ROLD

Teachers: Mario Guagliano, Amir Ardeshiri Lordejani Rold product innovation engineer: Dennis Ilare

2023

METHODS FOR ENGINEERING DESIGN REPORT - ROLD COMPANY PROJECT

Group 1

Sam Twarog 10948747

Chloé Descombes 10947339

Hong Peng 10899234

1 Introduction

1.1. Rold Company guidelines

1 2 Management tools

2 Design for X

2.1. Sensing design: comparison and selection

2.2. Product design: comparison and selection

3. Design for Manufacturing

3 1 Material selection

3.2. Bill Of Materials (BOM)

3 3 Injection molding calculations

3.4. Injection molding design guidelines

3.5. Table drivers of complexity

4. Design for Assembly

4 1 Reducing parts

4.2. Define the steps and use the classification system

4 2 Table of Efficiency Assembly

4.3. Selection of plastic joint: snap-fit system

5 Design for Environment

5.1. Identification of potential environmental impacts

5 2 Life Cycle Assessment

6 Design for Disassembly

6 1 Choice of materials, design and joining methods

6.2. Disassembly assessment

7. Design for Reliability

7 1 Reliability assessment: FMEA

8 Multi-Objective Optimization

8 1 Performance optimization: dispersive bands

1. Introduction

1.1. Rold Company guidelines

Project goals

Rold is a leading company that produces innovative solutions for the household and professional appliances sector.

This project is intended to find a way to stop cooling the entire fridge Instead, this new system will only cool the fridge shelf where the temperature is not the set temperature utilizing sensors on each fridge shelf

Our goals are the following:

- Sensing design to guarantee the right positioning

- Possibility of having different number of outlets (even closed or shorter)

- Possibility of reducing the number of different elements (number of molds)

- Solution must be less than 20€

Requirements

The instructions given by the company:

- The size of the diameter cannot change because of the size of the motor

- The other dimensions can be shorter if possible

- 2 outlet min - 6 outlet max

- Injection molding is recommended because it is the main process of the company

- Each outlet must have an individual opening and they also must be able to be opened simultaneously, there must be a position that closes the opening on the freezer machine (there is no more flow):

8 combinations at least - The parts of the system must be asymmetrical for assembly reasons

- Components must be resistant to temperatures of up to -20 or -30 degrees

- The sensor must always know the exact position of the cylinder even in the event of a power failure

1.2. Management Tools

Team skills

Being a group of 3 people with different skills was an asset as it allowed us to be complementary and efficient in this project

Chloé Descombes: general engineering and management

Sam Twarog: mechanical engineering

Hong Peng: design engineering

Implementation of a Gantt Chart

At the very beginning of our project we decided to set up a gantt matrix to organise ourselves and to be able to regularly review the progress of the project (Appendix 1)

2. Design for X

2.1. Sensing design: comparison and selection

Brainstorming

At the beginning of the project, we took the time to do a lot of thinking and creative effort in order to get as many ideas as possible to create a real innovation At the same time we listed the existing angular position sensors This allows us to get to know the market better and to be inspired to find a solution tailor-sized to our problem Here is a list of these existing sensors and their charcateristics:

- Magnetic sensor (non-contact technology): there are Hall effect sensors, magnetoresistive sensors and magnetoinductive sensors It offers high accuracy and resolution, they are reliable in severe environments so they meet the specifications, but are relatively more expensive than other types of sensors. Acceptable

- Optical rotary encoder (non-contact technology): A light source is directed onto or through a rotating disc, the grating structure of which allows the light to pass or to be blocked An optical sensor detects the passage of the light and generates a corresponding electrical pulse It provides highly accurate measurements but their main weakness is that they are simply too delicate to withstand harsh environments (vibration, shock, foreign objects, extreme temperatures, etc.). Not acceptable

- Incremental encoder (contact technology): These devices provide an electrical signal proportional to an angle. Most of these encoders can withstand temperatures down to -40 degrees. Low cost but if there is a power failure, the encoder loses the angular position and only regains it when there is a top-zero (requires reference information) Not acceptable

