NGUYEN TRONG HIEU STUDENT: MAI DANG KHOA NGUYEN ANH KHOA MAI TRAN XUAN PHONGHo Chi Minh City, March 2024RESEARCHING THE MANUFACTURING CAPABILITY OF MOMENT-COMPLIANT SOFT STRUCTURES USING
OVERVIEW
Overview of moment-resisting soft structure
Compliant mechanisms are devices which can transform motion or force by the shape change of its self-structure As compared with conventional mechanisms, the advantages of compliant mechanisms are prominent They can avoid the harmful effects of backlash, friction and wear, which are the inherent defects of conventional mechanisms Medical or healthcare devices assisting the rehabilitation of human joints often rely on functional mechanisms that could provide stable output torque
To achieve this target, available equipment usually uses motorized mechanisms combined with complicated sensorized control system
On this day, among countless types of complex structures, the constant-torque joint mechanism (CTJM) provides nearly constant torque within a specific range of rotation as the rotational speed increases Instead of using sensor control, CTJM passively maintains a constant torque Potential applications include dynamic and static balancing of machinery, joint function rehabilitation devices for humans, and assistive devices for human mobility To meet practical needs, CTJM must have a large constant torque region with sufficient flatness [1].
Overview of the Constant-Torque Joint Mechanism (CTJM)
CTJM stands for "Constant-Torque Joint Mechanism," which is a type of compliant mechanism capable of providing a constant torque output within a certain range of deformation This can find applications in various fields, particularly in devices or systems that require maintaining a stable torque without the need for external sensors and controllers In the specific context of the provided passage, CTJM is discussed in the context of compliant mechanisms that can maintain a constant torque level It is compared to other mechanisms like CFM (Constant-Force Mechanism) and various applications in the fields of mechanics and engineering [1]
• CTJM using lumped-compliance models
• CTJM using distributed-compliance models
CTJM using lumped-compliance models
The Constant Torque Joint Mechanism (CTJMs) designed using lumped- compliance models focuses on achieving a constant-torque output by carefully manipulating compliant members These models are classified into Groups A, B, and
C based on their principles for obtaining constant torque Group A, for instance, employs torsional springs for positive stiffness and linear springs for negative stiffness, combining them to create a constant-torque region The CTJM can have multiple identical limbs connecting the inner shaft to the outer fixed rim, providing stability [1]
Figure 1.1: Applications of CTJMs: (A) gravity balancing, (B) mobility-assisting device, (C) rehabilitative device, (D) dynamic-torque balancing [1]
CTJM using distributed-compliance models [1]
The Constant Torque Joint Mechanism (CTJM) designed with distributed- compliance models aims to achieve a constant-torque output by introducing flexibility and adaptability into the connecting limbs In contrast to lumped- compliance models, which rely on specific spring stiffnesses at distinct locations, distributed-compliance models offer additional degrees of freedom by making the entire limb compliant The distributed-compliance models overcome the limitations of the lumped-compliance models, providing a new perspective on CTJM design These models integrate linear and torsional springs along the entire limb, allowing for a more distributed and adjustable stiffness profile This design flexibility enables the creation of a larger constant-torque region compared to the restricted region in lumped-compliance models.
Reasons for choosing the topic
1.3.1 Why choose the CTJ M structure
Because the type of functional joint mechanism and its related applications are still unexplored, and the potential applications of CTJM in medical and research fields are recognized By using synthetic compliance models to design CTJM mechanisms, the team has delved into researching the manufacturing capability of moment-compliant soft structures using the plastic injection molding method The selection of research on the possibility of manufacturing soft structures by plastic injection molding method topic is motivated by several important reasons stemming from practical needs in the field of torsional strength Here are some specific reasons:
1 Real-world application: The chosen topic focuses on a specific problem, essential issue in a practical context in order to create valuable knowledge that can be applied in fields that use flexible and tolerant configurations
2 Plastic injection molding technology: It is a versatile and widely applied and is
4 suitable for research and manufacturing of products in the learning and working environment
3 The moment-soft structure: Nowadays, among various types of structures, the Constant-torque joint mechanism (CTJM) exhibits a constant torque when the rotational speed increases The constant torque joint mechanism (CTJM) provides nearly constant torque within a specific range of rotation without relying on sensor feedback [1]
The above reasons show the importance and necessity of choosing a research topic on moment-compliant shape soft structures using the injection molding method
1.3.2 Why choose moment-resisting soft structures using the plastic injection molding method?
There are numerous methods for processing and manufacturing soft structures:
CNC machining, Wire cutting method and 3D printing can manufacture the shape of product, but it creates two significant problems which are the outsourcing fees of product increasing and it can not be batched product
Thus, recognizing that the plastic injection molding method ensures stability, can produce in bulk, can ensure that the dimensions of products are similar and minimized error product There is fatigue testing machine available, has been instructed and using Haitain injection molding machine and many types of plastic provided for research purposes,
Topic objective
Research and summarize about plastic injection molding technology
Research and summarize about various types of flexible mechanisms
Designing two-plate molds for flexible moment-compliant
Manufacturing, assembling, and testing of molds.
