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.
In such a case, prospective mold downloadrs should ask about the details of the provided quotes, and check if the costs can be reduced through product redesign. To reduce uncertainty related to pricing and capability, many prospective customers maintain a list of qualified suppliers, who tend to provide faster turn-around, more uniform quality, and better pricing across multiple projects.
Now consider the view of the mold supplier. The mold designer must invest significant time developing a quote that may have a relatively small chance of being accepted. Sometimes, the mold designer may have to redesign the product and perform extensive analysis to provide the quote. While the quote may seem high to the prospective customer, the design may correspond to a mold of higher quality materials and workmanship that can provide a higher production rate and longer working life than some other lower cost mold.
This more expensive mold may quickly recoup its added costs during production.
From time to time, mold-makers and molders will adjust their quote based on whether or not they want the business. Such adjustments should be avoided since the provided quote does not represent the true costs of the supplier, which would become the basis in a long term and mutually beneficial partnership between the mold supplier and the customer.
The provided quote typically provides payment and delivery terms for the mold s and perhaps even the molded part s. The cash outlays for a typical project are plotted in Figure 3. The material and processing costs in month 3 are related to molding trials to validate and improve the mold design; a hundred or so pre-production parts may be sampled at this time for marketing and testing purposes.
Later, monthly costs are incurred related to production. Maintenance costs may appear intermittently throughout production to maintain the quality of the mold and moldings. There has been a trend in the industry towards large, vertically integrated molders with tightly integrated supply chains who can supply molded parts and even complete product assemblies.
Computer-Aided Injection Mold Design and Manufacture
As such, the structure of the quote can vary substantially with the structure of the business. With a vertically integrated supplier, there is typically an up-front fee for the costs associated with the development of the mold, followed by a fee for each molded part. Since the structure and magnitude of quotes will vary substantially by supplier s , a prospective downloader of plastic parts should solicit quotes from multiple vendors and select the quote from the supplier that provides the most preferable combination of molded part quality, payment terms, delivery terms, and service.
Figure 3. It is important to note that these costs do not include indirect costs such as overhead or profits. However, such indirect costs may be accounted through the adjustment of hourly rates and other costs.
While these two products are approximately the same weight, it is observed that the magnitude and proportion of costs are vastly different.
Typically, there is a trade off between the upfront investment in the mold and later potential savings related to the processing and material costs per part. Consider the data provided in Table 3. As indicated, the lower production quantity may be satisfied with a two cavity, cold runner mold. By comparison, the mold design for the higher production quantity utilizes a hot runner system allowing the simultaneous molding of 32 cavities with a lower cycle time and reduced material consumption.
In reality, the production schedules and quantities are not precisely known, so the molder and customer must carefully consider the possible result of using molds that are over or under designed.
For this reason, break-even analysis should be utilized to consider the sensitivity of different mold designs to the total molded part cost. Table 3. Consider the previous case for the two molds described in Table 3.
It is useful to consider the total costs incurred to produce a given quantity. For a given mold design, the marginal cost per piece will remain fairly constant across the life of the application though there may be cost decreases related to elimination of defects, reductions in cycle times, etc. To provide the best possible mold design and quote, multiple mold designs should be developed for different target production quantities, and the total production costs estimated and compared via break-even analysis.
Example: Consider the cost data provided in Table 3. Calculate the production volume where a hot runner mold becomes more economical than a cold runner mold.
Equation 3. While the cost function of Eq. For this example, the 2 cavity cold runner mold has a lower total cost up to the , part quantity, after which the 32 cavity hot runner mold provides a lower total cost. In the previous example, the upfront cost of the 32 cavity hot runner system can not be justified at low or moderate production quantities.
At very high production quantities, however, a hot runner system is essential to maximizing profitability since the marginal costs of operating the hot runner mold are significantly less than those of the cold runner mold.
While the breakeven analysis supports clear design deci- sions at very low and very high production quantities, the mold design can be less certain at intermediate production volumes.
