Master Thesis
Master's Programme in Mechanical Engineering, 60 Credits
IMPROVING THE SURFACE FINISH OF THE RUBBER WEIGHT PLATE
Mechanical Engineering, 15 Credits
Halmstad, 2021-05-28
Joyal Augustine, Steven Simons
Preface
The following study is a result of a master's thesis in mechanical engineering at Halmstad University associated with the HGF rubber factory located in Halmstad during the spring term of 2020. The work aimed to design and fabricate a machine for the improvement of the surface finish of rubber weightlifting plates which is being manufactured in the HGF company. The project helps to gain more knowledge in the mechanical production and development field.
Special thanks to all the professors and experts who have made a significant contribution to the form and completion of this thesis:
Dr. Aron Chibba director and supervisor in the mechanical engineering department at Halmstad University.
Dr. Håkan Petterson professor and examiner of the master program in the mechanical engineering department at Halmstad University.
Moreover, we would like to thank HGF for their willingness to participate in our study and the time they took to provide us profound information in the interviews.
In addition, we want to thank our opponents, fellow students, friends, and families for all their support during our studies.
Abstract
Flash is the unwanted or excess rubber material that presents on the outer surface of the molded rubber product. This will affect the surface finish; it is a cosmetic defect and it can be removed. It forms because of the leak or the excess molded rubber material between the surface of the mold, typically on the parting line, (Jordan Anderson, 2014). The presence of flash will reduce customer satisfaction. There are many methods to remove the flash. The method is selected according to the degree of flash extension and the location where it occurs.
The project aims to design a semi/full automated machine, which helps for having a smooth and fine surface finish of the weight plates. These plates are made up of rubber for the ELEIKO group. The weight plates have different weights from 10 to 20 kg, but the diameter of each plate stays the same, but the thickness will be different for each plate. The machine should be designed that removes all the excess rubber and should smoothen the outer surface of the weight. The purpose of this work is to gain knowledge about different product development methods, respective tools, and techniques that are used. The machine should be user- friendly, should not be complicated, should not damage the workpiece (marks or trace of the blade), should not put the employer in danger, and economically feasible.
This report presents the progress of designing of the product, product development, methods, and literature study. The designed model can construct in the industry for their problem they are faced by the flash. The model is very simple and unique so that everyone can perform the task without any previous experience. Material alternatives were evaluated as well as manufacturing possibilities. The designed machine was the offered for free as means for further research and development.
Keywords: flashing, additive manufacturing, Ullman method, Pugh matrix, rubber weight plates, lever arm, smoothening tool.
Table of Contents
1 Introduction ... 1
1.1 Background ... 1
1.2 Introduction of the client ... 2
1.3 Aim of the study ... 3
1.4 Problem definition ... 4
1.5 Identify tasks and research questions ... 4
1.6 Limitations ... 5
1.7 Study environment ... 5
2 Method ... 6
2.1 Alternative methods ... 6
2.2 Chosen methodology for this project ... 7
2.3 Preparations and data collection ... 8
3 Theoretical Framework ... 10
3.1 Systematic product design ... 10
3.2 Summary of the literature study and state-of-the-art ... 10
3.2.1 Ullman´s product design theory ... 10
Product discovery ... 10
Product definition ... 10
3.3 Chosen topic ... 11
3.3.1 Improving the Surface Finish of Rubber Weight Plate ... 11
3.3.2 Current Method ... 11
3.3.3 Need for a new method ... 14
3.4 CNC ... 15
3.5 Table and working area ... 16
3.6 Motor for spinning the weight ... 16
3.6.1 DC – Motors ... 16
3.6.2 AC Motors ... 17
3.7 Transmissions ... 18
3.8 Gears ... 18
3.9 Belt transmission ... 19
3.10 Lever-spring mechanism ... 19
3.11 Mechanical arm ... 20
3.12 Cutting tool ... 21
iv
3.13 Smoothening tool ... 22
4 RESULTS ... 23
4.1 Conceptual design ... 23
4.2 Product development ... 27
4.3 Product support ... 27
4.4 The final chosen design concept ... 27
4.5 Material Selection ... 34
4.6 3D DESIGN ... 35
5 Conclusion ... 37
6 Critical Review ... 38
6.1 Effect of chosen methodology and tools ... 38
6.2 Ethical Aspects and Standards ... 38
6.3 Environment Aspects ... 38
6.4 Health, Safety and Maintenance Aspects ... 39
6.5 Society/Social Aspects ... 39
6.6 Economy Aspects ... 39
References ... 40
Appendix ... 43
Appendix A: List to choose the right belt ... 43
Appendix B: Generic product development ... 44
Appendix C: Detailed Drawings ... 45
List of Figures
Figure 1-1 Product HGF company manufacture ("HGF”, n.d.) ... 3
Figure 1-2 Unwanted rubber formed on the surface of the workpiece (source: Pictures from HFG) ... 4
Figure 2-1 Flow chart of Ullman method (Ullman, 2017) ... 7
Figure 3-1 Injection mold machine source:( picture from HGF) ... 12
Figure 3-2 A knife that the company using for the flashing process. Source: Picture from HGF company ... 14
Figure 3-3 Mechanical arm follows the straight-line trajectory (Carvalho, 2017) .... 15
Figure 3-4 The basic Fanuc control panel (Mattson, 2009) ... 16
Figure 3-5 Picture of the table from the company. Source: picture from HGF ... 16
Figure 3-6 Gears ... 19
Figure 3-7 Example of belt transmission (Damir,2012) ... 19
Figure 3-8 Basic visualization of the lever-spring mechanism, source: by the authors ... 20
Figure 4-1 Rough diagram of design concept 1 (Source: Made by authors) ... 24
Figure 4-2 Rough diagram of design concept 2 (Source: Made by authors) ... 25
Figure 4-3 Design of the table (Source: Made by authors) ... 26
Figure 4-4 Pugh Matrix for selecting the best conceptual design for removing the flash (Source: Made by authors) ... 26
Figure 4-5 Properties of S235, source: Eurocode ... 29