Research methods
Refer to articles about CTJM structure to come up with product design ideas Refer to the documentation on plastic injection molds to create a mold set Use NX software to design molds
Use moldex 3D software to analyze flow after design
Research scope
Design the compliant-moment soft structure based on research articles, from which choose the design for the product
The project focuses solely on researching, designing, and calculating plastic injection molding based on the theoretical of plastic injection molding design Specifically, it involves the research on the manufacturing capability of moment- compliant soft structures using the plastic injection molding method
Research and progress on the two-plate, one-cavity mold set
Reasons for choosing the two-plate mold:
- Lower production cost compared to other types of molds
- For simple details such as moment-compliant structures, selecting the shape and location of the gate will be easier
THEORETICAL BASIS
Overview of plastic injection molding
Concept of plastic mold: The concept of “plastic mold” is related to the plastic production process and plastic products A plastic molding die, also known as a plastic injection mold, is a manufacturing tool used to produce specific plastic products through the plastic molding process This process typically begins with the design of the plastic molding, a three-dimensional shape of the desired final product The mold is often made from steel or other materials capable of withstanding high heat and pressure This mold will have a shape and size similar to the desired end product that the manufacturer aims to achieve [3]
Plastic injection molding is widely used in mass production of plastic products, from toys to automotive components and various other applications It is an efficient means of manufacturing plastic products with high precision and low cost when producing in large quantities [3]
2.3 Overview of plastic injection molding
Plastic injection molding technology is a widely used manufacturing process for creating plastic parts It involves injecting molten plastic material into a mold cavity under high pressure, where it cools and solidifies to form the desired shape
- Mold Design and Preparation: The first step involves designing the mold based on the desired specifications of the final product The mold is typically made of metal (such as steel or aluminum) and consists of two halves - the cavity side and the core side
- Plastic Pellet Feeding: Plastic resin pellets are fed into a hopper and then conveyed into a heated barrel Inside the barrel, the pellets are melted by heat and pressure
- Injection: Once the plastic is molten, it is injected into the mold cavity through a nozzle and runner system Injection pressure forces the material to fill the mold completely, taking the shape of the mold cavity
- Cooling: After the mold is filled, it is cooled to solidify the plastic Cooling can be done by circulating water or oil through channels in the mold Proper cooling is crucial for achieving the desired properties and minimizing cycle time
- Ejection: Once the plastic has cooled and solidified, the mold opens, and the part is ejected from the mold cavity using ejector pins or plates
- Trimming and Finishing: The ejected part may undergo additional trimming or finishing processes to remove any excess material or imperfections and achieve the final desired shape
- Automotive Industry: Injection molding is widely used in the automotive industry for manufacturing interior and exterior components, such as dashboards, bumpers, door panels, and lighting housings
- Consumer Goods: Many consumer products, including electronics, appliances, containers, and household items, are produced using injection molding
- Medical Devices: Injection molding is employed to manufacture various medical devices and components, including syringes, surgical instruments,
IV components, and diagnostic equipment
- Packaging: Plastic packaging containers, bottles, caps, and closures are commonly produced using injection molding due to its efficiency and versatility
- Toys and Games: Injection molding is extensively used in the toy industry for producing a wide range of plastic toys and game components
- Industrial Components: Various industrial components, such as gears, bearings, enclosures, and housings, are manufactured using injection molding for their durability and precision
2.3.2 Overview of plastic injection machines
Figure 2.3: Plastic injection molding machine [3]
The structure of the injection molding machine is divided into 5 basic systems [3]:
- In the injection molding support system, there are 4 subsystems that perform specific functions
- Machine body: Connects the machine's systems together