Table of Contents
If the production quantity is on the order of , parts, then the best mold design may utilize neither 2 nor 32 cavities for this application, but rather an intermediate quantity of 4, 8, or 16 cavities with or without a hot runner.
As such, multiple designs and cost estimates should be developed until a good balance is achieved between higher upfront investment and lower marginal costs.
If necessary, the customer can be given more than one design to select the design that they think will ultimately be best. Many molders and customers require a quick return on investment, and so will examine the total cost curve to accept the use of a hot runner system with high cavitation only if a desirably short payback period can be achieved.
The color change issue in hot runners will be revisited in Section 6. If the molder does not have the experience or auxiliaries required to utilize a hot runner system, then a cold runner mold may best be utilized. 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.
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. To avoid flash, the stripper plate remains in contact with the cavity plate and a gap is maintained between the cavity and core plate.
Visible ejection marks are usually not noted on components. Blade ejection—This type of ejection is preferred for thin, rectangular cross sections.
Rectangular blades are inserted in cylindrical pins or cylindrical pins are machined to rectangular cross sections to create an appropriate ejection length for the component. For easy accommodation of the ejection pin head, a counter bore is provided in the ejection plates.
By rotation of core internal threaded components —Used for threaded components, where the component is automatically ejected by rotating the core insert. Air ejection—Used to actuate the ejection pin fitted in the core using compressed air.
The ejection pin is retracted using a spring.
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Alignment[ edit ] Injection molds are designed as two halves, a core half and a cavity half in order to eject the component. For each cycle, the core and cavity are aligned to ensure quality. This alignment is ensured by guide pillar and guide bush. Usually, four guide pillars and guide bushes are used, out of which three pillars are of one diameter and one is of a different diameter, to force the plates into a single configuration based on the " POKE YOKE " [mistake proof] concept.
The register ring has interference fit in top plate and transmission fit with the injection molding machine pattern, aligning the machine pattern and top plate.
Desirable attributes of the mold cooling design include: Constant mold temperature for uniform quality Reduced cycle time for productivity Improved surface finish without defects Avoiding warpage by uniform mold surface temperature warpage caused by nonuniform cooling Long mold life Methods[ edit ] Cavity plate cooling by drilled holes—The cavity plate is drilled around the cavity insert and plugged with copper or aluminum taper plugs at the ends of openings.
Using pipe connected at the inlet and outlet ports, water is circulated to cool the mold. Direct cooling of core insert baffle system —The core is drilled by keeping sufficient wall thickness. A baffle plate is located between the drilled hole, dividing the hole into two halves, allowing the water to contact the maximum area in core so cooling may take place. Annular cooling of cavity insert—A circular groove is made on the core for water circulation. To prevent leakage, O-rings are used above and below the cooling channel.
Top plate—It is used to clamp the top half of the mold to the moving half of the molding machine and is usually made of mild steel. Cavity plate—The plate used to create a cavity via a gap that will be filled with the plastic material and form the plastic component.
Usually made of mild steel. Core plate—The core plate projects into the cavity place and creates hollow portions in the plastic component. This core plate is usually made of hardened hot die P20 steel without hardening after core machining. Sprue puller pin—The sprue puller pin pulls the sprue from the sprue bush. It is usually made of mild steel. Guide pillar and guide bush—The guide pillar and guide bush align the fixed and moving halves of a mold in each cycle.
The material cases are usually made of medium carbon steel and will have higher hardness. Ejector guide pillar and guide bush—These components ensure the alignment of the ejector assembly so that the ejector pins are not damaged. The guide pillar typically has higher hardness than the guide bush.
Ejector plate—This holds the ejector pins and is usually made of mild steel. 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.Top plate—It is used to clamp the top half of the mold to the moving half of the molding machine and is usually made of mild steel.
Stripper plate ejection—This ejection is preferred for components with larger areas. No visible ejection marks are apparent on the component. The mold gate restricts and controls the flow of plastic into the mold. As indicated in Figure 4. Afterwards, a mold base is selected and the inserts are placed in as simple and compact a layout as possible.
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. Sometimes, the mold designer may have to redesign the product and perform extensive analysis to provide the quote.