- Potentiometer (contact technology): it is an analogue sensor whereas the rotary encoder is digital, a potentiometer changes the value of a resistor, but has a limited number of turns. It is a widely used economical solution, but these systems suffer from wear and tear and reliability problems. Not acceptable

- Absolute encoder (contact technology): It allows the position to be known even in the event of a power cut. They are not affected by foreign bodies and they can simply be screwed onto the host system. However, they are more expensive. Acceptable

So, at this stage only the magnetic sensor and the absolute encoder have been considered

Innovative solution

We thought of a geometric design incorporating 3-bit coding, which can determine a position by assigning to it a number of 3 digits composed of 0 and 1 You need to be able to distinguish between the 8 different outputs that’s why we use 3-bit coding:

000 -> opening of all the outlets simultaneously

001 -> output 1

010 -> output 2

100 -> output 3

011 -> output 4

101 -> output 5

110 -> output 6

111 -> closing the flow from the fraser

The coding from hundreds to units corresponds to the engravings from the centre to the outside The red lines are markers

Ex: this one stands for 001

The sensors on the shelves send the set signal for the desired shelf to be cooled to an arduino board (3-bit coding) The arduino board rotates the motor until the desired position is found using the push buttons (or micro-switches) that detect the correct position engraved on the internal cylinder

When a particular position is passed, at least one of the buttons is pressed. This action sends the 3 bit code corresponding to the actual position to the arduino board. If this code is the same as the setpoint code (using the comparative interface) then it is the correct position and the motor should be stopped

For our prototype it is 3 buttons and a resistance of 10k ohms is needed

Improvement of our idea by changing the components

Thanks to the feedback from the mid-term review we learned about a system that uses the same idea of 3-bit coding but with other components This involves the use of a PCB (Printed Circuit Board) sensor made with thin copper foil that is attached to the inside of the outer cylinder on the side. These copper sheets are therefore distributed according to the 3-bit coding in the same way as the engravings were made 3 metal spikes are fixed on the inner cylinder which rotates thanks to the motor and each spike when rotating follows a circle which corresponds to a digit of the 3-bit coding (same circles as before). Thus, this creates an electrical signal when there is contact between the metal spikes and the copper sheets.

Arduino board with 4 micro-switches Arduino Forum

Internal cylinder with 3-bit coding engravings Rhino software

One of the most important points is to be sure that the window to let the flow pass will be welladjusted to the output desired It depends on the angular speed of the motor and also on the speed of transmission of the signal So it’s up to the Rold company to test and find the best width for the copper sheets so that when the signal is received, taking into account the relative time, the motor can stop at the exact right position.

There are no cumulative errors, because the system doesn’t remember the position Indeed, it compares each position to the desired set position. Today, printing and manufacturing techniques to create PCB sensors offer advantages in terms of cost, size and ease of integration

A PCB sensor cost less than 1€ for large production like ROLD's

PCB sensor with copper: similar to what we want

RS-online

It is important to note that not all PCB sensors are designed to withstand all harsh environments, this varies according to the manufacturer and the right one must be chosen to meet the product requirements

So, comparing the price of this sensor to the other solutions we selected as acceptable, the PCB sensor is by far cheaper while providing good accuracy and withstanding harsh environments. Thus, we finally choose the PCB sensor

2.2. Product design: comparison and selection

Our design has evolved as we have learned and worked through the project. There have been four major design iterations that will be introduced in this section I will start with our first idea and move through how our design changed One primary reason for design changes was to reduce part count, and thus cost The first design was mechanically very similar to ROLD's design, with six parts The only part reduction in this design was the incorporation of the sensor holder into the external cylinder.

The second design we came up with used a pyramid method of assembly, joined with snap fits The external cylinder was split in two halves and incorporated both the inlet and the sensor holder The internal cylinder was in one part and was placed inside one half of the external cylinder, then the other half was placed on top. The internal cylinder contained the shaft, resulting in a reduction of two more parts.