- Electrical system: Provides power for the motors to operate The design of the machine's electrical system focuses on safety for the operator The electrical system includes the electrical cabinet and wiring system [3]:
- Hydraulic system: Consists of pumps, valves, piping systems, motors, etc This is where the power is generated, such as creating the force to close and open the mold, maintaining clamping force, driving the screw motion, providing force for ejector pins, and the sliding of core surfaces [3]
- Cooling system: Provides water or Ethylene Glycol solution to cool the mold, solidifying the plastic into shape before being ejected from the mold [3]
The task of the injection system is to heat the plastic melt and maintain its liquefied state, compress it, and remove air during the injection process, injecting the plastic into the mold cavity and shaping the product [3]
The injection system consists of the following components: material hopper, material storage chamber, heating band, screw shaft, nozzle, and check valve [3]
It performs the function of opening and closing the mold, maintaining clamping force during the cooling process, and ejecting the finished product from the mold [3] The components forming the clamping system include:
The mold system is the part of the mold that shapes the product It consists of a stationary mold half containing the cavity and a movable mold half containing the core
The control system is the brain that operates the plastic injection molding machine Through the control panel, operators can monitor and adjust parameters
14 such as injection speed, temperature, pressure, screw position, and the position of components in the hydraulic system
To control these parameters, operators use buttons and view all displayed data on the computer monitor
During the molding process, the control system receives input parameters set by the operator The machine systems then carry out the injection molding operations according to those commands
2.4 Classification of plastic injection molds
Two-plate mold: The two-plate mold is a typical, simple, and reliable mold in the manufacturing process due to its straightforward structure Typically, the two-plate mold has few moving parts, including a stationary plate and a movable plate [3]
The two-plate mold is an injection mold using a runner system, with the runners lying horizontally on the mold surface The gate for injecting plastic is located on the side of the product, and when the mold is opened, there is only a small opening to remove the product and the runner channel [3]
For the two-plate mold, the gate design can be such that the product and the runner automatically separate or do not separate when the product and the runner are removed from the mold [3]
The method of using a two-plate mold is very common in injection molding systems The mold consists of two parts: the front mold (cavity mold) and the back mold (core mold) The mold structure is simple and easy to manufacture, but two- plate molds are typically only used to create products with easy gate placement [3] The main components of the two-plate mold
The two-plate mold is divided into two main parts [4]
- The cavity side determines the outer shape of the plastic product, called the cavity mold, and is usually attached to the movable plate of the injection molding machine
- The core side determines the inner shape of the plastic product and is typically attached to the fixed plate of the injection molding machine
2-plate mold has 1 cavity 2-plate mold with many mold cavities
Figure 2.5: Basic two-plate mold [4]
• Simple construction, easy operation in production
• Low manufacturing cost compared to other types of molds
• Helps save costs and time in mass production
• The two-plate mold is only suitable for parts that require lower accuracy
• Two-plate molds cannot be used to mold complex products Because the filling of plastic in the two-plate mold is uncontrollable, and products from the two- plate mold have very few injection points, so the process of injecting plastic into the product is very slow and can cause significant deformation to the product
DESIGN AND F ABRICATION OF MOLDS
Redesign product
Redraw the product using 2D shapes in Inventor software, the dimensions of the product for easy design and minimize errors
Since the detail has a circular and thin shape, we'll choose the middle parting surface
Step 1: Design the curves of the part
Step 2: Design 4 holes for mounting purposes
Figure 3.1: The mass and volume of the detail
Figure 3.3 shows mass of detail is 0.01kg and volume is 11365.701 mm 3
Shrinkage coefficient of the product
Shrinkage coefficient is a measure of the change in size of a product after it is shaped and cooled from the molten state of the plastic material For compliant moment mechanisms made of PP plastic (Polypropylene), the coefficient of thermal expansion is 1-2% Choosing a coefficient of thermal expansion for PP plastic as 1%.
