This book provides a structured methodology and scientific basis for engineering injection molds. The topics are presented in a top-down manner, beginning. Injection Mold Design Engineering 8/31/07 Edition. David Kazmer is a Professor in the Department of Plastics Engineering at the University of Massachusetts Lowell. The book Injection Mold Design Engineering provides a great amount of detail on polymer flow in plastic manufacturing. David O. Kazmer. Injection Mold Design Engineering. Book ISBN: eBook ISBN: For further information and order see.
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Cover for Injection Mold Design Engineering. Injection Mold Design Engineering. Book • 2nd Edition • Authors: 5 - Cavity Filling Analysis and Design. Injection Mold Design Engineering by David O. Kazmer, , available at Book Depository with free delivery worldwide. Hello Can anyone recommend a good Text book on injection mold designing? There are about eight of them that show up online right away.
Passage through the gate causes a frictional rise in material temperature, extending the materials flow into the mold. To remove trapped air and process gases during injection, a mold venting system is needed. The number and size of the vents are determined by part geometry, material type, viscosity, and the rate of injection.
These vents are ground on the parting line of the mold.
The hot thermoplastic remains in the mold under pressure until it cools. This cooling is usually achieved by water circulating in channels machined into the mold. Proper cooling contributes to controlled part shrinkage, part strength and quality. Overall, the speed of the injection molding cycle is controlled by the efficiency of the cooling system. Once the parts are sufficiently cooled and solidified, the mold opens and an ejector system, usually in the form of knockout pins, is used to aid in part ejection.
Ejector systems are mounted on the ejection side of the mold and are typically activated by pneumatic or hydraulic cylinders. For instance, it is not uncommon for molders to standardize on a specific type and size of mold to maximize production flexibility and reduce setup times. When an advanced molding application has special requirements, it may be critical to select a molder with a specialized set of molding capabilities and standard operating procedures.
The Ultimate Injection Mold Design Tutorial
Chapter 13 provides a survey of mold technologies, many of which require special molder capabilities. The following cost estimation method was developed to include the main effects of the part design and molding process while being relatively simple to use.
To use the developed method, the practitioner can refer to the cost data provided in Appendices A, B, and D, or provide more application specific data as available.
To demonstrate the cost estimation method, each of these cost drivers is analyzed for the laptop bezel shown in Figure 3. The example analysis assumes that 1,, parts are to be molded of ABS from a single cavity, hot runner mold.
The relevant application data required to perform the cost estimation is provided in Table 3. This example corresponds to the mold design shown in Figure 1. The reason for their expense is that they need to contain every geometric detail of the molded part, be made of very hard materials, and be finished to a high degree of accuracy and quality.
As previously suggested, the analysis should be conducted using application specific data for the material properties, part geometry, mold geometry, or manufacturing processes when such data is available. First, the dimensions of the core and cavity inserts are estimated. From the dimensions provided in Table 3. Since this is a tight tolerance part with a high production quantity, tool steel D2 is selected for its wear and abrasion resistance.
A mold maker in a high cost of living area such as Germany will tend to have a higher labor cost than a mold maker in a low cost of living area such as Taiwan. Furthermore, the labor rate will also vary with the toolset, capability, and plant utilization of the mold maker. For example, a mold maker using a 5 axis numerically controlled milling machine will tend to have more capability and charge more than a mold maker using manually operated 3 axis milling machines.
Some approximate cost and efficiency 3. The cavity machining time is driven by the size and complexity of the cavity details to be machined, as well as the speed of the machining processes used.
In theory, the exact order and timing of the manufacturing processes can be planned to provide a precise time estimate. In practice, however, this approach is fairly difficult unless the entire job can be automatically processed, for instance, on a numerically controlled mill.
To provide an approximate but conservative estimate, the assumption is made that the removal volume is equal to the entire volume of the core and cavity inserts. This may seem an overly conservative estimate, but in fact much of the volume must be removed around the outside of the core insert and the inside of the cavity insert.
The material removal rate is a function of the processes that are used, the finish and tolerances required, as well as the properties of the mold core and cavity insert materials. To simplify the analysis, a geometric complexity factor will later be used to capture the effect of different machining processes and tolerances needed to produce the required cavity details.
Machining data for different materials are provided in Appendix B, though application specific material removal rates can be substituted if the depth of cut, speed, and feed rates are known . Due to limitations in the process, the core and cavity inserts are typically machined from aluminum with very small end-mills used to provide reasonably detailed features.
While this mold-making approach does provide very precise cost estimates and low costs, the resulting molds are comparatively soft and often not appropriate for molding high quantities. Higher strength and wear resistant aluminum alloys, however, have recently been and continue to be developed that are increasingly cannibalizing conventionally manufactured steel molds.
David O. The goal of the mold layout design stage is to develop the physical dimensions of the inserts and mold so as to enable procurement of these materials. The mold layout design assumes that the number of mold cavities and type of mold has been determined. To develop the mold layout, the mold opening direction and the location of the parting plane are first determined. Then, the length, width, and height of the core and cavity inserts are chosen.