We built on this design with the idea of moving the inlet cylinder to the side of the product, therefore allowing us to have four parts without a large snap fit joint around the entire external cylinder The inlet cylinder would also work as the end of the external cylinder, and the entire internal cylinder and shaft, as one piece, would fit inside Although we liked this design, we rejected it because it requires changes to other parts of the fridge

Our final design iteration utilizes a small cap called as the side part, which houses the PCB sensor. This cap attaches to the external cylinder by means of snap-fits. As with our previous design we have four injection molded parts, however the inlet remains in the center of the design here, incorporated in our external cylinder The internal cylinder is slide into the external cylinder in this design, and a rod on the end of the internal cylinder picks up on circular indents in the inside end faces of the external

cylinder and the side cap. These joints align the internal cylinder, keeping the internal cylinder in the correct position and making for easy assembly The end cap and motor cover are then added with snap-fits

We needed to ensure that it is realistic to injection mold our design. Moldflow software was used to calculate filling and cooling times for our parts. Shown below are two of many software runs. Our external cylinder filled in less than 3 seconds and reached ejection temperature in 124 seconds We checked each of our parts to ensure that they would fill both quickly and completely We also checked all the parts to make sure the time to cool was not excessively long There is not space to show all our results, however none of them showed any red flags to us.

Time to fill the part: 2,8s

Time to reach ejection temperature: 124s

3. Design for Manufacturing

3.1. Material selection

We made a comparison of different materials that can be used in plastic injection moulding, to select the best one:

As you can see, some materials did not meet the desired criteria (shaded boxes in the table) and were therefore not acceptable: PVC, LDPE and HDPE

Among the last two materials we have chosen ABS because it's the most commonly used polymer for injection molding This amorphous material is resistant to chemical, detergents and corrosion, remoldable and partly recyclable but a bit more expensive than thermosets materials.

3.2. Bill Of Materials (BOM)

In order to accurately compare the cost of our proposed design to that of the ROLD company's design a BOM was required for both designs. We first made a BOM of ROLD's design, taking into account both variable and fixed costs, and came up with an estimated price per part and consequently an estimated total design cost The different cost aspects taken into account, are purchased material, machine and labor injection molding cost, assembly cost, and tooling cost The final cost of ROLD's design was 5.44 euros.

We next calculated the cost of our final design to compare with ROLD's cost We had fewer parts, and snap-fits instead of screws, which ended up greatly reducing the overall cost The final cost of our design was 3.03 euros.

To calculate purchased material cost, the volume of each part was multiplied by the cost of ABS plastic per centimeter cubed To calculate the processing cost, the machine work and labor rate of 55 euros an hour was found online for a machine of the size required for this work This was multiplied by the time required for one work cycle for each part.

To calculate assembly labor cost, an assembly efficiency table was used with industry standard conversions and assumptions Total unit variable cost is simply the sum of all aspects of each component's variable cost. Tooling and other non-recurring expenses (NRE) costs derive from the cost of the mold base for each component. This is a lengthy calculation process that was part of the injection molding calculations The tooling lifetime is assumed to be 100,000 parts The total unit fixed cost is the sum of the NRE divided by the number of parts that can be made before more NRE will arise Total cost for each component and total cost for the entire prototype is then summed (Appendix 2)

3.3. Injection molding calculations

A complex series of calculations were done to calculate the injection molding costs of both the ROLD prototype and our final design To start the cost of the mold cavity for each part if each mold base only had one cavity was calculated using formulas given to us This value for each part was used in the calculation of the optimal number of cavities for each part To calculate optimal cavities for each part, wall thickness of the part, injection pressure and power, volume of material, and time for one work cycle was used. All of these values had to be found with tables or calculations similarly to material provided to us

Wall thickness was found from our designs Injection pressure was found by first calculating the clamping force needed for each part, and then using tables to find the pressure required for each corresponding part. Injection power was found in a similar manner, using tables provided to us and using the forces needed for each part The volume of material needed was found from our CAD part models Time for one work cycle was found by calculating the time for injection, time for cooling, and time for part rejection for each part These three times were summed to get the time for one work cycle.

After finding the optimal number of cavities for each part, which for our final design was two cavities for each part, final mold cost estimation was able to be accomplished This calculation involved finding the cost of the mold base from the dimensions of the part and doubling it to account for custom work that needed to be done on the bases.