Manufacturing the mold
To easily remove the product from the mold, the inside and outside of the product must have a certain taper in the direction of mold opening This requirement also needs to be applied to details such as reinforcing ribs, grooves, etc
In molds with short cores or shallow mold cavities (less than 5mm), the taper angle should be at least 0.25 0 on each side When the depth of the mold cavity and core increases from 1 to 2 inches (25.4÷50.8mm), the taper angle should increase by
2 0 on each side It should be noted that the smaller the taper angle, the greater the ejected force required, which may damage the product if it has not completely hardened
=>But for the mold of this project group, because the design of the two mold faces is symmetrical, when the product is pushed out, the product has a lot of space to facilitate product removal, so the mold exit angle of the mold is detail is not too significant
3.3.2 Calculate the number of mold cavities [6]
Normally, the number of mold cavities can be calculated in the following ways:
- Calculated according to the number of product batches
- Calculated according to the spraying capacity of the machine
- Calculated according to the plasticizing capacity of the machine
- Calculated according to the mold clamping force of the machine
- Calculated according to the clamp size of the press
The steps to calculate the number of mold cavities below are all calculated based on HAITIAN plastics machinery (MA1200III/400eeco)
• Calculated according to the number of product batches
Where: n: Minimum number of cavities per mold
L: Number of products in 1 batch of products
K: coefficient due to waste products (%)
𝑡 𝑐 : Injection molding cycle time of a product (s)
𝑡 𝑚 : Time required to complete 1 batch of product (day)
• The number of mold cavities is calculated according to the injection capacity of the machine:
𝑊 Where: n: Maximum number of cavities per mold
S: Spray capacity of the machine (g/1 spray)
• The number of cavities determined by the production capacity of the molding machine.:
𝑋 × 𝑊 Where: n: Maximum number of cavities
P: Production capacity of the molding machine (g/min)
X: Estimated injection frequency per minute (1/min)
• The number of cavities calculated based on the clamping force of the molding machine:
𝑆 × 𝑃 Where: n: Maximum number of cavities
S: Average surface area of the product when the mold is closed (mm²)
P: Pressure inside the mold (MPa)
Fp: Maximum clamping force of the machine (N)
Given S"95.332 mm², Pu.65 MPa, Fp00 kN
Table 3.2: Table caculate number mold cavities
1 Spray capacity of the machine n ≤ 19.2
2 Plasticizing capacity of the machine n ≤ 24.3
Based on the calculations above, to save on mold-making costs and minimize molding time, it is feasible to choose one cavity
Table 3.3: Create workpiece and separate mold
Importing and declaring product information
→ Selecting PP plastic with a shrinkage factor of 1.010
Determining the mold release coordinate angle
Providing the coordinate system for the part
→ Choosing the coordinate system at the center of the product Selecting PP plastic with a shrinkage factor of 1.010
→ Selecting a workpiece with dimensions of 150x150x100 (mm)
Selecting the core and cavity surfaces
Selecting the surface on the cavity plate
Step 5: Fill in the gaps on the part
Fill in the gaps on the part
Plastic runner design
The plastic runner is the connecting section between the sprue and the nozzle Its task is to deliver plastic into the mold cavity [7]
Therefore, in the design process, it is necessary to adhere to a number of technical principles to ensure quality for most products Here are some principles that need to be followed [7]:
• Minimize changes in the cross-sectional area of the runner
• Plastic in the runner should easily escape the mold
• The entire length of the runner should be as short as possible to quickly fill the mold cavity, avoiding pressure loss and heat loss during the filling process
• The size of the plastic runner depends on the type of material being used On one hand, the runner should be small enough to reduce scrap, shorten cooling time (affecting the product cycle), and decrease clamping force On the other hand, it should be large enough to efficiently transfer a significant amount of material to fill the mold quickly and with minimal pressure loss
A runner is a channel in an injection molding machine that functions to guide the flow of plastic from the machine nozzle to the plastic delivery system In some cases, the runner directs the plastic directly into the product (for single-cavity molds)
The dimensions of the sprue for the design
Figure 3.2: Calculate the dimensions of the sprue [7]
𝑆 𝑚𝑎𝑥 = 10mm (Head height of sprue bushing) α = 3 0
Choosing a sprue length of 60 mm
Tmax is the maximum thickness of part
Figure 3.3: Table of common cross-sectional types of plastic runners
Choosing a circular cross-section for the runner
With Tmax is 5 mm (Tmax is the maximum thickness of product)
Can calculate using the formula
L: Length of the runner (mm)
→ The runner thickness is 2.3 mm
The fan-type nozzle is essentially a modified edge-type nozzle with a wider width This type of nozzle creates a smooth flow allowing rapid mold cavity filling, making it suitable for large and thick products runner
T = (0.5-0.8)t = 0.5 x 5 = 2.5 mm (with t = 5 thickness of product)
A fan gate is suitable for a circular cross-section runner The center hole of the product does not fit both the runner and the nozzle separately Based on feedback, the decision is made to combine the runner and the sprue as shown in the image below
Designing the ejection system
This is the most used ejection system The material typically used is T10A, hardened to over 50HRC and requiring a surface roughness of 0.8 The fit is tight H8/f8 Push pins are standard components with different diameters, lengths, and shapes