Figure 4-6 Start/stop scheme with 2 start buttons in Serie (by authors) ... 30
Figure 4-7 visualizing the weight and knife circle in mm (Source: Made by authors) ... 31
Figure 4-8 Starting position of the T-shape (Source: Made by authors)... 32
Figure 4-9 Ball and stem mechanism source (Sotoodeh,2019) ... 33
Figure 4-10 Sliding rail mechanism source:("sliding systems -Heavy duty drawer slides rails", 2018) ... 33
Figure 4-11 Sanding drum source: ("- Lee Valley Tools", n.d.) ... 34
Figure 4-12 3D-Design of the machine (Source: Made by authors) ... 35
Figure 4-13 3D image of the axis (Source: Made by authors) ... 35
Figure 4-14 3D image of the Lever (Source: Made by authors) ... 36
List of Tables Table 2-1 Method overview ... 9
Table 6-1 Cost Overview ... 39
Abbreviations
AB - Aktie Bolag
AC - Motor Alternating Current Motor CAD - Computer Aided Design
CEO - Chief Execution Officer CNC - Computer Numerical Control DC – Motor Direct Current Motor DIN - Deutsches Institute für Normung
DMAIC - Define – Measure – Analyze – Improve – Control DMEDI - Define – Measure – Explore – Develop – Implement ECHA - European Chemical Agency
EU - European Union
FHP - Fractional Horsepower HGF - Halmstads GummiFabrik HPS - HGF Production System HRC - Hardness Rockwell C NC - Numerical Control
PDP - Product Development Process PHR - Parts Per Hundred of Rubber
REACH - Registration – Evaluation – Authorization – Restriction of Chemical
1 Introduction
In modern times everyone lifts weight occasionally. The weights are now not only used for weightlifting but also other gym equipment. People sometimes drop those weights and would like to not damage the ground or other objects. Therefore, people starting to make the weight from other materials than metal. Nowadays most of the weights are made of rubber to keep the damage as low as possible, rubber plates are designed to be dropped so it will protect both the weight plate and the floor to a certain degree of damage, rubber plates are the same diameter across all weight, and iron plates vary in diameter, rubber plates tend to fit more widely on the bar because they get their density from their width, to reduce the manufacturing cost and it can be easily recycled. The company HGF (Halmstad GummiFabrik) is specialized in rubber products like weightlifting plates, horseshoe, floor mats, vibration mufflers, bellows, ergonomic mats, machines mounts, and gaskets. HGF would like to have a smooth and complete surface finish for their weight plates, which means it needs to have a smooth surface finish without any flash sticking out. Through this, they are seeking 100% customer satisfaction, (Ishaq et al., 2014).
At the moment the rubber weightlifting plates, which are produced by the HGF are not having a smooth surface, there is sticking of 0 to 0.5 mm flash out of the surface. This is not ideal and effecting in customer satisfaction so the company HGF wants to change it and needs to have a perfect surface finish for the product. The task of this thesis is to design a machine to get rid of this flash. To design this machine, we will test different methods and materials to cut the flash and smoothen the surface. We will try to make this process as less time-consuming as possible, the next question we will ask ourselves is, should we spin the weight plate manually or use a motor for it.
After this the arm will be the next focus, should we have full control over it or just make a numerical program for the movements? We will talk about all the options and we will compare them and eventually choose the best ones to design the optimal machine for this task.
1.1 Background
In this competitive world today, customer satisfaction is the trump card for an organization to be successful. Our thesis is concentrated on the design and fabrication of machine which can give a better surface finish for the weightlifting rubber plates.
According to (Ishaq et al., 2014) better surface quality will increase customer satisfaction and resulted in the growth of the organization. The surface finish of the rubber plates is a very important factor to be considered. The weight plate should be appeared finished and in good condition so it can be processed to the market/customer for further application.
As part of the master thesis, we got a great opportunity to collaborate our master thesis work with the HGF company, located in Halmstad, they are producing rubber products such as the horseshoe, floor mats, vibration mufflers, bellows, ergonomic mats, machine mounts, gaskets, and weightlifting plates. Here we are going to improve the surface finish of these weight plates by introducing a machine to peel off the excess rubber and then smoothening the surface of the plates. The material used by the company to produce the weight plate is Styrene-butadiene or styrene-butadiene rubber (SBR), (Hempel et al., 2000). This is from the families of synthetic rubbers which are derived from styrene and butadiene. This has good abrasion resistance and aging stability.
According to (Soukup et al., 2019) weight plates are made up of cast iron and rubber material. Weight plate made of rubber is known as bumper plates. These are of different colors, weights, and sizes. The bumper plates were designed mainly for Olympic lifting, where dropping the weight to the floor after lifting will not damage the plates and won't damage the floor also. They are quieter and don’t vibrate as much when they hit the floor. According to (Randolph, 2015) the bumper plates are calibrated, more weight must be lifted it should be more accurate for example if a weight of 200 kg is loaded with calibrated plates on the barbell then the lifter is pretty much on the point. In the case of the thickness of the plate, benefits of calibration are noted who lift heavyweights. But when the plates are thinner, the lifter can load more plates and keeps them close to the center of the bar this will reflect in less bending on the bar and less whip which makes it more stable and safer. Bumper plates are manufactured by pressing the mixture in a mold under high pressure and heat with a two-sided machined plate-like hub sandwiched with aid of a screw bolt on the central hole spline of the plate.