3.4. Injection molding design guidelines

Injection molding is a widely used manufacturing process for producing plastic parts To ensure successful and efficient injection molding, there are several design guidelines that should be followed.

1 Draft angles: Incorporate draft angles on vertical surfaces to facilitate easy ejection of the part from the mold In our case, we choose 1 5 degrees per side to prevent sticking or damaging the mold

2. Wall thickness: Design parts with consistent wall thickness throughout to promote uniform cooling and minimize warping or sink marks Avoid abrupt changes in wall thickness, as they can lead to uneven cooling and potential defects Our design always keep 2mm thickness for each part

3. Ribs and fillets: Use ribs or gussets to add strength to walls while minimizing overall part thickness. Incorporate fillets or rounded corners to reduce stress concentrations and improve mold flow. We are thinking to add ribs and fillets to hold sensors which we chose

4 Gate location: Place the gate in a way that allows for proper filling of the part without causing excessive flow lines or weld lines. Typically, gates are located on flat, thick sections or at the parting line. When we simulate our design in moldflow, the software could find the right gate location for our design

5 Undercuts and threads: Avoid undercuts or features that require complex side-actions or unscrewing mechanisms, as they increase tooling complexity and cost We delete the screws in the original model, replace it as snapfits

6. Material selection: Consider the properties and characteristics of the intended material when designing the part Different materials have different shrinkage rates, flow properties, and temperature sensitivities, which can affect the final part dimensions and quality Basically, we choose ABS plastic from the performance perspective and cost perspective

7. Tolerances: Specify realistic tolerances that can be achieved with injection molding. We should ensure that the tolerances are feasible and cost-effective

3.5. Table drivers of complexity

1 Number of new parts introduced to the manufacturing system: We conduct a thorough analysis of the product or products being manufactured Identify the different components or parts that make up the product and understand their individual characteristics, functions, and manufacturing requirements. So the results is changing 8 to 6.

2 Number of new vendors introduced to the manufacturing system: Defining the number of new vendors introduced to a manufacturing system involves careful evaluation and consideration of various factors. Like Supplier evaluation, Supplier requirements, Supply chain analysis, Request for Information.... In our case is 0.

3 Number of custom parts intoduced to the manufacturing system: It's important to strike a balance between customization and standardization based on market demand, technical feasibility, and costeffectiveness. Regular monitoring, evaluation, and communication with stakeholders are crucial to ensure that the number of custom parts introduced aligns with the overall objectives of the organization Our deisgn keep the same with Rold design, the number is 4

4 Number of new "major tools", ex molds or dies introduced to the manufacturing system: In this step, we should conduct a detailed analysis of the manufacturing processes involved in your system. Identify the critical steps and areas where major tools are required to improve efficiency, increase capacity, enhance quality, or address bottlenecks Our answer is from 3 to 2

5 Number of new production processes introduced to the manufacturing system: This phase we should onduct a detailed analysis of the manufacturing processes involved in our system. Identify the critical steps and areas where major tools are required to improve efficiency, increase capacity, enhance quality, or address bottlenecks Our answer is 0

4. Design for Assembly

4.1. Reducing parts

Rold's prototype: 8 parts

Our prototype: 4 parts

section view

Side part called as the cap to place the PCB sensor

Design detail

External part

Internal part

- Side part with the centre that comes out to support the internal cylinder and hole to let the sensor wires pass through.

- Inclined walls on the two insertion holes to have an easier insertion of the inner part into the outer one

- 2 snap-fits to close the external part with the side part, it's enough solid thanks to the calculations made (cf see dimensions of the sanp-fits) )and more easy to remove: thumb and index finger pressure of the right hand and use of the left hand to hold the structure and pull

4.2. Define the steps and use the classification system

Steps of assembly

Study of symmetry for classification system

Using the symmetry studies and the data on the dimensions of the different prototypes, the first classification code is determined You will find the details in the Appendix 3

4.3. Table of Efficiency Assembly

By obtaining the classification codes, all calculations can be made and the following results are obtained as you can see in Appendix:

- Operation time (handling+insertion):

Rold prototype: 163,7s

Our prototype: 35,8s

Thanks to the reduction of parts and joining components, as well as the optimisation of the assembly steps, there is a huge time saving on each product

- Operation cost:

Rold prototype: 1,3€

Our prototype: 0,3€

This cost is reduced by 1€ We have used the labor rate of 30$/h as mentioned in the course

- Design efficiency:

Rold prototype: 0,15

Our prototype: 0,42

Design efficiency is a very important factor in determining whether a product is well designed or not by evaluating the overall efficiency of a manufacturing process. Here this design efficiency factor was almost tripled with our prototype.

Appendix 4

4.4. Selection of plastic joint: snap-fit system

Snap fit calculation

First of all we selected the type of snap-fit that corresponded to our project:

- dismountable: important to be able to disassemble the product in case of repair and for recycling - rectangular snap-fit without taper: the most widely used and they provide a uniform beam

- we are in position 5 (cf picture) in relation to where the snap-fit is on the side part.

Thanks to these assumptions we have: K1=4 ; K2=1,5

Defining parameters

Tw=5mm

Tb=60%ofTw

No taper ⇒ Tb=Tr=t=3mm ⇒ Wb=Wr=b=5mm

α=25° ; β=45° (for a releasing lock with low external separation loads)

(must be between 5 and 10) ⇒ Lb=24mm ⇒ Y=2mm

Lr=16mm ⇒ Lt=L=40mm

Notch effect ⇒ in many cases: Kt=1,5

Good design standard: r=0,5xt=1,5mm

Position 5: reading the graph ⇒ Q=1,7

Maximum strain

ABS material: εall=0,018

So we want to check that εeff is less than or equal to 0,018.

Friction coefficient: µ=tanρ=0,6 for ABS

Young's modulus: E=2GPa

Pressure

Forces - Insertion - Separation

All of these forces are < 9 Newton, so it re ma

Snap-fits location

As we have seen just before: 2 snap-fits a And we are also using 2 snap-fits to cover

The circular relief in the middle of the s es to guide the circular PCB sensor for better ns (cf picture below) to attach the pcb sensor re ernal components and is therefore better for th

5. Design for Environment

5.1. Identification of potential environmental impacts

To identify potential impacts we went through each aspect of the life cycle of the part and brainstormed how each part would impact the environment. We found the most important aspects to be the material, the molding machine, the packaging, the quality, and waste management

For the material, it was important for us to chose one single material that was recyclable With one material it is much simpler to recycle the part with no waste

For the molding machine we would like the machine to be fully electric The environmental impact from the source of the electricity must also be considered However without significant investment, it is difficult to lessen this impact.

We must consider the impact of the packaging for several reasons The impact from the manufacturing of the packaging, the impact from the transportation of the product with the additional weight, and the impact from the material used must all be analyzed

The product quality must be of a sufficient level so that no maintenance is required and the lifespan should be equal to or greater than that of the fridge itself

5.2. Life Cycle Assessment

Determining the carbon footprint of a product is a long and tedious job because you have to pay attention to the data used and you have to consider the whole production chain from the import of materials to the recycling of the product. Here are the details of our approach

Definition of the needs

- Comparison of products

- Improvement of an existing product from an environmental point of view

- Getting quantitative information about the product's impact

Inventory

We created a flow chart to define the different stages of the process as well as the inputs and outputs. Appendix 5

To start it is necessary to make certain assumptions because we do not have all the data of the company:

- The system works 8 minutes per day: 5 seconds to find position and work every 15 mins

- Material transport km average: 70 => 23,1L consumed =>101,31kg CO2-eq

- Final product transport km average: 4000 =>1320L consumed =>4052,4kg CO2

- Use of hydraulic injection molding machine for Rold Prototype

- Cardboard packaging

- Real number of product per truck: 15000

Use phase of 10 years

Assessment of the environmental impacts

Classification

- Resource and energy depletion

- Global impacts: ozone layer disruption which lead to global warming

- Local impacts: ocean acidification, human toxicity, water and land contamination, eutrophication