Circular holes are easy to machine, making this system relatively simple and easy to implement However, machining long and precise circular holes can still be challenging, so it is necessary to widen the push pin holes by a certain length
Ejector retainer plate Ejector plate
Designing the cooling system
The importance of the cooling system cannot be overstated
Cooling time typically accounts for about 60% of the mold cycle time Therefore, finding ways to reduce cooling time while ensuring product quality is crucial The melt temperature of the plastic injected into the mold is usually between 150°C to 300°C When the plastic material is injected into the mold at this high temperature, a significant amount of heat from the plastic material is transferred to the mold and dissipated through the cooling system If the cooling system fails to efficiently remove heat from the mold for any reason, the temperature inside the mold will continue to rise, leading to increased production cycles Therefore, optimizing the cooling system is essential for maintaining production efficiency and product quality [7]
Mold opening time Open mold Injection molding time
Figure 3.9: The importance of mold cooling time [7]
Calculate the dimension of cooling system by theoretical
The cooling system should not only have one pathway, so create multiple cooling circuits simultaneously, with appropriate diameters to enhance cooling efficiency (typically diameters ranging from 8mm to 14mm) [7]
D = 8 ÷ 10 mm: diameter cooling , D = 8 mm a = 2 ÷ 2.5d = 2 𝑥 8 = 16 mm distance from cooling plate to the product wall b = 2 ÷ 3d = 2 𝑥 8 = 16: distance between 2 cooling
With the design of thin products and a two-plate mold, the team has designed a cooling system that encompasses both the cavity and core plates of the mold
The process of designing the cooling system
Table 3.4: Designing cooling system using NX software
Step 1: Select channel direction to determine the position of the water lines
Step 2: Apply and select the appropriate length of water lines for the mold
Step 3: Choose the cooling circuit to indicate the direction of the water lines
Step 4: Open the detail of the push-fit connector to be inserted into the pipe
8 water lines for cavity and core
Analysis of simulation results
Figure 3.12: Filling Melt Front Time
The result of figure 3.13 shows that the filling time at the farthest positions on the product is 0.577s
The filling process is represented by colors from red to blue Notice that, immediately after the injection molding process begins, the molten plastic is filled into the injection stem, and then the plastic is filled into the joint positions In other words, plastic is given priority to fill in the areas located near the nozzle first, the blue areas are the last to be filled
Comment: The filling process of the mold cavity proceeds logically and uniformly from the outside inward symmetrically, completely filling the mold cavity The time difference in filling between products with large volumes compared to those with small volumes is insignificant
Figure 3.14 shows all locations where air trap appears on the product Analysis showed that air trap was present around the edge and inner corners of the central edge of the product This does not greatly affect the torsional force resistance or structural durability during testing However, in terms of form, the structure will not achieve high aesthetics
Pressure max is: 92,175 MPa at t: 0,546s
The final pressure at the end of the filling process is: 75,651 MPa at t: 0,587s
With the test sample, the maximum required pressure according to the analysis is 90,175 MPa, which is relatively suitable for many types of injection molding machines
Figure 3.16 shows that the smallest temperature during the injection molding process is 76,764 degrees Celsius, the maximum temperature is 212,911 degrees Celsius, which is the suitable temperature for PP plastic, because when the temperature is too high, it will change the mechanical properties of the plastic leading to the process of analyzing the bearing capacity not achieving high accuracy
With the cross-section, the temperature is evenly distributed throughout the entire part
Based on the simulation results, we see that the joints show volume shrinkage in the region of 1.703% to 4.992% compared to the original volume Shrinkage areas
>7% are concentrated mainly on the edge of the product
Ignoring the red area, we see that the shrinkage density in the important locations of the details at the joints is distributed quite evenly The largest shrinkage is at the edge of the product, which does not greatly affect the product's bearing capacity
To reduce shrinkage, optimization is required in the product design thickness, avoiding sudden changes in product thickness while still meeting product usage requirements Injection molding pressure must be increased, and the power supply process must be uniform to ensure more uniform shrinkage
Figure 3.18: The temperature of the product after the cooling process
The maximum temperature of the product after the cooling process is 64.862 0 C
Figure 3.19: The efficiency of the cooling system
The red cooling lines indicate the best cooling performance (2,3) The green cooling lines represent average cooling performance (6,7) The cooling lines (1,4,5,8) have poor cooling efficiency
Figure 3.20: The product's curvature due to temperature and shrinkage
The chart representing the curvature due to temperature shows negligible effects, with the maximum curvature on the product being 0.024 mm
Figure 3.21: The parameters for evaluating the curvature of the product
The chart represents the maximum observable shrinkage curvature at 0.843 mm, accounting for 47.22% of the total Despite the relatively large shrinkage, for a moment-compliant mechanism where the force analysis primarily relies on the product's joints, the curvature exhibited by the joints is insignificant While the product's edges may exhibit the most curvature, they do not significantly affect the torsional failure analysis process.