1.2 Introduction of the client
We start our master thesis at HGF company which is in Halmstad Sweden. HGF (Halmstads Gummifabrik) is a very successful and developing manufacture, they are specialized in molded products made of rubber and thermoplastic elastomers (TPE).
HFG was founded in 1947, it is an under Swedish corporation. The headquarter of the company is in Halmstad, by mid of 2000, the company builds its second production unit in Latvia. In May 2016, HGF becomes a strong partner to customers in sectors like automotive, mining, and energy industries have also taken a step by switching to the Jeevasenterprise resource planning system. In this year they had revenue of 17 million euros. The company focused more on lean manufacturing and launched the HGF Production System (HPS), based on lean production principles. HGF is an organization which has characterized by a strong will to innovate and the ambition to
continuously improve extends to administrative processes. Today HGF operates in six business areas, which are Automotive, Industrial Products, Marine and Offshore, Mining and Construction, Sealing, and Sports. HGF was awarded the Hollandsk prize in 2009, second place in the “Swedish Lean Prize" in 2011, or the "Honda Excellent Overall Performance" price in 2015. The current CEO of HGF is Christian and our Industrial supervisor is Jakob Frank. All the employers were supportive and cooperative with us throughout the journey. They provided all the necessary data for our work and suggested their valuable ideas to us, (Gummifabrik, 2021).
Figure 1-1 Product HGF company manufacture (Gummifabrik, 2021)
1.3 Aim of the study
The project aims to design a semi/fully automated machine, which helps for having a smooth and fine surface finish of the weight plates. These plates are made up of rubber for the ELEIKO group. The weight plates have different weights from 10 to 20 kg, but the diameter of each plate stays the same, but the thickness will be different for each plate. The machine should be designed that removes all the excess rubber and should smoothen the outer surface of the weight. The purpose of this work is to gain knowledge about different product development methods, respective tools, and techniques that are used. The machine should be user-friendly, should not be complicated, should not damage the workpiece (marks or trace of the blade), should not put the employer in danger, and economically friendly.
The following steps considered as goals: Calculating the distance between the CenterPoint of the weight plate to the axis of the lever. Selecting the correct material and position for the blade. Selecting the proper tool for smoothening the surface.
Estimating the rotation speed for the motor. Design the entire system.
1.4 Problem definition
HGF operates in six business areas, which are Automotive, Industrial Products, Marine and Offshore, Mining and Construction, Sealing, and Sports. In which for the sports field they are manufacturing weightlifting rubber plates or bumper plates. As we have mentioned above in the background section the mixture of rubber is pressed in a mold, under high pressure and heat with a two-sided machined plate-like hub sandwiched with aid of a screw bolt on the central hole spline of the plate. While the rubber mixture is pressed, excessive rubber will appear on the surface of the weight plate. Currently, the operator must peel off the unwanted rubber around the plate with a knife manually and smoothen the surface with the same rubber material. The operator is very careful while peeling off to avoid the overcut of rubber and to avoid marks of the knife over the surface.
Figure 1-2 Unwanted rubber formed on the surface of the workpiece (picture from HGF)
Even a small overcut or mark of the knife will make the workpiece rejected. Since the operator must carry out two actions at the same time (rotating the plate manually and controlling the knife carefully) with a lot of concentration it is consuming a lot of time for this task. Even after the careful operation of removing unwanted rubber and smoothening also there will be a remaining 0.5 mm excessive rubber around the plate. In this competitive world customer satisfaction have a big role in the growth of the organization, (Yang and Li, 2018).
1.5 Identify tasks and research questions
The thesis is prepared by two persons as the authors and the mission was to answer the below-mentioned questions: How do we make the surface as smooth as possible?
How do we make the process as fast as possible? Should we use a motor to spin the weight? Should the employer have full control over the cutting tool?
1.6 Limitations
Every work has its limitation, for performing this work also there were certain limitations. The designing of the machine should not be complicated, the company required a very simple operation for the performance. The machine should be economically feasible to the company and it should work under different environmental conditions. The size and shape of the machine should be small since the tablespace for the operation is limited. The tools for operating should not disturb the operator for performing other tasks. Designing and positioning of the tools were very important that the workpiece should not get damaged by any overcut or marks of the tools. The company doesn’t wish to spend more time and money on the maintains of the machine so the mechanism should not be complex. Limitation for performing some practical tests was also troubling us during the thesis period.
1.7 Study environment
All the work related to our thesis is done by the following study environment:
Through Halmstad University, Microsoft teams, zoom meeting but mostly email communication between thesis writers, the supervisor in mechanical engineering faculty at Halmstad University, assistant CEO and production manager at HGF Group - AB Halmstads Gummifabrik. The literature resources were from the university library, there were also interviews between the thesis authors and the assistant CEO or CEO of the AB Halmstads Gummifabrik in the factory.
2 Method
2.1 Alternative methods
For product development many methods are being used all around the world some examples are Ulrich and Eppinger's product development process, Iterative process model Fredy Olsson´s, morphological chart, six sigma.
Ulrich and Eppinger is a product development process (PDP), to manage such processes, the company that does the PDP needs to set up a project team with a project leader. This team needs to have people with different skills, most of the time those people are from different departments of the company. It is important to have people with different skills to have a solution for every problem. The function in an organization can be defined by an area of responsibility, generally by specialized education or experience, (Eppinger and Ulrich, 2011). The Ulrich and Eppinger method is mostly focused on incremental improvements, this method will not be used for our thesis because a whole new product is getting designed. In appendix B a visualization of the steps is given.