Characterization

Calculations described in Appendix 6

Total CO2-eq : 4,44kg

Total CO2-eq : 2,93kg

With our prototype, we see an 11% reduction in equivalent CO2 emissions, from 4,44kg to 2,93kg with our design. This decrease is due to the lower volume of ABS required to manufacture our design as well as the partial use of recycled material

Interpretation of the results

After calculating the carbon footprint of the rold prototype, we realised that the most important source of CO2 emissions concerns the materials' sector. That's why we wanted to use only recycled ABS as a raw material, which would have reduced emissions by 80% However, for performance reasons, no more than 50% of rABS should be used So even if we didn't achieve the 80% reduction initially estimated, we still significantly reduced our carbon footprint as you can see on the category of materials in the graph: we went from 2,5kg to 1,1kg of CO2-eq.

Materials CO2-eq : 2,5kg

Materials CO2-eq : 1,1kg

Use category is the other field with significant emissions Nevertheless, we cannot influence this category because it depends on the energy mix used in the country

Using all-electric injection molding instead of hydraulic machines will reduce CO2 emissions of the production's sector by 50%. But as we now that replacing all the machines is a huge investment, we have not taken it into account and give it for informational purposes for the company

6. Design for Disassembly

6.1. Choice of materials, design and joining methods

We need to be able to disassemble the product for maintenance purposes We have chosen to use snap fits for reasons of ease of recycling (use of an single material) and for cost reasons because there is less labor cost (assembly) and material cost.

However, for the recycling part, once the engine has been removed, we don’t need to dismantle the product because we choose to make every part of the same material: ABS The product can therefore be granulated and used again as a raw material (rABS).

Active disassembly is interesting but is not useful if the product is made of one single material

We use 2 snap-fits in our design because it's enough solid with the dimensions we have designed (Fins=3N and Fsep=8N) and it's way more easy to remove Indeed, one person can do this alone by applying pressure with the thumb and index finger of the right hand and using the left hand to hold the structure and pull

6.2. Disassembly assessment

Scoring designs based on tool types

Rold prototype using screws: score=0,7

Our prototype using snap-fits (no tool is needed): score=1, which is the best one

Scoring designs based on possibel recovery rate

Rold prototype:

- TR=0% - Trecy=40%

- TI=40% - TL=20% Score=0,39

Our prototype:

- TR=50%

- Trecy=0%

- TI=35%

- TL=15% Score=0,65

Regardless of the method to evaluate the disassembly, we observe that in the context of our prototype the scores are better.

7. Design for Reliability

7.1. Reliability assessment

We carried out a risk analysis for our prototype using the FMEA method (Failure Modes and Effects Analysis) Thanks to this qualification of the risks, we have been able to put in place solutions to counter them, and thanks to their quantification, we have been able to classify them by priority with the RPN (Risk Priority Number).

So the risk of snap-fits not being correctly engaged requires the most attention with an RPN=128 (Appendix 7)

8. Multi-objective optimization

8.1. Performance optimization: dispersive bands

Some of the mixing tanks used in the industry are designed with baffles to maximise turbulence These baffles are raised structures integrated into the inner wall of the tank to disrupt the flow of fluids and promote better agitation and more efficient diffusion.

We therefore took inspiration from this mechanism to integrate it into our prototype. The main difference being that in our prototype there is no agitator but it is the cylinder that turns thanks to the motor However, the principle remains the same to agitate the particles and allow a better diffusion. These baffles are used where the old shaft was placed, i.e. at the fluid inlet of the fraiseur machine, to increase its agitation as it enters the cylinder

We have designed these blades to have a further performance purpose. In addition to increasing diffusion, the baffles are given a funnel shape to encourage the entry of milling fluid into the inner cylinder while reducing the possibility of its exit and thus leakage between the inner and outer cylinder

Cross-sectional diagram of stirred tank reactor Wikipedia

1.Gantt Chart

2.Bill Of Materials

3.Classification system

4.Efficiency Assembly

5.Life-Cycle flow chart

6.Inventory table and useful data

Rold prototype

Our prototype

7. Reliability Asessment

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Design for Optimization

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