Selecting standard components
Figure 3.22: Sprue bushing according to Misumi standard [8]
Selecting the type with a tapered angle 3 o D, inner diameter P = 3.5 mm, and a length L = 60 mm
Figure 3.23: Locating ring according to Misumi standard [8]
Selecting locating ring D0 mm, dp mm, T mm, A= 85 mm
Figure 3.24: Return pin according to Misumi standard [8]
Selecting return pin H mm, D mm, L0 mm, T=8 mm
Figure 3.25: Guide pin according to Misumi standard [8]
Selecting guide pin: D mm, H% mm, L mm
Figure 3.26: Guide bushing according Misumi standard [8]
Selecting guide bushing D0mm, H5mm, d mm, T=8mm, L=l mm
Figure 3.27: Ejector pin according to Misumi standard [8]
Selecting ejector pin P=4 mm, H=8 mm, T= 4mm, L= 100 xmm
THE MANUF ACTURING AND ASSEMBLY PROCESS
Workpiece preparation
Table 4.1: Dimensions of the mold parts
Number Name of part Dimension
Manufacturing process of core plate
4.2.1 Routing 1: Milling bottom surface, the side surface and machining holes
Figure 4.1: Installation of rough 1 4.2.1.1 Positioning
The Part is positioned with 5 degrees of freedom, 3 degrees of freedom on the dial 3 of part with a support plate, 2 degrees of freedom on the side with ETO movable jaw
The part is clamped by ETO jaw, clamping force is from right to left
Choose table 9.38 in book CNCTM volume 3, select the vertical milling machine 6H12
Technical parameters of milling machine CNC – VQC-20/50B
• Working surface of the table 320x1250
Select a hard alloy face end milling cutter, tool parameters: (see table 5.127 page
• Tool diameter: Dmm, number of teeth: Z = 10, material T5K10
This operation is divided into 2 steps (based on table 3.1 on page 38 in the CNCTM project manual): Rough milling Z= 1,5 mm, semi-finishing Z= 0.5 mm
4.2.1.6 Searching the cutting mode and calculate the machining time
• Coarse feed rate 𝑆 𝑧 = 0,18 𝑚𝑚/𝑡𝑜𝑜𝑡ℎ (table 5.125 page 112 in
• Cutting speed 𝑉 𝑏 = 282 mm/min (Table 5.126 CNCTM manual volume 2) => cutting depth t = 1,5 mm
• The adjustment factor depends on the hardness of steel Ct3 𝐾 1 = 0,42 because the hardness of the workpiece is steel Ct3 with HB73
• The adjustment factor depends on the tool life cycle 𝐾 2 = 0.8 because we want the actual life to be twice as long as the life given in the manual
• Adjustment coefficient depends on grade of hard alloy 𝐾 3 = 0.8
• Adjustment factor depends on the machined surface (shaped and pound) 𝐾 4 = 0,9
• Adjustment factor depends on milling width 𝐾 5 = 1
• The correction factor depends on the main tilt angle 𝐾 6 = 1
Corresponding to 𝜑 15 , the value 32 is close to 27.69, corresponding to φ=1.26 (table 4.7 in the CNCTM project manual)
65 = 5.1 According to table 4.1, we have for =1.26, we have 𝜑 7 = 5.04
So the number of revolutions according to the machine is
So the actual cutting speed is:
• Circular feed amount: 𝑆 0 = 0,24 𝑚𝑚 (table 5.125 in CNCTM manual volume 2)
• Cutting speed 𝑉 𝑏 = 249 𝑚𝑚/𝑚𝑖𝑛 (table 5.127 in CNCTM manual volume 2)
• The adjustment factor depends on the hardness of steel Ct3 𝐾 1 = 0,42
• Adjustment factor depends on tool life cycle 𝐾 2 = 0.8
• Adjustment coefficient depends on grade of hard alloy 𝐾 3 = 0.8
• The adjustment factor depends on the machined surface 𝐾 4 = 0.9
• Adjustment factor depends on milling width 𝐾 5 = 1
• The correction factor depends on the main tilt angle 𝐾 6 = 1
So the calculated cutting speed: 𝑉 𝑡 = 𝑉 𝑏 𝐾 1 𝐾 2 𝐾 3 𝐾 4 𝐾 5 𝐾 6 = 60 𝑚/ 𝑚𝑖𝑛
65 = 6.5 According to table 4.1 (CNCTM project manual) we have 𝜑 8 = 6.32
So the number of revolutions according to the machine is 𝑛 𝑚 65 × 6.32 = 411rpm
So the actual cutting speed is:
Low feed rate by machine selector 𝑆 𝑚 = 740 𝑚𝑚/𝑚𝑖𝑛
Table 4.2: Manufacturing process of core plate in rough 1
Drilling pilot holes for guide pins
4.2.2 Rough 2: Milling top surface, 2 sides left, insert cavity
Table 4.3: Manufacturing process of core plate in rough 2