According to (Alfonso and Botia, 2005) the iterative process model will refine a product by applying cycles of adjustment, each cycle will make the product better until the product reaches the specification that is needed. The base steps in this cycle are planning, design, implementation, testing, and a new cycle.
A Morphological chart is a visual method, which is very simple. At first, the product gets split into smaller chunks. These chunks can then be used to analyze and ideated independently. According to (Huang and Mak, 1999) this is done by defining the main product function as clearly as possible, the possible tasks and subtasks that are needed to tackle the design problem get identified. The tasks and subtasks get written down within a matrix. In the columns of the matrix are the tasks, in the rows are the components that can explain the tasks. Now a chart can be drawn where all the possible solutions are in, this is the morphological chart. According to (Asyraf et al., 2019) it represents the total solution space of the product, made up of combinations of subtasks According to Evans (2018), six sigma is a statical data-driven methodology to eliminate defects from a process. There are different approaches to this methodology.
DMAIC (Define, Measure, Analyze, Improve, Control) is a method that is used if a product is underperforming or needs to be improved. The methodology is mostly used in manufacturing processes where there are automated processes that can be measured very easily. DMEDI (Define, Measure, Explore, Develop, Implement) is a method that is used when a new product or process gets designed.
2.2 Chosen methodology for this project
After considering all the various available options, we decided to follow the David Ullman method and other basic methodologies such as literature review, observation, pugh matrix, and interviews.
Ullman product development is creating a product with new and various characteristics that provides extra benefits to the consumers. This includes the up- gradation of an existing product or its formulation of a different product that satisfies the market niche or the customers. Ullman's method consists of six phases: Product discovery, Project planning, Product definition, conceptual design, Product development, and Product support, (Ullman, 2017)
Figure 2-1Flow chart of Ullman method (Ullman, 2017)
The literature review had an important part in preparing the theoretical framework. It was the initial startup for any research. We have gone through and collected valid information from various books, documents, literature, reports, web pages, articles, graphs, videos, journals, zoom meetings, and calls. Literature regarding automotive machines, CNC machining, and molding systems has been gone through as well as the mode of operation, fields, and similar applications also. In this, we added the information we noticed from the organization while performing the task and we reviewed the procedures and current method they are using. Through proper observation, we were able to collect accurate information about people, their tasks, wishes, needs, and other problem which they are facing during the operation.
Observation includes information like action or process, picking out important
elements, focusing on significant details, and filtering out the rest of the information and purpose of arriving at an accurate judgment. According to (Ross, 2018), the observation method is not only passively looking and listening. It needs careful, conscious, and purposeful effort.
Pugh matrix method makes a comparison between concepts and helps to decide which potential solution is better than others. This is a type of qualitative technique, in this method, a matrix table is created that ranks concepts based on the comparison between potential designs. All the designs against our design criteria are scored and show the evaluation grade. and the total of this will show the appropriate selection, (Cervone, 2009). Pugh matrix helps in developing an optimal solution that can be a hybrid of other solutions.
Our company supervisor was very cooperative and supportive. He guides us through the proper channel which helps us to understand more about the company, product, problem, and what they needed. The supervisor also provided the details about the raw material and procedure they are following for manufacturing the product. He arranged a couple of meetings with the CEO as well as with the operators, so we were able to gather more information and understand their wishes and ultimate goals.
2.3 Preparations and data collection
For this research paper, we use different methods to collect the data, this is known to be triangulation. Triangulation is also viewed as a qualitative research method to check the validity through comparing the data from various sources. This includes interviews with the worker of the factory and supervisor, observation of the HGF workplace, and field notes we took when we observed the machinery. By recording the data these all come under interview. We have visited the company 12 times, 4 interviews with the supervisor, 2 interviews with workers, and 1 half time and 1 final presentation before the CEO of the company. In observation the physical settings, social environment, how workers and other staff interact with the working environment, the pattern for decision making. Field notes are done as soon as after the observation it also helps to give confirmations of findings and different perspectives of view for the same data collected from a different source, (Andrea j, 2020).
Here we used a mixture of the Ullman method with various other methods mentioned above. By collaborating with these methods, we were able to complete the work very effectively that meets all the criteria we needed. Table 2-1gives an overview of the methods we are using.
Table 2-1Method overview
3 Theoretical Framework
3.1 Systematic product design
Here we are following Ullman methodology which is the accurate tool that can be used for every stage, it is well known for practical application in different levels. Which considers customer satisfaction along with promoting creativity and conceptualization. Project itemization should be clear before any development of the product. Proper planning, identifying the underlying customers, functional concepts.
optimal concepts, testing, and evaluating according to development needs and possible responsibility after the product is introduced in form use and assembly. These all are the criteria below Ullman's methodology, (Ullman, 2010).
3.2 Summary of the literature study and state-of-the-art 3.2.1 Ullman´s product design theory
Product discovery
Product discovery is the initial and milestone step of Ullman's method. In this stage, we were able to know the technological push along with market pull for the product and determining the changes in between the potential project and their objectives. For the past many years, all the industries are focusing more on the technology push and improving their technology. Better technology brings better production, more customer satisfaction, ease to use, and more profit. In this case, the company is trying to increase customer satisfaction by providing better quality products to the consumers. For that, they are improving the current technologies they have, (Herstatt and Lettl, 2004). Improvement in technology in the aspect of finding an optimizing solution, higher quality, and quantity rate in the product, and better working environment for the operators. Here, the company wishes to bring a technology update for having a better surface for the workpiece. The current method they are using is not providing a 100% result in the operation and even the operators are under stress while performing the task. The market push for the product will be high because the companies now are in a competitive world, therefore the organization knows that’s better the quality more customer satisfaction. These all are the reasons behind the development of the product. The product will provide a better surface finish to the workpiece that will make customers more satisfied and increase the business for the organization. The assembly parts of the product are available in the market and even for many maintenances, it will be quite easy for the organization to do it.
