronger controller, which also makes the robot easier to control.
Safety was a big factor in the manufacturing and assembly process; at all time the team wore safety glasses and gloves when operating the disk grinder or drill press. Some safety concerns include students cutting their hands when performing cutting and drilling processes. Because one of the materials for the robot is steel, the group will have to cut steel rods first before the rest of the assembly, however, steel generates spark while cutting. While wear proper safety equipment, the student experienced sparks flying everywhere while cutting the steel rods.
Everyone in the group has put effort into this project and has a deep understanding of how the robot should be designed and made. From this experience, the group has learned to work as a team and help each other with difficult tasks and finally reach the goal together.

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