4.2.4 Rough 3: Drilling holes for water ways and connecting fittings
Table 4.4: Manufacturing process of core plate in rough 3
4.2.3 Manufacturing process of cavity plate
Rough 1: Milling bottom surface, 2 sides of plate and machining waterway holes on
Table 4.5: Manufacturing of cavity plate in rough 1
Deburring and polishing
• Remove burrs and sharp edges on mold plates
• Facilitate easier assembly of critical surfaces
• Tools for polishing the mold
Figure 4.14: Locating ring and sprue bushing
Mold assembly
Mounting sprue bushing into the clamp plate
Installing the locating ring and the upper mold plate onto the clamp plate
Installing guide pins into the core
Step 4: Install ejector pins, return pins into the retainer plate
Step 5: Insert the retainer plate into the core
Step 6: Install the ejector plate into the retainer plate
Step 7: Install the bottom clamp and plate support and the core
Step 9: Install the water inlet fitting and the retaining bolt
• Real mold assembly and product:
Figure 4.15: Two mold plate and product
Procedure
− Mount the mold onto the plastic molding machine
− Rectify mold if there are any defects
− Perform final test pressing and measurement
Parameters of the molding machine used
Figure 4.16: Haitian plastic molding machine
Test molding
• Common defects during product injection
Sink mark The product has burrs
Figure 4.17: Product defects during injection testing
Figure 4.17 illustrates that plastic products exhibit surface depressions and warping due to material shrinkage during molding The solution is to readjust the molding parameters
After completing mold machining, proceed to test the mold's pressing ability
Case Pinj Pforming Tmelt Tmold Tshaping
In case 1, with injection pressure of 65 MPa and mold holding time of 0s, the product is not fully filled with plastic due to insufficient mold holding time
In case 2, 3 with injection pressure of 75 MPa, melting temperature 200 0 C and
220 0 C and time shaping from 1 to 2s the product is fully filled
In case 4,5 when increase injection pressure at 80 MPa the product appears some defect like burr, plastic overflow
From the parameters of the 5 cases above, cases 2 and 3 have reasonable injection parameters It has been shown that the mold of this project works well and is suitable for pressing products and using those products for further research
After completing the project 'Researching the manufacturing capability of moment-compliant soft structures using plastic injection molding method, the following results were:
Overview of plastic injection molding technology:
- Understanding different types of molds
- Understanding the structure of injection molding machines
Summarizing the various soft mechanism types providing a foundation for designing two-plate molds
Designing and manufacturing a set of two-plate molds for a moment-compliant mechanism with a single cavity
The manufacturing, assembly, and testing of prototype molds are crucial next steps in the process, ensuring that the concepts are implemented accurately and efficiently
Using a plastic injection molding machine to consolidate the results of the product after the mold-making process
Finally, the project had achieved the following specific product:
- Complete Moment-compliant plastic injector molding set
- Made on a two-plate mold, based on the existing design
- Design injection molding set with single cavity of two -plate mold
- Redraw products from research articles
- Analysis fluid of plastic in moldex3D
- Using PP plastic to testing mold
Development and orientation Need to ugrade mold with more cavity to inject more products Researching about other design of moment-compliment soft structures better Optimizing Mold Design:
- Continue researching and developing mold designs to optimize the flexibility and precision of the soft mechanism product
- Implement advanced methods such as computer-aided design to optimize the structure and performance of the mold