Product definition
Our product is a semi-automated machine for peeling the flash around the rubber weightlifting plates which can be manually controlled by the operator. It can remove
all the unwanted rubber around the product as well as it can smoothen the surface for a better surface finish. It is constructed in a way that is kind to the environment. The machine is easy to use, move, assemble, and store. The product is designed according to relevant regulations and requirements of the company and the operator. The major risk faced by the company is the rejection of the workpiece due to the overcut of the blade and unfinished surface smoothening. Our newly designed product will solve this bygiving a smooth surface finish without any trace of blade marks. All the components using for the manufacturing of this product are available on market. The operator will be stress-free while operating the task. Since the mechanism using here is a lever spring the operator will have whole control over the movement of the arms. The weight plates are spins at minimum rpm which helps the operator to watch the entire process closely. By implementing our product, the company can achieve its goals in a much more effective manner.
3.3 Chosen topic
3.3.1 Improving the Surface Finish of Rubber Weight Plate
At the moment the rubber weightlifting plates, which are produced by the HGF are not having a smooth surface, there is sticking of 0 to 0.5 mm flash out of the surface. This is not ideal and effecting in customer satisfaction so the company HGF wants to change it and needs to have a perfect surface finish for the product. surface quality will increase customer satisfaction and resulted in the growth of the organization. The surface finish of the rubber plates is a very important factor to be considered. The weight plate should be appeared finished and in good condition so it can be processed to the market/customer for further application.
3.3.2 Current Method
The weightlifting plates are one of the know implementations used in resistance exercises. The variation in these is depended on the performance of training programs. Rubber weight plates are commonly using for heavyweight competition for the Olympics, (Chiu, 2010).
Figure 3-1Injection mold machine source:( picture from HGF)
The rubber weight plates are melded by applying heat and pressure to uncured rubber material. This will induce the vulcanization of the compound and forms the shape.
There are mainly 3 types of molding processes – compression, transfer, and injection molding. Here the company is using an injection molding machine. This is the most significant process of comparing with others. This can perform automatically therefore the need for an operator can be reduced. The rubber will be directly fed into the injection section. It will then undergo the heating and plasticizes process.
Using runners and gates the heated rubber mold will flow into the cavity, once it is fully vulcanized the mouth opens and eject the product, (Lindsay, 2000).
The material used by the company to produce the weight plate is Styrene-butadiene or styrene-butadiene rubber (SBR). This is from the families of synthetic rubbers which are derived from styrene and butadiene. This has good abrasion resistance and aging stability, (Ciesielski, 1999). The temperature at which the machine operates will also a crucial role in the process. The cure time and the degree of inversion are crosslinked. The poor conductivity of the heat on the rubber compound is the reason for this. It is very important to exercise very tight control. The mold should be between +2 or -2 C of the experimentally determined optimum operating temperature.
The aim is always to attain 90-100% crosslinking of rubber, (Lindsay, 2012).
The quality of the product should be checked before and after the process. Quality
control and process control have a similar objective, it has been a concern with the setting of standards for every level of manufacturing of the product. Microprocessors can perform sophisticated analyses of product quality. According to (Bhowmick, 1994) the quality of raw material used, degree of control, and the testing method are the three major factors that determine the efficiency of the finished product. Flash is the unwanted or excess rubber material that presents on the outer surface of the molded rubber product. This will affect the surface finish; it is a cosmetic defect and it can be removed. It forms because of the leak or the excess molded rubber material between the surface of the mold, typically on the parting line, (Jordan Anderson, 2014). The presence of flash will reduce customer satisfaction. There are many methods to remove the flash. The method is selected according to the degree of flash extension and the location.
According to (Bertolotti and Secchi, 2000) there are several flashes removing methods such as:
Buffing - A moving abrasive material is used to the rubber part to remove excess rubber by abrasive action.
Die Trim - A cutting tool, can be done with a hand or machine-mounted die. A force is applied perpendicular to the flash extension. This creates a shearing that removing the excess flash.
Machine Trim - The rubber part is passed through machine-mounted rotating or reciprocating cutting tools.
Tumble Trim - A rotating barrel in which the heavier rubber sections strike the thinner and more fragile flash breaks.
Hand Trim- Flash is removed by using hand tools such as knives, scissors, razor blades, or skiving knives.
Mechanical Deflashing – by the support of suitable mechanism and machines a deflashing equipment is created and completing the task
Here the company is using the hand trim method where they use knives for removing the flash around the rubber weight plate.
Trimming the flash is the most traditional method. The operator removes the excessive rubber by using a knife or any other cutting tool along the outside of the rubber product. The operator should be extremely high proficient to control the weight plate and tool.
This deflashing method doesn't need any high investment but the chance of error, accuracy, overcut, and damaging workpiece is high, (Spooner, 1984).
The surface of the product will have a more surface finish when it undergoes the smoothening process. Smoothening can be done by a different method. It depends on the material which is to be smoothened. The frictional method is the most common method for this process,(Persson and Volokitin, 2006).
Figure 3-2 A knife that the company using for the flashing process. Source: Picture from HGF company
3.3.3 Need for a new method
HGF wishes to have a new method for removing the flash to avoid the rejection of product due to overcut and marks happen while peeling off the flash manually and through this, they need to increase customer satisfaction. Our method was simple and more effective than the current version. Our designed product is a unique and simple mechanism which will help the operator for better performance as well as to helps the company to achieve their goals. HGF is very much concerned about customer satisfaction, (Gummifabrik, 2021).