Afterwards, a mold base is selected and the inserts are placed in as simple and compact a layout as possible. It is important to develop a good mold layout design since later analysis assumes this layout design and these dimensions are quite expensive to change once the mold making process has begun.
The primary purpose of the parting plane is to tightly seal the cavity of the mold and prevent melt leakage. The mold designer must first determine the mold opening direction to design the parting plane.
In fact, the mold usually opens in a direction normal to the parting plane since the moving platen of the molding machine is guided by tie bars or rails to open in a direction normal to the platen. It may appear that there is nothing about the mold opening direction to determine since the mold opens normal to the parting plane. However, it is necessary to determine the mold 68 4 Mold Layout Design opening direction relative to the mold cavity. There are two factors that govern the mold opening direction: 1.
First, the mold cavity should be positioned such that it does not exert undue stress on the injection mold.
Anybody has injection Mould Design Book?
The mold cavity is typically placed with its largest area parallel to the parting plane. This arrangement allows the mold plates, already being held in compression under the clamp tonnage, to resist the force exerted by the plastic on the surfaces of the mold cavity. Second, the mold cavity should be positioned such that the molded part can be ejected from the mold.
A typical molded part is shaped like a five-sided open box with the side walls, ribs, bosses, and other features normal to its largest area. Consider the cup and lid shown in Figure 4.
A section of the core and cavity inserts used to mold these parts was previously shown in Figure 1. There are only two potential mold opening directions relative to the part.
One mold opening direction is in the axial direction of the cup, while the second direction is in the radial direction of the cup. Figure 4. The two bold horizontal lines indicates the location of the parting plane where the two halves of the insert are split to form the cavity insert top and the core insert bottom. Consider next the same cavity block but with a radial mold opening direction for a portion of the cavity insert as shown in Figure 4. For this design, four bold lines separate the sides from the top and bottom.
The cavity insert, however, can be separated into three pieces that move along two different axes in order to remove the molded part. Of these two designs, the axial mold opening direction shown in Figure 4.
Injection mold construction
However, the second design is sometimes used in practice since it allows for a more complex part design as well as more options in locating the parting line. For instance, the second design might be required if a handle were added to the cup, or if it was necessary to move the parting line to a location away from the top lip.
As another example, consider the laptop bezel shown in Figure 3. There are again two potential mold opening directions. In this case, the mold section is split by two horizontal lines into a cavity insert forming the outside surface of the bezel and a core insert that forms the inner surface and ribs of the bezel.
When the core and cavity inserts are separated as indicated by the arrows, the molded bezel can be readily removed.
Ejector back plate—It prevents the ejector pins from disengaging; usually of mild steel material. Heel blocks—Provides a gap for the ejector assembly, so that the finished component ejects from the core. Bottom plate—Clamps the bottom half of the mold with the fixed half of the molding machine; usually made of mild steel. Rest button—Supports the ejection assembly and reduces the area of contact between the ejection assembly and the bottom plate.
It is most helpful when cleaning the injection molding machine, which is essential to ensure an "unmarked" finished component.
Small foreign particles sticking to the bottom plate may cause ejection pins to project out from the core and result in ejection pin marks on the component. The core is the male part which forms the internal shape of molding. The cavity is the female part which forms external shape of molding. Gate types[ edit ] The two main gate systems are manually trimmed gates and automatically trimmed gates. The following examples show where they are used: Sprue gate: Used for large components, the gate mark is visible in component and no runner is required.
Edge gate: Most suitable for square, rectangular components Ring gate: Most suitable for cylindrical components to eliminate weld line defect Diaphragm gate: Most suitable for hollow, cylindrical components Tab gate: Most suitable for solid, thick components Submarine gate: Used when auto de-gating is required to reduce cycle time Reverse taper sprue gate Pin gate : Generally used in three plate molds.
Winkle Gate: Its mainly used for electronics product gate flow the material under the core side Ejection system types[ edit ] Pin ejection—Cylindrical pins eject the finished component.
In the case of square and rectangular components, a minimum of four pins at the four corners are required. In the case of cylindrical components, three equidistant pins i. The number of pins required may vary based on the component profile, size and area of ejection.
This ejection system leaves visible ejection marks on the finished component. Sleeve ejection—This type of ejection is preferred for and limited to cylindrical cores, where the core is fixed in the bottom plate. In this system, the ejection assembly consists of a sleeve that slides over the core and ejects the component.
No visible ejection marks are apparent on the component.The basic mold base consists of two halves. In the previous example, the upfront cost of the 32 cavity hot runner system can not be justified at low or moderate production quantities.
Kazmer David O. Sign up now. The relevant application data required to perform the cost estimation is provided in Table 3. Stripper plate ejection—This ejection is preferred for components with larger areas.
He performs research and teaches courses related to plastics product and process development.