- Research and implement new, high-quality materials capable of withstanding pressure and ensuring durability, enhancing the quality and longevity of the mold
- Employ flexible and heat-resistant materials to ensure the final product is flexible and meets operational requirements
- Optimize the production process to increase efficiency and ensure high product quality
- Evaluate and improve steps in the production process to minimize waste and enhance flexibility in manufacturing
[1] Chia-Wen Hou, Chao-Chieh Lan, Functional joint mechanisms with constant- torque outputs, Mechanism and Machine Theory, 22 January 2013
[2] Phan Thanh Vu, Pham Huy Tuan, Design and analysis of a compliant constant- torque mechanism for rehabilitation devices, January 2020
[3] TS Phạm Sơn Minh, ThS Trần Minh Thế Uyên, Giáo trình Công nghệ khuôn mẫu, Nhà xuất bản Đại Học Quốc Gia TP.HCM 02/2022
[4] Cấu tạo và nguyên lý hoạt động của khuôn 2 tấm Internet: https://duytanmold.com/khuon-2-tam-cau-tao-va-nguyen-ly-hoat-dong-cua-khuon- 2-tam.html, 2017
[5] Khuôn 3 tấm, cấu tạo và nguyên lý hoạt động Internet: https://datako.vn/tin- tuc/khuon-3-tam-cau-tao-va-nguyen-ly-hoat-dong-khuon-3-tam.html
[6] Công thức tính Cavity và các hệ thống làm nguội Cavity cho khuôn ép nhựa Internet: https://itgtechnology.vn/cavity-la-gi-cong-thuc-tinh-cavity-va-he-thong- lam-nguoi-cho-khuon-ep-nhua/
[7] TS Phạm Sơn Minh, ThS Trần Minh Thế Uyên, Giáo trình Thiết kế và chế tạo khuôn phun ép nhựa, Nhà xuất bản Đại Học Quốc Gia TP.HCM.3/07/2014
[8] Linh kiện khuôn và ép phun Misumi Internet: https://vn.misumi- ec.com/pr/recommend_category/mold_injectionmold_component/?mid=mid_News _Feb
[9] Trần Quốc Hùng, Giáo trình Dung sai – Kỹ thuật đo, Nhà xuất bản Đại Học Quốc Gia TP.HCM 2/10/2012
[10] Th.S Phan Minh Thanh, ThS Hồ Viết Bình, Giáo trình Cơ sở công nghệ chế tạo máy, Nhà xuất bản Đại Học Quốc Gia TP.HCM 22/03/2013
[11] Nguyễn Ngọc Đào, Trần Thế Sang, Hồ Viết Bình, Chế độ cắt gia công cơ khí, Nhà xuất bản Đà Nẵng 13/06/2002
[12] Chế độ gia công căt gọt trong ngành cơ khí Internet: https://maycncnhapkhau.com/cac-thong-so-toi-uu-che-do-cat-trong-gia-cong-co- khi-co-ban/, 2020
[13] Catolo máy ép nhựa HAITIAN Internet: http://gdplastek.com/may-ep-nhua-haitian-ma-servo-motor, 2019
Milling mold cavity and machining holes
Table 4.8: Manufacturing of cavity plate in rough 2
Manufacturing process of top clamp plate
Rough 1: Milling bottom surface, 2 sides surface and machining holes
Table 4.9: Manufacturing of top clamp plate in rough 1
Milling surface for assemble locating ring
Milling surface for assemble sprue bushing
Rough 2: Milling top surface and another sides surface
Table 4.10: Manufacturing of top clamp plate in rough 2
Manufacturing process of spacer block
Rough 1: Milling bottom surface, 2 sides surface and machining holes
Table 4.11: Manufacturing of spacer block in rough 1
Rough 2: Milling top surface and another sides surface
Table 4.12: Manufacturing of spacer block in rough 2
Manufacturing process of retainer plate
Rough 1: Milling bottom surface, 2 sides surface and machining holes
Table 4.13: Manufacturing of retainer plate in rough 1
Counterbore sprue bushing pin holes ứ6
Rough 2: Milling top surface and another sides surface
Table 4.14: Manufacturing of retainer plate in rough 2
Manufacturing process of ejector plate
Rough 1: Milling bottom surface, 2 sides surface and machining holes
Table 4.15: Manufacturing of ejector plate in rough 1
Rough 2: Milling top surface and another side surfaces
Table 4.16:Manufacturing of ejector plate in rough 2
Manufacturing process of bottom plate
Rough 1: Milling bottom surface, 2 sides surface and machining holes
Table 4.17: Manufacturing of bottom plate in rough 1
Rough 2: Milling top surface and another sides
Table 4.18: Manufacturing of bottom plate in rough 2