The company needs us to design a fully automated / semi-automated machine that removes the flash around the weight plate. According to (Balaji and Allen, 2018), the automated machine serves as a link between different stages of expertise when designing the product and expedites the data science process. Many techniques are considered to address this.
HGF is using is Styrene-butadiene or styrene-butadiene rubber (SBR) as the raw material for manufacturing the weight plate. They are producing different weights like 10, 15, 20 kg but all the plates have the same diameter with different thicknesses.
The company is using SBR because it is the highest volume synthetic elastomer produced worldwide. There are generally marketed at low viscosity, it doesn't need any chemical peptizing. The composites were created by the incorporation of80 phr (parts per hundred of rubber) of devulcanized SBR-r, (Shan et al., 2011).
Removing flash from a product is well-known trouble in industry, there are various solutions for this been developed. The most common method to remove flash is manual deflashing. Our company is also following the same method. Manually the operator will remove the flash around the weight plate with a knife. This process is more operator-intensive.
Moreover, using sharp knives by the operator is hazardous to the operator as well as the chance of overcutting and damaging the workpiece is high, (Danchine and Musumur, 2000). Because of this, the company needs a newly designed product for taking over this task. For accomplishing the task of deflashing there are several methods, among the most advanced and simple versions is CNC machining. With the interviewing with the operator, he also suggested having a CNC program for the task, so it would be easier for them to finish the task quickly and safely. We have done some research work on the possibility of CNC machining in the company
3.4 CNC
One of the methods was implementing a computer program for operating the task.
The computation of derivatives in CNC programming can be divided into four:
Manually working and coding, Numerical differentiation, Symbolic differentiation, and Automatic differentiation, (Baydin et al., 2018). A machine that operates under a computerized numerical control system is commonly called a CNC machine. In other term, the machine tool is the body, the control unit act as the brain and its nerve center, (Smid, 2003) (Smid, 2003).
The movements controlled by the CNC program are very crucial. It needs the trajectory interpolators to determine the path between the marked points. Task programs in the mechanical arm provide the endpoint of the segments along the contour. Both NC and CNC machines are capable of linear and circular interpolation.
The principle behind this is relatively simple. The axes of motion of the mechanical arm will be perpendicular to each other, which will create a cartesian coordinate system, (Carvalho, 2017).
Figure 3-3 Mechanical arm follows the straight-line trajectory, (Carvalho, 2017)
According to (Smid, 2005), the operators can add their operation panel, with all the basic required switches and buttons to operate the CNC machine and its features.
Another component is the display screen, they are available to CNC programmers and used for the setup and to control the activities of the machine.
Figure 3-4 The basic Fanuc control panel (Mattson, 2009)
3.5 Table and working area
The table in the company is irreplaceable. It is also a punching machine for putting holes in the weight plates. The working area is limited so we must build over design in combining with this table. The dimension of the table is 0.45 x 0.9 m. we had to design our product within this limited space.
Figure 3-5 Picture of the table from the company. Source: picture from HGF
3.6 Motor for spinning the weight
For spinning the weight plate, a motor is installed under the table. The motor needs to spin the weight with a low RPM, but it needs to withstand some torque because there will be some cutting involved. There are a lot of different motors with different properties. Different motors will be discussed below.
3.6.1 DC – Motors
In DC motors, the effect of a magnetic field on current-carrying conductors is used to
convert electrical energy into mechanical energy. This effect is based on the Lorentz force that a current-carrying conductor experiences in a magnetic field. The operation of this motor is based on an alternating magnetic field. The direction of the magnetic field is therefore constantly changed mechanically in the motor with the aid of the commutator, or electronically in a brushless electric motor. The most important feature of the DC motor is that the rotation speed can be easily controlled. This makes such a motor particularly suitable for adjustable, (French and Widden, 2000).
DC-Motors are used everywhere in the industrial sector, from robotics to automobiles, they can be small or medium-sized, it all depends on the applications.
Because these motors have a wide variety of applications, there are various types of DC motors.
Permanent Magnet motor
This is a direct drive motor that directly drives the application.
Series motor
In this motor, the excitation coil is in series with the armature winding. This series winding is made up of turns of thick copper wire
Shunt motor
The permanent magnetic field of the stator is obtained by a winding that is parallel across the armature winding. The field winding is thus also supplied by the source voltage.
Compound motor
The compound motor is a combination of the series motor and the shunt motor. The best properties of both motors are combined into one.
3.6.2 AC Motors
An AC-Motor is an electric motor that is connected to an AC voltage, usually a three- phase voltage, but this can also be single-phase. Both types work with a rotating field and are therefore also called rotating field motors. This is usually accomplished by applying a three-phase electrical voltage and/or current shifter by 120° to a three- phase winding. With single-phase AC-Motors, the rotating field is generated in the motor itself, often in combination with coils or capacitors. The speeds of this kind of motors are directly proportional to the frequency of the applied voltage and are therefore fixed. This depends on the number of pole pairs and is always a multiple of the mains frequency 50 Hz, this is for most countries but in the US, this is 60 Hz.
Synchronous motor
The Synchronous motor is a three-phase electric motor. In contrast to the three-phase asynchronous motor. The synchronous motor is most used as a generator in the power grid.
Asynchronous motor
Unlike the synchronous motor, the rotational speed of the rotor lags that of the stator.
Because of this difference in speed, this is called an asynchronous motor.
3.7 Transmissions
Transmission is the collective name of the different techniques for transferring and converting power. A machine requires certain speeds, forces, or torques that will deviate from the speed and torque of the drive motor. That is the reason why a transmission must be used between the drive motor and the implement. The four main transmission groups mechanical, hydraulic, pneumatic, and electrical transmissions.
In this project, only mechanical transmission is used like gears and belt transmission.
3.8 Gears
Gear transmission consists of at least two gears. This transmission is not suitable for transmission over long distances, because the transmission distance is the sum of the radius of the two gears, but it’s suitable for transforming motion because it can have two gears with very different diameters without any problem. The formula for calculating the speeds of the gears is Z1 x n1 = Z2 x n2 with Z1 and Z2 the number of teeth on the first and second gear, n1 and n2 the rotation speed of the first and second gear in RPMAs said by Damir in 2015 the gears turn in the opposite direction.
If you want the first gear to be in the same direction as the second gear, an intermediate gear needs to be placed between the two gears. This intermediate gear does not change the speeds of the first and second gear.
3.9 Belt transmission
Figure 3-6 Gears(by the authors)
The belt transmission consists of two parallel shafts on which pulleys are mounted.
These two discs are connected by a belt. If the discs have the same diameter, they rotate at the same speed. If the diameters are not the same, they have different speeds.
The speeds can be calculated using the following formula: D1 x n1 = D2 x n2 with:
D1 and D2 the diameter of the first and second pulley in meters, n1and n2 the rotation speed of the first and second pulley in RPM. Both pulleys rotate in the same direction, this means if the first pulleys rotate clockwise, the second pulley will also rotate clockwise.As reported by Bucchi and Frendo (2020) This transmission technique is very useful if the transmission distance is high.
Figure 3-7 Example of belt transmission (by the authors)
3.10 Lever-spring mechanism
A mechanism is any device capable of changing the size, direction, or type of movement of force. To control this mechanism there needs to be some energy, this will be an operator controlling the arm. The result of these movements will be the movement of the mechanical arm, (French and Widden, 2000).
Figure 3-8 Basic visualization of the lever-spring mechanism, source: by the authors
Input: Employer pulling down the lever.
Process: Lever-spring mechanism + connection between arm and lever.
Output: Movement of the arm.
On the left picture, there is a lever with a spring that connects the lever with a fixed point. This will make the lever go back to its initial position if there is no more force applied to it. When a worker wants to move the arm, he needs to pull the lever, he applies a force on it, this force is F worker. When the lever is not in its starting position there also will be a force in the opposite direction of the F worker, the force of the spring, to keep the arm moving to the weight the worker needs to apply more force than the spring.
F worker > F spring (The lever is getting pulled down) The arm will move to the weight.
F worker = F spring (The lever stays in the same position) the arm will stay in position.
F worker < F spring (The lever goes back up)The arm will move back to its initial position.
These statements only hold if the frictional forces in the shaft are ignored, these will be low so these can be ignored.
3.11 Mechanical arm
For acting trimming and smoothening mechanical/ robotic arms are used. It is very important that the motion control portion of a mechanical arm control system, and the kinds of computations/ mechanism it needs to perform. The motion of the arm is caused by a series of links that are connected by one degree of free joints and the force
applied to these joints will make the arms move, (Waters, 1979). Coordinate transformation, trajectory calculation, and force calculation are three main sectors for the movement of arms. The targeted surface boundary is the desired outer surface boundary after the removal task completion and is contained within the volume enveloped by the initial surface boundary. According to (Kaljaca et al., 2020) the planned trajectory area will allow the cutting tool connected to the mechanical arm to remove the flash around the plate.
Since the diameter of all the plates is the same, fixing of arm axis is simple. The cutting tool is mounted to the mechanical arm, the arms are equipped with a compliance device (depend upon the solution using) for generating the required force between the cutting tool and peripheral surface of the weight plate. As the mechanical arm manipulates the blades, constant force should be maintained between the cutting blades and part to ensure consistent removal of flash around the entire surface of the plate, (Danchine and Musumur, 2000). The linking, connectors, and joints of arms are beneath the table. Therefore, it will not disturb the operator who is performing the task.
3.12 Cutting tool
The mechanical arm relates to a cutting tool with a sharp edge blade for the trimming process. A region of the blade is endowed with moving arms that are designed to peel off the flash. There exist different kinds of commercial deflashing tools. The most common example is hand‐held scissors, (Bosch et al., 1990). Since all the weight plate has the same diameter there is only one prefixed position and a single cutting direction. In any rubber flashing process, the blade accomplishes the removal of flash by overcoming the shear strength of the workpiece material that is Styrene-butadiene or styrene-butadiene rubber (SBR). Speed, feed rate, and force are the other parameters that affect the loading on the tool. As stated by (O’Sullivan and Cotterell, 2001) the total work done by the tool in trimming the flash can be calculated from the value of force components on the cutting tool. According to (Enomoto and Sugihara, 2010) the properties of the cutting tool can be defined by their geometry, mechanical features of the material, the properties of the surface. The material of the blade should have a high strength to mass ratio and high corrosion resistance. Cutting the flash with a handheld knife is a risky business, the operator should be skilled and must concentrate deeply on the performance. Modern technologies can be used instead of this to avoid damage. Most commonly all industries use loop knives for the deflashing process. It is very quick and safe, and it is manufactured with high-carbon steel blades. The CNC machine used codes created by the CAD graphical input will control the movements of the oscillating mechanical arm with the tool, (Grover and Group, 2004). Before 1870, Most of the tooling material was manufactured from plain
carbon steel which has low ‘hot hardness. These cutting blades will break at the edge after using a while. From the swiss watch research institute coating on the cutting tool was originated by using the chemical vapor deposition technique. The relation between strength, fracture toughness, wear rate, and contact pressure will determine the complete range of cutting tool material, (Smith, 2008).
The selection of knife blades has a crucial role in the flashing process. Factors like blade serration and insert a connection to the handle should be taken into count while selecting the blade. Blade serrations will allow the knife to remove the flash easier than a straight-edged knife. With all these ideas, the blade was selected based on function and cost (Sarris, n.d. 2005).
3.13 Smoothening tool
Even after clearing the flash from the outer surface of the weight plate by using a cutting tool, there will be a stick out of flash along the part line, by using different techniques and equipment to smoothen a surface of any material for better surface finish then that process is known as smoothening process, (Bosch et al., 1990). There are different types of the smoothening process each depends on the material where smoothening take place. Mechanical devices and tools are also used for smoothening the surface, even though in most precise dies will also result in some flashing. The product will be trimmed and polished, but generally, these finishing procedures are done by hand, this is time-consuming work as well as imprecise, so the smoothening process may not result in a completely clear smooth surface. According to (Nelson, 1992) the removal of these remaining small and irregular flash can be done by using some effective methods. As stated by (Lubenow, 1946) another method using for smoothening the surface is to use the same rubber material that cooled to a temperature at which they become hard when they are hard enough and the workpiece is hot while polishing with that piece will remove the flash aby agitating or tumbling in an inert liquid. Nowadays industries are using medium grit sandpapers for smoothening the rubber part. This technique is more effective and less time- consuming and provides a better surface finish to the workpiece. Using sanders for smoothening is an upgraded version of this method. Selecting grit for the sandpaper is very important, for rubber product medium grit (50-600) sandpaper is the best choice (Palija et al., 2019).
4 RESULTS
4.1 Conceptual design
In this section, our different concept process is being discussed. Based on the existing process that was followed by the company we were able to develop our new product for performing the flashing process. There any different concepts that could have been used such as thread cutting, knife cutting, rubber adhesion, heating thin wire peeling, (Roberts, 1979). Some concepts are eliminated because of the space limitation and other requirements of the company. The company needs a simple operating product that removes all the flash around the weight plate without leaving any marks on the workpiece within the limited space. The main aim of this design is to have a better surface, reduce workload and increase customer satisfaction. Using Catia, Autodesk Inventor, Sim Solid, and solid work software we designed multiple concepts of the product. Many factors are analyzed indeed which are important here which help us to develop an initial idea into a design the machine design is to find out the most reliable, maintenance-free, simple operating mechanism, (Kroll et al., 2001). Initially, we have some ideas about the product what the company required, a semi/fully automated machine that removes all the flash around the outer surface of the workpiece. Different designs we developed are later companies together and reach the final product.
Conceptual design for a product mechanism is a mixture of art and science based on the various designs, needs, and ideas of a designer, (Chiou and Sridhar, 1999). The following 3 concepts are the designs we generated and through the Pugh matrix we sort out the most suitable among them.
Design concept 1
After completing the molding process the operator will take the weight plate from the machine and placed it over a cylinder conical spindle structure which is fixed over the table, this conical structure acts as guidance for the plates for easy entering. The operator has suggested spinning the weight plates manually. A computer numerical program will be developed, the option in the touch screen will activate the mechanical arm with the U-shaped tool at its tip, one has a cutting device and other have a smoothening tool, these arms are positioned like a minute hand and hour hand of a clock (cutting tool followed by a smoothening tool). When the worker is ready, he can click on the start button on the screen then the arms will turn towards the weight plate and stops at the point where the sharp surface of the cutting tool exactly touches the outer surface of the workpiece. Since the CenterPoint and the diameter of all the weight plates are the same it is possible to position the cutting blade to the exact point where only the unwanted rubber gets trimmed. The plates are manually rotated in the opposite direction of sharp edges of the blade so the flash that is projected on the outer surface of the plates will start to get the flash off. Once he is satisfied then he
can press the next button on the screen and arms again start to rotate and the smoothening tool will come in the position of the cutting tool and will do the same process and start smoothing the remaining surface. The chance of overcutting is zero here because all the weight plates have the same diameter. Once the operator finishes both tasks (peeling and smoothening) he can click on the finish button that will retain the mechanical arm to its initial position. The operator is free while performing this and will get a smooth and clean surface finished workpiece. The total process will take a time of 4 to 5 minutes.
Figure 4-1 Rough diagram of design concept 1 (Source: Made by authors)
Design concept 2
In the second concept after molding process, the worker will take the weight plate and placed it on a cylinder conical spindle which is fixed on the table, this conical structure acts as guidance for the plates for easy entering. Here the spindle will be spinning by a motor placed under the table at low speed, so the operator doesn’t have to spin the weight plate manually. The speed of the motor will be adjusted accordingly. On the right side of the table, there will be a lever with a button at its tip. lever relates to a mechanical arm that has the cutting smoothening tool. when the operator applying pressure on the lever downwards, with help of gears attached, the arm will turn in the direction of the weight plate and reach the exact point where the blade touches the workpiece.
As we mentioned above the CenterPoint and diameter of all the weight plates are the same, the positioning of the blade will be accurate. This mechanism will give the operator good control over the movement of mechanical arms. Now the operator can start the motor which spins the workpiece in the opposite direction of the sharp edge blade. As the blades are in exact position all the flash will start to get the peel off.
Since all the workpieces have the same diameter, we can easily fix the axis for the mechanical arm. When he is satisfied with the trimming, he can switch the tool by pressing the button over the tip of the lever and start smoothening the surface. After both processes are completed, now the operator can release the pressure over the lever, the spring attached to the lever retains the lever to its initial position that will
